Alcidae Leach 1820 is a clade of pelagic wing-propelled-diving Charadriiformes Huxley 1867 including 23 extant species with an exclusively northern hemisphere distribution (del Hoyo et al. 1996). The fossil record indicates that alcid diversity during the Late Miocene (11.6–5.3 mya) and Early Pliocene (5.3–3.6 mya) equaled or exceeded extant alcid diversity (Olson 1985; Olson and Rasmussen 2001; Dyke and Walker 2005; Smith et al. 2007), although systematic evaluation of fossils referred to Alcidae is needed to refine estimates of paleodiversity in the clade. Additionally, the systematic position of most extinct species referred to Alcidae have yet to be evaluated in a phylogenetic analysis.

Primarily owing to the penguin-like characteristics of the flightless Great Auk Pinguinus impennis (Linnaeus 1758), alcids were grouped systematically with penguins and other ‘waterbirds’ including loons, grebes, and ducks by many ornithologists in the 18th and 19th centuries (Linnaeus 1758; Vigors 1825; Brandt 1837; Swainson 1837; Coues 1868), and this misconception lingered well into the 20th century (Verheyen 1958). However, there is consensus among modern classifications with regard to the placement of Alcidae in a monophyletic Charadriiformes (Ridgway 1919; Storer 1960; American Ornithologists’ Union 1998). Analyses of morphological (Strauch 1978; Björklund 1994; Chu 1995; Livezey and Zusi 2006, 2007; Livezey 2009, 2010; Mayr 2011) and molecular data (Sibley and Ahlquist 1972; Sibley and Ahlquist 1990; Ericson et al. 2003; Paton et al. 2003l; Thomas et al. 2004; Cracraft et al. 2004; Paton and Baker 2006; Fain and Houde 2007) support the charadriiform affinities of Alcidae. Furthermore, phylogenetic analyses of molecular data with dense taxonomic sampling for Alcidae support the monophyly of an extant alcid clade (Thomas et al. 2004; Baker et al. 2007; Pereira and Baker 2008). Previous morphology based analyses of alcid relationships have been limited with respect to taxon sampling. The compatability analysis of Strauch (1978) included only three alcid species and the subsequent analysis of alcid relationships (Strauch1985) did not include any outgroup taxa. The parsimony based analysis of alcid relationships by Chandler (1990a) was limited to a hypothetical outgroup terminal. The recent morphology based analyses of (Livezey and Zusi (2006, 2007) (Livezey (2009, 2010) and Mayr (2011) included Alcidae as a single, taxon level terminal.

Although all extant alcids are volant, two lineages of extinct flightless auks are known. These flightless auks superficially resemble penguins, and share many morphological features convergent with those southern hemisphere wing-propelled divers such as an elongated first metacarpal and humeri with anteriorly rotated humeral heads (Miller and Howard 1949; see Appendix 1). During the Miocene and Pliocene a diverse assemblage of alcids including the flightless Great Auk Pinguinus Bonnaterre, 1790, and other volant auks such as Alca Linnaeus, 1758 and Miocepphus Wetmore, 1940 were present in the Atlantic Ocean (Olson and Rasmussen 2001; Wijnker and Olson 2009). Similarly, during the Miocene and Pliocene the Pacific was inhabited by a lineage of flightless alcids known as the Mancallinae Brodkorb 1967. Although Mancallinae(contents = Mancalla Lucas, 1901 + Praemancalla Howard, 1966; sensu Brodkorb 1967; Olson 1985) and Pinguinus share several morphological characteristics related to extreme adaptation for wing-propelled diving and the subsequent loss of aerial flight (Fig. 1), phylogenetic results indicate that these taxa are not closely related within Alcidae. Pinguinus is consistently recovered as the sister taxon to Alca (Chandler 1990a; Moum et. al. 2002; Baker et. al. 2007; Pereira and Baker 2008), and previousphylogenetic analyses place Mancallinae as the sister taxon to all other Alcidae (Chandler 1990a; Smith 2008), suggesting that flightlessness evolved separately in Mancallinaeand Pinguinus.

Fossil records of Mancallinae are restricted to the northern Pacific Ocean basin. Miocene and Pleistocene aged fossils have been reported from Japan (Hasegawa et al. 1988; Kohno 1997; Fig. 2), although these remains have not been systematically described or figured in publication. In contrast to the sparse record of the clade from the western Pacific Ocean, thousands of mostly isolated remains are known from California, USA and northern Baja California, Mexico (Miller and Howard 1949; Howard 1966, 1968, 1970, 1971, 1976, 1978, 1981, 1982; Chandler 1990b; Fig. 2), and range in age from Late Mioceneto Late Pleistocene (Table 1). The northernmost occurrence is in Humboldt County California (Howard 1970; Kohl 1974) and the southernmost occurrence is in Baja California, Mexico (Howard 1971).

Discovery of an articulated partial skeleton referable to Mancallinae (SDSNH 68312) from the Early Pliocene Capistrano Formation of Orange County California prompted a re-examination of diversity and morphological variation within this clade. Previously reported Mancallinae remains are reviewed (Appendix 1), and the results of an extensive survey of Mancallinae remains are reported. Three new species of Mancallinae are described, and the systematic placement of Mancallinae within Alcidae, as well as the inter-relationships of Mancallinae species is evaluated in a combined phylogenetic analyses of morphological and molecular sequence data. This study represents the first time that relationships among all 23 extant alcids and 29 other charadriiform outgroup taxa have been assessed in the context of a combined phylogenetic analysis.

Description of anatomical features primarily follows the English equivalents of the Latin osteological nomenclature summarized by Baumel and Witmer (1993). The terminology of Howard (1929) is followed for features not treated by Baumel and Witmer (1993). Measurements follow those proposed by Von den Driesch (1976). All measurements were taken using digital calipers and rounded to the nearest tenth of a millimeter. Ages of geologic time intervals are based on the International Geologic Timescale (Gradstein et al. 2004; Ogg et al. 2008).

With the exception of species names (e.g., Fratercula arctica), which follow the 7th edition of the Checklist of North American Birds (American Ornithologists’ Union 1998) for extant species, all taxonomic designations (e.g., Fratercula) are intended as clade names as defined by the International Code of Phylogenetic Nomenclature (i.e., The PhyloCode v.4c; Cantino and de Queiroz 2010), regardless of use of italics or previous rank recognized by other authors, and are not intended to convey rank under the Linnaean system of nomenclature. The PhyloCode recommendation that all scientific names be italicized (Recommendation 6.1A) was not followed here. Only species names are italicized herein. Pursuant to Article 21.2 of the PhyloCode, the first word of species names are considered prenomen, not genus names (see also Dryat et al. 2008).

All extinct taxa were evaluated by direct observation of holotype and referred specimens. Whenever available, a total of five or more specimens of each extant species (Appendix 2) including both sexes were evaluated to account for intraspecific character variation and sexual dimorphism respectively. Only adult specimens, assessed based upon degree of ossification (Chapman 1965), were evaluated for osteological characters, and when available, specimens from multiple locations within the geographic range of extant species (i.e., subspecies) were examined to account for geographic variation within species. Reproductive, chick integument, dietary, and some myological characters were scored from published sources (Appendix 3). Descriptions of anatomical characteristics are followed by character numbers and character state symbols from Appendix 3 (e.g., 23:0 = character number 23, character state 0).

The cladistic matrix (Appendix 4) includes 72 terminals, scored for a maximum of 344 morphological characters (284 binary; 60 multistate;15 ordered). All 23 extant alcids, the recently extinct Great Auk Pinguinus impennis Linnaeus, 1758, 18 Mancallinae specimens, and a Mancallinae supraspecific terminal are included in the matrix. Twenty-nine other extant charadriiforms comprise the remainder of the taxa analyzed, and provide a dense outgroup taxonomic sample to test the monophyly of extant and extinct alcids. with respect to other charadriiforms.Morphological characters include osteological (n = 223), integumentary (n = 32), ethological (n = 16), myological (n = 24) and micro-feather (n = 52). One hundred and fifty-five characters were newly identified for this analysis. The other 189 characters were drawn from the work of Hudson et al. (1969; n = 24), (Strauch (1978, 1985; n = 39), Chandler (1990a; n = 63), Chu (1998; n = 11), and Dove (2000; n = 34). Only 34 of the 38 characters used by Dove (2000) varied in the taxa examined in this study. Of the 34 used in this analysis, eighteen were modified (i.e., split into 2 separate characters) according to the philosophy of character independence proposed by Hawkins et al. (1997), resulting in a total of 52 microfeather characters.

The cladistic matrix also includes a molecular sequence alignment of 11, 601 base pairs from eight DNA sequence types (including gaps). See Appendix 5 for details of sequence availability, inclusion for each species, and sequence authorship. Molecular sequence data (mitochondrial: ND2, ND5, ND6, CO1, CYTB; ribosomal RNA: 12S, 16S; and nuclear: RAG1) were downloaded from GenBank. Preliminary sequence alignments for each gene were obtained using the program ClustalX v2.0.6 (Thompson et al. 1997), and then manually adjusted using the program Se-Al v2.0A11 (Rambaut 2002).

A combined approach of phylogeny estimation was used to evaluate the systematic position of Mancallinae species. Simulations show that the combination of molecular and morphological data often provides a more accurate estimate of phylogeny with respect to both extant and extinct organisms (Wiens 2009). Phylogenetic analyses employed the parsimony criterion of phylogenetic inference as implemented in PAUP* v4.0b10 (Swofford 2002). Parsimony tree search criteria are as follows: heuristic search strategy; 10, 000 random taxon addition sequences; tree bisection-reconnection branch swapping; random starting trees (primary analysis only); all characters equally weighted; minimum length branches = 0 collapsed; multistate (e.g., 0&1) scorings used only for polymorphism. Bootstrap values and descriptive tree statistics including consistency index (CI), retention index (RI), and rescaled consistency index (RC) were calculated using PAUP* v4.0b10 (Swofford 2002). Bootstrap value calculation parameters included 1, 000 heuristic replicates, 100 random addition sequences per replicate. All other settings were the same as the primary analysis. Bremer support values were calculated using a script generated in MacClade v4.08 (Maddison and Maddison 2005) and analyzed with PAUP* v4.0b10 (Swofford 2002). Based on the results of previous phylogenetic analyses of charadriiform relationships (Strauch 1978; Sibley and Ahlquist 1990; Chu 1995; Ericson et al. 2003; Paton et al. 2003; Thomas et al. 2004;Baker et al. 2007) resultant trees were rooted with the clade represented by exemplars of Charadrius vociferus Linnaeus 1758 and Charadrius wilsonia Ord, 1814.

AMNH—American Museum of Natural History, New York, NY, USA; GCVP—Georgia College and State University Vertebrate Paleontology Collection, Milledgeville, GA, USA; IVPP—Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China; LACM—Natural History Museum of Los Angeles County, Los Angeles, CA., USA; LM—Loye Miller Collection, location presently unknown; NSM PO—National Museum of Nature and Science Paleontology Osteological Collection, Tokyo, Japan; NCSM—North Carolina Museum of Natural Sciences, Raleigh, NC, USA; SDSNH—San Diego Natural History Museum, San Diego, CA, USA; TMM—Texas Natural Science Center Vertebrate Paleontology Laboratory, Austin, TX, USA; UCMP—University of California Museum of Paleontology, Berkeley, CA, USA; USNM—National Museum of Natural History, Smithsonian Institution, Washington, D.C., USA.

AVES Linnaeus, 1758

CHARADRIIFORMES Huxley, 1867

PAN-ALCIDAE new taxon.

Pan-Alcidae (contents = Alcidae Leach, 1820 (i.e., the alcid crown clade) + Mancallinae) is differentiated from all other Charadriiformes by the following characteristics: quadrate apneumatic (38:1); reduced pneumatic foramen of anterior sternum (59:0); omal ext

Mancallinae (contents = Mancalla + Miomancalla gen. n.) is referable to Pan-Alcidae based upon dorsoventral compression of the humeral shaft (141:2). The humeral shafts of Pan-Alcidae are more dorsoventrally compressed than in all other Charadriiformes. Mancallinae is differentiated from all other alcids on the basis of the following unambiguously optimized humeral apomorphies: deltopectoral crest extends past the midway point of the humeral shaft rather than restricted to the proximal half of the humeral shaft (104:2); presence of a ‘mancalline muscle scar’ extending distally from the primary pneumotricipital fossa (discussed below; 120:1); capital groove communicates with transverse ligament sulcus resulting a notched rather than rounded appearance of ventral margin of the humeral head in anterior view (136:2); humeral head rotated anterodorsally rather than in-line with humeral shaft (139:1); humeral shaft arced rather than sigmoidal (140:1); presence of fossae in tricipital sulci (150:1); anterior surface of the ventral condyle rounded rather than flattened (153:0). Additional proposed apomorphies of Mancallinae include distal elongation (184:1) and anterior flattening of the first metacarpal (185:1). These characteristics are present in Mancalla cedrosensis Howard, 1971, Miomancalla howardi sp. n., and two additional associated specimens referable to Mancallinae (SDSNH 77966 and LACM 107028). Although these two characters are also diagnostic for Alcini Storer, 1960, the clade composed of Alca, Pinguinus, Alle Link, 1806, and Uria Brisson, 1760, the degree of distal elongation and anterior flattening in Mancalla exceeds that observed in Alcini.

Mancalla lucasi sp. n.

urn:lsid:zoobank.org:act:31389B4B-0A03-48E5-8A0B-C71CDBCE7164

Holotype.

SDSNH 25237: a partial postcranial skeleton comprising the following elements: right and left scapulae, partial sternum, right and left humeri, left femur (Fig. 3; Tables 1, 2 and 3). The holotype specimen was collected by H. M. Wagner in April, 1980.

Figure 3.

Holotype specimen of Mancalla lucasi (SDSNH 25237). A Fragment of anterior sternum in anterior view B Carinal apex of sternum in right lateral view C Right humerus in anterior view D Left humerus in proximal view E Left humerus in distal view F Left humerus in posterior view G Left scapula in lateral view H Right scapula in medial view I Left femur in anterior view. Anatomical abbreviations: a acromion process bc bicipital crest c caput ca carinal apex ce caudal extremity of scapula cg capital groove cs coracoidal sulcus ct coracoidal tubercle d deltopectoral crest dc dorsal condyle dsp dorsal supracondylar dst dorsal supracondylar tubercle fh femoral head fp flexor process gp glenoid process hs humerotricipital sulcus le lateral epicondyle pf1 primary pneumotricipital fossa ps pectoralis scar sc supracoracoidal crest si sulcus intercondylaris sr sternal rostrum ss scapulotricipital sulcus st scapulotricipital tubercle tc trochanteric crest tls transverse ligament sulcus vc ventral condyle vst ventral supracondylar tubercle vt ventral tubercle.

Table 2.

Measurements of Mancallinae holotype humeri (mm). Abbreviations: (Glh) greatest length of humerus; (Bph) breadth of proximal humerus; (Diph) diagonal of proximal humerus; (Whs) width of humeral shaft; (Bdh) breadth of distal humerus; (Ddh) depth of distal humerus. Measurements according to Von den Driesch (1976). ‘~’ signifies approximate measurement due to damage. ‘—‘ signifies missing data due to damage.

Species	Specimen #	Glh	Bph	Diph	Whs	Bdh	Ddh
Mancalla californiensis	USNM4976	~75.0	19.0	18.4	8.9	___	___
Mancalla cedrosensis	LACM15373	73.3	17.8	17.1	9.1	13.0	7.1
Mancalla lucasi	SDSNH25237	90.2	21.7	21.2	11.1	13.4	8.0
Mancalla vegrandis	SDSNH77399	61.8	15.1	14.3	7.4	9.5	5.8
Miomancalla wetmorei	LACM42653	~86.0	21.5	21.1	12.7	8.7	9.5
Miomancalla howardi	SDSNH24584	103.2	22.9	22.2	11.1	12.2	8.7
Miomancalla howardi	SDSNH68312	___	~25.0	~24.0	___	___	___

Table 3.

Measurements of new associated Mancallinae holotype specimens (in mm). ‘-’ = missing data due to damage or lack of comparable element.

	Miomancalla howardi	Mancalla lucasi	Mancalla vegrandis
	SDSNH 68312	SDSNH 25237	SDSNH77399
SKULL & MANDIBLE
Greatest length of skull	122.9	-	-
Greatest breadth of frontal	11.4	-	-
Greatest length of rostrum	84.2	-	-
Greatest height of rostrum	21.1	-	-
Greatest length of mandible	127.8	-	-
STERNUM
Smallest width between costal processes	-	-	5.9
FURCULA
Dorsoventral height of apophysis	-	-	2.8
CORACOID
Greatest length	-	-	45.8
SCAPULA
Greatest proximal height	-	15.1	10.9
CARPOMETACARPUS
Greatest length	46.8	-	-
Length of metacarpal one	23.2	-	-
Proximal breadth	11.9	-	-
PELVIS
Greatest length	127.8	-	74.8
FEMUR
Greatest length	79.9	67.8	-
Medial length	78.0	64.9	-
Proximal breadth	17.8	12.9	-
Proximal depth	10.9	9.2	-
Breadth of shaft	8.3	7.5	-
Distal breadth	18.0	12.5	-
TIBIOTARSUS
Greatest length (preserved)	113.7	-	-
Breadth of shaft	7.8	-	-

Etymology.

This new species is named in honor of Frederic A. Lucas who described the first known remains of Mancalla.

Locality and horizon.

Late Pliocene or Early Pleistocene (Zanclean or Calabrian) Niguel Formation of Orange County, California. Latitude, longitude, and elevation data are on file at SDSNH (locality 3202). Details of the geologic setting are provided in Appendix 6.

Referred specimen.

SDSNH 59049: a complete left humerus from the Middle Pliocene to Early Pleistocene San Diego Formation (SDSNH locality 3506; Fig. 4E).

Figure 4.

Mancalla referred humeri in anterior view. A Mancalla vegrandis SDSNH 28152 B Mancalla vegrandis SDSNH 42534 C Mancalla vegrandis SDSNH 75051 D Mancalla vegrandis SDSNH 42532 E Mancalla lucasi SDSNH 59049.

Differential diagnosis.

Scar extending into primary pneumotricipital fossa is raised in relief to the floor of the primary pneumotricipital fossa and the humeral shaft as in Mancalla cedrosensis, rather than an excavated pit as in Mancalla vegrandis sp. n. and Mancalla californiensis Lucas 1901 (121:1; Fig. 5); dorsal and ventral edges of scar extending into primary pneumotricipital fossa taper to a point as in Mancalla vegrandis, rather than remaining parallel as in Mancalla californiensis and Mancalla cedrosensis (123:1); humerus longer than Mancalla cedrosensis, Mancalla californiensis, and Mancalla vegrandis (Tables 2, 3).

Figure 5.

Line drawings for comparison of Mancallinae proximal humeri in posterior view (not to scale). A Miomancalla wetmorei B Miomancalla howardi C Mancalla californiensis D Mancalla cedrosensis E Mancalla vegrandis F Mancalla lucasi. Anatomical abbreviations: ms mancalline scar pf1 primary pneumotricipital fossa sc supracoracoidal crest vt ventral tubercle.

Anatomical description.

Both scapulae are preserved (Fig. 3G, H). As in all Alcidae, the scapular shaft is mediolaterally compressed throughout its entire length. The proximal end of the scapular shaft is more rounded in other Charadriiformes. As in Mancalla vegrandis, the acromion projects farther anteriorly than that of Mancalla cedrosensis and other alcids (e.g., Uria, Aethia). As in Mancalla cedrosensis, the coracoidal tubercle is less pronounced than in Mancalla vegrandis. As in Mancalla vegrandis and Mancalla cedrosensis, a scapulotricipital tubercle is present just distal to the glenoid process on the ventral margin of the scapular shaft. This feature is also present in other flightless wing-propelled divers such as Spheniscidae and Pinguinus, but is not known in any volant alcid. As in Mancalla vegrandis, the scapular shaft, including the caudal extremity, is slightly more robust than in other alcids (e.g., Alca, Aethia). The caudal extremity is less dorsoventrally expanded than in Mancalla vegrandis. The caudal extremity is not known for Mancalla cedrosensis.

Fragments of the sternum preserve the sternal rostrum, coracoidal sulci, and the carinal apex (Fig. 3A, B). These features are not preserved in Miomancalla howardi and comparisons are therefore limited to extant alcids and specimens of Mancallinae that are not presently referable to species. The morphology of the sternal rostrum is consistent with that of all other Alcidae. Although no coracoid is preserved in the holotype specimen of Mancalla lucasi, the shape of the coracoidal sulci of the sternum is consistent with the ~150° angle of the sternal articulation of the coracoid in Mancalla cedrosensis and Mancalla vegrandis. The sternal articulation of the coracoid, and the coracoidal sulci of the sternum in other alcids curves more acutely (e.g., ~90° in Alca torda; Fig. 6).

Figure 6.

Comparison of sternal facet curvature in charadriiform left coracoids (sternal view; not to scale). A Stercorarius B Mancalla C Alca D Aethia.

Complete right and left humeri are preserved (Fig. 3C, D, E and F). Based upon humeral proportions, Mancalla lucasi represents the largest known species of Mancalla (Table 2). As in other Mancalla species, the ventral margin of the ventral tubercle is convex, and the capital groove is relatively narrower than other Alcidae. The ventral tubercle does not project as far ventrally as in Mancalla californiensis (Fig. 5). The distal end of the deltopectoral crest transitions to the shaft more abruptly than in Mancalla vegrandis. As in other Mancalla, the humeral head is rotated anteriorly, and the supracoracoideus muscle scar does not broaden proximally. Mancallinae is characterized by a scar of unknown function that is positioned adjacent to the primary pneumotricipital fossa (hereafter referred to as the ‘mancalline scar’; Fig. 5). The position of the ‘mancalline scar’ suggests an accessory insertion of m. humerotriceps (Howard 1949), which can be divided into as many as four separate heads in some birds (Baumel and Witmer 1993). Other potentially homologous muscle scars include m. coracobrachialis cranialis, which is well developed in penguins (Ksepka et al. 2008), or m. scapulocranialis caudalis (see Matsuoka and Hasegawa 2007). However, the exact function of this feature is unknown because it is not present in any other charadriiform. The shape, position, and development of this scar is variable in Mancallinae (Fig. 5). The ‘mancalline scar’ of Mancalla lucasi is raised in relief like that of Mancalla cedrosensis, rather than excavated as in Mancalla californiensis and Mancalla vegrandis (Fig. 5). As in Mancalla vegrandis, the scar extends from a point just proximal to the junction of the bicipital crest with the humeral shaft, tapers to a point, and extends into the primary pneumotricipital fossa (Fig. 5). The dorsal and ventral margins of the ‘mancalline scar’ remain approximately parallel in Mancalla californiensis and Mancalla cedrosensis (Fig. 5). As in all Mancallinae, the humeral shaft is arced rather than sigmoidal or straight. As in other Mancalla, the dorsal supracondylar process is separated from the dorsal epicondyle by a small notch. A tubercle or papilla is present on the posterior side of the distal end of the humerus adjacent to the dorsal condyle (Howard 1976). As with all Mancallinae, the anterior surface of the ventral condyle is rounded, rather than flattened as in all other alcids. Rounded fossae are present at the proximal ends of the humerotricipital and scapulotricipital grooves. The flexor process extends distal to the ventral condyle as in all Mancallinae and Pinguinus.

The left femur is preserved (Fig. 3I) and is smaller (~15%; Table 2)than in Miomancalla howardi sp. n. (Table 3), and larger (~19%) than in Mancalla cedrosensis (Howard, 1971). Extant alcids do not display statistically significant degrees of sexual dimorphism in their size, plumage, or osteological morphology (Storer 1952; Nettleship and Birkhead 1985; Szekely et al. 2000). Thus, it can be reasonably assumed that extinct alcids were also not sexually dimorphic as the proposed sister taxon of all alcids, the Stercorariidae (Ericson et al. 2003; Thomas et al. 2004; Baker et al. 2007; Pereira and Baker 2008), as well as the closely related Laridae are also not sexually dimorphic. This range of size between Mancalla species is greater than the range of intraspecific variation documented for other alcids (~1-5%), including the flightless Great Auk (Moen 1991; Burness and Montevecchi 1992). As in Alle, Cepphus Mörhing, 1758, Synthliboramphus Brandt, 1837, and Brachyramphus Brandt, 1837, the femoral trochanter projects anteriorly in lateral view. The femoral trochanter in Uria, Aethia Merrem, 1788, Alca, and Pinguinus is not projected anteriorly (i.e., straight), and the trochanter is concave in lateral view in Fratercula Brisson, 1760 and Cerorhinca Bonaparte, 1828. Femora of Miocepphus are not known. No diagnostic characteristics of the femur of Mancalla lucasi were identified.

Remarks.

Mancalla lucasi corresponds in size and some humeral characteristics with material previously referred to Mancalla diegensis. However, Mancalla diegensis is considered Alcidae incertae sedis (see Appendix 1 for details of the taxonomic revision).

Mancalla vegrandis sp. n.

urn:lsid:zoobank.org:act:8F6D55BF-C827-47C3-AAB6-777632C92DB6

Holotype.

SDSNH 77399: a partial postcranial skeleton comprising the following elements: two cervical vertebrae, one costal and one vertebral rib, partial furcula, scapulae, left coracoid, partial right coracoid, partial sternum, left humerus, and pelvis (Figs 7 and 8; Tables1, 2 and 3). The holotype specimen was collected by W. T. Stein in October, 1961.

Figure 7.

Holotype specimen of Mancalla vegrandis (SDSNH 77399) A Cervical vertebra (C3?) in dorsal view B Cervical vertebra (C4?) in ventral view C Left humerus in posterior view D Costal rib E Vertebral rib F Pelvis in dorsal view. Anatomical abbreviations: ac acetabulum at antitrochanter ats antitrochanteral sulcus c capitulum of vertebral rib cg capital groove d deltopectoral crest dis dorsal illiac spine dsp dorsal supracondylar process fp flexor process h hypapophysis is iliosynsacral suture pf1 primary pneumotricipital fossa pz postzygapophysis sa sternal articulation of costal rib sc supracoracoidal crest tf tricipital fossae vt ventral tubercle.

Etymology.

The species name vegrandis reflects the diminutive size of this taxon compared to other known Mancalla species (vegrandis, from the Latin for small, diminutive or tiny).

Locality and horizon.

Middle Pliocene to Early Pleistocene (Zanclean-Calabrian) San Diego Formation of San Diego County, California. Latitude, longitude, and elevation data are on file at SDSNH (locality 4273). Details of the geologic setting are provided in Appendix 6.

Referred specimens.

SDSNH 42532: a complete left humerus from the Middle Pliocene to Early Pleistocene San Diego Formation of San Diego County, California (SDSNH locality 3468); SDSNH 42534: a complete right humerus from the Middle Pliocene to Early Pleistocene San Diego Formation of San Diego County, California (SDSNH locality 3468); SDSNH 28152: a complete right humerus from the Early Pliocene upper member of the San Mateo Formation of San Diego County, California (SDSNH locality 3161); SDSNH 75051: a complete right humerus from the Early Pliocene upper member of the San Mateo Formation of San Diego County, California (SDSNH locality 2643; Fig. 4A–D).

Differential diagnosis.

Dorsal and ventral edges of the mancalline scar extending into primary pneumotricipital fossa taper to a point as in Mancalla lucasi, rather than remaining parallel as in Mancalla californiensis and Mancalla cedrosensis (123:1; Fig. 5); mancalline scar extending into primary pneumotricipital fossa is an excavated pit as in Mancalla californiensis rather than raised in relief to the floor of the primary pneumotricipital fossa and the humeral shaft as in Mancalla cedrosensis and Mancalla lucasi (121:0); humerus shorter than other known Mancalla (Tables 2 and 3).

Anatomical description.

Two cervical vertebrae are preserved (Fig. 7A and B). Comparisons with Miomancalla howardi are limited to generalities regarding shape in dorsal view, for which the morphology of Mancalla vegrandis is consistent with that of Miomancalla howardi. Only thoracic vertebrae are known for Mancalla cedrosensis. One of the vertebrae (Fig. 7A) is mediolaterally narrower than the other (Fig. 7B). Although the width of cervical vertebrae other than the axis and atlas do not vary considerably in extant Alcidae, the 3rd and 4th cervical vertebrae of some charadriiforms (e.g., Larosterna inca Lesson, 1827) are mediolaterally narrower than cervical vertebra posterior to the 4th (i.e., C5, C6, C7). The dorsal surface of the broader vertebra (Fig. 7B) is perforated by a small foramen (i.e., perforation of laminae arcocostales). In extant alcids, only the third and fourth cervical vertebrae are perforated. Typically in extant Alcidae, the third cervical vertebra is punctured by a small foramina, whereas the foramina in the fourth cervical vertebra is much larger, leaving only a thin strut of bone bordering it laterally. The morphology of the preserved vertebrae is suggestive of C3 and C4; however, definitive assignment cannot be made at this time.

One complete cervical rib and one complete costal rib (Fig. 7D and E) are preserved along with several other rib fragments (not figured). No morphological differences were evident between the ribs of Mancalla vegrandis, Mancallinae specimen SDSNH 25236, and other alcids for which the ribs are known.

All but the omal extremities of the furcula are preserved (Fig. 8D). The furcular rami are mediolaterally compressed as in all other Alcidae. The anterior surface of the furcular rami dorsal to the apophysis is rounded or convex as in Uria, rather than grooved as in Cepphus. The furcular apophysis does not bear the ventrally expanded, bladelike interclavicular process characteristic of extant Alcidae. However, the possibility that this feature was lost to damage cannot be ruled out. No additional morphological differences were evident between the preserved portions of the furcula of Mancalla vegrandis and other alcids for which the furcula is known.

Figure 8.

Holotype specimen of Mancalla vegrandis (SDSNH 77399). A Right scapula in medial view B Left scapula in lateral view C Partial sternum in ventral view D Partial furcula in posterior view (dashed lines represent missing portion of left ramus) E Left coracoid in posterior view. Anatomical abbreviations: a acromion process ce caudal extremity of scapula cr sternal carina ct coracoidal tubercle fa furcular apophysis ff furcular facet of coracoid gp glenoid process lp latral process of coracoid lt lateral trabeculae of sternum pp procoracoid process st scapulotricipital tubercle.

The left coracoid is complete except for a small portion of the medial margin of the sternal facet (Fig. 8E). A fragment of the right coracoid preserves the medial margin of the sternal facet and the sternal portion of the coracoidal shaft (not figured). As in Mancalla cedrosensis the furcular facet is rounded, rather than oval as in Aethia and Fratercula. The head of the coracoid is apneumatic as in all Alcidae, but the brachial tuberosity is deeply undercut as in Alca and Pinguinus. The humeral articulation is more rounded than in extant Alcidae. As in Cepphus, the scar marking the position of m. supracoracoideus is less distinct than in other Alcidae. As in Mancalla cedrosensis, Aethia, and Alle, the procoracoidal process is not punctured by a foramen for passage of the tendon of m. supracoracoideus. The procoracoid process points dorsomedially as in all Alcidae except Aethia, in which the procoracoid points more ventromedially. As in Mancalla cedrosensis, Brachyramphus, Uria, Aethia, and Ptychoramphus Brandt, 1837, the sternal margin of the procoracoid process is concave, rather than convex as in Cerorhinca, Fratercula, and Pinguinus. As in many alcids (e.g., Alca, Brachyramphus) a single, distinct, straight ridge, which extends from the lateral angle of the sternal facet towards the humeral facet is present. This ridge does not extend sternally in Synthliboramphus, Cepphus, Fratercula, Aethia, Ptychoramphus, and Cerorhinca. This ridge is less pronounced and positioned farther laterally in Mancalla cedrosensis. A well-developed lateral process is present. This feature is absent in Mancalla cedrosensis. The dorsal margin of the medial sternal process is notched as in most alcids (e.g., Alca torda). As in Mancalla cedrosensis, the posterior surface of the sternal end of the coracoid is more excavated than in extant Alcidae and the sternal facet is curved ~150°.

Right and left scapulae are preserved (Fig. 8A and B). As in all Alcidae, the scapular shaft is mediolaterally compressed throughout its entire length. As in Mancalla lucasi, the acromion projects farther anteriorly than that of other alcids (e.g., Uria, Aethia). The acromion of Mancalla cedrosensis does not project as far anteriorly as that of Mancalla vegrandis. The coracoidal tubercle is more pronounced than in Mancalla lucasi and Mancalla cedrosensis. As in Mancalla lucasi and Mancalla cedrosensis, a scapulotricipital tubercle is present just distal to the glenoid process on the ventral margin of the scapular shaft. As in Mancalla lucasi, the scapular shaft, including the caudal extremity, is slightly more robust than in other alcids (e.g., Alca, Aethia). The caudal extremity is more dorsoventrally expanded than in Mancalla lucasi. The caudal extremity is not known for Mancalla cedrosensis.

Parts of the left distal end of the sternum including the distal end of the carina, and the left lateral process are preserved (Fig. 8C). Mancalla lucasi and Miomancalla howardi do not preserve the same portions of the sternum so comparisons cannot presently be made between the sterni of Mancallinae. As a result of the deep incisure of the lateral notches the lateral processes of Mancalla vegrandis are more elongate that any other alcids for which the sternum is known. In other Charadriiformes this condition is present only in the Glareolidae and Scolpacidae, and resembles the sternum in Spheniscidae (Fig. 9).

Figure 9.

Comparison of charadriiform and sphenisciform sterni. A Alca torda (USNM 502382) B Aethia psittacula (NCSM 18514) C Sterna anaethetus (NCSM 17085) D Hydrophasianus chirurgus (USNM 490566) E Eudyptula minor (TMM M-391).

The left humerus is preserved (Fig. 7C). Based upon humeral proportions, Mancalla vegrandis represents the smallest known species of Mancalla (Table 2). As in other species of Mancalla, the ventral margin of the ventral tubercle is convex, and the capital groove is relatively narrower than other Alcidae. The ventral tubercle does not project as far ventrally as in Mancalla californiensis. The distal end of the deltopectoral crest transitions to the shaft less abruptly than in Mancalla lucasi. As in other Mancallinae, the humeral head is rotated anteriorly and the supracoracoideus muscle scar does not broaden proximally. The ‘mancalline scar’ is excavated as in Mancalla californiensis, rather than raised in relief like that of Mancalla cedrosensis and Mancalla lucasi (Fig. 5). As in Mancalla lucasi, the ‘mancalline scar’ extends from a point just proximal to the junction of the bicipital crest with the humeral shaft and tapers to a point, and extends into the primary pneumotricipital fossa. The margins of this scar remain parallel in Mancalla californiensis and Mancalla cedrosensis. As in all Mancallinae, the humeral shaft is arced rather than sigmoidal or straight. As in other Mancalla, the dorsal supracondylar tubercle is separated from the dorsal epicondyle by a small notch. A tubercle or papilla is present on the posterior side of the distal end of the humerus adjacent to the dorsal condyle (Howard, 1966). As with all Mancallinae, the anterior surface of the ventral condyle is rounded, rather than flattened as in all other Alcidae. Rounded fossae are present at the proximal ends of the humerotricipital and scapulotricipital grooves. The flexor process extends distal to the ventral condyle as in all Mancallinae and Pinguinus.

The pelvis is preserved in dorsal view (Fig. 7F). Comparisons of pelves within Mancallinae are limited to Miomancalla howardi. As in all alcids the anteroposterior length of the pelvis is greater than two times the mediolateral width across the antitrochanters. The relative length of the pelves of other charadriiforms is anteroposteriorly shorter. The proximal end of the preacetabular ilium is wide as in Miomancalla howardi and most alcids (e.g., Brachyramphus). The distal end of the preacetabular ilium is relatively broader than in Miomancalla howardi. As in Miomancalla howardi the antitrochanteral sulcus does not extend proximally to contact the antitrochanter. As in most Alcidae (e.g., Brachyramphus), the post-acetabular dorsal ilium narrows, rather than broadens as in Uria, Cepphus, and some Fraterculinae. The iliosynsacral suture is perforated as in Uria, Alca, Pinguinus, and Synthliboramphus, rather than fused along its entire length as in Cepphus, Brachyramphus, and Fraterculinae. The dorsal iliac spine has a pointed tip as in all alcids other than Aethia and Ptychoramphus, in which the end of the spine is blunt.

Remarks.

Mancalla vegrandis corresponds in size and humeral characteristics with some material previously referred to Mancalla milleri Howard, 1970. However, Mancalla milleri is considered Alcidae incertae sedis (see Appendix 1 for details of the taxonomic revision).

Miomancalla howardi sp. n.

urn:lsid:zoobank.org:act:BF31D07E-0CFF-4202-BE8C-C5E97F49F625

Holotype.

SDSNH 68312: a partial skeleton collected by B. O. Riney on May 31, 1990 and comprising the following elements: partial skull, mandible, two cervical vertebrae, partial sternum, partial right humerus, left carpometacarpus, pelvis, femora, tibiotarsi, left tarsometatarsus (Figs 10, 11; Tables 1, 2 and 3).

Figure 10.

Holotype specimen of Miomancalla howardi (SDSNH 68312). A Photograph with contrast digitally adjusted to better display bone against similarly colored matrix B Line drawing of holotype specimen showing position of preserved elements with bones in light grey and matrix in dark grey.

Figure 11.

Photograph A and line drawing B of the skull of Miomancalla howardi compared with the skull of Pinguinus impennis (C; not to scale; USNM 346387). Cross-hatched lines on the premaxilla represent abrasion and dotted lines represent approximate reconstruction of incomplete elements. Anatomical abbreviations: a articular cmf caudal mandibular fenestrae en external nares f frontal j jugal l lacrimal m mandible n nasal pm premaxilla nfh nasofrontal hinge o orbit rmf rostral mandibular fenestra sq squamosal; ? unidentified bone fragment.

Etymology.

This new species is named in honor of Hildegarde Howard in recognition of her many contributions to the systematics of extinct Alcidae.

Locality and horizon.

Early Pliocene (Zanclean; Deméré and Berta 2005) upper siltstone member of the Capistrano Formation, San Clemente, Orange County, California. Latitude, longitude and elevation data on file at SDSNH (locality 4160). Details of the geologic setting are provided in Appendix 6.

Referred specimen.

SDSNH 24584, a left humerus (Fig. 12) from the Late Miocenelower member(Messinian) of the San Mateo Formation of San Diego County, California (SDSNH locality 3177). This specimen was noted but not named or described by Chandler (1985) and Livezey (1988).

Figure 12.

Referred left humerus of Miomancalla howardi (SDSNH 24584; dark outlined areas represent reconstructed areas obscured by repair). A posterior view B dorsal view C anterior view D ventral view E proximal view F distal view. Anatomical abbreviations: bs brachialis scar c caput cg capital groove d deltopectoral crest dc dorsal condyle dsp dorsal supracondylar process dst dorsal supracondylar tubercles fp flexor process hs humerotricipital sulcus pf1 primary pneumotricipital fossa ps pectoralis scar sc supracoracoidal crest ss scapulotricipital sulcus tc tricipital crest tf tricipital fossae tls transverse ligament sulcus vc ventral condyle vst ventral supracondylar tubercle vc ventral condyle vst ventral supracondylar tubercle vt ventral tubercle.

Differential diagnosis.

Differs from Miomancalla wetmorei in the following characteristics: ventral margin of ventral tubercle more deeply grooved; transverse ligament furrow deeper, with lateral lip extended farther medially; capital groove wider, and flatter; dorsal supracondylar process less dorsally projected; groove between dorsal supracondylar process and dorsal condyle wider; ventral supracondylar tubercle more prominent; tubercle present proximal to dorsal condyle as in Mancalla cedrosensis (155:1); humerus ~20% longer (Table 2; Livezey 1988, Fig. 3A).

Anatomical description.

The holotype specimen is preserved in a matrix of dark grey, highly indurated, siltstone (Fig. 10). Some elements areslightly crushed and many cortical bone surfaces are considerably abraded, obscuring fine morphological details in many portions of the specimen.

Elements of the skull are exposed in oblique right lateral view (Figs 10, 11). The premaxilla, maxilla, nasal, lacrimal, jugal, frontal, and squamosal are present. Additional fragments of bone adjacent to the posterior frontal may represent a portion of the parietal. An unidentified fragment of bone protrudes from the external narial opening. The premaxilla is relatively shorter and mediolaterally compressed in comparison with the only other known premaxillae referable to Mancallinae (LACM 103940; SDSNH 25236; Fig. 13), which resemble the more terete bills of some other Alcidae (e.g., Uria). The maxilla, which broadens anteriorly before fusion with the premaxilla, is complete but broken at approximately its midpoint. As in many alcids (e.g., Cepphus, Alca) the nasal contacts the maxilla at ~45° angle. This angle is ~60° in the puffins and auklets (i.e., Fratercula, Cerorhinca, Aethia, and Ptychoramphus). As in Pinguinus, and in contrast to other alcids, the lacrimal appears to be directed ventrally rather than posteroventrally. However, crushing of the skull may have changed the relative orientation of elements and it is possible that distortion is responsible for this condition. The jugal is preserved in contact with the mandible. Fusion between the jugal and the jugal process of the premaxilla is visible. The frontal is distorted by crushing and most morphological details obscured in this element. The outline of the right orbit is visible, but is deformed by ventrolateral displacement of the lateral margin of the frontal. The frontal bears a robust orbital rim as in Uria, Miocepphus, Alle, Alca, and Pinguinus.

Figure 13.

Skull of Mancallinae (SDSNH 25236). A Dorsal view of skull B Dorsal view of mandible C Left lateral view of skull D Left lateral view of mandible E Ventral view of skull F Ventral view of mandible (sketches by Michael Emerson).

The mandible is preserved in right lateral view (Figs 10, 11). The mandibular symphysis is elongate as in Uria and Fratercula. The mandibular rami are fused along a relatively shorter distance in some alcids (e.g., Alle). The proximal and distal ends of the mandible are dorsoventrally expanded, similar to the condition in Alca and Pinguinus. A pair of small posterior mandibular fenestrae is present as in other known Mancallinae mandibles (LACM 103940; SDSNH 25236; Fig. 13), Fraterculini Storer, 1960, and some charadriiforms (e.g., Stercorarius longicaudus Vieillot, 1819).

At least two cervical vertebrae are partially exposed on the surface of the slab (Fig. 10). Fine morphological details are obscured by matrix and the poor preservation of the vertebrae. One vertebra resembles the axis, but positive identification is hindered by matrix and damage to the element. The other is a cervical vertebra exposed in dorsal view. Mancallinae vertebrae are known only from the holotype specimens of Mancalla cedrosensis and Mancalla vegrandis. Comparisons with Mancalla cedrosensis are not possible because only a single thoracic vertebra is preserved in the holotype specimen. The shape of the dorsal surface of the cervical vertebrae of Miomancalla howardi is consistent with that of Mancalla vegrandis. Further preparation of the holotype specimen of Miomancalla howardi, or discovery of additional material referable to this species is necessary before more details of vertebral anatomy can be described for this species.

Fragments of the sternum are preserved adjacent to the humerus in what appears to be ventral view (Fig. 10). The craniolateral process appears to point dorsally, rather than anteriorly as in Mancalla lucasi, although the possibility that crushing of this element altered the relative orientation of that feature cannot be ruled out. Other morphological details are obscured by matrix and the poor preservation of the sternum.

The holotype specimen preserves the proximal end of the right humerus in posterior view (Fig. 10). In addition to the head of the humerus, which is slightly crushed, the outline of the proximal half of the humeral shaft is visible as an impression in matrix. A complete left humerus (SDSNH 24584; Fig. 12) is referable to Miomancalla howardi based upon its similar proportions (i.e., larger than any other known Mancallinae; Table 2), and the fact that the ventral surface of ventral tubercle is more deeply grooved than in any other alcid. The ventral surface of the ventral tubercle is also grooved in Pinguinus and Miomancalla wetmorei, but the degree of excavation of this groove is more pronounced in Miomancalla howardi. The ventral margin of the ventral tubercle of Mancalla is convex. The capital groove is relatively wider than that of other species of Mancallinae, and it is incised more deeply into the transverse ligament sulcus in anterior view than in Miomancalla wetmorei. The proximal end of the deltopectoral crest is less pronounced than in Miomancalla wetmorei. The distal end of the deltopectoral crest transitions to the shaft less abruptly than in Mancalla. The humeral head is rotated more anteriorly than in Miomancalla wetmorei, and is more similar to the condition in Mancalla. As in Miomancalla wetmorei and Fratercula, and in contrast to the condition in Mancalla species, the supracoracoideus muscle scar broadens proximally. In Miomancalla howardi and Miomancalla wetmorei the ‘mancalline scar’ extends from a point just proximal to the junction of the bicipital crest with the humeral shaft and tapers to a point that meets the dorsal border of the primary pneumotricipital fossa (i.e., crus dorsale fossae of Baumel and Witmer 1993: 99). The scar is relatively smaller in Miomancalla and Mancalla lucasi thanin comparison with other Mancallinae. The scar is an excavation in all Mancallinae except Mancalla cedrosensis and Mancalla lucasi, in which the scar is raised in relief to the floor of the primary pneumotricipital fossa and the humeral shaft. The shaft of the humerus is arced more so than in Miomancalla wetmorei or any other known alcid, and is less dorsoventrally compressed than in Pinguinus. As in all alcids other than Mancalla, the dorsal supracondylar process is continuous with the dorsal epicondyle, rather than separated from it by a small notch. The dorsal supracondylar process is less pronounced than in Miomancalla wetmorei. A tubercle or papilla on the posterior side of the distal end of the humerus adjacent to the dorsal condyle was described by Howard (1966), who used that characteristic to differentiate between species of Mancalla that possessed the tubercle, and species of Miomancalla (Praemancalla sensu Howard, 1966) that did not posses it. The tubercle is present in Miomancalla howardi. As with all Mancallinae, the anterior surface of the ventral condyle is rounded, rather than flattened as in all other Alcidae. Rounded fossae are present at the proximal ends of the humerotricipital and scapulotricipital grooves. That character cannot be evaluated in Miomancalla wetmorei or Mancalla californiensis owing to damage to the holotype specimens of those species and current lack of referable specimens. The flexor process extends distal to the ventral condyle as in all Mancallinae and Pinguinus.

The left carpometacarpus is preserved in dorsal view (Fig. 10). Although hundreds of Mancallinae carpometacarpi are known from Pliocene marine deposits in California, the holotype specimens of Miomancalla howardi and Mancalla cedrosensis are the only associated specimens that allow for species-level referral of carpometacarpi. The carpometacarpus of Miomancalla howardi is larger than that of Mancalla cedrosensis (~23%; Table 3; Howard 1971), and displays the distal elongation of metacarpal I that is characteristic of Mancallinae. The abraded preservation of this element limits further comparisons.

The pelvis is exposed in dorsal view (Fig. 10). Comparisons within Mancallinae are limited to Mancalla vegrandis. As in all alcids the anteroposterior length of the pelvis is greater than two times the mediolateral width across the antitrochanters. The relative length of the pelves of other charadriiforms is anteroposteriorly shorter. The proximal end of the preacetabular ilium is wide as in Mancalla vegrandis and most alcids (e.g., Brachyramphus). The distal end of the preacetabular ilium narrows more so than in Mancalla vegrandis. As with Mancalla vegrandis the antitrochanteral sulcus does not extend proximally to contact the antitrochanter. The dorsal iliac spine has a pointed tip as in all alcids other than Aethia and Ptychoramphus, in which the end of the spine is blunt.

The distal ends of both tibiotarsi are missing or embedded in matrix (Fig. 10). The poor preservation of these elements limits comparisons with the smaller holotype tibiotarsi of Mancalla cedrosensis to size (~26% larger; Table 3; Howard 1971).

The right femur is exposed in posterolateral view along the edge of the block but is severely abraded: however, the left femur is well-preserved and exposed in anterior view (Fig. 10). The femur is robust and less sigmoidal in shape in comparison with the femora of extant alcids such as Alle or Uria, resembling the condition in Mancalla lucasi and Mancalla cedrosensis, the only other Mancallinae from which the femur is known. The intercondylar sulcus is relatively broader and more well-defined proximally than that of Mancalla lucasi and Mancalla cedrosensis. As in Cepphus, Brachyramphus, and Synthliboramphus, the distally extending and anteriorly projected crest of the femoral trochanter is convex in shape. This feature is flattened (e.g., Alca and Uria) or concave (e.g., Fratercula and Cerorhinca) in other alcids. The femoral head appears relatively smaller in comparison with this element in Mancalla cedrosensis and Mancalla lucasi. The length of the femur is greater than in Mancalla cedrosensis and Mancalla lucasi (Table 3; Howard 1971).

The left tarsometatarsus is preserved in anterior view (Fig. 10). The anterior surface of the shaft is deeply grooved as in Mancalla cedrosensis and Fratercula. Associated specimens with tarsometatarsi that would allow for referral of isolated tarsometatarsi to species are not currently known from other Mancallinae. The outlines of trochlea are visible but the distal end of the element is too badly abraded to discern fine morphological details.

Owing to the incomplete and fragmentary preservation of most Mancallinae specimens referable to species, preliminary analysis of the systematic relationships of Mancalla resulted in an unresolved polytomy among Alcidae sub-clades (i.e., relationships between Mancallinae, Cepphus, Brachyramphus, Synthliboramphus, Alcini, and Fraterculinae (contents = Fraterculini Storer, 1960 + Aethiini Storer, 1960) unresolved at the base of a monophyletic alcid clade (results not shown). Two additional phylogenetic analyses were performed to investigate the position of Mancallinae within Charadriiformes, and the interrelationships of Mancallinae species. The primary phylogenetic analysis included a Mancallinae supraspecific terminal (SST) constructed by combining scorings from 19 Mancallinae specimens (including all holotype material; Appendix 4). The referral of all Mancallinae specimens used to construct the SST was evaluated based upon the unambiguously optimized apomorphies listed in the diagnosis section for Mancallinae above. Note that due to damage or missing elements in Mancallinae holotype specimens, five of the specimens used to construct the Mancallinae supraspecific terminal preserve morphological data not preserved by the holotype specimens, thus providing a more compete picture of morphological variation in Mancallinae than if only the holotype specimens were analyzed. The results of the first analysis were used to constrain the topology of trees accepted during a secondary tree search in which the species-level relationships of Mancallinae were evaluated.

The primary combined phylogenetic analysis of the cladistic matrix including a Mancallinae SST resulted in two most parsimonious trees (MPT’s) of 15, 974 steps (Fig. 14; CI: 0.38; RI: O.50; RCI: 0.19). Additional analyses performed with all characters unordered did not result in topological differences, or an increase in the number of MPT’s recovered. Pan-Alcidae is recovered as the sister to Stercorariidae, a result that is congruent with the results ofprevious molecular based analyses(Ericson et al. 2003; Paton et al. 2003; Thomas et al. 2004; Paton and Baker 2006; Baker et al. 2007), but conflicts with previous morphology-based analyses (Strauch 1978; Björklund 1994; Chu 1995, 1998; Chu et al. 2009; Livezey 2009, 2010; Mayr 2011). Alcidae and Stercorariidae have not been recovered as sister taxa in any previous morphology based analysis, suggesting that molecular sequence data is solely responsible for this hypothesis. There is, however, morphological character support for this clade (Table 4). The combined analysis estimate of relationships among the Alcidae crown clade is congruent with the results of recent analyses of molecular sequence data (Thomas et al. 2004; Paton et al. 2003; Baker et al. 2007; Pereira and Baker 2008), except that Synthliboramphus is placed at the base of Alcinae, rather than as the sister to Alcini (Fig. 14). However, the parsimony analysis by Pereira and Baker (2008) also recovered Synthliboramphus at the base of Alcinae in one of two most-parsimonious topologies. The positions of other species (e.g., Alca + Pinguinus), and sub-clades in Alcidae (e.g., Fraterculinae + Alcinae) are consistent with the results of recent molecular-based analyses (Baker et al. 2007; Pereira and Baker 2008) with dense taxonomic sampling for Alcidae. The only prior morphology-based analyses with sufficient taxonomic sampling for comparison to these results, those by Strauch (1985) and Chandler (1990a), resulted in topologies that strongly conflict with more recent hypotheses of alcid relationships in that they do not support a traditional Fraterculinae (i.e., monophyly of Fraterculini + Aethiini). The Aethiini (i.e., Ptychoramphus + Aethia) are placed basal to the Alcinae (Alca + Pinguinus + Cepphus + Brachyramphus + Synthliboramphus), rather than as sister to the Fraterculini (i.e., Cerorhinca + Fratercula) in the topology of Strauch (1985). Although the work by Chandler (1990a) represented an increase in the number of characters scored for Alcidae, the results of that analysis placed Alle alle and Cepphus in a clade with the Fraterculini, rather than in Alcinae. The combined analysis, as well as previous analyses (Watada 1987; Moum et al. 1994; Friesen et al. 1996; Thomas et al. 2004; Baker et al. 2007; Pereira and Baker 2008) strongly support monophyly of a Fraterculinae clade consisting of Ptychoramphus, Aethia, Cerorhinca, and Fratercula, and the sister-group relationship between Fraterculinae and Alcinae as defined here (Fig. 14).

Only the systematic position of Alle alle Link, 1806 remains unresolved within Alcini (Fig. 14). The systematic position of Alle alle is potentially the most contentious issue within alcid systematics, as it has been recovered as the sister to Alca + Pinguinus (Moum et al. 1994, 2002; Baker et al. 2007), sister to Alca + Pinguinus + Uria (Strauch 1985), sister to Uria (Thomas et al. 2004; Pereira and Baker 2008), sister to Fraterculinae (Chandler 1990a), and sister to Cepphus + Aethia + Brachyramphus (Chu 1998). Resolution of this issue will likely require a comprehensive analysis of alcid relationships including dense taxonomic sampling of extinct Alcidae.

Mancallinae is placed as the sister taxon to all other Alcidae (i.e., placed outside of crown clade Alcidae; Fig. 14). This result is consistent with the only previous analysis that included Mancallinae (Chandler 1990a). The clade composed of crown Alcidae + Mancallinae is therefore designated Pan-Alcidae. The monophyly of Pan-Alcidae is supported by fiveunambiguously optimized morphological characters with a CI = 1.0 (UOMC; Table 4).

The combined analysis recovered relationships among the 29 charadriiform outgroup taxa that are largely congruent with prior molecular-based analyses of the clade, but do not support previous morphology-based results. Larus and Hydrophasianus (i.e., gulls and jacanas) are recovered as more closely related to one another than either are to Charadriius (i.e., plovers), as in the results obtained by Hackett et al. (2008). Also consistent with the results of prior molecular analyses (Ericson et al. 2003; Paton et al. 2003; Paton and Baker 2006; Baker et al. 2007), Alcidae + Stercorariidae is placed as the sister to Laridae + Sternidae + Rynchopidae. In contrast to the combined analysis results presented herein and recent molecular based results, the results of the phylogenetic analyses of morphological data by (Livezey and Zusi (2006, 2007) and (Livezey (2009, 2010) place Alcidae as the sister taxon to Stercorariidae + Rynchopidae + Laridae. However, taxon sampling for Alcidae was limited to Uria in the analysis of (Livezey and Zusi (2006, 2007), and Alcidae was included as a single, taxon level terminal in the analyses of (Livezey (2009, 2010) and Mayr (2011). The morphology based phylogeny of Mayr (2011) placed Alcidae in a polytomy with Dromadidae, Stercorariidae, and a clade comprising Laridae + Sternidae + Rynchopidae. The results of the combined analysis are congruent with recent molecular-based analyses, which place Lari (e.g., alcids, gulls, and pratincoles) as the sister to Scolpaci (e.g., sandpipers and curlews), and place Charadri (e.g., plovers), at the base of Charadriiformes. This hypothesis contrasts with morphology-based results (Björklund 1994; Chu 1995), which were the result of parsimony-based re-analyses of the compatibility analysis of Strauch (1978). In the topology recovered by Björklund (1994) the Charadri and Scolpaci are placed in an unresolved polytomy basal to the Lari, whereas the Lari and Charadri are placed in an unresolved polytomy basal to the Scolpaci in the topology recovered by Chu (1995). The morphology based analyses of (Livezey (2009, 2010) and Mayr (2011) recover Scolpaci as an outgroup to a Charadri + Lari clade. The contents of Charadri, Scolpaci, and Lari estimated by the combined analysis are consistent with the composition of those clades recovered in prior molecular-based phylogenetic analyses (Sibley and Ahlquist 1990; Paton et al. 2003; Ericson et al. 2003; Paton and Baker 2006; Baker et al. 2007), supporting the monophyly of Charadri, Lari, and Scolpaci. An additional combined analysis was performed in which the tree was a priori rooted with the Scolpaci clade (i.e., Hydrophasianus, Tryngites, Numenius, and Bartramia) to mimic the phylogenetic results of (Livezey (2009, 2010) and Mayr (2011). This alternative rooting scheme did not affect relationships recovered among Alcidae or Lari species and clades, between Alcidae and Stercorariidae, or between Mancallinae and other alcids (results not shown).

Also of interest is the placement of Rynchops (i.e., skimmers). Recent molecular analyses recovered Rynchops as the sister to Laridae (Paton et al. 2003; Baker et al. 2007) or sister to Sternidae (Paton and Baker 2006). The morphology-based analyses by (Chu (1995, 1998) placed Rynchops as the sister to Sternidae + Laridae + Stercorariidae. The results of the combined analysis place the Black Skimmer Rynchops niger Linnaeus, 1758 as the sister taxon to the White Tern Gygis alba Sparrman, 1786. Considering the accepted placement of Gygis alba in Sternidae (American Ornithologists’ Union 1998, Brigde et al., 2005), this result would suggest Sternidae paraphyly. Although, this result is not entirely novel because an alternative hypothesis also places Gygis outside Sternidae, as the sister to Laridae + Sternidae (Baker et al. 2007). However, denser taxonomic sampling of Rynchopidae, Sterndidae, and other Charadriiformes may resolve this issue in the future.

Anous (i.e., noddies) was recovered as the sister to Sternidae + Laridae + Rynchopidae in the combined analysis, a placement consistent with the molecular-based results reported by Baker et al. (2007), and in conflict with the morphology-based results obtained by Chu (1998), which place Anous as thesister to Stercorariidae. The only study with dense taxonomic sampling of terns and noddies (Bridge et al. 2005) included a single larid (Larus delawarensis Ord, 1815) as an outgroup taxon, but placed Anous basally in Sternidae. Resolution of the systematic affinities of Anous will likely require denser taxonomic and character sampling across Laridae, Sternidae, Rynchopidae, Anous, and other non-Lari charadriiforms.

The secondary phylogenetic analysis, which evaluated the interrelationships among Mancallinae resulted in two MPT’s of 15, 971 steps (Fig. 15; CI: 0.37; RI: O.51; RCI: 0.19). Binary characters are interpreted as ambiguity (i.e., treated the same as ‘?’ scorings) when they are scored as polymorphic (e.g., 0&1 scorings), explaining the shorter tree length of the secondary analysis as compared to the primary analysis including the Mancallinae SST. The monophyly of Mancallinae is supported by eight UOMC’s (Table 4). Miomancalla wetmorei and Miomancalla howardi are placed as sister taxa, and Miomancalla monophyly is supported by three locally optimized morphological characters (LOMC; 105:0; 113:1; 134:1). Miomancalla is placed as the sister taxon to Mancalla. Mancalla monophyly is supported by one UOMC (137:1) and an additional LOMC (130:1). The placement of Mancalla californiensis as the sister taxon of Mancalla cedrosensis is supported by one UOMC (123:0), and an additional LOMC (109:1). Mancalla vegrandis and Mancalla lucasi are placed as successive outgroups to the clade composed of Mancalla californiensis and Mancalla cedrosensis (Fig. 15).

The taxonomic revision and description of new Mancallinae species herein confirms previous estimates of high diversity in Mancallinae (Howard 1970; Olson 1981; Chandler 1990a), and in combination with the phylogenetic results of the combined analysis, provide a new context for the interpretation of the evolutionary success of this lineage of flightless wing-propelled divers. Similar to the hypothesized independent evolution of flightlessness in penguins and plotopterids (Smith 2010), the placement of Mancallinae as the sister taxon to crown Alcidae suggests that flightlessness evolved independently in the Mancallinae and Pinguinus lineages, making the many osteological characteristics shared between these taxa an even more compelling example of morphological convergence. Phylogenetic support for the monophyly of Miomancalla and Mancalla also provides further contextualization for the interpretation of morphological differences between these sister taxa. Although known diversity is higher for Mancalla, there is an apparent trend towards decrease in size for more derived members of the clade, with the larger Miomancalla and Mancalla lucasi placed basally in the resultant topology (Fig. 15). Although it is tempting to infer large body-mass as the ancestral state for Pan-Alcidae, the reconstruction of this character is ambiguous according to the phylogenetic results, and there is an ~25Ma gap in the fossil record between the oldest known fossil alcid and the oldest Mancallinae fossils. The most important contributing factor regarding the ambiguity of ancestral states within Pan-Alcidae is the incompleteness of the early alcid fossil record. Although an abundance of taxa are known from the Miocene and Pliocene, only a single fragmentary alcid fossil is known form the Eocene (Chandler and Parmley 2002). The only Oligocene fossils that are currently referred to Alcidae are two fragmentary and isolated specimens from the Iwaki Formation in Japan (Ono and Hasegawa 1991). Eocene and Oligocene localities and collections should be targeted to increase knowledge of early diversity and ancestral states within Pan-Alcidae.

Although impressive with regard to the quantity of taxa sampled (n = 242) and the number of morphological characters scored for those taxa (n = 1107), comparisons with the results of a recent morphology based analysis of Charadriiformes (Livezey 2009, 2010) and the results of this study are limited to relationships among outgroup charadriiforms because Alcidae was included only as a suprageneric taxon. With respect to relationships among major charadriiform clades, some of the results of Livezey (2010) are admittedly in conflict with a growing consensus of molecular results based upon a variety of methods (e.g., parsimony, Bayesian) and sampling schemes (mitochondrial and nuclear DNA sequences). For example, although the placement of Charadriin a derived position within Charadriiformes to the exclusion of other clades (Livezey 2010) is in agreement with some previous hypotheses (Strauch 1978; Sibley and Ahlquist 1990; Christian et al. 1992; Björklund 1994; Chu 1995; Thomas et al. 2004; Livezey and Zusi 2007), these hypotheses are in contrast with the results of more recent multigene molecular based hypotheses that recovered Charadri in a more basal position. (Ericson et al. 2003; Paton et al. 2003; Paton and Baker 2006; Baker et al. 2007; Fain and Houde 2007; Hackett et al. 2008). There exists no metric with which to choose between the contrasting results of those many analyses, and thus systematic relationships between major clades of Charadiirformes remain somewhat uncertain. However, the combined analysis results reported herein represent the most inclusive analysis to date with respect to variety of phylogenetically informative data sampled.

Referral of specimens to named species, or recognition of new species, based solely upon size, or provenience, or age, or any combination of those three criteria, run the risk of incorrectly assigning specimens to species, or incorrectly assessing species diversity (Norell 1989; Stewart 2002b; Nesbitt and Stocker 2008; Bell et al. 2010). To avoid the possibility of recognizing two or more fossil species based upon different skeletal elements of the same species, recognition of new species must be predicated upon diagnoses or differentiation from previously named species within a taxon (Appendix 1). Occurrence within the same deposit or deposits of similar age is not considered strong evidence that fossils represent the same taxon. Similarly, a lack of recorded occurrences of a fossil taxon within a deposit or deposits of a particular age does not preclude the possibility that a taxon may have been extant during the time of deposition. For example, if the holotype specimen of a species is an isolated humerus, then only associated specimens with humeri consistent with that of the holotype specimen allow for initial referral of additional skeletal elements. When previously recognized holotype specimens consist of isolated elements, isolated material consisting of elements other than the holotype element cannot be referred to the species level until associated specimens are discovered that facilitate such referral. Although these criteria do not preclude the possibility that cryptic species may lead to underestimation of species diversity (see Stewart 2002b, 2007), these criteria do avoid overestimation of diversity and incorrect assignment of specimens that can result from less rigorous methods (i.e., size, provenience, or age based methods) of specimen referral and species recognition. In the case of Mancallinaeremains, there is little doubt that hundreds of isolated fossils are referable to that clade; however, to avoid future taxonomic confusion, referrals should only be made based upon the criteria outlined above. The morphological differences between Mancallinae holotype and referred specimens described and phylogenetically optimized herein provide a basis for the potential apomorphy-based referral of hundreds of additional isolated Mancallinae remains, which will facilitate future detailed study of interspecies morphologic and size variation in Mancallinae.

The etymology of Mancalla (mancus-from the Latin for crippled or lame, and ala from the Latin for wing; Brown 1956) reflects an antiquated view of flightlessness. The flightless condition observed in ostriches and some rails for example, in which the pectoral elements are diminished in size, has been attributed to lack of predatory pressures and energy conservation strategies (Livezey and Humphrey 1986; McNab 1994). The flightless condition observed in penguins, plotopterids and some auks (i.e., Mancallinaeand Pinguinus) reflects specialization for wing-propelled diving in the form of a functional ‘trade-off’ between aerial and sub-aqueous flight (Storer 1960; Olson and Hasegawa 1979; Bengston 1984; Livezey 1988; Habib 2010). This extreme specialization for wing-propelled diving results in characteristics that are shared not only among flightless alcids, but also with penguins and plotopterids. It was the outward resemblance of Spheniscidae to the familiar Great Auk Pinguinus impennis of the northern Atlantic Ocean that prompted sailors who first encountered Spheniscidae in the southern hemisphere to call them penguins (Olson and Lund 2007). Osteological characteristics shared between flightless alcids and penguins include decrease in range of motion and shortening of the distal wing elements in comparison with volant alcids (Raikow et al. 1988; Fig. 16), distal elongation of metacarpal one (Fig. 17), arced or curved wing elements (Fig. 1), an increase in the size of the tricipital crests of the distal humerus (Fig. 1), and a deeply grooved ventral margin of the ventral tubercle (Fig. 1). Mancallinae share additional convergent characteristics with Spheniscidae such as dorsoventral expansion of the omal extremity of the furcula, and deeply incised lateral sternal notches (Fig. 9). Although the functional significance of these modifications is not precisely known, the demands of wing-propelled pursuit diving for fish involving powered up-strokes and down-strokes likely played a role in the evolution of the convergent morphological characteristics shared by flightless alcids and penguins.

One characteristic that is unique to Mancallinae among all known flightless birds, is the shorter length of the ulna compared with that of the carpometacarpus (180:1). In most birds these proportions are opposite of that observed in Mancallinae, with the ulna being longer than the carpometacarpus. Three associated Mancallinae specimens (LACM 107028; SDSNH 77966), including the holotype specimen of Mancalla cedrosensis (LACM 15373) display this characteristic. Statistical analysis of osteological proportions of flightless alcids quantified the dorsoventral compression of wing elements and shortening of distal wing elements, but surprisingly, Livezey (1988) did not mention the unique relationship between the lengths of the ulna and carpometacarpus. A survey of the proportions of distal wing elements among extinct and extant birds was conducted to assess the distribution of this character state. The only other birds that are known to share this characteristic are several species of hummingbirds (e.g., Phaethornis pretrei; see Mayr 2004, Table 1). The precise functional significance of having a longer carpometacarpus than ulna would require detailed functional morphological study, but given the extreme pectoral specialization of both Mancallinae and Trochilidae, and the need of both of these taxa to produce thrust on both up-strokes and down-strokes, it seems reasonable to postulate that the increased dependence on thrust generated from primary feathers attached to the carpometacarpus (Chai 1997) may play a role in this osteological modification. Although the primaries of Mancallinae would likey have been much shorter than those of Trochilidae, water is a considerably more dense flight medium with different functional requirements than those for aerial flight (Habib 2010). Interestingly, this characteristic is not known in any extinct or extant penguin (J. Clarke, pers. com.).

The relatively large size of Pinguinus and some Mancallinae as compared to other alcids (Livezey 1988) may be linked with flightlessness, because the decreased buoyancy of large body size confers an advantage to piscivorous predators (Sparks and Soper 1987). Additionally, because these diving birds likely spent the majority of their time in the water (i.e., flightless, and came ashore only to breed), the thermal constraints imposed on them are decreased by large body size (Furness and Burger 1988). Furthermore, because Mancallinae were flightless, weight constraints related to maintaining the ability for aerial flight no longer restricted increases in body mass (Simpson 1946, Ksepka et al. 2006). Estimates of body mass in Mancallinae (excluding Miomancalla howardi) range from 1 kg in the smallest species (i.e., Mancalla californiensis) to 4kg in larger species (i.e., Mancalla lucasi; Livezey 1988). Although smaller than the 5kg mass estimated for Pinguinus, the estimated body mass of Mancallinae is greater than volant extant alcids (Livezey 1988). Miomancalla howardi is the largest known Mancallinae, and given the increased shortening and dorsoventral compression of wing elements of Mancallinae as compared to Pinguinus, it may have approached the mass of Pinguinus. Several Pliocene species of Alca are known to have exceeded the size of extant Alca torda (Olson and Rasmussen 2001; Smith and Clarke in review), and estimates based on fossils from Belgium indicate that at least one Pliocene Atlantic species, Alca stewarti Martin et al., 2001, was approaching the wing-loading threshold for flapping-flight (Martin et al. 2001; Dyke and Walker 2005). This apparent trend towards increased size in two separate alcid lineages, known from separate ocean basins during the Miocene and Pliocene is in stark contrast to the smaller body size of most extant alcids. The largest extant alcids are the Murres (Uria aalge and Uria lomvia), with an average body mass of 800-1000g, but the most speciose clade of extant alcids, the auklets Aethia and Ptychoramphus, are among the smallest of extant alcids with a body mass of 85-297g (del Hoyo et al. 1996). Additionally, the Mancallinae lineage and the Alca + Pinguinus lineage are considered the dominant seabirds in their respective oceans during the Pliocene (Olson 1985; Olson and Rasmussen 2001). This temporal disparity in size suggests that the conditions that led to radiations of large alcids in the Pacific and Atlantic Oceans are no longer in place, and that small to moderate size may have played a role in differential survival of alcid species since the Pliocene. However, the largest known alcid, the Great Auk, was not driven to extinction by competition from smaller species or lack of ability to adapt to a changing environment, but rather was exterminated through human exploitation (Bengston 1984; Fuller 1999).

Body size in extant alcids has been correlated with dive depth and feeding ecology (Piat and Nettleship 1985; Prince and Harris 1988; Watanuki and Burger 1999), andlarger body size in extant alcids is associated with piscivory (Bradstreet and Brown 1985). Foraging ranges, dive depths, and prey selection are similar in extant alcids and penguins (Prince and Harris 1988). Little is known about the feeding strategies of Pinguinus (Olson 1977), and there is no direct evidence of feeding strategies in Mancallinae; however, the large size of many Mancallinae and morphological comparisons with extant piscivorous alcids suggest that Mancallinae were specialized for piscivory. For example, the terete bill of Mancalla (e.g., LACM 103940) may be evidence of piscivory, because this characteristic in alcids has been linked with that feeding strategy (Bédard 1969).

The oldest unequivocal fossil alcid (GCVP 5690) is from Late Eocene deposits of the Hardie Mine, Gordon, Georgia, USA (Chandler and Parmley 2002). Likely because of the incompleteness of the specimen, phylogenetic results (not shown) place this specimen at the base of Alcinae in an unresolved polytomy with other Alcinae clades. However, this placement is based upon a single shared character (equal width of the tricipital sulci) and the possibility that characteristics shared with Alcinae are pleisiomorphic for Alcidae should be considered. Accordingly, this fossil is considered Alcidae incertae sedis, rather than Alcinae insertae sedis. The presence of alcids in Late Eocene (Chandler and Parmley 2002) is congruent with divergence estimates placing the origin of Alcidae in the Paleocene (Baker et al. 2007; Pereira and Baker 2008). Although, as pointed out by Wijnker and Olson (2009), those divergence estimates suffer from serious flaws with respect to the taxonomic status and ages assigned to fossils used as calibrations.

The taxonomic status of all but one earlier (i.e., Mesozoic, Paleocene, and Early-mid Eocene) fossil referred to Charadriiformes (Olson and Paris 1987; Harrison and Walker 1977) consists of unassociated, undiagnosable fragments (Hope 2002; Mayr 2005, 2009). The earliest known definitive charadriiform fossil is a humerus that is tentatively referred to the Charadri (Hou and Ericson 2002). Although no radiometric-based date is known for this fossil, the age of Jiliniornis huadianensis Hou & Ericson, 2002 (IVPP V.8323) is estimated to be Middle Eocene based on biostratigraphic correlation (Hou and Ericson 2002). A minimum age of divergence between Alcidae and other charadriiforms in the Eocene suggests that the charadriiform fossil record is quite incomplete (i.e., extensive ghost lineages inferred based upon the fossil record).

The fossil record of Mancallinae ranges in age from Middle Miocene through Late Pleistocene (i.e., Turtonian-Calabrian; Becker 1987). The oldest record of Mancallinae may be the holotype specimen of Miomancalla wetmorei (LACM 42653) from the Mid-Late Miocene Monterey Formation exposed in Laguna Niguel, California; although, the precise stratigraphic position of the holotype locality is unknown. Deposition of the Monterey Fm. spans ~10ma from 17.9-7.4 Ma (i.e., Turtonian; DePaolo and Finger 1991). The holotype specimen is from the upper part of the formation (Domning and Deméré 1984), and would therefore be ~12-7.4 Ma. Miomancalla howardi is known from the Late Miocene San Mateo Formation, which ranges in age from 8.7-4.9 Ma (Zanclean-Messinian; Deméré and Berta 2005). Miomancalla is replaced in Pliocene sediments by Mancalla, with four species known from the Capistrano, San Diego, San Mateo, Niguel, Almejas, and Purisima Formations. The San Mateo Fm. records the highest diversity of Mancallinae, with Miomancalla howardi found in the lower unit, and Mancalla cedrosensis, Mancalla lucasi, and Mancalla vegrandis from the upper unit. The Capistrano Fm., which may be correlative with the San Mateo Fm. (Deméré and Berta 2005), has produced remains of Miomancalla howardi from the lower unit and Mancalla californiensis from the upper unit. The most geographically widespread and chronologically long-lived species (~5.0 Ma - 470 ka) is Mancalla lucasi, known from the Pliocene San Mateo, San Diego, and Niguel formations, and also from the Pleistocene Hookton Formation (Howard 1970; Kohl 1974; Domning and Deméré 1984).

Just as coldwater upwelling is linked to biological productivity in modern seabird communities (Hyrenbach and Viet 2003; Briggs et al. 1987) the Miocene appearance of Miocepphus in the Atlantic Ocean and Miomancalla in the Pacific Ocean coincides with the formation of permanent Antarctic icecaps and shallowing of the Central American Seaway (CAS) that resulted in steeper latitudinal thermal gradients. This resulted in intensified gyral circulation of surface waters, and strengthened coastal and trade winds that promote upwelling (Ford and Golonka 2003). The Early Pliocene (~5 - 3.5 Ma) was a time of relative climate stability and high sea level that coincides with the appearance of speciose alcid lineages in the Atlantic and Pacific Oceans (Warheit 1992). High Mancallinae diversity in the Pacific Ocean, and high Alca diversity in the Atlantic Ocean (Olson and Rasmussen 2001; Smith and Clarke in review) coincides with documented cooling during the Late Miocene and Early Pliocene (~14-3.6 Ma), and establishment of the California current system in the Pacific (Zachos et al. 2008; Lariviere et al. 2009).Although the geology of eastern Pacific marine units is more complex than that of coeval geologic formations from the passive Atlantic margin, sea-level fluctuation records indicate that the same Early Pliocene cycles of transgression and regression are recorded on western Atlantic and eastern Pacific coasts (Haq et al. 1988). The Middle Pliocene (~3.5–3.0 Ma) was characterized by continued global cooling, continued shallowing of the CAS, and the beginning of northern hemisphere glaciation cycles which led to increased coldwater upwelling in the Pacific (Bartoli et al. 2005; Lawrence et al. 2006). The emergence of the Panamanian Isthmus and the final closure of the CAS at ~2.7 Ma resulted in increased northern hemisphere glaciation, which is associated with a severe drop in sea-level (~45m) and the establishment of the modern profile of the California ocean-current system on which Pacific alcids rely today (Hyrenbach and Viet 2003; Bartoli et al. 2005). The microfaunal record documents a southward shift in Atlantic and Pacific cold-adapted foraminiferal faunal regimes (Bartoli et al. 2005), separation of Pacific and Caribbean cocolith assemblages at 2.74 Ma in response to final closure of the Isthmus, and an increase in thermohaline circulation as a result of separation of the Atlantic and Pacific Ocean basins. By ~2.5 Ma the modern climate regime was in place, involving small (i.e., meter scale) fluctuations in sea level associated with Late Pliocene and Pleistocene glacial cycles (Bartoli et al. 2005). The apparent response of seabirds to these climate-related changes in the environment was a significant decrease in diversity (Warheit 1992; Olson and Rasmussen 2001; Dyke and Walker 2005), because only a single species of Alca survives today in the Atlantic, and only a single specimen of Mancalla is known from the Pleistocene (Howard 1970; Kohl 1974). Confirmation of causal links between these climatic shifts and decreased seabird diversity will require more intense sampling of Late Pliocene and Pleistocene seabird fossils and evaluation of other proposed factors such as competition for nesting grounds with pinnipeds (Warheit and Lindberg 1988).

Known diversity of extinct Atlantic alcids now approaches that of extinct Pacificalcids (~16–19 species ranging from Miocene-Pleistocene age; Smith and Clarke in review). The differential extinction of Atlantic alcids, compared with that of Pacific lineages, may be linked to climatic changes that effected the Atlantic and Pacific Oceans in different ways. The alcid Pacific Ocean origin hypothesis is based primarily on higher extant diversity in the Pacific Ocean; however, higher extant diversity in the Pacific is not evidence of origination area, and the two oldest known alcid fossils are both from Atlantic deposits (Wetmore 1940; Chandler and Parmley 2002; Wijnker and Olson 2009). Although the lack of older fossils from the Pacific may simply reflect a gap in the fossil record, hypotheses concerning Pacific ancestral origination of alcids based upon proposed greater extant Pacific species diversity should accordingly be re-evaluated. However, the basal position of Mancallinae and their restriction to the Pacific basin may be viewed as support for the Pacific origin hypothesis for Pan-Alcidae (Storer 1952; Kozlova 1957; Olson 1985; Konyukhov 2002; Pereira and Baker 2008).

Regardless of the ancestral area of the clade (i.e., Atlantic or Pacific), hypotheses regarding the spread of alcids from one ocean basin to another include dispersal by ice-free northern passage through the Bering Strait and Arctic Ocean, and southern dispersal across the submerged Isthmus of Panama (Olson 1985; Konyukhov 2002; Pereira and Baker 2008). These hypotheses are based upon the assumption of dispersal across water, and the first occurrence datum (FAD) for alcid clades, which until the discovery of an auk from the Eocene of Georgia, USA (Chandler and Parmley 2002), included Miocene examples of Mancallinae (Howard 1976), Cepphus (Howard 1982), and Uria (Howard 1981) from Pacific deposits, and Miocepphus (Wetmore 1940) and Alca (Wijnker and Olson 2009) from Atlantic deposits. The ornithological literature is replete with records of occurrences of alcids hundreds or even thousands of miles from their normal ranges (see Konyukhov 2002) and records of alcid ‘wrecks’, sometimes composed of thousands of individuals, that were blown many kilometers inland from the sea by storms (Fisher and Lockley 1954; Stewart 2002a). Given the expanse of geologic time being considered (Paleocene-Recent), the possibility that such events may have led to the dispersal of populations from one ocean basin to another ocean basin must be considered.

As suggested by Bédard (1985), the presence of Atlantic alcids in the Eocene (Chandler and Parmley 2002) confirms that the cold adapted lifestyle of some alcids (e.g., Uria) evolved from ancestors that were adapted to warmer (i.e., Eocene) climates. The development of basically modern ocean circulation patterns was not achieved until ~24–20 Ma when opening of Drake Passage initiated dramatic cooling of Antarctica and formation of a strong Antarctic current that resulted in a switch from high productivity in equatorial regions, to more northern coastal regions (Lear et al. 2000; Ford and Golonka 2003; Liu et al. 2009). Although the southern location of the earliest alcid fossil locality (Georgia, USA) cannot necessarily be interpreted as support for a southern route of dispersal, warm-adapted alcids in the Eocene likely were not restricted to a northern dispersal route.

Rigorous taxonomic evaluation of alcid fossil material resulted in a more refined picture of diversity within Mancallinae, and facilitated phylogenetic analysis of species-level relationships within the clade. The combined analysis and total evidence approaches adopted herein resulted in a well-resolved and strongly supported hypothesis of the position of Mancallinae with respect to other Charadriiformes, and the inter-relationships of Mancallinae species. The phylogenetic position of Mancallinae as the sister taxon to all other Alcidae (i.e., crown clade Alcidae) suggests extensive ghost lineages in Pan-Alcidae, provides further evidence that the charadriiform fossil record is quite incomplete, and demonstrates that flight was lost independently in at least two lineages of alcids. The stem-lineage position of Mancallinae recovered in this analysis is consistent with previous phylogenetic placement of this clade (Chandler 1990a), but contrasts with previous hypotheses of close relationship between Mancallinae and Alcinae (Olson 1985). Although extremely derived morphologically as a result of modifications related to flightlessness, Mancallinae do possess a unique suite of characters, some of which are otherwise found exclusively in Alcinae or Fraterculinae, and some of which are otherwise known only from non-alcid charadriiforms. Although it would not affect the number of inferred origins of flightlessness in Alcidae, the placement of Mancallinae at the base of Alcinae, or at the base of Fraterculinae, would only require an additional 2 steps of tree length (manually calculated in MacClade; Maddison and Maddison 2005), and thus the position of Mancallinae recovered here may be sensitive to the inclusion of additional fossil taxa with morphologies representing ancestral states for Pan-Alcidae. The hypothesized split between the lineages leading to Mancallinae and crown clade Alcidae raises questions about the evolution of flightlessness in charadriiforms, and the biological factors that may have led to the split between Alcidae and their proposed sister taxon, Stercorariidae.

Miomancalla howardi is placed as the sister taxon of Miomancalla wetmorei, and is the largest known species of Mancallinae. The large size and resemblance of the bill of Miomancalla howardi to that of the Great Auk Pinguinus impennis provides an example of within-lineage convergence between two species separated by time and geography. The independent acquisition of morphological characteristics in both lineages of flightless alcids (i.e., Mancallinae and Pinguinus), and the similarity of these modifications to those of penguins and plotopterids, strongly suggests correlation between these morphologies and mode of locomotion. The study of convergence within Alcidae may provide insights about the evolution of flightlessness in penguins, in which there are no known volant species.

Similarly diverse lineages of alcids inhabited the eastern and western coasts of North America during the Miocene and Pliocene. Approximately coeval Early Pliocene deposits in California and North Carolina record the replacement of Miocepphus by Alca in the Pliocene of the Atlantic, and the replacement of Miomancalla by Mancalla in the Pliocene of the Pacific. Global-scale environmental perturbations such as increased cooling following the MMCO, may have contributed to similar scenarios involving species turnover in Pan-Alcidae in both ocean basins.