Review of taxonomy, geographic distribution, and paleoenvironments of Azhdarchidae (Pterosauria)

Abstract The taxonomy, geographic distribution, and paleoenvironmental context of azhdarchid pterosaurs are reviewed. All purported pteranodontid, tapejarid, and azhdarchid specimens from the Cenomanian Kem Kem beds of Morocco are referred to a single azhdarchid taxon, Alanqa saharica. The four proposed autapomorphies of Eurazhdarcho langendorfensis from the lower Maastrichtian Sebeş Formation of Romania are based on misinterpretations of material and this taxon is likely a subjective junior synonym of Hatzegopteryx thambema. Among 54 currently reported azhdarchid occurrences (51 skeletal remains and 3 tracks) 13% are from lacustrine deposits, 17% from fluvial plain deposits, 17% from coastal plain deposits, 18% from estuarine and lagoonal deposits, and 35% from costal marine deposits. Azhdarchids likely inhabited a variety of environments, but were abundant near large lakes and rivers and most common in nearshore marine paleoenvironments.


Introduction
Azhdarchid pterosaurs (Azhdarchidae) are the most derived, successful and stratigraphically youngest group of pterosaurs and flourished during the Late Cretaceous after the decline of most other pterosaur groups (Witton 2007;Witton and Naish 2008). The toothed pterodactyloids (Ornithocheiridae) dominated during the Early Cretaceous and earliest Late Cretaceous (Cenomanian and early Turonian). Starting in the late Turonian all pterodactyloids were toothless: Pteranodontidae and Nyctosauridae in the Western Hemisphere and Azhdarchidae worldwide. This shift in dominance from toothed to toothless pterodactyloids apparently reflects some fundamental changes in Cretaceous ecosystems, which we still poorly understand.
The fossil record of pterosaurs is patchy and confined mostly to Konservat-Lagerstätten where exceptional depositional conditions facilitated preservation of fragile pterosaur bones . Unfortunately, such Lagerstätten are very rare for the Late Cretaceous when most of the evolutionary history of Azhdarchidae took place. Azhdarchidae currently represents a real nightmare for pterosaur taxonomists: most taxa are known from few fragmentary bones, which often do not overlap between named taxa, the few articulated skeletons are poorly preserved (Zhejiangopterus), and the best available postcranial material (Quetzalcoatlus) has remained undescribed for forty years. Nevertheless, the number of azhdarchid localities is impressive and undoubtedly reflect the important role that these pterosaurs played in the Late Cretaceous ecosystems.
The imperfect nature of the azhdarchid fossil record poses a problem for the taxonomic attribution of their isolated bones. It is a common practice to confine azhdarchid taxa to few diagnostic bones whereas other bones in the locality are classified as Azhdarchidae indet. Ibrahim et al. 2010). This superficially objective approach actually creates two taxa for the locality, a named taxon and a taxon left in open nomenclature (Azhdarchidae indet.). This approach violates Ockham's Razor, the principle of parsimony: entities must not be multiplied beyond necessity. In this particular case, the number of azhdarchid taxa in a given locality must not be multiplied unless it can be demonstrated by homologous skeletal elements with different structure. Another aspect of this problem is the creation of multiple named, presumably valid, closely related azhdarchid taxa based on materials from the same stratigraphic unit and the same or neighboring localities. For azhdarchids, this practice was introduced by Langston (1981: 102) who referred the smaller specimens of Texas pterosaur to Quetzalcoatlus sp. "in the absence of proof that it was the young of the species northropi." Kellner and Langston (1996: 222) were "convinced that the small individuals [Quetzalcoatlus sp.] most likely represent a different taxon," but arguments supporting this view have not been presented. This is wrong and misleading. Ontogenetic, sexual, and individual variation is to be expected in the population whereas the existence of closely related species in the same ecosystem is uncommon. Variability is the null hypothesis and taxonomic distinction should only be hypothesized if the size and morphological variation cannot be accounted for by ontogeny, sexual dimor-phism, or allometric scaling. Ignoring of this principle led to unjustified taxonomic inflation and unfounded hypotheses on taxic diversity, niche partitioning, and other aspects of azhdarchid evolutionary history Vremir et al. 2013).
This paper provides a review of the taxonomy and distribution of Azhdarchidae based on the principles outlined above. The revised and annotated list of azhdarchid localities is used to assess the preferred paleoenvironments of azhdarchid pterosaurs.  Kellner et al. 2007 (B), Rodrigues et al. 2011 (C), and Ibrahim et al. 2010 (F). The arrow indicates the beginning of the sagittal crest on the cross sections of the rostra. Abbreviations: naof -nasoantorbital fenestra; sc -sagittal crest.
does not project beyond the straight ventral border of the dentary in contrast to the dentary sagittal crest in ornithocheirids. Furthermore, on the dorsal surface of the mandibular symphysis, there is a variably developed medial crest whereas the ventral surface of the rostrum is gently concave. Also, the ventral side in lateral profile is less steep compared with the dorsal side of the rostrum (Fig. 1). Among the known fragments of the rostrum, BSP 1997.I.67 represents the earliest ontogenetic stage. Here the rostrum is relatively short and the sagittal crest, poorly differentiated from the rest of premaxilla, begins close to the jaw tip (Fig. 1A). The next stage is represented by MNUFRJ 7054-V, where the rostrum is relatively longer (Fig. 1B). The smallest fragment CMN 50859 most likely represents the tip of the rostrum of an adult or subadult individual, which has the sagittal crest far away from the rostral tip (Fig. 1C). The more complete specimen BSP 1993.I.338 comes from a younger individual because it has a relatively steeper dorsal profile of the rostrum at the anterior end, implying that the entire rostrum was shorter ( Fig. 1D). At this stage there is no indication of the sagittal crest in the crosssection of the rostrum. The crest was likely confined to the more posterior part of the skull. The mandibular symphysis BSP 1996.I.36 apparently comes from an individual of a similar ontogenetic age (Fig. 1E). Finally, the largest and presumably oldest specimen in the sample is represented by FSAC-KK 26, the holotype of A. saharica (Fig. 1F). It can also not be ruled out that sagittal crest was present only in males. The known complete cervical vertebrae of A. saharica (Rodrigues et al. 2011: figs 2, 4), which are likely IV (LINHM 014) and V (CMN 50801), markedly differ from the cervicals of Azhdarcho lancicollis in the unreduced neural spine, which is obviously a primitive feature of the Cenomanian taxon. The humerus of A. saharica (Rodrigues et al. 2011: fig. 7) is similar to that of Azhdarcho lancicollis except for the distally projecting entepicondyle.
In a recent phylogenetic analysis by Andres and Myers (2013) B. galaczi clustered in Tapejaridae. Indeed, this taxon is similar to juvenile specimens of Tapejara wellnhoferi (SMNK PAL 1137) in the lateral profile of the dentary symphysis, but the older specimens of the latter taxon have prominent ventral dentary crest (AMNH 2440), which has not been reported for B. galaczi. Furthermore, in the Hungarian taxon, the mandibular symphysis consists of two parts, the beak with its triturating surface, which was possibly covered by a keratinous sheath (as indicated by vascular foramina) and the coalesced dentary rami with a concave dorsal surface (Ősi et al. 2005: fig. 2). In T. wellnhoferi the dentary rami are separated posterior to the beak, which is the primitive condition for pterosaurs. The coalesced dentary rami posterior to the beak are present also in Quetzalcoatlus (Kellner and Langston 1996: fig. 6) and Azhdarcho (unpublished materials), and this character may prove to be a synapomorphy for Azhdarchidae not considered by Andres and Myers (2013). The elongated cervical vertebrae from Iharkút are undoubtedly azhdarchid and the attribution of B. galaczi to Azhdarchidae seems to be well supported.
Aralazhdarcho bostobensis. The taxon is known from several isolated bones, including atlas-axis and anterior fragment of mid-cervical vertebra, from the Santonian -lower Campanian Bostobe Formation at Shak-Shak in Kyzylorda Province of Kazakhstan (Nesov 1984c;Averianov 2004Averianov , 2007b. Samrukia nessovi is based on a mandible fragment from the Bostobe Formation of the nearby Akkurgan locality, originally misidentified as a bird ) but reinterpreted as a pterosaur (Buffetaut 2011), is similar to the mandible of Quetzalcoatlus (Kellner and Langston 1996: figs 4C, D, 5) in having a peculiar posterolateral process of the lateral cotyle of the mandibular articulation, which could be a synapomorphy for Azhdarchidae. Samrukia nessovi is referred here to Azhdarchidae and tentatively considered a subjective junior synonym of Aralazhdarcho bostobensis. A. bostobensis is similar to Quetzalcoatlus in the structure of posterior part of the mandible (poorly known in other azhdarchid taxa). It differs from all known azhdarchid taxa in the reduction of pneumatic foramina lateral to the neural canal on the cervical vertebrae and the convex rather than saddle-shaped humeral head.

Volgadraco bogolubovi.
The species is based on a snout fragment (SGU 46/104a, holotype) and few other isolated bones from the lower Campanian Rybushka Formation at Shirokii Karamysh 2 in Saratov Province, Russia ). The snout fragment (Averianov et al. 2008: pl. 5, fig. 1) was originally identified as part of the mandibular symphysis, but more likely it represents the rostrum . In addition to the previously described specimens, a distal syncarpal was recently found at the type locality. This taxon is likely synonymous with Bogolubovia orientalis, based on cervical vertebra fragment from the Rybushka Formation at Malaya Serdoba in Penza Province, Russia (Bogolyubov 1914;Nesov and Yarkov 1989). Because the holotype of V. bogolubovi is more diagnostic and that of B. orientalis is lost will be better to treat the latter taxon as a nomen dubium and refer all azhdarchid bones from Rybushka Formation to V. bogolubovi. Azhdarchid bones are also known from the Rybushka Formation at the Beloe Ozero localitiy in Saratov Province Averianov 2007bAverianov , 2008Averianov and Popov 2014). Lewy et al. (1992) reported on two natural endocranial casts, one of which is perfectly preserved, from the upper part of the Phosphorite Unit of the Phosphate Member of the uppermost Mishash Formation (uppermost Campanian) at Oron in southern Israel, which they referred to Titanopteryx sp. Although pterosaur nature of the figured endocast (Lewy et al. 1992: pl.1, figs 5, 6) cannot be ruled out (see, for comparison, Witmer et al. 2003), its small size (length around 3 cm) and reported bird-like structure suggest avian affinities.
Quetzalcoatlus northropi. The taxonomic history of this most widely known azhdarchid pterosaur and one of the most popular extinct animals is very confused. When it discovery was first announced it was simply called the Big Bend pterosaur (Lawson 1975b), referring to its provenance from the Maastrichtian Javelina Formation of Big Bend National Park in Texas, USA. In reply to the critique of the first paper, Lawson (1975a: 677) gave a name to the material and designated a type specimen (TMM 41450-3), an articulated wing, but did not provide a diagnosis of the new taxon, which thus is technically a nomen nudum (Sullivan and Fowler 2011). However, an obvious reference to a previous publication (Lawson 1975b), which contains a discussion of diagnostic characters for this taxon, makes the name available (ICZN 1999: Article 13.1.2). To date the only published formal diagnosis of the taxon was provided by Nesov (1991). Lawson (1975b: 947) indicated the presence of larger and smaller specimens at localities separated by 40 km, but decided without further discussion that "all can be referred to a single species because of the similarity of their humeri, proximal carpals, and second phalanges." Kellner and Langston (1996) restricted the name Q. northropi to the holotype, which represents the larger specimen, whereas smaller specimens, which are only half size of the holotype, were referred to a new undescribed species, which they left in open nomenclature as Quetzalcoatlus sp.
Eurazhdarcho langendorfensis. The most complete European azhdarchid is known from an incomplete and poorly preserved skeleton (EME VP 312) from the lower Maastrichtian Sebeş Formation at Lancrĕm in Transylvania, Romania ). The new taxon was diagnosed by four proposed autapomorphies: 1) the length of cervical III is 75% that of cervical IV (vs. about 60% in Zhejiangopterus and Quetzalcoatlus); 2) well-developed and elongated prezygapophyseal pedicles on cervical vertebrae that enclose an angle of 30° relative to the long axis; 3) well-developed preexapophysis with an anteriorly oriented articular facet, separated from the external prezygapophyseal diapophysis by a deep sulcus; 4) lateral pneumatic foramina small and situated lateroventrally to the neural canal. All of these autapomorphies are problematic. Character 1 is a preservational artifact: in cervical IV, the centrum condyle is missing and this was not taken into account when calculating its total length (Vremir et al. 2013: tab. 1). With the length of the centrum condyle added, the length of cervical III could be around 60% that of cervical IV, as in other azhdarchids. The prezygapophyseal pedicels are well developed and elongated in Azhdarcho and other azhdarchids, and E. langendorfensis does not really different from them in this respect. Similarly, the preexapophysis, the articular surface for the postexapophysis, is well developed in all azhdarchids, and the "deep sulcus" is the vertebrocostal sulcus, which contained the vertebral artery and vein and is present in all azhdarchids (Pereda Suberbiola et al. 2003;Averianov 2010). The description of neural canal, which potentially can be seen only on the preserved anterior end of cervical IV, is dubious. It is said that the neural canal is preserved as "a prominent internal mold positioned at mid-height between the preexapophyses" (Vremir et al. 2013: 7). However, the structure labelled as "neural canal" on the line drawing (Vremir et al. 2013: fig. 6c) is actually the hypapophysis of the cotylar articular surface of the centrum, as is clearly seen in the photograph (Vremir et al. 2013: fig. 8b).
In a better preserved cervical III from Râpa Roşie (Vremir 2010: fig. 16), the lateral pneumatic foramina are small and positioned lateral to the larger neural canal, as in most azhdarchids. This is interesting because Arambourgiania is unique among azhdarchids in having the lateral pneumatic foramina larger than neural canal (Martill et al. 1998: figs 5a, 6a, 7a). This argues against the synonymy of Arambourgiania and Hatzegopteryx proposed by Witton et al. (2010). The main problem of E. langendorfensis is that it cannot be differentiated from H. thambema by size-independent characters. Vremir et al. (2013) acknowledged that known materials on E. langendorfensis and H. thambema have no overlapping elements. Identification of EME VP 312 as an immature specimen of H. thambema remains a distinct possibility once this pterosaur becomes better known.
Hatzegopteryx thambema. The holotype of this giant pterosaur consists of associated parts of the skull (occiput and quadrate condyle with adjacent bones) and a fragment of the proximal portion of a humerus (FGGUB R1083) from the upper Maastrichtian Densuş-Ciula Formation at Vǎlioara in the Haţeg basin, Transylvania, Romania (Buffetaut et al. , 2003. Also a diaphysis of a very large femur (FGGUB R1625, preserved length 385 mm) from the same formation at the nearby locality Tuştea was originally referred to this taxon. Vremir et al. (2013) mentioned an anterior fragment of the mandibular symphysis of a large pterosaur from the type locality attributable to this taxon, as well as six specimens from other localities within Haţeg basin, which may belong to smaller individuals. Skeletal fragments of a very large azhdarchid, including a very large cervical III, are also known from the lower Maastrichtian Bozeş and Sebeş formations in the Transylvanian basin of Romania (Vremir 2010;Vremir et al. 2013).
H. thambema was originally diagnosed by the structure of the quadrate condyle, which is "massive, with smoothly rounded rather than angular condyles, and no notch posterior to the lateral condyle" (Buffetaut et al. 2002: 181). At that time the quadrate condyle was known only for Quetzalcoatlus (Kellner and Langston 1996). The construction of the quadrate condyle was interpreted as "helical," but, as was noted by Averianov (2010: 268), in H. thambema the lateral and medial condyles are separated by a groove, whereas in taxa with the helical craniomandibular joint (Pteranodon, Azhdarcho, Quetzalcoatlus) the condyles are separated by a ridge. In pterodactyloids with long skulls (Pteranodon, Quetzalcoatlus), the axis of the craniomandibular joint is perpendicular to the longitudinal axis of the skull and the jugal arches are parallel. If the craniomandibular joint is oriented perpendicular to the long axis in H. thambema, the angle between the jugal arches and the transverse axis of the skull is only ~62° (~90° in Pteranodon), which suggests a very short skull, certainly less than estimated length of 2.5-3 m (Buffetaut et al. , 2003Witton 2013).

Outgroup taxa and their paleoenvironments
Several conflicting phylogenetic hypothesis place different pterodactyloid taxa as the closest relatives of Azhdarchidae (Table 1). In this section, I review all possible azhdarchid outgroup taxa, including non-azhdarchid azhdarchoids, and their paleoenvironments.
Chaoyangopterus zhangi. The holotype (IVPP V13397) and a referred specimen (LPM R0076) are known from two different localities in the Jiufotang Formation of Dapingfang, Chaoyang, Liaoning Province, China (Wang and Zhou 2003;Zhou 2010). The holotype is a subadult (wing span 1.85 m) and the referred specimen is immature (wing span 1.45 m). I refer to this species also HGM 41HIII-305A from an unspecified locality in the same unit in Chaoyang County, the holotype of Shenzhoupterus chaoyangensis (Lü et al. 2008). The latter specimen is also immature (wing span 1.40 m), with the scapulacoracoid and extensor tendon process still unfused. The syncarpals "appear to be coossified" according to Lü et al. (2008: 892) but this claim is not supported by the description or illustration of the bones. The two characters, the unusually slender premaxillary bar bounding the nasoantorbital opening and the extension of the nasoantorbital opening posterior to the jaw joint, comprising the diagnosis of Chaoyangopteridae by Lü et al. (2008), are based solely on this specimen and cannot be observed in any other specimen referred to this family. The first character is likely a juvenile trait of HGM 41HIII-305A. The second character is possibly based on misinterpretation of the specimen. The skull might not be complete posteriorly and the posteroventral corner of the nasoantorbital fenestra is likely filled by cranial and possibly some postcranial bones. The Aptian Jiufotang Formation is the uppermost formation of the Jehol Group, an important Konservat-Lagerstätte producing numerous, often articulated specimens of diverse plants, invertebrates, and vertebrates Chang et al. 2008;Selden and Nudds 2012). The Jiufotang Formation consists of predominantly lacustrine deposits: sandstones, shales, and mudstones with intercalated tuffs. The volcanic activity was relatively weak compared to that recorded by the underlying Yixian Formation. The biota from the Jiufotang Formation is characterized by a distinct complex of freshwater fishes (Jinanichthys ichthyofauna) and by the abundance of ornithurine birds (Cathayornis-Chaoyangia aviafauna) (Chang et al. 2008). The paleoenvironment was dominated by wetlands and lakes.
Jidapterus edentus. This pterosaur is known from two specimens, the immature CAD 01, the holotype of Jidapterus edentus (Dong et al. 2003) and the adult GMN 03-11-002, the holotype of Eoazhdarcho liaoxiensis (Lü and Ji 2005), both from the Jiufotang Formation in Chaoyang County, Liaoning Province, China. In the data matrix by Andres and Ji (2008) the two taxa have 30 identical codings (27% of 111 characters) and differ only in the coding of two characters. In Jidapterus, one of the metacarpals (metacarpal III according to Andres and Myers (2013) or metacarpal I according to Lü et al. (2008)) articulates with the carpus, whereas in Eoazhdarcho metacarpals I-III do not articulate with carpus. The second character is the length of wing phalanx 2 relative to the length of wing phalanx 1, which was miscalculated for Eoazhdarcho. Actually this ratio is 0.78 (Lü and Ji 2005), nearly the same as in Jidapterus (0.71; Dong et al. 2003) and both taxa should be coded for the same character state. Wang et al. (2005) previously suggested that Jidapterus might be congeneric or even conspecific with Chaoyangopterus. The two taxa can be differentiated by the dorsal profile of the skull, which is straight in the former and distinctly concave in the latter. Jidapterus might also have a relatively longer rostrum and mandibular symphysis, but the skulls are insufficiently known in these taxa.
There are several mass-mortality horizons with numerous fish fossils. Terrestrial vertebrates are rare and were introduced from nearby shoreline environments. The climate was arid or semi-arid. The flora consists largely of plants of a xerophytic nature. It is dominated by the gymnosperm Brachyphyllum, which had succulent leaves, and cycadophytes.
Tupuxuara sp. An undescribed taxon, similar to T. longicristatus is known from the Aptian Crato Formation in Ceará State, Brazil. It is represented by a complete skeleton with skull in a private collection and several incomplete postcranial skeletons (Martill andFrey 1998a, 1999;Kellner 1998, 2007;Unwin and Martill 2007). For the paleoenvironment of the Crato Formation see locality 1 in the next section.
Cornet azhdarchoid. Dyke et al. (2011) identified MTCO 21269, a fragment of the anterior end of an elongated cervical vertebra, from the Berriasian-Valanginian Lower Bauxite Formation at Cornet, Romania, as a possible azhdarchid. The complete length of the vertebra is unknown, but its reduced neural spine and merged vertebral centrum and neural arch suggested affinities with Azhdarchidae. The rostrum fragment MTCO 18262 from the same locality (Benton et al. 1997: fig. 12E;Dyke et al. 2011: figs 7G, H, 8N, O) was referred to Dsungaripteridae because of the alveoli being confined to the posterior part of the rostrum. However, interpretation of these openings as neurovascular foramina rather than alveoli is equally possible and, if correct, this specimen may belong to Azhdarchoidea as well. There are some other pterosaur bones from the Cornet site that may belong to Azhdarchoidea (MTCO 17738 and 17755, fragments of proximal portions of humeri and MTCO 17642, fragment of a distal portion of a humerus). The Cornet locality documents an insular fauna inhabiting one of small islands along the northern shores of Tethys (Benton et al. 1997). The fossils were washed into deep fissures and caves formed within a karst of the latest Jurassic marine limestones. Charophytes, ostracods, and freshwater gastropods indicate a lacustrine paleoenvironment (Benton et al. 1997). The humid tropical climate favored the formation of bauxites. The vertebrate fauna includes abundant small ornithopods, rare ankylosaurs and non-avian theropods, birds and pterosaurs (Bock and Buehler 1996;Benton et al. 1997;Posmosanu and Cook 2000;Galton 2009;Dyke et al. 2011).
Palaeornis cliftii. This taxon should be considered a nomen dubium and is based on a humerus preserved as two fragments (NHMUK 2353 and 2353a) from the Valanginian Hastings Beds Group of the Weald Sub-basin (probably from the Upper Tunbridge Wells Formation) at the historical Tilgate Forest locality near Cuckfield in England ). The specimen was referred to Lonchodectidae by  based on comparison with the humeri from the Cambridge Greensand of England and alternatively referred to the toothless azhdarchoid Ornithostoma sedgwicki (Averianov 2012). The Hastings Beds have produced a rich vertebrate fauna, including fishes, turtles, plesiosaurs, crocodyliforms, dinosaurs, and mammals (Benton and Spencer 1995), which likely inhabited a coastal marine environment.
Vectidraco daisymorrisae. This taxon is based on a partial skeleton (NHMUK PV R36621; pelvis and associated vertebrae) apparently from the lower Aptian Chale Clay member of the Atherfield Formation of the Isle of Wight, England ). The Chale Clay Member (Atherfield Clay) is composed of silty clay with numerous small clay-ironstone nodules and accumulated in shallow marine conditions with storm events resulting in silty lags (Simpson 1985). It contains pyritized wood, remains of bivalves and rare ammonites, teeth of hybodontiform sharks and pterosaurs (Benton and Spencer 1995;Naish et al. 2013).
Ornithostoma sedgwicki. This taxon, reviewed by Averianov (2012), includes several edentulous jaw fragments, skull fragment, and some postcranial elements from the Upper Greensand Formation or Cambridge Greensand Member of the Lower Chalk Formation in Cambridgeshire, England (exact stratigraphic provenance for the most specimens is unknown). The fossils from both these stratigraphic units are phosphatized and partially reworked from the late Albian Gault Formation (Unwin 2001;Fischer et al. 2014). The Cambridge Greensand vertebrate assemblage includes diverse fishes, marine reptiles, birds, pterosaurs, and rare dinosaurs (Seeley 1870;Lydekker 1888;Hooley 1914;Collins 1970;Elzanowski and Galton 1991;Unwin 2001;Barrett and Evans 2002;Galton and Martin 2002;Martill and Unwin 2012;Rodrigues and Kellner 2013;Fischer et al. 2014). The abundance of phosphatized bones of diverse marine and terrestrial vertebrates likely reflects a shallow-water ecosystem based on planktonic organisms flourishing in upwelling waters rich in phosphorus and other minerals.

Grandpré azhdarchoid.
A mid-cervical vertebra identical to those of O. sedgwicki has been reported from the Albian Greensand (Sables verts) at Grandpré in the Ardennes, France (Buffetaut 2012). It was identified originally as Azhdarchidae indet. but cannot be referred to Azhdarchidae because of its unreduced neural spine. The Sables verts with phosphate nodules are comparable to the Cambridge Greensand in England. They were similarly deposited in the shallow basin with intensive upwelling. This phosphorite horizon can be traced further to the east in Poland and western Russia (Averianov 2004;Popov and Machalski 2014).

Bennettazhia oregonensis.
A humerus and two fused dorsal vertebrae (USNM 11925) from the Albian Hudspeth Formation at Nelson Creek, Oregon, USA, was originally described as Pteranodon(?) oregonensis (Gilmore 1928). Bennett (1989) first considered this specimen a possible azhdarchid, but later noted its similarity to Dsungaripteridae (Bennett 1994). Nesov (1991) erected a new genus Bennettazhia within Azhdarchidae for this species. It does not appear referable to Dsungaripteridae because of the thin bony walls of the humerus (Habib 2007). The humerus of USNM 11925 agrees well with the morphology of this bone in Azhdarcho lancicollis, except for the distally somewhat expanded deltopectoral crest and unusual shape of humerus in distal view, which is however poorly preserved in USNM 11925 (Averianov 2010). The two fused dorsals of USNM 11925 are possible not part of the notarium or synsacrum (Averianov 2010); the fusion of free dorsals may occur in old individuals. B. oregonensis is best considered a non-azhdarchid azhdarchoid.
The Hudspeth Formation consists of thick sequences of hemipelagic mudstone that contain subordinate siltstones and thin beds of turbiditic sandstone (Dorsey and Lenegan 2007). The fauna consists mostly of marine invertebrates (Vega et al. 2010). The holotype of B. oregonensis and an ichthyosaur centrum, found together with ammonites, are only vertebrate remains reported from this stratigraphic unit (Gilmore 1928;Merriam and Gilmore 1928).

Radiodactylus langstoni.
An isolated humerus (SMU 72547) from the upper Aptian -lower Albian Glen Rose Formation at Squaw Creek, Texas, USA, was initially attributed to Azhdarchidae indet. (Murry et al. 1991) but later referred to a new taxon, Radiodactylus langstoni (Andres and Myers 2013). According to Andres and Myers (2013), the capitulum (=ventral condyle) is damaged and missing some of its articular surface. But it seems more likely that only small portion of posterodorsal articular surface is missing, along with most of the ectepicondyle. SMU 72547 is unusual and distinctly different from the humeri of A. lancicollis and B. oregonensis in the nearly round shape of the humerus in distal view. The capitulum has almost the same width as the trochlea (=dorsal condyle), whereas in A. lancicollis it is about twice as wide (Averianov 2010: fig. 24C). A small pneumatic foramen on the distal surface of the humerus in SMU 72547 (Murry et al. 1991;Andres and Myers 2013) is certainly not compatible with the hypertrophied distal pneumatic foramen on the humerus in ornithocheirids and istiodactylids. In A. lancicollis some small foramina or pneumatic fenestrae may be also present in this region (Averianov 2010). The distal end of the humerus in "Tapejaridae" (Rodrigues et al. 2011: fig. 8B) is very similar to that of A. lancicollis, with the capitulum distinctly wider than the trochlea, the pneumatic foramen absent, and the ulnar tuberculum present (absent in SMU 72547). The phylogenetic position of R. langstoni as a non-azhdarchid azhdarchoid (Andres and Myers 2013) seems well corroborated. The Glen Rose Formation is composed of nearshore marine limestone with abundant marine invertebrates, pollen, and fossil wood, and represents a late Aptian to early Albian marine transgression in the region (Behrens 1965;Davis 1974;Perkins 1974;Jacobs and Winkler 1998). The Glen Rose Formation is famous for its dinosaur footprints (Jacobs 1995). The vertebrate fauna documented by skeletal remains includes diverse chondrichthyan and osteichthyan fishes, amphibians, crocodyliforms, and sauropods (Langston 1974;Winkler et al. 1990;Barck 1992;Welton and Farish 1993;Rogers 2000Rogers , 2003Tidwell and Carpenter 2003). The pterosaur assemblage consists of R. langstoni and the ornithocheirid Coloborhynchus wadleighi (Lee 1994;Andres and Myers 2013).
Cretornis hlavaci. This taxon is represented by a fragmentary wing skeleton from the middle-upper Turonian Jizera Formation (=Iser-Schichten) in the Czech Republic (Fritsch 1881a, b). The species epithet is often misspelled as hlavatschi following unjustified modification by Lydekker (1888). Jianu et al. (1997) have studied the holotype of C. hlavaci and found that it "clearly pteranodontid based on having a caudally directed ulnar crest, a warped deltopectoral crest, and a triangular cross-section of the distal end." All these claims are incorrect. In azhdarchoids, the ulnar crest is directed caudally (ventrally in flight position), similar to the condition in ornithocheirids and pteranodontids. Bennett (1989: fig.2(6, 7)) introduced this character based on comparison with the humerus USNM 11925 (holotype of Bennettazhia oregonensis), where the ulnar crest is almost totally missing. On the humerus of C. hlavaci the deltopectoral crest of is not "warped" and its distal end is not triangular in distal view (see description and discussion below). C. hlavaci is a valid taxon of azhdarchoid pterosaurs. A redescription is currently in preparation by Averianov and Ekrt. The Jizera Formation is composed mostly of marlstones and siliciclastic sandstones and dated as middle-late Turonian. It is underlying by the lower Turonian Bílá Hora Formation and overlying by the upper Turonian -Coniacian Teplice Formation (Uličný 2001;Wiese et al. 2004). The Jizera Formation is part of a transgressive-regressive cycle and was deposited during the regressive phase after the maximum transgression characterized by the Bílá Hora Formation, which is composed of marlstones and micritic limestones. The vertebrate fauna of Jizera Formation, except the pterosaur Cretornis hlavaci, consist of diverse chondrichthyan and osteichthyan fishes and marine reptiles (Fritsch 1883;Ekrt et al. 2008;Kear et al. 2014).

Montanazhdarcho minor. The holotype (MOR 691) is a partial skeleton from an unspecified locality within the upper Campanian Two Medicine Formation in
Glacier County, Montana, USA (Padian et al. 1995;McGowen et al. 2002). Originally this taxon was referred to Azhdarchidae but its short wing metacarpal, which is only 89% of the ulna length, and the pneumatic foramen on the distal portion of the radius suggest that it is a non-azhdarchid azhdarchoid. A redescription of this specimen will be published elsewhere. For the paleoenvironment of the Two Medicine Formation see locality 30 in the next section.

Review of localities of skeletal fossils of Azhdarchidae
Locality 1. Unspecified localities within Crato Formation (Fig. 2) Geographic position. Area between Nova Olinda, Santana do Cariri and Tatajuba, in southern Ceará, Brazil.

Stratigraphy. Nova Olinda Member of Crato Formation.
Age. Late Aptian -early Albian (Batten 2007). Depositional environment. Laminated micritic limestone deposited in lower energy waters. Originally the environment of deposition was considered lacustrine, but, based to more reliable data, much of the formation was deposited under saline conditions with marine waters entering the Crato lagoon (Selden and Nudds 2012). Most likely the water was hypersaline due to the arid climate, which is supported by salt pseudomorphs after hopper-faced halite and a thick sequence of evaporates in the overlying Ipubi Formation Selden and Nudds 2012). Life at the bottom of the Crato lagoon was prevented by a salinity-stratified water column with hypersaline, oxygen-deficient bottom waters (Selden and Nudds 2012). Thus benthic organisms, except cyanobacterial mats, and signs of bioturbation are lacking in the laminated layers of Crato Formation. These factors also account for the good preservation of the fossils on the lagoon bottom, which often show remains of soft parts, making this unit an important Konservat-Lagerstätte. The fishes from the Crato Formation, notably the most common gonorhynchiform Dastilbe (Davis and Martill 1999;Dietze 2007), were likely euryhaline and great numbers of their fossils could be explained by mass mortality caused by influx of marine waters led to sudden increase in salinity (Selden and Nudds 2012). These fish mortality events may have attracted pterosaurs to the Crato lagoon in great numbers. The bodies of terrestrial vertebrates were possibly washed into the Crato lagoon by rivers entering the basin; such finds are exceptionally rare.
Paleoenvironment. Coastal lagoon. Most pterosaur specimens from the Crato Formation are subadult to adult (Unwin and Martill 2007), which suggests that nesting sites were quite far from this environment.
References. Martill and Frey 1998a, b;Sayão and Kellner 1998;Martill and Frey 1999;Frey et al. 2003;Unwin and Martill 2007. Comments. SMNK PAL 2342 was referred to Azhdarchidae because of the Tshaped cross-section of the second and third wing phalanges (Martill and Frey 1998a: figs 4, 5;1999: figs 2, 3). This attribution was questioned by Kellner (2004) and Sayão and Kellner (2007). The latter authors stated that the T-shaped cross-section of the second and third wing phalanges is also found in the "Tapejaridae" from Crato Formation of Brazil and Jiufotang Formation of China. Following this critique, SMNK PAL 2342 was identified as Tapejaridae indet. by Unwin and Martill (2007) and . The only cited Brazil "tapejarid" with T-shaped wing phalanges is MNUFRJ 4729-V (Sayão and Kellner 1998), a wing skeleton whose attribution to Tupuxuara or a related taxon cannot be demonstrated and which is referred here to Azhdarchidae based on this feature. The tubercle on the posteroventral margin of the coracoid, a purported synapomorphy for "Tapejaridae" (Kellner 2004;Aires et al. 2014), has not been mentioned for this specimen (Sayão and Kellner 1998). Concerning the Chinese "tapejarids," the presence of T-shaped wing phalanges have never been demonstrated for them, and it was explicitly stated that the lack of this feature exclude them from Azhdarchidae (Lü et al. 2006: 321). SMNK 3843 was previously identified as a possible tapejaroid (Frey et al. 2003: fig.1c), non-azhdarchid azhdarchoid (Elgin and Campos 2012), or an azhdarchid (Geist et al. in press). The scapulacoracoid of SMNK PAL 3843 has a coracoid flange rather than a tubercle and is more similar to that of azhdarchids (Frey et al. 2003: fig. 1b;Averianov 2010)  Stratigraphy. "Continental Intercalaire" (Lavocat 1949). Kem Kem beds (Sereno et al. 1996). Ifezouane Formation (Cavin et al. 2010).
Age. Early-middle Cenomanian. Depositional environment. The Kem Kem beds include a lower part consisting of red sandstones with cross-bedded stratifications (Ifezouane Formation) and an upper part with lagoonal gypsiferous marly sandstones and green marls (Aoufous Formation). The latter formation is overlain by limestones of the Akrabou Formation, which record a major late Cenomanian-Turonian transgression. The depositional environment was fluviatile or deltaic for the Ifezouane Formation and lagoonal for the Aoufous Formation (Ettachfini and Andreu 2004;Cavin et al. 2010;Ibrahim et al. 2010). The Aoufous Formation was deposited under hypersaline conditions (Cavin et al. 2010).
The diversity of hybodontiform sharks and presence of two species of marine lamnoid sharks suggests that the fluvial beds of Ifezouane Formation were deposited under brackish-water estuarine rather than freshwater conditions. This is also supported by the abundance of sclerorhynchid teeth. Pristids, the closest modern relatives of sclerorhynchids, are marine, brackish and freshwater (Wueringer et al. 2009).
Non-azhdarchid pterosaurs are represented by ornithocheirids, which are known from isolated teeth, a rostrum fragment, and some other bones Averianov 2007aAverianov , 2008 Nesov (1990a: 8) reported a "fragment of small edentulous jaw" from Khodzhakul, which is different from ZIN PH 61/44, but cannot be presently located in the collection.
Stratigraphy. Bissekty Formation (Nesov 1990b;Archibald et al. 1998;. Age. Middle-late Turonian. Depositional environment. The Bissekty Formation is dominated by well-sorted, medium-grained, quartz-dominated, and heavily cross-bedded sandstone with 12 laterally discontinuous intraformational conglomerates. The depositional environment has been interpreted as a braided fluvial system periodically flooded by marine waters, which deposited intraformational conglomerates Redman and Leighton 2009). Nesov intensively collected microvertebrates at Dzharakuduk sites during the period from 1977 to 1994. The microvertebrate remains accumulated on outcrop surfaces due to the wind denudation of the sand matrix and thus Nesov mostly employed surface collecting. However, the surface is contaminated by the fossils from the overlying marine Aitym Formation, notably by numerous teeth of several species of marine sharks. To explain the paradoxical coexistence in one site of marine, freshwater, and terrestrial species Nesov hypothesized that the locality was formed in a channel connecting the estuaries and freshwater basins and the mass mortality of freshwater and brackish-water organisms was caused by wind driven influx of marine or freshwater respectively (Nesov 1990a(Nesov , 1997Roček and Nesov 1993). Screen-washing of about 76 tons of freshly excavated matrix from the Bissekty Formation at Dzharakuduk from 1997 to 2006 showed that only few shark species are present in the fluvial part of the Bissekty Formation (see list below) .
Comments. The bone fragment ZIN PH 183/44, identified as a preaxial carpal in Averianov (2010: fig. 29), is actually a fragment of a juvenile ulna. This bone as well as some other newly recognized bones will be described elsewhere. The Dzharakuduk locality has been mistakenly confused with the nearby locality Itemir and the locality Beleuta in Kazakhstan (Bakhurina and Unwin 1995;Unwin 2001). Kurgan 3 (Fig. 4).

Locality 8. Zenge
Geographic position. Right bank of the Amu Darya River between the villages of Bezergen and Kulatau, Khorezm District, Uzbekistan.
Stratigraphy. Conglomerate of the Bissekty (?) Formation. Age. Turonian. Depositional environment. There are some marine elements in the fauna (Heterodontus sp., Hispidaspis sp., enchodontiforms), which are absent in the fluvial deposits of the Bissekty Formation at Dzharakuduk, northeast of Zenge Kurgan 3. These marine elements and conglomerates may indicate deposition in a submarine delta.

Locality 11. Bayshin Tsav
Stratigraphy. Upper part of Baynshire Formation. Age. Late Turonian -Santonian (Averianov and Sues 2012a). Depositional environment. Alternating thin layers of fining−upward units (from coarse sands to mud) intercalated with many layers of yellowish brown to reddish brown, coarse−grained sandstone and relatively fine−grained conglomerate, probably representing point-bar deposits. The bone-bearing bed is one of the bluish white, fine− to coarse−grained sandstone layers that alternate with gray mudstone layers, containing isolated dinosaur bones and teeth (Watabe et al. 2009). The section of Baynshire Formation at Bayshin Tsav has been interpreted as a cycle of alluvial-lacustrine deposits (Tsybin and Kurzanov 1979).
References. Watabe et al. 2009. Depositional environment. The Mifune Group is subdivided into three informal formations, "basal," "lower," and "upper." The "Basal" and "Upper" formations are non-marine in origin and the Lower Formation was deposited under shallow-water marine conditions with Cenomanian-age ammonites, inoceramid and trigoniid bivalves, and sharks (Matsumoto 1939;Matsumoto and Noda 1986;Ikegami et al. 2000;Ikegami and Tomida 2003;Sha 2007;Kitamura 2013). The vertebrate remains are confined to the several levels within the "Upper" Formation (800-1000 m), which is composed of red mudstone, greenish fine-grained sandstone, and dacitic tuffaceous beds. MDM 349 was found in the middle part of the "Upper" Formation in a coarse sandstone bed, which is about 30 cm thick and has muddy patches between two tuff beds (Ikegami et al. 2000). The "Upper" Formation contains broad-leaf angiosperm megafossils (Protophyllum and Populus) and is interpreted as terrestrial, including swamp, deposits under the influence of a warm climate with alternating dry and wet seasons (Matsukawa and Obata 1994).
Stratigraphy. Csehbánya Formation. Age. Santonian. Depositional environment. The Csehbánya Formation consists of channel and alluvial plain deposits, including sandstone bodies and paleosol horizons, and the bone beds probably formed in a shallow channel or pond that was episodically filled by debris flows Makádi 2013;Rabi et al. 2013). The pycnodontiform fishes and mosasauroid lizards lived in freshwater based on geochemical analysis of their remains (Kocsis et al. 2009).
Paleoenvironment. Coastal plain around marine bay along the shores of the Turgai Strait.
Material. Aralazhdarcho bostobensis: Anterior fragment of mid-cervical vertebra (holotype) and other isolated bones in ZIN PH collection.
Stratigraphy. Grünbach Formation, Lower Gosau Subgroup. Age. Early Campanian (Sachs and Hornung 2006;Summesberger et al. 2007). Depositional environment. The Gosau Group is a marginal continental to shallow marine succession of Late Cretaceous and Paleocene age, deposited in several small synclinal basins along the northern margin of the Eastern Alpine zone (Faupl et al. 1987;Wagreich and Marschalko 1995). The Lower Gosau Subgroup (upper Turonian-Campanian) is characterized by terrestrial to shallow-water marine facies associations: alluvial fan and fan delta deposits, shallow-marine sandstones and sandy limestones, and storm-influenced nearshore and shelf deposits (Wagreich and Faupl 1994). The Grünbach Formation comprises interbedded coal seams, coaly siltstones, sandstones, and conglomerates that were deposited under freshwater to nearshore marine conditions (Kvaček and Herman 2004;Sachs and Hornung 2006;Rabi et al. 2013).
Paleoenvironment. An estuarine, brachyhaline-brackish environment based on its fauna, flora, and lithofacies (Sachs and Hornung 2006). Plant fossils indicate a subtropical climate with seasonal aridity and a paleoenvironment of coastal freshwater ponds and oxbow lakes surrounded by swampy lowlands (Kvaček and Herman 2004;Herman and Kvaček 2007).

Age. Early Campanian (Kennedy and Cobban 1993).
Depositional environment. At the northern end of its occurrence, the Merchantville Formation is mainly a sequence of thin very fine to fine-grained sandy and silty beds and, less commonly, thick beds of glauconitic sand. Discontinuous layers of rounded pale-gray siderite concretions are abundant in the thin-bedded sequence. In the west-central outcrop area, the Merchantville Formation is a thick-bedded sequence of dark-gray clayey quartz silts and dark-greenish-gray quartz-glauconite sands. In the southwest, the formation is a dark-gray massive silty fine to very fine glauconite-quartz sand. Fossil casts are abundant, and locally in the southwest, very fossiliferous siderite concretions are common in the lower part of the formation (Owens et al. 1970).
References. Baird and Galton 1981. Comments. Bennett (1994) thought that these specimens might belong to Pteranodon. Referred to ?Pteranodon by Barrett et al. (2008). According to Howse (1986: 316) YPM-PU 21820 is not referable to Pteranodon because of lack of preexapophyses and it differs from Nyctosaurus by its much larger size.
Stratigraphy. Middle Member of Tangshang Formation. Age. Early Campanian (Mu and Cai 1992;Cai and Wei 1994). Depositional environment. The Tangshang Formation (250-2600 m) consists of alternating volcanics and sandy conglomerates (Chen and Chang 1994). The Tangshang Formation in western part of Zhejian Province consists of Lower Cretaceous strata which have Albian radiometric dates (Lu et al. 2006;Jin et al. 2007). Near Linhai city a black shale occurs within the upper part of the conglomeratic suite and contains specimens of the teleostean fish Paraclupea and the conchostracan Linhaiella (Chen and Chang 1994). At the pterosaur locality the Tangshang Formation is composed of lacustrine sediments interbedded with calcareous tuffs . The locality was formed in a large fresh or brackish-water inland lake (Chen 2000 : figs 3, 4).
Associated fauna. The non-avian theropods and dinosaur eggs reported from the Tangshang Formation apparently come from the Early Cretaceous part of the formation (Dong 1979;Mateer 1989). At the pterosaur locality, only a complete skeleton of a small theropod, possible a dromaeosaurid, has been found .

Stratigraphy. Hakobuchi Formation or Group.
Age. Late Campanian. Depositional environment. The local stratigraphy of the Cretaceous deposits on Hokkaido is very complex due to local tectonics and the stratigraphic nomenclature differs considerably from author to author (Ando et al. 2001(Ando et al. , 2010. According to Shigeta et al. (2010), the Hakobuchi Formation consists mainly of sandstone and is divided into the four lithological units (in ascending order): IVa, sandstone in association with conglomerate, sandy mudstone and coal beds; IVb, sandy mudstone; IVc, sandstone with intercalations of conglomerate and sandy mudstone beds; and IVd, sandy mudstone. Based on ammonites, unit IVa is late Campanian and IVb is early Maastrichtian in age. The pterosaur fossil was found with the ammonite Metaplacenticeras subtilistriatum and thus come from unit IVa of the Hakobuchi Formation (Chitoku 1996;Shigeta et al. 2010: fig. 6). The Hakobuchi Formation in the Nakagawa area, close to Enbetsu town, consists mainly of sandy shallow-water marine facies, which suggests a storm-dominated shore face to shelf environment. Fluvial and estuarine sediments are limited to the western sections, indicating the paralic to fluvial nature of the sediments occasionally recorded as incised valley fills (Ando et al. 2010).
Paleoenvironment. Coastal marine. The pollen from the coal beds is dominated by angiosperms and indicates a subtropical climate (Sato 1961;Miki 1977).
Comments. Referred to ?Ornithocheiridae by Barrett et al. (2008). Not referable to the Ornithocheiroidea because of small lateral pneumatic foramen.
Stratigraphy. Seidan Formation, Izumi Group. Age. Late Campanian. Pachydiscus awajiensis Zone (Saegusa and Furutani 2004). Depositional environment. The Campanian-Maastrichtian Izumi Group is distributed in a narrow, long area along Shikoku, Awaji Island and the Kii Peninsula to the south-west. This group was likely deposited in a strike-slip basin and exhibits an upward-deepening sequence from a nearshore to slope basin, which is dominated by turbidites. The Izumi Group of Awaji Island is divided, in ascending order, into the Seidan, Anaga, Kita-ama, Nada and Shimonada formations (Morozumi 1985).
The Seidan Formation is composed of mudstones, sandstones, and alternating beds of sandstone and mudstone (Misaki et al. 2014).
References. Saegusa and Furutani 2004;Tanimoto 2010. Comments. A wing-metacarpal shaft fragment UMUT MM 7978 from the lower Maastrichtian Kita-ama Formation of Awaji Island, referred to ?Azhdarchidae (Obata et al. 2007), may indeed belong to this group but this cannot be firmly established.
Stratigraphy. Dinosaur Park Formation. Age. Late Campanian. Depositional environment. The Dinosaur Park Formation (70 m) is divided into lower sandy zone, middle muddy zone, and upper Lethbridge Coal Zone (Eberth 2005). The lower zone consists primarily of fine-to medium-grained, cross-bedded sandstones and was deposited in fluvial-channel environments. The middle zone consists primarily of massive to laminated, organic-rich mudstones with abundant root traces, and thin beds of bentonite. It was deposited in overbank and floodplain environments. The upper zone consists of several seams of low-rank coal interbedded with mudstones and siltstones. The Dinosaur Park Formation was deposited on an alluvial plain near the coast of the Bearpaw Sea, a large inland sea that was part of the Western Interior Seaway. There are two paleoecological assemblages in the formation: inland in the lower zone and coastal in the middle zone (Brinkman 1990;Brinkman et al. 2005b). These two communities and the lithology of the Dinosaur Park Formation reflect a transgression of the Bearpaw Sea, which culminated in the deposition of marine shales of Bearpaw Formation above the Dinosaur Park Formation (Eberth 2005). The Lethbridge Coal Zone represents transitional terrestrial-marine environment, a tidally influenced estuary, with marine chondrichthyans and mosasaurs (Beavan and Russell 1999;Brinkman et al. 2005a;Caldwell 2005). The coastal community is characterized by a diverse chondrichthyan fauna, whereas in the freshwater fluvial beds only three chondrichthyan taxa are present (Brinkman et al. 2005b;Neuman and Brinkman 2005). Unfortunately, there is no published information on the stratigraphic positions for occurrences of pterosaur bones in the Dinosaur Park Formation.
Paleoenvironment. Fluvial coastal plain and estuarian (Eberth and Brinkman 1997;Eberth 2005  References. Russell 1972;Currie and Russell 1982;Currie and Jacobsen 1995;Godfrey and Currie 2005;Sullivan and Fowler 2011. Comments. Godfrey and Currie (2005) distinguished two forms of azhdarchids from the Dinosaur Park Formation: a smaller form, similar in size to Montanazhdarcho minor, and a larger one, similar to Quetzalcoatlus sp. Two smaller fragments of humeri (RTMP 82.16.303 and 97.12.163) have fully ossified distal ends whereas in specimens about twice as large (RTMP 92.83.4 and 1991.36.374) the distal ends are poorly ossified. Actually, the distal epiphysis may not be fused to the shaft in the figured specimen RTMP 92.83.4 (Godfrey and Currie 2005: fig. 16.6C-E). The presence of two forms may well be explained by sexual dimorphism or interspecies variation within two closely related species. The two known fourth metacarpals (RTMP 87.36.16 and 92.83.1) have "normal" proportions, not markedly shortened as in the holotype of M. minor. I see no reason to infer the presence of Montanazhdarcho in the Dinosaur Park Formation. Godfrey and Currie (2005) cited also another, non-azhdarchid pterosaur in the Dinosaur Park Formation. This identification is based on two similar specimens, RTMP 79.14.247 and 88.50.1. The former specimen was interpreted as the distal end of a pterodactyloid tibia (Currie and Padian 1983) or distal end of a wing metacarpal (McGowen et al. 2002). However, most recently this specimen was reinterpreted as an avian tibiotarsus (Buffetaut 2010). Currently there is no evidence for the presence of non-azhdarchid pterosaurs in the Dinosaur Park Formation. (Figs 6, 7) Geographic position. Near Choteau, Montana, USA.

Locality 30. Egg Mountain
Stratigraphy. Upper Two Medicine Formation (Padian 1984). Age. Late Campanian (Rogers et al. 1993). Depositional environment. The upper part of the Two Medicine Formation was deposited during the final stages of the Bearpaw transgression (Horner et al. 1992). It contains a lacustrine varve-like sequence associated with a pulmonate-dominated gastropod fauna. The climate was characterized by sporadic or possibly seasonal precipitation (Varricchio 1993). The pterosaur remains occurred in a well-laminated freshwater limestone (Padian 1984). The bones were associated with stromatolites and unionid freshwater bivalves and embedded in a limestone concretion.
This large azhdarchid possible coexisted with the non-azhdarchid azhdarchoid Montanazhdarcho minor, which was found at an undisclosed locality in the Two Medicine Formation in Glacier County, Montana, USA (Padian et al. 1995;McGowen et al. 2002).
Paleoenvironment. Coastal plain. According to Padian (1984), the region at the time of deposition was part of a "proximal lowland" about 700 km from the midcontinental seaway. According to the paleogeographic map used here (Fig. 7a) this distance is only about 270 km.

Stratigraphy. Grès à Reptiles Formation.
Age. Late Campanian -early Maastrichtian. Depositional environment. The non-marine Late Cretaceous in Saint-Chinian area of southern France is represented by red beds consisting of conglomerates, sandstones, and clays and by freshwater limestones, known as the "Grès à Reptiles", overlain by basal Cenozoic red clays (Buffetaut 2005). Vertebrate remains occur, sometimes in abundance, in all these facies, the most productive localities being in the clay layers.

Stratigraphy. Grès à Reptiles Formation.
Age. Late Campanian -early Maastrichtian. Depositional environment. The vertebrate-bearing beds of the Grès à Reptiles Formation in the region consist of clays and sandstone lenses. The bones atthe Bastide-Neuve locality come from yellowish sandy clays (Buffetaut et al. 2006).
Age. Late Campanian. Depositional environment. The Cretaceous deposits at the Laño quarry consist of the lower alluvial system, lower palustrine system, upper alluvial system, and the lower coastal system (Astibia et al. 1991(Astibia et al. , 1999. The lower coastal system contains teeth of marine reptiles and sharks, including the myliobatiform Rhombodus binkhorsti. The remains of terrestrial vertebrates are confined to three associated fossiliferous beds (known as L1A, L1B and L2) at the bottom of the lower alluvial system. The sedimentary structures of these beds are consistent with channel areas within an extensive braided river (Pereda Suberbiola et al. 2000).
Depositional environment. The fossils come from the boulders composed of hard, grey, medium-grained calcareous sandstone (Keyes 1977;Wiffen 1980). Except macrofossils, the boulders contain terrestrial pollen and spores and also marine dinoflagellate cysts in some samples (Vajda and Raine 2010). The boulders occur as concretions within the thick sandstone sequence exposed in the stream banks, which is of identical composition to the boulders, but slightly less calcareous. The fossiliferous beds were deposited on the continental shelf, apparently under shallow-water nearshore conditions (Wiffen and Molnar 1988).
Comments. The cervical was originally described as an internal cast (Monteillet et al. 1982). According to Buffetaut (2004: 574), however, it is a cast of the outer surface.
Age. Late Campanian -early Maastrichtian (Leanza et al. 2004). Depositional environment. The Allen Formation is composed mainly of a red or yellowish lower sandy member, a middle lacustrine section with grey-greenish shales and an upper part with gypsum, limestones and stromatolitic limestones (Leanza et al. 2004). It was deposited during a major marine transgressive phase occurring in the Late Cretaceous (Cazau and Uliana 1972;Uliana and Dellape 1981). Facies vary from intertidal environments in the eastern part of basin to tide-dominated estuarine in the western part (Gasparini et al. 2003;Gómez et al. 2008).
Paleoenvironment. Coastal marine. The paleoenvironment of the Allen Formation has been interpreted as a nearshore to restricted-marine setting (Uliana and Dellape 1981). The locality was situated on the shore of an epicontinental sea covering most of the Patagonia during the Late Cretaceous (Apesteguía and Jones 2012: fig. 4C). The fish fauna includes variety of freshwater forms (dipnoans, amiids, lepisosteids, siluriforms, and possible perciforms) as well as euryhaline taxa (batoids, aspidorhynchids) (Brito 1997;Martinelli and Forasiepi 2004;Apesteguía et al. 2007;Bogan et al. 2010).
The presence of plesiosaurs (Gasparini et al. 2003) suggests at least an estuarine environment. MPCN-PV 0054 was collected from a horizon with fish vertebrae and scales, chelid shells, and elasmosaurid remains, indicating a nearshore marine depositional environment for this layer .
Age. Latest Campanian -earliest Maastrichtian . Depositional environment. Transitional marine-brackish sequence. The pterosaur wing phalanx was found in the brackish estuarian facies (Vremir 2010;Csiki-Sava et al. 2012). Age. Usually considered late or «middle»-late Maastrichtian (Hunt and Lehman 2008). The tuff bed below the two Quetzalcoatlus sites has isotopic dates of 69.0±0.9 Ma (Lehman et al. 2006), which is early Maastrichtian. Because of the division of the Maastrichtian into two substages and the early/late substage boundary set at about 66 Ma (Gradstein et al. 2004), an early Maastrichtian age is accepted here for the Quetzalcoatlus localities.
Depositional environment. The Javelina Formation consists of well-indurated conglomeratic fluvial sandstones and variegated mudstone intervals with paleosol horizons. These strata were deposited in fluvial flood-plain and associated lacustrine environments more than 400 km (Lawson 1975b) or several hundred km (Wick and Lehman 2013) inland from the Late Cretaceous shoreline. According to the paleogeographic map used here (Fig. 7b) this distance is about 290 km. Pterosaur bones occur in several concentrations, which are very closely spaced stratigraphically (Kellner and Langston 1996). These bone concentrations are within shallow alkaline-lake deposits in abandoned stream channels. One such concentration, comprising some 235 disarticulated but closely associated to randomly scattered bones of at least 9 individuals, represents a non-attritional mass mortality, and suggests possibly gregarious behavior among these pterosaurs. The enclosing lacustrine facies lacks other vertebrate fossils, but contains charophytes, gastropods, bivalves, and arthropod trace fossils (Lehman and Langston 1996). Lawson (1975b) noted a close association of pterosaur and sauropod remains.
Paleoenvironment. Lacustrine. The land adjacent to the lake was vegetated with palms, whereas the floodplains supported a tropical forest dominated by Javelinoxylon and araucarian conifers. The climate was warm, dry, and non-seasonal, with mean annual temperatures exceeding 20° and rainfall less than 1000 mm per year (Lehman and Langston 1996). Q. northropi was a member of southern Alamosaurus tetrapod community (Lehman 1987(Lehman , 2001Vavrek and Larsson 2010).
References. Lawson 1975a, b;Langston 1981;Langston 1994, 1996;Lehman and Langston 1996;Andres and Myers 2013. Comments. The smaller specimens come from the Amaral site (Kellner and Langston 1996). The type locality for Q. northropi is separated from this site by 40 km (Lawson 1975b).
Stratigraphy. Sierra Perenchiza Formation. Age. Middle-late Campanian. The vertebrate-bearing beds of Chera contain the charophyte Peckichara pectinata, which is a biostratigraphic marker for the middle to late Campanian (Company et al. 2005).
Depositional environment. The Sierra Perenchiza Formation represents the beginning of the continental sedimentation, which took place in shallow, lacustrine basins during the final Cretaceous marine regression (Company et al. 2005). It consists mainly of interbedded carbonate marls and lacustrine limestones, interpreted as deposits of small ephemeral lakes and ponds of a coastal environment (Company and Szentesi 2012). These sediments were periodically exposed and subjected to pedogenic modification, developing swampy regressive sequences.
Material. Azhdarchidae indet.: MGUV 2271, fragment of posterior portion of cervical IV ; other fragmentary cervicals and miscellaneous limb fragments in MGUV and MPV collections.
Locality 42. Maple Hill (Fig. 6) Geographic position. Pender County, North Carolina, USA. Stratigraphy. Rocky Point Member of the Peedee Formation. Age. Late Maastrichtian (Christopher and Prowell 2002). Depositional environment. The Peedee Formation consists of dark greenish to gray, micaceous, glauconitic massive sands. The upper part of this formation has been divided into two members, the lower Rocky Point and the upper Island Creek (Harris and Self-Trail 2006). The Rocky Point Member is composed of well-cemented sandy molluscan-mold grainstone to calcareous cemented quartz arenite to unconsolidated quartz sand. The pterosaur specimen came from the bed of calcareous glauconitic arenite (Parris et al. 2004).
Comments. A partial skeleton possibly referable to A. philadelphiae has been found recently at a new Maastrichtian locality in Jordan (Wilson and Zalmout 2006). The two endocranial casts from the upper Campanian Mishash Formation of Israel referred to Arambourgiania sp. (Lewy et al. 1992) possibly belong to birds. (Fig. 6) Geographic position. Near Khouribga, central Morocco.
Age. Late Maastrichtian (Cappetta 1987;Pereda Suberbiola et al. 2003). Depositional environment. Fish vertebrae, shark and teleost teeth, and mosasaur vertebrae and teeth were found in the matrix around the skeleton and indicate marine depositional environment (Pereda Suberbiola et al. 2003). It is also confirmed by the analysis of the whole fauna (Arambourg 1952). Except for the pterosaur, the only record of a terrestrial animal found in this locality is a partial skeleton of a titanosauriform sauropod, a possible remnant of a floating carcass that drifted over a distance from a land area (Pereda . Associated fauna. Marine chondrichthyan and osteichthyan fishes, bothremydid turtles, plesiosaurs, mosasaurs, sauropods (Arambourg 1952;Cappetta 1987;Noubhani and Cappetta 1997;Pereda Suberbiola et al. 2003Bardet et al. 2004).
Paleoenvironment. Coastal marine. Highly productive upwelling waters indicating by intensive deposition of phosphates and very abundant and diverse remains of fishes and other marine vertebrates.
Depositional environment. The Sebeş Formation succession is dominated by coarse, mainly cross-bedded channel fills (gravels, sandy gravels, cross-laminated sandstones) with occasional interbedding by finer-grained red or brownish-red overbank and floodplain associations (fine laminated sandstones, silty claystones, massive mudstones), all of which was formed by a high-sinuosity fluvial system (Brusatte et al. 2013). Deposition took place under various conditions, from proximal alluvial fans to the medium and distal facies of meandering, occasionally braided, fluvial systems that exhibit local evidence for well-developed lacustrine, forested-swampy, short evaporitic stages and extensive pedogenized floodplain deposits. The vertebrate fossils originate mainly from the red overbank deposits .
Depositional environment. The Lower Member of the Densuş-Ciula Formation is mostly lacustrine but strongly influenced by volcanic eruptions to the west; a volcanic overprint is also present in the fluvial/lacustrine Middle Member, whereas the Upper Member comprises clastic sediments (Grigorescu 1992;Grigorescu et al. 1999).
Associated fauna. Gastropods, holostean and teleostean fishes, albanerpetontids, anuranans, basal cryptodiran turtles, lizards, crocodyliforms, sauropods (skeletal remains and eggs), theropods, and multituberculates (Grigorescu et al. 1990(Grigorescu et al. , 1994(Grigorescu et al. , 1999Weishampel et al. 1991;Buffetaut et al. 2003 References. Buffetaut et al. , 2003Vremir et al. 2011Vremir et al. , 2013 Comments. The first pterosaur bones at Sînpetru and Vǎlioara were collected by Baron Franz Nopcsa at the turn of the nineteenth and twentieth centuries (see Buffetaut et al. 2003). Jianu et al. (1997) referred these specimens to the Sânpetru Formation and mentioned additional pterosaur material (two notaria, humerus, and femur) from the "same locality," not explaining which locality they meant. These bones were referred to Pteranodontidae because of fused notarium with supraneural plate and humerus with "warped" deltopectoral crest and a caudally (ventrally in flight position) directed ulnar crest. Bennett (1989: 675, fig. 2(6, 7)) introduced "ulnar crest directed posteriorly" as a synapomorphy of Pteranodontidae based on comparison with USNM 13804, the holotype of Bennettazhia oregonensis, where the ulnar crest is actually missing. In azhdarchoids, the ulnar crest has the same direction (ventral or posterior depending on bone orientation) as in pteranodontids and azhdarchids. The identification of "warped" deltopectoral crest is dubious because Jianu et al. (1997) gave the same determination for the deltopectoral crest in Cretornis hlavaci, which is not "warped" at all. The fused notarium is present in all large pterodactyloids. Thus the bones mentioned but not described by Jianu et al. (1997) may well belong to an azhdarchid. This is in agreement with the reported absence of pneumatic foramen on posterior side of the humerus (Jianu et al. 1997). Depositional environment. The fossil locality is in the uppermost sequence of the Marnes d'Auzas Formation, a freshwater to brackish deposit with some marine intercalations (Bilotte and Ségura 1991). ME1 04 was found at the base of a thick bed of coarse sandstone overlying a bed of sandy clay (Buffetaut et al. 1997).
Depositional environment. The Miria Formation occurs as a thin unit in the Cretaceous succession of the Giralia Anticline, which forms the Giralia Range (Henderson and McNamara 1985). Its deposition started with a late Maastrichtian marine transgression (Bennett and Long 1991). It consists of a cream-colored calcarenite (0.6-2 m) with abundant phosphatic grains and nodules. The fossils are usually preserved as phosphatic molds.
References. Estes 1964. Comments. Estes (1964: 145) referred this specimen to Pterosauria with reservation and thought that it might represent a "coccygeal structure." Lawson (1975b) first noted that it is a cervical vertebra similar to those of Quetzalcoatlus. This specimen was subsequently referred to Azhdarcho sp. (Nesov 1984c) or Azhdarchidae indet. (Averianov 2010).
Stratigraphy. Hell Creek Formation. Age. Latest Maastrichtian. Depositional environment. Strata exposed at the collecting locality preserve a fining upward sequence of sediments. The basal unit is a thick, poorly sorted, and weakly cross-bedded sandstone. BMR P2002.2 was found near the top of this sandstone. Occasional specimens of angiosperm leaves were the only other fossils encountered in this sandstone unit, which is thought to represent point bar deposits. The sandstone is overlain by a clay-ball conglomerate, which is, in turn, overlain by laminated clays containing abundant remains of aquatic plants. The sequence of strata preserved at the fossil localiy is interpreted as representing a stream avulsion and subsequent development of an oxbow lake (Henderson and Peterson 2006).
Stratigraphy. Middle part of Haman Formation of the Hayang Group. Age. Aptian-Albian. Depositional environment. The Haman Formation is mainly composed of reddish shale, sandy shale, and white to greenish and gray sandstones with minor intercalated tuffaceous and pebbly sandstone. The pterosaur and dinosaur track-bearing sandstone occurs in the middle part of the Haman Formation, which consists of centimeter-scale, rhythmic alternations of fine-grained siliciclastic sediments. The vertebrate footprints and invertebrate trace fossils are accompanied with the ripple marks, mud cracks, and raindrop imprints which indicate a lakeshore environment (Kim et al. 2012).
Stratigraphy. Upper part of the Uhangri Formation of the Haenam Group. Age. Santonian -early Campanian (Hwang et al. 2002;Kim et al. 2003). Depositional environment. The Uhangri Formation comprises a clastic fluviolacustrine sequence with minor volcaniclastic deposits (Chun and Chough 1995). Vertebrate tracks were found at three different levels in the upper part of the Uhangri Formation. Pterosaur tracks, associated with numerous bird and dinosaur tracks and ripple marks, were only found in the lowest track level, which consists of a well-laminated black shale. This part of the formation represents the shallow margin of a lake (Hwang et al. 2002).
Associated fauna. Ostracods, invertebrate trace fossils attributed to arthropods, footprints of non-avian dinosaurs and web-footed birds Hwang et al. 2002).
Locality 54. El Pelillal (Figs 6, 7) Geographic position. Coahuila Province, Mexico. Stratigraphy. Cerro del Pueblo Formation. Age. Latest Campanian. Depositional environment. The tracksite is located stratigraphically high in the sequence of the Cerro del Pueblo Formation in a reddish to light brown, fine-grained, intensely bioturbated and ripple-marked sandstone (Rodriguez-De La Rosa 2003), which may document a freshwater depositional environment with possible tidal influence (Rodriguez-De La Rosa and Cevallos-Ferriz 1998).
Toothed pterosaurs apparently did not survive the Cenomanian-Turonian mass extinction. Ornithocheiridae is not known after the Cenomanian and Lonchodectidae after the Turonian (Unwin 2001;Barrett et al. 2008;Andres and Myers 2013;Rodrigues and Kellner 2013). Milner (2002) reported ornithocheirids from the Santonian of England but this record is based on isolated vertebrae whose attribution to Ornithocheiridae is problematic. From the Turonian onward, all identifiable pterosaur remains belong to toothless groups (Pteranodontidae, Nyctosauridae, and Azhdarchoidea). There are a number of post-Cenomanian localities with fragmentary pterosaur bones that cannot be positively identified but possibly belong to Azhdarchidae (Table 2).
Other putative records of skeletal remains of Azhdarchidae Sayão and Kellner (2001) reported on elongated cervical vertebrae from the Kimmeridgian-Tithonian Tendaguru beds in Tanzania and referred them to Azhdarchidae. However, the lack of illustrations or detailed descriptions of these specimens does not allow assessment of this identification. Elongated cervical vertebrae are also present in Ctenochasmatidae and non-azhdarchid Azhdarchoidea. Howse (1986) referred Doratorhynchus validus, represented by a long mid-cervical from the Berriasian Durlstone Formation of England (Seeley 1875(Seeley , 1901, to Azhdarchidae. This referral was accepted by some other authors (Wellnhofer 1991;Padian and Smith 1992;Kellner 2003). The taxonomy of pterodactyloids from the Purbeck beds is confusing and was partially revised by Howse and Milner (1995). In my opinion, all specimens described in the latter paper can be safely referred to a single taxon of Ctenochasmatidae, Gnathosaurus macrurus (including Doratorhynchus validus and Plataleorhynchus streptophorodon). Bakhurina and Unwin (1995: 230) mistakenly claimed that Nesov also included "Doratorhynchus" in Azhdarchidae. He in fact explicitly stated that "Doratorhynchus" does not belong to Azhdarchidae because of presence of a pneumatic foramen on the lateral side of the vertebra (Nesov 1991: 19). This mid-cervical (Martill et al. 2013: fig. 11B) cannot be attributed to Azhdarchidae also because of its continuous neural spine, which is disrupted in the middle and confined to the anterior and posterior ends in mid-cervicals of Azhdarchidae. There are also no reasons to attribute a wing metacarpal from this locality to Azhdarchidae (Martill et al. 2013: figs 4, 5). It can be referred to G. macrurus.
The fragmentary humerus PMOL AP00018 from the Aptian Doushan Formation of the Qingshan Group at Laiyang City, Shandong Province, China, considered as the stratigraphically oldest record of Azhdarchidae (Zhou 2010c), most likely belongs to Dsungaripteridae, known previously from this locality (Young 1958(Young , 1964. It was identified as Azhdarchidae indet. based on a single character, the swollen terminal expansion of the deltopectoral crest (Zhou 2010c), which is an ontogenetic trait not particularly diagnostic for Azhdarchidae. In other aspects of its structure, this specimen does not differ from the humerus of Dsungaripterus.
Undescribed skeletal remains of Azhdarchidae have been reported from Aptian Elrhaz Formation in Ténéré Desert of central Niger (Sereno et al. 1998) and the Maastrichtian of Jordan (Wilson and Zalmout 2006).
An isolated vertebra from the Maastrichtian Lapurr sandstone of Kenya, identified originally as a posterior cervical of ?Azhdarchidae (O' Connor et al. 2011), is a caudal vertebra of a mosasaur. Hone et al. (2012) reported on heavily digested pterosaur bones within a rib cage of the dromaeosaurid theropod Velociraptor mongoliensis from the Djadokhta Formation at Tugrikin Shireh, Mongolia. These bones were referred to Pterosauria because of thin bony walls and to Azhdarchidae because 1) this pterosaur group dominated in the Late Cretaceous; 2) azhdarchid are known from the Baynshire Formation (Watabe et al. 2009); and 3) azhdarchids "likely favoured terrestrial environments" (Hone et al. 2012: 29). This interpretation of the fossils is a good example of circular reasoning: first, they were referred to azhdarchids because these animals were terrestrial and then this finding was used to support terrestrial habits of azhdarchids (Witton and Naish In  Buffetaut et al. 1996 press). These bones, however, have no morphological features that would allow referral to Azhdarchidae. Furthermore, I even doubt the pterosaurian nature of these bones. The bones could have been digested to such an extent that only a thin cortical bone layer remained.

Paleoenvironments of Azhdarchidae
In a previous most recent review of azhdarchid distribution (Witton and Naish 2008), 32 localities of these pterosaurs have been listed. From this list two localities are actually duplicates: the Oldman Formation and the Dinosaur Park Formation in Alberta, Canada. The first find (Currie and Russell 1982) came from the Judithian part of the Oldman Formation, which has been subsequently separated as the Dinosaur Park Formation (Eberth and Hamblin 1993). Similarly, the Ksar es Souk and Kem Kem region of Witton and Naish (2008) are considered here as a single locality named Taouz. The Two Medicine locality for Montanazhdarcho minor and the Glen Rose locality for Radiodactylus langstoni are excluded here because these taxa are not azhdarchids. The records from the Bexen [=Montplasir] , Illd Formation, Upper Yezo Group (Obata et al. 1972), and Kita-ama Formation, Izumi Group (Obata et al. 2007) are excluded because the pterosaur material is too fragmentary and cannot be confidently attributed to Azhdarchidae. The Portezuelo Formation is excluded because the material cannot be determined beyond Azhdarchoidea indet. (Kellner et al. 2006;Novas et al. 2012). Thus the revised list of azhdarchid localities provided by Witton and Naish (2008) includes only 24 localities. Here I present a much more extensive list of azhdarchid localities, including 51 localities with skeletal remains and three localities with tracks. According to Witton and Naish (2008: 3) "most azhdarchids are found in continental fluvial deposits […] a condition perhaps best demonstrated by the occurrence of Quetzalcoatlus 400 km from the nearest contemporary shoreline." However, as was discussed above (locality 39) Quetzalcoatlus remains come from the lacustrine deposits only ~170 km from the nearest shoreline. In Asia, the two Santonian-age localities, Bayshin Tsav and Burkhant, are located well within the Asian landmass, but these localities are confined to prominent system of lakes that were possibly connected to Tethys (Figs 4 and 5). Other azhdarchid inland localities are usually placed very close to the contemporaneous coastlines. Based on the data presented here, 13% of azhdarchid occurrences are from lacustrine deposits, 17% from fluvial-plain deposits, 17% from coastal plain deposits, 18% from estuarine and lagoonal deposits, and 35% from coastal marine deposits (Fig. 8). There is a distinct trend of increase of azhdarchid occurrences from inland to coastal marine paleoenvironments. This trend cannot be explained only by taphonomic reasons (Witton and Naish in press), because fragile pterosaur bones could not be transported for long distances from the inhabited areas. If there was transport of pterosaur bones from more inland "terrestrial" environments to coastal marine facies, why are the latter facies not full of dinosaur bones? Dinosaur bones are generally more solid, and dinosaurs were undoubtedly more numerous than pterosaurs. In the aforementioned facies pterosaurs are more frequently found than dinosaurs. Azhdarchids likely inhabited a variety of environments, but were abundant near large continental water bodies (lakes and rivers) and most common in nearshore marine paleoenvironments, as along with the majority of other pterodactyloids.