Corresponding author: Paul C. Sereno (
Academic editor: Hans-Dieter Sues
Heterodontosaurids comprise an important early radiation of small-bodied herbivores that persisted for approximately 100 My from Late Triassic to Early Cretaceous time. Review of available fossils unequivocally establishes
In 1861 Owen described diminutive heterodontosaurid jaws a few centimeters in length as
Heterodontosaurid localities.
Current knowledge of the morphology of heterodontosaurids is based largely on the South African genus
Heterodontosaurid remains have been found in recent years in continental areas other than southern Africa or the southern coast of England, including Argentina (
Despite their critical role in early dinosaur evolution as the most diverse subclade of ornithischians (
In this paper I attempt to clarify the generic and specific taxonomy of heterodontosaurids and important aspects of their dental, cranial and postcranial morphology. Then I address heterodontosaurid body size, skeletal proportions, tooth replacement, tooth wear, and jaw mechanics. Finally, I present new character data bearing on heterodontosaurid phylogenetic and paleobiogeographic history.
Specimens currently known for established heterodontosaurid species. Asterisks indicate holotypic, lectotypic and paralectotyopic specimens. Localities in England and southern Africa are shown in Figure 1. Erroneous spellings for some of the localities in southern Africa are given in parentheses.
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*NHMUK RU B54 | Nosi (“Noosi“) | Skull and partial skeleton |
NHMUK no number | “ “ | Partial fragmentary skeleton | |
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*NHMUK 48209, 48210 | Mammal Pit | Partial skull (lectotypes) |
*NHMUK 48211 | “ “ | Right maxilla | |
*NHMUK 48212 | “ “ | Right maxilla | |
*NHMUK 48213 | “ “ | Left dentary | |
*NHMUK 48214 | “ “ | Right edentulous dentary | |
*NHMUK 48215a | “ “ | Right dentary | |
*NHMUK 48215b | “ “ | Left dentary | |
NHMUK 48229 | “ “ | Jaw fragment | |
NHMUK 40723 | “ “ | Dentary fragment | |
DORCM GS 1164-5, 1167, 1171 | Lovell’s Quarry | Isolated teeth | |
DORCM GS 1194, 1212-6, 1222-3 | Sunnydown Farm | Isolated teeth | |
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*LACM 115747 | Fruita Paleontological Area | Partial jaws and postcranial skeleton |
LACM 115727 | “ “ | Partial postcranial skeleton | |
LACM 120478 | “ “ | Partial fore- and hind limbs of a subadult | |
LACM 120602 | “ “ | Distal caudal vertebrae, distal limb bone | |
LACM 128258 | “ “ | Premaxilla, maxilla, dentaries and vertebrae of a subadult | |
LACM 128303 | “ “ | Partial left dentary | |
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*SAM-PK-K337 | Tyinindini (“Tyindini“); | Adult skull and partial skeleton |
SAM-PK-K1332 | Voisana | Adult skull and nearly complete skeleton | |
SAM-PK-K10487 | “ “ | Anterior portion of juvenile skull | |
SAM-PK-K1334 | “ “ | Partial left maxilla | |
SAM-PK-K1326 | “ “ | Partial maxilla | |
SAM-PK-K1328 | southern Africa | Vertebrae, partial pelvic girdle and parts of forelimb and hind limb; | |
NM QR 1788 | Tushielaw | Fragmentary snout from an adult | |
AMNH 24000 | southern Africa | Posterior portion of juvenile skull | |
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*SAM-PK-K3606 | Paballong | Partial left dentary (now a natural mold) |
*UCRC PVC10 |
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Silicone cast from natural mold of holotypic specimen | |
NHMUK RU A100 | Paballong | Partial disarticulated skull | |
BP/1/4244 | Buck Camp | Maxilla | |
BP/1/5253 | Bamboeskloof Farm | Maxilla | |
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MPEF-PV 3211 | Queso Rallado | Partial disarticulated skull and skeleton lacking limbs |
MPEF-PV 1718, 1719, 1786, 3810, 3811; | “ “ | Isolated teeth | |
SAM-PK-K10488 | Voisana | Postorbital, right and left dentaries, and predentary | |
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*PVL 2577 | Agua de Las Catas | Right maxilla and dentary, a few vertebrae, an impression of the central portion of the right pelvic girdle, and partial right hind limb |
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*STMN 26-3 | Liaoning | Partial articulated skeleton with skull |
IVPP V17090 | “ “ | Partial articulated skeleton with skull |
Early heterodontosaurid discoveries.
Several of the dentaries preserve a large alveolus for a lower caniniform tooth (
Early heterodontosaurid discoveries from southern Africa.
The damaged holotype and only known specimen of
Recently
Published taxonomic opinion regarding heterodontosaurids from southern Africa. Authors included in the table have made specific taxonomic inferences on the basis of available material.
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this paper |
African heterodontosaurids (
South American heterodontosaurids are known from two formations in Argentina. The fluvial-overbank sequences in the fossiliferous Ischigualasto Formation in San Juan and La Rioja Provinces (
The Middle Jurassic Cañadón Asfalto Formation of Chubut Province in Patagonia recently has yielded a partial skeleton and isolated teeth of the heterodontosaurid
Controversial early heterodontosaurid specimen from southern Africa. Drawing of specimen NHMUK RU A100 as embedded in matrix in
Two additional maxillae with worn teeth were collected by C. Gow and J. Kitching from the Transkei (Herschel) District of South Africa. The first (BP/1/4244) was discovered in the early 1970s at Buck Camp and originally described as
In 1966-1967 an expedition composed of members from four institutions (South African Museum, British Museum, Yale University, University College London) returned to this area and discovered a nearly complete skull and skeleton of
Four additional specimens referable to
More recent heterodontosaurid discoveries from southern Africa.
Cranial remains of
Postcranial remains of
Several of the bones originally part of the holotypic specimen were lost since their description by
Although Irmis et al. (2007) confirmed most of the additional descriptive detail on
Irmis et al. (2007) also suggested, contrary to
The basal constriction between crown and root, the buccal emargination on the maxilla and dentary, and the coronoid process on the dentary suggest ornithischian affinity (
The relatively short crowns, limited variation in crown size, and well developed low-angle wear facets resemble the condition in the heterodontosaurid
Based on the foregoing,
Skeletal remains of
Skull, axial, and long bone lengths (mm, above) and proportions (%, below) in the best known heterodontosaurids. Measurements average long bone lengths when both sides are available. Parentheses indicate estimated length or proportion.
STMN 26-3 |
LACM 120478 |
LACM 115747 |
NHMUK 48215 |
Kayenta taxon; MCZ9092 | NHMUK RU A100 |
MPEF-PV 3211 |
SAM-PK-K10488 |
NHMUK RU B54 |
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Length; (mm) | Skull1 | (67) | 65 | (60)6 | (75)8 | (62)9 | (53)9 | (145)9 | (71)9 | (73)9 | (82) | 11510 |
Humerus | 33 | (27) | 37 | (46)8 | — | — | — | 50 | 83 | |||
Radius | — | 17 | — | — | — | — | — | (36) | 58 | |||
Metacarpal 3 | — | 5 | — | — | — | — | — | 15 | 22 | |||
Femur | (54)5 | 51 | (62)7 | (78)8 | — | — | — | 78 | 112 | |||
Tibiotarsus | 82 | 73 | 74 | (93)8 | — | — | — | 100 | 145 | |||
Metatarsal 3 | (44) | (43) | — | — | — | — | — | 53 | 68 | |||
Body length2 | (450) | — | — | — | — | — | — | — | (1080) | |||
Neck & trunk (precaudal column) | (102) | — | — | — | — | — | — | — | (324) | |||
Caudal column | (296) | — | — | — | — | — | — | — | (659) | |||
Proportion; (%) | Skull/body length | (12) | — | — | — | — | — | — | — | (9) | ||
Skull/femur | (125) | 127 | (97) | (97) | — | — | — | (105) | 103 | |||
Precaudal/body length | (30) | — | — | — | — | — | — | — | (23) | |||
Caudal/body length | (65) | — | — | — | — | — | — | — | (61) | |||
Humerus/forelimb3 | — | 53 | — | — | — | — | — | (50) | 51 | |||
Proportion; (%) | Radius/forelimb | — | 36 | — | — | — | — | — | (36) | 36 | ||
Metacarpal 3/forelimb | — | 10 | — | — | — | — | — | (15) | 14 | |||
Tibiotarsus/femur | 152 | 143 | (119) | (119) | — | — | — | 128 | 130 | |||
Femur/hind limb4 | 30 | 31 | — | — | — | — | — | 34 | 35 | |||
Tibiotarsus/hind limb | 46 | 44 | — | — | — | — | — | 43 | 45 | |||
Metatarsal 3/hind limb | 24 | 26 | — | — | — | — | — | 23 | 21 | |||
Humerus/femur | 61 | 53 | (60) | (60) | — | — | — | 64 | 74 | |||
Forelimb/hind limb | — | 29 | — | — | — | — | — | (44) | 50 |
1Skull length is measured or estimated from the tip of the premaxilla to the posterior edge of the squamosal.; 2Body length is composed of three successive lengths: functional skull length (measured from the premaxilla to the occipital condyle) + precaudal column length (as measured with natural curves) + caudal column.; 3Forelimb length equals the sum of humerus + radius + metacarpal 3.; 4Hind limb length equals the sum of femur + tibia + metatarsal 4.; 5The reported length of the left femur (51 mm) is more reliable than the considerably shorter length estimate (40 mm) for the incomplete right femur (
More recent heterodontosaurid discoveries from northern locales.
Starting in the mid 1970’s, field parties led by Farish Jenkins, Jr. from Harvard University discovered a locality rich in microvertebrate remains about 50 kms southeast of Tuba City in north-central Arizona (
An exceptionally preserved, small heterodontosaurid named
In
Wear facets tend to be approximately planar, and so the task at hand is to describe the angle of the plane of wear relative to a frame of reference. The terms
Cheek tooth terminology.
For both of these frames of reference,
Tooth identification uses a letter abbreviation for location in the dentary (d), premaxilla (pm), or maxilla (m) and a number for position (e.g., “pm4” = fourth premaxillary tooth). For tooth shape,
Anatomical terms for teeth are described here using “apical” and “basal”, rather than dorsal or ventral, with reference to the crown of the tooth, so that these terms may be applied with similar meaning to both upper or lower tooth rows. The tooth is divided into
The cingulum can round smoothly onto lingual and labial crowns faces, or it can have a well-defined apical margin here termed a
For structures along the carina of the crown,
The teeth in heterodontosaurids are anchored in individual sockets. Mesial and distal extremities of the crowns sometimes overlap
Small-bodied ornithischians with the following features that may constitute heterodontosaurid synapomorphies in phylogenetic context: (1) three or fewer premaxillary teeth; (2) premaxillary teeth increase in size distally; (3) dentary caniniform tooth associated with an arched premaxilla-maxilla diastema; (4) nasal fossa, dorsomedian with rounded lateral margins; (5) jugal flange, ventral embayment of jugal-quadratojugal embayment; (6) jugal horn below orbit, laterally directed and dorsoventrally compressed; (7) postorbital body, arcuate fossa with raised anterior rim; (8) quadrate head included within laterotemporal fossa; (9) quadrate condyle, articular surface ventrolaterally inclined at approximately 30°; (10) quadratojugal T-shaped; (11) predentary processes (lateral, ventral) rudimentary; (12) dentary ramus stoutly proportioned, substantial depth at mid ramus compared to length; (13) fibular mid-shaft and distal end reduced.
The most inclusive clade containing
This stem-based phylogenetic definition (
Late Triassic (Norian) to Early Cretaceous (Barremian-Aptian), ca. 216–125 Ma (
Many of the cranial and postcranial apomorphies listed in the emended diagnosis were known previously only in
NHMUK 48209 (
NHMUK 48211 (
“Mammal Pit” located high on the coastal cliff section near the Zig Zag Path at Durlston Bay, Isle of Purbeck, Dorset, southern England (
Either the Marly or the Cherty Freshwater Member, Middle Purbeck Beds of the Purbeck Formation; Lower Cretaceous, Berriasian, ca. 146-140 Ma (
The species name
Heterodontosaurid ornithischian characterized by the following six autapomorphies: (1) slender, nearly straight caniniform first maxillary tooth with unornamented anterior and posterior carinae; (2) edentulous anterior dentary margin (as long as two alveoli); (3) only 9 dentary teeth posterior to the caniniform tooth; (4) dentary crowns in the middle of the tooth row that are proportionately taller than opposing maxillary crowns (the apical 50% of middle dentary crowns are denticulate versus 25% of mid maxillary crowns); (5) anteroposteriorly elongate dentary symphysis (maximum length approximately 3 times maximum depth); (6) symphyseal flange ventral to primary dentary symphysis.
The original description of
The ventral portions of the left and right premaxillae were originally preserved in mutual articulation in NHMUK 48209 (
Despite two diagonal fractures and some crushing, several details of the left premaxilla have not been described previously. An anterior premaxillary foramen is present and split in two by a fracture with each half slightly separated (
The posterior end of the alveolar margin is broken away along with part of the root of the third premaxillary tooth, as the specimen is now preserved (
The dorsal portion of right and left premaxillae is broken away.
Finally, the position of the premaxilla relative to the maxilla is unknown, as the premaxillae are disarticulated and displaced anteroventral to the maxillae in the only partial cranium known for
Thus it is likely that much of the anterior end of the snout was originally preserved in NHMUK 48209. In
Premaxilla of
Maxilla of
Maxilla of
Partial skull of
A buccal emargination, or cheek embayment, is present along the entire length of the tooth row (
Close inspection of the single maxilla exposing this feature, however, casts doubt on this interpretation (NHMUK 48211;
The anterior end of the same maxilla provides key evidence for the presence of an arched diastema to accommodate the apical end of a lower caniniform tooth (
Portions of both of these bones are preserved attached to two of the maxillae. In NHMUK 48210, the ventral ramus of the left lacrimal, including a portion of the orbital margin, is preserved posterodorsal to the left maxilla (
The anterior end of the jugal is preserved in articulation in two specimens. The first is preserved posterior to the antorbital fenestra (
The right palatine is preserved in partial disarticulation from its lateral contact with the maxilla (
In NHMUK 48210 the palatal bone posteromedial to the maxilla may be a left ectopterygoid. Immediately adjacent to this bone is an articular scar running across the maxilla-jugal suture. This is the lateral anchor for the ectopterygoid in many ornithischians (
Although the predentary is unknown in
The anterior end of the dentary in
The dentary does not have a well-defined surface dorsal to the foramen for articulating with the predentary, and so a projecting lateral predentary process probably was not present. The ventral aspect of the anterior end of the dentary has as a subtle smooth articular facet (
Dentary of
Dentary of
Dentary end of
Previously
The dentary is best known from paired right and left sides (
The dentary in
The coronoid process is distinctly expanded at mid-length, resulting in a diamond-shaped, rather than tapered, process (NHMUK 48215a, 48213;
The symphysis at the anterior end of the dentary is V-shaped (
The anterior ends of the dentary are not inturned to form a spout shape as in most ornithischians. The symphysis in
There are three premaxillary teeth in middle and posterior portions of the premaxilla, preceded by an edentulous margin several alveoli in length (
There are nine maxillary teeth (
Owen briefly described a second more mesial caniniform tooth in the maxilla based on a fragment and possible impression (
There are seven or eight postcaniniform teeth. Owen described the two lectotypic specimens that represent part and counterpart of a single specimen that was split from a single block of matrix. He indicated how the tooth rows on the opposing pieces should be aligned (
The first postcaniniform tooth (second maxillary tooth) has taller crown proportions than succeeding maxillary teeth; the crown is narrower and the denticulate portion of the crown is approximately 45% total crown height (
The enamel is symmetrical on each side of the maxillary crowns as is visible in the cross-section of several crown tips. Wear facets are present on raised areas of the lingual face of the crowns of all fully erupted maxillary crowns that are well preserved and exposed in lingual view (
The dentary tooth row has 11 teeth, based on evidence from three dentaries with nearly complete alveolar margins (NHMUK 48214, 48215a, 48215b). The first dentary tooth must have had a very small peglike crown as in
The small first dentary alveolus has never been described.
There are eight and nine postcaniniform dentary teeth, respectively, in the left and right dentaries of NHMUK 48215. The left dentary, however, is incomplete posteriorly (
The crowns of postcaniniform dentary teeth are well separated from their roots and have taller proportions than opposing maxillary crowns (
The enamel is symmetrically distributed on each side of the dentary crowns as in maxillary crowns. Enamel also appears to cover a flattened subtriangular area on the mesial and distal sides of the crown base between the crown faces and root. This surface, which is present only on the largest crowns, was described previously as exposed dentine and highlighted as unique to
Dentary of
Skull of
The reconstruction of the snout and dentition of
LACM 115747, adult with partial maxillae and dentaries, cervical, dorsal, sacral and caudal vertebrae, proximal right femur, proximal and distal ends of the tibiae, and partial right metatarsal 1 (
LACM 115727, adult partial postcranial skeleton with partial cervical, dorsal and caudal vertebrae, partial right and left femora, and an articulated distal left tibia and coossified astragalocalcaneum; LACM 120478, subadult with left humerus, distal left femur, and an articulated left tibia, fibula and coossified astragalocalcaneum; LACM 120602, distal caudal vertebra, left astragalocalcaneum, partial metatarsus and pes; LACM 128258, subadult with right premaxilla, partial left maxilla, partial left and right dentaries, and one dorsal and one distal caudal vertebra; LACM 128303, anterior left dentary (
Fruita Paleontological Area, approximately 10 kms southwest of Fruita, Mesa County, west-central Colorado, USA; approximately
Just above the “clay change” near the base of the Brushy Basin Member and about 100 m from the base of the Morrison Formation (
Heterodontosaurid with (1) a discordantly small dentary tooth immediately distal to the caniniform dentary tooth and (2) a prominent anteromedial flange on the distal end of the tibia.
This suite of features constitutes a differential diagnosis—a unique combination of the features that describes a monospecific genus rather than a set of autapomorphies hypothesized to have arisen in the immediate ancestry of the taxon (
One dental feature listed in the revised diagnosis may be an autapomorphy but is homoplasious among heterodontosaurids. The dentary tooth immediately distal to the caniniform tooth in
The other features listed in the diagnosis by
The separation of the ascending process of the astragalus as a separate ossification was listed among the autapomorphies. The suture separating the distal tip of the astragalar ascending process, however, seems to continue laterally as a fracture line across the distal shaft of the fibula. The ascending process had been viewed as a separate ossification in the theropod
The six available specimens of
The holotype of
The dentary in
A jaw fragment housing three teeth was identified as a right premaxilla (
The maxilla in
The location, size and shape of the anterior dentary teeth differ between
The third dentary tooth in
The premaxillary teeth described by
The largest maxillary crowns in the distal portion of the series have a bulbous cingulum with well-defined basal and apical edges (
Computed-tomographic scans show active tooth replacement in
STMN 26-3, partial skeleton laying on its left side preserving most of the skull in left lateral view, the ventral portion of a skull and articulated skeleton lacking the mid and distal caudal vertebrae, right coracoid, left carpus, portions of the left manus, and portions of the right hindlimb (
IVPP V17090 (
Jianchang County, Liaoning Province, PRC; collected privately but localities are probably in the vicinity
Probably from the Lujiatun Beds of the Yixian Formation, Jehol Group; Lower Cretaceous (Barremian-Aptian), ca. 125 Ma (
Heterodontosaurid with (1) only two premaxillary teeth, (2) rectangular dentary ramus with parallel dorsal and ventral margins, (3) extremely reduced forelimb that is less than 30% the length of the hindlimb, (4) manual digit III and metacarpal 3 shorter than manual digit II and metacarpal 2, respectively, (5) tail increased in length, (6) subtriangular chevrons in mid caudal vertebrae, and (7) numerous parallel ossified epaxial and hypaxial ossified tendons in the mid and distal regions of the tail.
The holotype is a mature skeleton as evidenced by fusion of sacral centra, fusion or tight articulation of the neural arch and centrum of all other preserved vertebrae, and fusion between the tibia and proximal tarsals and between the bases of the metatarsals. The stratigraphic origin and geological age of
The following brief description is based on two skeletons, the holotype (STMN 26-3;
The cranium is well represented in the holotype and referred specimens, although several portions remain poorly understood ( Partial skeleton of the heterodontosaurid Skull of the heterodontosaurid Anterior portion of skull of the heterodontosaurid Anterior portion of skull of the heterodontosaurid
In both skulls the alveolar margin of the premaxilla is tilted slightly anteroventrally and is positioned ventral to the maxillary tooth row (
The subtriangular maxilla forms the posterior portion of the inset, arched diastema (
The predentary is a small, wedge-shaped bone that lacks discrete processes (
The dentary ramus is straight and parallel-sided for most of its length (
The sutures between the postdentary bones are poorly preserved in the two available specimens. The coronoid process rises well above the level of the dentary crowns as in
There are two premaxillary teeth, the first a small tooth known only from its broken base and the second a large caniniform tooth (
The total number of dentary teeth in
Successive dentary crowns 3-10 become slightly larger in the holotypic and referred skulls. In these postcaniniform dentary teeth, the bulbous cingulum has well-defined margins, a cingular ectoloph raised above the remainder of the crown surface including the primary ridge. The cingulum curves apically, terminating mesially and distally in prominent apically projecting denticles. Toward the posterior end of the dentary series, the prominence of the apical, mesial and distal basal denticles gives the crown a tricuspid appearance. The penultimate tooth, dentary tooth 9, is the largest in the series. The most distal tooth, dentary tooth 10, has a considerably smaller crown, as seen in several referred skulls.
The total number of maxillary teeth is currently unknown given the available evidence in the holotypic and referred skulls. In the right maxillary series of the holotypic skull, the crowns of the smallest teeth just behind the caniniform dentary tooth are broken at their bases (
Maxillary and dentary crowns are subtriangular, the dentary crowns somewhat deeper than opposing maxillary crowns as in
Maxillary dentition of the heterodontosaurid
Theholotype preserves the posterior one-half of the cervical series (C5-9), and much of the dorsal column is preserved in the referred skeleton. Centrum length is nearly constant, measuring approximately 5 mm (
The proximal one-half of the caudal series is preserved in the holotypic skeleton and nearly as much in the referred skeleton (
Tail of the heterodontosaurid
Both scapulocoracoids are preserved in opposition in the referred skeleton (
Proximally, the scapula broadens gradually to the acromial process as in
The humerus, which is best preserved in STMN 26-3, has a bulbous head, prominent deltopectoral crest, gently curved shaft and prominent distal condyles as in
The manus probably retained all five digits as in
The two phalanges of manual digit I diverge medially from the others. The nonungual phalanges have proximal intercondylar processes articulating between paired distal condyles with well-formed collateral ligament pits as in
Forearm and manus of the heterodontosaurid
Forearm and manus of the heterodontosaurid
Little can be said about the ilium, which is poorly preserved in both skeletons. The ischia and pubes are preserved in lateral view (STMN 26-3;
Of the pubis, only the postpubic process is preserved (STMN 26-3;
The femoral head is large and round, and the femoral shaft is robust with a proximally placed pendant fourth trochanter (IVPP V17090). Whether the anterior trochanter is separate as in the Kayenta heterodontosaurid and
In the pes, the proximal ends of metatarsal 1-4 appear to be coossified. Pedal digit I is very short, the tip of its ungual extending just beyond the condyles of metatarsal 2 (
Pes of the heterodontosaurid
Pes of the heterodontosaurid
Skeleton of the heterodontosaurid
Measurements (mm) of the cranium and axial skeleton of the Early Cretaceous heterodontosaurid
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Cranium | Length, premaxilla to posterior edge of squamosal | 65 |
Preorbital length, anterior rim of orbit to tip of premaxilla | 30 | |
Occiput height, quadrate condyle to parietal occipital flange | (23) | |
Antorbital fossa maximum length | 15 | |
Antorbital fossa maximum height | 9 | |
Quadrate height | (15) | |
Dorsal Vertebrae | D7 centrum length | 5 |
D8 centrum length | 5 | |
D9 centrum length | 5 | |
D10 centrum length | 5 | |
D11 centrum length | 5 | |
D12 centrum length | 5 | |
Sacral Vertebrae | S1 centrum length | 5 |
Caudal Vertebrae | CA1 centrum length | — |
CA2 centrum length | 5 | |
CA3 centrum length | 5 | |
CA4 centrum length | 6 | |
CA5 centrum length | 6 | |
CA6 centrum length | 6 | |
CA7 centrum length | 7 | |
CA8 centrum length | 7 | |
CA9 centrum length | 8 | |
CA10 centrum length | 8 | |
CA11 centrum length | 8 | |
CA12 centrum length | 8 | |
CA13 centrum length | 8 |
Measurements (mm) of the girdles and limb bones of the Early Cretaceous heterodontosaurid
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Pectoral girdle | Scapula length | (23) |
Scapular blade, minimum neck width | 2 | |
Scapular blade, distal width | — | |
Coracoid length | 4 | |
Coracoid height | 7 | |
Proximal forelimb | Humerus length | (27) |
Radius + carpus + manus (radial head to tip of digit II) | 381 | |
Radius length | 17 | |
Ulna length | (19)1 | |
Manual digit I | Manual digit I length | 161 |
Metacarpal 1 length | 61 | |
Phalanx I-1 length | 51 | |
Ungual I-2 length | 41 | |
Manual digit II | Manual digit II length | 211 |
Metacarpal 2 length | 71 | |
Phalanx II-1 length | 3.51 | |
Phalanx II-2 length | 41 | |
Ungual II-3 length | 41 | |
Manual digit III | Manual digit III length | 161 |
Metacarpal 3 length | 51 | |
Phalanx III-1 length | 2.51 | |
Phalanx III-2 length | 21 | |
Phalanx III-3 length | 31 | |
Ungual III-4 length | 31 | |
Proximal hind limb | Femur length | 51 |
Tibiotarsus length | 73 | |
Tibiotarsus proximal end, anteroposterior length | 11 | |
Tibiotarsus mid shaft, anteroposterior diameter | 5 | |
Pedal digit I | Metatarsal 1 length | 251 |
Phalanx I-1 length | 61 | |
Ungual I-2 length | 91 | |
Pedal digit II | Metatarsal 2 length | (39)1 |
Phalanx II-1 length | 10.51 | |
Phalanx II-2 length | 9.51 | |
Ungual II-3 length | 91 | |
Pedal digit III | Metatarsal 3 length | (43)1 |
Phalanx III-1 length | 121 | |
Phalanx III-2 length | 91 | |
Phalanx III-3 length | 81 | |
Ungual III-4 length | 81 | |
Pedal digit IV | Metatarsal 4 length | (40)1 |
Phalanx IV-1 length | 8 | |
Phalanx IV-2 length | 6 | |
Phalanx IV-3 length | 5 | |
Phalanx IV-4 length | 6 | |
Ungual IV-5 length | 6 |
1Left.
Small-bodied ornithischians with the following features that likely would constitute synapomorphies in phylogenetic context: (1) cheek tooth crowns that are taller than wide, (2) jaw joint set below the axis of occlusion between maxillary and dentary teeth.
The most inclusive clade containing
Earliest Jurassic (Hettangian-Sinemurian) to Middle Jurassic or earliest Late Jurassic (Aalenian-Callovian), ca. 197-165 Ma (
Authorship of family group names is given to the author of the first name coined within the family group (
NHMUK RU B54, ventral portion of a skull and articulated skeleton lacking the mid and distal caudal vertebrae, right coracoid, left carpus, portions of the left manus, and portions of the right hindlimb (
Stream-side exposure by the town Nosi (= “Noosi”), 8.2 km east of Whitehill, southern Lesotho;
Top unit (dull red sandstone) of the Upper Elliot Formation; Lower Jurassic, Hettangian, ca. 202-197 Ma (
Heterodontosaurid ornithischian characterized by the following autapomorphies: (1) premaxillary tooth 2 and 3 with tall, subcylindrical crowns, the latter possibly representing a reduced caniniform tooth; (2) dentary tooth 2 with subcylindrical crown, possibly representing a reduced caniniform tooth; (3) maxillary and dentary teeth with flat lateral and medial crown surfaces lacking discrete marginal or median ridges; and (4) maxillary crowns in the middle of the tooth row have deep parallel-sided crowns that do not expand in mesiodistal width toward their apex. Unlike other heterodontosaurids, there is no dentary or premaxillary caniniform teeth, although both the dentary and premaxillary have teeth with subcylindrical crowns that may be reduced caniniform teeth.
A small set of autapomorphies diagnose this genus and species, which otherwise closely resembles
The recent revision of the diagnosis by
The holotypic skeleton of
Preserved in two pieces, the skull is transversely compressed and better exposed in left lateral view (
Skull of
Both premaxillae are partially preserved with the right shifted slightly ventral to the left. Portions that are broken on both sides include sections of the alveolar border, the internarial processes, and the distal end of both posterolateral processes (
The posterolateral process of the premaxilla narrows slightly posterior to the external naris and then broadens in transverse width distally, which in
Thulborn suggested, nonetheless, that caniniform crowns in heterodontosaurids might be sexually dimorphic, that NHMUK RU B54 may represent a female, and that a deep arched diastema may have been present in
Snout of A
The maxilla has a dorsoventrally deep buccal emargination, which is bordered dorsally by an arched row of large neurovascular foramina and the everted and gently arched external rim of the antorbital fossa. The narrow width of the anterodorsal ramus brings the premaxilla in close proximity to the antorbital fossa as in
The subtriangular lacrimal may be slightly broader dorsally than in
The partially preserved quadratojugal and ventral end of the quadrate form a T-shaped junction in
The dentary has a deep, arched buccal emargination that dissipates anteriorly near the subconical second tooth (
The posterior margin of the dentary is not well preserved; the notched posterior margin of the right dentary suggests that an external mandibular fenestra of moderate size may have been present as in
There are three premaxillary crowns as in other heterodontosaurids (rather than two,
A complete maxillary series probably included 14 teeth, as estimated from the 12 preserved maxillary teeth in the left maxilla and the space between these and the anterior end of the maxilla on the right side (
The cingulum is reduced in
In labial view, mesial and distal crown edges are nearly parallel, with no development of marginal ridges like those in
The maxillary crowns are canted at a slight angle to their roots, directing the crown lingually. Low-angle wear facets graze the lingual side of the maxillary crowns. As in
There is indisputable evidence for active tooth replacement in
Maxillary teeth of
The left dentary has 14 teeth, which may comprise a complete tooth row (
The remaining dentary teeth have diamond-shaped crowns that are shorter than opposing maxillary crowns (
The reconstruction of the partial skull and dentition of
Skull of
The articulated cervical series is only partially exposed. The atlas and axis are incomplete, and C3-9 are exposed in dorsal view. Judging from their neural arches, length decreases markedly from C6-9 as in
In C3 the neural spine is low and ridgelike and the postzygapophyses have smooth dorsal surfaces lacking any development of epipophyseal processes. In
Ossified tendons are associated with the neural arches of the dorsal and sacral vertebrae, but as in
The scapula, the only bone of the pectoral girdle that is exposed, shows a prominent acromial expansion and strap-shaped proximal scapular blade. Little else can be said without further preparation.
The right forelimb is nearly complete with most of its bones in articulation or near their natural location and with the manus in ventral view overlapping the left orbit of the skull (
Skull of
Forelimb of
The radius and ulna are preserved on both sides but are incomplete distally and only partially exposed (
The carpus is composed of many elements, which may have been assembled in articulation with a compact arrangement as in
The metacarpals are proportionately elongate relative to either the bones of the forearm or humerus as in
The proximal ends of the metacarpals show edges that appear to square the base of the bone as in
The right metacarpus, exposed in ventral view, provides the best information regarding the disposition of the digits (
The phalangeal formula is poorly known in
The ilium, preserved in part on both sides, is very similar to that in
Ilium and hindlimb of
Measurements (mm) of the holotypic skeleton of the South African heterodontosaurid
|
|
|
---|---|---|
Skull | Length | (100) |
Scapula | Blade, minimum width | 5 |
Humerus | Length | 50 |
Deltopectoral crest length | 17 | |
Ulna | Length | (39) |
Radius | Length | (36) |
Manus | Metacarpal 1 length | 13 |
Metacarpal 2 length | 16 | |
Metacarpal 3 length | 151 | |
Metacarpal 4 length | (9)1 | |
Metacarpal 5 length | 4 | |
Phalanx I-1 length | 10 | |
Phalanx II-1 length | 8 | |
Phalanx III-1 length | 5 | |
Phalanx V-1 length | 2 | |
Ilium | Blade length | 623 |
Blade, height dorsal to acetabular rim | 11 | |
Preacetabular process length | 212 | |
Postacetabular process length | 19 | |
Pubic peduncle length | 11 | |
Ischial peduncle length | 7 | |
Femur | Length | 78 |
Minimum shaft diameter | 8 | |
Head to distal end of fourth trochanter | 30 | |
Tibia | Length | 100 |
Minimum shaft diameter | 7 | |
Pes | Digit III length | (108) |
Metatarsal 1 length | 31 | |
Metatarsal 2 length | 47 | |
Metatarsal 3 length | 53 | |
Metatarsal 4 length | (48) |
1Left.; 2Right.; 3Composite measurement based on overlap of right and left sides.
The general form of the femur does not depart significantly from that in
In
The tarsus includes the astragalus, calcaneum, and lateral and medial distal tarsals, which do not appear to be coossified (
The metatarsal shafts are not coossified, and the pes as preserved is less compact than in
SAM-PK-K337, nearly complete, articulated skull.
SAM-PK-K1332, articulated skull and skeleton lacking only a few mid and distal caudal vertebrae; SAM-PK-K10487, anterior portion of a juvenile skull including the left orbit with palpebral and anterior portion of the lower jaws with the predentary; SAM-PK-K1328, partial postcranial skeleton including dorsal and caudal vertebrae, forelimbs and hindlimbs; SAM-PK-K1334, left maxilla with six teeth and portions of adjacent bones preserving the antorbital fenestra, the ventral end of the lacrimal, and the anterior end of the jugal; AMNH 24000, posteroventral portion of skull with articulated lower jaws preserving the posterior half of maxillary and dentary tooth rows, parts of the right jugal, quadratojugal and quadrate, posterior half of the right lower jaw, and traces of the anterior cervical vertebrae.
On the mountainside behind the trading store in Tyinindini at an altitude of 1890 m, Transkei (Herschel) District, Cape Province, South Africa;
Upper Elliot Formation and Clarens Formation (
Heterodontosaurid ornithischian characterized by the following autapomorphies: (1) cheek tooth crowns subrectangular in cross-section; (2) prominent crown margins and primary ridge resulting in mesial and distal paracingular fossae on labial and lingual faces of maxillary and dentary crowns, respectively; (3) asymmetrical enamel on maxillary and dentary crowns (reduced in thickness on lingual and labial sides of maxillary and dentary crowns, respectively); (4) lacrimal with shallow lateral fossa; (5) jugal with extension of antorbital fossa onto the orbital ramus; (6) jugal flange posteroventrally inclined; (7) trapezoidal anterior surangular foramen; (8) axis and C3 neural spine with lateral flange; (9) C5 and C6 neural spines project anterodorsally; (10) C3-C7 with subcylindrical parapophyses; (11) mid dorsal vertebrae (D6-D10) with Y-shaped transverse processes (for di- and parapophyses); (12) scapulocoracoid foramen absent; (13) humeral epicondyles present; (14) lobe-shaped distal expansion of the iliac preacetabular process; (15) ischial peduncle narrow, columnar; (16) ischial shaft with laterally-directed crescentic flange at mid-length; (17) femoral anterior and greater trochanters coossified; (18) tibiofibulotarsus coossification (possibly variable); (19) tarsometatarsus coossification.
The initial diagnosis of
The recent revision of the diagnosis in
Two of the seven dental features cited by
Six of the 10 postcranial features cited by
The aim of the following descriptive comments is to correct and extend where needed available accounts of the skull and skeleton of the best-known heterodontosaurid,
Snout of the heterodontosaurid
Snout end of
Posterior end of the skull of
Posterior dentition of
Posterior dentition of
Tooth structure, occlusion, and replacement in
Tooth structure, occlusion, and replacement in
Tooth structure, occlusion, and replacement in
Tooth structure, occlusion, and replacement in
Tooth structure, occlusion, and replacement in
Tooth structure, occlusion, and replacement in
Tooth structure, occlusion, and replacement in
Tooth structure, occlusion, and replacement in
Tooth structure, occlusion, and replacement in
Tooth structure, occlusion, and replacement in
The postcranium was originally described on the basis of a single nearly complete skeleton (SAM-PK-K1332;
The premaxilla, best preserved in SAM-PK-K1332, exhibits several unusual features that also characterize other heterodontosaurids. The narial fossa is deep ventral to the external nares, and the fossa extends close to the alveolar margin of the premaxilla (
The internarial bar is broken in all specimens preserving the end of the snout, as reported by
The posterolateral process of the premaxilla is quite broad at its base dorsal to the diastema in
The maxilla forms the ventral and anterodorsal borders of the triangular external antorbital fenestra (
In addition to these openings, there is an additional blind recess within the antorbital fossa near its anterior corner, here labeled the
The ventral border of the external antorbital fenestra is straight, relatively sharp-edged, and strongly everted, as in all heterodontosaurids preserving this region of the maxilla (
The posteroventral corner of the antorbital fossa extends onto the jugal below the orbit, tapering to an end at the base of the jugal horn (
In dorsal view of the snout, a median fossa is present on the nasals (median “sulcus”;
The jugal horn has a flattened subrectangular shape and projects laterally (
The quadrate head is not expanded transversely in lateral view, nor is there a gap between the quadrate shaft and the squamosal and quadratojugal as sometimes reconstructed (
The form of the jaw joint carried particular functional significance and is well preserved in SAM-PK-K1332 and AMNH 24000. In both specimens, an axis through the quadrate condyles angles anteromedially at about 45° as seen in ventral view (
The predentary is smaller relative to the anterior end of the dentary, which is expanded dorsoventrally (
A well-defined, smooth articular surface for the predentary is present on the anterior end of the dentary, which is well preserved in SAM-PK-K1332 and SAM-PK-K10487 (
The dentary symphysis is restricted to the ventral portion of the dentary, and is slightly thickened and rugose (
Between the symphysis and the base of the caniniform tooth is a dorsoventrally concave surface with large vascular foramen that runs anteriorly toward the predentary (
The arched buccal emargination is deepest below the center of the dentary tooth row and extends from the base of the caniniform tooth anteriorly to the base of the coronoid process posteriorly (
A large oval depression, here termed the
The articulation for the quadrate is cup-shaped and fitted tightly to the lateral condyle of the quadrate. The external rim of the articular socket is everted and curled dorsally, rising to a low process immediately posterior to the posterior surangular foramen, as in
The first two premaxillary teeth (pm1, 2) are preserved in the holotypic skull (
The third premaxillary crown (pm3), in contrast to the mesial two, is caniniform with markedly greater size, more pronounced recurvature, and more lateral compression of the upper crown (
There are 11 or 12 maxillary teeth in the best-preserved adult skulls. The small broken crown base of a twelfth tooth was shown on the right side of the holotypic specimen (
The maxillary tooth row is not straight as reconstructed in ventral view by
Mesiodistal crown width increases gradually from m1 to m8 and then decreases slightly in m9 and m10 and then more so in m11 (
The maxillary and dentary crowns in
The labial surface is dominated by a strong primary ridge that is flanked by mesial and distal paracingular fossae, the former extending slightly farther toward the crown base than the latter (
The lingual surface of mesial maxillary crowns is best exposed in SAM-PK-K1332, which have short primary and secondary ridges (
In occlusal view the maxillary crowns are butted against each other, the mesial margin often slightly concave and the distal margin flat or slightly convex in cross section (
The cheek teeth in
Tooth structure in
Tooth structure in
Posterior dentition of
Postcaniniform dentary tooth row of
Unlike
There are 10 postcaniniform dentary crowns (d2-11) opposing 11 maxillary crowns. The dentary tooth row, nonetheless, terminates distally even with (SAM-PK-K1332), or distal to (AMNH 24000), the last maxillary tooth, because d1-4 crowns are relatively broader than their counterparts in the maxilla (
Skull of
Skull of
Skull of
The vertebral column includes a well exposed cervical series starting anteriorly with the axis (
The parapophysis and diapophysis of cervical vertebra 3 and successive cervical vertebrae are more prominently developed than in other basal ornithischians such as
The postzygapophysis of C4 bears an epipophysis that is joined by a ridge from the prezygapophysis. Although developed as a prominent process, the epipophysis does not extend beyond the postzygapophysis. The neural spine also has a broad base that may be incomplete distally (
The postzygapophyses of C5 and C6 are joined to the prezygapophyses by a low ridge but no epipophyseal processes are present. A marked change in the shape of the prezygapophysis occurs between C5 and C6, the latter more erect and supporting a broad hook-shaped articular surface (
The length of the centra varies along the cervical column with C6-C9 noticeably shorter in length, as observed by Santa Luca (
Santa Luca tentatively identified the transition between cervical and dorsal vertebrae, and further information supports his conclusions. The best indicator of the transition from cervical to dorsal vertebrae in ornithischians is the abrupt dorsal shift of the parapophysis from the centrum to the base of the transverse process on the neural arch. The position of the parapophysis on the anterodorsal corner of the centrum in C9 is similar to that in preceding cervical vertebrae (
Jaws of
Jaw joints of
Presacral vertebrae of
Presacral vertebrae of
Dorsal and sacral counts hinge on the interpretation of the transverse process and rib in presacral vertebra 21 (girdle contact, not central fusion, is the arbiter regarding status as a sacral vertebra). Although the transverse process is broken at its tip, a portion of its rib is preserved projecting under the preacetabular process of the ilium (
In most ornithischians, the end of the preacetabular process is free of sacral rib articulations. In the euornithopod
Santa Luca (1980: 173, fig. 23) mentioned the possible presence of a sternal plate, but he did not figure this bone and omitted it from his skeletal reconstruction. Subsequent skeletal reconstructions show ossified sternal plates (
A pair of crescentic ossified sternal plates is present in SAM-PK-K1332, resembling in shape those in basal neornithischians such as
Although the axial rib is not preserved, a prominence straddling the neurocentral suture probably represents the diapophysis for a small two-headed axial rib (
Ossified tendons are present from the anterior dorsal through the sacral vertebrae (
Pectoral girdle and forelimb of
The reconstruction of the forearm presented by Santa Luca (1980: Figs 13, 15) did not remove postmortem fracturing and movement that is visible in the right forearm. A fracture crosses the mid-shafts of the right radius and ulna (
Santa Luca reconstructed the metacarpus with the base of metacarpal 2 inset into the carpus relative to metacarpal 1, such that its base articulates medially with distal carpal 1 (
Metacarpals 1-4 have squared bases that abut one another (
The right manus as preserved in
The distal end of metacarpal 1, which is best preserved on the right side, shows asymmetric distal condyles very similar to the condition present in many theropods. The lateral condyle is larger and raised above the medial condyle (
Forelimb of
Carpus and manus of
Limbs of
Hip and posterior trunk of
Hindlimb of
In SAM-PK-K1332 the tibia, fibula, astragalus and calcaneum are coossified as a tibiotarsus as noted by Santa Luca. That coossification, however, is not as complete and homogeneous as in avians. The distal suture between the fibula and calcaneum, for example, is visible, and the distal end of the fibula is expanded anteroposteriorly and transversely (
Santa Luca described three distal tarsals. This would be an unusual condition for an ornithischian, which usually retain two distal tarsals interpreted as distal tarsals 3 and 4. The usual pair of distal tarsals, however, are present, the flatter broader medial distal tarsal split by a crack in the block containing the right distal tarsus and pes (
Distal tarsal 3 is partially coossified with the metatarsus, the suture between its thinner medial portion and metatarsal 1 obliterated medially and posteriorly. The cuboid distal tarsal 4 is partially coossified with the medial distal tarsal and the proximal end of metatarsal 4. It is slightly wasted with an everted dorsal rim and a foramen on its anterior face (
The proximal end of metatarsal 1 is reduced proximally to a thin narrow splint (
Hindlimb of
Pes of
Skeleton of
Measurements (mm) of the skull and axial column of the holotypic skeleton of the South African heterodontosaurid
|
|
|
---|---|---|
Cranium | Length, anterior tip to occipital condyle | 115 |
Height, parietal to quadrate condyle | 66 | |
Cervical vertebrae | C2 centrum length | 16 |
C3 centrum length | 14 | |
C4 centrum length | 16 | |
C5 centrum length | 16 | |
C6 centrum length | 13 | |
C7 centrum length | 13 | |
C8 centrum length | 13 | |
C9 centrum length | (13) | |
Dorsal vertebrae | D1 centrum length | (13) |
D2 centrum length | 13 | |
D3 centrum length | 14 | |
D4 centrum length | (13) | |
D5 centrum length | 15 | |
D6 centrum length | 15 | |
D7 centrum length | 15 | |
D8 centrum length | 15 | |
D9 centrum length | 15 | |
D10 centrum length | — | |
D11 centrum length | (15) | |
D12 centrum length | 15 | |
Sacral vertebrae | S1 centrum length | 14 |
S2 centrum length | (13) | |
S3 centrum length | — | |
S4 centrum length | — | |
S5 centrum length | — | |
S6 centrum length | 14 | |
Caudal vertebrae | CA1 centrum length | 14 |
CA2 centrum length | — | |
CA3 centrum length | 15 | |
CA4 centrum length | (15) | |
CA5 centrum length | 16 | |
CA6 centrum length | 16 | |
CA7 centrum length | 16 | |
CA8 centrum length | 17 | |
CA9 centrum length | 18 | |
CA10 centrum length | 18 | |
CA11 centrum length | 18 | |
CA12 centrum length | — | |
?CA19 centrum length | 16 | |
?CA20 centrum length | 16 | |
?CA21 centrum length | 16 | |
?CA22 centrum length | 17 | |
?CA23 centrum length | 16 | |
?CA24 centrum length | 17 | |
?CA25 centrum length | 16 | |
?CA26 centrum length | 16 | |
?CA27 centrum length | 16 | |
?CA28 centrum length | 17 | |
?CA29 centrum length | 16 | |
?CA30 centrum length | 16 | |
?CA31 centrum length | — | |
?CA32 centrum length | 16 | |
?CA33 centrum length | 16 | |
?CA34 centrum length | — | |
Chevrons | Ch1 length | 23 |
Ch2 length | 23 | |
Ch3 length | 22 | |
Ch4 length | 23 | |
Ch5 length | 23 | |
Ch6 length | 24 | |
Ch7 length | 24 | |
Ch8 length | 24 | |
Ch9 length | 22 | |
Ch10 length | 17 | |
Ch11 length | 15 | |
?Ch20 length | 19 | |
?Ch21 length | 20 | |
?Ch22 length | 19 | |
?Ch23 length | 17 | |
?Ch24 length | 18 | |
?Ch25 length | 15 | |
?Ch26 length | 15 | |
?Ch27 length | 17 | |
?Ch28 length | 16 | |
?Ch29 length | 15 | |
?Ch30 length | 15 | |
?Ch31 length | 16 |
Measurements (mm) of the pectoral girdle and forelimb bones of the holotypic skeleton of the South African heterodontosaurid
|
|
|
---|---|---|
Scapula | Blade length | 86 |
Blade, minimum width of neck | 8 | |
Blade, maximum width at distal end | 22 | |
Humerus | Length | 83 |
Proximal end, maximum width | 21 | |
Deltopectoral crest length | 35 | |
Shaft, minimum diameter | 7 | |
Distal end, maximum width | 19 | |
Ulna | Length | 68 |
Shaft, minimum diameter | 4 | |
Radius | Length | 58 |
Shaft, minimum diameter | 4 | |
Manual digit I | Metacarpal 1 length | 18 |
Phalanx I-1 length | 17 | |
Ungual I-2 length | 17 | |
Manual digit II | Metacarpal 2 length | 23 |
Phalanx II-1 length | 15 | |
Phalanx II-2 length | 17 | |
Ungual II-3 length | 18 | |
Manual digit III | Metacarpal 3 length | 22 |
Phalanx III-1 length | 14 | |
Phalanx III-2 length | 12 | |
Phalanx III-3 length | 15 | |
Ungual III-4 length | 17 | |
Manualdigit IV | Metacarpal 4 length | 15 |
Phalanx IV-1 length | 7 | |
Phalanx IV-2 length | 5 | |
Manual digit V | Metacarpal 5 length | 7 |
Phalanx V-1 length | 6 | |
Phalanx V-2 length | 4 |
Measurements (mm) of the pelvic girdle and hind limb bones of the holotypic skeleton of the South African heterodontosaurid
|
|
|
---|---|---|
Ilium | Blade length | 97 |
Blade, height dorsal to acetabular rim | 15 | |
Preacetabular process length | 46 | |
Postacetabular process length | 24 | |
Femur | Length | 112 |
Minimum shaft diameter | 9 | |
Head to distal end of fourth trochanter | 46 | |
Tibiotarsus | Length | 145 |
Minimum shaft diameter | 9 | |
Pedal digit I | Metatarsal 1 length | 38 |
Phalanx I-1 length | 17 | |
Ungual I-2 length | 18 | |
Pedal digit II | Metatarsal 2 length | 59 |
Phalanx II-1 length | 19 | |
Phalanx II-2 length | 16 | |
Ungual II-3 length | 21 | |
Pedal digit III | Metatarsal 3 length | 68 |
Phalanx III-1 length | 22 | |
Phalanx III-2 length | 16 | |
Phalanx III-3 length | 14 | |
Ungual III-4 length | 18 | |
Pedal digit IV | Metatarsal 4 length | 61 |
Phalanx IV-1 length | 17 | |
Phalanx IV-2 length | 12 | |
Phalanx IV-3 length | 11 | |
Phalanx IV-4 length | 10 | |
Ungual IV-5 length | 16 | |
Pedal digit V | Metatarsal 5 | 15 |
SAM-PK-K3606, left dentary with 11 teeth (preserved mostly as a natural mold; UCRC PVC10 was cast from the natural mold;
NHMUK RU A100 (formerly BMNH A100), partial skull preserving the right premaxilla, right nasal, right maxilla, the posterior two-thirds of the right lower jaw, and the anterior third of the left lower jaw; BP/1/4244, left maxilla with 12 teeth (holotype
Paballong, near Mount Fletcher, Transkei (Herschel) District, Cape Province, South Africa;
Upper Elliot Formation; Lower Jurassic, Hettangian, ca. 200-196 Ma (
Heterodontosaurid ornithischian characterized by the following two autapomorphies: (1) prominent ridge on the distal crown margin running from the first denticle to the cingulum (labial aspect of maxillary crowns, lingual aspect of dentary crowns); (2) lingually curved maxillary and dentary tooth rows.
The validity of
The NHMUK RU A100 is preserved on a single block of matrix with bone exposed on both sides. In its current state of preparation, the block preserves the right premaxilla (medial view), right maxilla (lateral view), anterior end of the left lower jaw (medial view), and mid and posterior parts of the right lower jaw (partial medial and lateral views) (
A flat broad bone next the right maxilla is here tentatively identified as the posterodorsal ramus of the maxilla, preserved near its natural position relative to the remainder of the bone (
The left lower jaw (
The more complete right lower jaw is also exposed on both sides of the block (
With the identifications proposed here, there is no reason to doubt that NHMUK RU A100 represents a single, probably adult individual with worn upper and lower cheek of similar form, worn premaxillary teeth, and large upper and lower caniniform teeth. The specimen preserves the right side of the snout and lower jaw and a matching anterior portion of the left lower jaw. This important specimen, the salient features of which are outlined below, should be fully prepared and described in more detail.
Block with remains of the heterodontosaurid
Block with remains of the heterodontosaurid
The right premaxilla is preserved in ventromedial view, exposing the median articular surface for the left premaxilla and the palatal shelf medial to the premaxillary teeth (
The palatal surface is flat with a near horizontal orientation as in
The right maxilla, which is broadly exposed in lateral view (
The body of the maxilla thickens transversely from the alveolar margin to the ventral rim of the antorbital fenestra, which protrudes laterally as in other heterodontosaurids (
The edges of the arched diastema and the anterior end of the anteromedial process of the maxilla are broken away (
Upper jaw of the heterodontosaurid
Premaxilla of the heterodontosaurid
Maxilla of the heterodontosaurid
Lower jaw of the heterodontosaurid
The right lower jaw is exposed mainly in lateral view and is complete except for the retroarticular region and small areas of breakage (
Lower jaw of the heterodontosaurid
The dentary is a robust bone approximately 17 mm in depth at mid-length and some 70 mm in length. The ventral margin of the ramus is thickened, and the tooth row is inset by a ventrally arched, deep buccal emargination (
Medially the dentary is overlapped by a broad, tongue-shaped splenial, which appears to have been displaced anteriorly toward the symphysis on the right side (
The retroarticular region is broken away, so the exact location of the jaw articulation is unknown. Judging from the preserved margin of the surangular and the location of the dentary tooth row, the jaw articulation was probably offset ventrally at least as much as preserved in
The three premaxillary teeth (pm1-3) are preceded by an edentulous margin approximately one-third of the length of the ventral margin of the premaxilla (
The large, caniniform third premaxillary tooth lacks any constriction between the crown and root (
The wear facets on pm2 and 3 are planar but are not “flat” as described by
The right maxilla of NHMUK RU A100 has alveoli for 14 fully developed teeth (
The distinguishing feature of the lateral aspect of the maxillary crowns is the accentuated distal edge, which is raised as a distal marginal ridge (
Skull of the heterodontosaurid
The posterior portion of a small dentary tooth (d1) is preserved anterior to the caniniform tooth (
Eleven postcaniniform teeth (d3-13) are present in the holotypic dentary, which lacks the distalmost teeth. In NHMUK RU A100, the first and second postcaniniform crowns (d3, 4) are smaller and proportionately taller than more distal dentary crowns (
The lingual side of the dentary crowns has a prominent, slightly mesially offset, vertical eminence that is stronger than that on the labial aspect of the maxillary crowns (
The roots of the dentary teeth in NHMUK RU A100 appear to be swollen. The left dentary and one of its posterior teeth are exposed in cross-section (
Maxillary and dentary crowns have an imbricate arrangement with the mesial edges of the crowns angled mesiolingually. Although some adjacent crowns are in contact, there is little overlap of crown edges in either the holotypic dentition, the tooth rows of NHMUK RU A100, or the two referred maxillae. As described by
The partial skull reconstruction (
The premaxillary teeth, which are based on NHMUK RU A100, are inset from the anterior margin of the premaxilla with the first two premaxillary teeth set back into their sockets. The premaxillary tooth row is positioned below the level of the maxillary tooth row (
MPEF-PV 3211, partial skull and postcranial skeleton lacking the forelimbs, hindlimbs, and caudal vertebrae (
MPEF-PV 1718, 1719, 1786, 3810, and 3811, isolated teeth.
Queso Rallado, 2.3 km west of Cerro Cóndor, Chubut Province, Argentina (
Cañadón Asfalto Formation (
Heterodontosaurid ornithischian characterized by the following four autapomorphies: (1) external mandibular fenestra absent; (2) denticules on the margins of individual denticles; (3) mesially divergent basal denticle on mesial margin in some dentary crowns; (4) mesial denticulate margin approximately 60% the length of the distal margin.
The revised diagnosis above restricts cited features to those interpreted as potential autapomorphies for
Only a portion of theskull roof and braincase are preserved and figured (
As noted by
The maxilla has a laterally protruding rim along the ventral margin of the antorbital fossa as in other heterodontosaurids. Pol et al. (2011: 371) suggested that an arched diastema may not have been present. The anterior margin of the maxilla, however, is not well preserved (
The prominent laterally projecting jugal horn is very similar in form and location to that in
The postorbital has a particularly deep posterior ramus compared to
Partial skull of
The lower jaw is proportionately short with a deep dentary similar to that in
The jaw joint is offset ventral to the maxillary tooth row as in
There appears to be approximately 11 teeth in maxillary and dentary tooth rows and a diastema between the caniniform and postcaniniform teeth, judging from the preserved portions of the tooth row in the right dentary (
The dentary crowns also resemble the new African species in the mesial bowing of the central axis of the crown. The mesial carina, in addition, is shorter than the distal carina in both species, although this asymmetry is more strongly expressed in
The skull reconstruction presented here (
Portions of the axial column and pelvic girdle are preserved (
The pelvic girdle exhibits a fully open acetabulum and a laterally prominent ischial peduncle on the ilium (
From the Greek
Same as for only known species.
SAM-PK-K10488, fragmentary skull preserving right and left dentaries and the predentary.
Voyizane (= Voisana), Transkei (Herschel) District, Cape Province, South Africa;
From “Latin
Heterodontosaurid ornithischian characterized by the following four autapomorphies: (1) proportionately deep predentary with a dorsal margin about 70% the anteroventral margin; (2) predentary dorsal margin angled anteroventrally at approximately 45°; (3) postcaniniform dentary crowns with an mesially-bowed primary ridge that angles from the apical denticle toward the mesial side of the crown base; (4) slightly concave denticulate crown margins to either side of a prominent apical denticle.
The holotypic represents a small heterodontosaurid that is preserved on a small block of sandstone matrix (
Partial skull of the heterodontosaurid
Lower jaws of the heterodontosaurid
Lower jaw of the heterodontosaurid
The predentary is a wedge-shaped bone that is very short anteroposteriorly (
The robustly proportioned right and left dentaries are exposed in lateral and medial views, respectively (
The lateral aspect of the right dentary preserves a deep buccal emargination including several matrix-filled foramina. A small anterior dentary foramen is present near the predentary and is not associated with an impressed vessel tract as in
The flat ventral portion of the dentary symphysis is exposed in medial view of the left dentary (
The right postorbital is preserved in medial view (
There are probably 11 dentary teeth. Most of the right tooth row is preserved in lateral view from the caniniform tooth (d1) to d8 (
The caniniform tooth (d1) has straight mesial and distal carinae, the former with serrations (
There is a significant diastema in the right dentary tooth row between the caniniform tooth and d2, the relatively small first postcaniniform crown (
Right d6 and d7 have a dorsal crown profile like all more distal crowns. Concave apical margins are present on either side of the apical denticle, the mesial apical margin of which is shorter and more apically positioned than the distal apical margin (
Dentary teeth of the heterodontosaurid
Dentary teeth of the heterodontosaurid
The medial crowns surface is most completely preserved in distal teeth (d7-11) on the left side (
The roots are only partially exposed in cross-section of the right lower jaw. The most complete of these, which probably belongs to d10, has a relatively large diameter and central lumen. The roots in
The crowns of right d5-8 and left d6-9 have an imbricate arrangement relative to one another (
All postcaniniform teeth in the right dentary are worn to varying degrees except perhaps the small crowns of d2-4 (
Differential wear along the tooth row strongly suggests cyclic tooth replacement, despite the general alignment of wear surfaces and the absence of replacement foramina. Direct evidence of replacement is present in the left dentary tooth row. A small replacement crown is emerging at the base of the heavily worn crown of d10 (
Lower jaw of the heterodontosaurid
The reconstruction of the dentary of
The most unusual feature of the preserved portion of the skull is the shape of the predentary. Despite many similarities to
Two major concerns in heterodontosaurid systematics include the tentative heterodontosaurid status of
It is possible that (1) reduction of the premaxillary tooth row to three teeth (
Other heterodontosaurid synapomorphies now apparent in the original material of
In sum, there is substantial character evidence, that
Galton (1973a: 71) stated that there is no basis for Thulborn’s reference of NHMUK RU A100 to
Taxonomic controversy, in sum, involves the validity of the genus and species
The reidentification of several of the bones of specimen NHMUK RU A100 (
Maxillary and dentary crowns inNHMUK RU A100 and
Several misleading statements have been made regarding the teeth of NHMUK RU A100.
Two of the four specimens of
These unusual proportions give
Compared to
There is extensive evidence, however, for tooth replacement in all known heterodontosaurid species. The evidence consists of direct observation of erupting crowns visible near the alveolar margin or within tooth crypts, as shown in computed tomographic scans (
Active tooth replacement is readily observed in all heterodontosaurids with simple subtriangular crowns, including
Tooth replacement also occurs in heterodontosaurids with deeper crown proportions, such as
Tooth eruption may have decreased or ceased entirely in mature specimens of
Heterodontosaurids may have suppressed replacement of caniniform teeth in the premaxilla, maxilla and dentary, as shown by currently available specimens. The only specimens showing active eruption in these tooth positions are clearly subadult individuals (e.g., Kayenta heterodontosaurid) (
In sum, there is no evidence in favor of periodic complete replacement of the cheek teeth in heterodontosaurids (
The tapered roots of cheek teeth in heterodontosaurids with simple subtriangular crowns, such as
The pulp cavity collapses during growth, and is usually restricted to the root in a mature ornithischian tooth (
Similar shearing wear facets are present in the premaxillary teeth of other heterodontosaurids. In
The crown of pm2 provides evidence for three kinds of tooth wear. First, a large planar wear facet from abrasion against the bill of the predentary is present on the lingual side of the crown (
The caniniform crown (pm3) preserves a large planar wear facet on its lingual side similar to that described above in
Premaxillary teeth are also preserved on both sides of the holotypic skull (SAM-PK-K337), although none is as complete and as well exposed as in SAM-PK-K1332 (
None of these wear facets or the polished breakage surfaces have been described as such in
The caniniform crowns thus were put to considerable use in cropping and possibly in rooting functions. Crown breakage in the premaxillary series suggests at least occasional contact with hard materials, as may occur in the course of agnostic or rooting behaviors. Loss of the crown tip or obliteration of marginal serrations, furthermore, does not appear to have curtailed their function, as might be the case if they played a significant role in carnivory.
In
“there is no obvious caniniform occlusion that might have generated such a facet. One possibility is that this facet reflects some malocclusion with the opposing caniniform. Other (much less likely) proposed of the uses of the caniniforms for digging and or some type of agonistic behavior might be considered as potential means for accounting for such a facet . . . but the absence of more general indications of wear and retention of marginal denticles [
Inspection of the crown tip under magnification, however, casts doubt on its identification as a wear facet. The tip of the crown is broken, leaving an irregular rather than planar surface, the edges of which show clear signs of abrasive polishing. The same pattern of breakage with subsequent abrasive polishing is described above in premaxillary crowns, although in dentary caniniform crowns there is no evidence of planar shearing wear facets.
When the jaws of SAM-PK-K1332 are drawn apart, the tips of the enlarged pm3 and d1 caniniform teeth are positioned near one another in effective opposition for a nipping bite (
In
Tooth wear in heterodontosaurine cheek teeth is usually very well developed. In some genera, such as
In
In the worn dentition of SAM-PK-K1332, both maxillary and dentary facets are gently transversely concave, the dentary wear facets more strongly concave than maxillary wear facets (
The tooth rows of SAM-PK-K1332 suggest that the inclination of wear facets increases from low- to high-angle at the mesial end of the dentary and maxillary tooth series (
Sustained wear is the most likely explanation for the stark increase in the angle of incidence of the wear facets between subadult AMNH 24000 and the two adult skulls (SAM-PK-K3606, -K1332). The crowns in AMNH 24000 preserve secondary ridges in maxillary crowns, apical portions of the dentary crowns, and active tooth eruption. With more sustained wear in SAM-PK-K1332, few secondary ridges remain on maxillary crowns, most of the posterior dentary crowns are obliterated, and there are no erupting crowns in either tooth row (
Two general kinds of isognathous jaw mechanisms have been proposed to account for the truncating, high-angle wear facets observed in the teeth of
(1)
(2)
(3)
(4)
The second mechanism is a cross-section showing
The third jaw mechanism, identified here and listed above as
Hypotheses for jaw movement during tooth-to-tooth occlusion in
Occlusion and wear between maxillary and dentary teeth in
The saddle-shaped predentary-dentary joint, which is also present in
In
In the opinion of this author, the skull of
1) Jaw movement is isognathous and fundamentally arcilineal rather than propalinal, based on mesowear (i.e., macroscopic evidence of wear direction) and the form of the jaw joint;
2) Shearing between upper and lower premaxillary teeth and the edges of keratinous upper and lower bill sheaths results in near vertical wear facets on premaxillary teeth and would have limited transverse movement at the anterior end of the lower jaws;
3) Wear facets are high-angle (~ 45-65°) in the central portion of upper and lower cheek tooth rows;
4) Wear facets are gently transversely concave in the central portion of upper and lower cheek tooth rows, a feature more pronounced in the lower than the upper tooth row.
5) Wear facets tend to be lower-angle in the premaxillary teeth and the mesial end of upper and lower cheek tooth rows.
If the prevention of long-axis rotation was important, furthermore, a deeper more vertical symphysis would provide more effective resistance. In
A partial subadult skull of
Thus the jaw articulation is a well-fitted rotary joint, unsuitable for significant anteroposterior motion of the quadrate condyle. The deep anterior wall of the socket, in particular, would prevent any significant posterior motion of the lower jaw relative to the quadrate. The anteroposterior width of the socket equals the width of the quadrate condyle in the subadult skull (AMNH 24000); socket width may be slightly greater than the width of the quadrate condyle in SAM-PK-K1332 (
Several aspects of the lower jaw joint in
Mesowear also strongly contradicts propalinal jaw movement as a viable hypothesis to explain tooth wear in
Almost nothing has been said about the jaw joint in discussions about masticatory movement in heterodontosaurids. In
It is important to determine the effect of a canted jaw joint on the arc of the lower jaw, as it nears occlusion with the maxillary tooth row. To better understand this, a physical model of upper and lower jaws was created at 10 times natural size to exaggerate subtle transverse displacement. In the model as in
Some medial flexion (“wishboning” or “scissoring”) of the dentaries at the predentary-dentary joints may also have occurred (
The relation between upper and lower caniniform teeth in
In heterodontosaurids with simple subtriangular tooth crowns, the variable form of the predentary-dentary joint does not suggest similar predentary mobility. In
Although many ornithischians show similar attachment fossae for the adductor musculature along the margins of the laterotemporal fenestra (
Other notable structures of potential relevance for reconstructing the adductor musculature include the jugal flange, the robust dorsal margin of the surangular, the thin-walled external mandibular fossa, and the everted, thickened ventral margin of angular. The jugal flange is a stout, transversely compressed pendant process that is found only in heterodontosaurids. It does not resemble the pyramidal jugal horn in
The robust dorsal margin of the surangular is notable for the large anterior surangular foramen and the associated impressed vessel tract, which arches posteriorly toward the posterior surangular foramen (
The enlarged surangular foramen, impressed vessel tract, external mandibular fossa, and everted ventral margin of angular in
Snout and upper dentition in
Premaxillary dentition in
Configuration of jaw articulation and long axis of the lower jaw in
Relative position of the lower jaw in
Previous jaw muscle reconstructions in
Jaw musculature and keratin sheathing in
Jaw adductor musculature in
Jaw adductor musculature and keratin sheathing in a psittaciform bird and parrot-beaked dinosaur. Differentiation of facial components of the adductor muscle mass to increase bite force
An alternative muscle reconstruction for
(1) Maintains the usual archosaurian insertion for the M. adductor mandibulae externus superficialis on the dorsal margin of the surangular;
(2) Positions the insertions for both the M. adductor mandibulae externus profundus and medialis as in archosaurs on the prominent coronoid process formed by the dentary and coronoid;
(3) Avoids the everted edge of the quadrate shaft by filling the posterior portion of the squamosal-paroccipital fossa with the origin of the M. depressor mandibulae;
(4) Reconstructs a separate muscle mass, the M. adductor mandibulae externus ventralis, originating on the ventral margin of the jugal flange and inserting on the everted ventral margin of the angular.
The differentiation of a M. adductor mandibulae externus ventralis, which is depicted originating on a prominent lateral crest on the maxilla and jugal flange and inserting on the raised ventral margin of the angular (
The other muscle in archosaurs that might insert on the swollen ventral margin of the angular is the M. pterygoideus ventralis, which originates on the posterior palate and wraps around the ventral margin of the lower jaw (
The other proposed function of the jugal flange is that it formed the later wall of a bony slot, into which slid the surangular when the jaws are closed (
More recently,
Snout and anterior dentition of dinosaurian carnivores. Snout and anterior dentition in left lateral view of coelophysoid theropods
1.
2.
3.
4.
5.
1.
2.
3.
4.
Skulls of extant lepidosaurian carnivores. Skulls in left lateral view (from
Flesh reconstruction of the head and neck of
Initial phylogenetic hypothesis for heterodontosaurid relationships. Qualitative parsimony analysis by
Phylogenetic hypotheses for heterodontosaurids by Butler and colleagues.
Heterodontosaurids with primitive subtriangular crowns were known to exist on northern landmasses, but so little was known about their morphology that they did not impact the aforementioned phylogenetic hypotheses. The heterodontosaurid status of
More recently, heterodontosaurids have been reinterpreted as basalmost ornithischians (Butler et al. 2007,
Recent discovery of several skeletons of the Chinese heterodontosaurid
Comparison of character data is key to resolving the position of heterodontosaurids among ornithischians—or at least isolating the characters and/or character state scores that support alternative hypotheses (
Several features previously considered to characterize heterodontosaurids have been omitted, because they also occur in basal saurischians and thus may constitute dinosaurian symplesiomorphies. These include the absence of replacement foramina and features of manus, such as metacarpals 1-3 with block-like bases and dorsal extensor pits for hyperextension and trenchant manual unguals with prominent flexor processes (Sereno, 1986;
Butler et al. (2010: 6; 2012: 3) recently listed eight features in a diagnosis of the family, four of which overlap those listed below (apomorphies i, iii, xi, xiii). The other four (constriction between humeral head and medial tubercle, rod-shaped fourth trochanter, astragalocalcaneal fusion, proximal pedal phalanges with distal extensor pit) are problematic as heterodontosaurid autapomorphies, because of variation among included taxa (astragalocalcaneal fusion), presence in other basal dinosaurs (proximal pedal phalanges with distal extensor pit, as in
At present heterodontosaurid synapomorphies reside almost entirely in the skull and most of these are concerned with the number and form of the anterior teeth, the form of the loosely attached predentary, and the stout proportions of the dentary. There is only one postcranial synapomorphy listed below, the reduced shaft and distal end of the fibula. This synapomorphy is questionable if
The present study makes a much stronger case that
(i) Three or fewer premaxillary teeth (
(ii) Premaxillary teeth increase in size distally (
(iii) Dentary caniniform tooth associated with an arched premaxilla-maxilla diastema
(iv) Nasal fossa, dorsomedian with rounded lateral margins (
(v) Jugal flange, ventral embayment of jugal-quadratojugal embayment. (
(vi) Jugal horn below orbit, laterally directed and dorsoventrally compressed (
(vii) Postorbital body, arcuate fossa with raised anterior rim (
(viii) Quadrate head included within laterotemporal fossa (
(ix) Quadrate condyle, articular surface ventrolaterally inclined at approximately 30° (
(x) Quadratojugal T-shaped (
(xi) Predentary processes (lateral, ventral) rudimentary (
(xii) Dentary ramus stoutly proportioned, substantial depth at mid ramus compared to length (
(xiii) Fibular mid-shaft and distal end reduced (
The link between “BMNH A100” and
Reanalysis of 224 of these characters (3 are uninformative) confirms their result in a strict consensus tree (summarizing 2246 minimum-length trees of 520 steps), although the supporting character evidence among heterodontosaurids was not discussed and is problematic. Ordering of one character (premaxillary tooth count;
Reanalysis of 227 of these characters (3 are uninformative) confirms their result (1629 minimum-length trees of 551 steps), although the issues cited above regarding character evidence among heterodontosaurids remain. The single unambiguous synapomorphy uniting African heterodontosaurids to the exclusion of
All heterodontosaurid genera (eight) are included except the problematic taxon
More inclusive phylogenetic hypothesis for heterodontosaurids. Parsimony analysis of
Maximum parsimony analysis yields six minimum-length trees (38 steps) with relatively high consistency and retention indices (
Considering trees one step longer than minimum length (39 steps, 12 trees), resolution of a Laurasian heterodontosaurid clade breaks down (
Phylogenetic hypothesis for heterodontosaurids based on character data assembled in this study. Consensus tree summarizing 6 minimum-length trees (38 steps) based on maximum parsimony analysis of 30 characters in 8 heterodontosaurid genera (consistency index = 0.79; retention index = 0.88; Appendix I). Outgroups (constrained as shown) include basal saurischians (
The present dataset, therefore, strongly supports (1) the monophyly of heterodontosaurids and (2) the basal position of
The analysis allows a more detailed understanding of heterodontosaurid evolution (
Evolution of key masticatory specializations among heterodontosaurids.
Heterodontosaurines are characterized by a postcaniniform diastema, lowered jaw articulation, an enlarged, inset surangular foramen, and an external mandibular fossa (Appendix I: characters 5, 26-28;
All of the derived features that evolved in heterodontosaurines are plausibly interpreted as trophic specializations for procuring and more efficiently processing plant materials (
Phylogenetic analysis provides weak support for an initial split among heterodontosaurids prior to the earliest Jurassic into low-crowned Laurasian and deeper-crowned Gondwanan subclades (
The Gondwanan subclade,
Biogeographic distribution in time for heterodontosaurids included in the phylogenetic analysis. Localities for included taxa are plotted on an Early Cretaceous (Berriasian-Valanginian) paleogeographic map (
Review of available heterodontosaurid fossils unequivocally establishes
Tooth replacement and tooth-to-tooth wear is more common than previously thought among heterodontosaurids. In
Heterodontosaurines evolved remarkably sophisticated masticatory adaptations comparable in complexity to those of euornithopod neornithischians of the Late Jurassic. Comprising the most diverse early radiation of ornithischians, heterodontosaurids ranged across both Laurasia and Gondwana, persisting on various landmasses into the Early Cretaceous for a total duration of at least 100 My.
I am indebted to C. Abraczinskas for her skillful renderings from bones, tracing from photographs, and labeling of all figures as well as her layout and final drafts of photographs, tracings from photographs, and two-dimensional reconstructions by the author. For the elegant three-dimensional skull reconstructions, flesh sculpting, and jaw muscle reconstructions of
The character statements listed below vary among heterodontosaurids and are informative for relationships within
0 four or more
1 three or fewer
0 subequal with largest within series
1 increase distally
0 present
1 absent
0 present
1 absent
0 absent
1 present
0 14 or more
1 12 or less
0 subequal
1 central crowns more than twice as large as mesial and distal crowns
0 less than 1.5
1 greater than or equal to 1.5
0 absent
1 mesially bowed
0 marked expansion of crown base
1 reduced, weak expansion of crown base
0 absent
1 present
0 straight
1 bowed dorsally (maxilla) and ventrally (dentary)
0 absent
1 present
0 absent
1 present
0 absent
1 present
0 flat
1 arcuate fossa with raised anterior rim
0 narrow, basal width approximately 1/3 length
1 broad, basal width approximately 1/2 length
0 excluded
1 included
0 horizontal
1 ventrolaterally inclined at approximately 30°
0 L-shaped
1 T-shaped
0 present
1 rudimentary or absent
1 flat
2 saddle-shaped
0 tapered, subtriangular
1 dorsoventrally expanded, rounded
0 less than 25%
1 25% or more
1 shallow groove
2 impressed canal
0 small or absent, shallow groove on anterior side
1 large, impressed channel on posterior side
0 absent
1 present
0 less than 10%
1 more than 10%
0 minimum depth 40% or more of length, greater than minimum depth of preacetabular process
1 minimum depth 30% of length, subequal to minimum depth of preacetabular process
0 25% or more
1 less than 25%
X = too transformed to score; ? = not preserved; A = states 0 & 1
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|
|
||
Eoraptor | 00X0000101 | 0010000000 | 0000000000 | 100 |
Eodromaeus | 0?X0010101 | 0000000000 | 00000?0010 | 93 |
Lesothosaurus | 00X0000000 | 0000000000 | 0000000000 | 100 |
Neornithischia | 00X0000000 | 0000000000 | 0000000000 | 100 |
Thyreophora | 00X0000000 | 0000000000 | 0000000000 | 100 |
Echinodon | 1101010000 | A0???????? | 10011????? | 57 |
Fruitadens | ??01010000 | 10???????? | ??011????1 | 47 |
Tianyulong | 11?10?0000 | 101??????? | 1001?000?1 | 63 |
Lycorhinus | 1101100100 | 00???????? | ??01?111?? | 57 |
Manidens | ???1?11111 | 00?1111111 | 1??1?1110? | 70 |
Pegomastax | ??11111111 | 00????1??? | 11110????? | 53 |
Abrictosaurus | 1101001101 | 01???????1 | 11110??111 | 70 |
Heterodontosaurus | 1111111101 | 0111110111 | 1111011111 | 100 |
Video of coronal cross sections. (doi:
Video of sagittal cross sections. (doi:
Video of horizontal cross sections. (doi: