Heterodontosaurus, CROMPTON & CHARIG, 1962

Norman, David B., Crompton, Alfred W., Butler, Richard J., Porro, Laura B. & Charig, Alan J., 2011, The Lower Jurassic ornithischian dinosaur Heterodontosaurus tucki Crompton & Charig, 1962: cranial anatomy, functional morphology, taxonomy, and relationships, Zoological Journal of the Linnean Society 163, pp. 182-276 : 187-192

GENUS: HETERODONTOSAURUS CROMPTON & CHARIG, 1962

Generic diagnosis: As for species (below)

Type species: H. tucki Crompton & Charig, 1962

Synonymy

Lycorhinus tucki (Crompton & Charig) Thulborn, 1970a: 244 .

Lycorhinus tucki (Crompton & Charig) Thulborn, 1974: 161 .

Generic and specific characteristics

General: Basal ornithischian dinosaur, known stratigraphical range: Sinemurian/Pliensbachian.

Cranial (*indicates autapomorphy – see also discussion in Phylogenetic Relationships section): Deep buccal emargination is formed by a strongly dorsoventrally compressed and transversely expanded maxillary ridge, which forms the ventral margin of the external antorbital fenestra and is thickened along its lateral margin*; antorbital fossa extends posteriorly to form a channel on the external surface of the jugal*; quadratojugal forms a thin wing that overlaps the entire external surface of the quadrate (contacting the squamosal dorsally and terminating ventrally just above the articular condyle) and contacts the jugal via a narrow bridge of bone*; quadratojugal has a constricted scarf suture with the jugal*; narrow and obliquely orientated ventral jugal projection closely aligned against the lateral surface of the lower jaw*; prominent laterally expanded ‘boss’ on the jugal*; sharply defined curved ridge on the external surface of the postorbital that is continuous with a similar ledge on the dorsolateral margin of the squamosal*; remnants of intracranial pneumatism preserved as pits on the paroccipital process and quadrate, and as sinuses on the jugal boss and anteromedial process of the maxilla*; narrow and deep pterygoid flanges lie close to the medial surface of the lower jaw (forming a slot-like guide with the ventral process of the jugal)*; paroccipital wings perforated by a discrete vascular/neural canal*; basisphenoid flanges are large, oblique and extend medial to the pterygoids and enclose narrow fossae on either side of the ventral midline of the braincase; surangular develops two finger-like rami that form much of the dorsal margin of the coronoid eminence anterior to the jaw joint*; elongate, slot-shaped surangular foramen*; broad depression on the lateral surface of the angular*.

Dentition (*indicates autapomorphy): Premaxillary and dentary caniniforms have fine, blunt, serrations (six per mm) running down their posterior margins; premaxillary caniniform lacks serrations along its anterior edge; dentary caniniform has widely spaced, rounded denticulations running down the upper portion of its anterior edge*; columnar maxillary and dentary teeth have crowns that are only slightly expanded either anteroposteriorly or transversely above the root (the ‘cingulum’ and ‘neck’ at the crownroot junction are completely absent)*; labial surface of maxillary crowns possess three prominent ridges that separate equal-sized, clearly defined excavated regions*; lingual surface of dentary crowns display a mesially offset principal ridge and crown margins that create subequal adjacent crown areas*; extensive wear facets on the upper and lower dentitions display a warp because successive teeth are worn at differing angles*.

Postcranial characters (*indicates autapomorphy – see also discussion in Phylogenetic Relationships section): (derived from Santa Luca, 1980 – with additions and modifications) axial vertebral column: 21 vertebrae (9 cervical, 12 dorsal)*, sacrum: 6 fused vertebrae*, caudal vertebrae: 34+; prominent epipophyses present on anterior cervical postzygapophyses*, ossified tendons distributed across the neural spines of dorsal and sacral vertebrae only; scapular blade narrow and elongate with expanded distal (extrascapular) portion; humerus with a large deltopectoral crest and large entepicondyle*; humerus lacks a posterior (olecranon) fossa; ulna with prominent olecranon; manus length more than 40% of the combined length of humerus and radius; nine carpal bones; manus digits 1–3 parallel, digits 4–5 reduced in size and divergent; penultimate phalanges of digits 2 and 3 more elongated than the proximal phalanges; extensor pits present on the dorsal surface of distal end metacarpals and phalanges; manual unguals strongly recurved, and with prominent flexor tubercles. Ilium, with a narrow vertical facet on the ischial peduncle that resembles an avian antitrochanter*; prepubic process short and deep, postpubis as long as ischium; obturator process absent; ischial shaft marked by an elongate lateral ridge that is drawn out to form a prominent lateral shelf along the mid-section of the shaft*; femoral greater and anterior trochanters not separated by a cleft; transverse axis of distal femoral articular surface obliquely orientated; fibula reduced and fused to tibia distally*; astragalus and calcaneum fused*; astragalocalcaneum fused to the distal ends of tibia and fibula*; three distal tarsals present but fused to proximal ends of their metatarsals*; metatarsals 1–4 fused together*.

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Holotype

SAM-PK-K337 – Iziko South African Museum, Cape Town ( Figs 1–3 , 7 , 20–22 and Appendix 3); see also Crompton & Charig, 1962: fig. 1; Charig & Crompton, 1974: figs 10, 11; Galton, 1986: fig. 16.6r,s; Báez & Marsicano, 2001: fig. 5C). Nearly complete skull and lower jaw embedded in greyish-yellow sandstone. The surface of the skull is encrusted by an adherent, and very tough, layer of haematite that has been removed partially using a small diamond saw. Most of the preparation was carried out by Arthur E. Rixon, formerly in charge of the Palaeontological Laboratory of the British Museum (Natural History); one of the authors (A. W. C.) continued preparation as far as seemed prudent at the time. Postcranial remains were also listed by Crompton & Charig (1962: 1075) but the whereabouts of this potentially extremely important material is currently unknown.

During fossilization the specimen has been compressed laterally. The skull roof slopes steeply toward the right (at an angle of about 35° from the horizontal, the latter being taken as normal to the sagittal plane – see Fig. 7 ). Structures on the right side have been displaced ventrad and a little backwards with respect to those in the mid-line. The skull is nevertheless reasonably well preserved on the right side ( Fig. 1 , Appendix 3A). A short section of the dentary ramus, just behind the dentary– predentary contact, is missing. On the left side the superficial bones of the skull have largely been eroded away, revealing parts of the palate and braincase; the only trace of the left lower jaw is the anterior tip of the dentary and adjacent predentary ( Fig. 2 , Appendix 3B).

Provenance: 1890 m above sea-level on the mountain behind Tyindini trading store, Herschel District, Eastern Cape Province, Republic of South Africa (30°32′S, 27°32′E; Kitching & Raath, 1984: table 1). Discovered by A. W. C. during the 1961/1962 joint British/South African expedition to the Upper Triassic outcrops in South Africa and Basutoland (= Lesotho). Stratigraphical occurrence: Clarens Formation (formerly ‘Cave Sandstone’, Stormberg Series): Hettangian-Sinemurian ( Olsen & Galton, 1984), Pliensbachian-Toarcian ( Yates et al., 2004). The most probable age for the Clarens Formation: latest Sinemurian-Pliensbachian ( Jourdan et al., 2005, 2007, 2008).

Referred specimens

SAM-PK-K1332

Articulated skull, lower jaw ( Figs 4–7, 16–18 , 23–27 and Appendices 4–6; see also Santa Luca et al., 1976: fig. 1; Santa Luca, 1980: figs 1, 2; Weishampel & Witmer, 1990: fig. 23.4; Norman et al., 2004c: fig. 18.10A), and postcranial skeleton ( Santa Luca et al., 1976: fig. 1; Santa Luca, 1980: figs 1, 3–22). Preparation of this skull was undertaken by Mrs Ione Rudner at the Iziko South African Museum, Cape Town. A considerable number of minor breaks (probably having their origin in post-mortem deformation, as well as some caused by the mechanical preparation and by later mishandling) have been repaired by adhesive; additionally, a moderate-to-thick layer of adhesive-consolidant has been applied to the surfaces of bones and teeth, which obscures finer anatomical details (consolidant on the occlusal surfaces of the teeth has since been removed by L. B. P.). A detailed photographic record (including stereo-pair images) made at the time of the original preparation for A. W. C. has been archived at the Sedgwick Museum, Cambridge, UK.

The specimen was preserved in red sandstone. The skull (as with the holotype) has suffered lateral crushing and displacement; however, it is more complete and its preservation overall is better than that of the holotype. Unlike the holotype, the skull was not covered in a layer of haematite.

Provenance: At an altitude of about 1770 m on the northern slopes of Kromspruit (alternative spelling Krommespruit) Mountain, Voyizane (= ‘Voisana’; 30°34′S, 27°26′E; Kitching & Raath, 1984: table 1), Herschel District , Eastern Cape Province, South Africa .

Discovered by A. W. C. on the 1966–67 joint South African Museum, Yale University, British Museum (Natural History), University of London expedition to the ‘Red Beds’ of South Africa and southern Lesotho ( Attridge & Charig, 1967; Crompton, 1968).

Stratigraphical occurrence: From the upper part of the Elliot Formation (formerly ‘upper Red Beds’), Stormberg Series; probably of Early Jurassic age (stratigraphically lower than the horizon at which the holotype was found): Hettangian-Sinemurian ( Olsen & Galton, 1984) or Pliensbachian-Toarcian ( Yates et al., 2004). The most probable age for the upper part of the Elliot Formation is upper Sinemurian (R. Irmis pers. comm. 2010).

SAM-PK-K1334

Partial left maxilla containing seven erupted crowns and three replacement crowns, with attached fragments of the jugal and lacrimal bones ( Figs 30–33 ).

Provenance: Site 18a, Voisana, Kromspruit 9 Farm, Herschel District , Eastern Cape Province, South Africa (30°34′S, 27°26′E; Kitching & Raath, 1984). Collected on the 1966–67 expedition of the South African Museum , Yale University, British Museum (Natural History) and University of London. Reports and letters exchanged between A. J. C. and A. W. C. suggest that it was recovered from the same locality (Voyizane/Voisana) in Herschel District that yielded the complete, articulated heterodontosaur skeleton (SAM-PK-K1332) and several other specimens .

Stratigraphical occurrence: Upper Elliot Formation (as above).

SAM-PK-K10487

Partial skull ( Figs 28 , 29 ; see also Butler et al., 2008a: figs 1–3, 4B, 5) of a demonstrably ontogenetically immature specimen.

Provenance: Kromspruit area, Herschel District, Eastern Cape Province, South Africa.

Stratigraphical occurrence: Probably upper Elliot Formation.

Specimens provisionally referred to Heterodontosaurus sp. pending further study

NMQR 1788: Partial skull, undetermined stratigraphical horizon, Tushielaw, Barkly East, Eastern Cape Province, South Africa (L. B. Porro et al., in press).

SAM-PK-K10488: Partial lower jaw with evidence of replacement crowns, and fragments of upper jaw. Upper Elliot Formation, Eastern Cape Province. (L. B. Porro, unpubl. data).

Figures

Figure 1. Heterodontosaurus tucki Crompton & Charig, 1962. SAM-PK-K337 (holotype). A, right lateral view drawn from the perspective in which the skull roof is aligned to the horizontal plane. B, annotated outline drawing of the same (even grey tone represents adhering matrix and/or plaster infill). See also Appendix 3. Abbreviations: An, angular; aof, antorbital fossa; apf, anterior premaxillary foramen; Ar, articular; D, dentary; emf, external mandibular fenestra; itf, infratemporal fenestra; J, jugal; jb, jugal boss; jp, ventrolateral jugal process; Mx, maxilla; mxr, lateral maxillary ridge; N, nasal; nf, narial fossa; nsul, internasal sulcus; paf, posterior antorbital fenestra; Pd, predentary; Pf, prefrontal; Pmx, premaxilla; Po, postorbital; por, postorbital ridge; Ppb, palpebral; Q, quadrate; qf, quadrate (paraquadratic) foramen; Qj, quadratojugal; Sa, surangular; sc, sagittal crest of the parietal; Sq, squamosal; sqr, squamosal ridge.

Figure 2. Heterodontosaurus tucki Crompton & Charig, 1962. SAM-PK-K337 (holotype). A, left lateral view drawn from slightly ventrolateral perspective. B, annotated outline drawing of the same (even grey tone represents matrix and/or plaster infill). See also Appendix 3. Abbreviations: af, internal mandibular adductor fossa; An, angular; Ar, articular; aof, antorbital fossa; Bo, basioccipital; Bs, basisphenoid; bsf, basisphenoid flange; bst, basisphenoid tuber; Co, coronoid; D, dentary; fm, foramen magnum (internal wall of right side) imf, internal mandibular fenestra; lbpt, left basipterygoid process; Ls, laterosphenoid; Mx, maxilla; N, nasal; nf, narial fossa; Os, orbitosphenoid; ovc, occipital vascular canal; Pa, parietal; Part, prearticular; Pd, predentary; pocc, paroccipital; Pro/Op, proötic-opisthotic; Prs –?presphenoid; Psp, parasphenoid; Pt, pterygoid (right); ptf, pterygoid flange; ptmr, pterygoid medial ridge; Q, quadrate; qf, quadrate (paraquadratic) foramen; Qj, quadratojugal; qpt, quadrate wing of the pterygoid; rbpta, right basipterygoid articular facet; S, supraoccipital; Sp, splenial; Sq, squamosal (broken fragment); V, trigeminal fossa (cranial nerve 5).

Figure 3. Heterodontosaurus tucki Crompton & Charig, 1962. SAM-PK-K337 (holotype). A, dorsal view. B, ventral view. Even grey tone represents matrix and/or plaster infill. Abbreviations: Ar, articular; Bo, basioccipital; bpt, ‘footplate’ of basipterygoid; Bs, basisphenoid; bsf, basisphenoid flanges; bst, basisphenoid tubers; D, dentary; imf, internal mandibular foramen; jb, jugal boss; Mx, maxilla; N, nasal; nsul, internasal sulcus; Pa, parietal; Pd, predentary; Pf, prefrontal; Pmx, premaxilla; Po, postorbital; Ppb, palpebral; Pt, pterygoid; pft, pterygoid flange; pocc, paroccipital; Q, quadrate; Qj, quadratojugal; Sa, surangular; Sp, splenial; Sq, squamosal.

Figure 7. Heterodontosaurus tucki Crompton & Charig, 1962. Occipital views. A, SAM-PK-K337 (holotype). B, SAM- PK-K1332 (referred specimen). Sheared surfaces that cut obliquely across the posterior left portion of the holotype skull – SAM-PK-K337 – are indicated by even grey tone, as is the foramen magnum, which is partially plugged with matrix. Abbreviations: Bo, basioccipital (condyle visible in B); bpt, basipterygoid process; bst, basisphenoid tuber; Ex, exoccipital; jb, jugal boss; lbpt, left basipterygoid process; nc, nuchal crest; Op, wing of opisthotic (A, left opisthotic sheared off at its base against the remainder of the braincase); ovc, occipital vascular canal; Pa, parietal;?pn, possible pneumatic opening in quadrate; Po, postorbital; pof, post-temporal fenestra; pocc, paroccipital process; ptf, pterygoid flange; Q, quadrate; qf, quadrate (paraquadratic) foramen; Qj, quadratojugal; rPt, right pterygoid; S, supraoccipital; Sq, squamosal.

Figure 16. Heterodontosaurus tucki Crompton & Charig, 1962. SAM-PK-K1332 (referred specimen). Left lower jaw in (A) lateral view (B) annotated outline drawing (see Appendix 6A). For full list of abbreviations see end of paper.

Figure 17. Heterodontosaurus tucki Crompton & Charig, 1962. SAM-PK-K1332 (referred specimen). Left lower jaw in (A) medial view (B) annotated outline drawing, see also Appendix 6B. For full list of abbreviations see end of paper.

Figure 18. Heterodontosaurus tucki Crompton & Charig, 1962. SAM-PK-K1332 (referred specimen). Right lower jaw (anterior portion only) in (A) lateral and (B) medial views, see also Appendix 5C,D. For full list of abbreviations see end of paper.

Figure 20. Heterodontosaurus tucki Crompton & Charig, 1962. SAM-PK-K337 (holotype). Anterior dentition preserved on the right side of the skull (based on a photograph taken during early preparation – prior to the complete removal of matrix from the lateral surface of the dentary caniniform. Note, the first premaxillary caniniform is not preserved on this side of the skull; the first premaxillary incisiform is only preserved on the left side of the skull. Inset diagram: sketch of the profiles of the left premaxillary dentition of SAM-PK-K337 (prepared by A. W. C./A. J. C.). For full list of abbreviations see end of paper.

Figure 21. Heterodontosaurus tucki Crompton & Charig, 1962. SAM-PK-K337 (holotype). A, the right maxillary dentition (M.2–M.12) in lateral view (see Fig. 22 for details of M.1–M.4); B, occlusal plan view of crowns M.8–M.11 to demonstrate the minor imbrication between adjacent crowns.

Figure 22. Heterodontosaurus tucki Crompton & Charig, 1962. SAM-PK-K337 (holotype). Anterior maxillary teeth (M.1–M.4) of the right maxilla, as preserved. The presence of M.1 is inferred from the ghost-like impression preserved in the matrix. For full list of abbreviations see end of paper.

Figure 23. Heterodontosaurus tucki Crompton & Charig, 1962. SAM-PK-K1332 (referred specimen). A, photograph of the left maxillary dentition as preserved in lateral view. B, photograph of the right maxillary dentition in lateral view.

Figure 24. Heterodontosaurus tucki Crompton & Charig, 1962. SAM-PK-K1332 (referred specimen). The upper dentition in: A, occlusal view based on original specimen as preserved; B, partial reconstruction of the lateral view of the maxillary dentition alone, with the isolated M.1 added in position; C, reconstruction of the medial view of M.1– M.3. For full list of abbreviations see end of paper.

Figure 25. Heterodontosaurus tucki Crompton & Charig, 1962. SAM-PK-K1332 (referred specimen). Dentary dentition. A, right dentition in lateral view (top) and medial view (bottom). B, left dentition in lateral view (top) and medial view (bottom).

Figure 26. Heterodontosaurus tucki Crompton & Charig, 1962. SAM-PK-K1332 (referred specimen). Line drawings of the right dental battery (De.2–De.11). A, lateral view; B, medial view; C, occlusal view of De.2–De.4.

Figure 27. Heterodontosaurus tucki Crompton & Charig, 1962. SAM-PK-K1332 (referred specimen). Line drawings based on scanning electron micrograph images of right dentary teeth: De.7–De.9. A, worn surfaces of the teeth in oblique dorsolateral aspect showing the lipped lower edges of the wear facets and the minor imbrication between crowns (the overlap pattern is the reverse of that seen in the maxillary dentition – see Fig. 21B). B, close-up of De.9 to show details of the wear facet and the lower ‘lip’ at the base of the wear facet. For full list of abbreviations see end of paper.

Figure 28. Heterodontosaurus tucki. SAM-PK-K10487 (referred specimen). Partial skull of a juvenile heterodontosaur as preserved in: A, left lateral aspect; B, right lateral aspect. For full list of abbreviations see end of paper. (See also Butler et al., 2008b.)

Figure 29. Heterodontosaurus tucki. SAM-PK-K10487 (referred specimen). Partial skull of a juvenile heterodontosaur as preserved in: A, oblique left lateral aspect to show details of the maxillary dentition; B, ventral view. For full list of abbreviations see end of paper.

Figure 30. Heterodontosaurus tucki. SAM-PK-K1334 (referred specimen). Posterior portion of the left maxilla. Segmented image prepared from computed tomography scans of the original. A, lateral aspect. Bones displayed as grey, erupted crowns shown in yellow. B, semi-transparent image of the maxilla to show the extent and arrangement of individual teeth in the maxilla. Red areas indicate the presence of replacement crowns embedded within the body of the maxilla. For full list of abbreviations see end of paper.

Figure 31. Heterodontosaurus tucki. SAM-PK-K1334 (referred specimen). Posterior portion of the left maxilla. Segmented image prepared from computed tomography scans of the original. A, medial aspect. Bones in grey, erupted crowns shown in yellow, replacement crowns shown in red. B, semi-transparent image to show the position and extent of erupted and replacement teeth within the maxilla. For full list of abbreviations see end of paper.

Figure 32. Heterodontosaurus tucki. SAM-PK-K1334 (referred specimen). Medial view of the alveolar wall and adjacent bone and crowns. A, line drawing of the dentition showing the details of the groove (gr) that connects ‘special foramina’ (‘pit’) above the alveolar margin, the apical tip of replacement crown ‘M.5’ and the revealed crown of ‘M.2’; the anterior half of this area is quite badly eroded so bone surface details are unclear. B, magnified detail of the replacement crown above ‘M.2’. For full list of abbreviations see end of paper.

Figure 33. Heterodontosaurus tucki. SAM-PK-K1334 (referred specimen). Isolated teeth, extracted from the original computed tomography image. A, medial/lingual aspect to show the long hollow roots to the fully erupted crowns and the position of the replacement crowns on the medial side of the roots of functional teeth. B, oblique view of the same to show the curvature of the roots and crowns, the angulation of the wear facets and the relative positions of the replacement crowns. For full list of abbreviations see end of paper.