Heterodontosauridae Kuhn, 1966

Sereno, Paul C., 2012, Taxonomy, morphology, masticatory function and phylogeny of heterodontosaurid dinosaurs, ZooKeys 226, pp. 1-225 : 12-13

Heterodontosauridae Kuhn, 1966

Emended diagnosis.

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.

Phylogenetic definition.

The most inclusive clade containing Heterodontosaurus tucki Crompton and Charig 1962 but not Parasaurolophus walkeri Parks 1922, Pachycephalosaurus wyomingensis ( Gilmore 1931), Triceratops horridus Marsh 1889, Ankylosaurus magniventris Brown 1908.

This stem-based phylogenetic definition ( Sereno 2005b) includes, but does not reach beyond, all currently known heterodontosaurids under all proposed phylogenetic interpretations of the position of heterodontosaurids within Ornithischia (e.g., Sereno 1999; Butler et al. 2008). The first and only previous phylogenetic definition proposed for Heterodontosauridae ( Sereno 1998: 61) is similar but lacks the negative specifiers of the present definition that stabilize its taxonomic content under alternative phylogenetic relationships.

Temporal and geographic range.

Late Triassic (Norian) to Early Cretaceous (Barremian-Aptian), ca. 216-125 Ma ( Gradstein and Ogg 2009; Martinez et al. 2011); global distribution includes northern localities (northern China, western North America, Europe) and southern localities (southern South America, southern Africa) (Fig. 1). The record of heterodontosaurids from the Late Triassic currently depends upon the interpretation of the poorly known Pisanosaurus mertii ( Bonaparte 1976; Sereno 1991) and other fragmentary remains from Upper Triassic rocks elsewhere in Argentina ( Báez and Marsicano 2001).

Comments.

Kuhn (1966) is identified as the author of the taxon Heterodontosauridae , although Romer (1966) independently proposed the same taxon in the same year (synchronous publication noted by Kuhn 1967: 77, 122). In the literature, some cite Romer as the author of the taxon (e.g., Smith 1997; Sereno 1998; Sereno 2005b), some Kuhn (e.g., Norman et al. 2004, 2011), and some Kuhn and Romer with one author in parentheses (e.g., Steel 1969). Establishing priority by publication date in this case is no longer possible, and, unlike Romer, Kuhn also briefly diagnosed the family-level taxon. Here Kuhn is recognized as the author of Heterodontosauridae (P. Galton, pers. comm.).

Many of the cranial and postcranial apomorphies listed in the emended diagnosis were known previously only in Heterodontosaurus tucki but now are known in at least one other heterodontosaurid. When coded into a phylogenetic analysis, some of these features might be repositioned at nodes within Heterodontosauridae (under delayed transformation), given the large amount of missing data in known taxa. The list, nonetheless, attempts to capture as many skeletal modifications that are shared by Heterodontosaurus tucki and at least one other basal heterodontosaurid and may characterize the group. The features listed are discussed in more detail below (under Heterodontosaurid monophyly) and in Appendix I.