Heterodontosauridae
Heterodontosauridae is a family of small, early-diverging ornithischian dinosaurs, most of them fox-sized and less than two meters long including a long tail. Their fossils are relatively rare, but the group achieved a near-worldwide distribution, turning up on every continent except Australia and Antarctica and ranging from the Early Jurassic into the Early Cretaceous. The family is best known for its strongly heterodont dentition: enlarged, canine-like tusks in both the upper and lower jaws, set off by a gap called a diastema, together with chisel-shaped cheek teeth whose overlapping crowns formed a continuous grinding surface convergent with the dental batteries of later hadrosaurs and ceratopsians. Its members include the South African Abrictosaurus, Lycorhinus, and Heterodontosaurus, along with later and more far-flung forms such as Echinodon, Fruitadens, and the filament-bearing Tianyulong, with the more derived, largely southern-hemisphere genera grouped in the subfamily Heterodontosaurinae. Their diet was herbivorous or possibly omnivorous, and their long, slender hindlimbs suggest they were fast, primarily bipedal runners.
Under dispute
Heterodontosauridae is placed as an early-diverging clade near the base of Ornithischia, outside Genasauria, following the prevailing view (Butler and colleagues, 2008; Boyd, 2015); Sereno's (2012) reanalysis of the Butler and colleagues matrix also leaves heterodontosaurids in a polytomy at the base of Ornithischia. Dieudonné and colleagues (2020) instead recover heterodontosaurids as a paraphyletic grade of basal Marginocephalia within Pachycephalosauria.
Diagnosis
- Enlarged caniniform teeth in both the premaxilla and the dentary
- Postcaniniform diastema separating the caniniform from the cheek-tooth row
- Cheek-tooth crowns with a swollen base and well-developed apical wear facets
- Reduced or episodic tooth replacement rather than continuous replacement
- Small body size with elongate, gracile, cursorial hindlimbs
Clades within Heterodontosauridae
- Heterodontosaurinae 5 genera
Genera placed directly in Heterodontosauridae
- Echinodon Berriasian (143.1–137.1 Ma)United Kingdom
- Fruitadens Kimmeridgian (154.8–149.2 Ma)United States
- Geranosaurus Nomen dubium Sinemurian–Pliensbachian (199.5–184.2 Ma)South Africaincertae sedisunder dispute
- Tianyulong Callovian–Oxfordian (165.3–154.8 Ma)China
References
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Kuhn, O. (1966). Die Reptilien [The reptiles]. Die Reptilien. Verlag Oeben.
Origin of the family-group name Heterodontosauridae.
kuhn1966a -
Sereno, P. C. (2012). Taxonomy, morphology, masticatory function and phylogeny of heterodontosaurid dinosaurs. ZooKeys 226: 1-225. Pensoft Publishers. doi:10.3897/zookeys.226.2840
Monographic revision and phylogenetic definition of Heterodontosauridae.
sereno2012a -
Butler, R. J.; Upchurch, P.; Norman, D. B. (2008). The phylogeny of the ornithischian dinosaurs. Journal of Systematic Palaeontology 6(1): 1-40. doi:10.1017/S1477201907002271
Ornithischian phylogenetic analysis recovering Heterodontosauridae outside Genasauria, close to the base of Ornithischia.
butler2008b -
Dieudonné, P. E.; Cruzado-Caballero, P.; Godefroit, P.; Tortosa, T. (2020). A new phylogeny of cerapodan dinosaurs. Historical Biology 33(10): 2335-2355. doi:10.1080/08912963.2020.1793979
Recovered heterodontosaurids as a paraphyletic grade of basal Marginocephalia within Pachycephalosauria
dieudonné2020a -
Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Ornithischians. Princeton University Press.
Places Heterodontosauridae as the first-diverging branch of Ornithischia, noting an alternative placement at the base of Pachycephalosauria.
jones2026a -
Boyd, C. A. (2015). The systematic relationships and biogeographic history of ornithischian dinosaurs. PeerJ 3: e1523. PeerJ. doi:10.7717/peerj.1523
Recovered Heterodontosauridae as an early-diverging ornithischian clade.
boyd2015a