Heterodontosauridae
Basal ornithischian dinosaurs with distinctive tusks and chewing teeth.
Heterodontosauridae is a family of ornithischian dinosaurs that were likely among the most basal members of the group. Their phylogenetic placement is uncertain but they are most commonly found outside of the group Genasauria. Although their fossils are relatively rare and their group small in numbers, they have been found on all continents except Australia and Antarctica, with a range spanning the Early Jurassic to the Early Cretaceous. Heterodontosaurids were fox-sized dinosaurs less than 2 metres in length, including a long tail, and are known mainly for their characteristic teeth, including enlarged canine-like tusks and cheek teeth adapted for chewing, analogous to those of Cretaceous hadrosaurids. Their diet was herbivorous or possibly omnivorous.
- time_range
- Early Jurassic to Early Cretaceous
- size
- Less than 2 metres (6.6 feet) in length
- diet
- Herbivorous or possibly omnivorous
- distinctive_feature
- Heterodont dentition with canine-like tusks and grinding cheek teeth
- fossil_distribution
- All continents except Australia and Antarctica
Lore & Background
Among heterodontosaurids, only Heterodontosaurus itself is known from a complete skeleton. Fragmentary skeletal remains of Abrictosaurus are known but have not been fully described, while most other heterodontosaurids are known only from jaw fragments and teeth. Consequently, most heterodontosaurid defining features have been described from the teeth and jaw bones. Heterodontosaurus measured just over 1 meter in length, while the fragmentary remains of Lycorhinus may indicate a larger individual. Tianyulong from China appears to preserve filamentous integument which has been interpreted to be a variant of the proto-feathers found in some theropods, including a crest along its tail, suggesting that both ornithischians and saurischians were endothermic.
Reader's Guide
Heterodontosauridae holds significance as one of the most basal ornithischian families, providing key insights into early dinosaur evolution and the origins of complex chewing mechanisms. Their heterodont dentition—with small conical teeth, enlarged caniniform tusks, and chisel-shaped cheek teeth—represents an early experiment in oral food processing that later convergently evolved in hadrosaurs and ceratopsians. The presence of filamentous integument in Tianyulong suggests that endothermy may have been widespread among dinosaurs. Their fossils, though rare, span multiple continents and a long temporal range, indicating a successful but poorly understood lineage. The unique spheroidal jaw joint and slow tooth replacement rate highlight a specialized feeding strategy. Their phylogenetic position remains uncertain, but they are most commonly placed outside Genasauria, making them critical for understanding the early diversification of ornithischians.
Did You Know?
- Heterodontosaurids have been found on all continents except Australia and Antarctica.
- Only Heterodontosaurus itself is known from a complete skeleton; most other species are known only from jaw fragments and teeth.
- Tianyulong preserves filamentous integument interpreted as a variant of proto-feathers, suggesting endothermy in ornithischians.
- The lower jaws of heterodontosaurids could rotate outwards as the mouth closed, grinding cheek teeth against each other.
More in Ancient Reptiles 25-40
Elsewhere in the Ancient Reptiles universe
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record