Heterodontosaurids and their unusual teeth

Heterodontosaurids were generally small-bodied ornithischian dinosaurs known from fossils spanning parts of the Late Triassic and Jurassic, with debated records extending into the Early Cretaceous. They are best known for jaws in which different teeth could have different shapes. The name refers to this variation, but tooth diversity is not identical in every species, and the group should not be reduced to a single diet or lifestyle.

Heterodontosaurus tucki from Early Jurassic South Africa preserves one of the most informative skulls. Its jaws include small front teeth, larger cheek teeth and enlarged canine-like teeth. These structures are direct anatomical evidence. How the teeth were used, and how much plant or animal material the animal ate, must be inferred from wear, jaw mechanics and comparisons with other animals.

What the skull shows

The holotype skull of Heterodontosaurus, SAM-PK-K337, and a second referred skull, SAM-PK-K1332, have helped researchers describe the proportions of the snout, tooth rows and jaw joints. The skull has a beak-like front region and a more complex cheek-tooth battery than a simple row of uniform teeth. Researchers have also examined the jaw muscles and the way the teeth meet when the mouth closes.

The enlarged canine-like teeth are prominent, but their presence does not by itself prove that the animal hunted large prey. They may have had more than one function, and their role may have differed between individuals or sexes. Proposals involving display or combat are hypotheses that must be tested against the shape, wear and distribution of the teeth and any associated injuries.

Feeding and tooth replacement

Some heterodontosaurids show tooth wear consistent with processing tough food, and their jaw anatomy has prompted comparisons with more specialised plant-eating dinosaurs. Yet wear can vary across a tooth row, and a single specimen records one individual at one point in life. It cannot provide a complete picture of seasonal diet or behaviour.

Heterodontosaurid teeth were set in individual sockets. This differs from the tightly packed tooth batteries of later hadrosaurs, in which numerous teeth formed broad grinding surfaces. It is misleading to call every complex cheek-tooth row a true battery. Tooth replacement patterns and wear provide evidence about how jaws functioned, but soft-tissue cheeks and exact feeding movements are not directly fossilised.

Small body size is common among described members, but size estimates depend on the completeness and growth stage of each specimen. A juvenile can differ in skull proportions from an adult, and poorly preserved bones may distort comparisons. The fossils do not establish that every heterodontosaurid was equally small or that all had the same growth pattern.

A changing position on the family tree

Heterodontosaurids are usually discussed among early ornithischians, but their exact placement has changed as new taxa and anatomical characters have entered phylogenetic analyses. Some trees place the group close to the base of Ornithischia; others nest it within a broader set of early-diverging ornithischians. Differences can arise from incomplete fossils, alternative character definitions and changes in the sampled species.

That uncertainty affects how researchers reconstruct the early evolution of beaks, tooth specialisation and plant processing. It does not make the distinctive skull anatomy uncertain: the teeth and bones are preserved, while their evolutionary sequence and function are reconstructed from comparisons.

Read the species account for Heterodontosaurus alongside this group overview. The genus is unusually informative, but it cannot stand in for all heterodontosaurids.