Heterodontosaurus tucki, the “different toothed lizard”

Heterodontosaurus

image by Dr Laura Porro

Dr Laura Porro, postdoctoral researcher, writes:

Dinosaurs capture our imaginations for many reasons: they dominated life on Earth for an extraordinary 130 million years; they evolved body shapes and lifestyles unlike those of any living animal; and some grew to immense sizes, including the largest creatures to ever walk on land.

Not all dinosaurs were enormous, however. Scurrying among the feet of such giants as Diplodocus and Stegosaurus was a cast of tiny dinosaurs. One such group was the heterodontosaurs, which form one aspect of my research.

Little known outside scientific circles, these dinosaurs were found in Africa, Asia, Europe, and North and South America. They lived from the Late Triassic until the Early Cretaceous – more than 80 million years. The largest species, Heterodontosaurus, grew only as big as a fox while the smallest species weighed less than a gray squirrel even when fully grown.

Heterodontosaurs are fascinating animals. Their name means “different toothed lizards”. Heterodontosaurs have a beak and flat, incisor-like teeth for nipping at the front of their mouths; behind these are long, sharp caniniform teeth; at the back of their jaws are large, molar-like teeth. These differently-shaped teeth are common in mammals (including humans) but unusual among lizards, crocodiles and other dinosaurs.

What did heterodontosaurs eat? Close examination of their teeth reveals heavy wear as in modern herbivores. Computer modeling of the Heterodontosaurus skull and jaw muscles have shown that it used complex jaw movements to chew food, again similar to living plant-eaters. However, the knife-like canine teeth and large, sharp claws on the hand of Heterodontosaurus resemble those of meat-eating dinosaurs. Many palaeontologists think that heterodontosaurs were omnivorous, feeding mostly on plants but occasionally eating insects or small vertebrates.

Heterodontosaurs are surprising for reasons other than their teeth. Since the mid-1990s, palaeontologists have discovered numerous dinosaurs with preserved feathers. Nearly all of these have been theropods, meat-eating dinosaurs such as Velociraptor and T. rex. Living birds evolved from theropods, and it was thought that only these carnivores possessed feathers. But the 2010 discovery of Tianyulong, a heterodontosaur from China, stunned scientists: the back, neck and tail of Tianyulong sported rows of long, primitive feathers. Tianyulong is only distantly related to birds, and the presence of feathers in this animal suggests that many plant-eating dinosaurs may have been rather ‘fuzzy’ as well!

image by Li Da Xing

Studying heterodontosaurs can be challenging. The delicate nature of such tiny bones means that specimens are often damaged during fossilization; preparing these fossils using traditional tools (such as drills, brushes or acids) risks further damage. In 2010, my colleagues and I described the heterodontosaur Fruitadens, the smallest adult dinosaur known from North America. I CT-scanned the specimen and then used computer software to ‘digitally’ prepare the specimen, producing detailed 3D models of the bones, teeth and even internal structures like blood vessels!

fruitadens

During our visits to museums, zoos and wild places we are awed by animal giants—looming tyrannosaurs, trumpeting elephants, and icons of conservation such as the tiger, whale and giant panda. These animals are magnificent, indeed, but it is also important to consider some of the tiny wonders of evolution—both extinct animals like Heterodontosaurus worthy of study and living creatures worthy of conservation.

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