The Cavern Dinosaur

Heterodontosaurus was one of the smallest dinosaurs, about half man-size. It often walked on its hind legs, and its three-toed footprints can be found in the Cave Sandstone surrounding The Cavern. “Heterodont-“ means having teeth of more than one design – unusual in anything other than a mammal. Some individuals, presumably males, had pointed “canines”, probably used to fight other males. All the cheek teeth formed a flat grinding battery suitable for chewing plants.

The way in which the flat-topped teeth were perfectly aligned suggests that they slid back and forward rather than up and down when chewing, so were evenly worn down. But some jaws have been found where brand-new unworn teeth protruded above the main battery. The animal would not have been able to feed with the teeth like this. All dinosaurs constantly replaced old teeth from below; no problem with conventional chewing, where teeth in all stages were found in the same mouth. So Heterodontosaurus having high, unworn teeth can be best explained by a season in which it did not feed at all, although tooth replacement was continuous. Very likely it aestivated – the summer equivalent of hibernation. It literally dozed off in a safe, shady corner during the long hot dry summer. North African snails do this today.

Animals that aestivate do all their feeding in the cooler winter rainy season when plants grow. This life-style is linked to a near-desert climate. Although The Cavern today is temperate and green, this was not the case 200 million years ago. The climate then was very similar to that of the present-day Saharan fringes. We know this because the sand making up the sandstone was a wind-blown dry land deposit. Its grains are rough-edged, whereas marine sand grains are rounded.

The continuity of tooth growth also suggests that Heterodontosaurus was at least partially warm-blooded. Despite a generally lizard-like appearance – it had a long tail – it would have much more the ecological equivalent of a duiker than of any modern reptile.

David Johnson

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