Dinosaurs & Reptiles

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Dicynodonts are a kind of mammal-like reptile, part of a group called therapsids. This ancient hippo-like reptile, extinct elsewhere, existed in Australia for another 110 million years—alongside the dinosaurs that wiped them out in other places, palaeontologists have found.

This animal should not be living alongside our Cretaceous dinosaurs. But in 2003, scientists took a closer look at pieces of a fossil skull that had been stored in the Queensland Museum for nearly ninety years. It had been collected from rocks near Hughenden in Queensland dated at 105 million years old. The six fragments of the left side of a skull were identified as dicynodont. The skull fragments show clear signs of the characteristic tusks and the unusual beak. Dinosaurs became extinct 65 million years ago, which is less than the 105 million years between the time when dicynodonts were believed to have disappeared and the dating of this new Australian specimen.

They were mostly about the size of a sheep or a pig, about 1m high. It had front legs that sprawled sideways like a lizard’s, but had back legs that were straight and looked more like the legs of a mammal. They had barrel-shaped bodies and large heads with two small, downward-pointing tusks and a blunt beak like a tortoise. We don’t know if they had fur, but their fossils have a single hole in the side of the skull behind the eye socket that is typical of mammals. Also the way that their back legs are located directly beneath their body instead of splaying out sideways is also more like a mammal than a reptile. The name dicynodont means ‘two dog teeth’ and was given to them because their tusks are like canine teeth, or dog teeth. Some species of dicynodont have obvious differences between the males and females (the males have tusks and the females don’t), which again is more like mammals than reptiles. However, most of the skeleton of a dicynodont is more like a reptile’s than a mammal’s.

Dicynodonts were plant eaters. They ate the coarse vegetation of the time (there was no grass) by tearing it off with their beaks and grinding it between their jaws that could slide backwards and forwards. It probably lived near rivers and lakes, grazing vegetation on the banks during the day and going into the water after plants that grew half submerged. Some researchers have suggested that the tusks might have been used for digging, but it’s most likely that they were used for fighting and display. A study of hundreds of fossils of the type of dicynodont called Diictodon has concluded that the best explanation for the tusks is that they were used by males to tussle with each other to win a mate. About 50% of the Diictodon fossils had no tusks and were probably females. This means the tusks can’t have been used to dig up food, or the females would have starved.

The last of the dicynodonts may well have survived in Australia, but very few dicynodont fossils are found here. In many parts of the world, dicynodont fossils are common. But it wasn’t until 1983 that any dicynodont fossils at all were discovered in Australia and these consist of only a few fragments that aren’t enough to give a name to. This makes it all the more surprising that parts of a skull kept in the Queensland Museum for decades have proved to be from the most recent specimen (by one hundred million years) of dicynodont known anywhere in the world. But the fact that dicynodont fossils are rare doesn’t necessarily mean that the animals were rare at the time. Species of animals in which the males have tusks tend to live together in herds. Males can’t fight and show off if they’re living alone. The best bet is that the new Australian dicynodont lived in small herds.


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