Dicynodonts were a group of plant eating stem-mammals (often called mammal-like reptiles), which with their toothless beaks and tusks looked a bit like a mix between a hippo and a tortoise, without the shell.
These animals were the most diverse and abundant herbivores in the second half of the Permian and during the Triassic periods, around 270 and 201 million years ago, after which they went extinct worldwide. Or at least so we thought…
In early 1914, a pastoralist in northern Queensland in Australia picked up some pieces of fossil bone in a gully on his property, which he donated to the Queensland Museum.
One of the fragments in particular, which preserved a large curved tooth, showed some resemblance to dicynodonts found in South Africa. However, in the area where the fossil was found, there are no Permian or Triassic rocks, only Cretaceous, which are nearly 100 million years younger.
It’s similarity to dicynodonts and it likely originating from Cretaceous rocks, caused researchers in the early 2000’s to conclude that dicynodonts had found a refuge from the end-Triassic extinction, in Australia!
This was not a far-fetched idea, as a group of amphibians called temnospondyls had already been shown to have done exactly that. While they had gone extinct elsewhere at the end of the Triassic, they had survived for millions of years later in Australia. The only problem was that the Cretaceous dicynodont material was very fragmented, causing contention amongst palaeontologists as to its real biological origin.
A study led by Senior Curator of Palaeontology for the Museum of Tropical Queensland and James Cook University Dr Espen Knutsen, published in Gondwana Research, looked closer at this possibly highly significant material using both traditional and state-of-the-art analytical techniques.
The results show that rather than belonging to a Cretaceous dicynodont, the fossils are that of a much more recent diprotodontid, a wombat-like animal the size of a hippo, which lived in Australia around 2.5 million years ago.
By searching through 100-year-old museum archives, the study found that another fossil was found by the same pastoralist, only months prior in the same gully, meters away from the dicynodont fragments. This fossil, however, was from the left upper jaw of a diprotodontid.
Letters from the pastoralist to Queensland Museum, states that he believed the fossils all belonged to the same individual. To test this, the researchers analysed the trace element concentrations in the fossilised bone. By comparing the elemental signatures of the bones, the researchers showed unequivocally that the fossils came from the same rock unit, and likely the same individual.
What more, after CT scanning the dicynodont material at the Australian Synchrotron, it became clear that its anatomy did not match that of dicynodonts, but rather that of diprotodontids.
The give-away came in the form of the distribution of enamel on the large tooth, which only covered the front. This is what is normally seen in the front teeth of diprotodontids and other mammals with so-called ever-growing incisors.
Another interesting find was a pit in the bone just in front of the large incisor, the result of an abscess. As the fossil remains suggests the animal was a young individual, it is likely this infection led to an agonising early death.
Dr Espen Knusten is the Senior Curator, Palaeontology at Museum of Tropical Queensland
