Teleocrater rhadinus: Early Dinosaur Relative Had Surprising Crocodile-Like Look

Paleontologists have long wondered what the earliest dinosaur relatives looked like. Most assumed that they would look like dwarf dinosaurs and walk on two legs. The discovery of Teleocrater rhadinus, however, has overturned popular predictions.

A reconstruction of Teleocrater rhadinus feasting on a relative of early mammals. Image credit: Mark Witton / Natural History Museum, London.

Teleocrater rhadinus lived during the Middle Triassic epoch more than 245 million years ago — pre-dating the first true dinosaurs by 10 million years.

This ancient creature appears in the fossil record just after a large group of reptiles, known as archosaurs, split into a bird branch (leading to dinosaurs and eventually birds) and a crocodile branch (leading to alligators and crocodiles).

Teleocrater rhadinus had a long neck and tail and was 7- 10 feet (2.1-3 m) in length. Rather than walking on two legs, it walked on four crocodilian-like legs.

“The discovery of such an important new species is a once-in-a-lifetime experience,” said Dr. Sterling Nesbitt, a researcher at Virginia Tech and the lead author of a report published this week on Teleocrater rhadinus in the journal Nature.

The discovery overturns widely-held preconceptions about the morphology of early dinosaur relatives, with many paleontologists anticipating that such creatures would be smaller, bipedal and more ‘dinosaur-like.’

“Teleocrater rhadinus fundamentally challenges our models of what the close relatives of dinosaurs would have looked like,” said Richard Butler, a professor of paleobiology at the University of Birmingham, UK, and co-author on the paper.

The late paleontologist F. Rex Parrington first discovered Teleocrater rhadinus fossils in the Ruhuhu Basin of southern Tanzania in 1933. The late Alan J. Charig, then-curator of fossil reptiles, amphibians and birds at the Natural History Museum of London, UK, was the first to study those original specimens in the 1950s.

However, due to a lack of crucial bones, such as the ankle bones, Charig could not determine whether Teleocrater rhadinus was more closely related to crocodylians or to dinosaurs. The new specimens, found in 2015, clear up those questions.

The intact ankle bones and other parts of the skeleton helped Dr. Nesbitt, Prof. Butler and co-authors determine that Teleocrater rhadinus is one of the oldest members of the archosaur tree and had a crocodilian look.

“It’s astonishing to think that it’s taken more than 80 years for the true scientific importance of these fossils to be understood and published,” Prof. Butler said.

“My colleague Alan Charig would have been thrilled to see one of ‘his’ animals finally being named and occupying such an interesting position in the Tree of Life,” said co-author Prof. Paul Barrett, from the Natural History Museum of London.

“Our discovery shows the value of maintaining and re-assessing historical collections: many new discoveries, like this one, can be made by looking through museum collections with fresh eyes.”

The team’s next steps are to return to Tanzania to find missing parts of Teleocrater rhadinus’ skeleton.

“It’s so exciting to solve puzzles like Teleocrater rhadinus, where we can finally tease apart tricky mixed assemblages of fossils and shed light on broader anatomical and biogeographic trends in an iconic group of animals,” said co-author Dr. Michelle Stocker, a paleobiologist at Virginia Tech.

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Sterling J. Nesbitt et al. The earliest bird-line archosaurs and the assembly of the dinosaur body plan. Nature, published online April 12, 2017; doi: 10.1038/nature22037