Discovery of early, 'croc-like' reptile sheds new light on evolution of dinosaurs

A new species of ancient reptile has been described by scientists at the University of Birmingham, filling a critical gap in the fossil record of dinosaur cousins and suggesting that some features thought to characterise dinosaurs evolved much earlier than previously thought.

A life reconstruction of the new species Teleocrater rhadinus, a close relative of dinosaurs, feasting on an ancient mammal 
relative, Cynognathus, in the Triassic of Tanzania. The large dicynodont Dolichuranus is seen in the background 
[Credit: Natural History Museum, London, artwork by Mark Witton]

Described in a paper published in Nature, the carnivorous reptile, Teleocrater rhadinus, was approximately 7-10 feet in length, had a long neck and tail, and walked on four crocodile-like legs.

It roamed the Earth during the Triassic Period more than 245 million years ago – pre-dating the first true dinosaurs by around ten million years – and 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 (eventually leading to today’s alligators and crocodiles). Teleocrater and its kin are the earliest known members of the bird branch of the archosaurs.

Scientists excavate the remains of Teleocrater rhadinus and other animals in southern Tanzania in 2015. Christian 
Sidor (left), Sterling Nesbitt (middle left), Kenneth Angielczyk (upper right), Michelle Stocker (lower right)
[Credit: Roger Smith]

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

‘Teleocrater fundamentally challenges our models of what the close relatives of dinosaurs would have looked like,’ says Professor Richard Butler from the University of Birmingham.

A simplified depiction of phylogenetic relationships within Archosauria, including Teleocrater rhadinus 
[Credit: Credit: Dr Richard Butler, University of Birmingham]

‘Dinosaurs were amazingly successful animals. It’s natural to want to know where they came from, and how they became so dominant. Teleocrater is hugely exciting because it blows holes in many of our classic ideas of dinosaur origins.’

All the specimens used to describe Teleocrater were collected from a rock unit called the Manda Beds, in the Ruhuhu Basin of southern Tanzania, Africa. Teleocrater fossils were first discovered in the region in 1933 by palaeontologist F. Rex Parrington, and subsequently studied by Alan J. Charig, former Curator of Fossil Reptiles, Amphibians and Birds at the Natural History Museum, in the 1950s.

However, due to a lack of crucial bones, such as the ankle bones, Charig could not determine whether Teleocrater was more closely related to crocodylians or to dinosaurs. Unfortunately, he died before he was able to complete his studies.

Re-examination of Charig’s specimens by Butler and colleagues, combined with the discovery of additional fossils by a US-led team in Tanzania in 2015, has finally allowed the surprising relationship between Teleocrater and its dinosaur cousins to be revealed.

‘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,’ says Professor Butler.

Life model of the new species Teleocrater rhadinus, a close relative of dinosaurs, preying upona juvenile cynodont, 
a distant relative of mammals [Credit: Museo Argentino de Ciencias Naturales]

Professor Paul Barrett from the Natural History Museum, one of the other main authors of the work on Teleocrater, 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.

‘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.’

Source: University of Birmingham [April 12, 2017]