‘Missing link’ between dinosaurs and crocodile ancestors discovered

13 Apr 2017

Life model of the species Teleocrater rhadinus, a close relative of dinosaurs, preying upon a juvenile cynodont, a distant relative of mammals. Image: Museo Argentino de Ciencias Naturales

Weighing in at up to 65lb, and stretching as far as 10ft from nose to tail, a monitor-lizard-like discovery offers palaeontologists a whole new look at dinosaur evolution.

“Surprisingly, early dinosaur relatives were pretty profoundly not dinosaur-like.”

That’s according to Ken Angielczyk, The Field Museum’s associate curator of fossil mammals, and co-author of a new paper detailing a teleocrater.

Divide, conquer

In a broad sense, it was believed that certain carnivorous dinosaurs evolved into creatures still alive today – birds, crocodiles, lizards etc – due to a gradual reduction in size, moving in a bipedal manner around the planet until they found a more appealing option.

However, the teleocrater could change that.

On all fours, with hips about two feet high, the species resembled a monitor lizard, with crocodilian features such as amenable ankle joints. It also enjoyed features that distinguish it from modern lizards, with bird-like jaw muscle attachments at the back of its skull.

This is odd.

All dinosaurs are part of a group called archosaurs, consisting of dinosaurs, birds, pterosaurs (flying reptiles) and crocodilians.

University of Waterloo researchers found that around 250m years ago, a major division occurred, whereby a bird-like group evolved into dinosaurs, birds, and pterosaurs; and a crocodile-like group saw the ultimate evolution of today’s alligators and crocodiles, as well as countless (now extinct) species.

The newly named species Teleocrater. Image: Museo Argentino de Ciencias Naturales

The newly named species Teleocrater. Image: Museo Argentino de Ciencias Naturales

A cousin, of sorts

The newly described Teleocrater rhadinus is the earliest member ever discovered of the bird-like side of the family but is more of a cousin than a direct ancestor, according to the report, which was published in Nature.

Interestingly, the fact that it also shares plenty of crocodilian features means a reappraisal of how dinosaur features evolved.

“We used to think that many of the distinctive features of bird-line archosaurs evolved very quickly after they diverged from the crocodile line, because early bird-line archosaurs like Marasuchus, Dromoeron, and Lagerpeton were small and very dinosaur-like,” said Angielczyk.

“However, teleocrater shows us that bird-line archosaurs initially inherited many crocodile-like features from the common ancestor of all archosaurs, and that the ‘typical’ bird-like features evolved in a step-wise fashion over a longer period of time.

“Scientists generally don’t love the term ‘missing link’, but that’s kind of what teleocrater is: a missing link between dinosaurs and the common ancestor they share with crocodiles.”

The discovery, while new in parts, actually dates back decades. It was first identified by a British palaeontologist named Alan Charig in the 1950s, using fossils that were collected in the 1930s. However, contemporary understanding finally allows the installation of teleocrater into a specific part of the evolutionary chain.

Park life

Earlier this year, dinosaur footprints preserved in 140m-year-old Australian rocks were described by palaeontologists as the country’s equivalent to Jurassic Park.

Among these track variations, five different types of predators, six long-necked herbivorous sauropods, four two-legged herbivorous ornithopods and six armoured dinosaurs were confirmed.

Steve Salisbury, lead author of the study published in the Journal of Vertebrate Paleontology, said the diversity of the tracks made the area the “Cretaceous equivalent of the Serengeti”.

Finders keepers

However, one of the most significant dinosaur discoveries ever came by accident only a few weeks earlier, as a researcher from China was strolling through an amber market in Myanmar last year.

Spotting a chunk with some feathers inside, Lida Xing from the China University of Geosciences in Beijing immediately knew something was up.

The seller thought it was just amber, the size of a dried apricot, with perhaps some plant fragments trapped inside. Xing believed otherwise, secured the deal without letting on (which would have pushed up the price) and began taking a closer look.

A small coelurosaur approaching a resin-coated branch on the forest floor. Image: Chung-tat Cheung

A small coelurosaur approaching a resin-coated branch on the forest floor. Image: Chung-tat Cheung

Realising that the trapped elements were feathered remains from a vertebrate, Xing sent it off for further tests. The results were remarkable – Xing was right.

Dating from around 99m years ago, the remains are from a non-avialan theropod that existed during the Cretaceous era, which Ryan McKellar, co-author of the paper published in Current Biology, called a “once-in-a-lifetime find”.

Gordon Hunt was a journalist with Silicon Republic