Paleontologists have got some things not quite right about dinosaurs throughout the years and understandably so – they’re working with dust, sap, and bones from millions of years ago. But now, a once-in-a-lifetime discovery changes the very look and history of early dinosaur relatives.

"Surprisingly, early dinosaur relatives were pretty profoundly not dinosaur-like," said co-author Ken Angielczyk, The Field Museum’s associate curator of fossil mammals, in a statement. In a study published in Nature, the team introduces to the world to Teleocrater rhadinus.

The 6-foot (1.8-meter) carnivore had a long neck and an even longer tail, with a weight that clocked in at 20-65 pounds (9-30 kilograms). It stood 2 feet (0.6 meters) at the hip and had quite the swagger – its ankle joints could rotate from side to side as well as flex up and down. 

This might sound like a typical dinosaur, but it’s actually not the gait of dinosaurs or birds as we know it. Instead, it’s more similar to the splayed walk of modern crocodiles.

This is an incredible find as it thwarts previous assumptions about the family tree of dinosaur relatives. The discovery tells researchers that the earliest cousins of dinosaurs had many features in common with crocodilians. Its jaw muscles, however, are much more similar to bird-like archosaurs with the attachments at the back of its skull.

^{Life reconstruction of the new species Teleocrater rhadinus, a close relative of dinosaurs. Credit: Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" (Buenos Aires, Argentina), artwork by Gabriel Lio.}

All dinosaurs belong to a group called archosaurs (“ruling reptiles”), which contain dinosaurs, birds, and crocodilians. However, 250 million years ago, that group split into two – one was bird-like with dinosaurs, birds, and pterosaurs, and the other crocodile-like with alligators, crocodiles, and some now-extinct relatives. T. rhadinus is the earliest discovery of the bird-like side of the family (check image below).

It’s important to note, Teleocrater is not a dinosaur, but instead part of a lineage separate from dinosaurs.

“Based on previously available fossils, paleontologists thought that the earliest members of this lineage probably were fairly dinosaur-like in many ways (i.e., they were probably small, lightly built, bipedal animals with upright limbs and hinge-like ankles),” said Angielczyk to IFLScience. “Teleocrater obviously doesn't fit that model; it almost looks more like a living varanid lizard than a dinosaur. It also retains a number of primitive features that it inherited from the common ancestor of bird-line and crocodile-line archosaurs.”

This means the many distinctive features found in bird-line archosaurs initially had crocodile-like features and evolved in a step-wise fashion over a longer period of time.

This “missing link” was initially discovered in the 1930s by British paleontologist Alan Charig. His discovery included many vertebrae and parts of the pelvis and limbs. However, the fossils were hardly considered a goldmine, with the connection to dinosaurs not even recognized at the time.

^{Image in text: A simple tree to illustrate where Teleocrater rhadinus belongs. Credit: Sterling J. Nesbitt et al.}

It wasn’t until a recent dig in Tanzania unearthed more prehistoric Teleocrater bones that scientists finally knew what they had. This find included more of the vertebrae, part of the skull, some of the pelvis and limbs, as well as bones of the hands, feet, and ankles, Angielczyk told IFLScience.

"We found fossils that we thought might be from Teleocrater, but it wasn’t until we were back in the lab that we realized we’d found something really amazing," said Angielczyk.

The team has called the dinosaur cousin Teleocrater rhadinus ("slender complete basin") in reference to the creature's closed hip sockets and lean frame.

At the time Teleocrater roamed the land, there was one giant supercontinent called Pangaea. The global climate was hotter and probably drier than it is today, with no flowering plants, mammals, or birds. There were trees and animals, of course, including Dolichuranus that superficially resembled a hippo in appearance.

To place Teleocrater in the archosaur family tree, the team used phylogenetic analysis, which involved recording detailed anatomical information for the various parts of the body in archosaurs and other reptile species. They then used a computer algorithm to find the tree (or trees) that best explain the data according to an optimality criterion called parsimony. 

They next conducted bone histology of Teleocrater to reveal that the creature experienced relatively rapid growth in a manner similar to many other members of the bird-line archosaurs.

"The discovery of such an important new species is a once-in-a-lifetime discovery," added lead author Sterling Nesbitt. "Teleocrater fundamentally changes our ideas about the earliest history of dinosaur relatives." 

^{Excavating the remains of Teleocrater rhadinus and other animals in southern Tanzania in 2015. Sterling Nesbitt (left) and Christian Sidor (right). Credit: Roger Smith.}

^{Excavating 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.}

^{Labeling the plaster jackets containing the bones of Teleocrater rhadinus at night in 2015. Credit: Roger Smith.}

^{Life model of the new species Teleocrater rhadinus, a close relative of dinosaurs, preying upon a juvenile cynodont, a distant relative of mammals. Credit: Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" (Buenos Aires, Argentina), model constructed by Marcelo Miñana.}