About 250 million years ago, a decisive division in the pedigree of the then dominant archosaurs made its mark: the ancestors of today's crocodiles and alligators split off from the ancestors of dinosaurs, birds and pterodactyls. But as the first representatives of these so-called Avemetatarsalia looked, was previously unknown. "We thought so far that many of the characteristic features of this bird line of the archosaurs evolved very quickly after that tribe separated itself from the crocodile-like archosaurs, " explains co-author Kenneth Angielczyk of the Chicago Field Museum of Natural History. These features included a predominantly bipedal locomotion, a predatory lifestyle and a rather small body size. However, from the beginning of this tribal line, there have been virtually no fossils. Almost all known finds date back to the late Triassic, and thus from a time when the main groups of this dinosaur line, the dinosaurs and the pterosaurs, were already fully trained and highly specialized.
Now, however, the discovery of the oldest known representative of this dinosaur line throws a whole new light on the evolution of Dino ancestors. The identification of Teleocrater rhadinus baptized prehistoric reptile was made possible by fossil finds made by paleontologists in southern Tanzania in 2015. Already in 1933 bones of dinosaurs were discovered in this area, but they could not be assigned more closely because crucial skeletal parts such as the ankle joints were missing. Only the discovery of further, complete fossils of the same species now allowed the clear assignment of these animals. According to paleontologists, the teleocrater, who lived about 245 million years ago, belongs to a hitherto unknown group of early avemetatarsalia, the Aphanosauriern. He is no direct ancestor of the dinosaurs, but her oldest known cousin.
The really exciting thing about Teleocrater, however, is not its age, it's its appearance: it does not resemble the classic image paleontologists had of the first Avemetatarsalia representatives. This dinosaur, with a length of two to three meters, the long neck and tail and a weight of up to 30 kilograms, was significantly larger and heavier than the previous idea of these primeval dinosaurs corresponded. In addition, he did not run on his hind legs, but waddled on all fours through his habitat. Similar to the crocodiles, he put his legs sideways. While the dinosaurs, pterosaurs, and first birds were unable to do so because their ankles allowed only up and down movements, Teleocrater retained the ability to move his ankles sideways as well. "Teleocrater has unexpectedly crocodile-like features, " says Angielczyk. "The early relatives of the dinosaurs were definitely not very dinosaur-like."
For the first time, the newly discovered dinosaur demonstrates that the early cousins of the dinosaurs, pterosaurs and early birds have retained much more primitive features than the common ancestors of all the archosaurs. The more bird-like features that characterize the Avemetatarsalia strain evidently did not develop as quickly as thought. "Scientists usually do not like the term 'missing link', but that's pretty much what Teleocrator is: a link between the dinosaurs and the common ancestor they share with the crocodiles, " says Angielczyk. First author Sterling Nesbitt of the Virginia Polytechnic Institute adds, "Teleocrater fundamentally changes our notions of dinosaur relatives' earliest history." Ad
- Sterling Nesbitt (Virginia Polytechnic Institute, Blacksburg) et al., Nature, doi: 10.1038 / nature22037