A newly described prehistoric reptile is giving scientists a surprising look into how some ancient animals changed the way they moved as they grew. Researchers say this “unusual” crocodile relative likely started walking on all fours and adopted a two-legged stance as an adult.
a species called Sonselascus cedarbelonged to a group of reptiles known as Shubosauridae. Many members of this group closely resembled the ornithomimid dinosaurs that coexisted with them during the Late Triassic period (about 225-201 million years ago).
Fossil evidence of bipedalism
In a peer-reviewed study published in Journal of Vertebrate Paleontologyscientists from the University of Washington’s Department of Biology and the Burke Museum analyzed the fossil remains and noticed unusual limb proportions. These findings suggest that this small, poodle-sized reptile may have developed the ability to walk on two legs later in life.
“By analyzing the proportions of the limb skeletons of different animals, they found that their bipedal posture (standing on two legs) may be the result of different growth patterns,” explains lead author Elliott Armor-Smith.
“This is what we think Sunselasuchus When young, the forelimbs and hindlimbs were more proportionate, and the hindlimbs became longer and more robust as adults.
“Basically, it is thought that these creatures started life on four legs…and then as they grew older they started walking on two legs.
“This is particularly strange.”
Graduate student Armer Smith conducted the research with Burke Museum professor Christian Sydow.
Huge amount of fossils discovered in Arizona
Professor Sidor was part of the excavation team that discovered 950 fossils. Sunselasuchus Petrified Forest National Park in Arizona in 2014. More than 10 years of excavation and preparation have unearthed more than 3,000 fossilized bones at the site, making it one of the richest finds of its kind.
Fossils also provide insight into what reptiles looked like. It is thought to have been about 25 inches tall and had a toothless beak, large eye sockets, and hollow bones.
Uniquely evolved dinosaur-like features
nevertheless Sunselasuchus Although similar to certain dinosaurs, scientists emphasize that these features evolved separately.
“Although it resembles ornithomimid dinosaurs, these traits would have evolved separately,” Armor-Smith explains. “And this similarity is probably due to the fact that crocodilian and avian archosaurs evolved in the same ecosystem and converged on similar ecological roles.
“Also, although features such as bipedalism, toothless beaks, hollow bones, and large orbits are characteristic of ornithomimid theropod dinosaurs, Sunselasuchus This shows that these features have also evolved in Crocoline. ”
Life in the Triassic Forest
This animal is thought to have lived in a forest environment. Its species name is Cedarrefers to the cedar tree, an evergreen conifer similar to those present in forests during the late Triassic period.
genus name Sunselasuchus (pronounced “sawn-SAY-la-SOOK-us”) pays homage to the formation in which the fossil was found, known as the Sonsela Formation of the Upper Triassic Chinle Formation. This rock formation has yielded many important discoveries over time.
10 years of continuous discovery
For Professor Sidor, this research represents more than a decade of collaboration with the National Park Service.
“Since we began fieldwork at the Petrified Forest in 2014, we have collected more than 3,000 fossils from the Petrified Forest. Sunselasuchus It’s a bone bed and it doesn’t seem to show any signs of slowing down,” Professor Sidor said.
“In addition to Sunselasuchusbone beds have yielded fossils of fish, amphibians, and even dinosaurs and other reptiles. More than 30 University of Washington students and volunteers have participated over the years. It’s great to see that this site continues to yield new and interesting fossils. ”
