Paleontologists have unveiled a groundbreaking discovery: a new bipedal shubosaur archosaur, Rubble Jascus Expetatus, found in New Mexico. This finding enriches our understanding of the diverse prehistoric creatures that inhabited North America over 200 million years ago during the Triassic period.
Rubble Jascus Expetatus traversed its prehistoric environment on two legs, equipped with tiny arms and a beak-like structure devoid of teeth. Image credit: Jorge Gonzalez / NHMLAC Dinosaur Institute.
Rubble Jascus Expetatus belongs to the newly classified Shubosauridae family, which consists of ancient crocodilian relatives resembling bipedal theropod dinosaurs.
“Shubosauridae represents a unique group of Triassic poposauriforms found in western North America and Argentina,” explained Dr. Alan Turner of Stony Brook University and his team.
“These agile, bipedal, toothless creatures demonstrate a remarkable convergence with the ornithomimid theropod dinosaurs that thrived in the Cretaceous period.”
Currently, three recognized species of shubosaurs include Shubosaurus inexpectatus from the Cooper Canyon Formation in Texas, Ephigia ochiferae from the Coelophysis Quarry at the Chinle Formation in northern New Mexico, and Syrossuchus longiservicus found in the Lower Ischigualasto Formation of western Argentina.
Rubble Jascus Expetatus effectively bridges the fossil timeline between Shubosaurus inexpectatus and Ephigia ochiferae.
This fossil, estimated at around 212 million years old, was excavated from the Hayden Quarry in the Chinle Formation fossil forest of northern New Mexico, USA, yielding significant partial skeletons and other fossilized remains.
Paleontologists note that Rubble Jascus Expetatus exhibits minimal differences compared to its relatives, reinforcing a trend of remarkable skeletal conservatism within the Shubosauridae family.
“The anatomical similarities between the skeletal remains of these species suggest that this morphological consistency has persisted within the Shubosauridae of western North America for at least 10 million years,” the researchers stated.
“Rubble Jascus Expetatus aligns well with the hypothesis of morphological conservatism and fits within the known stratigraphic range of North American shubosaurs.”
This discovery further supports the hypothesis that shubosaurs were primarily endemic to western North America, suggesting a unique pattern distinguishing them from many other rare Triassic reptile groups.
“Our phylogenetic analysis positions this shubosaur within the same clade as two other North American shubosaurs, reinforcing the concept of an endemic group of small, bipedal, toothless forms in the southwestern United States,” the researchers concluded.
The findings are detailed in a paper published in the May 26th edition of the Journal of Vertebrate Paleontology.
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Alan H. Turner et al. New Shubosaurid (Archosaur, Poposauridae) unearthed from the Late Triassic (Norian) Hayden Quarry in New Mexico, USA Journal of Vertebrate Paleontology, Published online on May 26, 2026. doi: 10.1080/02724634.2026.2618182
Source: www.sci.news
