The Triassic reptiles that were mistaken for dinosaurs for nearly a century

Nature · Published 3 October 2026 Swipe more like this →

In short: Poposauroidea was a diverse group of pseudosuchians that evolved striking similarities to dinosaurs, including bipedal movement and open hip sockets. Because of these convergent traits, paleontologists frequently misidentified their fossils as theropod dinosaurs until the late 20th century, when better remains finally revealed their true evolutionary history.

Poposauroidea represents a clade of advanced pseudosuchians that thrived during the Triassic period. The group is defined by a unique combination of anatomical features, most notably in the structure of the snout and pelvis. Unlike their relatives, poposauroids possess elongated anterodorsal processes on the premaxillary bone and an open acetabulum, or hip socket. This open hip structure is a trait typically associated with dinosaurs and crocodylomorphs, which led early researchers to misclassify members like Poposaurus and Shuvosaurus as theropod dinosaurs for decades.

The ecological diversity within this clade was immense. Some members, such as the robust ctenosauriscids and Lotosaurus, were quadrupeds characterized by elongated neural spines that formed sails similar to those of spinosaurids. Others, including Poposaurus and shuvosaurids, were short-armed bipeds. Dietary habits were equally varied; while Qianosuchus and Poposaurus were sharp-toothed predators, Lotosaurus and shuvosaurids were toothless, beaked herbivores. This disparity makes it difficult to reconstruct the appearance of the ancestral poposauroid, though their evolutionary trajectory is marked by a clear trend toward increasing skeletal specialization.

The classification of these reptiles has undergone significant revision. In 1923, Franz Nopcsa first used the term Poposauridae, but it was not until 2007 that Jonathan C. Weinbaum and Axel Hungerbühler formally defined Poposauroidea. Sterling Nesbitt’s 2011 phylogenetic analysis provided further clarity, placing Qianosuchus as the most basal member and establishing the group's relationship to other archosaurs. Despite their success, poposauroids went extinct at the end of the Triassic, leaving behind a fossil record that continues to challenge our understanding of convergent evolution in early archosaurs.

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