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New Triassic Croc-Line Reptile Grew From Four-Legged Juvenile to Bipedal Adult

Hundreds of fossils from a dense Late Triassic bonebed let researchers quantify limb growth that signals a shift in how the animal moved.

Overview

  • The peer‑reviewed study in the Journal of Vertebrate Paleontology formally names Sonselasuchus cedrus from the Norian Sonsela Member of the Chinle Formation.
  • Sonselasuchus is represented by over 950 specimens from at least 36 individuals recovered at the Kaye Quarry, part of a collection exceeding 3,000 fossils since 2014.
  • Quantitative allometry shows the forelimb grew on a negative trajectory relative to the hindlimb, consistent with juveniles moving quadrupedally and adults adopting bipedal locomotion.
  • Osteology indicates a dinosaur‑like body plan with a toothless beak, large orbits, and hollow bones that resemble ornithomimid theropods through convergent evolution on the croc line.
  • Phylogenetic analysis places the species within Shuvosauridae in an unresolved clade with Effigia and Shuvosaurus, reflecting gaps in overlapping skull data.