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Scientists Describe Sonselasuchus Cedrus, a Croc‑Line Reptile That Grew From Four Legs to Two

A Journal of Vertebrate Paleontology paper ties the gait change to limb allometry in a large Petrified Forest bonebed.

Overview

  • The peer‑reviewed study formally names Sonselasuchus cedrus from the Norian Sonsela Member of the Chinle Formation at Petrified Forest National Park, Arizona.
  • Morphometric analyses show the forelimb-to-hindlimb proportion shrank from roughly 75% in juveniles to about 50% in adults, indicating a shift from quadrupedal to bipedal locomotion.
  • Researchers attribute approximately 950 fossil elements to the species from a minimum of 36 individuals, drawn from a bonebed that has yielded over 3,000 specimens since 2014.
  • Anatomical traits such as a toothless beak, large eye sockets and hollow bones resemble ornithomimid dinosaurs yet reflect convergent evolution on the croc-line.
  • Phylogenetic results place the new taxon within Shuvosauridae in an unresolved cluster with Effigia and Shuvosaurus, likely due to non-overlapping missing data.