Triassic Archosaur Had Armored Plates Above Its Backbone

For immediate release ‐ August 03, 2023


Contact: Jon Pishney, 919.707.8083. Images available upon request

Mambachiton fiandohana lived in what is now Madagascar during the Middle-Late Triassic transition, around 235 million years ago — the time of the first appearance of dinosaurs.

Mambachiton fiandohana backbone and diagram showing osteoderms. Articulated cervical vertebra and osteoderm series of Mambachiton fiandohana (UA 8-25-97-132) in right lateral view as a photograph (A) and line drawing (B). Grey shading in (B) indicates sandstone matrix. Arrow indicates anterior direction. Scale bar = 5 cm. Image © Nesbitt et al.

By Sci News staff

Archosaurs are reptiles that are divided into two major branches: the bird-line, which includes pterosaurs and dinosaurs, including living dinosaurs (birds); and the crocodilian line, including crocodiles, alligators, caimans, and gharials.

Mambachiton fiandohana is the earliest diverging member of the bird line of archosaur evolution.

Unexpectedly, [Mambachiton fiandohana] had an extensive series of bony plates called osteoderms covering its backbone.

Although osteoderms are common in crocodilians and their relatives, they are rare in bird-line archosaurs, with the exception of dinosaurs like stegosaurs, ankylosaurs, titanosaur sauropods, and at least one theropod.

Mambachiton fiandohana shows definitively that the bird-line archosaur group was ancestrally armored.

This armor was lost in the evolution of dinosaurs and pterosaurs but then re-appeared later several times, independently, in the dinosaur lineage.

“The loss and re-evolution of armor is an important aspect of the story of dinosaur evolution — freeing them from some of the biomechanical body constraints of the ancestral archosaurs and potentially contributing to some of the locomotor shifts as dinosaurs diversified into a dizzying array of different ecology and body forms,” said Dr. Christian Kammerer, a research curator in paleontology at the North Carolina Museum of Natural Sciences.

Read the full article here

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