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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.
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.