Thursday, March 12, 2015

Triassic Thursday II: Aetosaurs

Aetosaurs, of the family Stagonolepididae, were prominent herbivores during the mid- to Late Triassic. I love aetosaurs: their snouts and prominent body armor made them the ecological equivalent of warthogs covered in spikes. They were a globally-dispersed species, with specimens being found in the Americas, Europe, Asia, and Africa. Before low-browsing dinosaurs evolved, these guys were the herbivorous powerhouses.

The main difference between aetosaur species is the arrangement and shape of body armor. However, most species contain an armadillo-like covering of osteoderms, protecting their neck, back, tail, and stomach from large predators such as the dino-mimicking rauisuchians with which they shared their environment. The most extensively-covered and elaborately-adorned aetosaur of them all was, without a doubt, Desmatosuchus, which I think bears an uncanny resemblance to the nodosaur Sauropelta. Clearly, the big shoulder spine look was not a fad limited to the Triassic.

The spike-shouldered aetosaur Desmatosuchus. Reconstruction by Dr. Jeff Martz.

Most other aetosaurs were not as well-equipped as Desmatosuchus. Most had parallel rows of TV remote-shaped scutes running down their backs. Still, this thick armor was enough to deter some of the biggest predators of the Triassic.

There is some evidence out there that aetosaurs constructed nests. Simple bowl-shaped depressions in the ground found in Arizona may belong to motherly aetosaurs. Archosaurs in general are known for parental care and nest construction, so the fact that these large nests may belong to aetosaurs is entirely within the realm of possibility.

Material from the new aetosaur Gorgetosuchus (Heckert et. al 2015).

Aetosaurs are particularly topical because a brand new species was just identified from North Carolina. Dubbed Gorgetosuchus, it had a ring of osteoderms surrounding its neck, like a huge bony collar. Despite being heavily-armored and generally of the same body shape, the diversity of aetosaurs in the mid- to Late Triassic is pretty incredible considering that the earth was still in recovery. The Triassic was a time of great proliferation, especially of reptiles.

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