August 18. Permian reptiles

Bradysaurus, a Permian reptile

Reptiles were better suited to the dry, arid climates that were common during Permian time than amphibians, and reptiles proliferated and diversified during this time. The Pareiasaurs were large herbivores, two to nine feet long, with bony plates armoring their bodies. Reconstructions look rather like big horned toads. In some varieties the bony plates have grown together, suggesting that this group may be ancestors of modern turtles, but the group was extinct at the end of the Permian and it is not certain that they gave rise to descendents that became turtles. It may be that the coalescing bony plates, somewhat like turtles’ shells, might have developed independently in both lineages.  

Mesosaurs, of early Permian age, were among the first reptiles to return to the water. They were clearly adapted to an aquatic life, with webbed feet and a long, streamlined body. Its leg joints – wrists and ankles – were designed in a way that would have made it impossible for them to walk on land, but they might have waddled ashore to lay eggs as modern sea turtles do, but embryo fossils of mesosaurs are not associated with egg shells, so an alternative interpretation is that they bore their young alive. If so, they are among the first animals to do so.

A lot of the known Permian reptiles are lizard-like, several inches to a foot or so long, and many are presumed to have been insectivores, filling the ecological niche that similar reptiles do today. The basic body plan of these animals seems to have been well established by the Permian. One lizard-like Permian reptile called Eudibamus was described in 2000 from a fossil found in Germany. It is possibly the first bipedal reptile. And another, known from Madagascar, had a wide skin layer between its ribs that probably allowed it to glide like modern flying squirrels. All of these adaptations make it clear that the Permian was a time of experimentation and expansion for the reptiles.

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On the night of August 17-18, 1959, the strongest earthquake recorded in the Northern Rocky Mountains struck the upper Madison River Valley near Hebgen Lake west of Yellowstone National Park. It measured about 7.4 on the moment magnitude scale and it triggered a huge landslide in Madison Canyon. The slide buried a campground, killing at least 26 people and damming the Madison River, which backed up to form a new lake, Quake Lake. The earthquake re-set the rhythms of geysers in Yellowstone Park and damaged buildings as far away as Butte and Bozeman. The fault scarps were as much as 19 feet high and can still be seen 50 years later. The faults were normal faults, dropping the Hebgen Lake basin down relative to the adjacent mountains.

—Richard I. Gibson

Drawing by Nobu Tamura (http://spinops.blogspot.com) used under GFDL

Reference:
Road Log for the Hebgen Lake Earthquake Area, by Michael Stickney, Tobacco Root Geological Society Guidebook (2012), p. 71