El Reno Group

It preserves fossils dating back to the Permian period.

The Chickasha Formation, which is part of this group, contains the geologically most recent Permian continental vertebrates (Roadian) known from North America.

[1] These include one of the most recent lepospondyls,[2] a dissorophoid,[3] and some fragmentary fossils of Steppesaurus that Everett C. Olson interpreted as one of the oldest known therapsids,[4] an interpretation that has not been widely accepted.

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