BARON CUVIER IN NORTH TEXAS: EARLIEST CLASSIC EXTINCTION OF LARGE LAND HERBIVORES, IN THE EARLY PERMIAN CLEAR FORK GROUP

Between 1785 and 1812, Baron Cuvier defined mass extinction events using the terminal Pleistocene pattern: the largest land herbivores (larger than 100kg) lost many taxonomic families; the largest land carnivores lost many genera but few families; the largest freshwater aquatics (turtles and crocodilians) and small terrestrial species suffered little. Cuvieran extinction was ecologically ubiquitous, striking wet forests and swamps as well as arid grasslands.

Terminal Cretaceous extinctions were Cuvieran: all large herbivores and carnivores died out but freshwater aquatics and small-bodied families suffered far less. Extinctions were ubiquitous, striking swamp forests and dry floodplains. Everett Olson mapped what appeared to be the earliest known Cuvieran extinction within the mid Lower Permian of Texas. Only two families of large herbivores existed, diadectids and edaphosaurids. Both had long histories before Olson’s Event, and both disappeared at or near the end of the time recorded by the “Arroyo Formation”. Families of freshwater aquatics and small land tetrapods suffered little.

To evaluate ubiquity in Olson’s Event, we have censused 65 sites across the rich “Arroyo” outcrops at the Craddock Ranch. Some large predator genera disappear at the Event. Both families of large herbivores remain common up until their extinction. Anatomy suggests they occupied disparate habitats. Diadectids had massively muscled fore limbs and wide front feet tipped with shovel-shaped claws, adaptations for digging roots and tubers and perhaps excavating burrows for escaping predators. Edaphosaurs had small hands but exceptionally deep tails, adaptations for escaping predators by swimming. The Craddock sample corroborates predictions. All diadectids occur in red clay-rich soils with calcareous nodules, developed in ponds and floodplains. Over 86% of edaphosaurs occur in channel conglomerates and sandstone. Immediately after the extinction, both habitats exist but contain no large herbivores. These data indicate that Olson’s Event did indeed strike all large herbivores in all recorded habitats, matching the ecological ubiquity of a Cuvieran extinction.