A REMARKABLE TRIASSIC TETRAPOD ASSEMBLAGE FROM THE DEEP RIVER BASIN OF NORTH CAROLINA

A remarkable Late Triassic tetrapod association has been found in massive red fluvial mudstones of Lithofacies Association II of the Durham subbasin (near Raleigh, NC), providing a unique glimpse at Triassic continental tropic interactions. A 70%-complete partially-articulated skeleton of a new poposaurid rauisuchian similar to Postosuchus, has stomach contents that include a skeleton of the aetosaur Aetosaurus (Stegomus) cf. A. arcuatus, a partial skull and postcranial elements of the traversodont cynodont Plinthogomphodon herpetairus, a dicynodont toe, and a dermal bone of a temnospondyl amphibian. Beneath the torso of the rauisuchian lay a beautifully preserved, nearly complete, articulated sphenosuchian crocodylomorph similar to Saltoposuchus, which has a bite mark on its neck of the appropriate size for the rauisuchian. Both the rauisuchian and the sphenosuchian may have died in mutual combat, and based on associated teeth, the rauisuchian at least appears to have been scavenged by phytosaurs.

Adjacent exposures have produced another partial skeleton of Aetosaurus (Stegomus) cf. A. arcuatus and fragmentary phytosaurs and ?metoposaurs. A stratigraphically-close lacustrine unit contains a new species of the minute hybodont shark Lissodus, coelacanths, the fish Turseodus, Synorichthyes, Cionichthyes, Semiontus, and numerous decapods, conchostracans, ostracodes, fragmentary insects, and clams.

The facies that produced this tetrapod assemblage is extremely common in the Triassic-Jurassic rifts of eastern North America, but is usually thought to be barren. This and other discoveries shows that this assumption is fundamentally wrong. Based on the presence of Aetosaurus, this assemblage belongs in the Neshanician Land Vertebrate Age of Huber et al. (1993) supposedly of Norian age. However, while the general aspect of the tetrapod faunule is in agreement with this, dicynodonts are not known from Norian strata, elsewhere. This suggests either that the range of Aetosaurus must extend into the Carnian, or dicynodonts must have lasted into the Norian, indicating that the Carnian-Norian tetrapod transition is not so distinct as often assumed.