A NEW MICROVERTEBRATE FAUNA FROM THE UPPER TRIASSIC (NORIAN) CUMNOCK FORMATION, DURHAM SUBBASIN, NORTH CAROLINA, USA

Exposures equivalent to the upper portion of the Upper Triassic Cumnock Formation at a Chatham County brick quarry yield a diverse microvertebrate assemblage. Fossils recovered include abundant osteichthyan fossils as well as less common, but diverse, amniotes. Strata at the Moncure Pit consist of ~33 m of "red-bed" siliciclastics, principally mudstone and thin (<1.5 m) lenses of siltstone and sandstone. The fossils occur in a lens of purplish gray, pedogenically modified siltstone, ~19 m above the base of exposure locally. Osteichthyan fossils are predominantly indeterminate teeth and scales, but also include recognizable elements of palaeoniscoids, redfieldiids, and semionotids as well as the first dipnoan (lungfish) teeth reported from the Newark Supergroup. The latter are minute (3-8 mm long), and are tentatively referred to cf. Arganodus here although they are much smaller than typical Arganodus records. A single intercentrum and some textured bone fragments may pertain to amphibians. Amniotes are represented primarily by teeth, but also by vertebrae and limb elements. Larger (cm-scale) amniote fossils are teeth of phytosaurs, rauisuchians, and other archosauriforms, including the first teeth of the enigmatic archosaur Revueltosaurus reported from outside the southwestern U.S.A. Smaller (mm-scale) fossils include records of several indeterminate reptiles, multiple archosauriforms, a possible sphenodont, and at least two synapsid taxa, including teeth tentatively referred to aff. Microconodon sp. and Traversodontidae indet.

The fauna is exceptionally diverse taxonomically, preserving a dozen taxa identified at the family level or lower as well as numerous specimens that probably represent other, less-well-known taxa. This diversity, coupled with the new records reported here (cf. Arganodus, Revueltosaurus sp.) demonstrates the value of microvertebrate studies generally, and screenwashing in particular, to maximize knowledge of vertebrate paleobiodiversity.