BIOTIC PROVINCIALITY OF THE LATE TRIASSIC EQUATORIAL HUMID ZONE

Discoveries of diverse and well preserved tetrapod assemblages from Virginia and North Carolina document a hitherto unknown temporally persistent biotic province limited to a narrow swath around the Pangean Equator. These assemblages are characterized by the presence of small traversodont cycnodonts, and are of two ages. Early Late Carnian age assemblages of the Sanfordian LVA are from the Vinita (Richmond Basin, VA) and Pekin (Sanford subbasin, NC) formations and an ?Early ?Norian faunule of the Neshanician LVA from the Durham subbasin (NC).

In addition to surprisingly abundant traversodonts (e.g. Boreogomphodon), the Sanfordian faunules contain aetosaurs, rauisuchians, the crocodylomorph Euscolosuchus, phytosaurs, rhynchosaurs, Doswellia and Uachitodon, teeth of ornithischian dinosaurs, the dicynodont Placerias, the advanced cynodont Microconodon, numerous small lepidosauromorphs, and rare procolophonids. The Neshanician assemblage consists of the traversodont Plinthogomphodon, a fragmentary dicynodont, the aetosaur Aetosaurus (Stegomus), a new poposaurid rauisuchian, a crocodylomorph similar to Saltoposuchus, and fragmentary phytosaurs and temnospondyl amphibians.

In both the Sanfordian and Neshanican assemblages prococolophonids are conspicuous by their rarity, unlike contemporaneous assemblages from more northern areas, where prococolophonids are abundant and small traversodonts absent. Strata producing the Sanfordian and Neshanician faunules from the Richmond and Deep River basins are characterized by humid facies, while those from the similarly-aged more northern assemblages are from more arid facies. The persistence of this distinct traversodont faunal association in the humid tropics over at least 10 my argues for a climatic control of biotic provinciality. Because of the northward drift of central Pangea, progressively more southern basins passed the equator, and strata that should contain younger Norian and Rhaetian equatorial assemblages now lie buried in southeastern North America and on the west African continental shelf. Hence, it is possible this association could have persisted through the rest of the Triassic in these unsampled areas, and the amount of significant ecological change through the Late Triassic might be much less than usually assumed.