HIGH ABUNDANCE AND LOW DIVERSITY OF TETRAPOD VERTEBRATES IN THE SOLITE QUARRY LAGERSTÄTTE (UPPER TRIASSIC, VIRGINIA-NORTH CAROLINA)

The Dan River Basin spans the Virginia-North Carolina border, and belongs to the larger network of Triassic basins of the Newark Supergroup. Within this basin sits the Solite Quarry, which contains a Late Triassic (Carnian) shale lagerstätte with hundreds of fossil plants, insects, and vertebrates. Among the plant fossils preserved, cycad fronds and stems of conifers are common, belonging to taxa such as Pagiophyllum and Eretmophyllum. In addition, numerous fossils insects and other arthropods have been collected from a three cm thick unit, including over 1,600 individual specimens, with several more to be catalogued. These insects pertain to at least 11 different orders and 17 different families. The dominance of aquatic insects such as belostomatids (giant water bugs) and notonectids (backswimmer water bugs) suggests a shallow lake basin, but the phenomenal preservation and black sediments suggest a deeper, anaerobic setting. In either case, the site represents a relatively low-energy freshwater lake environment.

Vertebrate fossils are not as abundant as the plants or insects, but over 484 specimens have been collected thus far. The rarest vertebrate species within the assemblage is the gliding reptile Mecistotrachelos apeoros (represented by four specimens, including the holotype), which was likely non-aquatic. Fish account for at least 140 of the vertebrates, including coelacanths, semionotiforms (Semionotus sp.), and palaeonisciforms (Turseodus). The only other vertebrate from this site is the aquatic reptile Tanytrachelos ahynis. 340 individual specimens of this species have been collected. Based on this sample, over 70% of the vertebrates and over 98% of the tetrapods belonged to a single species. Although nearly all vertebrate and most plant fossils lie stratigraphically above the insect layer, the same or similar species of insects were likely still present during the time of abundant Tanytrachelos. The high abundance of insects and low abundance of predatory competition may explain why the Tanytrachelos are so common at Solite. Despite a high level of sampling, there appears to be low levels of tetrapod alpha diversity. Further study of this and other Late Triassic basins may help reveal the reasons for such dominance of a fossil lagerstätte by a single vertebrate taxon.