TINY TRIASSIC FISH FROM THE NEWARK SUPERGROUP: WHAT DO SMALL SHARKS AND LITTLE LUNGFISH SAY ABOUT PALEOENVIRONMENTS OF NORTH AMERICA’S TRIASSIC RIFT BASINS?

The first ~150 years of vertebrate fossil collecting in the Newark Supergroup yielded numerous localities with diverse osteicthyan assemblages but no lungfish (Dipnoi) and only one published Triassic shark (Carinacanthus jepseniBryant from the Lockatong Formation in Pennsylvania). Recently recovered microvertebrates from the Deep River Basin of North Carolina demonstrate that these taxa are present, but remarkably small, even in comparison to similar forms from contemporaneous basins to the west (Chinle in USA) and east (Argana in Morocco).

Diminutive lungfish (< 5 mm maximum dimension) are now known from Cumnock-equivalent strata in the Sanford sub-basin and Lithofacies Association II in the Durham sub-basin. Some appear juvenile, with unworn tubercles, but others are badly worn and may represent adults of a smaller species. Both palatal and splenial toothplates possess 5-7 ridges radiating though 120˚ and thus are similar to Arganodus dorotheae from the American Southwest, albeit at half the linear dimensions and thus ¼ the occlusal surface area. These are the only known lungfish from the Newark Supergroup.

A productive locality in Lithofacies Association II in the Durham sub-basin has yielded numerous tiny (< 1 mm maximum dimension) hybodont shark teeth characterized by elongate, simple crowns that lack accessory cusps but possess a pronounced labial peg. They are most similar to the Lissodus and/or Lonchidiion, specifically L. humblei Murry or perhaps L. minimus Agassiz. Key measurements of these teeth (n=34) are: crown length (mean/median 723/738 µm), crown height (323/328 µm), crown width (324/325 µm), and labial peg length (171/167 µm). All appear to be from the most mesial tooth whorls, and could even represent a single individual. These teeth are similar in size, but morphologically simpler than, an unpublished tiny hybodont from the older Tomahawk locality (Vinita Formation) of Virginia and thus probably represent a different taxon. Nonmarine Triassic chondrichthyans are typically small, but the North Carolina hybodonts are among the smallest ever reported.

Although the microvertebrate record of the Newark Supergroup is sparse, it is perhaps telling that it yields different assemblages than its lacustrine record and, possibly, taxonomically distinct from other contemporaneous assemblages.