VERTEBRATE BIOSTRATIGRAPHY FROM AN EARLY PERMIAN (LEONARDIAN) MARINE LIMESTONE IN NORTH-CENTRAL TEXAS

While the near shore, freshwater, and terrestrial vertebrates of the early Permian Period are well understood, North America contains virtually no complex vertebrate communities from fully oceanic rocks. In Shackleford County, Texas, the lower Lueders Formation (Leonardian) is found to contain a complex community of early chondrichthyans and bony fish. The biostratigraphy of this locality shows increased diversity in a pair of bone beds, which indicate periods of slowed carbonate growth. Three taxa however, are seen well past these bone beds: Deltodus mercuri can be found much lower, while a lungfish and paleoniscoid fish can be found much higher in section. This evidence suggests that these taxa were more resistant to environmental changes while the carbonates were being laid down. The exact mechanism for this resistance may relate to the preference for crushing the shelly fauna which made up the sea bed, or an ability to move from the oceanic realm into estuaries or even freshwater, or both.