LATE PENNSYLVANIAN ICHTHYOLITHS FROM CARRIZO ARROYO, CENTRAL NEW MEXICO

At Carrizo Arroyo, Valencia County, NM, the late Virgilian Red Tanks Member of the Bursum Formation is well known for its Lagerstaetten that contain micro- and mega-plants, eurypterids, insects, and marine invertebrates, as well as aquatic and terrestrial vertebrates. More than 500 ichthyoliths from 82 m above the base of the Red Tanks Member at New Mexico Museum of Natural History locality 3432 represent three classes of fish, Chondrichthyes, Acanthodii and Sarcopterygii. The chondrichthyan teeth belong to the freshwater shark Orthacanthus sp., and the sarcopterygian is a coelacanth very similar to an indeterminate coelacanth from the earliest Virgilian Kinney Brick Quarry, New Mexico. The acanthodians are represented by two different scale types, the histology of which places them in the family Acanthodidae. Isolated teeth and tooth fragments may belong to actinopterygians, but are not diagnostic. It is difficult to make paleoecological inferences about the fish from locality 3842 based on their isolated scales, bones and teeth. However, the environment was freshwater based on the presence of Orthacanthus teeth and charophytes. Both coelacanths and acanthodians lived in marine, brackish, and freshwater environments, and the fish of these types at locality 3432 are most likely freshwater or brackish forms. The low diversity of the ichthyolith assemblage suggests that environmental stresses may have limited fish diversity or that there were few species of Late Pennsylvanian fish adapted to living in floodplain lakes.