OSTEICHTHYANS FROM THE CLAYTON LIMESTONE UNIT OF THE MIDWAY (PALEOGENE: PALEOCENE) OF HOT SPRING COUNTY, ARKANSAS

The Clayton Limestone Unit of the Midway Group (Paleocene) in southwestern Arkansas preserves one of the oldest osteichthyan Cenozoic assemblages yet reported from the Gulf Coastal Plain of the United States. The fauna is dominated by pycnodont, albulid and phyllodont taxa including: Pycnodus sp.; Albula oweni (Owen, 1840); Paralbula marylandica Blake, 1940; and cf. Phyllodus toliapicus Agassiz, 1839. Also present are osteichthyan vertebral centra and fin spines of indeterminate origin. The Clayton Limestone Unit osteichthyans are of limited species diversity and dominated by individuals with crushing dentitions evolved from families that survive the Cretaceous-Paleocene extinction event. Exposures of the Clayton Limestone Unit occur, geographically near to, and stratigraphically directly above, a site exposing an assemblage of Maastrichtian osteichthyans from the upper Arkadelphia Formation marl. Comparison of the two assemblages suggests that the Cretaceous-Paleocene extinction event decimated osteichthyans throughout this region, particularly those with pisciverous dentitions. Pycnodonts, albulids and phyllodonts from the Paleocene are known to radiate throughout the early Cenozoic. Some of these taxa give rise to modern reef fishes with similar crushing dentitions across the Eocene-Oligocene transition.