OSTEICHTHYANS FROM THE ARKADELPHIA FORMATION (UPPER CRETACEOUS: LATE MAASTRICHTIAN) OF HOT SPRING COUNTY, ARKANSAS

The Arkadelphia Formation (late Maastrichtian) in Hot Spring County Arkansas preserves an extensive and diverse osteichthyan assemblage. Faunal types are represented by teeth, scales and skeletal elements belonging to: Pseudoegertonia cf. P. granulosus, cf. Hadrodus priscus, Paralbula casei, Atractosteus sp., Lepisosteus sp., Cylindracanthus ornatus, Enchodus gladiolus, Enchodus ferox, Enchodus petrosus and indeterminate osteichthyans with probable affinities to the pycnodontiforms and beryciforms. Osteichthyans are concentrated within a lag deposit that separates the underlying marls of the Arkadelphia Formation from the overlying Tertiary Midway Group limestone. Outcrop exposures of this lag deposit occur within the Ouachita River and are expressed as a series of partially submerged, recumbent fold limbs that strike obliquely to water flow. The osteichthyans recovered in this study span a broad and diverse range of paleobathymetries, foraging behaviors, and dietary preferences which indicate extensive transport, exhumation and reburial associated with storm activity and sea level cyclicity across a shallow Upper Cretaceous marine shelf. Lag deposits such as those found in the Arkadelphia Formation are common throughout the Upper Cretaceous of North America and provide new insights into the application of sequence stratigraphic principles to taphonomic modeling and paleoecological reconstructions.