EOCENE (JACKSONIAN) ESTUARINE VERTEBRATE FAUNAS FROM CROWLEY'S RIDGE, ARKANSAS

Jackson Group outcrops in Arkansas have yielded remains of numerous marine and estuarine vertebrates. The earliest record of archaeocete whales from Arkansas is that of an isolated vertebra of Basilosaurus cetoides from Jacksonian deposits on Crow Creek in St. Francis County, reported by Palmer in 1939. More recently, Crow Creek outcrops yielded remains of Zygorhiza kochii. An isolated vertebra, cf. Pontogeneus brachyspondylus, was collected near Redfield in Jefferson County, at Red Bluff.

Crassostrea alabamensis-rich beds exposed along Crow Creek contain a diverse chondrichthyan fauna. The taxa include Ginglymostoma serra, Carcharias hopei, Galeorhinus sp., Hemipristis curvatus, Abdounia enniskilleni, Galeocerdo latidens, Negaprion gibbesi, Pristis sp., Propristis schweinfurthi, Dasyatis sp. and Myliobatis sp. Osteichthyan fishes include Lepisosteus sp., cf. Arius sp., Sphyreana sp. and Trichiuris sp. This is a hyposaline, warm water assemblage which preferred water temperatures above 21oC and water depths less than 10 m. Reptilian taxa include Trionyx sp., a crocodylid, and Pterosphenus schucherti. Continental mammals present are cf. Diplobunops matthewi and a pantolestid. Jacksonian deposits exposed on Crow Creek are probably correlative with the Moodys Branch Formation of Mississippi.

The Lover's Leap local fauna from outcrops along Copperas Creek in Cross County includes the sand tiger shark, Carcharias hopei, and the giant sea snake Pterosphenus schucherti. This suite of vertebrates along with the archaeocete whale, Basilosaurus cetoides, whose vertebrae were found on a Copperas Creek tributary, indicates that Eocene deposits exposed along Copperas Creek are Jacksonian in age, although the Geologic Map of Arkansas (1993) indicates they are Claibornian.