A new species and biology of the Late Cretaceous 'blunt-snouted' bony fish, Thryptodus (Actinopterygii: Tselfatiiformes), from the United States

Abstract

Thryptodus zitteli Loomis (Actinopterygii: Tselfatiiformes) is an enigmatic Late Cretaceous bony fish with a massive blunt rostrum that lived in the Western Interior Seaway of North America. Here, a second species of Thryptodus, T. loomisi sp. nov., is described on the basis of two skulls and some isolated rostra from the Britton Formation (Cenomanian–lower Turonian) of Texas, USA. In addition, the type species, T. zitteli, is redescribed and a nearly complete skeleton of the species from the Austin Chalk of Texas is examined to further decipher the biology of Thryptodus. Thryptodus primarily lived in offshore environments and reached up to about 1.8 m in total length. With a massive head, the fossil fish had a dorsal fin that spanned much of the body length, elongate pectoral, pelvic, and anal fins, and a small forked caudal fin, suggesting that Thryptodus was a sluggish swimmer. The function of the peculiar blunt rostrum in Thryptodus remains uncertain. Likewise, the exact diet of Thryptodus remains unknown. However, the skull construct suggests that Thryptodus had powerful lower jaws and hyoid-based suction feeding.