BILLFISHES OF THE GULF AND ATLANTIC COASTAL PLAIN DURING THE EOCENE AND OLIGOCENE

There are five families of extinct and extant billfishes (perciform fishes with their premaxillary bones elongated into a non-protrusible rostrum or bill), but only two inhabited the Gulf and Atlantic Coastal Plain (GACP) during the Eocene and Oligocene. The extinct family Palaeorhynchidae is represented in the GACP by three species of Aglyptorhynchus Casier, 1966 [A. robustus (Leidy, 1860) and two undescribed species] from the late Oligocene, South Carolina. Aglyptorhynchus is distinguished primarily by having a rostrum with one to two pairs of lateral longitudinal canals and an unpaired central canal, a tripartite occipital condyle, an opisthocelous first vertebra, and a maxillary flange. The family Xiphiidae, which includes the modern swordfish (Xiphias Linnaeus, 1758), is represented in the GACP by three species of the extinct genus Xiphiorhynchus van Beneden, 1871 [X. cf. X. eocaenicus (Woodward, 1901), middle Eocene, England and Mississippi; X. kimblalocki Fierstine and Applegate, 1974, late Eocene, Louisiana and Mississippi; X. rotundus (Woodward, 1901), late Oligocene-?early Miocene, South Carolina]. Xiphiorhynchus is distinguished by having a round or oval rostrum that contains two pairs of longitudinal canals with the dorsal pair closer to the mid-line than the ventral pair. During both the Eocene and Oligocene, Xiphiorhynchus inhabited the ancient Tethys Sea (or Parathethys) and Atlantic Ocean. In contrast, Aglyptorhynchus was restricted to the ancient Tethys Sea (or Parathethys) during the Eocene, but in the Oligocene, the genus was distributed in the eastern Pacific and Atlantic oceans as well as the Tethys Sea. Aglyptorhynchus and Xiphiorhynchus have been recovered from nearshore, shallow deposits and oceanic (>100 m) deposits. Both genera existed for approximately 27 million years before becoming extinct. Their demise may have been caused by having upper and lower jaws of equal length making them less adapted for spearing than the modern genera that have disproportionately longer rostra.