Xiphiorhynchus Kimblalocki, a New Billfish from the Eocene of Mississippi with Remarks on the Systematics of Xipi1joid Fishes

Xiphiorhynchus kimblalocki, a new species of extinct billfish from the Eocene of Mississippi, is described. This is the first record of Xiphiorhynchus outside of western Europe, and the material consists of a well-preserved rostrum, three partial vertebrae and two fin spine fragments. Xiphiorhynchus kimblalocki is compared with other living and extinct billfish and appears to be intermediate in morphology between the Xiphiidae and Istiophoridae. Various genera of fossil billfish are critically discussed and we suggest that the Blochiidae, Paleorhynchidae, and the "Cylindracanthus-group" should be placed in Xiphioidei lncertae sedis until better evidence indicates that they are billfish. We speculate that Xiphiorhynchus is an extinct offshoot from an unknown pre-Eocene common ancestor between Xiphiidae and Istiophoridae and is closer to the Istiophoridae than to the Xiphiidae. We also agree with earlier workers that the lineages of the Xiphiidae and Istiophoridae run back separately into basal Eocene times and that any common ancestry to each other and to the scombroids must have been prior to the Eocene and may have extended into the Cretaceous. Billfish remains have been described in rocks from able evidence and to make order out of chaos the Cretaceous Age (Dixon, 1850) to the Pleisto­ (Woodward, 1901; Leriche, 1905; Carter, 1927; cene (Fierstine and Applegate, 1968). The exact Casier, 1946, 1966). Unfortunately, even the taxon to which many of these remains belong has puzzled paleontologists because identifications 1 Dept. Biological Sciences, California Polytechnic are usually based on isolated skeletal parts, partic­ State University, San Luis Obispo, California 93401 ularly the rostrum. Detailed anatomical compari­ and Research Associate, Dept. Vertebrate Paleontol­ sons of recent genera are lacking and the lack of ogy, Natural History Museum of Los Angeles County, Los Angeles, California 90007. information has led to nomenclatorial confusion 2 Dept. Vertebrate Paleontology, Natural History and misidentification of the fossil forms. Various Museum of Los Angeles County, Los Angeles, Cali­ attempts have been made to synthesize the availfornia 90007. 1974 NEW BILLFlSH FROM EOCENE OF MISSISSIPPI 15 latest monograph (Casier, 1966) has failed to apply the well-established nomenclature and bio­ logical knowledge used by recent ichythyologists (Greenwood, Rosen, Weitzman, and Myers, 1966; Gosline, 1968; Howard and Ueyanagi, 1965; Morrow and Harbo, 1969; Nakamura, Iwai, and Matsubara, 1968; Robins and de Sylva, 1960, 1963). Thus, it is the object of this paper to describe a new species from the Eocene of Mississippi and to put at least a part of the fossil billfish problem in a more modern perspective. SYSTEMATIC DESCRIPTION