CONTRIBUTED PAPERS 



Section 1 . — Species Identification . 



The Paleontology of Billfish — The State of the Art 



HARRY L. FIERSTINE 1 



ABSTRACT 



The major ostcological features are described for living billfishes. All billfish remains are reviewed 

 critically and some questionable forms are placed in Xiphioidei Incertae Sedis (uncertain status). The 

 remaining xiphioids are placed into three families: Istiophoridae, Xiphiidae. and Xiphiorhynchidae. A new 

 undescribed xiphiid from Mississippi shows that the billfish lineages must have diverged prior to the 

 Eocene. Areas of research are suggested that will help place the paleontological studies on a more secure 

 foundation. 



Although billfish fossils have been known for over 

 130yr(Agassiz, 1838), Regan (1909) and Berg (1940) 

 have been tne only ones to summarize the paleon- 

 tological knowledge of this important group. This 

 paper reviews all fossil groups that are generally 

 considered to be billfish and separates the question- 

 able from the unquestionable forms. In order to put 

 the paleontological and phyiogenetic discussion on a 

 firm foundation, I have summarized some of the 

 major osteological features. In addition, I have 

 pointed out some areas of research that will aid fu- 

 ture paleontological studies. 



OSTEOLOGICAL INFORMATION 



Since crania, rostra, and vertebrae are the most 

 common billfish structures found in the fossil record, 

 the following review of recent osteology will em- 

 phasize them. 



Various authors (Gregory and Conrad, 1937; 

 Nakamura, 1938; Nakamura, Iwai, and Matsubara. 

 1968; Ovchinnikov, 1970) have shown that the 

 rostra, skull, and vertebrae differ greatly between 

 the Xiphiidae (swordfish). on the one hand, and the 

 Istiophoridae (marlin, sailfish, and spearfish), on the 

 other hand. In general, the skeleton is lighter and 



'Biological Sciences Department. California Polytechnic State 

 University. San Luis Obispo. CA 93407. and Research As- 

 sociate, Vertebrate Paleontology. Natural History' Museum of 

 Los Angeles County. Los Angeles. CA 90007. 



less ossified in the Xiphiidae than in the Is- 

 tiophoridae. The swordfish (Fig. 1) has a flattened 

 rostrum, a short occipital region of the skull, and a 

 one-piece lower jaw without a symphyseal joint. 

 The istiophorids (Fig. 2) have a rounded rostrum, a 

 comparatively longer occipital region, and a lower 

 jaw with a predentary bone and a symphyseal joint. 

 The vertebrae (Fig. 3) of the swordfish (when com- 

 pared with the istiophorids) lack the overlapping 

 processes, the centra are more cube-like than elon- 

 gate, and the caudal skeleton (Fig. 4) has more 

 separate bones (Fierstine and Applegate, 1968; 

 Fierstine and Walters, 1968). 



Comparative osteology has been little help in dis- 

 tinguishing between the various members of the fam- 

 ily Istiophoridae. Tetrapturus and Istiophorus have 

 12 + 12 = 24 vertebrae and Makaira has 11 + 13 = 

 24 vertebrae. Since only isolated vertebrae have 

 been found in the fossil record for istiophorids, this 

 vertebral difference has not been useful to paleon- 

 tologists. In general, there is generic similarity in 

 bone morphology. In Makaira the bones are usually 

 more massive than the other genera and the vertebral 

 centra are much wider anteriorly (Fig. 5) than 

 posteriorly (Nakamura et al, 1968). 



The bones of the branchial apparatus and limb 

 girdles have been studied by Nakamura (1938) and 

 Nakamura et al (1968), and they have very briefly 

 discussed the similarities and differences between 

 the various species. These studies will prove useful 

 when complete fossil skulls of istiophorids are found 

 or when individual bones are recognized. 



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