At this time it is difficult to propose any 

 phylogenetic scheme. Evidence seems to suggest 

 that at least three billfish groups had differentiated 

 and were living contemporaneously during the 

 Eocene. Members of the recent genera were living in 

 Miocene seas and they may be conspecific with 

 those that are alive today. Whatever form was the 

 common ancestor to the istiophorid and xiphiid 

 lineages had to be in existence prior to the Eocene. 



AREAS OF RESEARCH 



Comparative osteological studies on recent bill- 

 fish are needed in order to reasonably evaluate the 

 fossil forms. Good osteological collections are rare 

 because museums and universities lack the neces- 

 sary storage space; thus they usually avoid the prep- 

 aration of large skeletons. Therefore, my first 

 suggestion would be for more skeletons. A study of 

 the relative size and dimensions of the rostra and 

 vertebrae would be very useful. Since these struc- 

 tures are usually found separate from the rest of the 

 skeleton, simple comparative morphometric data 

 would aid their identification. Even though paleon- 

 tologists have placed importance on the histology of 

 fossil bills, the placement and number of nutrient 

 canals and the structure of the denticles are not 

 known for many of the recent forms. 



The functional anatomy of the feeding apparatus 

 and the method of locomotion are not known. For 

 example, the function of the predentary bone has 

 been surmised (Fierstine and Applegate, 1968) and 

 the role of the bill itself is just conjecture (Wisner, 

 1958; Tibbo, Day, and Doucet, 1961). The presence 

 of the predentary bone may be an adaptive feature 

 for large "slab-sided" fish with elongated upper or 

 lower jaws. Aspidorhynchid holosteans (Fig. 13) 

 have a predentary bone (Orlov, 1964; Zittel, 1932) 

 and the extinct clupeiform suborder Saurodontoidei 

 has an edentulous predentary which extends the 

 lower jaw well beyond the upper (Bardack, 1965). 

 Neither of these groups are thought to be directly 

 related to each other or to the istiophorids (Green- 

 wood, Rosen, Weitzman, and Myers, 1966;Gosline, 

 1968, 1971). 



No one has reliably measured the swimming speed 

 of a billfish or analyzed their swimming movements. 

 It is fairly obvious that the size and behavior of these 

 fish are difficult barriers, but they could be over- 

 come. A better understanding of the feeding and 

 locomotory apparatuses would help us explain the 

 differences between the istiophorids (rounded bill. 



predentary bone, elongate centra with overlapping 

 processes, fused caudal skeleton) and the xiphiids 

 (depressed bill, no predentary bone, cube-like centra 

 with no overlapping processes, no pelvic fins). 



Figure 13. — Two other examples offish with predentary 

 (pmd) bone. A. Aspidorhynchus acutirostris from the 

 Jurassic of Solenhofen, Germany. (From Zittel, 1932.) B. 

 Unidentified saurodontid. Age (probably Cretaceous) and 

 location unknown. 



The European fossil billfish need to be studied by 

 someone who is familiar with the recent forms. 

 There is no fossil group that does not need review. 

 What is Brachyrhynchusl Is it a synonym of some 

 recent istiophorid? Is Acestrus an istiophorid? 

 Paleorhynchids are now well-known from Russia 

 (Danil'chenko, 1960). Their large size and body 

 shape may be adaptive features that result from con- 

 vergence and are not a result of any relationship to 

 the xiphioids. Since their upper and lower jaws are 

 nearly equal in length, the paleorhynchids remind 

 me of a huge needlefish (Order Beloniformes). Are 

 the smaller paleorhynchids just the juveniles of the 

 much larger Pseudotetrapturus luteus'l If nothing 

 else, the quality of the illustrations of P. luteus needs 

 to be improved. 



The study of Blochius would be especially reward- 

 ing. Of all the uncertain groups, it seems to be the 

 most likely candidate to be included in the 

 Xiphioidei proper. Dr. George Myers (pers. comm.) 

 once told me that Blochius had a predentary bone. 

 No mention is made of this structure in the literature. 

 In addition Blochius needs to be redrawn, as all 

 available figures stem from a diagrammatic line 

 drawing in Woodward (1901). 



41 



