212 ELOPIFORM FISHES 



The Phyllodontidae are related amongst themselves and distinguished from the 

 Albulidae by having a phyllodont pattern of tooth replacement and in lacking ptery- 

 goid tooth plates (Estes 1969a : 328). Estes considers the absence of pterygoid 

 tooth plates to be the more important of these characters. 



The Albian genus Casierius Estes (1969b) has been placed in the Albulidae even 

 though tooth replacement in this form is phyllodont. Estes (1969b) uses a similarity 

 in the contours of the basibranchial plate and the presence of associated pterygoid 

 tooth plates as justification for the inclusion of Casierius within the Albulidae. 



It appears to the present author that Casierius, in showing a phyllodont dentition, 

 is clearly related to the Phyllodontidae. To dissociate it from the phyllodonts only 

 because it has pterygoid tooth plates (Estes 1969b) seems untenable. The poten- 

 tiality to replace teeth in phyllodont fashion, either from directly beneath (Phyllo- 

 dontinae) or in alternate fashion (Paralbulinae), would appear a trenchant difference 

 from the albulids. 



The first albulid appears in the Lower Cenomanian while Casierius is found in 

 the Albian, and by this time it already had a wide geographical distribution in- 

 dicating an earlier origin. The phyllodont dentition is clearly more specialized 

 than the albulid type and, disregarding the time factor, a derivation of phyllodontids 

 from albulids would appear more logical than the converse. 



If albulids were present in the Lower Cretaceous it would be expected that tooth 

 plates referable to this family should have been discovered, since these are as robust 

 as those of the phyllodontids. One is left with three possibilities regarding the 

 position of the phyllodontids : they were derived from the Osmeroididae separately 

 from the Albulidae and at an earlier time ; they stand ancestral to the Albulidae ; 

 or they evolved in parallel to the Albulidae. 



It is difficult to comment on the possibility that the phyllodontids were derived 

 from the Osmeroididae. Certainly no known osmeroidid shows a phyllodont denti- 

 tion or any kind of replacement pattern comparable with the Phyllodontidae. 



That the Phyllodontidae stand ancestral to the Albulidae is unlikely since the 

 phyllodont dentition is so advantageous in grinding food that to revert to a much 

 simpler type of dentition yet still retain a similar feeding method is unlikely. 



A separate but parallel evolution of the Albulidae and the Phyllodontidae appears 

 possible. Phyllodontids and Casierius are only known by tooth plates which cannot 

 be referred to any more completely known fish. Until phyllodontid material other 

 than tooth plates is known it is better to accept the classification within the phyllo- 

 dontids as being artificial. The fact that the tooth plates belong to a fish at about 

 the ' elopiform grade ' seems a reasonable supposition but the possibility of holostean 

 or halecostome affinities cannot be ruled out. 



V. SUMMARY 



Descriptions are given of the Recent and fossil Elopiformes represented in the 

 collections of the British Museum (Natural History). The basic systematic conclu- 

 sions are as follows : 



1. The Elopiformes are a primitive group of teleostean fishes distinguished 

 from other teleostean orders by the combination of three primary characters : a 



