FOSSIL AND RECENT 195 



canal, and the more advanced type of caudal skeleton in which there is a differentia- 

 tion of the uroneural series (p. 91). 



Between the remainder of the osteoglossomorphs and the elopiforms there is an 

 even greater ' incompatibility ' of specialized features, particularly in aspects of 

 caudal anatomy. In short, the present state of palaeontological knowledge suggests 

 that the osteoglossomorphs and the elopiforms are not related above the pholi- 

 dophorid level. 



A comparison between the Elopiformes and primitive members of the Euteleostei 

 (salmonoids, osmeroids, esocoids, argentinoids, chanoids and gonorynchoids) is 

 difficult since the early history of euteleosteans is very poorly known. That all 

 euteleostean fishes were derived from a single teleost ancestor has yet to be demon- 

 strated, and the relationships between the primitive euteleosteans mentioned above 

 are not clear. It seems certain, however, that the euteleostean complex is an ancient 

 one since specialized members occur in Cenomanian times (Goody 1969b ; Patterson 

 1967b). In view of the uncertainty concerning the origin and early evolution of the 

 euteleosteans, remarks will at this stage be kept brief. 



Elopiformes and each of the euteleostean groups appear divergently specialized 

 and any relationship of ancestor-descendant type between these two groups appears 

 impossible. However, the possibility of there having been an ancestor common to 

 the elopiforms and the euteleosteans cannot be ruled out. 



In this connection the Upper Jurassic Anaethalion is of interest. The anatomy of 

 Anaethalion is poorly known, particularly with respect to cranial details. One of 

 the contained species, A. vidali from the Kimmeridgian of Spain, shows a pectoral 

 splint bone and is thus referred to the Elopidae (p. 36). I have examined a few 

 specimens of the species described by Nybelin (1967b) and am unable to determine 

 the presence or absence of a comparable splint bone in the Bavarian forms. For 

 the time being therefore the systematic position of most Anaethalion species must 

 remain in limbo (see also pp. 35-44). I would, however, like to draw attention to 

 certain features of the caudal skeleton of the genus. 



The tail of many euteleostean fishes shows several distinctive features. Firstly, 

 the last few neural and haemal spines show the development of median expansions 

 of laminar bone (Patterson 1970b ; Greenwood & Rosen 1971). Secondly, in some 

 euteleosts, there are well-developed neural arches associated with the first preural and 

 first ural centra, which in these fishes may fuse with the first uroneural forming the 

 stegural (Paterson 1970b). The fate of these neural arches varies during the evo- 

 lution of different euteleostean lineages (for a discussion of the primitive euteleostean 

 tail see Patterson 1970b). Thirdly, the epural series of euteleosteans is composed of 

 two or three epurals which are usually of equal length, unlike the graded series seen 

 in the caudal skeleton of elopiforms. 



Within the genus Anaethalion these ' euteleostean ' features are variously deve- 

 loped. Two forms mentioned by Nybelin (1967b), A. (?) cf. subovatus and A. sp. 

 (' £/o^>s-ahnlicher Fisch ', Nybelin 1963, 1971) show few of the above features. A. 

 angustissimus shows laminar bone, moderately well developed neural arches and 

 epurals of equal length (Text-fig. 18C, Nybelin 1971). A. knorri (Text-fig. 18D, 

 Nybelin, 1971) and A. angustus (Text-fig. 18B) both show laminar bone, but the 



