210 ELOPIFORM FISHES 



Since there is a trend to reduce the dentition, the albulids may be held to be more 

 primitive in the retention of palatine and vomerine teeth (feature viii). However, 

 the teeth borne by these elements are needle-like and differ from the teeth in a similar 

 position in the Osmeroididae. The vomerine teeth in albulids are raised on a short, 

 transversely orientated pedicel to bring them on a level with the palatine teeth. 

 Together these teeth form a complete semicircle of backwardly pointed teeth lying 

 within a similarly shaped band of premaxillary teeth. Thus, while their retention 

 may be primitive, their form is specialized. 



The coronoid process of albulids is situated posteriorly while that in Pterothrissus 

 among pterothrissids is situated anteriorly and is forwardly directed. This differ- 

 ence may be related to the position of the quadrate/mandibular articulation, which 

 lies beneath the posterior half of the orbit in the Pterothrissidae and the anterior half 

 of the orbit in the Albulidae. The anteriorly situated coronoid process in Ptero- 

 thrissus has the same disposition with respect to the lateral ethmoid as in Albula, 

 where the process is situated posteriorly. The insertion of the A 2 + A 3 division 

 of the adductor mandibulae is correlated with the position of the coronoid process 

 and it is suggested that in Pterothrissus the forwardly situated coronoid process has 

 in some measure compensated for the more posterior position of the jaw articulation. 



The difference between the families in the number of branchiostegal rays (feature 

 x) may also be related to the position of the quadrate/mandibular articulation. In 

 both Albula and Pterothrissus the jaw rami are close together in the ventral mid-line 

 and the anterior end of the hyoid bar (Tchernavin 1953) does not extend between the 

 jaws to any great extent. The distance between the ventral end of the hyomandibular 

 and the rear end of the mandible is relatively greater in Albula than in Pterothrissus 

 and the hyoid bar is longer. As the number of branchiostegal rays is proportional 

 to the length of the attachment area (Gosline 1967) the pterothrissids would be 

 expected to show a lower branchiostegal count. 



It is of interest to note that in Lebonichthys (Albulidae) the large gular plate 

 separates the jaw rami and although the jaw articulation is in the ' pterothrissid 

 position ' the hyoid bar is long and extends well between the jaw rami. The loss, 

 or great reduction, of the gular plate may have indirectly affected the shortening of 

 the hyoid bar. 



The Albulidae are known by representatives from the Eocene of Africa and 

 Europe and the Upper Cretaceous of Asia and North America. All but one of these 

 fossil representatives have been found in shallow-water deposits, which is in agree- 

 ment with the habitat of the Recent Albula vulpes. The exception is the Albula from 

 the Campanian of Alabama (Mooreville Chalk) which is reported to be a deep water 

 deposit (Applegate 1970). The evolution of the Albulidae probably began in Albian 

 or Lower Cenomanian times since Lebonichthys lewisi (Middle Cenomanian) already 

 shows an albulid tail and well-developed hemispherical teeth within the mouth. 



The Pterothrissidae are poorly represented in the fossil record, the only well known 

 fish being Istieus from the Campanian of Germany. It is possible that Hajulia 

 from the Middle Cenomanian of Lebanon is also a pterothrissid (see p. 152). In 

 part this lack of a fossil record may be a consequence of the deep-water habit, which 

 was probably adopted early in their history. 



