FOSSIL AND RECENT 



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a few club-shaped gill-rakers, dental plates with minute needle-like teeth ; cavernous 

 sensory canal system ; caudal skeleton with two uroneurals and six hypurals. 



The origin of these two families is to be found in the Osmeroididae. The Albulidae 

 and Pterothrissidae differ from one another in several respects (some of which have 

 been referred to above) . Each family has retained and developed features not found 

 in the other and these are listed in Table II. 



Table II 

 Differences between the Albulidae and the Pterothrissidae 



A Ibulidae 



i. Gular plate present 

 ii. No median connection of supraorbital 



canals 

 iii. Parietals shorter than broad and 



irregular in shape 

 iv. Interorbital septum often ossified 

 v. Parasphenoid broad, sutured with lateral 



ethmoid 

 vi. Dentition of grinding teeth on 



parasphenoid and endopterygoid, 



opposed by basibranchial tooth plate 



bearing a similar dentition (basihyal 



tooth plate edentulous or absent) 

 vii. Maxillary teeth absent (except in 



Lebonichthys lewisi) 

 /iii. Vomer and palatine with needle-like 



teeth 

 ix. Infraorbitals behind eye completely 



covering the cheek region 

 x. Branchiostegals not less than 12 in 



number 

 xi. Dorsal fin short (slightly elongate in 



Lebonichthys), anal short 

 xii. Caudal skeleton with complete neural 



spine on second preural centrum, caudal 



scute present above and below peduncle. 



Hypurals broad, narrow gap between the 



second and third hypurals. Usually two 



epurals 



Pterothrissidae 



Gular plate absent 



Supraorbital canals of either side united 



Parietals square or longer than broad and 



regular in shape 



Interorbital septum never ossified 



Parasphenoid narrow, not sutured with 



lateral ethmoid 



Dentition of conical teeth on 



parasphenoid, endopterygoid and 



ectopterygoid opposed by basihyal and 



basibranchial tooth plates bearing a 



similar dentition 



Maxillary teeth present 



Vomer and palatine edentulous 



Infraorbitals behind eye narrow and 

 incompletely covering the cheek region 

 Never more than 10 branchiostegals 



Dorsal fin long, extending along most of 

 back, anal slightly elongated 

 Caudal skeleton with a half spine on 

 second preural centrum, no caudal 

 scutes. Hypurals slender, large gap 

 between second and third hypurals. 

 Usually three epurals 



Many of the above features are self-explanatory and little discussion is given here. 



Some of the differences are specializations due to varying diets (features iv, v, vi) 

 or different body form (xi). The reduction of the cheek covering (ix) in the 

 Pterothrissidae may be related to the reputed deep-sea habit since a reduction of 

 ossification is often noted in fishes from this environment. In features i and ii the 

 Pterothrissidae are more advanced while the Albulidae are more advanced in features 

 iii and vii. 



M 



