33^ 



Evolution and Distribution of Fishes 



late Wealden or early Neocomian period, along with evolv- 

 ing members of the sharks and dogfishes, and temporarily 

 became important factors in the marine life of the times, 

 and this also over a wide area. 



But the Pycnodonts and Pachycormids represented two 

 totally different types of organization and evolution, though 

 starting in late Triassic days from related ancestral fresh- 

 water organisms. For the short sub-circular and com- 

 pressed body, the heavily-plated head, the small mouth, 

 the rounded and pavement teeth, the small paired fins, and 

 the rather slender tail fin of typical Pycnodonts, (Fig. 

 ^^) all suggest bottom-feeding, and crushing of small 

 molluscs, crustaceans or other marine invertebrates. In 

 contrast the elongate fusiform body, the tapered head, the 

 expanded mouth with strong carnassial teeth, the well- 

 developed paired and caudal fins of Pachycormids like 

 Protosphyraena that closely resembled the more ancient 

 Hypsocormus (Fig. ^6)^ not to say the presence along 

 the intestinal tract of fossilized fish-prey in process of 

 digestion, all proclaim strong carnivorous propensities. 



Fig. 56. Hypsocormus insignis, a freshwater Jurassic fish, close- 

 ly related to the more recent Cretaceous and marine genus Proto- 

 sphyraena. One-eighth natural size. (After A. S. Woodward). 



The preliminary remarks made on the previous page 

 for origin of the Pachycormidae, would apply almost per- 

 fectly for the Amiidae, that in many details of structure 

 show ancestral affinity with the Eugnathidae. The family 

 includes, according to the varying views of palaeontologists, 

 four or five genera, namely Liodesmus from the litho- 

 graphic slates of Bavaria; Megalurus mainly known in four 



