In Carboniferous and Permian Epochs 171 



Fig. 21. Palaeoniscus macro pomus. From Kupferschiefer beds 

 in Upper Permian of Ilmenau, Thuringia. One-third natural size. 

 (From restoration by Traquair.) 



sisted there, only some genera of elasmobranchs having 

 migrated into sea waters and became rather abundant along 

 coastal regions during Carboniferous time. The latter 

 seem largely or wholly to have died out in the sea during 

 Permian days. In habit and habitat the earlier fishes were 

 mainly clumsy ground-feeders, but during deposition of 

 Old Red strata, they became more active, aggressive, and 

 strongly carnivorous. This was most true of the elasmo- 

 branchs with taper body, lithe movements, and well-devel- 

 oped teeth. So temporarily they were able to migrate 

 into the sea and live for a time there against competitive 

 organisms. The other groups, the Dipneustei, the Cros- 

 sopterygii, and Chondrostei remained wholly freshwater, 

 or a very few may rarely have become anadromous in 

 habit. The type of fish thus evolved was largely adapted 

 therefore to shallow, and often decidedly putrid water, as 

 Baldwin Spencer has shown to be true for the existing 

 Neoceratodus (op. cit. p. 3). As an aid, therefore, to gill 

 action most of the groups evolved an air-bladder, which, 

 though now absent as an evident structure in the marine 

 Elasmobranchii of today, seems feebly indicated, according 

 to Miklucho-Maclay in some sharks (727:448) as a small 

 open dorsal diverticulum of the oesophagus. While still 

 retained in the Dipnoi, Chondrostei, and Crossopterygii, as 

 well as in most freshwater Teleostei of more recent origin, 

 it has largely or wholly been absorbed in the existing Elas- 

 mobranchii and marine Teleostei, since it must have become 

 a hindrance rather than a help when the latter groups 

 passed into the restless highly oxygenated waters of the 

 ocean. 



