300 Evolution and Distribution of Fishes 



have been effected over the Russo-Scottlsh area, and that 

 they spread outward, during succeeding epochs, as will be 

 further traced below, over nearly the entire earth. 



The genus Ceratodus continued the succession above 

 hinted at. For while Sagenodus still lingered on in the 

 Permian and Permo-Triassic, from Illinois and Texas east- 

 ward through Bohemia and Russia to Australia, species of 

 the former genus were rapidly spreading over an even more 

 extensive area. For the highly resistant dental plates and 

 denticles of Ceratodus have been found in the freshwater 

 beds of the Upper Muschelkalk and superincumbent Let- 

 tenkohle-Keuper o£ Central Germany and of England. 

 Others however have been found in the South African 

 Stormberg rocks of Triassic age; in probably contempor- 

 aneous rocks of the Kota-Maleri beds of India {226: 300) ; 

 and in the Hawkesbury beds of Australia. Remains of 

 the genus in the Rhaetic of England and Germany; in the 

 Stonesfield Slate of Central England; and in the Jurassic 

 from Colorado on the west to Victoria in Australia on 

 the east, demonstrate its extensive generic range. 



But a suggestive theoretical proposition deserves now 

 to be made. As is well known the only living genera beside 

 Neoceratodus of Australia is Lepidosiren paradoxa of the 

 Amazon and Paraguay river regions, also Protopterus 

 whose three species extend over a great part of central 

 Africa. The common and fundamental characters of all 

 three existing genera, but at the same time the subdivisional 

 differences of Neoceratodus as compared with the other 

 two — that are strongly emphasized by Eastman {Sgigy 

 99) — would seem to indicate that at an early period geo- 

 logically a common lepidoslrenid ancestor to Gosfordia, 

 Lepidosiren, and Protopterus may have spread westward 

 from Australia. This could well occur along the Gondwana 

 continental line, during Jurassic and early Cretaceous times, 

 when many similar migrations of plants and animals took 

 place. 



The existing distribution of the three species of Protop- 

 terus in Africa is fully 2000 miles lengthwise by 3,500 

 miles in greatest width, while it is quite possible that in 

 Eocene-Miocene ages the range may have been considerably 



