ELEMENTS OF VERTEBRATE PHYLOGENY 137 



etc.) and the spoonbills or paddlefishes, Polyodon and Psephurus. Very 

 soon after their own origin, the chondrosteans gave rise to a group of 

 fishes with bony skeletons, the Holostei — formerly lumped with the 

 Chondrostei in an artificial group called the 'ganoids'. The Holostei had 

 their heyday long ago, and have but two living genera, the bowfin 

 (Amia) and the gars or gar-pikes, Lepisosteus spp. From primitive 

 holosteans came the Teleostei, the most conspicuous group of modem 

 fishes, including such familiar forms as the trout, perch, herring, and 

 goldfish. Defeating the holosteans in competition for habitats and food, 

 the teleosts have taken the place in the seas and fresh waters formerly 

 occupied in succession by the chondrosteans and holosteans. But the 

 teleosts are a blind-alley group from which no higher forms have been 

 derived. 



Fig. 61 — The transition from water to land. 



a, an existing dipnoan, the Australian 'dyelleh', Neoceratodus forstert. After Ley. 



b, a giant stegocephalian, Mastodonsaurus giganteus (redrawn by E. C. Case, from a 

 restoration by Fraas); in life, the animal was about fifteen feet long, p- site of pineal eye. 



It was probably from swamp-dwelling crossopterygians that the first 

 land vertebrates came. These were the extinct amphibians which we call 

 the Stegocephali, from their characteristic head-armor. Some adult stego- 

 cephalians were but a couple of inches long, but most of them were gross, 

 sluggish beasts of little brain (Fig. 61b) — very different from the pert 

 little salamanders and agile frogs of the present time. It is possible that 

 the Stegocephali are not a natural group, but comprise two groups with 

 independent origins. It is also barely possible that some of the modern 

 amphibians originated directly from air-breathing fishes and not from 

 the Stegocephali. These questions have only recently been raised and 

 are not yet settled. At any rate, it is certain that the Stegocephali were 



