xv. i SEYMOURIA 389 



On the other hand, there are many considerations that would lead 

 one to classify this fossil as an amphibian. (1) The skull bones were 

 conspicuously pitted or 'sculptured' ; (2) the pattern of the bones was 

 very like that of early amphibians ; for instance an intertemporal bone 

 was present; (3) the teeth still showed a labyrinthine structure and 

 the palatal teeth were distributed in pairs as in many labyrinthodonts ; 

 (4) the structure of the otic notch, across which the tympanic mem- 

 brane was stretched, and certain other features of the auditory appara- 

 tus suggest amphibian rather than reptilian affinities; (5) other fossils 

 are known which, though clearly related to *Seymouria, show trends 

 such as flattening and reduced ossification of the skull that are charac- 

 teristic of late labyrinthodonts rather than early reptiles; (6) perhaps 

 the most significant point of all is that some adult specimens show 

 signs of the presence of lateral line canals. Since the structure of the 

 skeleton of *Seymouria suggests terrestrial habits, the presence of 

 these canals suggests that the animal may have passed through an 

 aquatic larval stage in which they were functional. Hence the case for 

 classifying * Seymouria as an amphibian becomes very strong. 



It must be added that * Seymouria may show other features charac- 

 teristic of both early amphibians and primitive reptiles. The neck, 

 for example, was short, with the pectoral girdle lying close behind the 

 skull. There was little differentiation between the vertebrae, all those 

 in the cervical region bore ribs. The ribs were double-headed, a 

 feature that has been retained by some more advanced reptiles. 



*Seymouria itself existed too late to have been a direct ancestor of 

 the more advanced groups of reptiles, since some of the latter had 

 already appeared by the early Permian. Whether it should actually 

 be classified as an amphibian or a reptile is uncertain; in Romer's 

 recent Osteology of the Reptiles it and its allies are placed in the latter 

 group. It may be regarded as a most interesting link between the 

 labyrinthodonts and the primitive stem-reptiles (Cotylosauria), from 

 which soon arose a great variety of descendants, which came to 

 dominate not only the land but also the sea and air throughout the 

 subsequent Mesozoic period. 



The cotylosaurs must have existed throughout the later part of the 

 Carboniferous, though they did not become prominent before the 

 beginning of the Permian. From the Red Beds of Texas we have, 

 besides ^Seymouria, forms such as *Limnoscclis, *Captorhinus y and 

 *Labidosaurus, all with the rather high narrow skulls and pointed nose 

 characteristic of reptiles rather than amphibians, but differing from 

 the latter in the absence of the otic notch. This and other features 



