PRIMEVAL SALAMANDERS. 



313 



the adult. Varying from the size of a small newt to that of a crocodile, the 

 primeval salamanders are of especial interest to the evolutionist, as it is pretty 

 certain that not only are they the descendants of primeval fishes, but that 

 they are the ancestors both of the modern Amphibians and the extinct Anomodont 

 Reptiles. And it is probable that Mammals have originated, either directly from 

 them or from a lost group intermediate between them and the Anomodont 

 Reptiles. They appear to have been spread over the whole globe, and they have 

 been divided into several subordinal groups. Among 

 these the highest are the true Labyrinthodonts, 

 typically represented by the gigantic Mastodonsaurus 

 and the somewhat smaller Metoposaurus of the Trias. 

 These were crocodile -like animals, generally with 

 disc-like vertebrae in the adult, the teeth more or 

 less plicated, and the surface of the skull marked 

 with sculpture and mucous canals. In the Permian 

 Archegosaurus, the vertebrae were, however, of the 

 complex primitive type. The Gilled Labyrinthodonts, 

 as represented by Protriton and Pelosaurus, are a 

 group of much smaller forms, characterised by their 

 barrel-shaped vertebrae, pierced by a remnant of the 

 canal of the primitive notochord ; short and straight 

 ribs, articulating by a single head ; simple teeth, and 

 the absence of ossification in the occipital region of 

 the skull, as well as in the wrist and ankle-joints ; a 



further point of distinction being the development of internal gills in the young. 

 The Permian and Carboniferous Snake-like Labyrinthodonts are characterised by 

 the snake-like form of the body, and the apparent absence of limbs. The vertebrae 

 were elongated and without spines, while the ribs were slender and barbed like 

 those of fishes, and 'the teeth smooth and simple. Probably the external gills 

 persisted throughout life. In Britain the group is represented by the small 

 Dolichosoma ; but Palceosiren of Bohemia is estimated to have been over 40 feet 

 long. If these creatures prove to be the ancestors of the Worm-like Amphibians, 

 it would show that the latter are distinct from the newts and salamanders. The 

 Microsauria, include small lizard-like forms, such as Ceratoerpetum and Hylonomus 

 from the Carboniferous of Europe and Nova Scotia, which appear more highly 

 organised than the preceding, and thus connect the Amphibians with the Beaked 

 Reptiles. Their vertebrae are long and constricted, with traces of the notochord ; 

 the ribs are generally long, curved, and two-headed ; the teeth have large central 

 pulp-cavities, but no plications ; the occiput is ossified ; but the wrist and ankle are 

 either ossified or cartilaginous ; and in some cases the back is covered with bony 

 scales. In several forms the bony scales on the under surface are so slender as to 

 assume the appearance of abdominal ribs like those of the Beaked Reptiles. 



SKULL OF THE METOPOSAUR 



( J nat. size). 



