Among the living tetrapods, amphibians are best defined 

 as lacking the amniote type of egg (see Chapter 7) and hav- 

 ing a larval form that metamorphoses into the adult. The 

 question here is whether or not there are also identifying 

 cranial features. 



Living amphibians belong to three groups: the frogs and 

 toads, the salamanders, and the Apoda or Gymnophiona. 

 Only the first two groups will be described; the last contains 

 little-known, worm-like, burrowing forms, the coecilians. A 

 check-list of the bones of the amphibian head skeleton is 

 given in Table 4-3. 



Salamander or urode/e Two American salamanders, Cryp- 

 tobranchus alleghemensis (Figure 4-17) and Necturus maculatus, 

 illustrate much of the range of variation seen in urodeles. 

 In shape, the skulls of these two genera are quite unlike. 

 Neither has retained an apparent outer roof, but the parie- 

 tal bones form the top of the endocranium. Postparietals and 

 supratemporals are lacking in this group as is the parietal 

 foramen. The nasal and maxilla are lacking in Necturus but 

 not in Cryptohranchus. Neither has a labial arch and the 

 quadratojugal if present is fused to the quadrate. The 



prefrontal 

 lacrimal 



frontal 



postorbital 

 parietal 



premaxilla maxilla palatine 



suprooccipital 



squamosal 



quadrate 



quadratojugal 



articular 



A dentary 



maxilla 

 premaxilla 



splenial 



suproangular 

 angular 



porasphenoid |uga| q"°d'°'°i"9°l 

 palatine 1 \ / / - 



Figure 4-15. Skull and mandible of Archoeopteryx. (After Heilmonn, 

 1927, and Kleinschmidt, 1951) 



lacrimal 



jugal 



coronoid process 

 parietal 



alisphenoid (epipterygoid) 



y2,V3 

 prootic 



parasphenoid 



squamosal 

 exoccipital 



XII 

 quadrate 



uadrate 



opisthotic 



carotid canal 



VII 

 fenestra vestibuli 

 jugular foramen 



Figure 4-16. Skull and mandible of Diarthrognathus. A, lateral view; B, lateral view of cranium 

 with zygomatic arch; C, palatal view; D, inner view of posterior end of mandible. (After Crompton, 

 19581 



OTHER TETRAPODS • 79 



