644 REPTIL1A. 



Extinct Reptiles 



The first known occurrence of fossil Reptiles is in Permian 

 strata ; in the Trias most of the orders or classes are repre- 

 sented ; while the " golden age " of the group was un- 

 doubtedly during Jurassic and Cretaceous times. 



Some of the modern Reptiles are linked by a series of 

 fine gradations to very ancient progenitors, the Crocodiles 

 of to-day lead back to those of the Trias, the New Zealand 

 Hatteria to the Triassic Rhynchocephalia ; but we have no 

 example of a Reptilian genus which has persisted from age 

 to age as Ceratodus has done among Fishes. Among the 

 fossil forms we find "generalised" types, which exhibit 

 affinities with groups which in our classification of recent 

 forms may be very widely separated. 



The following types of extinct reptiles seem to have 

 entirely disappeared : 



Theromorpha. Lizard-like terrestrial animals with limbs adapted 

 for walking, found in the Permian and Trias. The group shows a 

 remarkable combination of reptilian and mammalian characters. In 

 illustration of reptilian characters we may note the pineal foramen, the 

 complex lower jaw, usually articulating with a firmly fixed quadrate, the 

 usual presence of pre- and post- frontals. Mammalian features are 

 illustrated in some types by the differentiation of the teeth into incisors, 

 canines, and molars ; by a single temporal arcade like a zygomatic 

 arch ; by the way the limbs raise the body off the ground ; by the union 

 of the pelvic bones into an os mnominatum (pubes and ischia forming a 

 stout ventral symphysis) ; by the reduction of the quadrate ; by the 

 share the squamosal may take in forming the articulation for the 

 lower jaw. 



Examples. Pareiosaurus, Dicynodon, Elginia. 



Plcsiosauria. Amphibious and marine reptiles represented from the 

 Trias to the Chalk, without exoskeleton, usually with a long neck and 

 short tail. The skull has a single broad temporal arcade, pterygoids 

 meeting in the middle line, fixed quadrates, and a pineal foramen. 

 There are strongly developed pectoral and pelvic girdles. The limbs 

 vary ; in the earlier, more generalised, forms they are adapted for 

 walking on land ; but in the more specialised types they are modified 

 into powerful paddles, like those of Chelonia. The nearest affinities 

 are with the Chelonia. Nothosaurus had limbs adapted for progression 

 on land; Plesiosaurus (40 ft. in length) and Pliosaurtis were carni- 

 vorous forms adapted to an aquatic life. 



Ichthyosauria. Large marine carnivorous Reptiles, represented 

 from the Trias to the Chalk, with tapering body like that of a shark, 

 large dorsal and caudal fins, and two pairs of paddle-like limbs. In 



