644 REPTILIA. 
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 veptz/éan 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 innominatum (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.—FParetosaurus, Dicynodon, Elginia. 
Plesiosaurta.—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. Vothosaurus had limbs adapted for progression 
on land; leszosaurus (40 ft. in length) and Pléosaurus 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 
