The Reptiles of the present day include, 1st, the Lacertilia (Monitors, Chameleons, Wall-lizards); 2d, the Ophidia
(Snakes); 3d, the Crocodilia (Crocodile, Alligator); 4th,
the Chelonia (Turtles); and numerous extinct forms. As
the reptiles that live at the present day are but a small
portion left of those that have once lived, and as these
extinct forms are not always entirely preserved, and from
the nature of petrifaction very little of their soft parts can
be known except from analogy, naturally the ancestors of
the reptilian class have not been positively determined.
Premising that the tree of the Reptiles, like all other such
trees, is only a provisional one, the following line of descent
is offered with diffidence. As long ago as 1710 the Proterosaurus—which, when translated, means "first lizard"—was described by Spener, a physician of Berlin. Since
that time other reptiles, allied to Proterosaurus, have been
discovered, as Belodon, Paleosaurus, etc., which have been
classed together as Thecodonts. The skeleton of Proterosaurus resembles most closely, among living reptiles,
that of the Varanus, the large African lizard; but among
the Thecodonts have been found also scales of a crocodilian
nature, so that the Thecodont group seems to be the forerunner in the Proterosaurus of the lizards and crocodiles,
while the Paleosaurus and Belodon are the first of a series
leading to the Dinosauria. The Snakes are probably an
offshoot of the Lizard, to which they are closely allied; the
Sepidae (Fig. 68), among the Lacertilia, leading to the
Anguidae (Fig. 67) among the Snakes. The Anemodonts,
of which the Pterodactyle is a remarkable representative,
lead to the Turtles through forms like Rhynchosaurus. The
Dinosauria were represented by huge reptiles like Iguanodon and Hadrosaurus, of which some were more than thirty
feet long. They are very interesting on account of their
affinities to birds. The different orders of Reptiles seem
to have branched off from a common stock represented by
Thecodont forms, which are allied to the Salamanders
among the Batrachia. Until some better theory of the
origin of Reptiles is offered, this one will be provisionally
accepted.
Page:Evolution of Life (Henry Cadwalader Chapman, 1873).djvu/86
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62
EVOLUTION OF LIFE.