The neck is sometimes moderately
long, but oftener very short, as the great size and weight of
the head would have led one to anticipate. Bony plates seem in
some species to have formed an at any rate partial covering to
the skin; but it is not certain that these integumentary appendages
were present in all. Upon the whole, there can be no doubt but
that the Mosasauroid Reptiles--the true "Sea-serpents" of the
Cretaceous period--were essentially aquatic in their habits,
frequenting the sea, and only occasionally coming to the land.
[Illustration: Fig. 210.--Skull of _Mosasaurus Camperi_, greatly
reduced. Maestricht Chalk.]
The "Mosasauroids" have generally been regarded as a greatly
modified group of the Lizards (_Lacertilia_). Whether this reference
be correct or not--and recent investigations render it dubious--the
Cretaceous rocks have yielded the remains of small Lizards not widely
removed from existing forms. The recent order of the _Chelonians_
is also represented in the Cretaceous rocks, by forms closely
resembling living types. Thus the fresh-water deposits of the
Wealden have yielded examples of the "Terrapins" or "Mud-Turtles"
(_Emys_); and the marine Cretaceous strata have been found to
contain the remains of various species of Turtles, one of which
is here figured (fig. 211). No true Serpents (_Ophidia_) have
as yet been detected in the Cretaceous rocks; and this order
does not appear to have come into existence till the Tertiary
period.
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