The Ichthyosaurs lived upon fishes and cuttlefish, as is indicated by their dentition and the shape of the snout, and proved by the coprolites, most of which are full of fragments of bones and ganoid scales of fishes, and of the beaks and shells of cuttlefish; the larger of these true coprolites (literally "petrified dung"), in coprolite-beds, contain also an abundance of other fossils, such as Ammonites, Terebratulae, molluscs and fish-remains; they are several inches long, and many of them show on the outside ring-like impressions, undoubtedly caused by a spiral valve of the intestinal canal. In conformity with their absolutely aquatic life the Ichthyosaurs were viviparous. Several well-preserved adult specimens have been found, which contain the skeletons of one or more rather large young within the body, in exactly the position in which such foetal creatures would lie, namely, with the head in the pelvic region of the mother, while the rest of the body stretches along the vertebral column towards the chest. The suggestion that these young Ichthyosaurs have been swallowed by their cannibal elders is too idle to require serious refutation.
Until within a few years Ichthyosaurs were always restored with a smooth and even back, but several well-preserved specimens have come to light in Würtemberg which show the complete contour of the animals, with a long, somewhat jagged fin on the middle of the back. Since then not a few specimens in various collections have on closer examination revealed the same feature, except, of course, those in which the outlines of the fin had been chiselled away in order to "improve" the look of the slab. The fins were undoubtedly of the "adipose" kind;–raised folds of the skin. The latter is now known to have been covered, at least at the bases of the dorsal fins, with hard little scales, probably osteoderms.
Many specimens are beautifully preserved, others present a very peculiar appearance. They look, namely, like long rolls of clay, and nobody but an expert would suspect an Ichthyosaurus within such a log. The explanation is simple. The dead creature was rolled about by the waves of the surf on the Liassic muddy beach until it was wrapped in a mantle of clay and then imbedded on the shore.
The distribution of Ichthyosaurs in time and space is wide. The earliest are found in the Middle Trias; in the Lias they are very common, fairly frequent in the Oolites, dying out with the Cretaceous epoch. They have left no descendants, being far too specialised, and their origin is quite unknown. Mixosaurus, the oldest genus, occurred in Europe, and has also been found in the Triassic strata of Spitsbergen. Ichthyosaurus, the chief genus, is known from the Liassic, Oolite, and Cretaceous strata of Europe, a famous place being Lyme Regis; and also from the Cretaceous strata of Queensland and New Zealand. The Jurassic of Wyoming has yielded Baptanodon.
Fig. 115.–Restored outlines of Ichthyosaurus quadriscissus. (After Fraas.)
Order ICHTHYOSAURI.
The few genera are easily recognised.
Mixosaurus, Triassic, with radius and ulna still elongated, a longitudinal space occurring between them. Both jaws with numerous uniform teeth.
Ichthyosaurus, with much shortened radius and ulna; both jaws with uniform series of teeth. Many species are known, some with four to five, others with several additional and incomplete rows of fingers and toes. I. trigonodon of the Lias in Würtemberg seems to have reached the size of 30 feet, the vertebrae showing a diameter of 9 inches, while the skull is 6 feet long. I. communis and I. tenuirostris are common in the English Lias. The long-snouted I. campylodon, with large, spaced teeth, occurs in the Gault of Cambridge, Dover, and France; and there are many others. Ophthalmosaurus, of the Upper Oolitic and Cretaceous formations of England, had very small vestigial teeth.