ICHTHYOSAURI 483 



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 Eegis ; and also from the Cretaceous 



FIG. 115. Kestored outlines of Ichthyosaurus quadriscissus. (After .Kraas. ) 



strata of Queensland and New Zealand. The Jurassic of 

 Wyoming has yielded Baptanodon. 



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 incom- 

 plete rows of fingers and toes. /. trigonodon of the Lias in 

 Wiirtemberg seems to have reached the size of 30 feet, the 

 vertebrae showing a diameter of 9 inches, while the skull is 6 

 feet long. /. communis and /. tenuirostris are common in the 

 English Lias. The long-snouted /. campylodon, with large, spaced 

 teeth, occurs in the Gault of Cambridge, Dover, and France ; and 



