16 



NATURAL HISTORY OF THE TKIMEVAL WORLD. 



reptiles which haunted the shadows of these primeval 

 forests are represented by the Lcibijrmthodon, which 

 descends towards the sea on the right, and whose oiui- 

 oiis footprints have been preserved, imprinted in the 

 indurated sand, down to our own days, as if designed 

 to answer the interrogations of science by their strange 

 memorials of a long-vanished age. 



THE JURASSIC PEBIOD. 



We now come, in our survey of the animal life of 

 the primeval world, to the Jurassic period, so named 

 from tiie Jura mountains in France, which consist of 

 the rocks deposited by the seas of this era. 



It is subdivided into two sub-periods : tlie Lias and 

 the Oolite. 



Both in its fauna and its flora it displays " a very 

 striking assemblage of characteristics : " many genera 

 of animals belonging to the preceding formations have 

 disappeared, and their places been filled up by new 

 genera, comprising a very peculiarly organized group, 

 which included not less than four thousand species. 



Tlie Lias. — This is the name given by English geo- 

 logists to an argillaceous limestone, mixed with marl 

 and clay, which forms the base or lower stratum of the 

 Jurassic formation, and have a mean thickness of about 

 three hundred feet. 



Herein the naturalist meets with zoophytes, molluscs, 

 and fishes of a singular organization ; but, above all, 

 with reptiles of a size so extraordinary and a structure 

 so marvellous, as to give the Liassic seas an interest and 

 a character of their own. 



First let us examine the Plesiosaunts, which Cuvier 

 pronounced the most monstrous animal that has yet been 

 dug out of the ruins of a former world. 



We gather from its name — 'irXrjgioi, " near," and 

 auuDo;, ''lizard " — that it was nearly allied by its organi- 

 zation to the Sanrians. But in appearance it seemed 

 a compound of many animals; it had a lizard's head, 

 a crocodile's teeth, a neck of excessive length resem- 

 bling a swan's, the ribs of a chameleon, a body and fail 

 whose jiroportious were those of an ordinary quadruped, 

 and, finally, the paddles of a whale. Such was the 

 apparentlygrotesque and fantastic monster which roamed 

 through the Liassic ocean, seeking what it might devour. 



The head of the Plesiosaunis, says Figuier, in his 

 popular history of "The World before the Deluge," 

 presented a combination of the characters belonging to 

 the ichthyosaurus, the crocodile, and the lizard. Its 

 long neck consisted of a greater number of vertebrce 

 than the neck of either the camel, the giraffe, or even 

 the swan, which of all the feathered race has the longest 

 neck in proportion to the bulk of its body. And in 

 birds it is to be noted, that contrary to the structure of 

 the Mammalia, where the vertebra of the neck are never 

 more or less than seven, their vertebrae increase in 

 immber as the neck increases in length. 



The body of the Plfsiosaurus was rounded and 

 cylindrical, like that of the C/ielonice, or great marine 

 turtles. Some authors suppose it to have been invested 

 in a carapace or scaly armour ; but of this there is no 

 proof, and no traces of any such covering have been 

 recognized with the fossil remains hitherto examined. 



In its breast, pelvis, and the bones of its anterior and 



posterior extremities, the Plcsiosaurus possessed an 

 apparatus which permitted it, like the Cetacea of our 

 present seas, to sink in the water or ascend to the sur- 

 face at pleasure. That they were air-breathing and 

 cold-blooded animals is proved, as Professor Owen 

 shows, by the position and conformation of the nasal 



Tclitbyosriurus platytlon. 



passages, as well as by the bony mechanism of tlie 

 thoracic duct and abdominal cavity. 



Many points in the anatomical structure of this huge 

 animal are particularly worthy of the naturalist's atten- 

 tion. The vertehrre of its back were not arranged, as 

 is the case with fishes, in hollow cones, but their surfaces 

 were nearly flat, and tlius the column had a firmness 

 and solidity like that which exists in the back of terres- 

 trial creatures. Such a contrivance was rendered neces- 

 sary by its immense length and bulk. For the same 

 purpose the articulating processes were locked into one 

 another, just as the architect, in erecting a column, 



