NATURAL HISTORY OF THE PRIMEVAL WORLD. 



17 



clamps togetlier the massive stones as be rises stage 

 by stage. Rapidity of motion was not essential for 

 the Plcsiosaurus, whose colossal proportions rendered 

 it formidable to nearly all then existing animals, and 

 which, for oSensive and defensive purposes, could trust 

 to its size and strength. Its tail, therefore, was com- 

 paratively short, and not used, like the tail of a fish, as 

 an instrument of swift impulsion ; but rather as a steer- 

 ing apparatus, by which it directed its course along the 

 water, and its movements of ascent and descent. 



Rapidity of motion was, in truth, impossible for an 

 animal with so elongated a neck, situated at such a dis- 

 tance in front of the anterior paddles. 



The total number of vertebrse in the entire column 

 ■was about ninety. 



If we now turn to the structure of its ribs, we shall 

 see that they were admirably adapted to give it the 

 power of compressing air within its lungs, and con- 

 sequently of remaining for a lengthened time at the 

 bottom of the water. 



They consisted of two parts, one vertebral and one 

 ventral ; tlie ventral portions of one side uniting with 

 those on the opposite by an intermediate transverse 

 bone, in such wise that each pair of ribs girdled the 

 huge body with an unbroken belt, made up of five 

 parts. A close similarity of structure may be observed, 

 among existing animals, in the chameleon, and in two 

 species of iguana, the Lacerta marmorahi, and Lacerta 

 anubis. 



It has been conjectured, from the great size of the 

 lungs of tlie Plcsiosaiirus, as shown by this conforma- 

 tion of the ribs, and the varied intensity of its inspira- 

 tions, that it possessed the power of changing at will the 

 colour of its skin. We have no means of verifying this 

 conjecture, but admit that such a provision would have 

 been invaluable for an animal so heavy and unwieldy, 

 which, 



" Like a wounded snake, drew its slow lengtli along," 



as defending it by concealment from its most formid- 

 able antagonist, the Ichthyosaurus. In any contest 

 with the latter, its chances otherwise must have been 

 very few : it could not cope with it in assault, owing to 

 its diminutive head and long slender neck ; it could not 

 escape from it by flight, owing to its limited powers of 

 locomotion. 



The Plesiosaurus being an air-breathing animal, 

 would require to ascend to the surface frequently for 

 respiring purposes. This was effected by the agency 

 of an ingenious apparatus in the chest and pelvis, and 

 in the bones of the arms and legs, which enabled it to 

 ascend and descend in the " fluent tracts of ocean " like 

 our modern Cetacea — its legs being converted into long 

 and very powerful paddles. 



If we compare these extremities with those of other 

 vertebrated animals, we shall discern a perfectly regular 

 series of "links and gradations," from the corresponding 

 parts of the highest Mammals to their rudimentary forms 

 in the fins of fishes. 



The fore paddle of the Plesiosaurus presents us, 

 typically, with all the essential parts of the fore-leg of 

 a quadruped, even of a human arm. First, the scapula, 

 or shoulder-bone; then the humerus, or arm-bone; 



next, the radius and the ulna, which are succeeded by 

 the bones of the carpus and metacarpus; and these 

 followed by five fingers, each composed of a continuous 

 series of phalanges, or joints. Similar analogies to the 

 leg and foot of the Mammalia may be detected in the 

 posterior paddle : the pelvis and femur, or thigh-bone, 

 are succeeded by tibia and fibula, which duly articulate 

 with the bones of the 

 tarsus and metatarsus, 

 followed by the numerous 

 phalanges of five long 

 toes. 



Founding his conclu- 

 sions upon these inter- 

 esting data, Professor 

 Conybeare remarks : — 

 That the Plesiosaui-us 

 was aquatic is evident 

 from the form of its pad- 

 dles ; that it was marine, 

 is almost equally clear 

 from the remains with 

 which it is universally 

 associated; that it may 

 have occasionally visited 

 the shore, we infer from 

 the resemblance of its 

 extremities to those of 

 the turtle. On land, 

 however, its motion must 

 have been singularly 

 awkward ; its long neck 

 must have impeded its 

 progress through the 

 water; presenting a re- 

 markable contrast to the 

 organization which so 

 admirably fitted the Ich- 

 thyosaurus for cleaving 

 the waves. 



May it not, therefore, 

 be concluded — since, in 

 addition to these circum- 

 stances, its respiration 

 must have necessitated 

 frequent supplies of fresh 

 air — that it swam upon, 

 or near, the surface ; 

 arching back its long 

 neck like the swan, and 

 occasionally darting it 

 down at the fish which 

 came within its reach ? 



At times, too, it may 

 have lurked in the weedy 

 shoals along the coast, where, buried among the rank 

 luxuriance of the aquatic plants, and raising its nostrils 

 to a level with the surface from a considerable depth, it 

 may have found a secure asylum from the attacks of its 

 formidable enemies. The length and flexibility of its 

 neck must to a great extent have counterbalanced the 

 deficient strength of its jaws, and its incapacity for rapid 

 motion on land or water, by the suddenness and direct- 

 c 



m 



Skeleton of Plesiosaurns doliclm- 

 deirns restored. (Conybearo 

 principally.) 



