TRIASSIC PERIOD 79 



creatures probably still spent a good portion of their time on 

 land. This may be inferred from the limbs not having 

 acquired that complete paddle structure which characterised 

 the later forms. 



Other reptiles known as ichthyosaurs or " fish-lizards " ichthyo- 

 — also probably descended from land-haunting ancestors — saurians 

 had certainly gone steps further from terrestrial life, and had 

 become whale-like in shape (Mixosaurus). They were short- 

 necked, long-jawed creatures, with sharp, conical teeth. The 

 tail in its lower lobe was possessed to its extremity by a sharp 

 down-curvature of the spine — a curvature reverse in direction 

 to that in the old-fashioned fish-tail. This novel construction, 

 no doubt, facilitated the ascent of the animal when seeking 

 the surface for fresh supplies of air ; but it cannot have been 

 so efficient for that purpose as the tail with horizontal 

 lobes such as whales possess. All four Umbs to out- 

 ward appearance were fins or paddles ; but fingers and 

 toes, although undergoing modifications, were still defined 

 within. 



The largest of the Triassic forms did not exceed a yard 

 in length. They were doubtless consumers of fishes ; but 

 they developed a great partiality for belemnites. These 

 they must have found highly nutritious, as will be seen 

 later. 



Forerunners of tortoises had appeared in the Permian chelonians 

 Period ; and this Order of reptiles was now represented by 

 animals not far short in development of modem forms. The 

 ancestral sluggishness had been confirmed ; and an unearned 

 increment of armour-wealth had resulted. There seem to have 

 been both " hidden-necked " (Cryptodira) and " side-necked " 

 (Pleurodira) animals as at the present day — some that could 

 telescope the neck and envelop the head in the box-like 

 armour (Chelyzoon), and some that could only shelter the 

 head by bringing it round under the side-edge of the upper 

 shield (Proganochelys, Pleurosternum). 



Triassic chelonians probably spent placid, uneventful lives 

 in the swamps and rivers, and never ventured out to sea. 

 They doubtless had foes among the less lethargic reptiles ; 

 but they were fairly safe within their bony walls. 



