838 LIFE : OUTLINES OF GENERAL BIOLOGY 



conditions in Triassic times, and with this may be associated the 

 waning away of many of the older spore-bearing plants and a new 

 impulse to the seed-bearers. The difficulty of linking the Mesozoic 

 vegetation to the Palaeozoic has led some botanists, notably Church, 

 to the theory that there was a recurrent colonisation of the land 

 from the primeval marine plants — an inexhaustible Algoid stock. 



Zoologically we think of the Triassic Period as one in which the 

 dominant reptiles made many tentatives of habit and showed many 

 divergences in detailed structure. Probably associated with the 

 aridity was the acquisition of a bipedal mode of progression by some 

 of the Dinosaurs. It is interesting to notice that the large (up to 

 5 feet) Collared Lizard (Chlamydosaurus) of Australia is at home in 

 arid conditions, and is strikingly bipedal; and there are other 

 instances of the correlation. The first known remains of mammals 

 are Triassic; they seem to have been pigmies as compared with the 

 reptiles, but there was a promise of victory in their brains. 



Fish-Lizards or Ichthyosaurs. — Ichthyosaurs were once com- 

 mon in the ancient seas; they ranged from the Triassic, through 

 the Jurassic, to the Cretaceous, when they disappeared. We do not 

 know from what simpler stock they may have been evolved ; and we 

 do not know that they had any descendants. Appearing in large 

 numbers from an unknown ancestry, they had their Golden Age 

 for millions of years. For some unknown reasons they then began 

 to decline, and there is no trace of any after the Chalk Period. Their 

 remains show no particular resemblance to those of any other order 

 of reptiles, extinct or extant; they form a somewhat homogeneous 

 order of reptiles, quite by themselves and in many ways unique. 



We know that Ichthyosaurs were marine, and that they were 

 carnivorous ; that they varied in size from a yard in length to 30 or 

 40 feet; and that, apart from the somewhat primitive Mixosaurus 

 and the somewhat decadent Ophthalmosaurus, they were all very 

 Hke one another, being similarly adapted to swift swimming in the 

 sea and to catching cuttlefishes and true fishes. This meant some 

 expertness in swimming, and for this the shark-shaped or dolphin- 

 like body was well suited. It says something for palaeontology that 

 a diet of cuttlefishes can be safely inferred from the fossils, for the 

 parrot-beak-like jaws, characteristic of Cephalopods, are easily 

 recognisable inside the petrified body. It may be that the appetite 

 of the Ichthyosaurs accounts for the disappearance of some of the 

 ancient types of cuttlefishes long since extinct. 



Picture a lithe body, almost neckless, more porpoise-like than 

 shark-like, with a long-snouted skull and two pairs of somewhat 

 paddle-shaped limbs. Perhaps "trowel-shaped" would be a more 

 accurate term, for they tapered to a point. On the back there is a 

 jagged fatty fin, or a succession of several. There may be some 



