WAYS OF THE WILD.

Auckland Star, Volume LXVI, Issue 98, 27 April 1935, Page 1 (Supplement)

WAYS OF THE WILD.

ICHTHYOSAURS.

FISH-LIKE LIZARDS,

(By A. T. PYCROFT.)

The ichthyosaurs (from two Greek words, fieli lizard), which varied in length from two to thirty or more feet, presented a startling similarity in outward form to the long-nosed dolphins, and, like these and other whales, they were descended from land-living ancestors, which, through a long course of evolution, had become perfectly adapted for a life in the ocean. They had a cylindrical streamlined body, with a long, slender snout, the jaws armed with sharp recurved teeth, which occu- | pied a groove in the jaws and were not set in separate sockets as in the crocodiles and similar reptiles. There was little evidence of a neck, ana the smooth, scaleless body tapered to a long, powerful tail, ending in a vertically-placed two-lobed caudal, or tail, fin resembling that of certain fishes, while the end of the backbone was continued downwards into the lower lobe. In the whales the caudal fin is placed horizontally, no doubt a provision to enable these warmblooded animals to make a quick ascent to the surface. The eyes were very large, and the eyeball was surrounded by a strong ring of bones, the purpose of which was doubtless' to protect the eye and give greater control over vision. This provision probably indicates that the ichthyosaurs were accustomed to descend to great depths in the ocean waters, where the pressure is considerable. The joints of the backbone were disc-like, and deeply concave at both ends like those of fishes. No doubt in life the hollows were filled with elastic tissue, which imparted pliancy to the vertebral column. The animals had two pairs of flippers, of which the front pair were the more powerful. The bony structure of these flippers was very remarkable, considering that the ichthyosaurs are descended from terrestrial forbears with limbs adapted for progression on land. The upper arm and upper leg bones were short and thick, and the remaining bones of the limbs were so numerous and so different in shape from those of other reptiles that at first sight it is hard to believe that these paddles can have been evolved from normal reptilian limbs. They have more than the regulation five fingers and five toes, and the bones of the fingers and toes are not limited to the usual three, but are numerous and have a polygonal shape, fitting closely together to form a sort of mosaic.

A Peculiar Order of Extinct Reptiles,

Dr. Anderson, Director of the Australian Museum, states that many fine specimens of these interesting extinct reptiles have been found in various parts of the world, including Australia, and we now have a very good knowledge, not only of their bony structures, but also of their bodily appearance and their habits. Specimens found in California are estimated to be 180 million years old, as against 150 million for the beds of the Jurassic system. And knowledge of their immediate ancestors, their nearest relatives, and their evolution, is still incomplete. The rocks in which ichthyosaurs are found are always marine in origin, hence it is clear that they.lived in the ocean, and it is unlikely that they ever came ashore. The ichthyosaurs and the dolphins present an instructive example of what is known as convergence in evolution, for here we have two entirely different kinds of animals which nevertheless have, in each case, become fish-like and perfectly adapted to a life in the water, though their ancestors were land-living creatures, with normal walking or crawling limbs. Our knowledge of the mode of life of the fisli-lizards has been summed up by the great American naturalist. Professor H. F. Osborn, who, after tracing the ichthyosaurian paddle into a limb of the type of that of the existing terrestrial tuatara (splienodon) of New Zealand, which is regarded as nearly related to the ancestral stock of the group, points out that these reptile? had a dorsal and a caudal fin, a naked, scaleless skin, and a spiral valve to the intestine similar to that of sharks, while, from the inclusion of skeletons of young within the ribs* of full-grown individuals, it is evident that they produced living young. This viviparous condition is, of course, an adaptive modification, similar to that which occurs in the sea snakes of to-day, rendered necessary by the pelagic habits of these reptiles.

Early Discoveries. Towards the close of the seventeenth century, a Welshman named Lliuyd published a work containing illustrations of the remains of Ichthyosaurs, which he believed to be fishes. Lhuyd accounted for these and other fossils by supposing that they grew in the earth from germs derived from living animals, the spawn of fish and eggs of other animals' being carried up in vapours to the clouds, when they descended in rain. Koenig, sometime keeper of geology in the British Museum, was in 1821 the first to use the name ichthyosaurus, fish lizard, apparently regarding the animals as being intermediate between fishes and reptiles. In succeeding years the structure of these creatures was carefully studied by various learned men and, it was clearly recognised that they constituted a peculiar order of extinct reptiles. The food of ichthyosaurs was mainly fish, for the capture and retention of which their teeth were well adapted, but apparently squids also formed part of tlicir menu, for the hard parts of these are also found. One ichtliyosaur specimen has been found in the stomach of which is a mass composed of the remains of more than two hundred belemites, extinct relatives of modern squids. It is evident that the jaws of ichthyosaurs could not be opened widely, as is the case with snakes, and their prey must have been mostly of small size. The fact that their remains are found in such abundance in certain localities would indicate that they were gregarious in habit, as are the marine mammals, such as seals, dolphins, and porpoises.

In Australia, remains of ichtliyosaurs have been discovered in rocks of the Cretaceous age, tlie period following on the Jurassic, which was apparently the golden age of the European forms. The first to record the occurrence of ichtliyosaurs in Australian rocks was the late Sir Frederick McCoy, who, in 1807, described certain remains from the Flinders River, Queensland, the latest discovery being in 1922. It is evident that so far the ichthyosaurian remains found in Australia are by no means complete, but it is evident that these interesting reptiles did exist in the Cretaceous sea of Australia, and it is possible that more and better specimens may yet be discovered there.