Samuel Wendell Williston

“ Did they occur rarely in organisms they would not trouble us much; but they are everywhere in nature, and the problem of all classification is to distinguish between them and those characters due to heredity. Until we have learned to distinguish them our classification must remain more or less artificial.
The true end of all classification is genealogy. Some time in the Carboniferous period there was but a single kind of reptile, differing very slightly from its ancestors, and from this reptile has descended all the kinds that have ever lived. ”

“ Doubtless the species of the past geological ages outnumbered many times, perhaps hundreds of times, all those now living, since many of these latter are merely the remnants of far more varied and extensive faunas. At times the conditions for the preservation of the remains of animal life have been more favorable than at others, and, under such favorable conditions, a fairly good glimpse is sometimes given us of the fauna of some isolated epoch and locality in the earth’s history. ”

“ In no reptiles is the pelvis more aberrant than in the Crocodilia (Fig. 121) . So characteristic is its structure that it at once distinguishes the order from all others. The ilium is a strong bone firmly united with the two pairs of stout sacral ribs, of which the posterior is the larger. Below, the ilium articulates with the ischium only, to form the acetabulum. In front of the acetabulum it is produced forward to join ligamentously with an anterior process of the ischium, enclosing between them a foramen of considerable size for the passage of the obturator nerve. ”

“ None of the crocodiles which we have considered, whether ancient or modern, can truthfully be called purely aquatic. They never ceased to use their limbs for locomotion on land, more or less of the time, or for the support of the body; and many of them have subsisted, in part at least, on land animals. How easy it may have been for some of them to become almost wholly emancipated from land habits we may easily conjecture. The gavials, as we have seen, are more at home in the water than upon land; their food is chiefly found in the water ”

“ The pelvic girdle or pelvis, in reptiles, as in other air-breathing vertebrates, is composed of three bones on each side, more or less firmly coössified in the adult, and collectively known as the innominate; the girdle is completed by the sacrum on the dorsal side with which the pelvis is never closely united in reptiles, not even in the Pterosauria. The upper or dorsal bone of the three, that to which the sacral ribs or transverse process of the lumbar vertebra are attached, is the ilium; the one on the lower or ventral side in front is the pubis ”

“ There are now living upon the earth more than four thousand kinds or species of cold-blooded animals which we call reptiles, all of which are easily distinguishable into four principal groups: the serpents and lizards, the crocodiles, the turtles, and the tuatera. Their habits and forms are very diverse, but they all possess in common certain structural characters which sharply distinguish them from all other living creatures. A reptile may be tersely defined as a cold-blooded, backboned animal which breathes air throughout life. ”

“ In no reptile did the atlas attain the specialization of the mammals, even approximately, but it most nearly approached it in the Theriodonts. In very few do the two bones of the arch fuse with the intercentrum into a complete arch ring, or does the pleurocentrum unite with the axis as a real odontoid. In few is there any degree of rotation about it, not more than between the axis and the following vertebra. This lack of torsion, in most reptiles at least, was compensated for by the ball-and-socket joint between the single condyle and the atlas, lost in mammals. ”

“ As a rule one can seldom be quite sure of the species of a reptile unless the larger part of the skeleton, or at least the skull, is available, although almost any bone of the skeleton, if one is expert, will permit a decision as to the family, if not the genus.
One must often depend upon the positions and relations of the bones, as found in the rocky matrix, for the final determination of many characters. One can, for instance, never be sure of the number of bones in the neck, trunk, tail, or feet of a reptile, until specimens have been found with all such bones in position. ”

“ It is in the limbs that most extraordinary differences from all other animals are seen. So great are these differences that it has been a puzzle to naturalists to understand how they could have arisen. In no other animals above the fishes, that is, in no other reptiles, in no amphibians, birds, or mammals, are there ever more than five fingers or five toes, the number with which air-breathing animals began. Fingers and toes may be lost and often are lost in all groups of life, until a single one in each limb may remain, as in the domestic horse. ”

“ There have been many animals of high and low rank which in the past and present have gone back from a terrestrial existence to a life in the water, finding at last a congenial home away from the shores. Or, perhaps, like the monitor lizards of today, they have found temporary safety in the water when hard pressed by their land enemies, and finally found, not only protection, but an abundant supply of easily obtainable food therein. As in every vocation of life there have been many failures in such attempts, many partial successes only. ”

“ But not a few have found abounding and enduring success and final prosperity—success that has led possibly to undue adaptation to surroundings, and to the acquirement of great size, for that has been the invariable end of water air-breathers of long duration—specializations which finally prevented them from meeting new exigencies. It seems to be a law of evolution that no large creatures can give rise to races of smaller creatures; and as we shall see, the largest sea-animals have been the final evolution of their respective races. ”

“ It is apparently a law that evolution is irreversible, that it never goes from the special to the general, that an organism or an organ once extinct or functionally lost never reappears. And it is also a law in evolution that the parts in an organism tend toward reduction in number, with the fewer parts greatly specialized in function, just as the most perfect human machine is that which has the fewest parts, and each part most highly adapted to the special function it has to subserve. ”

“ It is evident that a movable neck of considerable length would not only be of no use to the swiftly swimming fish, but a positive disadvantage to it. The body is quickly and easily turned by the powerful tail fin, and a long neck could be of no use that the tail would not better subserve. It is therefore of interest to learn that, as a rule, aquatic animals of all kinds having a powerful propelling tail have also a short neck, acquired either by the loss of neck vertebrae, or, as in the mammals, by the shortening and coalescence of the normal number of seven. ”

“ In the adaptation to water life the first to become modified for the control of the body are the front legs. The hind legs never have any really important use when the tail is a powerful propeller. The hind legs of the geosaurs are still essentially legs and not paddles, and they were doubtless used either occasionally for propulsion on land, or perhaps for pushing the body about on the bottom of shallow waters. And the presence of a well-developed ventral armor of bony ribs possibly also indicates more or less of the terrestrial crawling habit. ”

“ But a single skull of a true land lizard has been discovered in the Triassic deposits of South Africa, a skull of a form so nearly like that of the modern iguana of America that its discoverer, Dr. Broom, has called it Paliguana. The lizards must have been in existence, probably many thousand species of them, during all the great interval of time between the Middle Triassic and the close of the Cretaceous, since it is a law which can have no exception, that a type of life once extinct never reappears. ”

“ Woodward has said that the fate of all fishes, if they continue their evolution long enough, is to become eel-like.
Not only was the tail greatly elongated in swimming reptiles, but it was also more or less flattened. In the beginning of water adaptation the flattening was throughout the tail, as in the living alligators and crocodiles. As the adaptation to water life became more perfect, the flattening became more and more restricted to the extremity; that is, the flattening begins like that of a salamander and in the end becomes like that of a fish, a terminal fin. ”

“ Indeed, with the exception of some of the lowliest and most generalized forms, or man himself, no species are the same throughout the earth today. Inasmuch as we must depend upon the fossils in the rocks for the determination of the ages, where none is quite the same in strata of remote localities the identification becomes very difficult or even impossible. Nor are the periods, as accepted, of equal or even approximately equal duration; the Cretaceous period, for instance, was longer than all the remainder of the Mesozoic, longer perhaps than all the time which has elapsed since its close. ”

“ It is an interesting fact in the history of the vertebrates, as of all other groups of animals and plants, that the chief divisions arose early in geological history. Every known order of amphibians and reptiles, unless it be that including the blind-worms, was differentiated by the close of the Triassic period. The frogs are now known from the Jurassic. The mammals and birds also quite surely date their birth from the Triassic. And this early differentiation of the chief groups is doubtless due to the fact that the potentialities of diverse evolution are limited by specialization. ”

“ Hence, classification simply represents the present condition of our knowledge, our present opinions as to genealogies. It was the fashion a dozen years ago to draw all sorts of genealogical trees on the slightest pretext, to trace in beautifully clear lines the precise descent of all kinds of animals; [Pg 14] and very few have been worth the paper on which they were printed. When facts are numerous enough, conclusions are patent even to the novice; when facts are few and obscure, one can guess about as well as another. ”

“ Because the legs are no longer needed for the support or propulsion of the body in long-tailed air-breathers, their connection with the body becomes less and less firm, long before their entire disappearance. In animals using the legs for crawling or walking the bones of an arm and thigh are elongated, and the joints are always well formed, permitting varied, extensive, and firm movements. Just the reverse is the tendency in all those animals that propel themselves by the aid of the tail in the water, since here what is needed is broad, short limbs, not long and slender ones. ”

“ THE SKELETON OF REPTILES
The bony framework, or skeleton, that which gives form and stature to the body, and which serves for the support of the soft parts and the attachment of muscles, is, with rare exceptions, all that is ever preserved of fossil animals. Because, therefore, students of extinct animals must rely so much, if not exclusively, upon the skeleton much attention has been given to the study of comparative osteology, the science of bones. ”

“ As would be expected, the greatest modifications of structure in the adaptation of air-breathers to water life are found in the limbs. No other parts of the body have such different functions in water and on land as the limbs and fins. The limbs of a dog, or a cat, or a man are feeble organs for swimming in comparison with the fins of a fish, and if the land animal must compete with fishes to prey upon them for food it must acquire like swimming powers. ”