NOTHOSAURIA
A few years after the discovery of the plesiosaurs by Conybeare, the remains of animals of allied kinds were found in the Triassic rocks of Bavaria. At first they were supposed to be those of true plesiosaurs, and even the astute Cuvier was not very clear about them. Cuvier was the first to call attention to them, expressing the opinion that some of the fossils were of previously unknown animals allied to the crocodiles, lizards, and plesiosaurs. It was von Meyer, however, who first introduced a nothosaur to the scientific world under the name Conchiosaurus. A year later Count George of Münster described other forms under the name Nothosaurus, meaning “false lizard.” Count von Münster was a most zealous collector of the fossils of the Triassic deposits of Bavaria, amassing, after thirty years of active and enthusiastic labor, a very large amount of material, which, at his death, was purchased by the King of Bavaria and placed in the hands of von Meyer for study. Von Meyer was to Germany what Owen was to England, a man of deep learning, having an extensive knowledge of comparative anatomy, and being thorough and critical in his work. His descriptions and illustrations of these rich collections made by von Münster are masterpieces of scientific thoroughness. He recognized in Nothosaurus and other allied forms from the Bavarian Triassic a distinct group of semiaquatic reptiles allied to the plesiosaurs, and his conclusions have never been gainsaid. In more recent years additional remains of these animals from Bavaria and other places in Europe have been described, but none are known from other parts of the earth, or from other than Triassic rocks. Altogether about ten genera and about twice as many species have been described, probably all belonging in one family, and all by common consent now classified with the Sauropterygia.
Fig. 45.—Head and neck of Nothosaurus;
photograph of specimen in the Senckenberg Museum,
from Dr. Dreverman.
Fig. 46.—Pectoral girdle
of Nothosaurus, from
photograph by E. Fraas:
icl, interclavicle; cl, clavicle;
sc, scapula; cor, coracoid.
Fig. 47.—Pelvic bones of
Nothosaurus: il, ilium;
ac, acetabulum; p, pubis;
is, ischium.
(After Andrews.)
The Nothosauria were much smaller reptiles than the plesiosaurs, none of them perhaps exceeding the size of the smallest known plesiosaurs. They were semiaquatic in habit, with many curious resemblances to other semiaquatic reptiles of a later time known, as the dolichosaurs. The neck is more or less elongated, having about twenty vertebrae in the longest-necked forms; the body is moderately long, and broad, and the tail is relatively short. The vertebrae and ribs are quite like those of the plesiosaurs, that is, the vertebrae are gently concave at each end, and the dorsal ribs are attached by a single head to the transverse process high up on the arch; the cervical ribs are double-headed, precisely like those of the older plesiosaurs, one of the characters which insistently proves the relationships of the two groups. The bones of the shoulders ([Fig. 46]) also have many resemblances to the extraordinary ones of the plesiosaurs, though they are much less specialized. There was no sternum; the coracoids are large, though very much smaller than those of the plesiosaurs. The collar-bones are large and strong, joining each other in front of the coracoids and firmly united with the shoulder-blades at the outer extremity. Four vertebrae are united to form a sacrum, and their union with the hip bones ([Fig. 47]) was much firmer than was the case with the plesiosaurs. The limbs are elongated, but it will be observed in the figures ([Fig. 48]) that the radius and ulna, tibia and fibula, that is, the bones of the forearm and of the leg proper, are relatively very short as compared with the humerus and femur, a sure indication of the beginning of aquatic habits. The toes and fingers were doubtless webbed, and there was no increase in the numbers of bones in the digits, so conspicuous in the plesiosaurs. The external nostrils are large, but are not situated so far back near the eyes as in the plesiosaurs. There is a large pineal opening in the top of the skull, as in the plesiosaurs, but no sclerotic or bony plates have been observed in the eyes. They had ventral ribs like those of the plesiosaurs.
Fig. 48.—Legs of Lariosaurus balsami, an Upper Triassic nothosaur: h, humerus; r, radius; u, ulna; i, intermedium; ue, ulnare; f, femur; fi, fibula; t, tibia; a, astragalus; c, calcaneum. (After Abel.)
No impressions of scales or bony plates have ever been found with the remains of the nothosaurs, and it is the belief that the skin was bare. A good idea of their general appearance will be gained from the accompanying restoration adapted from that of Professor Fraas ([Fig. 44]) and the restoration of the less highly specialized Lariosaurus, made from a very complete skeleton in the Frankfort museum ([Fig. 49]).
It has been thought that these nothosaurs, so intermediate in structure between the true plesiosaurs and land reptiles, were the actual ancestors, but this is rather doubtful. It is probable that they were only very closely akin to the real ancestors, since in some ways they had become specialized too much, and, as we have already explained, highly specialized characters or organs can never go back to their earlier condition. The nothosaurs do prove beyond all possibility of doubt that the plesiosaurs were at least the descendants of animals closely allied to them, so closely, indeed, that it is doubtful whether we could distinguish external differences were all of them actually living at the present time.
Fig. 49.—Lariosaurus balsami.
We have repeatedly seen that all aquatic animals have some or all the bones of the limbs shortened, and it is of interest to observe that the early plesiosaurs had longer forearm and foreleg bones than the later ones, just as we have seen was the case with the early ichthyosaurs. It would seem probable that all the early plesiosaurs had long necks, though some of the late ones in Cretaceous times had relatively short necks, shorter even than the known nothosaurs possessed.
The nothosaurs doubtless lived about the shores of the ancient seas, spending much of their time in the water, leaving it perhaps when hard pressed by their enemies, as do some modern reptiles, or to rear their young. The teeth of the nothosaurs are long and slender in front, shorter behind. The animals must therefore have been carnivorous in habit, feeding probably upon such fishes as they could catch, and the various invertebrates which live in shallow water. The structure of the jaws and their attachments are quite as in the plesiosaurs, proving that they could not have swallowed large objects; but the skull is broader and flatter than that of most plesiosaurs, indicating habits not unlike those of the modern alligators and crocodiles.
Some time we shall doubtless find remains of nothosaurs or nearly allied animals elsewhere than in Europe, but probably not from later deposits than the Triassic. So far as we now know, their geological range and geographical distribution were much restricted; they evidently wholly died out shortly after the plesiosaurs appeared.
CHAPTER VII
ANOMODONTIA
LYSTROSAURUS
Over a large area of South Africa, chiefly along the Orange River and its tributaries, there is an extensive series of deposits many hundreds of feet in thickness, usually called the Karoo beds, which, for more than fifty years, have been widely famous among scientific men for the many and remarkable vertebrate fossils which they have yielded. These deposits seem to represent the whole of the vast interval of time from the Carboniferous to the Jurassic, that is, the whole of the Permian and Triassic, though not many fossils have been found in the lowermost strata. Among the fossils of the lower strata are those of the strange creatures described in the following pages as Mesosaurus. From the deposits representing the Upper Permian and the Triassic the fossils that have been obtained are both abundant and diverse. Unfortunately, however, of the scores of forms that have been discovered few are known completely, and still fewer are known sufficiently well to enable us to picture the living animals.
From the Upper Permian Karoo rocks two orders of reptiles have been recognized, the Cotylosauria, represented by more specialized forms than those from the Lower Permian of North America; and the order or group called by Broom the Therapsida. While the forms of this latter group have certain definite structural relationships with each other, they show so great a diversity among themselves that, when they shall be better known, it will be found necessary perhaps to separate them into several distinct orders.
At least five groups of the Therapsida are now recognized by Broom, the Dromasauria, Dinocephalia, Anomodontia, Therocephalia, and Theriodontia. Of all these the members of the last-mentioned group have attracted the greatest interest among geologists and naturalists, because of their intimate relationships to the mammals—so intimate, indeed, that they seem almost to bridge over the interval between the two classes. From higher Karoo beds primitive representatives of the more crocodilian types have been discovered, forms which seem to be the beginning of that order described on later pages as the Parasuchia.
It would lead us too far astray to mention even, let alone describe, the many forms of reptiles that have been discovered in the Karoo beds; nor indeed is it possible for anyone who has not attentively studied their remains to get a very clear conception of many of them, so incompletely have they been made known.
Doubtless from among all these diverse forms there have been not a few which sought wider opportunities in the water, but, if so, we have as yet very little knowledge of them. One form only, so far as the writer is aware, has been credited with aquatic habits, a remarkable reptile belonging to the group originally called by Sir Richard Owen, the Anomodontia, a word meaning “lawless teeth,” and to the genus Lystrosaurus, also described by the same noted paleontologist. A restoration of the skeleton of Lystrosaurus has recently been published by Watson. This restoration the writer has reproduced in the present pages, though he has taken the liberty of making some minor changes, to accord better with what he believes must have been the position of the shoulder-blades and the hind legs. And he would also suggest that the tail in life did not turn down so much at its extremity as depicted by Watson.
Both Broom and Watson believe that this animal was a powerful swimmer, and thoroughly aquatic in habit. To the present writer, however, this does not seem so evident. He is rather inclined to believe that the creature was chiefly terrestrial in habit, living probably in marshy regions, and perhaps seeking its food in shallow waters and in the mud. Aside from the position of the nostrils, which it will be observed are rather close to the eyes, a position so characteristic of many swimming reptiles and mammals, there is but little indication of aquatic adaptations elsewhere in the skeleton.
Fig. 50.—Skeleton of Lystrosaurus,
as restored by Watson, slightly modified.
The skull is of most extraordinary form. The face is turned downward, leaving the nostrils high up, in front of the eyes. The jaws were doubtless covered with a horny shield, like that of the turtles, having a cutting edge. There is a single pair of elongated canine teeth, possibly a sexual character. The lower jaws are heavy and stout, and Watson has said that the animal doubtless had the ability to open its mouth very widely. The quadrate, the bone with which the lower jaws articulate, is firmly fixed to the skull, and there is a single opening on the side of the skull posteriorly, a character common to all the Therapsida.
The vertebrae are stout, and they have stout spines. The tail is remarkably short, stout, and stumpy; it could have been of no use whatever in the water for propulsion or even for steering. The front legs are short and stout; the forearm bones are short, suggesting either swimming or digging habits, and the foot is short and broad. The pelvis or hip bones are massive and were very firmly connected with the backbone by the aid of six vertebrae, a very unusual number in reptiles. The hind legs, as figured, show no indications whatever of aquatic adaptation, unless possibly the very slight shortening of the shin may be so construed. Watson believes that the bones of the pelvis, indicate, aside from its strong union with the backbones, strong swimming powers, but of this again the present writer is very skeptical. The very strong ischia and the flatness of the pelvis are both characters found among American Permian reptiles, which do not show otherwise the slightest indications of water habits.
If then Lystrosaurus was a powerful swimmer, as has been maintained, it is very evident that the hind legs must have been used as the seals or sea-otters use them, to propel and to guide; but they in nowise resemble the legs of these swimming mammals. It seems altogether more reasonable to suppose that Lystrosaurus lived in the marshes, feeding upon vegetable food obtained by aid of its strong jaws and tusks—if the tusks were possessed by both sexes; and that the position of the nostrils may be ascribed to causes like those which brought about their recession in the Phytosauria, and not to strictly aquatic habits. Possibly the animal had habits somewhat similar to those of the hippopotamus; that it was an expert swimmer appears, to the present writer, improbable. The powerful front legs may be indicative of digging habits; the animal may have used them as an aid to its powerful jaws and tusks in uprooting marsh and water plants. However, Lystrosaurus, whatever may have been its habits, was a curious reptile. It was about three feet in length, massive in all its structure, and doubtless of slow and sluggish gait.
CHAPTER VIII
ICHTHYOSAURIA
Early in the eighteenth century a curious work in the Latin language was published by a famous physician and naturalist—a professor in the University of Altorf by the name of Scheuchzer—entitled Querulae Piscium, or “Complaints of the Fishes.” The work was illustrated by many expensively engraved figures of various fossil remains, including one of some vertebrae which the author referred to as “the accursed race destroyed by the flood”! The history of the finding of these famous bones is recorded by Cuvier as follows:
Scheuchzer, while walking one day with his friend Langhans in the vicinity of Altorf, a village and university of Nuremburg, went to the vicinity of the gallows to make some researches. Langhans, who had entered the inclosure of the gallows, found a piece of limestone containing eight dorsal vertebrae, of a black color and shining. Seized, says Scheuchzer, with a panic terror, Langhans threw the fragment of limestone beyond the wall of the inclosure, and Scheuchzer, picking it up, preserved two of the vertebrae which he believed to be human, and which he figured in his book, Piscium Querulae.
About the same time another observer by the name of Baier discovered other and similar vertebrae in the vicinity of Altorf which he described and figured as those of a fish; and there was much earnest contention between Scheuchzer and Baier, as also between their friends, as to their supposed nature. Scheuchzer’s figure was often cited as indubitable evidence of the destruction of mankind by a universal flood, and it was not until nearly a century later that Cuvier showed that the bones were really those of a marine reptile.
Fig. 51.—Restoration of Ichthyosaurus
with young, by Charles R. Knight.
(By permission of the
American Museum of Natural History.)
It must be recollected, in extenuation of so extraordinary a blunder on the part of so learned a man as was Scheuchzer, who, as a physician and professor, one would think ought to have been able to distinguish between vertebrae so different as are those of an ichthyosaur and a man, that, during all of the eighteenth century and well into the nineteenth, the belief was prevalent that all fossils were the relics of animals and plants that had perished in the great biblical flood. The science of geology was yet in its infancy, and there was no known record, other than the biblical one, of any great inundation of the earth’s surface which might account for the remains of sea-animals in rocks remote from the seas. This belief, so long held by even the wisest and most learned of scholars, so long welcomed by the theologians as proof of the literal accuracy of the Bible, was one of which Scheuchzer was quite convinced. His Piscium Querulae was largely a fantastic discussion of the supposed great world-catastrophe, the Noachian Deluge, by which the fishes had been destroyed and long imprisoned in the rocks through no sin of their own.
It was the same author who, in a subsequent work, described and figured the fossil skeleton of a large salamander which he believed to be that of a child destroyed in the flood, and which he called “Homo diluvii testis.” In this specimen, which was discovered in the Tertiary rocks of Oeningen, and which is still preserved among the historically as well as scientifically famous fossils of the museum at Haarlem under the name Andrias Scheuchzeri, Scheuchzer thought that he detected, not only the skeleton of a child, but even its brain, liver, muscles, etc.! His engraving of this “Witness of the Flood,” the “sorrowful skeleton of an old sinner drowned in the Flood,” as also that of the ichthyosaur vertebrae of Altorf, were afterward printed in the famous “Copper Bible” as positive proof of the literal accuracy of the biblical record.
Earlier than the publication of these figures by Baier and Scheuchzer, at the very close of the seventeenth century, a Welsh naturalist by the name of Lluyd, in a large and beautifully illustrated work, figured—perhaps for the first time—remains of ichthyosaurs, which he believed to be those of fishes. But Lluyd accounted for these and all other fossil remains by a very different theory from that of Scheuchzer and the theologians—a theory which at one time had many adherents among scholars. He believed that the spawn of fishes or the eggs of other creatures had been carried up from the seas and lands in moist vapors into the clouds, whence they had descended in rain, penetrating the earth to give origin to the fossils; in other words, he believed that all fossils grew in the earth from germs of the living animals that inhabited the land and seas. Certainly the old philosophers were hard driven to make facts agree with theories!
Remains of ichthyosaurs, abundant as they were and are in many deposits in England and Germany, attracted very little attention from the naturalists of the eighteenth century after the time of Scheuchzer and Baier, and nothing more was written about them until 1814, when Sir Everard Home, an English comparative anatomist, in an extensive series of large and finely illustrated, though rather discursive, works, described and figured a number of good specimens. To the animal the remains of which he rather vaguely and imperfectly described, he gave in 1819 the name Proteosaurus, in the belief that it was allied to the living Proteus, a salamander.
In 1821 the curator of mineralogy of the British Museum—Koenig by name—after a more critical study of other remains, reached the conclusion that these animals were intermediate between the fishes and the reptiles, and gave to them the generic name Ichthyosaurus, meaning fish-reptile, a name by which the chief forms have ever since been known. Within the next few years many specimens of ichthyosaurs were carefully and fully described by Conybeare, Cuvier, Owen, and others of England, France, and Germany, making very clear all the more important details of their skeletal structure. Blaineville, in 1835, thought that the ichthyosaurs constituted a distinct class of vertebrates equivalent to all other reptiles, the birds, and the mammals, which he called Ichthyosauria, the first appearance in literature of the name by which the order is properly known. Five years later, however, the famous English anatomist and paleontologist, the late Sir Richard Owen, united the ichthyosaurs with the plesiosaurs as a single order of reptiles, to which he gave the name Enaliosauria, meaning sea-reptiles, a name which has long been current in textbooks and general works on natural history. Moreover, Owen rather arbitrarily changed Blaineville’s name Ichthyosauria to Ichthyopterygia, a name which is often, though incorrectly, used to designate this order of reptiles. These briefly given and perhaps dry details will make clear how necessary is that rule of priority upon which naturalists so often insist. When anyone may change the names of organisms at will there will be no stability and no uniformity, because there is no one to decide, and the prestige of a great name, like that of Owen, will carry authority till someone else with greater authority appears. Whether or not the name Proteosaurus, first given to any member of this order, should take precedence over the later Ichthyosaurus is still in doubt, since Home gave no specific name to his species, and the very particular purists of modern times have decided that a genus is not named unless the species is also! We moderns sometimes are inclined to impose very stringent conditions upon the older naturalists; let us hope that we shall be treated more leniently by the future naturalists!
It will lead us too far astray to follow in detail the history of the further discoveries of the ichthyosaurs during the early part of the nineteenth century. It may briefly be said, only, that no other group of extinct backboned animals excited more interest among scientific men. One incident will suffice. More than sixty years ago, an interesting deduction as to the living form of the ichthyosaurs was made by Sir Richard Owen. He observed that many of the known skeletons, as they were found in their rocky matrix, had a remarkable dislocation of the vertebrae at a certain place near the end of the tail, and, although such an appendage was quite unknown in other reptiles either living or extinct, concluded that the living animals had a terminal, horizontal, fleshy fin, very much like that of the whales and sirenians. Sure enough, discoveries made forty years later disclosed impressions in the rocks, not only of a large caudal fin, but also of a dorsal fin, as well as outlines of the flesh-covered paddles. The dislocation of the vertebrae at the place where the fleshy fin joined the more slender tail was due to the action of currents of water, or simple gravitation, upon a thin vertical fin and not, as Owen supposed, to the twisting of the terminal part as it fell to a horizontal position after partial decomposition of the soft parts.
About twenty-five years ago, Professor E. Fraas, the present director of the Stuttgart Museum, described and figured very fully, not only specimens showing impressions of the fins and paddles, but also others of well-preserved and very complete skeletons of different species of ichthyosaurs from the Jurassic deposits of Würtemberg, in which remains of these animals occur in great profusion. His researches, and those of several authors since then, supplementing and confirming or disproving those of the many observers made during the preceding seventy years, have finally determined almost perfectly the complete structure of the more typical ichthyosaurs, enabling us to infer not a little as to their habits and distribution in the old Jurassic oceans. Within the past few years the discoveries of Professor J. C. Merriam of California have likewise added greatly to our knowledge of the earlier ichthyosaurs. It may now truthfully be said that of no group of extinct reptiles do we have a more complete and satisfactory knowledge than of the ichthyosaurs.
Fig. 52.—Ichthyosaurus quadricissus.
Photograph of specimen in Senckenberg museum,
from Dr. Dreverman.
Nevertheless we have yet very much more to learn about the order Ichthyosauria as a whole—whence they came and how they originated; what their nearest kin were among other reptiles; and especially, more about the connecting links between them and terrestrial reptiles. They have, as an order, so isolated a position, are so widely separated from all other reptiles in structure, that they have long been a puzzle to paleontologists. Like the whales and other cetaceans among mammals, we know the ichthyosaurs well in the plenitude of their power and the fulness of their development, but have yet only an imperfect knowledge of their earlier history, and none whatever of their earliest. However, as will be seen farther on, the recent discoveries by Merriam have shed much light on some of the stages of their evolution. So nearly perfectly were all the later ichthyosaurs adapted to their life in the water that it was believed by nearly all paleontologists until about a score of years ago that they had descended directly from fishes. But this belief has been quite abandoned by all, not only because the recent discoveries of the earlier ichthyosaurs have demonstrated a positive increase in the aquatic adaptations of the later forms, but also because a double origin of any type of animal life is quite out of accord with all known facts and principles of paleontology. It is quite possible for animals, in becoming adapted to peculiar environmental and food conditions, to acquire certain resemblances to other animals, but quite impossible for them to acquire their actual structure. The ichthyosaurs are true reptiles, and all reptiles must have had a common origin.
Fig. 53.—Baptanodon (Ophthalmosaurus). Skull from the side, from above, and from below (after Gilmore): ang, angular; bs, basisphenoid; d, dentary; fr, frontal; j, jugal; la, lacrimal; mx, maxilla; na, nasal; oc, occipital condyle; p, palatine; pa, parietal; pm, premaxilla; po, postorbital; ps, parasphenoid; pt, pterygoid; pf, prefrontal; sa, surangular; sp, splenial; sq, squamosal; st, supratemporal; q, quadrate; qj, quadratojugal.
Fig. 54.—Occiput of Baptanodon (Ophthalmosaurus): pa, parietal; soc, supraoccipital; sq, squamosal; exoc, exoccipital; op.o, paroccipital; sta, stapes; st, supratemporal; qu, quadrate; qj, quadratojugal; pt, pterygoid; bs, basisphenoid; sag, surangular; ag, angular; art, articular; pra, prearticular. (After Gilmore.)
We are sometimes in doubt, however, as to whether characters resembling those of other animals are really acquired as adaptations to peculiar environments, that is, parallel, convergent, or homo-plastic characters, or whether they are due to heredity from remote ancestors. The reptilian characters of the ichthyosaurs, however, are so emphatic that they can only be ascribed to heredity. Ichthyosaurs are as truly reptilian as crocodiles or snakes, notwithstanding their fish-like form and habits. The ichthyosaur ancestors were once truly land reptiles—of that we are as sure as we well can be. Some have thought that those ancestors were the primitive Rhynchocephalia, but most are now convinced that they were among the most primitive of reptiles, a branch probably from the cotylosaurs or cotylosaurian ancestors. Probably of all the extinct forms that we know the Proganosauria come the nearest; indeed it is not impossible that they may have been the actual forbears of the ichthyosaurs.
The ichthyosaurs varied in length from two to thirty feet, but the different species, especially all the later ones, resembled each other pretty closely in shape; the beak was more slender in some than in others, and the shapes of the fins and paddles varied not a little, as we shall see. The jaws were long and slender, provided with numerous rather small but sharp and recurved teeth, especially well fitted for the seizure and retention of slippery prey. The teeth were inserted, not in separate sockets, as are those of the crocodiles and many other reptiles, but in long, deep grooves, and were easily lost, indeed so easily lost that one late American form was originally described as edentulous, and it was not till a number of years had elapsed that the teeth were found. The nostrils were small, and situated far back on the sides of the face, near the eyes. The eyes were very large, not only in proportion to the size of the skull, but, in the largest species, actually attaining in some, perhaps, the size of a human head. The eyeball was surrounded in front by an extraordinarily large and strong ring of ossifications in the sclerotic membrane, giving not only protection to the eye under the varying pressure of the water, but also greater control over vision. The neck was very short, so short, in fact, that no construction was visible in the living animal between the head and body; it was capable of only slight movement. The trunk was elongated and relatively slender, sometimes with more than fifty vertebrae in it. The tail also was long and flattened, ending in all the later species in a large fleshy fin, resembling the caudal fin of many fishes in shape and doubtless also in function. There was also a large dorsal fin, supported by hardened or calcified sinews, in shape like the dorsal fin of most fishes and many cetaceans. This character is absolutely unique among reptiles, so far as is known, and was one of the extreme specializations of water life. The hind limbs were smaller, often much smaller than the fore ones, and both were quite fin-like in life, or rather flipper-like, though not at all fin-like in structure. The skin was smooth and bare. In brief, to quote Fraas’s words:.
The general aspect of the ichthyosaurs was very dolphin-like. The body was everywhere naked and probably dark in color. The head was produced in front into a long, slender snout, and was closely joined to the body posteriorly without indications of a neck. The body itself was cylindrical, expanded in front by the large thorax and abdomen, but rapidly diminishing into the long, slender, and strong tail. Close behind the head were the front paddles, which in some species were broad and shovel-like, in others elongated and pointed. The hind paddles were smaller than the front ones, sometimes greatly reduced in size, their function replaced by that of the very broad tail.
From the foregoing descriptions and the restoration shown in [Fig. 51], we see how very fish-like, or rather dolphin-like, these animals were in the external form—so fish-like that the name Ichthyosaurus is not misleading, though Koenig gave it in the mistaken belief that they were really allied to the fishes. When to these external features certain other fish-like details of the skeleton are added, we do not wonder that the early observers were so long in doubt about them. A more careful examination of the skeleton will, however, disclose so many truly reptilian characters that their external appearance and habits lose all significance.
The vertebrae are deeply biconcave and fish-like, it is true, but a consideration of the reasons therefor will convince us that any other kind of vertebrae would be more remarkable. At the time when the ichthyosaurs must have originated, at the time when the first known ichthyosaurs appeared in geological history indeed, all reptiles had biconcave vertebrae, and for the most part at least deeply biconcave ones. The vertebrae remained fish-like throughout all their history, perpetuating their type until most other reptiles had developed a firmer one, because such vertebrae were best adapted for the quick, pliant movements of the spinal column so necessary for the well-being of the animals in the water. In the modern dolphins, animals in shape, size, and habits most wonderfully allied to what these old reptiles must have been, the small, flat-ended vertebrae are widely separated by disks of flexible cartilage.
Not only were their vertebrae fish-like in form, but there are other characters in the spinal column of a primitive or generalized nature. As in all aquatic animals, the articulating processes between the vertebrae are either weak or wanting in the posterior part of the column. And they were not only small, but were situated, in many, high up, very remarkably resembling the peculiar arrangement of the articulations in the dolphins.
There is no sacrum, that is, there were no united vertebrae posteriorly for the attachment and support of the pelvis, as no such support was needed. In only one other group of aquatic reptiles was the sacrum lost, though it has wholly disappeared in the cetaceans and sirenians among mammals. The chevron bones of the tail, usually bony arches on the under side of the tail for the protection of the blood-vessels, in crawling reptiles, were very imperfectly developed in the later forms, though normal in shape in the early ones. The ribs are numerous, long, and slender, very much resembling those of the fish-eating dolphins. They usually had, however, two attachments to the body of the vertebra and none to the arch, differing in this respect from all other animals.
Of the shoulder bones, the scapula or shoulder-blade, as usual among water animals, is short and broad. In the place of a sternum the coracoids joined each other broadly in the middle, just as they did in the oldest known land reptiles. And there were clavicles and an interclavicle. Below the abdomen behind were numerous slender bones called ventral ribs. The pelvis is very weak, and was suspended below the spinal column in the fleshy walls of the abdomen. The hind legs were so small that little support was necessary for them, and, because they were not used either for the support of the body or for propulsion, they did not require a firm union with the skeleton. Doubtless had the ichthyosaurs continued to the present time, they would have lost entirely the hind legs, as have the cetaceans.
Fig. 55.—Pectoral girdle of Baptanodon (Ophthalmosaurus), an American Upper Jurassic ichthyosaur. (After Gilmore.)
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. An increase of fingers and toes, however, seems to be an impossibility in evolution, and doubtless of real fingers and toes it is an equal impossibility. All naturalists are now agreed that a specialized character can never revert to a generalized condition, or rather to a generalized structure, that an organ once functionally lost can never be regained by descendants. A character once lost is lost forever; horses of the future can never have more than one finger or one toe in each limb.
Fig. 56.—Front paddle
of Ophthalmosaurus
(after Andrews):
h, humerus; r, radius; u,
ulna; p, pisiform; re, radiale;
int, intermedium; ue, ulnare.
Fig. 57.—Front
paddle of Merriamia,
a Triassic ichthyosaur.
(After Merriam.)
Explanations as in
Fig. 56.
And there was an increase in the ichthyosaurs, in some not only of the number of digits in each limb, but in all of the number of bones in each digit, a character found also in the unrelated mosasaurs and plesiosaurs. This increase in finger and toe bones, or hyperphalangy as it is called, is one of the most peculiar of all the adaptations to water life, changing the feet and hands from the ordinary walking type to the fish-like swimming type. The bones beyond the humerus and femur in the ichthyosaurs were so increased in number and so changed in form and relations that they bear little resemblance to the corresponding bones of other reptiles. They are merely polygonal platelets of bone, articulating on all sides and fitting closely together, permitting flexibility, but not much else.
It is now believed that the increase, not only of additional digits, sometimes to as many as ten in each hand and foot, but of the finger and toe bones as well, was the result of a sort of vegetative reproduction. The margins and ends of the flippers were doubtless hardened by cartilage or fibrous material, and because of the action of the limbs this cartilagenous material broke up into nodules each of which took on ossification finally. Among the whales, where hyperphalangy also occurs, though to a less extent, it has been thought that the increase in number has been due simply to the ossification of the parts of each bone normally present, that is, to the epiphyses, which became separated from the shaft of each bone. But this explanation will hardly suffice for the fingers and toes of the plesiosaurs and ichthyosaurs, for there are altogether too many such ossifications; and besides, the bones in these animals, as in most reptiles, did not have epiphyses, or terminal separate ossifications of the bones of the skeleton.
It will be observed from the figures that the arm and thigh bones of Ichthyosaurus are very much shortened—a striking adaptation to water life, so conspicuously seen in the modern whales and dolphins as well as in the mosasaurs, thalattosaurs, etc. So characteristic indeed is this shortening that, were every other bone of the skeleton of an ichthyosaur unknown save the humerus or femur, it would be quite certain from these alone that the animal was thoroughly aquatic in habit.
About sixty years ago a rather aberrant form of ichthyosaur, now known as Mixosaurus, was discovered in rocks of Triassic age, that is, of much greater age than any ichthyosaurs previously found, in which not only the forearm but also the lower leg bones were longer, resembling more the corresponding bones of land animals. It was from the examination of specimens in 1887 of these mixosaurs that the late Professor Baur became convinced that the ichthyosaurs were the descendants of land reptiles, and not directly of the fishes as they were universally thought to have been at that time. As Professor Baur very pertinently said, if the ichthyosaurs were descended from the fishes directly, the earliest forms should be more nearly like the fishes than the later ones, whereas just the opposite was the real fact. The arguments which he gave in support of his contention were so convincing that they found immediate acceptance among all naturalists. Fortunately within the past fifteen years many other remains of early ichthyosaurs from the Triassic rocks of California have been brought to light by Professor Merriam, remains which throw a flood of light upon the early, though not the earliest, history of these strange reptiles. He has recognized among the forms he has discovered, not only new species, but several new genera, and perhaps new families of ichthyosaurs. His studies have demonstrated so well the stages of evolution between the early ichthyosaurs and the later ones in their progressive adaptation to water life that it will be of interest to summarize them here.
In the early ichthyosaurs locomotion was largely by the aid of the limbs; in the later ones almost exclusively by the aid of the caudal fin. In the former the paddles were larger and the bones longer, more like those of land animals; in the latter they were relatively smaller and shorter, and more fin-like. In the digits of the early forms the finger and toe bones were more elongated and fewer in number. The hind limbs were nearly as large as the front ones in the Triassic, often very much smaller in the later ichthyosaurs; and the increased number of digits occurs only in the later forms.
In the Triassic ichthyosaurs, all classed in the family Mixosauridae, the pelvis was larger and more firmly connected with the body than in the later forms.
The skull of the early forms was relatively shorter, as compared with the trunk, the jaws shorter as compared with the head, the eyes were relatively small, the teeth in some less numerous, and set in distinct sockets like those of land reptiles; the vertebrae were relatively longer and less fish-like, and their articulations more like those of land reptiles.
The distal part of the tail was not bent downward so sharply, that is, the terminal fin was smaller, or the tail may have been simply flattened near its end and not really fin-like. The scapula was longer and less fan-like in shape.
And all these are remarkable evidences of an increased adaptation to water life in the more recent ichthyosaurs over the older ones. Were someone now so fortunate as to find ichthyosaurs in late Permian rocks, we should doubtless have the nearly complete chain between the most highly specialized type of water reptiles and their terrestrial ancestors.
Fig. 58.—Caudal fin of Ichthyosaurus, after Baur (left figure); caudal fin of Mixosaurus, after Wiman (right figure).
From the structure of the skeleton alone the early observers were justified in inferring much concerning the shape and habits of the living ichthyosaurs. Later discoveries have added so many definite facts that, at the present time, we know more about their habits than we do of any other extinct reptiles. In various places in England and Germany, especially in Würtemberg, the remains of ichthyosaurs are found in extraordinary abundance and perfection, not only whole skeletons lying in the positions which they had assumed after the decomposition of their bodies, but also often the actual remains, carbonized, of the skin, muscles, and ligaments, as well as delicate impressions of external parts. Many of these skeletons are obtained from the numerous stone quarries, where they are a sort of “by-product,” the sums received for them adding not a little to the income of the quarrymen. So many are obtained in this and other ways that specimens of ichthyosaurs are perhaps more frequently seen in the museums of the world than those of any other extinct backboned animal. Fairly complete skeletons may now be purchased of dealers in such things for from fifty to seventy-five dollars. As may be supposed, the best and most complete collections of these fossil remains are those of the British Museum in London and the museum in Stuttgart. From a study of those of the last-mentioned museum Professor Fraas has learned many interesting facts and reached many interesting conclusions regarding the life-habits of the ichthyosaurs. In the accompanying figure ([Fig. 59]) is shown a photographic reproduction of a very complete specimen, in which not only is the outline of the whole body shown, but also much of the carbonized remains of the muscles and skin has been detected.
Fig. 59.—Ichthyosaurus quadricissus. (From a photograph from B. Hauff, Paleontologisches Atelier, Holzmaden.)
The attachment of the paddles to the body was broad antero-posteriorly, proving conclusively that they could not have been much used in propulsion, either in the water or upon land, since such use would require a fore-and-aft movement, and a consequent twisting or rotation of the whole arm or leg, which, because of the broad attachment, must have been very difficult, if not impossible.
Microscopic examination of the remains of skin preserved disclosed an abundance of dark pigment, indicating, Professor Fraas believes, that the skin was dark colored above. Doubtless, also, the under side, as in nearly all swimming animals of the present time, was of a lighter color, because such coloration rendered the animals much less conspicuous in the water when seen either from above or below. That the skin was bare is proved by many impressions or molds of it that have been discovered in the rocks, in which many fine creases are seen, but nothing suggesting scales or bony plates, save on the front edge of the paddles, where impressions of overlapping scales have been observed. This is an interesting fact, bearing witness that their land ancestors had been covered everywhere with scales, much like those of existing lizards and other reptiles. Scales or bony plates were not only useless to the ichthyosaurs in the water, since they could afford no protection, but would have been detrimental in increasing the resistance in swimming.
That the ichthyosaurs were predaceous animals is of course evident from their teeth, adapted for the seizure and retention of slippery prey, but not for tearing or comminuting. The fossilized remains of food found between the ribs of some specimens, in the place where the stomach was, together with fossil excrement, called coprolites, usually attributed to these animals, prove that they fed largely upon fishes, squids, belemnites, and probably other invertebrates. One ichthyosaur specimen preserved in the Stuttgart Museum has preserved in its stomach contents a mass composed of the remains of more than two hundred belemnites.
Most interesting of all is the fact that, not very rarely, embryonic skeletons of ichthyosaurs have been found associated with the remains of adult animals, in such positions that they must have been inclosed within the body cavity at the death of the animals. As many as seven such embryonic skeletons have been observed with a single specimen. At first it was supposed that these skeletons were of small ichthyosaurs which had been swallowed whole as food, since it is not at all likely that these predaceous reptiles were discriminative in their choice of food when hungry. It is not improbable that in some cases this is the true explanation of the smaller skeletons within the larger ones, but it cannot be true of all, since wherever the small skeletons are identifiable they have been found to belong to the same species as the adult, and it would be absurd to suppose an ichthyosaur bent upon its prey would be at all likely to select as many as seven young animals, all of the same size and all of its own species. Furthermore, some of these young skeletons have been found in such positions as would indicate that they were inclosed within their egg-covering at the time of their death. Some of these embryos measure as much as twenty inches in length.
Because the ichthyosaurs were born alive, and because so many of their skeletons are found with their various parts in orderly relation to each other, it is inferred with much probability that they were inhabitants, in large part at least, if not exclusively, of the open and deeper oceans. Had they been oviparous they must necessarily have laid their eggs upon the beaches, since no reptiles of the present time lay eggs in the water, and we have no other indications that the reptiles of the past have ever done so. And such habits would necessitate the periodical return to land. Had they been denizens of shallow waters, like the mosasaurs and plesiosaurs for the most part, their skeletons must surely have been disturbed by the currents and tides, as also by predaceous fishes, breaking up or displacing them or carrying away their bones. In shallow waters, also, the decomposing bodies would have been more liable to despoliation by the many scavengers of the seas.
The ichthyosaurs must have been quite helpless upon land, their limbs being of little more use for locomotion than are the fins of fishes. Breathing air as they did, they were of course not suffocated when exposed, unless, as is the case with the whales, the feeble attachment of the ribs prevented the action of the respiratory muscles. If accidentally thrown upon the beaches, they doubtless were able to return to their home element more easily than the fishes can, by flopping, wriggling, and turning. As we have seen, the food consisted in part, perhaps the larger part, of small invertebrates, and because the bones of the lower jaws were closely united, permitting little or none of that expansion so characteristic of the snakes, all their prey must have been of relatively small size. In habit the ichthyosaurs were doubtless, like the dolphins and gavials, inoffensive and harmless, so far as animals of larger size were concerned. The abundance of their remains often found in restricted localities, while deposits of like age and character not far distant may be almost free from them, suggests that in all probability the ichthyosaurs, or the later ones at least, were more or less gregarious in habit as are the sea-mammals. They probably lived in schools, as do the porpoises, each species keeping to its restricted locality and not wandering far.
The ichthyosaurs began their existence, so far as we now know, about the middle of Triassic times and continued to near the middle of Upper Cretaceous, when they disappeared forever from geological history. As we have seen, however, the earliest forms that we know were true ichthyosaurs in all respects, though more primitive than the later ones, indicating a long previous existence of which we yet have no knowledge. Their remains have been found widely distributed in Triassic rocks of Europe, Spitsbergen, Australia, and North America. During the Jurassic period they lived in great numbers and variety throughout the region that is now Europe. In North America the only marine rocks of this period that we know of have yielded numerous remains. These American ichthyosaurs were, however, among the most specialized of all ichthyosaurs—the culmination of their development. They were originally named Sauranodon in the belief that they were toothless, but in recent years their teeth, small and numerous, have been discovered. And the genus seems also to be identical with one previously named from the Jurassic of Europe called Ophthalmosaurus. The last known remains of ichthyosaurs have recently been found in the Benton Cretaceous of Wyoming. Scanty remains of ichthyosaurs are also known from Australia and New Zealand. Why the ichthyosaurs should have gone out of existence before the plesiosaurs and mosasaurs did, one cannot say; possibly their stock had grown old and feeble.
CHAPTER IX
PROGANOSAURIA
MESOSAURUS
There is some doubt whether those little creatures of Paleozoic times, to which some years ago the late Professor Baur gave the ordinal name Proganosauria, are really entitled to so much distinction among reptiles. The question of their rank has been much disputed for the past twenty years without any positive conclusion. Nor were they wholly aquatic in habit, though they did possess many aquatic adaptations. That they were skilful and fleet swimmers, and capable of rapid evolutions in the water is quite certain, and, as the oldest known water reptiles, they are of more than passing interest.
Fig. 60.—Mesosaurus; life restoration, after McGregor,
the posture of hind leg slightly modified.
But two genera and three or four species of the group are known, and of them, even, our knowledge in some respects is not as complete as one could desire. The first description of any member of the group was by the late Professor Gervais of Paris in 1867. He had only the anterior part of a single skeleton, from the Karoo beds of South Africa, to which he gave the name Mesosaurus, a rather meaningless term signifying “middle” or “intermediate” saurian. Nothing more was learned about any form till 1885, when the late Professor Cope described a specimen from the supposed Carboniferous of Brazil, which he believed to be closely related to Mesosaurus, though he had only a very imperfect specimen. He called it Stereosternum, also a meaningless term, since none of the animals has a “solid sternum,” nor any sternum at all, in fact! A few years later, in 1888 and 1892, the late Professor Seeley of England studied a number of specimens of Mesosaurus, adding not a little to our knowledge of the animals. More recently Dr. Woodward of England and Professor Osborn of America have given us still further information concerning them, and within the past few years Dr. McGregor of Columbia University has figured and described excellent specimens of a new species from Brazil, which he calls Mesosaurus brasiliensis. Not only were Dr. McGregor’s discoveries of great interest as settling many doubtful points in their structure, but they were still more so from the fact that he found his species so nearly like that from Africa that he placed it in the same genus. Since the proganosaurs were purely fresh-water or terrestrial animals, one can only wonder how they crossed from Africa to America, or, what is more probable, how they migrated from America to Africa, across the broad Atlantic Ocean, so long ago. The geologists tell us that the Atlantic and Pacific, in the main, have always been oceans since the beginning of terrestrial life upon the earth. Possibly the tribe of proganosaurs migrated by the very circuitous route of Europe and North America, or Asia and the Northwest; but that is very improbable, since nothing whatever resembling them has ever been found in the Northern Hemisphere, and it is quite certain that in the many thousands of years it must have taken them to travel from southern Africa to South America many of the reptiles must have perished on the way and left their remains in the rocks. The only conclusion that seems probable is that there was a direct land communication in those olden times between Africa, or at least India, and South America across what is now the Atlantic Ocean. Of course this route will be very difficult to prove, since we can never get to the bottom of the ocean to hunt for fossil proganosaurs. Were this peculiar distribution of the proganosaurs an isolated example, one might perhaps ascribe our lack of knowledge of any fossil proganosaurs in the Northern Hemisphere to the meagerness of the fossil records, but there are many other examples of similar import among other early animals.
Fig. 61.—Mesosaurus; restoration of skeleton.
(After McGregor)
The age of the South American proganosaurs is now believed to be lower or lowermost Permian, like that of the African Mesosaurus; possibly, however, the age first described to Stereosternum (Carboniferous) may be correct.
The known skeletons are all small, none exceeding a few feet in length. The skull, as shown in the figure by Dr. McGregor, is elongate, and its teeth are extraordinarily so, and very slender. The external nostrils are situated close to the eyes; and no sclerotic bones have been discovered. There are small teeth in the bones of the palate. The neck is elongate, composed of ten or twelve vertebrae. The trunk also is long and slender, and the tail is not only long, but also much flattened or compressed. All these are very characteristic of water life. The limbs, however, show a much less complete adaptation for swimming—not much more so in fact than do those of the living Crocodilia. The upper arm and the thigh bones are relatively long, while those of the forearm and the leg are shorter than among terrestrial reptiles, the first indication of swimming habits to appear in crawling animals. The digits are not much elongated, and they have no additional finger bones, save perhaps in a lately discovered form in Africa, in which Dr. Broom reports supernumerary bones in the fifth or “little” toe.[3] The fingers and toes have only blunt terminal bones, that is, they were not distinctly clawed, and they were probably connected with each other by a membrane, as in a frog’s foot. This webbing of the feet is probable, not only because of the positions in which the bones have been found, but also because of the great length of the “little” toe, which is the longest in the foot, a character quite abnormal for a land reptile and quite characteristic of certain aquatic mammals, like the seals and sea-otters. There is a strong sacrum of two vertebrae, however, the pelvis and hind legs being connected with the spinal column firmly, clearly proving that, like the crocodiles, the proganosaurs had by no means lost their land proclivities.
Their vertebrae, as would be expected in such old reptiles, are quite primitive in structure, that is, they are deeply concave in each end, probably being perforated for the remains of the notochord. The pelvis also is of the old-fashioned type, that is, without an opening or vacuity between the bones below. The shoulder bones are old fashioned too. The shoulder-blade, especially, shows a decided adaptation to water life in its short, fan-like shape, very much like those of the mosasaurs, ichthyosaurs, whales, etc. Just why swimming animals should have short and broad shoulder-blades has not yet been explained, but doubtless they afforded better attachment for those muscles used more especially in swimming. The ribs are remarkably flat and heavy, and were not very firmly attached to the vertebrae. Heavy ribs are unusual among free swimming animals, but do occur in the modern sirenians, which live on the bottoms of shallow bays, etc., feeding upon plants. We may perhaps infer from this peculiar structure of the ribs that the proganosaurs lived more on the bottoms of shallow waters, feeding upon such fishes or invertebrates as they could capture, coming to the surface to breathe from time to time. Possibly they sought the shores for safety from their enemies, as do the Galapagos lizards, figured on [p. 142]; and doubtless they laid and hatched their eggs on land. A character which suggests that the proganosaurs lived only in the shallow waters is the elongated neck, reminding one of those two other groups of swimming reptiles, the dolichosaur lizards and the nothosaurs of the Sauropterygia, the only known reptiles besides the plesiosaurs having an abnormal number of neck bones. Still more suggestive of shallow, fresh-water habits is the absence of eye bones, as in the modern crocodiles.
The long snout, with the long and slender teeth, and the position of the external nostrils far back near the eyes, together with the flattened and long tail and the webbed feet, are sufficient proof of expert swimming habits. The legs still functioned more or less for the support and propulsion of the body on the land, and they probably were only of slight service in the water. The alligator swims sinuously with its front legs collapsed and extended by the side of the body; its hind legs are used more as propellers, with the knee flexed and the feet turned outward and expanded. The legs of the proganosaurs doubtless were used in the same way, as shown in the restoration, which has been modified from the original of Dr. McGregor in accordance with this probable use of the legs.
There seems to be an incongruity between the posterior nostrils and the heavy flat ribs, the former suggesting free swimming and diving habits, the latter shallow water and bottom habits. Possibly the position of the nostrils has been the result of the great elongation of the face in front of the nostrils; and we know that their posterior position in the phytosaurs ([Figs. 95] and [96]) has not been due to swimming habits only.
Nothing has been discovered to indicate the nature of the external covering of the body. Possibly, even probably, the skin was more or less covered by horny scales or plates, though it may have been quite bare, as in the salamanders.
To which other reptiles the proganosaurs are nearest related has long been a subject of dispute, and still is. The more probable view, however, is that they were a very early branch of the most primitive stock of reptiles, the Cotylosauria, one that soon perished, leaving no descendants, unless possibly the ichthyosaurs were their progeny. Some writers have thought that they were the early ancestral stock of the plesiosaurs, and they are often classified with the Sauropterygia. Still others have believed that they were an early side-branch of the great group of Rhynchocephalia. And this doubt has been chiefly due to our imperfect knowledge of the bones of the cranium. As has been explained, very much stress in the classification of reptiles has been laid by students on the possession of one, two, or no openings on the side of the skull back of the eyes. And this part of the skull of the Proganosauria has not yet been satisfactorily made out. Dr. McGregor thought that there are two openings in the temporal region, allying the group with the Rhynchocephalia. Dr. Huene is more positive that there is but one, like that of the ichthyosaurs. In this state of indecision, the proganosaurs may be dignified by giving them an ordinal position by themselves.