Popular Science Monthly/Volume 53/June 1898/The Serpentlike Sea Saurians
|THE SERPENTLIKE SEA SAURIANS.|
IN the latter part of the Mesozoic age there was a great inland ocean, spreading over a large part of the present continent. The lands then above water were covered with a flora peculiar to the times and were inhabited by some of the animals which later distinguished the Cenozoic age. In the seas were reptiles, fishes, and turtles of gigantic proportions, armed for offense or defense. There were also oysterlike bivalves, with enormous shells, three or four feet in diameter, the meat of which would have fed many people. In time, this great ocean, swarming with Adgorous life, disappeared. Mountain ranges and plains gradually arose, casting forth the waters and leaving the monsters to die and bleach in Tertiary suns. As the waters remaining divided into smaller tracts, they gradually lost their saline stability. The stronger monsters gorged on the weaker tribes, until they, too, stranded on rising sand bars, or lost vitality and perished as the waters freshened. In imagination, we can picture the strongest, bereft of their food supply at last, and floundering in the shallow pools until all remaining mired or starved. It would be interesting to know how much of the great Cretaceous ocean forms a part, if any, of the vast oceans of to-day. If any part so survived, what became of the saurians carried forth into new ocean areas? Were they beaten on jagged rocks by powerful currents and destroyed, or did some of them escape only to perish in after ages? Water, as a rule, seeks its level; sometimes it is evaporated. If the Cretaceous ocean merely drained off into other areas before rising lands, it is perhaps not unreasonable to suppose that the descendants of some of the saurians might have survived in the Atlantic or Pacific as they had existed in the Mesozoic age. We can therefore only assume that the Cretaceous seas evaporated or gradually freshened until all the life they contained became extinct.
During the past twenty-five years explorers have collected tons of skeletons of the stranded sea serpents, or better, perhaps, serpentlike sea saurians. A sensational world has ever been on the lookout for sea serpents. It is possible that such tendencies are inherited from a very remote ancestor, a primeval, manlike animal, whose curiosity was aroused by glimpses of some surviving pythonomorph.Almost everywhere on the expanse of the Cretaceous ocean might have been seen the snakelike forms of the elasmosaurs, the heads arrow-shaped, upheld by swanlike necks, rising from ten to twenty feet above the surface and scanning the sea or air for prey or enemies. The prey located below, they dived; the enemy seen
Mossaurs; 1, Platecarpus coryphœus (Cope); 2, Tylosaurus Proriger (Cope); 6, Mosasauris Horridus (Williston); all restored by Williston. 3, Marine turtle: Protostega gigas (Cope), restored by Case. 4, Bulldog fish: Portheus Molossus (Cope). 5, Pterosaur: Pteranodon, or Ornithostoma ingens (Marsh), restored by Williston. 7, Plesiosaur: Plotycotylus latipinnis, as restored by Dames.
The mosasaurs were more elongated and graceful in form. Their heads were large, flat, and conical, with the eyes directed laterally. The tails were long. They had fore and aft paddles with webbed digits, attached to the body with wide peduncles. With paddles and flattened tails they swam with ease and speed. Like snakes, they had four rows of formidable teeth on the roof of the mouth, not for mastication, but for seizing prey and holding it. Like snakes, they swallowed their prey entire, but, unlike snakes, they had not elastic throats. The jaw was, however, so articulated, jointed so far back between the ear and chin, ball-and-socket fashion, that the immense opening made up for the lack of expansibility of throat. The ends of the jaws were bound by flexible ligaments, permitting the passage of large fish or other prey. The mouth of the gullet was prolonged forward while swallowing, evidently being loose and baggy. The same habit pushed forward the glottis, or opening of the windpipe in front of the gullet. Like a serpent, the mosasaur hissed, owing to these formations. The tongue was long and forked, and when at rest was inclosed in a sheath beneath the windpipe and thrown out when the jaws were in motion. And thus, too, are the nearest living forms.
The mosasaurs attained great length, reaching from ten to fifty feet. They had long, projecting muzzles, somewhat like that of the blunt-nosed sturgeon of to-day, although the branches of the lower jaw were correspondingly massive. With such ramlike jaws the mosasaur possessed terrible powers of collision. They were scaled animals, and fragments of their hide and scales have been found in good condition of preservation.
The first mosasaur discovered was found by Major Drouin in 1776, on the banks of the river Meuse, near Maestricht, Germany, On this specimen was founded the genus Mosasaurus, given it by Conybeare in 1822, although the skeleton was previously described
by Cuvier in 1808. The interesting history of the specimen, which created a profound sensation in the world of learning and became mixed up in the history of nations, is herewith reduced from Owen. The skull was found in the quarries of St. Peter's Mount by M. Faujas Saint-Fond, Commissary for Sciences of the French Army of the North. In one of the galleries or subterraneous quarries in which the cretaceous stone of St. Peter's Mount was worked, about five hundred paces from the entrance and ninety feet below the surface, the quarrymen exposed part of the skull in a block of the stone which they were engaged in detaching. On this discovery they suspended work and went to inform Dr. Hofmann, surgeon of the forces of Maestricht, who for some years had been collecting fossils at this quarry, remunerating liberally the workmen for the discovery and preservation of them. Dr. Hofmann arrived at the spot and saw, with extreme pleasure, the indications of a magnificent specimen. He directed the operations of the men so that they worked out the block without injury to the skeleton, and he then with his own hands cleared away, by degrees, the yielding matrix, exposing the extraordinary jaws and teeth, which have been the subject of so many drawings, descriptions, and discussions. This fine specimen, which Hofmann had transported with so much satisfaction to his collection, soon, however, became a source of chagrin to him. Dr. Goddin, one of the canons of Maestricht, who owned the surface of the soil beneath which was the quarry whence the fossil had been obtained, when the fame of the specimen reached his ears, pleaded certain feudal rights in support of his claim to it. Hofmann resisted, and the canon went to law. The whole chapter supported their reverend brother, and the decree ultimately went against the poor surgeon, who lost both his specimen and his money, for he was made to pay the costs of the action. The Canon Goddin, leaving all remorse to the judges who had pronounced the iniquitous sentence, became the happy and contented possessor of this unique example of its kind. But justice, though tardy, comes at last. When the town was bombarded by the French, directions were given to spare the suburb where the famous fossil reposed. After the capitulation, the grenadiers discovered, seized, and bore off the specimen in triumph to the commissarial residence. The excellent soldiers always knew how to appreciate and respect the monuments of art and science. The mosasaur was transplanted and still remains in the Museum of the Garden of Plants, Paris, and is the subject of more literature than any extinct animal.
Remains of the mosasaurs were first discovered in England in 1833, at Lewes. In America, mosasaurs were first found in the cretaceous beds at Great Bend, Missouri, about the year 1820, by Major O'Fallon, Indian agent. He found a fine specimen, and took it to his home in St.Louis. Dr. Goldfuss first described it in 1843, with accompanying plates, the skeleton having been taken to Germany by Prince Maximilian. He defined the parietal and jugal arches, pterygoids and vomers, the position of the quadrate, and the presence of the sclerotic plates. Since that time our knowledge of the mosasaurs has been largely increased by the explorations and efforts of Cope, Marsh, Dollo, Owen, Leidy, Williston, Baur, Merriam, Gaudry, Gervais, and others. Cope, perhaps, defined the largest number of species. Marsh defined the stapes, columella, transverse and hyoid, and the presence of hind limbs. Dollo has materially increased the data of mosasaurs and has added four new genera. Baur gave the first complete description of the skull of a species of Platecarpus. Williston and Case first described the vertebral column and extremities and the general form of mosasaurs. The former has contributed most to our knowledge of mosasaurs in the Kansas Cretaceous, and made the first correct restoration, which is made one of the bases of this paper.
Professor S. W. Williston, University of Kansas, because of his perfected restorations and wide studies of the sea-serpent like saurians, the mosasaurs and other marine saurians, must rank as the highest
authority-. It is largely on his material that it is possible to present something like a complete view of the gigantic monsters that swam the Cretaceous seas and gave origin to our notions of mythical sea serpents. Kansas is the great center of the Cretaceous time of occupation, and it is within its borders that the largest number of species and genera of sea serpents have been discovered. It is natural, perhaps, that living in the vicinity of the most prolific Cretaceous remains, Professor Williston should be better able than scientists more remote to complete our knowledge of marine saurians.
There are three groups of the serpentlike sea saurians—the ichthyosaurs, plesiosaurs, and mosasaurs. Of the mosasaurs, Kansas has produced the largest number of species, twelve of which have been satisfactorily described. New Jersey, Alabama, Carolina, and Mississippi have perhaps ten valid species. Dakota has favored us with three species. It is estimated that of fifty species attributed to North America, about twenty-five or thirty will be distinguished as distinct. It is expected that in the Fort Pierre formation of the Dakota region other species will be found, as it has been but imperfectly explored. Europe has about a dozen species, and New Zealand several more. Probably only about forty species of twice as many alleged to have been discovered in the world will stand the test of critical examination.
Of plesiosaurs, America has produced about ten and the Old World many more species that will stand. Many species of ichthyosaurs are recorded from Europe, India, Africa, Australia, New Zealand, and the arctic regions, and one or two in America, the toothless Baptanodon from the Jurassic of Wyoming being the type. All three groups had paddles with webbed digits, but none had claws. Williston thinks that the ancestors of the mosasaurs were land lizards. Dollo thinks that the ancestors were the peculiar group of lizards which appeared in the commencement of the Cretaceous known as Dolichosauria. Baur would derive the mosasaurs from even more specialized lizards, and believes that their relationship is very close to the monitors of the present day.
The ichthyosaurs are thought by Cope to be derived from Homœosaurus (beakless lizards) of the Jurassic; and these from the Palæohatteria (ancient hatteria), a rhynchocephalian (snout-head) which flourished as early as Permian times; and these from the Labitosaurus, an ancestor below the Carboniferous in the Palæozoic age; from which also sprang the lizardlike saurians, the dimetrodons (Otocœlius), which gave origin to the turtles (Testudinata). Some members of the group to which the plesiosaurs belong were land animals, and hence the origin of the whole group is clearly from land species. It is not now presumed that the marine saurians had much power of progression on land, but they may have climbed on to the beaches to lay their eggs. It is further presumed by Morris that in later times the eggs of saurians were devoured by other animals, contributing to the extinction of all saurians.
Three species of representative genera of Kansas mosasaurs have been restored by Williston from material in the University of Kansas.
Clidastes velox (Marsh) is a typical mosasaur, the perfected skeleton of which is twelve feet in slender, with short heads. The vertebræ were firm, closely articulated with the best system of interlocking of any of the mosasaurs. The limbs were flexible and strong, with closely articulating bones and fully developed tarsus and carpus. The aggregate of these characters indicates the most snakelike form and method of progression through water of all the mosasaurs. The genus Clidastes was founded by Cope in 1869, but may ultimately give way to the genus Mosasaurus of Conybeare. Cope's views of Clidastes conclude that the animals were not as large as those of the genus Liodon (Owen), but more elegant and flexible, with an additional. Pumilus, of the same genus, is given as six feet in length, which would rank it as perhaps the smallest mosasaurian. The clidastes of Kansas had short, powerful propelling tails, which would indicate a lesser speed than that of their longer-tailed contemporaries. The clidastes had small hind limbs, showing further deficiency in speed. The animals were
pair of articulations at either end of each vertebra—the zygosphenes—to prevent dislocation by contortions. A larger and still more elegant species was Clidastes tortor (Cope), with lithe movements which enabled it to capture fish by means of its knife-shaped teeth, which were very numerous. Tortor was very slender, with a long and lance-shaped head. It was upward of twenty feet in length, with a head two feet and a half long, the vertebral column elongate and the head narrow and pointed.
The second-type mosasaur perfected by Williston is Platecarpus coryphæus (Cope). Its special characteristics are a short muzzle, slender vertebræ, and an imperfect interlocking zygosphene. The hind paddles are smaller than those forward, but thought to have been more powerful propelling functions than those possessed by other genera. A type skeleton measures fourteen feet, and may have been a young animal. The teeth were very curved and pointed, and formed effective weapons. The neural spines, not closely connected, indicate flexibility. The general characters suggest a ful predaceous sea serpent. The genus was founded by Cope in 1869; it has a wide distribution, and seven or eight species belong to it.
Tylosaurus proriger (Cope) is the third of Williston's type Kansas specimens perfected in restoration. It is considered the most specialized of the mosasaurs. The skeleton in hand is twenty-three feet in length, and shows a wholly cartilaginous carpus and tarsus, more elongated digits, and a greater number of phalanges than possessed by any other genus, the result of long aquatic habits. The hind paddles are the largest, and the fifth digit has undergone but little reduction, indicating characters of a very primitive rank. The vertebræ are more flexible than in other genera, but they are relatively smaller and not at all strong. The skull is more elongated anteriorly. In the same genus was a much larger species, T. dyspelor (Cope), which was one of the most formidable of the mosasaurs. Another perfected sea serpent of terrible powers was Mosasaurus horridus (Williston), which had a ram nose, and evidently battered its foes when he could get at them. Williston's perfect skull from Dakota enabled him to correct many errors in vogue. The new genus Brachysaurus, formed by Williston, contains one species defined by him—Overtoni, from Dakota. It had a stout, very broad head, stout jaws and teeth, and stout, broad paddles. In appearance it suggests a terrible fighter, unadapted to rapid pursuit or flight.
A number of remarkable skeletons of mosasaurs have been discovered of late, some of which are expected to develop new species and, perhaps, new genera. Few of the "finds" of explorers create such sensational interest in scientific circles as the unearthing of the gigantic saurians. Three new skeletons were lately taken by an exploring party of the American Museum of Natural History. Prof. W. T. Lee, of the University of Denver, was so fortunate not long since as to secure the first skeletons of mosasaurs ever taken in Colorado, and adds so much to the geographical distribution of the animals. One skeleton was taken at Flagler and another at Canyon City. The Flagler specimen was exposed for sixteen feet, the vertebral column containing ninety vertebrae. There were also taken portions of the head and paddles. Flagler is situated in the St. Pierre Cretaceous in all probability. The specimen, not yet named, has a massive jaw and teeth, the latter very compressed. The vertebral column is one of the most complete yet unearthed. The tail is particularly fine, and gives a good impression of depth and compression.
Williston thinks that the food of the sea-serpentlike saurians must have consisted of fishes of moderate size, with occasional victims of their own kind. He says: "While the flexibility and loose union of the jaws undoubtedly permitted animals of considerable size to be swallowed, the structure of the thoracic girdle would not have permitted any such feats of deglutition of which the python and boa are capable. The animals must have been practically helpless on land. They were not sufficiently serpentine to move about without the aid of limbs, and these were not at all fitted for land locomotion. They lived in open seas, often remote from the shores. Their pugnacity is amply indicated by the many scars and injuries they received, probably from others of their own kind."
Among the fishes which were the prey of mosasaurs was Portheus molossus (Cope), the most formidable, and whose bulldog teeth and looks indicate that it leveled matters of justice by capturing smaller mosasaurs at times. The head of molossus was twice as large as that of a grizzly bear, the jaws deeper in proportion to length. The muzzle was stouter and deeper than a bulldog's. The teeth had sharp, cylindric fangs, smooth and glistening and of irregular size. Occasionally the teeth projected three inches above the gums, sinking one inch into the pits, as long as the fangs of a tiger and more slender. Two pairs of these long fangs crossed each other on each side of the snout.
Over the water were the flying saurians of formidable proportions, and which may have been both pursued and pursuer, according to size of mosasaur and pterosaur. The pterosaur had a wing expanse of eighteen to nineteen feet, as instanced in Ornithostoma umbrosum (Cope), the largest in size, and O. ingens (Marsh). The pterosaurs flew with leathery wings over the waves, plunging to seize unwary fishes or perhaps to be seized by mosasaurs, or soaring at a safe distance while watching the combats of swimming saurians. At nightfall they trooped along the shores, at last to suspend themselves to the cliffs by the claws of their wing limbs.
If tortoises were food for mosasaurs, there were plenty of marine turtles to choose from. The turtle was the boatman of the Cretaceous seas. The Protostega gigas (Cope), figured herein from a drawing by Prof. E. C. Case, of Wisconsin, was the largest, its flippers having a spread of fifteen feet. Wieland has recently described an immense species, Protostega ischyros, from Wyoming.Inasmuch as the earlier skeletons of mosasaurs were so incomplete as to leave the matter in doubt, it is interesting to note Professor Williston's discoveries of quite perfect fore and aft paddles of
mosasaurs, and the fact that marine saurians had scale-covered skins. The paddle was formerly a matter of conjecture, and, in the absence of such remains, the saurians were supposed to have had marine turtlelike flippers. Prof. O. C. Marsh, of Yale College, was the first naturalist to discover sufficient of the missing parts of skeletons to determine that marine saurians propelled themselves with paddles rather than flippers. As to the scales and skin found perfectly preserved by Snow, they do not differ materially from those of the Old World lizards, the monitors, existing to-day. The paddles, skin, and scales are very delicate functions, and it is remarkable that they should have been preserved through millions of years. Williston says of the paddles: "The specimen figured by Chancellor F. H. Snow, of the University of Kansas, has been thoroughly cleaned from the matrix, enabling an accurate drawing to be made, also a photographic reproduction as it lies on a chalk slab. The parts concealed beneath the ribs and vertebræ have been carefully laid bare from the opposite side and their position shown. The position of the paddle is a natural one, and the fact is of interest as showing the general expansion and curvature of the digits." The limb is very flexible, with considerable space between the bones, which were but partly filled out with cartilage, and must have had very free articulations. The remains of the skin were found between the bones, indicating a thin, pliable membrane, and extending fully between the fingers to their tips. Small scutelike scales extended as far as the metacarpals. The fifth finger is long. The paddles are slenderer, more flexible, and relatively longer than in other genera, which, with other characteristics, would show that Tylosaurns was the least lizardlike of the Pythonomorpha (Cope). As to the structure of the hind paddle, it is of interest in having five functional toes, although Williston thinks that the fifth toe was undergoing reduction, and that the first toe was not as long as in the front paddle. He concedes five toes to the hind paddle of Platecarpus (Cope), but doubts, in the absence of a complete skeleton, if Clidastes had more than four functional toes, as in Mosasaurus. Upon this character, together with the absence of a sternum, he has established two families, Tylosauridæ and Mosasauridæ, and the two typical genera, representing the extremes of development of this order of reptiles.
Mosasaurs are known to have existed in many parts of the world, New Zealand, North and South America, and Europe, the oldest being regarded as the New Zealand types, Liodon and Taniwhasaurus. Dollo thinks that New Zealand was the center of their irradiation, where they appeared in the end of the Cenomanian, to appear in America in the Turonian, whence they migrated to Europe and appeared in the Senonian, and finally became extinct there in the Mæstrichtian. They also have been reported from South America in the Purus of the Amazon, corresponding to the Mæstrichtian times. Professor Marsh's Baptosaurus appears to be the last of the American forms, found in the Upper Green Sand of New Jersey and the Niobrara of Kansas.
In this connection it is interesting to note the views of certain scientific men of the times in which these gigantic sea serpents existed.
The views of Prof. Frank C. Baker, curator of the Chicago Academy of Sciences, follow: "At the time the great sea lizards lived, North America was shaped something like the following: It
included all of northeastern Canada and Nova Scotia; the shore line was the same as at present as far as New York, where it was deflected to the southwest and went through the western part of New Jersey, Delaware, and Maryland, and then went directly across the middle of Alabama, north again to the mouth of the Ohio River where it meets the Mississippi River, then north into Iowa, and finally north and northwest across the United States and British America. Herein existed a great inland sea in which the sea lizards lived. The past history of the world tells us that thousands of animals of gigantic size lived in the ancient seas. In old Jurassic and Cretaceous times we had such queer combinations as Ichthyosaurus (or fish lizard) and Plesiosaurus. Not only were reptiles found in the water; they flew about in air. The latter were represented by the Rhamphorynchus, a birdlike reptile which had wings like a bat, teeth like an alligator, and the tail of a lizard. In the Connecticut Valley we find the footprints of huge reptiles in the red sandstones whose feet measured from those of a few inches in length to the footprints of the gigantic Otozoum, which measured twenty-two inches in length, having a step of some five feet."
An immense amount of literature has been printed on the subject of the Cretaceous formation and its inhabitants. Very recently there have been immense advances made in the restoration of species existing in Cretaceous times. This article, therefore, is in the nature of scientific news, and a separation of facts from a mass of errors. In looking over the works of others, one is impressed by the many mistakes made by specialists, owing to imperfect skeletons and collections. A careful study of these errors has been made in the light of the latest skeletons reconstructed and the latest discoveries made.
The Kansas University, in securing three perfect type specimens of three genera of mosasaurs, presents three important items of scientific news. These skeletons teach us the errors and pitfalls into which specialists have fallen who lacked certain parts of the skeletons and filled out the gaps by aid of the imagination. Only recently the country was startled by the alleged discovery of the skeleton of a supposed reptile, having a length of two hundred and fifty feet. The newspapers gave startling pictures of the supposed appearance of this reptile while on earth. Professor Williston naturally wanted to see this gigantic animal, the largest ever discovered. On examination of its bones he saw at once that it was a whale. It can safely be asserted that no animal ever attained a length of two hundred and fifty feet. Perhaps as serious errors as this may be found in many of our text-books and monographs, due, of course, to former incomplete skeletons. The appearances of the skulls, the jaws, and the teeth have been painfully distorted in like publications and on charts in class rooms, and demand a thorough overhauling before our youth are further taught errors. With late complete discoveries, we have now exact appearances of the functions of the heads from which we can derive correct views. It was formerly thought that the eyes of the mosasaurs were directed upwardly; to-day it is known that they were directed laterally, as in living lizards. It has been supposed that mosasaurs attained a length of one hundred feet; no skeleton has been found which would show a length of more than fifty feet. The great majority of skeletons taken range from sixteen to twenty feet in length. It was formerly supposed that mosasaurs had the powers of running, springing, and climbing on land; it is now known that they were wholly confined to salt water, and merely climbed the beaches in order to lay eggs. It is not an easy step from mosasaurs to modern snakes; it is an utter impossibility. Professor Marsh formerly thought, and it has been taught in the class rooms, that the bodies of mosasaurs had bony scales; they had skins, and were scaled throughout like modern lizards and snakes. The Rhamphhorynchus has been held up to us as a "lizardlike bird"; it was no more like a bird than is a bat; it was a birdlike reptile. These suggestions certainly point to the necessity of a revision of the text-books and charts in use in class rooms, which in many instances should become obsolete because of perfected restorations.
Specialists regard the marine saurians as having existed some millions of years ago. They conclude that these animals had at least a million years of existence in various forms. While it may be venturing
into the domain of the encyclopædia to state the causes of these conclusions, a word here may not be out of place. The Cretaceous formation, in which the marine saurians are found, is of chalk, green sands, etc., and ranges in thickness from ten thousand to twenty thousand feet or more. It existed in the last part of the Mesozoic realm. From the thickness and position in geological strata scientists deduce its age and place in Nature. As the remains of marine saurians are found only in the Cretaceous deposits, specialists speak of them as existing several million years ago. At that time were numerous fishes, birds, reptiles, and plants.
On previous pages some remarks have been passed in reference to origin and distribution of the sea saurians. It may not be out of place to exploit further the evolution and sequence of other saurians existing before and contemporaneously with the salt-water group. To do so in a brief way presupposes that the reader has some general knowledge of the times in which these remarkable animals existed. The evolution of animal life can only be discussed in general terms, as completer skeletons are needed to determine the whole subject.
The duration of saurians extended from the Carboniferous period of the Palæozoic realm through the entire Mesozoic realm which followed. The original saurian, so far as discovery to date shows, was a cotylosaur, found in the coal measures of Ohio by the late Professor Cope. This ancestor, Isodectes punctulatus (Cope), was eight inches in length, resembling somewhat the farm-fence lizards of to-day. In the Permian era, closing the Pelæozoic realm, other cotylosaurs appeared in numbers, first of moderate size, then gradually increasing in bulk. Of these were the larger Theromera, such as the lizardlike Dimetrodons, some with forty-inch spines on their backs, and the shell-backed, lizardlike Otocœlidæ, the ancestors of the marine turtles (Testudinata), ranging from three to ten feet in length. The Mesozoic realm, following, was the most extraordinary period of earth for its forms of animal life. In its first section, the Triassic, the saurians that appeared assumed wide orders, functions, and greater proportions. These lizardlike saurians were termed Palæoctonus, Ætosaurus, Dystrophacus, Thecodontosaurus, and Palæohatteria.
The Triassic, Jurassic, and Cretaceous formations, following, formed the most remarkable period of types of animal life. An examination shows that the marine Jurassic beds of Colorado were overlaid by a former fresh-water area, or lake, in which abounded iguanodons, megalosaurs, and cetiosaurs of diverse species, which swarmed in vast numbers and grew to gigantic proportions. The forests and jungles abounded in saurians which walked upon four legs and were so armed as to preserve peace while they fed on vegetation. The Cretaceous agathaumas resembled somewhat in form the rhinoceros, and the Jurassic stegosaur partook of the bulk of the elephant.
Agathaumas had a powerful skull, with two long horns over the eyes pointing upward and one over the nose pointing forward. The stegosaurs had a wonderful dermal armor of plates and spines arising along the spinal column. Such were the more specialized types of the forest. The plains and fields swarmed with saurians which ran or leaped on two hind legs and tail, tripod fashion, and whose fore limbs were used for seizing prey or supports. Those of the kangaroo type are represented by the Laramie Cretaceous Lælaps incrassatus (Cope), which preyed upon the Western Hadrosaurus mirabilis (Leidy), and the Cretaceous Lælaps aquilunguis (Cope) of New Jersey, which preyed upon the Eastern Hadrosaurus Foulkii.
The lakes were infested with saurians which waded or swam, either or both. These types are represented only in the Jurassic. The Amphicœlius altus (Cope) was one of the largest of dinosaurs, which waded but never swam. It traveled mainly on the bottom of the lakes, raising its long neck and head occasionally to browse upon the overhanging branches, but never venturing ashore, where its weight would have caused a collapse of its structure. It doubtless could not swim. Amphibious and omnivorous, it ate everything edible it could reach or seize—a saurian in structure, everything in habits.
The Cretaceous ocean teemed with the serpentlike saurians which form the subject of this article. With the Mesozoic realm terminated the period of existence on earth of all the large saurians. In the following Cenozoic realm their successors appear in the diminutive saurians, snakes, and crocodiles.
- Thought by Cope to have been the multituberculate Prototheria.
- Professor Case, the authority on this marine turtle, says: The skin must have been smooth and leathery, with supporting ridges or folds of dorsal integument to strengthen the back, perhaps two or three on either side of the central ridge. The back must have been quite flat. There were no claws on the front foot. The skull was as represented in the drawing.
- Subdivisions of the Cretaceous formation.
- Subdivisions of the Cretaceous formation.