REPORT ON THE STRATIGRAPHY AND PLIOCENE VERTEBRATE PALEONTOLOGY

OF NORTHERN COLORADO.

BY EDWARD D. COPE, A. M.

The water-shed between the South Platte River and the Lodge-Pole Creek, is composed superficially of formations of the Pliocene epoch, as defined by Hayden. The latter stream flows eastwardly through the southern parts of Wyoming and Nebraska, and empties into the South Platte near Julesburg, Nebraska. The Territorial and State boundaries traverse this water-shed from west to east. The springs on its southern slope, which form the sources of the northern tributaries of the South Platte, issue from beneath the beds of the formation above named. At or near this point is an abrupt descent in the level of the country, which generally presents the character of a line of bluffs varying from two to nine hundred feet in height. This line forms the eastern border of the valley of Crow Creek, until it bends to the eastward, when it extends in a nearly east and west direction for at least sixty miles.* At various points along it portions have become isolated through the action of erosion, forming buttes. Two of these at the head of Little Pawnee Creek are especially conspicuous landmarks, forming truncate cones of about nine hundred feet in elevation, as Mr. Stevenson of the survey informs me. They are called the Pawnee or sometimes the White Buttes. Near them stand two others, the Castle and Court-House Buttes.

The upper portion of this line of bluffs and buttes is composed of the Pliocene sandstone in alternating strata of harder and softer consistency. It is usually of medium hardness, and such beds, where exposed, on both the Lodge-Pole and South Platte slopes of the water-shed, appear to be penetrated by innumerable tortuous friable silicious rods and stem-like bodies. They resemble the roots of the vegetation of a swamp, and such they may have been, as the stratum is frequently filled with remains of animals which have been buried while it was in a soft state. No better preserved remains of plants were seen. The depth of the entire formation is not more than seventy-five feet, of which the softer beds are the lower and vary in depth from one foot to twenty. The superior strata are either sandstone conglomerate or a coarse sand, cf varying thickness, and alternating relations; the conglomerate contains white pebbles and rolled Pliocene mammalian remains.

This formation rests on a stratum of white friable argillaceous rock of Miocene age, probably of the White River epoch, as I believe from the presence of the following species which I detected in it: Hyaenodon horridus, H. crucians; Oreodon culbertsonii, O. gracilis; Poebrotherium vilsonii, Aceratherium occidentale, Hyracodon nebrascensis, Anchitherium bairdii, Palaeolagus haydenii, Ischyromys typus, Mus elegans, etc. The formation extends to a depth of several hundred feet, and rests on a stratum of a fine-grained, harder, argillaceous rock of a dark-brown color. Some of its strata are carbonaceous, and contain vegetable remains badly preserved; others are filled with immense numbers of fresh and brack*See Berthoud Proceed. Acad. Nat. Sci., Phila., 1872, p. 48, where they are mentioned.

ish water shells, including oysters. I do not know the depth of this bed, but followed it to the southward until it disappeared beneath the Loess of the South Platte. The age of this formation is no doubt, in the main, identical with that which underlies the fresh-water basins of Dakota and Wyoming, according to Hayden, and concerning which difference of opinion exists among paleontologists. Mr. Conrad, to whom I have submitted a number of shells, pronounces them to be species of Cyrena. Believing, as I do, that the evidence derived from the vertebrate remains requires the reference of the Bitter Creek Coal Series to the Cretaceous period,* and having pointed out on similar grounds that the horizon of the Great Lignite from which vertebrate remains have been procured on the Missouri River is undoubtedly Mesozoic, although usually regarded as Tertiary, I suspect that the corresponding strata in Colorado will be found to pertain to the same section of geologic time.‡

It is thus evident that the relations of these three formations are similar to those observed by Hayden to obtain between the Lignite, White River, and Loup Fork epochs, in the West generally, and they are in all probability to be referred to as near to those horizons. Prof. Marsh has already stated the existence of the White River Tertiary in Colorado,§ but subsequently in describing the Elotherium crassum and other species,|| remarks that the formation "probably belongs to a different horizon."

In the Pliocene strata above described, mammalian remains are exceedingly abundant over limited areas, those of horses in an especial manner. Those obtained are as follows:

The most important paleontological results are: (1) The discovery that the camels of this period possessed a full series of upper incisor teeth; (2) that the horses of the genus Protohippus are, like those of Hippotherium, three-toed; (3) that a Mastodon of the M. ohioticus type existed during the same period.

* See Proceed. Acad. Nat. Sciences Phila., 1872, p. 279.

+ Extinct Batrachia and Reptilia of North America, 1869, pp. 40-98.

Since the above was written and set up, I have obtained abundant evidence of the correctness of this induction. In examining a collection from this formation, made by one of my assistants, I find a series of Mesozoic genera of vertebrates as follows: Dinosauria, Cinodon arctatus, gen. et sp. nov.; Polyonax mortuarius, gen. et sp. nov.; Agathaumas milo, sp. nov.; Testuvinata, Compsemys sp.; Trionyx is also represented, and a genus of Crocodilia nearer to the cretaceous form Bottosaneus than any other, so far as the remains are indicative. Cinodon is a herbivorous saurian, to be referred to the Hadrosauride. The maxillary teeth are rod-like, with a narrow enamel face on the inner side, the remainder of the surface being like a rat-tail file. The teeth have no stem, and the successional crowns occupy an excavation on the posterior or outer side of the shaft. They push the functional teeth inwards and upwards, so that the grinding surface exhibits at one time a transverse section of three teeth, viz: an outer young crown, a middle worn crown, and an internal stump. Longitudinally, three teeth also exhibit the relative stages of protrusion, so that every third cross row is identical in character. Enamel smooth, with a medium keel, and entire margin. Various parts of the skeleton indicate an animal of the size of a horse.

Amer. Jour. Sci. Arts, 1870, p. 292.

|| Loc. Cit., 1873, p. 486.

Represented by a portion of the left ramus of the mandible, which contains alveoli for and portions of I. 3, c. 1, and P. m. 4. The incisors are closely crowded by the huge canines, which have larger proportions than dogs generally, resembling more those of the bears, or large feline carnivora. The first premolar is one-rooted and separated by a long diastema from the canine. The second premolar is two-rooted and separated from the first by a short diastema. The third is also separated by a distema from the second, which exceeds that in front of the latter. The fourth follows the third immediately. The mental foramina are two, one large, below the first premolar, the other smaller, but little below the alveolar margin opposite the posterior margin of the second premolar.

This large species is about as large as the Canis haydenii of Leidy, and differs from the type in the the anterior postion of the mental foramina, perhaps an individual variation. It is characterized among dogs, by the weakness of its premolars as much as by the strength of its canines.

CANIS SAEVUS Liedy, Anc. Fauna, Nebraska, p. 28.

TOMARCTUS BREVIROSTRIS Cope, Paleontological Bulletin, No. 16,

p. 2.

MARTES MUSTELINUS, Cope, Paleontological Bulletin,* No. 14, p. 1. (Aelurodon.)

PERISSODACTYLA.

APHELOPS MEGALODUS Cope, Pal. Bull., No. 14, p. 1.

This large species and the A. crassus, Leidy, were very abundant during the Pliocene period in Western North America. Their remains are every where mingled with those of horses and camels. The former, and probably the latter, is to be referred to a genus distinct from both Aceratherium and Rhinocerus on account of the existence of but three premolar teeth in the mandibular series, and probably in the maxillary also. One of our specimens exhibits the missing superior premolar on one side. The outer incisor below, is a large tusk, while the inner is small and caducous, points in which this genus resembles the genera above-named, and differs from the African and tichorhine species, or genus Atelodus of Pomel.

A posterior upper molar represents the A. crassus in the original collections described by Leidy. A well developed tubercle which rises from the bottom of the valley between the inner extremities of the

* These publications may be procured at the Naturalists' Agency, Salem, Mass., or of the writer.

cross-crests in the last and penultimate molars of A. megalodus is wanting in the A. crassus; partly on this account I refer my second large Pliocene rhinoceros to the latter.

APHELOPS CRASSUS Leidy, Anc. Fauna, Nebr., &c., p. 228.

Leidy states that the formula of dentition of this species is identical with that of the Indian rhinoceros, and elsewhere that it is probably a true rhinoceros as distinguished from Aceratherium. He does not appear to have possessed material to verify these statements.

An imperfect mandibular ramus containing the last molar and alveoli of the four teeth which precede it, differs from the corresponding one of A. megalodus in the greater thickness in proportion to the depth. It is absolutely both shallower and thicker than a corresponding ramus of the allied species, while the teeth are larger, the last three occupying exactly a space equal to that supporting the last four of A. megalodus. The last molar s larger than the penultimate in A. crassus (larger in A. megalodus) and encroaches on the base of the coronoid process; in all the jaws of A. megalodus, this tooth is considerably in advance of this process, which rises more abruptly than in it. This tooth is shown to be the last molar, by the absence of any trace of alveolus or crown of a successional tooth behind it in the various jaws in question. In A. crassus the coronoid process rises gradually from the front of the last molar.

The last molar is not quite protruded in the type specimen of A.

crassus.

Near to the specimen just described, I found the left maxillary bone with nasal, frontal, and other elements of a rhinoceros which differ in some respects from corresponding parts of A. megalodus. The rather larger teeth would coincide with the type of A. crassus, but that the specimens belong to the same individual is not certain. It is charcterized by the same increase in size posteriously of the molars, the M. 2 exceeding that of A. megalodus, while the P. m. 2, (the first,) is considerably smaller. The latter measures less than half M. 2, while it is .8 the diameter of the same in the A. megalodus. There is no rudiment of P. m. 1, hence this specimen displays fully the characters of the genus Aphelops. The nasal bones are long, acuminate, straight, and not coössified. They are tectiform, and distally compressed, instead of flattened, as in two specimens of A. megalodus; they are also quite rugose at the extremity. These characters may be only sexual. As in A. megalodus, they did not support a horn.

HIPPOTHERIUM SPECIOSUM Liedy, Anc. Fauna, Dakota, Nebraska, p. 282.

HIPPOTHERIUM PANIENSE, sp. nov.

Indicated by molar teeth in the collection. Two of these have elongate curved crowns; the longer is a left posterior, the more abraded a right median. The latter is characterized by the generally greater

simplicity of the enamel boundaries of the lakes as compared with the same portions of H. speciosum, with which it agrees in size. The only plications to be observed are the usual opposite ones entering the lakes from the middle of their adjacent boundaries, and a slight one at their inner angle of the same border of the anterior lake. The inner crescents are united, the posterior retaining its width posteriorly and giving off the posterior inner column from its anterior half. Both the internal columns are longitudinally oval and rather small, the anterior well separated. The adjacent enamel border gives of the usual projecting fold. Outline of crown nearly quadrate.

A second molar, less worn, presents therefore a little greater complexity of enamel folds. Thus the anterior inner part of each lake is folded into a loop, and there is a second pair of opposite folds outside the usual pair on the adjacent borders of the lakes.

A third molar is much more worn than either of the preceding, so as to throw the inner and median posterior areas together. The anterior median is well isolated and subround. There are no folds of the en-. amel plates whatever.

From the neighborhood of the Pawnee Buttes, Colorado.

PROTOHIPPUS LABROSUS. Sp. nov.

Having obtained a number of fragmentary and entire crania referable to species of the present genus, it becomes possible to correlate the mandibular with the maxillary forms, dentition, etc., as it has not been possible to do heretofore. Of mandibles there are four types, which refer to species as follows: Symphysis, flat, shallow; no diastema between their incisor and canine teeth; P. labrosus. A diastema, in front of canine; symphysis narrower, deep; inferior molars smaller; P. sejunctus. Symphysis narrow, deep, contracted, and smaller; lower molars larger; P. perditus.

These comparisons are instituted on one mandible of the first, two entire and three incomplete ones of the second, and two of the third types, all but two accompanied by superior molars or crania.

The specimen of P. labrosus embraces also the right maxillary bone, containing five molars; a second specimen includes three superior molars of the left side; it is also represented by several isolated molars.

Protohippus labrosus resembles the two species described by Leidy as Merychippus, in the short crowns and long roots of the molar teeth, with thickened external ridges separated by thin bands of cementum. It therefore differs from Protohippus perditus and P. placidus, resembling the first named in size. It is exactly intermediate between the P. insignis and P. mirabilis in size, and to it is no doubt to be referred Dr. Leidy's No. 4 of the latter.* Either there are three species of the present char

*Ancient Fauna Dakota and Nebraska, p. 300; figured pl. xvii, figs. 8-9.