£ MEMOIRS 01 THE CAENEGIE MUSEUM, Vol. VII. No. 6. THE AMERICAN DICERATHERES. By O. a. Peterson. (Plates LVII-LXVI.) Introductory. At the outset the writer wishes to acknowledge his indebtedness to Dr. W. J. Holland for much valuable assistance and advice in the preparation of the following paper, and for permission freely to use the material in the Carnegie Museum. To the authorities of the Peabody Museum of Natural History at Yale University thanks are due for their courtesy in allowing me to study and illustrate the types of Professor 0. C. Marsh. I wish to express my gratitude Xo Professor F. B. Loomis, of Amherst, for granting me free access to his collection of types and drawings. I wish to gratefully acknowledge the kindness of the authorities of the American Museum of Natural History for granting me the privilege of exam- ining the material from the John Day beds forming a part of the collection of the late Professor Cope, and allowing me to describe a new species of the genus Dicera- therium. Thanks are also due to the Librarian of Congress for literature for- warded for consultation to the Carnegie Museum, to Mr. James W. Gidley, of the U. S. National Museum, and to Mr. Harold J. Cook for information. Mr. Syndey Prentice has carefully executed the drawings here reproduced. 399 400 memoirs of the carnegie museum. Earlier Investigations. A number of papers dealing with the subject of this memoir have from time to time appeared, based upon material obtained by different parties, who in the past two decades have worked in western Nebraska and contiguous territory. Some of these papers possess genuine value. Other papers have also appeared, which indicate that the study given by their authors was hasty and of only a preliminary nature, often containing mistakes, which cause more or less difficulty to the student. One marked error has been the attribution of specific value to certain characters of the dentition and other parts, which after a more exhaustive study are clearly seen to be misleading. It is hoped that the following pages may prove to be a stimulus to further study and the exercise of greater care in this field of investigation. In earlier contributions relating to the Diceratheres published by the author it has been stated that a more detailed study of the large collection obtained in the Agate Spring Fossil Quarries would be forthcoming, after the process of extracting the fossils from the matrix should be completed. Since that announcement much work has been done. The writer having at his command material consisting of the remains of some two hundred or more individuals, was induced to question the validity of some alleged specific characters. It is hoped that the following pages may supply safeguards against error in the future. With only a few specimens before him, a student may establish species to his own satisfaction upon characters selected by him at the time, but which after more abundant material is accessible to him may prove to be invahd. In various publications^ there have been reported to be in the Agate Spring Fossil Quarries and their immediate neighborhood no less than seven species of the genus Diceratherium, besides a new genus, Metacoenopus. At first glance it might appear that the characters relied upon by the authors in estabhshing the different forms are valid, but after a more intensive study it is found that some species must be abandoned, and others must be regarded as doubtful. The result of our recent investigations proves that in this case we must either condense the number of proposed species, or establish an infinite number of additional new forms. The latter course would be eminently unscientific, though justifiable if we accept as valid the characters employed and relied upon in discriminating the various 1 Loomis, F. B., Amer. Jour. Sci., Vol. XXVI, 1908, p. 51-64. Cook, Harold J., Amer. Naturalist, Vol. XLII, 1908, p. 543-545; Nebraska Geol. Surv., Vol. Ill, 1908, p. 245-247. Barbour, E. H., Science, N. S., Vol. XXIV, Dec. 14, 190fi, p. 780-781. Peterson, O. A., Science, N. S., Vol. XXIV, Aug. 31, 1906, p. 282-283. PETERSON: THE AMERICAN DICERATHERES. 401 species which have been proposed. Whether the views expressed in the work upon the Diceratheres here offered shall prove to be conclusive, can only be ascer- tained in the light of the future. The improbability of having been able to reach an absolutely final conclusion is abundantly realized by the writer. Stratigraphy. Since the earliest descriptions of the European forms of the Diceratheres by Pomel (1853), Duvernoy (1854), and the final determination of the genus by Marsh (1875), many papers treating of the Rhinocerotidse have appeared in America as well as in the Old World. Through the studies of Professor Osborn and Mr. Hatcher, based upon some early American forms, we learn that the phylum Dicera- therince had already acquired incipient nasal horns in the White River Oligocene of South Dakota. It is now known that the forms, not alone of Diceratherium from the succeeding John Day beds, but all other mammalian remains available for comparison from the same horizon of the John Day in which Diceratherium is found, represent an earlier facies than those from the Nebraska-Dakota Miocene. In order to give conveniently a clear view of the stratigraphic correlation the diagram on page 402 is inserted. The Ohgocene in South Dakota, as is well known, is much more extensively developed than in Nebraska. It comprises, besides the three usually recognized faunal zones, the Titanotherium beds (= Chadron beds), the Oreodon, and the Leptauchenia beds ( = Brule beds) , two other easily recognized divisions, one the Metamynodon beds included in the Brule beds, and the other, the Protoceras cHfMTA- sandstones, bt)th in the Leptauchenia clays^ which arose from deposits made by streams. The Miocene section of South Dakota falls into two (Lower and Upper Rosebud beds), instead of the four divisions, recognized in Nebraska. The four divisions of the Nebraska Miocene comprise the Gering, the Monroe Creek, the Lower and the Upper Harrison. The latter is regarded by the writer as the base of the Middle Miocene. The lower portion of the John Day beds may be regarded as of transitional character and should therefore be classed as either uppermost Oligocene or lowermost Miocene, the only difference being that they are not separated from the Middle John Day beds by any apparent stratigraphic break. The MascaU beds of the John Day are somewhat later than the Upper Harrison beds of Nebraska, as indicated by a comparison of the faunae. We know the earlier progenitors of Diceratherium less clearly, though it is held that Coenopus occidentalis (Leidy) from the middle Oligocene and Coenopus 402 MEMOIRS OF THE CARNEGIE MUSEUM. South Dakota. Nebraska. John Day. European. § Snake River Beds. Sand and soft sand- stones, thinly bedded. Rattlesnake Formation. Upper Rosebud. Soft sandstone and sandy clays. Upper Harrison Base of Massive soft Middle sandstone. Miocene Mascall. Tuffs, ashes, etc. Upper and Middle Miocene. m Lower Harrison . Interstratified with harder sandstone led- ges. Dicera- therium cooki; D. nio- brarense. Columbia. Lava, basalt, and tuffs. g s Lower Rosebud. Soft sandstone and sandy clays. Dicera- thenium. gregorii sp. nov. Monroe Creek Beds. Hard sandstone. Upper John Day Lower Miocene (Aquita- nian). Gering. Soft Dicera- sandstones and ther. sp. sandy clays. [ Middle and D. an- Lower John nectens; Day. D. arma- ium. Dicerathe- rium pleu- roceros. Upper Brule Leptauchenia clay and Proto- eeras sand- stones. Canopus tridacUj- lus; C. da- kotensis sp. nov. Upper Brule. Leptauchenia clay. Lower John Day transi- tional from Miocene to Oligocene. Rhinoce- roses, spp. ind. Upper Oli- gocene (Stampian) Lower Oli- gocene (Sannois- ian). !5 O O O O Loiver Brule. Heavy bedded clays, Metamy- nodon sand- stones. Canopxis occiden- talis; C. copei. Lou'er Brule. Clays and thin sandstone ledges. Protacer- atherium. {Dicerathe- rium) mi- nutum. Chadron. Clay and sandstones, Titanotherium Beds. Chadron. Clays and sandstones. Titanotherium Beds. copei (Osborn) from the lower Oligocene (ISIetamydon beds) may be looked upon as at least in the line of this family. - While the general trend of the characters of Coenopus tridactylus and Coenopus dakotensis sp. nov. is obviously in the direction of Dicer atherium, it is in the John Day that we first recognize the genus as occurring in America. The South Dakotan and especially the Nebraskan series of Diceratheres are a later group belonging to the lower Miocene, closely following the species of the John Day, while the so-called R. oregonensis Marsh is an inadequate type, which furnishes infor- mation altogether too meager to be assigned to Diceratherium as is done by Pro- - O.sborn, H. F., Mem. Amer. Mus., Vol. 1, 189,8, p. 164. PETERSON: THE AMERICAN DICERATHERES. 403 fessor Loomis. Among Professor Osborn's third phylum of the later Miocene Rhinoceroses"' we may find a representative of this phylum. In Europe Diceratherium pleuroceros (Duvernoy) is the most completely preserved type from the Aquitanian. Its geological horizon apparently approxi- mates in age the John Day beds of North America. From the cast of this European species (Fig. 1) it is seen that the cranium back of the orbit is very suggestive of D. annectens. The brain-case has similar small Fig. 1. Diceratherium pleuroceros (Duvernoy). From a plaster replica in the Carnegie Museum. X 1/6. proportions, the supra-orbital ridges converge gently to form a similarly short sagittal crest, though less prominent and more rounded in the European form. The inion is also somewhat higher in the latter. The muzzle is long, though higher, and perhaps having more the proportions of that part in D. niobrarense from the Nebraska Miocene. The basi-cranium in the cast of D. pleuroceros is short and the mastoid process is in touch with the post-glenoid process. Thus the contour of the skull of the European species apparently has combined char- acters of D. annectens from the John Day and of D. niobrarense from the Nebraska Miocene. The dentition of the European form is too much worn to allow accurate comparison. By regarding such forms as Protaceratherium* {"Diceratherium^') minutum (Cuvier) of the Stampian as approximately parallel to Coenopus of the upper and middle Oligocene of North America, it appears that the family may be traced back to nearly the same geologic time in Europe and North America,^ ' Bull. Amer. Mus., Vol. XX, 1904, p. 321; Ap/ieZop.s {1 Peraceras) planiceps, p. 322; Aphelops {? Diceratherium) brachyodus p. 324. * Abel, 0., "Kritische Untersuchungen iiber die palaogenen Rhinocerotiden Europas," Abh. der K. K. Geologischen Reichsanstalt, Band XX, Heft 3, 1910, p. 10. ^ Osborn, Henry F., "Phylogeny of Rhinoceroses of Europe," Bull. Amer. Mus. Nat. Hist., Vol. XIII, 1900, p. 229-267; "Age of Mammals," p. 90. 404 MEMOIRS OF THE CARNEGIE MUSEUM. while according to recent work by European authors Prohyracodon orientale Koch is regarded as the earUest and most primitive representative of the Rhinocerotidse.*^ Diceratherium armalum of the John Day formation has the dentition as well as certain other features of the skull in a much less advanced stage of development 2 3 Fig. 2. Diceratherium minutum (Cuvier). M^ X i. After Cuvier. Fig. 3. Diceratherium douvillei. M^ X i- After Osborn. than D. annectens of the same deposit (Compare PI. LVII with text-figure 11, also with PL LXIII, fig. 6, and PI. LXVI, fig. 1). In the latter form we naturally might expect to meet with a greater range of anatomical variations, especially in connection with the dentition. We may reasonably expect to find grinding teeth, having crests ranging from those which are quite plain to those which have the various incipient projections, as crista, crochet, anti-crochet, etc. It is far from my mind to depreciate some, or all, of these characters; on the contrary, indeed, it is reasonable to expect that the dentition should be one of the first parts of the organism to undergo modification with a change in the environment. It is never- theless questionable whether the absence or presence of a crista, a crochet, and anti-crochet, more or less developed, or of a cingulum of greater or less prominence, should constitute a valid specific character in Diceratherium. I very much doubt whether these characters are of sufficient constancy to be relied upon to establish specific distinctions in a large collection of individuals from a given locality. Stress has in times past been laid upon the development of branches or spurs of different lobes of the cheek-teeth. It is plainly evident that D. annectens, as the result of its mode of life, was already in the time of the John Day more advanced, having filled out the grinding surface of its teeth more than its contemporary, D. armatum. In animals representing a later development in geological time, we should expect to find similar evidence of progression, and in a large assemblage of individuals that not all the specimens, say of D. cooki for example, are provided with crista and crochet united on the premolars and with crista small and crochet larger on the molars, but that these features, being in a plastic stage of development, would be found in an endless number of combinations from those less developed to those having more complex forms, and all within one species. « Abel, 0., I.e., p. 24, 44-45, 49. PETERSON: THE AMERICAN DICERATHERES. 405 Another feature, which often has been misinterpreted in connection with the study of the Diceratheres, is the difference in the contour of the skulls. It is a well- known fact that in individuals of almost any group of mammals the contour of the skuU changes until well after complete maturity. Furthermore the sexual differ- ences in the form of the skull in the Diceratheritie branch of the Rhinocerotidse are surprising. In the early development of the phylum the difference between the sexes was weU indicated by the form of the skull. ^ This is undoubtedly due in great measure to the possession of the prominent nasal horns by the male. In a young male, for instance of D. cooki, there are found the incipient horn-cores, the nasals are quite long and pointed in front of the horns, while back of the horns there is relatively small lateral constriction of the nasals, the temporal ridges are generall}^ weak and not united to form a sagittal crest, the zygomatic arches are slender, often without, or with very shght, rugosities on the posterior angles. This is also quite generally true of the skull of an adult female, with the exception that in the latter there is a gradation from skulls without any horn-cores in the young, to those having incipient horn-cores in some of the fully adult and old, and that there is considerable variation in the prominence of the temporal ridges and the manner of their convergence before they reach the inion. I have as yet never seen a well-developed and heavy horn-core, the ends of the nasals short and blunt, the skull much constricted laterally back of the horn-cores, saddle-shaped on top, with a sudden lateral expansion and heavy rugosities on the posterior angles of the zygomatic arches in D. cooki, except in association with well-worn or very old dentitions. It is very plain to me that more latitude should be assigned to the significance of the contour of the skull in the genus Diceratherium than has some- times been done. In study and comparison especial pains should be taken (1) to ascertain whether the skull is that of a male or a female, or of the young, or not entirely adult animal; (2) skulls of fully adult or old males are more uniform in contour than anj^ others, and therefore more reliable in establishing species; (3) the significance of the crushing received by the specimen in one direction or the other should be noted. The following table of comparisons represents fairly well the large number of skuUs of Diceratherium cooki in the collection of the Carnegie Museum. Remains of very young animals are not included in this table, but will be treated separately. The object of the descriptions given under H, Nos. 2816, 2463, and 2478 in the following table are to draw attention to the great ease by which misinterpreta- tions may result with only a portion of the skull in hand and displaying charac- ters, some of which may be only pathological. ' Osborn, Henry F., "The Extinct Rhinoceroses," Mem. Am. Mus. Nat. Hist., Vol. I, Part III, 1898, p. 162. 406 MEMOIRS OF THE CARNEGIE MUSEUM. Contour of Skull compared with the Dentition. Contour of Skull. Dentition. A. No. 1572. Type of D. cooki. Old male. B. No. 1S41. Paratype of D. cooki. Young male. C. No. 1923. Young male. Skull symmetrical in the region of the parietals, occiput, zygomatic arches, and palatal regions, but very slightly depressed by crushing in the frontal and nasal regions. Horn-cores prominent, nasals blunt and constricted back of horns, frontal region broad and flat, temporal ridges moderatelj^ promi- nent, but not united to form a sagit- tal crest, brain-case broad, arches suddenly expanded posteriorly, heavy and rugose on posterior angle. Skull comparatively broad and low. Skull somewhat distorted by crushing and otherwise unreliable on account of immature age. Horn-cores incipient, nasals pointed, not projecting over the premaxil- laries, due partly to crushing, a considerable constriction of nasals back of horn-cores; f rentals com- paratively narrow and slightly con- vex from side to side, due partly to crushing and partly to immaturity. Temporal ridges less prominent and not united to form a sagittal crest, but quite broadly united with the occiput, brain case broad, zygomatic arches expanded posteriori}' and plainly indicating the usual rugo- sities formed in mature males. Skull comparatively narrow, partly due to immaturity and partly to crushing. Top of skull more symmetrical than in No. 1841, but considerable lateral crushing has taken place, especially noticeable in the region of the palatines. Base of skull open at suture and basioccipital lost. Horn-cores incipient, nasals pro- jecting over the premaxillaries, more than in some specimens, slightly less pointed anteriorly and more constricted back of the horns than in No. 1841; frontals convex from side to side and proportionally narrow, due to crushing and imma- turity; temporal ridges quite weak especially on right side, not united to form a sagittal crest; brain-case wide, zygomatic arches heavy, indi- dicating that on further develop- ment of the skull the rugosities on posterior angle would be heavy as in old males generally. Skull comparatively narrow and high. Dentition considerably worn. Crista of premolars worn off, me- dian valley on P- and P' isolated by wear, crochet of P- and P^ united with ectoloph, cingulum on P'^ cjuite strong, crochet on P"* not entirely united with ectoloph; crochet united with ectoloph, median valley open and post-fossette isolated on M'; crista slight, crochet heavy, and post-fossette open posteriorly on M*; crista weak and crochet strong on IVP. Permanent incisors just appearing in the alveoli of the premaxillaries. P' considerably worn, causing the post-fossette to have already become isolated. P'^ very slightly worn, crista and crochet very slightly de- veloped and not united on tooth of the right side, while that on the left side has crista and crochet better developed and would on much wear form an isolated medifossette; anti- crochet slightly indicated. P^ has crista and crochet quite well de- veloped and united. P* is well worn, has a small tubercle in the median valley between proto-and metalophs, crochet well developed, nearly meeting the crista, which is only slightly indicated on the tooth of the right side. M' with well de- veloped crista and crochet nearly meeting to isolate the medifossette. M^ just erupted, and shows even less development of crista, but with strong crochet. M' buried in the maxillary. P' in same stage of wear as in No. 1841, P^ quite simple, no crista, a weak crochet, which on further wear of the tooth would practically disappear; post-fossette very large. P^ not as yet worn, both crista and crochet weak, but showing a ten- dency to unite so as to isolate the medifossette on further wear of the tooth; post-fossette broadly open posteriorly. D.P^ much worn, me- dian valley nearly isolated by wear of proto- and metalophs; a tubercle of small size in the median val- ley; post-fossette isolated. M' with double, though small, crista; crochet heavy nearly reaching the protoloph; post-fossette broadly open poste- riorly. M- just starting to receive wear, crista extremely weak, crochet stronger than usual. M' buried in the maxillary. PETERSON: THE AMERICAN DICERATHERES. 407 Contour of Skull compared with the Dentition. — Continued. Contour of Skull. Dentition. D. No. 2467. female. Fully adult E. No. 1855. Paratype of D. cooki. Female. F. No. 2809. Male. Skull somewhat crushed back- ward and to one side, though of quite symmetrical appearance. Only a suggestion of horn-cores, nasals not projecting over the pre- maxillaries, quite long and pointed in front of the horn-cores and very little constricted back of them; frontals quite broad, though slightly injured by lateral crushing; tem- poral ridges prominent, and remain- ing well apart throughout to the oc- cipital crest; brain-case large, zygo- matic arches light. Skull propor- tionally high and narrow. Skull somewhat crushed to one side. Nasals broken well back, but the sides do not indicate as great a con- striction as in skulls of males. Frontals broad; temporal ridges quite prominent and placed quite close together before reaching the inion, but not forming a sagittal crest. Brain-case broad, zygo- matic arches light. Skull rather broad and low, to a great extent brought about by crushing. Skull slightly depressed by crush- ing. Nasal horn-cores very robust, nasals extend in front of premaxil- laries, bluntly pointed anteriorly and gently constricted back of horn- cores; frontals broad; temporal ridges prominent and remaining far apart all the way back to the occi- put. Brain-case large; zygomatic arches very robust on the posterior angle. Skull rather low and broad. Small functionless and persistent canines indicated on both sides. P' much worn. P^ with no crista, but a weak crochet, the latter being double on tooth of left side; a small antecrochet present on this tooth of the right and left jaws and the post-fossette nearly enclosed. P^ without crista, crochet also poorly developed, crenulated, and post-fos- settes isolated by wear. P^ with weak crista and crochet. All the premolars with strong cingulum in- ternally. M' with no crista, but heavy crochet, a minute tubercle in the median valley; a large post- fossette and no cingulum on internal face of the tooth. IV'P with weak crista but strong crochet, a very minute tubercle in the median vallej', post-fossette broadly open and cingulum only faintly indicated on the internal faces of the tooth. M' has received little or no wear. Crista and crochet very poorly de- veloped. P^ much worn. P- with medi- and prefossettes quite distinct; crochet with crenulated border, post-fossette large. P^ quite worn, but medifossette indicated. Crochet nearly united with ectoloph. Post- fossettes quite large. P'' with medi- fossette (especially on the tooth of right side) isolated, prefossette and median valley united. Post-fossette large. Premolars with heavy cin- gulum. M' much worn, no crista, crochet nearly united with ectoloph; post-fossette large, cingulum weak. M^ with strong crista and crochet (the two nearly meeting on tooth of right side). Post-fossette large. ]\'P with crista and crochet much better developed on tooth of left side, cingulum weak on molars. Dentition represented onlj' by P^ and P* and IVP and M^. P^ with no crista; crochet strong, crenulated internally and nearly united with ectoloph. Post-fossette large. P^ with no crista, crochet strong an crenulated, as on tooth in advance of it. Post-fossette large. IV'P with no crista, but strong crochet, which on a little further wear would unite with the ectoloph. Post-fossette nearly isolated by wear. M^ with prominent crista and crochet. A tendency to develop a small tubercle in the median valley. Post-fossette large. The premolars have cingulum better developed than on the molars. 408 MEMOIRS OF THE CARNEGIE MUSEUM. Contour of Skull compared with the Dentition — Continued. G. No. 2408. Paratype of D. cooki. Rather young female. H. No. 2463. Old female with pathological de- formity. No. 2816, Male. No. 2478, Male? Contour of Skull. Skull somewhat depressed by crushing, especially over the poster- ior part of the nasals and the fron- tals. Nasals not projected in front of the premaxillaries, pointed, no horn- cores indicated, but nasals thickened in this region ; little or no constriction back of the thickened region; fron- tals broad and flat; temporal ridges fairly prominent and early united to form a sagittal crest before the inion is reached (the latter is broken off) ; brain-case broad; zygomatic arches slender. Skull proportionally broad and low, due partly to crushing. Dentition. Skull crushed so as to produce an unusually, high occiput. Frontal and nasal regions quite symmetrical. Anterior portion of nasals and pre- maxilla^ broken off. Anterior portion of skull not un- like that of No. 1572 (type of D. cooki) in fact the general contour is similar. However, the sagittal re- gion is narrower, there being a de- cided sagittal crest in the present specimen. Zygoma lighter, without the ru- gose area on the posterior angle. The comparatively light structure of the skull clearly indicates a fe- male specimen. The greater portion of skull No. 2816 is preserved, while No. 2478 is only represented by a portion of the top and back. These two specimens are no less unique than No. 2463 just de- scribed. The chief feature is the inflated condition of the frontals, which is not unlike that in Rhinoceros bicornis, except that in the fossil specimens the swollen area is confined more to the posterior portion of the frontals. In No. 2478 the inflated area is more pronounced than in 2816 and also differs in the median line from the latter, 'having this inflated region continued backward as a promi- nent rounded ridge between the tem- poral ridges. Judging from the heavy and ru- gose zygomatic arches on No. 2816 the skull is undoubtedly that of a male. Dentition comparatively little worn. P' well worn. P^ with medi- fossette isolated, especially on tooth of right side, tiny crenulation on the face of the crochet wall, post-fossette widely open behind. P with medi- fossette isolated, crenulation on crochet as on preceding tooth, post- fossette large. P'' with medifossette isolated, especiallj' on tooth of left side, post-fossette large; prominent cingulum on internal faces of pre- molars. M' with moderate rounded crista and heavy crochet, but not united to form a closed medifossette, post-fossette broadly open poster- iorly. M* with more prominent crista, which very nearly unites with the crochet, post-fossette large. M' well erupted, but not yet in contact with the lower teeth, crista and crochet rather delicately developed. Cingulum little developed on the internal faces of the molars. P' of left side represented only by an e.xtremely thin band of dentine. P^ and M' closely succeeding one another, nearly closing up the space for P''. This was accomplished dur- ing the life of the animal. M' of both sides have curious metastyles located on the postero-internal angle, a deep fissure separating them from the main body of the teeth; median valley open, but crista and crochet well shown. Dentition much worn (See Fig. 4.) The dentition of No. 2816 is essen- tially that of D. cooki, while in No. 2478 there are no teeth represented. PETERSON: THE AMERICAN DICERATHERES. 409 In comparing (D) No. 2467 in the above table with tlie description by Dr. Loomis of his proposed species Diceratherium schiffi it will at once be observed that while the general contour of the skull agrees fairly well, the dentition totally disagrees in the presence of the minute canines^ and the difference of the config- FiG. 4. Upper dentition of Diceratherium cooki, C. M., No. 2463, showing the reduced condition of P^ of right side and accessory tubercles on M^. X J. uration of the grinding surfaces of the teeth. We are not permitted, therefore, according to the usually accepted view to refer this specimen to the above pro- posed species. The same comparison with ((?) No. 2408 shows that while the dentition agrees, the contour of the skull is less in accordance with the above- mentioned description, and corresponds better with the original type of D. cooki, sexual characters excepted. With another female skull (E) No. 1855, one of the original specimens used as a paratype in my earliest paper, D. schiffi seems to agree best, except that the temporal ridges come closer together before reaching the inion. It is thus seen that in comparing female skulls it is frequently found that, dentition and contour of skull do not both agree; on the contrary the material affords numerous different combinations. There are of course female skulls which occasionally answer to the description by Loomis somewhat more closely than in the cases stated above. However, it is quite obvious that we would create a difficult task for the systematist and student, not to say a non-scientific record of the subject, were we to establish additional species founded upon our abundant material. The different patterns of the premolar and molar teeth which were formerly regarded as satisfactory for the establishment of species are obviously not to be relied upon, at least not in connection with the study of the material from the Agate Spring Fossil Quarries. The differences to which allusion is here * The canines are probably deciduous teeth, which sometimes abnormally persist and their presence may be regarded as only an individual peculiarity. Professor Owen speaks of a canine in the foetal skull of Rhinoceros indicus ("Odontography," p. 592). 410 MEMOIRS OF THE CARNEGIE MUSEUM. made should rather be regarded as in the main due to the varying extent to which speciahzation has operated in the individual. The teeth, especially of the smaller American species of the Diceratheres of the Nebraskan Miocene, may be said to be in a stage of rather rapid and progressive change. It is hardly probable that we shall be able to perfect anj' satisfactory adaptive radiation of forms, such as has recently been suggested,'' from the study of this material. In paleontology we are debarred from the finer subdivisions used in recent zoology. We have to content ourselves with characters which stand out more prominentlj- and which may be used not only to clearly determine species, but to give aid in the question of cor- relations of faunse and demarcations in geology. From the studj' of the collection above tabulated, we are forced to regard the variations shown as being individual, sexual, juvenile, and pathological. 1. Rhinoceros C?Diceratherium) pacificus Leidy," incertce sedis. Type. — Upper molar, left side. United States National Mu- seum. Horizon. — ? Miocene. Locality. — "Alkali Flat" John Day region, Oregon. Fig. 5. Di- Paratype. — A mutilated fragment of the upper jaw of the right ceratheriutn pa. gi^g^ with portions of the fangs of the true molars and an inferior cificum Leidy, ^lolar tOOth. . ,^ ' .r Horizon. — ? Miocene. After Leicly. Locality. — Bridge Creek, John Day region, Oregon. As indicated in Leidy 's original description this material from "Alkali Flat" in the John Day region, Oregon, was provisionally referred to Coenopus (R.) occi- dentalis. Receiving more material from the same general region Leidy again restudied the "Alkali Flat" specimens and finallj' placed them, together wdth the material from Bridge Creek, under his species R. pacificus. This type like that of the John Day material referred to as R. hesperius we now find to be inadequate, or of very doubtful generic value. Leidy was appar- ently not clear as to the true association of these different fragments and teeth. On page 222 (I.e.) he states that the second molar described, "may be a true molar of the preceding species" [R. hesperius] described in his report. I am miable to agree with Dr. Loomis in accepting this species as valid and am obliged, as the result of the study I have made, to regard this type as incertm ' Loomis, F. B., I.e., p. 53. '» Proc. Acad. Nat. Sci., Philadelphia, 1870, p. 112; 1871, p. 248; U.S.G.S. Terr., Vol. I, 187.3, p. 221. Plates II, VII, Figs. 6-7, 24-25; Amer. Jour. Sci., Vol. XXVI, 1908, p. 55-56, Fig. 6. PETERSON: THE AMERICAN DICERATHERES. 411 sedis. It pertains to an animal no larger than, for instance, D. annectens (Marsh), but that is about all I feel justified in positively stating. 2. Rhinoceros (?Diceratheriuni) hesperius Leidy," incertce sedis. Type. — A third upper molar. Location of the type uncertain. Horizon. — Miocene? Locality. — ^John Day region, Oregon. The material from the John Day of Oregon, which Leidy finally referred with a question to the Californian species "Rhinoceros hesperius,"^" is, as Leidy himself states, inadequate. The more important features of the remains of the skull appear to be the position and size of the infra-orbital foramen and the position of the base of the zygomatic process of the jugal. Of material referred to R. hesperius Leidy says (I.e., U. S. G. S., Vol. 1, p. 220) : "The anterior extremity of the space included by Fig- 6. Di- , 1 !■ 1 1 J ceratherium the zygoma extends to a hne with the mterval oi the second and hesperium. third molars; in Rhinoceros \Coenopus] occidentalis it extends only to a (Leidy) M'. . X - After line with the back part of the last molar. The infra-orbital foramen Lgi^y. is large and occupies a position above the second premolar; in R. [C] occidentalis it is over the third premolar." This description agrees with D. cooki so far as the zygomatic arch is concerned, but the infra-orbital foramen of the latter species is usually opposite the interval between P- and P^ both in D. annectens and D. cooki. In D. annectens the space included by the zygoma referred to by Leidy is slightly more posterior. In comparing the measurements of well-known species of Diceratherium with the figures of specimens referred to R. hesperius and R. pacificus it is seen that M^ of hesperius might well go with the molar of pacificus. So far as the difference in size and even the configurations of the crowns in these teeth go, there is now no valid reason for separating the two on the evidence produced. The tubercle of the median valley of M' of R. hesperius may well be questioned as a specific character, and is in all probability, as Leidy suggests, "merely an individual peculiarity." In my opinion these remains are generically and specifically unidentifiable, but hold the historic position of being the first material of the Rhinocerotidse obtained in the John Day region of Oregon. "Proc. Acad. Nat. Sci. Phila., 1865, p. 176-177; 1870, p. 112; 1871, p. 248. U. S. Geol. Surv. Terr., Vol. I, 1873, p. 220, PI. II, Figs. 8-9. Amer. Jour. Sci., Vol. XXVI, 1908, p. 55, Fig. 5. 1- Professor Osborn has placed this Californian specimen with Coenopus platycephalus, "The Extinct Rhinoceroses," Mem. Amer. Mus., Vol. I, 1898, p. 144. 412 MEMOIRS OF THE CARNEGIE MUSEUM. 3. Rhinoceros (?Diceratherium) oregonensis Marsh/^ incertce sedis. Type. — Penultimate upper molar. Peabody Museum of Natural History No. 10,002. Horizon. — ("Pliocene deposits of Oregon") Mascal formation. Locality. — John Day region, Oregon. In reference to this fragment Marsh says : '. . . At the union of the transverse posterior ridge with the outer cusp, there is a deep cavity, nearly circular, and enclosed by a vertical cylinder of enamel. The anterior crest, also, is divided, a strong branch being sent inward and backward from the posterior side into the main transverse valley." Whether or not this specimen pertains to a Dicerathere may never be settled. I have recently examined this tooth and may state that it may equally well belong to a middle Miocene Rhino- ceros (Teleoceras) . I cannot now see any reason for regarding this type as anything except of indeterminate value. 4. Diceratherium (?) truquianum (Cope), incertce sedis. Type. — A symphysis of the lower jaws with all the incisors and the posterior portion of the ramus with Ms and M3. American Museum Natural History (Cope Collection) No. 7333. Horizon. — Lower John Day, Miocene(?). Fig. 7. (?Di ceratherium) Rhi noceros oregonen- sis Marsh. M^ X i. After Loomis. Fig. S. Diceratherium truquianum (Cope). No. 7333, Coll. Am. Mus. Symphysis and portion of left ramus. X i. In describing an incomplete mandible from the ("Truckee beds"^*) (Lower John Day) Professor Cope says that the specimen "supports molar, canine [= lateral incisor], and incisor teeth. . . . The crowns of the canines [= lateral incisors] are considerably wider than those of the incisors [= median incisors], but do not project very far beyond them. They are sub-triangular in outline, " American Journal Science, Vol. V, 1873, p. 410. Ibid., Vol. XXVI, 1908, p. 60, Fig. 13. " American Naturalist, Vol. XIII, 1879, p. 333. PETERSON: THE AMERICAN DICERATHERES. 413 having a prominent shoulder at the base on their inner side. . . . Diastema long; ascending ramus vertical, flat in front. Depth of ramus at last molar .065; length of crown of canine [= lateral incisor] .027; width of do. at the base .024." This type specimen, now in the Cope collection of the American Museum of Natural Historj^ has recently been studied by the writer. After a comparison with fragments of the lower jaw associated with a skull (No. 10,005) of Diceratherium armatum in the Yale Museum I think it possible that this specimen may pertain to that species. The thick and rather shallow ramus of Cope's type is character- istic of D. armatum. The symphysis is similarly long and heavy, the mental foramen is below Pi, as in the latter species, and the comparative measurements of the two specimens agree fairly well. The question of the relationship of these two species cannot, however, be entirely satisfactorily settled until more complete material of the John Day forms is obtained. Additional Measurements of Type of D. truqui.\num Cope. Antero-posterior diameter of crown of median incisor 6 mm. Transverse " " " " " " 8 " Height " " " " " gi " " " lateral " 26i " Transverse " " " " " " 23 " Antero-posterior " " " " M^ 44 " Transverse " a « > o > 00 w o w <; c/0 P5 W z o H a PL, O 462 MEMOIRS OF THE CARNEGIE MUSEUM. EXPLANATION OF PLATE LIX. Fig. L Diceratherium gregorii, type. Side view of skull. American IMuseum of Natural History, No. 12933. Fig. 2. Diceratherium gregorii, type. Palatal view of the same skull. All figures § natural size. X o > w C/3 O W PS < 00 z o a H W 464 MEMOIRS OF THE CARNEGIE MUSEUM. EXPLANATION OF PLATE LX. Fig. L Diceratherium cooki type. Carnegie Museum, No. 1572. Fig. 2. Diceratherium niobrarense type. Carnegie Museum, No. 1271 Fig. 1, I natural size; Fig. 2, | natural size. Memoirs Carnegie Museum, Vol. VII, Plate LX, D. cooki Peterson and D. niobrarense Peterson. 466 MEMOIRS OF THE CARNEGIE MUSEUM. EXPLANATION OF PLATE LXL Fig. 1. Diceratherium cooki, type. Carnegie Museum, No. 1572. Fig. 2. Diceratherium niobrarense, type. Carnegie Museum, No. 127L Fig. 1, ^ natural size; Fig. 2, | natural size. Memoirs Carnegie Museum, Vol, VII. Plate LXI. D. cooki Peterson and D. niobrarense Peterson. 468 MEMOIES OF THE CARNEGIE MUSEUM. EXPLANATION OF PLATE LXII. Fig. L Diceratherium cooki, type. Carnegie Museum, No. 1572. Fig. 2. Diceratherium viobrarense, type. Carnegie Museum, No. 127L Fig. 1, I natural size: Fig. 2, | natural size. Memoirs Carnegie Museum, Vol. VII. Plate LXII. D. cooki Peterson \nd D. niohrarense Peterson. 470 MEMOIRS OF THE CARNEGIE MUSEUM. EXPLANATION OF PLATE LXIII. Fig. L Diceratherium cooki, ulnar view of manus, Carnegie Museum, No. 2473. Fig. 2. Diceratherium cooki, palmar view of manus, Carnegie Museum, No. 2473. Fig. 3. Diceratherium cooki, radial view of manus, Carnegie Museum, No. 2473. Fig. 4. Diceratherium cooki, dorsal view of manus, Carnegie Museum, No. 2473. Fig. 5. Diceratherium cooki, dorsal view of pes, Carnegie Museum, No. 1888. Fig. 6. Diceratherium annectens hypotype, American Museum Natural History, No. 7324, Cope Coll. Fig. 7. Diceratherium cooki, plantar view of pes, Carnegie Museum, No. 1888. All figures | natural size except Fig. 6, which is | natural size. Memoirs Carnegie Museum, Vol, VII Plate LXIII. D. cooki Peterson and D. annectens (Marsh). 472 MEMOIRS OF THE CARNEGIE MUSEUM. EXPLANATION OF PLATE LXIV. Diceratherium cooki. Carnegie Museum, No. 1888. Fig. 1. Calcaneum, dorsal view. Fig. 2. Calcaneum, distal view. Fig. 3. Calcaneum, plantar view. Fig. 4. Calcaneum, tibial view. Fig. 5. Calcaneum, fibular view. Fig. 6. Astragalus, tibial view. Fig. 7. Ectocuneiform, proximal view. Fig. 8. Ectocuneiform, distal view. Fig. 9. Ectocuneiform, tibial view. Fig. 10. Astragalus, fibular view. Fig. 11. Astragalus, plantar view. Fig. 12. Astragalus, dorsal view. Fig. 13. Cuboid, proximal view. Fig. 14. Cuboid, tibial view. Fig. 15. Entocuneiform, fibular view. Fig. 16. Entocuneiform, distal view. Fig. 17. Navicular, distal view. Fig. 18. Navicular, posterior view. Fig. 19. Navicular, fibular view. Fig. 20. Navicular, proximal view. Fig. 21. Cuboid, distal view. Fig. 22. Mesocuneiform, distal view. Fig. 23. Mesocuneiform, fibular view. Fig. 24. Mesocuneiform, tibial view. Fig. 25. Mesocuneiform, proximal view. Fig. 26. Metatarsal III, dorsal view. Fig. 27. Metatarsal III, fibular view. Fig. 28. Metatarsal II, fibular view. Fig. 29. Metatarsal II, tibial view. Fig. 30. Metatarsal IV, tibial view. Fig. 31. Metatarsal III, tibial view. Fig. 32. Metatarsal III, plantar view. Carnegie Museum, No. 2453. Fig. 33. Scaphoid, proximal view. Fig. 34. Scaphoid, distal view. Fig. 35. Scaphoid, ulnar view. Carnegie Museum, No. 2453. Fig. 36. Lunar, proximal view. Fig. 37. Lunar, radial view. Fig. 38. Lunar, distal view. Fig. 39. Lunar, ulnar view. Fig. 40. Cuneiform, radial view. Fig. 41. Cuneiform, distal view. Fig. 42. Cuneiform, ulnar view. Carnegie Museum, No. 1853, Fig. 43. Pisiform, radial view. Fig. 44. Trapezium, ulnar view. Fig. 45. Trapezoid, radial view. Carnegie Museum, No. 2453. Fig. 46. Trapezoid, ulnar view. Fig. 47. Trapezoid, distal view. Fig. 48. Trapezoid, proximal view. Fig. 49. Magnum, distal view. Fig. 50. Magnum, ulnar view. Fig. 51. Magnum, radial view. Fig. 52. Magnum, proximal view. Fig. 53. Unciform, radial view Fig. 54. Unciform, proximal view. Fig. 55. Unciform, ulnar view. Fig. 56. Metacarpal II, radial view. Fig. 57. Metacarpal II, ulnar view. Fig. 58. Metacarpal III, radial view. Fig. 59. Metacarpal III, ulnar view. Fig. 60. Metacarpal IV, radial view. Fig. 61. Metacarpal IV, ulnar view. Fig. 62. Metacarpal V, radial view. Fig. 63. Metacarpal V, palmar view. All figures are | natural size. z o 474 MEMOIRS OF THE CARNEGIE MUSEUM. EXPLANATION OF PLATE LXV. Fig. L Diceratherium cooki, young male, side view of skull. Carnegie Museum, No. 1848. Fig. 2. Diceratherium cooki, Palatal view same as Fig. L Fig. 3. Diceratherium? annectens, deciduous upper teeth, American Museum collection. Fig. 4. Diceratherium cooki, top view of skull, same as Figs. 1 and 2. All figures | natural size. Memoirs Carnegie Museum, Vol, VII. Plate LXV. Hi dz as (J4, Mil Jin z inB D. cooki Peterson and D. anncctens (Marsh). 476 MEMOIRS OF THE CARNEGIE MUSEUM. EXPLANATION OF PLATE LXVI. Fig. I. Dicer atherium annectens,hypotype , Side view of skull, American Museum, No. 7324, Cope Coll. Fig. 2. Diceratherium cooki, upper contour of lower jaws and crown view of den- tition. Carnegie Museum, No. 2499. Fig. 3. Diceratherium cooki, outer view of mandible in very young stage of develop- ment. Carnegie Museum, No. 1820. Fig. 4. Diceratherium cooki, outer view of mandible of fully adult male. Carnegie Museum, No. 2499. Fig. 5. Diceratherium cooki, alveolar border of lower jaw and crown view of den- tition. Carnegie Museum, No. 1923a. Fig. 6. Diceratherium cooki, alveolar border of lower jaw and crown view of den- tition. Carnegie Museum, No. 1841. Fig. 7. Diceratherium cooki, alveolar border and crown view of dentition. Carnegie Museum, No. 2476. Fig. 8. Diceratherium cooki, inner view of mandible, very young stage of develop- ment, Carnegie Museum, No. 1820. Fig. 9. Diceratherium cooki, upper contour of lower jaw and crown view of den- tition, same as Nos. 3 and 8. Fig. 1 is J natural size; Figs. 2 and 4 are \ natural size; Figs. 3, 5, 6, 7, 8, and 9 are 1 2 33 m K < Q Z < Z O m H a