Matthew, William Diller, 1871-1930.

Thomson, Albert.

American Museum of Natural History Scientific Publications

AMERICAN MUSEUM NOVITATESPublished byNumber 540 THEc AmERICAN MUSEUM oF NATURAL HIESTORY Jue1,93New York City un 16, 193256.9 (1182: 78.2)NEW FOSSIL MAMMALS FROM THE SNAKE CREEKQUARRIES'BY W. D. MATTHEW2The collection made by Albert Thomson for the Museum in 1923 inSioux County, Nebraska, includes considerable additions to the materialfrom the Upper Snake Creek and Lower Sheep Creek beds (Hipparionaffine zone, Merychippus primus zone). Some references to certainspecimens were made in my last contribution to this fauna. A nuimber ofnew or little known genera and species are described in the followingpages.Sthenictis bellus, new speciesTYPE.-NO. 20501, a right ramus of the lower jaw, with p2-ml preserved.HORIZON AND LocALITY.-Sheep Creek beds, Horizon A, Stonehouse draw'quarry.Fig. 1. Sthenictis bellus, sp. nov. Type, No.20501. Lower jaws-outer and crown views,natural size.CHARACTERS.-Size much less than S. dolichops, about equal to Mionictis incertaor Brachypsalis matutinus, but agrees with Sthenictis and differs from the other twoin the construction and proportions of the carnassial and premolars. The second.third and fourth premolars are two-rooted, compressed, not crowded, p4 with welldeveloped posterior accessory cusp. The shear of the carnassial is nearly antero-posterior, the metaconid well developed but not nearly as high as in Mionictis or'Snake Creek Contribution No. 4.'The manuscript of this paper is one of several left at the American Museum by Dr. Matthew atthe time of his death in September, 1930. It was apparently written about 1924, a year after the materialwas collected, and had been held awaiting illustrations. The section on Archteohippus was added sub-sequent to 1925. The paper is printed wnthout additions or alteration.-Walter Granger.AMERICAN MUSEUM NOVITATESBrachypsalis. The last molar has a single alveolus, which apparently contained alarge anterior and smaller posterior root, closely connate. In S. dolichops the alveolusis round-oval apparently for a single root.So far as the characters of the type jaw permit one to judge, thisspecies is the ancestor in the M. primus zone of S. dolichops of the M.paniensis zone.Cynarctus mustelinus, new speciesTYPE.-NO. 20502, lower jaw fragment with ml-2. Paratype, No. 20503, lowerjaw with P3-4 and m2-3. Both from the Sheep Creek beds, M. primus zone, at Stone-house draw quarry.2'tFg. 20Fig. 2A.M.20503Fig. 3Fig. 2. Cynarcdus mustelinus, sp. nov. Type, No. 20502. Lower jaw-outerand crown views, twice natural size.Fig. 3. Cynarctus mustelinus. Paratype, No. 20503. Lower jaw-outer andcrown views, twice natural size.Size much less than either C. saxatilis Matthew or C. crucidens Cook and moreprimitive than either species; the second molar two-thirds the length of ml; in C.2 [No. 5401932] NEW FOSSIL MAMMALS FROM SNAKE CREEKsaxatilis of the M. paniensis zone it is nearly three-fourths and in C. crucidens of theHipparion zone it is approximately seven-eighths as long, the breadth increasing inabout the same proportion. The last molar in C. mustelinus is very small, only a thirdthe length of m2; in C. saxatilis it is three-fifths as long, in C. crucidens, over two-thirds.MEASUREMENTS IN MILLIMETERSC. mustelinus C. saxatilis C. crucidensLength of ml 8.5 16.1 10.5" "m2 5.7 11.6 9.2"S m3 2.0 7.0 6.3Width of trigonid of ml 3.7 6.7 4.5" " heel of ml 3.7 7.2 5.3It will also be observed that the width of the carnassial talonid increases pro-gressively, relative to the width of trigonid.This species serves to indicate a probable derivation of Cynarctusfrom the Nothocyon group of the John Day and Lower Miocene forma-tions, more particularly from N. lemur and N. latidens, rather than fromthe type species of Nothocyon, N. geismarianus. 'Cynarctus' acridensCook of the Upper Harrison beds, Lower Miocene, of Nebraska is inter-mediate in age and apparently in character, but so far as one can judgefrom the inadequate type, a jaw fragment with ml, it is nearer to Notho-cyon of the Lower Miocene than to Cynarctus of the Middle and UpperMiocene, and should be referred to the former genus, already knownfrom skulls and parts of skeleta from the Lower Miocene of SouthDakota as well as from the typical John Day skulls and skeletons. Theadaptation and skull and skeletal characters of Cynarctus remain ob-scure; it parallels Arctonyx but can hardly be related.Desmathyus validus, new speciesTYPE.-NO. 20506, upper jaw, young, with dp3-ml and p3-4 preformed. Stone-house draw quarry, Merychippus primus zone.CHARACTERS.-Slightly larger than D. pinensis; P3 sub-oval in form, nearly aslarge as p4 and similar in cusp construction. In D. pinensis the inner crescent ofP3 is smaller and imperfect, giving the tooth a sub-trigonal outline.This species is clearly a stage further advanced than its LowerMiocene predecessor D. pinensis of the Upper Rosebud, which in turn isa little more advanced than D. siouxensis of the Harrison. The thirdmolar has completed its inner crescent and become entirely like thefourth. Like Platygonus and unlike the Prosthennops-Dicotyles-Mylo-hyus group, the premolars remain bicuspid and do not become progres-sively molariform. Possibly D. validus is an ancestral type for Platy-gonus, but the intermediate stages are unknown.3AMERICAN MUSEUM NOVITATESIt may be observed in this connection that Prosthennops and Mylo-hyus are not ancestral to Dicotyles, and the very common assumptionthat the "peccaries" of the American Pleistocene indicate a warmerclimate is based on the mistaken notion that they are extinct species ofthe existing tropical genus. This is true as to the tapirs but not as tothe peccaries. Whether the climatic inference is warranted even withthe tapirs may be open to question; the relationship is no closer in thatcase than between the tropical Elephas indicus and the arctic E. primi-genius. But the Pleistocene peccaries, both Platygonus and Mylohyus,~~A.M.20506Fig. 4Fig. 4. Desmathyus validus, sp. nov. Type, No. 20506. Left, crown view ofdp3-4 and ml. Right, crown view of unerupted p3-4. Both natural size.are extinct genera decidedly more specialized in skull,teeth and feet than the modern peccaries, as well as largerl in size. The relationship of Mylohyus to Tagassu is perhapscomparable to that between the woolly rhinoceros (Coelodontaantiquitatis) and the modern white rhinoceros (Ceratother-ium simum), while Platygonus is about as distant from themodern peccaries as Elasmotherium from the modernrhinoceroses.A.M.20489Castor sp.Fig. 5.Castor sp. A single lower tooth, p4, A.M. 20489, from the UpperN o. 20489. Snake Creek beds, agrees so nearly with the existing CastorLower pre- that I am obliged to refer it to that genus. It is about themolar-outer maximum of size for existing species and comes within thenews, nat- variation limits of dental structure, generic and individual,ural size. that I find in comparing with a series of modern jaws.4 [No. 5401932] NEW FOSSIL MAMMALS FROM SNAKE CREEK 5This is the first Tertiary record of true Castor in America, theTertiary species formerly referred to it having been removed to othergenera. It occurs in the Pliocene of Europe; according to Dep6ret,it first appears in the Pontian zone.Gaillardial thomsoni, new genus and speciesTYPE.-NO. 20508, a lower jaw, left ramus complete, with P3-4, m3 and alveoliof remaining teeth, from the Upper Snake Creek beds.DIAGNOSIS.-Dentition probably 1. .4.3. Jaw long, slender, proportioned as inTalpa, condyle knot-like, not transversely expanded, angular process a short flattransverse plate set at right angles to the plane of the jaw, coronoid process long,4 m~~~~~3m2 m/ P4 P3 P2 PI c3A.M. 20508Fig. 6. Gaillardia thomsoni, gen. et sp. nov. Type, No.20508. Lower jaw-outer, crown and under views, twice naturalsize.projecting backward at 450 to line of teeth and but little recurved at tip, dentaryportion of jaw long and slender, shallowed under premolars as in Talpa, posteriormental foramen under ml. Tooth row continuous without diastemata, teeth neitherspaced nor crowded. Las molar brachyodont, tritubercular, the trigonid shorterand wider than in Talpa or Condylura, the heel lower than trigonid and of about thesame width. Third and fourth premolars of equal size, two-rooted, simple, robust,resembling those of Myogale; in front of these are two alveoli, probably for a P2longer than p3 or p4, then a single socket of sub-ovate outline, probably for pi; infront of that is a double socket for a two-rooted canine; each of the two alveoli'In honor of Claude Gaillard, distinguished palunontologist, who has contributed largely to ourknowledge of Tertiary Insectivora. The species name is in honor of the discoverer, Albert Thomsonof the Museum staff.AMERICAN MUSEUM NOVITATESSlightly larger than that of pi; and at the anterior end, a single enlarged socket for apartly procumbent tooth.I cannot place this jaw in any of the described genera of Talpidse.It is distinguished from most of them by the reduction of the incisors to a.single enlarged tooth; this also separates it from Myogale and Galemys,to which the premolars suggest relationship. The twinned alveoli be-hind this enlarged root cannot well be anything but a double-rootedcanine. Were they for two incisors, the alveoli would be more separateat the alveolar border, for the dentition is evidently not crowded. Theyare also too closely connate to interpret the posterior one as the anteriorroot of a two-rooted first premolar (an improbable feature at best inthis group). No other alternate can be suggested. From Amphido-zotherium it is separated by the simple non-molariform p4. It resemblesCondylura in its slender proportions, more elongate than in Talpa, butthe premolars are of different type, with robust and simple crowns, whileCondylura has slender, sharp-pointed premolars with well developedheels and accessory cusps. Scalops and Scapanus have much shorterjaws with higher crowned molars. None of the Talpidae have the peculiarconstruction of angle and coronoid seen in Gaillardia; Condylura per-haps comes nearest, but the angle in that genus is a long slender spine,extending backward and curving upward. No other Insectivora, Chirop-tera or Menotyphla present these peculiar characters, so far as I havebeen able to make comparisons.Procamelus near robustus LeidyNo. 20478, a lower jaw with part of skeleton associated, is from apocket of somewhat uncertain horizon. It lay directly on top of theeroded surface of the Sheep Creek, at a level a little below the top ofthat formation, and lower than some other marginal specimens whichcertainly belong in the paniensis phase. It may, nevertheless, be apocket of later age, let down to the lower level; as no other specimenswere found with it, this cannot be verified. The species does not agreeclosely with any of the known Camelidae, but is nearest to P. robustus,as represented by Leidy's type and various jaws in our collection, someof which are topotypes. It is a little smaller than robustus; the premolarsare slightly less reduced. As compared with Alticamelus leptocolon,the teeth are of about the same size, but premolars 2 and 3 more reduced,m3 more narrow and hypsodont. It differs from Protolabis angustidensin the larger relative size of the anterior molar and the premolars; fromP. heterodontus also in the equal spacing of pi between c and P2. These6 [No. 5401932] NEW FOSSIL MAMMALS FROM SNAKE CREEKare the nearest among the described species. Protolabis is separated,moreover, by the entirely different proportions of limbs and feet. Alti-camelus is similarly separated, though by no means so clearly, by a dis-proportion in limbs and feet, in the opposite sense.While the horizon of this specimen is uncertain, it is probably nearerto Lower than to Upper Snake Creek. It suggests that Procamelus is aderivative of Alticamelus, but that Protolabis is a distinct phylum.A.M.204783Fig. 7. ProcamelUs near robustus. No. 20478. Outer view of lower jaw andcrown view of cheek teeth, one-third natural size.Archsohippus penultimusA number of immature palates and jaws, with some foot bonesassociated, Nos. 21532-35, were found together by Mr. Paul C. Miller in1925, along with jaws of Blastomeryx and Dyseomeryx. The horizon isthe Lower Sheep Creek beds in Aphelops draw, Snake Creek Quarries,Sioux County, Nebraska. No other Equida remains were present.The milk teeth and the unworn permanent molars are preserved,and the characteristic deep restricted preorbital fossa very well shown.The foot bones are metatarsals II, III, IV, three phalanges of digit III,calcaneum, part of navicular, magnum, unciform, etc.; there are alsomost of the ulno-radius, tibia, three cervical vertebrae and manyfragments.Archaeohippus was regarded by Gidley as intermediate betweenHypohippus and Parahippus. The evidence of these specimens indicatesthat it is much closer to Parahippus than to the anchiteriine genera.9AMERICAN MUSEUM NOVITATESThe teeth agree except for the lack of any trace of crochet. They sharethe rugose enamel, the broken protoloph, with protocone half separate,the rounded and well separated metaconid and metastylid, the unre-duced MI. The peculiar type of preorbital fossa, shown clearly in ourspecimens, as also in the type of A. ultimus, is unlike any of the Mioceneequines excepting Parahippus pristinus of the Lower Rosebud. Theulnar shaft is much reduced but completely separate from the radius asin Parahippus. This, however, has no great significance as the animalwas immature. The metatarsal is like those of small Parahippi and ofMerychippus primus in that the inner cuneiform has no footing on itshead. In Anchitherium, Kalobatippus and Hypohippus the metatarsalhas a well developed proximal facet for the inner cuneiform, as also inEquus, Pliohippus, the European hipparions and the later Americanspecies. The shafts of the lateral metatarsals are reduced about as inParahippus pristinus, rather less than Merychippus primus, and thecross section of the shaft is yound oval as in the protohippine horsesgenerally (including Parahippus) in contradistinction to the anchitheriinehorses in which it retains the flat form of Mesohippus. The phalangesare moderately elongated as in Parahippus and the protohippine horses,in contrast to the very short, wide and flattened phalanges of the anchi-theriine horses (including Mesohippus).The above data show that Archa?ohippus is very closely related toParahippus, and belongs without question in the protohippine group,not in the anchitheriine group. Whether it is deserving of generic separa-tion is very doubtful; it certainly does not represent, as Gidley at firstconsidered, a third phylum of Miocene brachyodont horses as differentfrom Hypohippus and Parahippus as these are from each other. Para-hippus includes, indeed, a wide variety of species and should probablybe split up into a number of subgenera. Of these, Archweohippus mightbe one, and should probably include P. pristinus as well as A. ultimus,penultimus and mourningi.8 [No. 540

New fossil mammals from Snake Creek

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