8 p. : ill. ; 24 cm.Includes bibliographical references (p. 7-8)

Cope, E. D. (Edward Drinker), 1840-1897.

Leidy, Joseph, 1823-1891.

Wood, Albert Elmer, 1910-

American Museum of Natural History Scientific Publications

AMERICAN MUSEUM NOVITATESPublished byNumber 822 THE AMERICAN MUSEUM OF NATURAL HISTORY March 9, 1936New York City56.9 32 C (118:7)THE CRICETID RODENTS DESCRIBED BY LEIDY ANDCOPE FROM THE TERTIARY OF NORTH AMERICABY ALBERT ELMER WOODIn the course of studying the fossil Cricetids of North America in anattempt to unravel their evolution, it was immediately obvious that verylittle progress could be made until the original type specimens had beenrestudied and refigured, due to the inadequate nature of the originalfigures and descriptions of these small rodents. An opportunity tostudy these fossils was presented while I was Cutting Traveling Fellow inColumbia University. This study was further assisted by a grant fromthe Marsh Fund of the National Academy of Sciences. I wish to expressmy thanks to the authorities of the American Museum of Natural His-tory, the United States National Museum, and The Philadelphia Acad-emy of Natural Science for permission and facilities to study these speci-mens. The illustrations are by the author.Eumys elegans Leidy, 1856Figure 1, and Leidy, 1869, P1. xxvi, figs. 12-13GENOHOLOTYPE.-Acad. Nat. Sci. Phila. No. 11027, left mandible with M2, partof M1, and alveolus of M3.HORIZON AND LoCALITY.-Middle Oligocene Brule of South Dakota.DIAGNOSIS.-M2 quadrate, longer than broad; anterior cingulum continuousacross whole front of tooth, with subequal buccal and lingual moities; posterior armof protoconid free from both metaconid and entoconid, reaching almost to lingualmargin of the tooth; central cusp small, with no lingual crest and very weak buccalone; hypoconulid apparently reduced; posterior cingulum reaching entoconid uponwear.The characters as listed above are found in a considerable number ofthe Oligocene rodents hitherto referred to this species, though by nomeans in a majority. The specimen figured by Schaub (1925, P1. II,fig. 16). is distinguished from E. elegans by the shortness of the posteriorarm of the protoconid, by the well-developed buccal crest of the centralcusp, and by a slight difference in the shape of the tooth, the posteriorhalf being slightly buccad of the anterior. This last difference seems oflittle importance, but the first two would probably warrant specific sepa-AMERICAN MUSEUM NOVITATESration, when taken together with the differences doubtless existing in therest of the animal. A consideration of this question, as well as of thephylogenetic position of E. elegans, is reserved for a future study. Ac-cording to Schaub's interpretation of the phylogenetic sequence of Cri-cetids, however (Schaub, 1925), the small size of the central cusp(Schaub's "mesostylid"), and particularly the absence of the lingualcrest of the central cusp (Schaub's" mesostylidsporn"), together with thelength of the posterior arm of the protoconid, would be progressive char-acters, indicating advances over the conditions found in the most primi-tive forms of Cricetodon. The feature in which this genus is mostclearly separated from Cricetodon is in the length of the posterior arm ofthe protoconid, which is longer than the lingual crest of the central cusp,a condition never seen in Cricetodon (Schaub, 1925).A.M.N.H. No.7018Acad.NNat.SN.No.10227Fi.q.4-A.M.N.H. No.7022A.M.N.H. No.7028Fiq. 5U.S. N.M. No. 12 04Fig. 1. Eumys elegans, Leidy. Holotype, M2 left, X1O. Acad. Nat. Sci.Phila., No. 11027.Fig. 2. Leidymys nematodon (Cope). Holotype, Ml-3 left, X5. A.M.N.H.No. 7018.Fig. 3. Leidymys lockingtonianus (Cope). Holotype, MI-3 right, reversed, X5.A.M.N.H. No. 7028.Fig. 4. Paciculus insolitus Cope. Holotype, Ml-2 right, reversed, X5. A.M.N.H. No. 7022.Fig. 5. Copemys loxodon (Cope). Holotype, M,-2 right, X5. U.S.N.M. No.1204.[No. 82221936] CRICETID RODENTS OF NORTH AMERICALEIDYMYS, NEW GENUSGENOTYPE.-Hesperomys nematodon, Cope, 1879, a species represented by a skullwith the cheek teeth, from the Upper Oligocene Middle John Day Beds of Oregon.DIAGNOSIS.-Skull roof flat, with temporal crests widely spaced, and showing nosigns of convergence, as is the case in Eumys; M1-2 not essentially different from thoseof Eumys; Ml large, with well-developed hypocone, posterior cingulum, and excep-tionally large central cusp and associated crests.SPEcIEs.-Leidymys nematodon (Cope) and L. lockingtonianus (Cope), both fromthe Middle John Day.Leidymys nematodon (Cope), 1879Figure 2, and Cope, 1885, P1. LXVI, figs. 33-33aHesperomys nematodon Cope, 1879.Eumys nematodon (Cope), Cope, 1881a.Hesperomys nematodon Cope, Cope, 1881c.Peromyscus nematodon (Cope), Hay, 1902.HOLOTYPE.-A.M.N.H. No. 7018.HORIZON AND LoCALITY.-Upper Oligocene Middle John Day Beds of the JohnDay River, Oregon.DIAGNOSIS.-Skull top with broad level area between temporal crests; cusps ofmnolars rounded as in Eumys; two crests from protocone to anterocone of Ml; centralcusp indistinct, with well-developed buccal crests, which do not, however, reach thebuccal margin of the tooth except on Ms; cingula complete on all teeth; slight damsacross median valleys of Ml-2.This species is clearly distinct from skulls which may unhesitatinglybe referred to Eumys, on the basis of the skull top and the third uppermolar. No specimen of Eumys with which I am familiar shows any-thing except the simple sagittal crest, whereas this form has paired tem-poral crests extending well behind the orbit, which never unite to forma sagittal crest but remain as clearly defined ridges following the superiorborder of the orbit. This cannot be an age character, as the type of L.nematodon has fairly well-worn teeth, and specimens of Eumys with muchless worn teeth have quite different arrangement of the crests. Nor canit be a sexual difference, as it seems most unlikely that one sex should befound only in Oregon, while the other was found throughout the GreatPlains deposits.The type of Ml-2 falls within the range of variation that might beallowable for Eumys, the distinctions that could be made being probablyof no more than specific value. In M3, however, the two genera arequite distinct. M3 of Leidymys has a well-developed hypocone, thoughit is smaller than in the first two molars. This cusp is either absent oressentially aborted in the third molar of Eumys. In connection withthis, the lingual valley of M3 in Eumys runs anterad as in Ml-2, whereas3AMERICAN MUSEUM NOVITATESin Leidymys it is directed posterad. The central cusp of this tooth is alsovery well developed, sending a crest to the postero-external margin of thetooth. There is thus some similarity between M3 of L. nematodon andthat of Plesiosminthus myarion (Schaub, 1930, Fig. 6). The upper in-cisors of L. nematodon are smooth and rounded, though not as round as inspecimens referable to Eumys, and are quite distinct from those ofPlesiosminthus.Leidymys lockingtonianus (Cope), 1881Figure 3, and Cope, 1885, P1. LXIV, figs. 10-lO10eEumys lockingtonianus Cope, 1881a.Paciculus lockingtonianus (Cope), Cope, 1881b.HOLOTYPE.-A.M.N.H. No.7028, a fairly complete skull.HORIZON AND LoCALITY.-Upper Oligocene Middle John Day, The Cove, JohnDay River, Oregon.DIAGNOSIS.-Tooth pattern similar to that of L. nematodon, as far as can be told;supraorbital crests much weaker; upper incisors compressed, with no grooves, butwith two faint ridges toward the lateral side.The teeth of this specimen are so badly worn that very few charactersare visible. The buccal crest of the central cusp clearly reaches almost, tothe buccal margin of the tooth, as in L. nematodon, and the general con-figuration, particularly of the third molar, is quite different from that ofEumys. There is no trace of the antero-posterior compression of theparacone and metacone, which seems to be characteristic of Paciculus,nor is the buccal crest of the central cusp as long as in that genus. Thereis a faint crest near the center of the upper incisor, and a rather strongerone at the buccal side, features which have not been observed in anyother North American Tertiary Cricetids.The infraorbital foramen seems much larger ahd more Dipodid inappearance than in the Cricetids, which was doubtless one basis for Hay'sreference of this form to the Zapodidae. A large part of this resemblance,however, is due to breakage of the foramen in the fossil, although thereseem to have been some differences from the type of foramen found inEumys. The anterior palatine foramina are very large, as are also theauditory meatus and the interparietal.Paciculus insolitus Cope, 1879Figure 4, and COPE, 1885, P1. LXVI, Figs. 31-32GENOHOLOTYPE.-A.M.N.H. No.7022, palate with M'-2 of both sides.HORIZON AND LOCALITY. Upper Oligocene Middle John Day Beds, The Cove,John Day River, Oregon.4 [No. 8221936] CRICETID RODENTS OF NORTH AMERICADIAGNosIs.-M'-2 with five compressed transverse crests, all of subequal widthand length; paracone and metacone little if any more prominent than central cusp; allfive crests subparallel; protocone uniting with.lingual margin of anterocone.The tooth pattern of this form is close to that of Leidymys and Eumysin some respects, but differs rather fundamentally in the great antero-posterior compression of the paracone and metacone, a character notseen among contemporary Cricetids, but found among the Sicistids. Itis this, in part, that has led Hay (1902) to assign this genus to the Zapo-didae. There is, however, no trace of P4, and the large anterocone ofM' indicates that there has been a considerable lapse of time since thepremolar was lost. The teeth are shorter and narrower than in Leidy-mys, but the difference is probably too small to have much significance.The palate is short, as in Leidymys.There is a considerable resemblance between Paciculus and some ofthe more primitive Sicistids, especially Plesiosminthus myarion from theAquitanian (Schaub, 1930). The elongation of the central crest and thepentalophoid character of the tooth are Sicistid features. There is,however, sufficient distinction in the anterior end of the tooth row, andparticularly in the entire absence of the upper pre2nolar, so that there isno question but that this form cannot belong to either the Sicistidae orthe Zapodidae, and is certainly nearer to the Cricetidae than to anyother group. Moreover, the valley between the paracone and the an-terior cingulum of the second molar opens freely at its buccal end, in-stead of being closed as in Plesiosminthus. The reference of this form tothe Cricetidae is strengthened by the occurrence of a very similar typeamong the European members of the family, Heterocricetodon stehlin(Schaub, 1925, P1. iv, fig. 7) having a very similar type of pattern,though derived from a different source from that of Paciculus.COPEMYS, NEW GENUSGENOTYPE.-EUmYS loxodon Cope, 1874a.DIAGNOSIS.-Lower molars tending toward alternation of external and internalcusps; central cusp apparently absent; posterior arm of protoconoid of M1 extendedas crest to lingual margin of tooth; protoconoid free from metaconoid; no hypoconu-lid on M2, posterior cingulum arising from external border of hypoconid.Copemys loxodon (Cope), 1874Figure 5, and Cope, 1877, P1. LXIX, fig. 15Eumys loxodon, Cope, 1874a.Hesperomys loxodon (Cope), Cope, 1874b.Eumys loxodon Cope, Cope, 1875.Eumys loxodon Cope, Allen, 1877.SAMERICAN MUSEUM NOVITATESPeromyscus loxodon (Cope), Hay, 1902.HOLOTYPE.-U.S.N.M. No. 1204, lower jaw with M1-2 right.HORIZON AND LOCALITY.-Santa F6 Miocene or Pliocene Beds of New Mexico.DIAGNOSIS.-The same as that given above for the genus.This species has had rather a varied taxonomic history, as indicatedabove. It differs materially from Hesperomys and Peromyscus in havingmore brachydont teeth, the crowns being little if any higher than inEumys. The alternation of the cusps, while at first suggestive of a ten-dency toward the Peromyscus pattern, is, however, actually leading ina rather different direction. The peculiar position of the posteriorcingulum of M2 is like nothing with which I am familiar. It is possiblethat the long central crest is a growth from the central cusp, andit is also possible that it represents merely the posterior arm of theprotoconid.There can be no question but that this form represents a genus thatis much more progressive than Eumys, and one that is fairly specializedin its own direction, though that direction does not appear to be towardany other late Tertiary or recent group of Cricetids, with the exceptionof certain species from the Miocene and Pliocene of California and Ne-vada, which have been described as Peromyscus.DENTAL MEASUREMENTS(all measurements in millimeters)M1-3Ml, antero-posteriorwidth, anterior lophwidth, protolophwidth, metalophM2, antero-posteriorwidth, protolophwidth, metalophM3 antero-posteriorwidth, protolophwidth, metalophTABLE I. UPPER TEETHLeidymys Leidymysnematodon lockingtonianusA.M.N.H. A.M.N.H.No. 7018 No. 70286.41 6.782.61 2.770.89 1.111.75 1.941.79 1.982.02 2.091.86 2.081.83 1.941.83 1.841.83 1.841.50 1.48PaciculusinsolitusA.M.N.H.No. 70225.652.321.821.901.901.942.011.896 [No. 8221936] CRICETID RODENTS OF NORTH AMERICATABLE II. LOWER TEETHEumys Copemyselegans loxodonA.N.S.Phila. U.S.N.M.No. 11027 No. 1204Ml-3, alveolar length 7.00Ml, antero-posterior .. 1.70width, metalophid .. 1.10width, hypolophid .. 1.15M2, antero-posterior 2.26 1.57width, metalophid 1.96 1.22width, hypolophid 1.95 1.27BIBLIOGRAPHYALLEN, J. A. 1877. 'Synoptical list of the extinct Rodentia of North America.'Rept. U. S. Geol. Surv. Terr., XI, pp. 943-949.COPE, E. D. 1874a. 'Notes on the Santa F6 Marls and some of the contained verte-brate fossils.' Proc. Acad. Nat. Sci. Phila., XXVI, pp. 147-152.1874b. 'Report on the vertebrate paleontology of Colorado.' U. S. Geol.Surv. Terr., Ann. Rept. 1873 (1874), pp. 429-533.1874c. 'Report upon vetebrate fossils discovered in New Mexico, with de-scriptions of new species.' Appendix FF, Annual Rept., Chief ofEngineers. Govt. Printing Office. 18 pp.1875. 'Report on the geology of that part of northwestern New Mexicoexamined during the field season of 1874, by E. D. Cope, paleon-tologist and geologist.' Appendix LL, Annual Rept., Chief ofEngineers, pp. 61-116. Govt. Printing Office.1877. 'Report upon the extinct vertebrata obtained in New Mexico byparties of the expedition of 1874.' Geogr. surv. west of 100thMerid., Lt. G. M. Wheeler in charge, IV, pp. 1-370, Pls. xxii-LXXXIII.1879. 'Second contribution to a knowledge of the Miocene fauna of Ore-gon.' Proc. Amer. Phil. Soc., XVIII, pp. 370-376.1881a. 'On the NimravidAe and Canidae of the Miocene Period.' U. S.Geol. and Geog. Surv. Terr., VI, No. 1, pp. 165-181.1881b. 'Review of the Rodentia of the Miocene period of North America.'U. S. Geol. and Geog. Surv. Terr., Bull. VI, part 2, pp. 361-386.1881c. 'The Rodentia of the American Miocene.' Amer. Nat., XV, pp.586587.1885. 'The vertebrata of the Tertiary formations of the West.' Rept.U. S. Geol. Surv. Terr., III, pp. i-xxxv, 1-1009, Pls. I-LXXva.HAY, 0. P. 1902. 'Bibliography and catalogue of the fossil vertebrata of NorthAmerica.' U. S. Geol. Surv., Bull. 179.78 AMERICAN MUSEUM NOVITATES [No. 822LEIDY, J. 1856. 'Notices of remains of extinct mammalia, discovered by Dr. F. V.Hayden in Nebraska Territory.' Proc. Acad. Nat. Sci. Phila.,VIII, pp. 88-90.1869. 'Extinct mammalian fauna of Dakota and Nebraska, including anaccount of some allied forms from other localities, together with asynopsis of the mammalian remains of North America.' Jour.Acad. Nat. Sci. Phila., (2) VII, pp. 1-472, Pls. i-xxx.SCHAUB, S. 1925. 'Die hamsterartigen Nagetiere des Tertiairs und ihre lebendenVerwandten.' Abh. Schweiz. Pal. Ges., XLV, No. 3, pp. 1-114,15 figs., 5 pls.1930. 'Fossile Sicistinae.' Schweiz. Pal. Ges., Eclog. Geol. Helvet., XXIII,No. 2, pp. 616-637, 17 figs.

Cricetid rodents of North America

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