Peabody Museum of Natural History Yale University New Haven, CT 06520 Postilla Number 172 14 December 1977 An Unusual New Mammal from the Early Eocene of Wyoming Kenneth D. Rose Thomas M. Bown Elwyn L. Simons (Received 26 July 1976) Abstract A newly discovered maxillary dentition from the Early Eocene rocks of the Bighorn Basin, Wyoming, is unlike that of any mammal previ- ously known from this intensively collected region. It represents a new genus and Species, here named Alocodon atopum. The new form bears superficial resemblance to Various mammals, but specific features Suggest a real relationship only to palaeano- donts, particularly Tubulodon taylori, a form of Uncertain family ties, and the epoicotheriid Pentapassalus pearce/. The most significant features of the molars are their cylindrical Shape, their odd Cusp arrangement, and their reduced enamel. Because of its similarity to Tubulodon, Alocodon is tentatively allocated here to the Epoicotheriidae (Pholidota, Palaeanodonta). lf correctly assigned, it rep- resents the oldest known member of this Poorly represented family and the first from the Bighorn Basin. Introduction Collecting in the Willwood Formation of the Bighorn Basin in northwestern Wyoming across nearly a hundred years has yielded a wealth of fossils that document the varied and abundant mammalian fauna of Wasatchian (Early Eocene) time; see papers by Cope, Osborn, Wortman, Loomis, Sinclair, Matthew, Granger and Jepsen, among others, cited by Van Houten, 1944, 1945). In 1972, a Yale Peabody Museum expedition directed by E. L. Simons recovered a specimen of an un- Usual mammal while surface prospecting on the south fork of Elk Creek, Big Horn County, Wyoming, in upper “Gray Bull” horizons (see discussion of latter term, Gingerich, 1976). This specimen constitutes postcranial frag- ments associated in a nodule with a right maxilla and several teeth that are wholly unlike any earlier known specimen from the Bighorn Basin area. Comparisons of this specimen with dentitions of a wide variety of fossil and recent mammals have revealed superficial similarities to several diverse groups but probably significant resemblances to only one, the suborder Palaeanodonta. Recovery of such a distinctive new mammal from an intensively collected area is instruc- tive, for it serves as a reminder that fossil col- lecting from a particular geographic region can possibly never document true species diversity. Even so, the Early Eocene faunas of the Bighorn Basin are among the most com- pletely known Early Tertiary mammalian as- semblages, and discoveries of such unusual additions to the fauna are not common. Systematic Paleontology Class Mammalia Order Pholidota Weber, 1904 ?Suborder Palaeanodonta Matthew, 1918 ?Family Epoicotheriidae Simpson, 1927 Alocodon, new genus Type species: A/ocodon atopum, new and only known species. Horizon: upper ‘Gray Bull” beds, Lower Willwood Formation, Early Eocene. Known Distribution: Bighorn Basin, Wyoming. 2 New Eocene mammal from Wyoming Postilla 172 Etymology: Greek: a/ox, furrow, and odon- tos, tooth, in reference to the molar configura- tion. Diagnosis: Upper molars longer than wide, and uniquely specialized; M'-? with median longitudinal furrow, several cusps arranged in line on lingual and buccal borders of crown, and no enamal on top of crown. M' slightly larger than M2, both much larger than M3; Ms greatly reduced, single-rooted, with very low bulbous crown. P’ premolariform, with large paracone, rudimentary metacone, small low protocone. P'-? tiny, single-rooted. Canine of moderate size, triangular in section. Alocodon atopum, new species ia lneono: Holotype: Yale Peabody Museum (YPM) 30790, fragmentary right maxilla with canine, P3, P4 (crown damaged), M'8, and roots of P! and P2, right premaxilla with alveolus for in- cisor, and left maxilla with canine, in concre- tion with possibly associated postcranial bone fragments; collected by Leonard O. Greenfield. Hypodigm: Holotype only. Locality: YPM Locality 348, Sect. 33, TSON R94W, Big Horn County, Wyoming. Etymology: Greek: atopos, unusual, strange. Diagnosis: Only known species of the genus. Measurements given in Table 1. Table 1. Measurements (in mm) of teeth of the holotype of Alocodon atopum. YPM 30790. Length Breadth Canine 1.90 Alea) ee Crs: 0.80* p2 saa ee 2.00 1.80 Pe a so M! 2.60 Eels M2 2.45 2a Ms 1.40 0.80 “Measured in November 1972 This tooth is now missing. Description As noted above, the type maxilla occurs to- gether with many bone fragments in a hard, fist-sized calcareous and iron oxide nodule. Because of the tenacious matrix, the speci- men has so far defied significant preparation beyond minor cleaning of P? and MS. The os- seous remains are so badly fractured that further preparation is unlikely to yield any im- portant information. (There is no assurance that the postcranial fragments are from the same animal as the dentition, for similar con- cretions from the same area sometimes con- tain remains of several taxa.) Much of the right side of the rostrum and the floor of the palate are present but were crushed during fossiliza- tion and details are thus obscured. Con- sequently, dicussion here will be restricted to the dentition. The upper dental formula of Alocodon ap- pears to be |! +?) -C'—P4— M3. Fragments of the right premaxilla anterior to the canine con- tain part of the alveolus for a lateral incisor; its root is slightly smaller than that of the canine (see Figs. 1 and 3). Other incisors may have been present, but none are discernible in the somewhat dissociated premaxillary fragments. The canine has a single massive root whichis, like the crown, roughly triangular in cross- section (see Fig. 3). The crown has three sur- faces: enameled buccal and posterointernal faces and an anterointernal face lacking enamel. This last surface appears to be somewhat pitted rather than perfectly smooth, and typical wear striations are not visible on it. The enamelis unevenly distributed at the neck of the canine with a greater extent on the buc- calthanon the lingual side. This fact, together with the absence of enamel on the occlusal surfaces of M' and M? (see discussion below) suggests that the anterointernal surface of the canine originally had very thin enamel or none. The canine is of moderate size, protrud- ing ventrally beyond the occlusal plane( see Fig. 1 and 2). The right canine, nearly com- plete, measures about 2.6 mm in height from the alveolar border to the tip. An apparent gap between the canine and the first preserved cheek tooth was occupied by 3 New Eocene mammal from Wyoming _ Postilla 172 Fig. 1 Crown view of the holotype of Alocodon atopum, YPM 30790, stereopair. Approximately x 6. 4 New Eocene mammal from Wyoming Postilla 172 two tiny single-rooted premolars, now indi- cated only by indistinct alveoli which are circu- lar in cross-section. When the specimen was first studied by one of us (T.M.B.) in 1972, the crown of P' was present, but was later lost. It was simple and bulbous with no cingula or cristae. The shape and outline of the cross- section of the root of P? is like that of P'’, and presumably its crown was similar (see Fig. 3). Fig. 2 Lateral view of canine of the holotype of Aloco- don atopum, YPM 30790. P3 is premolariform and considerably larger than P! but is smaller than the molars. It ap- pears to have three roots. A broken root now situated just anterior and slightly external to the tooth is probably its anterobuccal root, displaced by postmortem fracturing of the maxilla. P? is roughly triangular in occlusal view and is dominated by a high blunt paracone with slight traces of wear on its posterior surface. The diminutive metacone, slightly worn, has more the appearance of a node on the postparacrista than of a distinct cusp. Behind the metacone there is a slightly worn, minute and inconspicuous cusp at the posterolabial corner of the tooth. A low bulb- ous protocone Is present lingually, towards the posterior part of the tooth, making P% ap- pear to be skewed posterolingually. On the posterior face of the protocone is a broad wear surface. Noconules are present on P3. A very faint lingual cingulum is slightly better defined on the anterior face of the P? pro- tocone, and enamel covers the entire crown. P4 is badly damaged, and nearly all crown detail has been lost. From what remains, this appears to have been a tooth of roughly quad- rangular outline smaller than the molars and Fig. 3 Crown view of the holotype of Alocodon atopum, YPM 30790. Roots of P', P2 indicated; rP3 is an- teriorly displaced root of P3. 5 New Eocene mammal from Wyoming Postilla 172 Slightly larger than PS. Although the crown Structure cannot be determined with certainty, a small section remaining at the front of the tooth appears to be more like M' than P®. The molars are the most distinctive teeth. M’ is the largest and best preserved tooth. It has two Jabial roots; the presumed lingual root is Not visible. In occlusal aspect, it is rectangular and somewhat oval in outline with the long axis oriented anteroposteriorly. The posterior Margin of M! is convex whereas the anterior Margin is marked by an inflection at the mid- line. The most conspicuous feature of the °cclusal surface is the deep longitudinal fur- row, devoid of enamel, extending down the anteroposterior midline of the tooth. Cusps are arranged lingually and labially on the Periphery of the tooth and the labial cusp Series is less peripheral than the lingual row. The tooth is inflated buccally at the base of the Crown. The cusps vary in definition and ap- Pear more as digitations of the high, crestlike €namel rim bordering the furrow, than as Separate cusps. This feature, together with the lack of enamelon top, creates a scalloped Pattern of enamel at the periphery of the °Cclusal surface (see Fig. 1 and 3). Labially there are three cusps, an anterior crestlike One occupying the front half of the crown. Behind the latter Cusp and separated from it by a well-defined notch are two smaller cusps, the first is of moderate size and the more pos- terior one is smaller and lower. The lingual Cusps are not as well defined, but consist of a Moderate-sized short cusp anteriorly, sepa- rated by a broad notch from a rim of enamel ©CCupying the posterior two-thirds of the lin- gual edge of the tooth. A small indentation in the enamel suggests the former presence of two cusps in this region, but heavy wear has rendered their expression indistinct. The tooth lacks cingula. The enamel on the sides of the Crown of M' is very thin (approximately 0.1 Mm). Obvious wear is confined to the Periphery of the crown and there are no dis- tinct wear surfaces or striations on the Dasined part of the tooth. This appears to indi- Cate that enamel never covered the top of the Crown. M? is slightly smaller than M' but is of essen- tially the same morphology. Its long axis trends anterolabially-posterolingually. As a result of inflation of the base of the crown anterolabially and reduction of the posterola- bial part, the tooth is somewhat tapered pos- teriorly in occlusal view. In contrast to M', M2 seems to have only one large labial root. Lin- gual roots are not visible. The cusps of M? are even less distinct than those of M’ but are otherwise similar in position and relative size, the only difference being the presence of a minute bulbous cusp anterior to the large an- terolabial cusp. M2, like M', lacks cingula, a stylar shelf and enamel on its occlusal sur- face. Ms is a diminutive, oval, peglike tooth with a single root. Its crown is bulbous and has a cusplike bulge in the center. A small eroded area on the posterior surface of the cusp seems to be due to fracture rather than wear. Thin enamel covers the crown. M’° is situated well above the occlusal plane of the other cheek teeth and comsequently did not occlude with lower teeth. This is probably the original position of M$ (an interpretation sup- ported by the apparent lack of wear). It is situated behind and labial to the midline of M2 and abuts against its reduced posterolabial border. Discussion Introduction The right maxillary and premaxillary of Aloco- don atopum contain at least nine teeth: at least one incisor, a canine, four premolars, and three molars. Since P* may be morphologi- cally similar to M', the possibility that there are actually three premolars and four molars, al- though improbable, cannot be dismissed. Moreover, the molars of Alocodon bear some resemblance to those of at least one Early Tertiary group of marsupials (see below). That Alocodon is most likely a eutherian is suggested principally by the structure of P3, the presence of a canine, and the probably eutherian dental formula. Nevertheless, if a eutherian, Alocodon is unusual in its pecul- iarly specialized molars and uncertain cusp 6 New Eocene mammal from Wyoming Postilla 172 homologies. Many Early Tertiary eutherians have evolved diversely specialized molars (e.g. pantodonts, uintatheres, picrodontids, mesonychids, and taeniodonts), but in most of these the fundamental cusp homologies are more readily perceived. Thus, the relationships of Alocodon are con- jectural. We have compared it with a diversity of fossil and recent mammals, and have so- licited opinions on the specimen from many vertebrate paleontologists. After comparison with many mammalian groups (outlined be- low) we believe that Alocodon bears signifi- cant resemblance only to the palaeanodonts, and especially to Tubulodon and and Pen- tapassalus. Because the dentition of Aloco- don is so bizarre, however, we present a summary of our comparisons. Detailed Comparison The elongate polycuspidate M'-? of Alocodon bear a superficial resemblance to those of multituberculates, but possibly resemble the upper premolars of some ptilodontid mul- tituberculates more closely than they do their molars. Furthermore, P’ of Alocodon is tribo- sphenic (therian-like) and not at all like the PS of multituberculates. Retention of the canine, as occurs in Alocodon, is unknown in any multituberculate. There is also some re- semblance between M'-? of Alocodon and teeth of haramiyids, a group known only from the latest Triassic of Europe (see Hahn, 1973). These similarities, however, are surely con- vergent. A somewhat closer approximation to the mo- lars of Alocodon is seen in the molars of caenolestoid marsupials of the Early Tertiary family Polydolopidae and Middle Tertiary sub- family Abderitinae (Caenolestidae) Polydolopids (see Simpson, 1948; Paula Couto, 1952), are approximately contempor- ary with Alocodon but are known only from South America. Their molars are similarly basined and polycuspidate, but the crowns are often covered with crenulated enamel and the cusps differ in number, form and distribu- tion from those of Alocodon. Where known, the ultimate premolar is enlarged and tren- chant (a quite different situation from that in Alocodon) and M! is similarly modified, though smaller, in at least one genus (Polydolops). Although in a majority of polydolopids M? is larger than M3 and M¢ is reduced, only in Epidolops is the last molar reduced to such a degree as in Alocodon. Epidolops, however, contrasts sharply with Alocodon in the antemolar dentition (see Paula Couto, 1952). The latter is true also for Polydolops, the only other polydolopid in which the antemolar teeth are known. Most of these observations pertain to the Abderitinae as well (see Simpson, 1928). The extreme re- duction of the last molar and the lack of specialization of the last upper premolars in Alocodon do not strictly rule out affinity with the Caenolestoidea, but they are important contrasts which, when considered along with the fundamental differences in molar struc- ture, are strong evidence against their having close relationship. Among the pteropodid bats (Megachiroptera) several forms possess elongate upper molars with a median longitudinal furrow. In pteropodids, Ms and the anterior premolar have been lost, recalling their vestigial state in Alocodon. The details of the molar crowns, however, differ markedly from those of Aloco- don. No well-defined cusps can be distin- guished. Although the enamel in the pteropodids Rousettus and Pteropus is thin, the whole of the labial part of the crown is enameled, unlike the condition of M'-2 in Alocodon. In pteropodids, the front of M' and M? is taller than the back, whereas in Aloco- don the front and back of the cusp rows are more orless of equal height. Megachiropteran dentitions vary considerably between taxa, however, and most forms bear little or no re- semblance to Alocodon. Further, the available evidence (Russell and Sigé, 1970: Walker, 1969) suggests that megachiropterans dif- ferentiated from a generalized chiropteran ancestor sometime after the Early Eocene and before the Early Miocene. The oldest known 7 New Eocene mammal from Wyoming Postilla 172 megachiropteran, the Early Oligocene Ar- Chaeopteropus, possessed tuberculate teeth More like those of microchiropterans than Megachiropterans. Thus, the occurrence of Alocodon in beds as old as the earliest known bats (see Jepsen, 1966) but much older than the earliest known fruit bats (which are and were presumably restricted to the Old World) does not support a possible megachiropteran affinity. The Palaeanodonta is a rare group of small, Early Tertiary mammals that possess a promi- nent canine and very modified cylindrical Cheek teeth in which the enamel is reduced or absent. These derived features also apply to Alocodon, and suggest that it may be related to the Palaeanodonta. In most palaeanodonts, the teeth are reduced to pegs and con- sequently they bear no other special re- semblance to those of Alocodon. However, ‘wo palaeonodonts, Pentapassalus and €specially Tubulodon, show interesting and Probably significant resemblances to Aloco- don. Tubulodon taylori is an enigmatic taxon from the late Early Eocene (“Lostcabinian”) of the Wind River Basin, Wyoming (Jepsen, 1932). Unfortunately, Tubulodon is known only from incomplete lower jaws and cannot be directly Compared to Alocodon; nevertheless, its lower teeth have features in common with the Upper teeth of Alocodon which we believe May be significant. In Tubulodon, as in Alocodon, the molars are val (the long axis trends anteroposteriorly) and possess several poorly-defined cusps ar- fanged marginally. The occlusal surfaces lack enamel, appearing at first glance to be heavily worn but as Jepsen (1932) observed, the teeth are still relatively high-crowned and the Cusps remain evident, unlike the condition of heavily-worn teeth. Hence the absence of €namel is apparently the original condition of the teeth. Moreover, wear facets are not dis- tinct and appear only on the enameled edges Of the margin of the crown. This is the same general pattern as in Alocodon. Where still ta visible, the enamel of the molars can be seen to have ascalloped margin, reminiscent of the condition in Alocodon. Alocodon resembles Tubulodon in another feature, but one of dubious significance, the presence of microscopic tubules in the teeth (Jepsen, 1932). The presence of tubules in Tubulodon was cited by Jepsen as a feature indicative of relationship to the Tubulidentata; however, Colbert (1941) cogently argued that the tubules are unlike those in tubulidentate teeth, and he opposed tubulidentate affinities of Tubulodon. |n addition, Gazin (1952), re- ported a new Early Eocene epoicotheriid, Pentapassalus, that bears some resemblance to Tubulodon, including the presence of tubules. Gazin noted tubules in other similarly preserved specimens from the same area, however, and he concluded that in his speci- men the tubules were a postmortem feature with no taxonomic importance. As did Gazin, we have found that tubules like those in Alocodon and Tubulodon are present in teeth of various small mammals from the Willwood fauna, provided the enamel is light-colored and relatively clear. Rather than a peculiar preservational feature, they may be the denti- nal tubules that are present in teeth of virtually all mammals (Peyer, 1968). Their particular salience in Tubulodon and Alocodon is prob- ably associated with the characteristic reduc- tion of enamel, a factor which enhances the visibility of the tubules. It probably does not indicate extreme tubular development in these taxa. The lower teeth of Tubulodon are about the same length as the corresponding upper teeth of Alocodon but are narrower trans- versely. It is no surprise that they do not occlude well with those of Alocodon. In Tubulodon, M1 and Me are subequal and Ms is single-rooted and reduced, but much less so than in Alocodon. Ms of Tubulodon is cus- pate, like Mi—2 (Guthrie, 1971), in contrast to the diminutive peglike M8 of Alocodon. Tubulo- don molars do not have a well-developed lon- gitudinal furrow New Eocene mammal from Wyoming Postilla 172 These comparisons present the tantalizing but as yet unprovable possibility that Aloco- don is related to Tubulodon. If they were from the same horizon, it might be tempting to speculate that they could be upper and lower teeth from the same taxon. Despite their similarities, however, the evident morphologic and stratigraphic disparities between them argue against this and justify generic separa- tion, We turn now to the epoicotheriid Pentapas- salus from the Lostcabinian of southwestern Wyoming, in which Gazin (1952) saw dental resemblance to Tubulodon. Pentapassalus is known from both upper and lower teeth and is, therefore, more easily compared with Aloco- don. It possesses several features reminis- cent of Alocodon:; reduced enamel (lacking on the occlusal surface and thin elsewhere), general form of upper molars (longer than wide), peglike M3, and canine form (triangular in section with the anteromedial face honed and devoid of enamel). In contrast to Aloco- don, however, the three molars are almost equal in size, with M? slightly longer than M', and the canine and M® are noticeably larger. The occlusal morphology of the upper teeth of Pentapassalus differs from that of Alocodon. Gazin (1952:39) described the occlusal sur- faces as nearly flat with two planes of occlu- sion meeting at a widely obtuse angle in alow transverse ridge, generally near the middle of the tooth “presenting a faintly gabled appear- ance somewhat as in armadillos.”” No cusps are evident, a feature in Gazin’s view probably due to wear. Perhaps the differences between Alocodon and Pentapassalus are accen- tuated by differences in degree of wear. In- deed, the teeth in Pentapassalus are much lower crowned than in Alocodon and appear to be heavily worn. Unworn teeth of Pentapas- salus may have resembled those of Alocodon more closely. To summarize, Alocodon appears to be closest to Tubulodon, among all taxa examined, and to show some resemblances to Pentapassalus. The affinities of Tubulodon remain obscure, but it is best regarded as a palaeanodonrt, and it has been referred tenta- tively to the Epoicotheriidae (Simpson, 1959; Emry, 1970), a family transferred to the Pholidota in the latter work. Alocodon geolog- ically predates both Tubulodon and Pen- tapassalus and, if related to them, it would be the oldest described epoicotheriid. It is unfortunate that the potential alliance of Alocodon and Tubulodon to each other or to the Epoicotheriidae does little to elucidate the origin of any of these peculiar mammals. Epoicotheriids may have been derived from an unknown Paleocene paleanodont (Simpson, 1931) but known forms are pre- cluded from an ancestral position because of their greatly reduced dentitions. The origin of palaeanodonts remains unkown. The occurrence of Alocodon ina fauna as well sampled as that of the “Gray Bull” suggests that our knowledge of the composition of Early Tertiary faunas in the Rocky Mountain region is still far from complete and may be biased by sampling of strata which probably record typ- ical but not inclusive paleoenvironments (see Black, 1967; McKenna, 1972). Acknowledgments Acknowledgements are due to Drs. D. Baird, Princeton University; M. C. McKenna and K. Koopman, The American Museum of Natural History; R. Purdy, National Museum of Natural History; and E. T. Hooper, University of Michi- gan Museum of Zoology, for loan of or access to specimens in their care. Drs. K.S. Thomson and J. E. Rodman, Yale University, Friderun Ankel-Simons, The University of North Carolina at Chapel Hill, P. D. Gingerich, Uni- versity of Michigan Museum of Paleontology, and J. A. Lillegraven, University of Wyoming, gave us helpful comments on the manuscript Dr. R. Purdy provided useful information and measurements of the holotype of Pentapas- salus. We are grateful to the many vertebrate 9 New Eocene mammal from Wyoming Secs Postilla 172 Paleontologists who offered their opinions on the holotype of Alocodon. Karoly Kutasi photographed the specimen for Figure 1, and Mark Orsen prepared Figure 3. Funds for these illustrations and for the 1972 field ex- Pedition (during which the type of Alocodon atopum was found) were awarded from the John T. Doneghy Fund, Peabody Museum, Yale, and the Boise Fund, Oxford. Simons completed his work on this manuscript while at the University of Kassel, as a recipient of the Alexander von Humboldt Senior Scientist Award on leave of absence from Yale Univer- sity. Literature Cited Black, C. C. 1967. Middle and Late Eocene mammal communities: a major discrepancy. Science 156: 62-64. Colbert, E.H. 1941. A study of Orycteropus gaudryi from the island of Samos. Bull. Amer. Mus. Nat. Hist. 78 (4): 305-351 Emry, R. J. 1970. A North American Oligocene pangolin and other additions to the Pholidota. Bull. Amer. Mus. Nat. Hist. 142 (6): 455-510. Gazin, C. L. 1952. The Lower Eocene Knight Formation of western Wyoming and its mammalian faunas. Smithsonian Misc. Coll. 117 (18): 1-82. Gingerich, P. D. 1976. Paleontology and phylogeny: patterns of evolution at the species level in Early Tertiary mammals. Am. J. Sci. 276: 1-28. Guthrie, D. A. 1971. The mammalian fauna of the Lost Cabin Member, Wind River Formation (Lower Eocene) of Wyoming. Annals Carnegie Mus. 43 (4): 47-113. Hahn, G. 1973. Neue Zahne von Haramiyiden aus der Deutschen Ober-Trias und ihre Beziehungen zu den Multituberculaten. Palaeontographica Abt. A, Band 142, Lfg. 1-3: 1-15. Jepsen, G. L. 1932. Tubulodon taylori, a Wind River Eocene tubulidentate from Wyoming. Proc. Amer. Philos, Soc. 71 (5): 255-274. ——— 1966. Early Eocene bat from Wyoming. Science 154:1333-1339. Matthew, W. D. 1918. Edentata. /n Matthew, W. D. and W. Granger. A revision of the Lower Eocene Wasatch and Wind River Faunas. Part V. Insectivora (cont’d.), Glires, Edentata: Bull. Amer. Mus. Nat. Hist. 38 (16):565-657. McKenna, M. C. 1972. Vertebrate paleontology of the Togwotee Pass area, northwestern Wyoming. In Guidebook, Field Conference on Tertiary biostratigraphy of southern and western Wyoming, R. M. West, Coordinator (privately distributed). Paula Couto, C. 1952. Fossil mammals from the beginning of the Cenozoic in Brazil—Marsupialia: Polydolopidae and Borhyaenidae. Amer. Mus. Novitates, no. 1559: 1-27. Peyer, B. 1968. Comparative Odontology. Chicago: Univ. Chicago Press, 347 pp Russell, D. E., and B. Sigé. 1970. Révision des chiroptéres lutétiens de Messel (Hesse, Allemagne). Palaeovertebrata 3 (4): 83-182. Simpson, G. G. 1927. A North American Oligocene edentate. Ann. Carnegie Mus. 17(2):283-298. —— 1928. Affinities of the Polydolopidae. Amer. Mus. Novitates, no. 323: 1-13 ——— 1931. Metacheiromys and the Edentata. Bull. Amer. Mus. Nat. Hist. 59 (6):295-381. ~—— 1948. The beginning of the age of mammals in South America. Part |. Bull. Amer. Mus. Nat. Hist. 91 (1): 1-232. ~——— 1959. A new Middle Eocene edentate from Wyoming. Amer. Mus. Novitates, no. 1959: 1-8 Walker, A. 1969. True affinities of Propotto leakeyi Simpson 1967. Nature 223: 647-648. Van Houten, F. B. 1944. Stratigraphy of the Willwood and Tatman formations in northwestern Wyoming. Bull. Geol. Soc. Amer. 55 (2): 165-210. ~—— 1945. Review of latest Paleocene and early Eocene Mammalian faunas. J. Paleont. 19: 421-461. Weber, M. 1904. Die Saugetiere. Einfihrung in die Anatomie and Systematik der recenten und fossilen Mammalia: Jena, Gustav Fischer Verlag, .866 pp. New Eocene mammal from Wyoming Postilla 172 The Authors Kenneth D. Rose. Museum of Paleontolo- gy, University of Michigan, Ann Arbor, Michi- gan 48104. Thomas M. Bown. Formerly of Department of Geology, University of Wyoming, Laramie, Wyoming 82071. Currently at: U.S. Geological Survey, Paleontology/Stratigraphy, Building 25-Mail Stop 919, Denver Federal Center, Denver, Colorado 80225. Elwyn L. Simons. Formerly of: Division of Vertebrate Paleontology, Peabody Museum of Natural History, Yale University, New Haven, Connecticut 06520. Currently at: Department of Anthropology, Duke Universi- ty, and Duke University Primate Facility, Durham, North Carolina 27705.