The imagery on this page is the basis for a paper entitled The anatomy of Herpetotherium cf. fugax COPE, 1873, a metatherian from the Oligocene of North America, by I. Horovitz, S. Ladevèze, C. Argot, T.E. Macrini, T. Martin, J.J. Hooker, C. Kurz, C. de Muizon, and M.R. Sánchez-Villagra (2008, Palaeontographica Abteilung A 284:109-141). The Summary is as follows:

              The recent discovery of well preserved specimens of Herpetotherium cf. fugax Cope, 1873 in the        Early Oligocene White River Formation of Wyoming has allowed a better understanding of its        morphology, phylogenetic position, and locomotor adaptations. We describe in detail its enamel        microstructure, petrosal morphology, cranial endocast, and postcranial skeleton.

              The molar enamel consists of radial enamel with a thick layer of prismless external enamel which        represents the plesiomorphic marsupial condition. Prisms describe a single turn from 45° to 0°        inclination on their way from the enamel dentine junction (EDJ) to the outer enamel surface.        Interprismatic matrix is oriented perpendicular to the EDJ. Enamel tubules occur within the prisms.

              Many features of the auditory region of Herpetotherium highlight a close relationship with        Marsupialia (understood as the crown group within Metatheria) and some characters clearly        distinguish it from the ancestral condition of Marsupialia. The reconstruction of the osseous inner ear        shows that Herpetotherium has less cochlear turns (and therefore is more primitive) than the        hypothetical ancestor of Marsupialia. The bony labyrinth exhibits a peculiar feature of the lateral and        posterior semicircular canals that form a second crus commune, as in certain basal marsupials.

              The cranial endocast of Herpetotherium has relatively large olfactory bulb casts, relatively small        and lissencephalic cerebral hemisphere casts, a relatively large cerebellar cast, and relatively large        subarcuate fossae suggesting presence of large paraflocculi. It is unclear if a rhinal fissure was        present on the endocast because the lateral surfaces are incomplete. Herpetotherium has a small        endocranial volume relative to skull length in comparison to extant marsupials.

              The articular relationship of astragalus and calcaneum is more primitive than in living marsupials,        with the sustentacular facet of the calcaneum directed practically medially in its anterior end as in        other basal metatherians excluded from crown group Marsupialia. In the latter, in contrast, this facet        presents the derived condition of being directed dorsally.

              The morphology of the hind limb suggests terrestrial locomotor habits. Some of these characters        are a deep intertrochanteric fossa, a femur that is almost as deep as it is wide in its distal end, a        sharp tibial crest, and a rather sagittally restricted upper ankle joint.

This specimen was collected 18.4 meters above the Chadronian/Orellan North American Land Mammal Age Boundary (Eocene/Oligocene boundary), section 33, Township 32 North, Range 70 West in Wyoming. It was scanned using a Micro-CT-Scan RayScan 200 at the Fachhochschule Aalen, Arbeitsgruppe Metallguss, Germany. It was made available to DigiMorph by Dr. Ted Macrini of the American Museum of Natural History. Funding for additional image processing was provided by a National Science Foundation Digital Libraries Initiative grant to Dr. Timothy Rowe of The University of Texas at Austin. Endocast image processing by Ted Macrini and petrosal image processing by Thomas Schmelzle (Munich) and Sandrine Ladevèze (see Additional Imagery).

The specimen was scanned using a Micro-CT-Scan RayScan 200 at the Fachhochschule Aalen, Arbeitsgruppe Metallguss, Germany. The interslice spacing is approximately 0.03197 mm and the interpixel spacing is 0.0331 mm.

Literature

ARCHER, M. (1976): The basicranial region of marsupicarnivores (Marsupialia), interrelationships of        carnivorous mammals, and affinities of the insectivorous marsupial peramelids. – Zool. J. Linn. Soc., 59:        217-322.
ARGOT, C. (2002): Functional-adaptive analysis of the hindlimb anatomy of extant marsupials and the        paleobiology of the Paleocene marsupials Mayulestes ferox and Pucadelphys Andinus. – J. Morphol.,        253: 76-108.
BECK, R., GODTHELP, H., ARCHER, M. & HAND, S. (2006): 'Ameridelphian' and crown australidelphian        marsupials from the Early Eocene of Australia. – Annu. Symp. Vertebr. Palaeontol. Comp. Anat. Oral        Present., http://www.svpca.org/years/2006_paris/oral_presentations.php
BEIER, K. (1981): Vergleichende Zahnuntersuchungen an Lasiorhinus latifrons Owen, 1845 und Vombatus        ursinus Shaw, 1800. – Zool. Anz., 207: 288-299.
BENTON, M.J. (1985): First marsupial fossil from Asia. – Nature, 318: 313.
BININDA-EMONDS, O.R.P., CARDILLO, M., JONES, K.E., MACPHEE, R.D.E., BECK, R.M.D., GRENYER, R., PRICE,        S.A., VOS, R.A., GITTLEMAN, J.L. & PURVIS, A. (2007): The delayed rise of present-day mammals. –        Nature, 446: 507-512.
BOWN, T.M. & SIMONS, E.L. (1984): First record of marsupials (Metatheria, Polyprotodonta) from the        Oligocene in Africa. – Nature, 308: 447-449.
BOYDE, A. (1971): Comparative histology of mammalian teeth. In: DAHLBERG, A.A. (Ed.): Dental morphology        and evolution. – (Univ. Chicago Press), Chicago and London, 81-94.
BUTLER, A.B. & HODOS, W. (1996): Comparative vertebrate neuroanatomy: evolution and adaptation. -        (Wiley-Liss), New York, 514 p.
CASE, J.A., GOIN, F.J. & WOODBURNE, M.O. (2005): "South American" marsupials from the Late Cretaceous        of North America and the origin of marsupial cohorts. – J. Mamm. Evol., 12: 223-255.
CIFELLI, R.L. (1993): Early Cretaceous mammal from North America and the evolution of marsupial dental        characters. – Proc. Natl. Acad. Sci. U.S.A. , 90: 9413-9416.
–,– (2004): Marsupial mammals from the Albian-Cenomanian (Early-Late Cretaceous) boundary, Utah. – Bull.        Am. Mus. Nat. Hist., 285: 62-79.
CIFELLI, R.L. & MUIZON, C. DE. (1998): Marsupial mammal from the Upper Cretaceous North Horn Formation,        Central Utah. – J. Paleontol., 72: 532-537.
CLEMENS, W.A. 1966. Fossil mammals of the type Lance Formation, Wyoming. Part 2. Marsupialia. Univ. Calif.        Publ. Geol. Sci., 62: 1-122.
COLBERT, M.W., RACICOT, R. & ROWE, T. (2005): Anatomy of the cranial endocast of the bottlenose dolphin        Tursiops truncatus, based on HRXCT. – J. Mamm. Evol., 12: 195-207.
COPE, E. (1873): Third notice of the extinct Vertebrata from the Tertiary of the Plains. – Paleontol. Bull.,        16: 1-8.
CROCHET, J.Y., THOMAS, H., SEN, S., ROGER, J., GHEERBRANT, E. & ALSULAIMANI, Z. (1992): Découverte        d'un Péradectidé (Marsupialia) dans l'Oligocène inférieur du Sultanat d'Oman: nouvelles données sur la        paléobiogéographie des marsupiaux de la plaque arabo-africaine. – C. R. Acad. Sci. Paris, 314: 539-545.
DOM, R., FISHER, B.L. & MARTIN, G.F. (1970): The venous system of the head and neck of the opossum        (Didelphis virginiana). – J. Morphol., 132: 487-496.
DOZO, M. (1989): Estudios paleoneurológicos en Didelphidae extinguidos (Mammalia, Marsupialia) de la        Formación Chapadmalal (Plioceno Tardio), Provincia de Buenos Aires, Argentina. – Ameghiniana, 26: 43-       54.
EVANOFF, E. (1993): Stratigraphy of the White River Formation Converse County, Wyoming, Ph.D.        Dissertation, Univ. Colorado, Boulder.
EVANOFF, E., PROTHERO, D. & LANDER, R. (1992): Eocene-Oligocene climatic change in North America: The        White River Formation near Douglas, east-central Wyoming. In: PROTHERO, D. & BEGGREN, W. (Ed.):        Eocene-Oligocene climatic and biotic evolution. – (Princeton Univ. Press), Princeton, 116-130.
FERREIRA, J.M., PHAKEY, P.P., PALAMARA, J., RACHINGER, W.A. & ORAMS, H.J. (1989): Electron-microscopic        investigation relating the occlusal morphology to the underlying enamel structure of molar teeth of        the wombat (Vombatus ursinus). – J. Morphol., 200: 141-149.
FLYNN, J.J. & WYSS, A.R. (1999): New marsupials from the Eocene-Oligocene transition of the Andean Main        Range, Chile. – J. Vertebr. Paleontol., 19: 533-549.
FOX, R.C. (1983): Notes on the North-American Tertiary marsupials Herpetotherium and Peradectes. – Can.        J. Earth Sci. , 20: 1565-1578.
GABBERT, S. (1998): Basicranial anatomy of Herpetotherium (Marsupialia: Didelphimorphia) from the Eocene        of Wyoming. – Am. Mus. Novit., 3235: 1-13.
GAUDIN, T.J., WIBLE, J.R., HOPSON, J.A. & TURNBULL, W.D. (1996): Reexamination of the morphological        evidence for the cohort Epitheria (Mammalia, Eutheria). – J. Mamm. Evol., 3: 31-79.
GAZIN, C. (1935): A marsupial from the Florissant beds (Tertiary) of Colorado. – J. Paleontol., 9: 57-62.
GILKESON, C. (1997): Tubules in Australian marsupials. In: KOENIGSWALD, W.V. & SANDER, P.M. (Ed.): Tooth        enamel microstructure. – (Balkema), Rotterdam, 113-121.
GOIN, F. & CANDELA, A. (2004): New Paleogene marsupials from the Amazon basin of eastern Perú. In:        CAMPBELL, K. (Ed.): The Paleogene mammalian fauna of Santa Rosa, Amazonian Perú. -Nat. Hist. Mus.        Los Angel. Cty., Sci. Ser. 40: 15-60, Los Angeles.
GOIN, F.J., PASCUAL, R., TEJEDOR, M.F., GELFO, J.N., WOODBURNE, M.O., CASE, J.A., REGUERO, M.A.,        BOND, M., LOPEZ, G.M., CIONE, A.L., SAUTHIER, D.U., BALARINO, L., SCASSO, R.A., MEDINA, F.A. &        UBALDON, M.C. (2006): The earliest Tertiary therian mammal from South America. – J. Vertebr.        Paleontol., 26: 505-510.
HAIGHT, J.R. & MURRAY, P.F. (1981): The cranial endocast of the early Miocene marsupial, Wynyardia        bassiana: an assessment of taxonomic relationships based upon comparisons with Recent forms. –        Brain Behav. Evol., 19: 17-36.
HERSHKOVITZ, P. (1982). The staggered marsupial lower third incisor (I3). In Buffetaut, E., Janvier, P., Rage,        J.-C. & Tassy, P. (Ed.): Phylogénie et Paléobiogeographie: livre jubillaire en l'honneur de Robert        Hoffstetter. Geobios, Mém. Spéc., 6: 191-200.
–,– (1995): The staggered marsupial third lower incisor: hallmark of cohort Didelphimorphia, and description        of a new genus and species with staggered i3 from the Albian (Lower Cretaceous) of Texas. Bonn.        Zool. Beitr., 45: 153-169.
HOCHSTETTER, F. (1896): Beitraïge zur Anatomie und Entwickelungsgeschichte des Blutgefässsystems der        Monotremen. – Semon's Zool. Forschungsreis. Aust., 5: 189-243.
HOOKER, J.J. (1998): Mammalian faunal exchange across the Paleocene-Eocene transition in Europe. In:        AUBRY, M.-P., LUCAS, S.G. & BERGREEN, W.A. (Ed.): Late Paleocene-Early Eocene climatic and biotic        events in the marine and terrestrial records. – (Columbia Univ. Press), New York, 428-450.
HOOKER, J.J., SÁNCHEZ-VILLAGRA, M.R., GOIN, F.J., SIMONS, E.L., ATTIA, Y. & SEIFFERT, E.R. (In press): The        origin of Afro-Arabian 'didelphimorph' marsupials. – Palaeontol.
HOROVITZ, I. (2000): The tarsus of Ukhaatherium nessovi (Eutheria, Mammalia) from the Late Cretaceous of        Mongolia: an appraisal of the evolution of the ankle in basal therians. – J. Vertebr. Paleontol., 20: 547-       560.
JERISON, H.J. (1973): Evolution of the brain and intelligence. - (Academic Press), New York, 482 p.
–,– (1991): Fossil brains and the evolution of the neocortex. In: FINLAY, B.L., INNOCENTI, G. & SCHEICH, H.        (Ed.): The neocortex: ontogeny and phylogeny. -NATO Adv. Sci. Inst. Ser. A: Life Sci. 200: 5-19,        (Plenum Press), New York.
JOHNSON, J.I. (1977): Central nervous system of marsupials. In: HUNSAKER, D. (Ed.): The biology of        marsupials. – (Academic Press), New York, 157-278.
KIELAN-JAWOROWSKA, Z., CIFELLI, R.L. & LUO, Z. (2004): Mammals from the age of dinosaurs: origins,        evolution, and structure. - (Columbia Univ. Press), New York, 630 p.
KIRSCH, J.A.W., LAPOINTE, F.J. & SPRINGER, M.S. (1997): DNA-hybridisation studies of marsupials and their        implications for metatherian classification. – Aust. J. Zool., 45: 211-280.
KOENIGSWALD, W. & GOIN, F. (2000): Enamel differentiation in South American marsupials and a comparison        of placental and marsupial enamel. – Palaeontographica Abt. A, 255: 129-168.
KOENIGSWALD, W.V. (1988): Enamel modification in enlarged front teeth among mammals and the various        possible reinforcements of the enamel. In: RUSSELL, D.E. & SIGOGNEAU-RUSSELL, D. (Ed.): Teeth        revisite. Proceedings of the VIIth international symposium on dental morphology, Paris 1986. – Mem.        Mus. natl. Hist. nat. C 53: 148-165, Paris.
–,– (1994): Differenzierungen im Zahnschmelz der Marsupialia im Vergleich zu den Verhältnissen bei den        Placentalia (Mammalia). In: KOHRING, R. & MARTIN, T. (Ed.): Festschrift Bernard Krebs. -Berl. Geowiss.        Abh. E 13: 45-81, Berlin.
–,– (1997): Evolutionary trends in the differentiation of mammalian enamel ultrastructure. In: KOENIGSWALD,        W.V. & SANDER, P.M. (Ed.): Tooth enamel microstructure. – (Balkema), Rotterdam, 203-235.
KOENIGSWALD, W.V., RENSBERGER, J.M. & PRETZSCHNER, H.U. (1987): Changes in the tooth enamel of Early        Paleocene mammals allowing increased diet diversity. – Nature, 328: 150-152.
KOENIGSWALD, W.V. & STORCH, G. (1992): The marsupials: inconspicuous opossums. In: SCHAAL, S. &        ZIEGLER, W. (Ed.): Messel. An insight into the history of life on the Earth. – (Clarendon Press), Oxford.
KORTH, W.W. (1992): Fossil small mammals from the Harrison Formation (Late Arikareean: earliest Miocene),        Cherry County, Nebraska. – Ann. Carnegie Mus. Nat. Hist., 61: 69-131.
–,– (1994): Middle Tertiary marsupials (Mammalia) from North-America. – J. Paleontol., 68: 376-397.
KURZ, C. (2001): Osteologie einer Beutelratte (Didelphimorphia, Marsupialia, Mammalia) aus dem Mitteleozän        der Grube Messel bei Darmstadt. – Kaupia, 11: 83-109.
–,– (2005): Ecomorphology of opossum-like marsupials from the Tertiary of Europe and a comparison with        selected taxa. – Kaupia, 14: 21-26.
–,– (In press): The opossum-like marsupials (Didelphimorphia and Peradectia, Marsupialia, Mammalia) from the        Eocene of Messel and Geiseltal - Ecomorphology, diversity and palaeogeography. - Kaupia.
LADEVÈZE, S. (2004): Metatherian petrosals from the Late Paleocene of Itaboraí (Brazil), and their        phylogenetic implications. – J. Vertebr. Paleontol., 24: 202-213.
–,– (2007): Petrosal bones of metatherian mammals from the Late Paleocene of Itaboraí (Brazil), and a        cladistic analysis of petrosal features in metatherians. – Zool. J. Linn. Soc., 150: 85-115.
LADEVÈZE, S. & MUIZON, C.DE (2007): The auditory region of early Paleocene Pucadelphydae (Mammalia,        Metatheria) from Tiupampa, Bolivia, with phylogenetic implications. – Palaeontol., 50: 1123-1154.
LAMBE, L.M. (1908): The Vertebrata of the Oligocene of the Cypress Hills, Saskatchewan. – Contrib. Can.        Paleontol., 3: 1-65.
LESTER, K. & HAND, S. (1987): Chiropteran enamel structure. – Scanning Microsc., 1: 421-436.
LESTER, K., HAND, S. & VINCENT, F. (1988): Adult phyllostomid (bat) enamel by scanning electron        microscopy with a note on dermopteran enamel. – Scanning Microsc., 2: 371-383.
LOO, Y.T. (1930): The forebrain of the opossum, Didelphis virginiana. – J. Comp. Neurol., 51: 13-64.
LUO, Z.-X., JI, Q., WIBLE, J.R. & YUAN, C.X. (2003): An Early Cretaceous tribosphenic mammal and        metatherian evolution. – Science, 302: 1934-1940.
LUO, Z.-X., KIELAN-JAWOROWSKA, Z. & CIFELLI, R.L. (2002): In quest for a phylogeny of Mesozoic mammals. –        Acta Palaeontol. Pol., 47: 1-78.
MACPHEE, R.D.E. (1981): Auditory regions of primates and eutherian insectivores: morphology, ontogeny,        and character analysis. – Contrib. Primatol., 18: 1-282.
MACRINI, T.E., MUIZON, C. DE, CIFELLI, R.L. & ROWE, T. (2007a): Digital cranial endocast of Pucadelphys        andinus, a Paleocene metatherian. – J. Vertebr. Paleontol., 27: 99-107.
MACRINI, T.E., ROUGIER, G.W. & ROWE, T. (2007b): Description of a cranial endocast from the fossil mammal        Vincelestes neuquenianus (Theriiformes) and its relevance to the evolution of endocranial characters        in therians. – Anat. Rec., 290: 875-892.
MACRINI, T.E., ROWE, T. & VANDEBERG J.L. (2007c): Cranial endocasts from a growth series of Monodelphis        domestica (Didelphidae, Marsupialia): a study of individual and ontogenetic variation. – J. Morphol.,        268: 844-865.
MACRINI, T.E., ROWE, T. & ARCHER, M. (2006): Description of a cranial endocast from a fossil platypus,        Obdurodon dicksoni (Monotremata, Ornithorhynchidae), and the relevance of endocranial characters        to monotreme monophyly. – J. Morphol., 267: 1000-1015.
MARSHALL, L.G., CASE, J.A. & WOODBURNE, M.O. (1990): Phylogenetic relationships of the families of        marsupials. In: GENOWAYS, H. (Ed.): Current Mammalogy, vol. 2. – (Plenum Press), New York, 433-505.
MARSHALL, L.G. & MUIZON, C. DE (1988): The dawn of the age of mammals in South America. – Natl.        Geogr. Res., 4: 23-55.
–,– (1995): Part II. The skull. In: MUIZON, C. DE (Ed.): Pucadelphys andinus (Marsupialia, Mammalia) from the        early Paleocene of Bolivia. – Mem. Mus. natl. Hist. nat., 165: 21-90, Paris.
MARSHALL, L.G. & SIGOGNEAU-RUSSEL, D. (1995): Pucadelphys andinus (Marsupialia, Mammalia) from the        early Paleocene of Bolivia. – (Mem. Mus. Natl. Hist. Nat.), Paris, 164 p.
MARTIN, T. 2004. Evolution of incisor enamel microstructure in Lagomorpha. – J. Vertebr. Paleontol., 24:        411-426.
MARTIN, J.E., CASE, J.A., JAGT, J.W.M. SCHULP, A.S. & MULDER, E.W.A. (2005): A new European marsupial        indicates a Late Cretaceous high-latitude transatlantic dispersal route. – J. Mamm. Evol., 12: 495-511.
MCGREW, P.O. (1937): New marsupials from the Tertiary of Nebraska. –J. Geol., 45: 448-455.
MENG, J. & FOX, R.C. (1995a): Osseous inner-ear structures and hearing in early marsupials and placentals.        – Zool. J. Linn. Soc., 115: 47-71.
–,– (1995b): Therian petrosals from the Oldman and Milk River Formations (Late Cretaceous), Alberta. – J.        Vertebr. Paleontol., 15: 122-130.
MUIZON, C. DE (1992): La fauna de mamíferos de Tiupampa (Paleoceno inferior, Formación Santa Lucía),        Bolivia. In: Suárez-Soruco, R. (Ed.): Fósiles y Fácies de Bolivia. Vol. I. Vertebrados. – (Revista Técnica,        Yacimientos Petrolíferos Fiscales Bolivianos), Santa Cruz, Volume 12 (3-4), 575-624.
–,– (1998): Mayulestes ferox, a borhyaenoid (Metatheria, Mammalia) from the early Paleocene of Bolivia.        Phylogenetic and palaeobiologic implications. – Geodiversitas, 20: 19-142.
–,– (1999): Marsupial skulls from the Deseadan (Late Oligocene) of Bolivia and phylogenetic analysis of the        Borhyaenoidea (Marsupialia, Mammalia). – Geobios, 32: 483-509.
MUIZON, C. DE, CIFELLI, R.L. & CÉSPEDES PAZ, R. (1997): The origin of the dog-like borhyaenoid marsupials of        South America. – Nature, 389: 486-489.
NIEUWENHUYS, R., TEN DONKELAAR, H. & NICHOLSON, C. (1998): The central nervous system of vertebrates. -        (Springer Verlag), Berlin, 2219 p.
NILSSON, M.A., ARNASON, U., SPENCER, P.B.S. & JANKE, A. (2004): Marsupial relationships and a timeline for        marsupial radiation in South Gondwana. – Gene, 340: 189-196.
NORELL, M.A. (1992): Taxic origin and temporal diversity: the effect of phylogeny. In: NOVACEK, M.J. &        WHEELER, Q.D. (Ed.): Extinction and phylogeny. – (Columbia Univ. Press), New York, 89-118.
NOWAK, R.M. (1999): Walker's mammals of the world. - (John Hopkins Univ. Press), Baltimore, 2160 p.
PFRETZSCHNER, H.U. (1988): Structural reinforcement and crack propagation in enamel. In: RUSSELL, D.E.,        SANTORO, J.-P. & SIGOGNEAU-RUSSELL, D. (Ed.): Teeth revisited. Proceedings of the VIIth        international symposium on dental morphology, Paris 1986. -Mem. Mus. natl. Hist. nat. C 53: 133-144,        Paris.
REIG, O.A., KIRSCH, J.A.W. & MARSHALL, L.G. (1987): Systematic relationships of the living and Neocenozoic        American "opossum-like" marsupials (Suborder Didelphimorphia), with comments on the classification of        these and of the Cretaceous and Paleogene New World and European metatherians. In: ARCHER, M.        (Ed.): Possums and opossums: studies in evolution. – (Surrey Beatty & Sons Pty Limited), Chipping        Norton, vol. 1, 1-89.
ROSE, K.D. (2006): The beginning of the age of mammals. - (Johns Hopkins Univ. Press), Baltimore, 428 p.
ROUGIER, G.W. (1993): Vincelestes neuquenianus Bonaparte (Mammalia, Theria), un primitivo mamífero del        Cretácico Inferior de la Cuenca Neuquina, Doctoral Dissertation, Universidad Nacional de Buenos        Aires, Argentina.
ROUGIER, G.W., WIBLE, J.R. & NOVACEK, M.J. (1998): Implications of Deltatheridium specimens for early        marsupial history. – Nature, 396: 459-463.
ROWE, T. (1996a): Brain heterochrony and origin of the mammalian middle ear. In: GHISELIN, M. & PINNA, G.        (Ed.): New perspectives on the history of life. -Calif. Acad. Sci., Mem. 20: 71-95, San Francisco.
–,– (1996b): Coevolution of the mammalian middle ear and neocortex. – Science, 273: 651-654.
SAHNI, A. (1979): Enamel ultrastructure of certain North American Cretaceous mammals. –        Palaeontographica Abt. A, 166: 37-49.
SÁNCHEZ-VILLAGRA, M.R. (2002): The cerebellar paraflocculus and the subarcuate fossa in Monodelphis        domestica and other marsupial mammals- ontogeny and phylogeny of a brain-skull interaction. – Acta        Theriol., 47: 1-14.
SÁNCHEZ-VILLAGRA, M. & SCHMELZLE, T. (2007): Anatomy and development of the bony inner ear in the        woolly opossum, Caluromys philander (Didelphimorphia, Marsupialia). – Mastozool. Neotrop., 14:53-60.
SÁNCHEZ-VILLAGRA, M.R., LADEVÈZE, S., HOROVITZ, I., ARGOT, C., HOOKER, J.J., MACRINI, T.E., MARTIN, T., MOORE-FAY, S., MUIZON, C.DE, SCHMELZLE, T. & ASHER, R.J. (2007a): Exceptionally preserved North        American Paleogene metatherians: adaptations and discovery of a major gap in the opossum fossil        record. – Biol. Lett., 3: 318-322.
SÁNCHEZ-VILLAGRA, M.R., SEIFFERT, E.R., MARTIN, T., SIMONS, E.L., GUNNELL, G.F. & ATTIA, Y. (2007b):        Enigmatic new mammals (?Marsupialia) from the late Eocene of Egypt. – Paläontol. Z. 81:.
SÁNCHEZ-VILLAGRA, M.R. & WIBLE, J.R. (2002): Patterns of evolutionary transformation in the petrosal bone        and some basicranial features in marsupial mammals, with special reference to didelphids. – J. Zool.        Syst. Evol. Res., 40: 26-45.
SCHMELZLE, T., MAIER, W. & SÁNCHEZ-VILLAGRA, M.R. (2007): Labyrinth evolution in diprotodontian        marsupials. Mamm. Study, 32: 83-97.
SCHMELZLE, T., NUMMELA, S. & SÁNCHEZ-VILLAGRA, M.R. (2005): Phylogenetic transformations of the ear        ossicles in marsupial mammals, with special reference to diprotodontians: a character analysis. - Ann.        Carnegie Mus. Nat. Hist., 74: 189-200.
SEGALL, W. (1970): Morphological parallelisms of the bulla and auditory ossicles in some insectivores and        marsupials. – Fieldiana: Zool., 51: 169-205.
STEINER, C., TILAK, M., DOUZERY, E.J.P. & CATZEFLIS, F.M. (2005): New data from a transthyretin nuclear        intron suggest an Oligocene to Miocene diversification of living South American opossums (Marsupialia:        Didelphidae). – Mol. Phylogenet. Evol., 35: 363-379.
STOCK, C. & FURLONG, E.L. (1922): A marsupial from the John Day Oligocene of Logan Butte, eastern        Oregon. – Univ. Calif. Publ. Geol. Sci., 13: 311-317.
SWOFFORD, D. (2002): PAUP 4.0b10. Program and Documentation. - (Sinauer Associates, Sunderland,        Massachussets).
SZALAY, F.S. (1994): Evolutionary history of the marsupials and an analysis of osteological characters. -        (Cambridge Univ. Press), Cambridge, 481 p.
SZALAY, F. & TROFIMOV, B. (1996): The Mongolian Late Cretaceous Asiatherium, and the early phylogeny        and paleobiogeography of Metatheria. – J. Vertebr. Paleontol., 16: 474-509.
SZALAY, F.S. AND SARGIS, E. J. (2001): Model-based analysis of postcranial osteology of marsupials from the        Palaeocene of Itaboraí (Brazil) and the phylogenetics and biogeography of Metatheria. Geodiversitas,        23: 139-302.
TOMES, J. (1849): On the structure of dental tissues of marsupial animals and more especially of the        enamel. – Philos. Trans. R. Soc. Lond. B, 139: 403-412.
TROFIMOV, B.A. & SZALAY, F.S. (1994): New Cretaceous marsupial from Mongolia and the early radiation of        Metatheria. – Proc. Natl. Acad. Sci. U.S.A. , 91: 12569-12573.
WIBLE, J.R. (1983): The internal carotid artery in early mammals. – Acta Palaeontol. Pol., 28: 281-293.
–,– (1990): Petrosals of Late Cretaceous marsupials from North America, and a cladistic analysis of the        petrosal in therian mammals. – J. Vertebr. Paleontol., 10: 183-205.
–,– (2003): On the cranial osteology of the short-tailed opossum Monodelphis brevicaudata (Didelphidae,        Marsupialia). – Ann. Carnegie Mus., 72: 137-202.
WIBLE, J.R. & HOPSON, J.A. (1995): Homologies of the prootic canal in mammals and non-mammalian        cynodonts. – J. Vertebr. Paleontol., 15: 331-356.
WIBLE, J.R., ROUGIER, G.W., NOVACEK, M.J. & MCKENNA, M.C. (2001): Earliest eutherian ear region: a        petrosal referred to Prokennalestes from the Early Cretaceous of Mongolia. – Am. Mus. Novit., 3322: 1-       44.
WILSON, D.E. & REEDER, D.M., editors. (2005): Mammal species of the world. - (Johns Hopkins Univ. Press),        Baltimore, 2 volumes, 142 p.