Browsing by Author "Asher, Robert J."

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    Cranial anatomy in tenrecid insectivorans : character evolution across competing phylogenies. American Museum novitates ; no. 3352
    (New York, NY : American Museum of Natural History, 2001) Asher, Robert J.
    Soft-tissue characters from the cranial vasculature and anterior nasal fossa are described and figured for several tenrecs and other insectivoran-grade mammals. A number of variations in blood supply and anterior nasal anatomy exist among observed specimens, including the involution of certain branches of the stapedial artery, blood supply to the jaw, relation of the external carotid to pharyngeal musculature, connections of the vomeronasal duct and paraseptal cartilage, presence of a papillary cartilage, and others. When the observed anatomy is distilled into 20 discrete anatomical characters and optimized onto recent insectivoran phylogenetic trees, these soft-tissue characters are more consistent with a reconstruction based on osteological and dental characters than with one based on molecular characters. Nevertheless, all recently proposed phylogenies require homoplasy from this dataset, and potential synapomorphies for both a monophyletic Lipotyphla and endemic African clade can be optimized onto recent phylogenetic proposals.
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    The eutherian mammal Maelestes gobiensis from the late Cretaceous of Mongolia and the phylogeny of Cretaceous Eutheria. (Bulletin of the American Museum of Natural History, no. 327)
    (New York : American Museum of Natural History., 2009) Wible, John R.; Rougier, Guillermo W.; Novacek, Michael J.; Asher, Robert J.
    Maelestes gobiensis Wible et al., 2007, is the second new eutherian mammal to be named from the rich Mongolian late Cretaceous locality of Ukhaa Tolgod, Ukhaatherium nessovi Novacek et al., 1997, being the first. Maelestes is only the seventh late Cretaceous eutherian known from the skull and the upper and lower dentitions, and the fifth known from some postcranial elements. The type and only known specimen, PSS-MAE 607, is described and illustrated in detail. The type is amended to include: an incomplete skull, left dentary, atlas, axis, last cervical and first 11 thoracic vertebrae, 11 partial ribs, incomplete scapula, clavicle, humerus, and proximal radius and ulna. An astragalus on a separate block was referred to Maelestes by Wible et al. (2007), but it is too large to belong to this taxon and is removed from the isotype. Several corrections and updates are made to the phylogenetic analysis of Wible et al. (2007). The original analysis and the one in this report include 408 morphological characters (127 dental, 212 cranial, and 69 postcranial) in Maelestes along with 68 other taxa (four stem therians, three metatherians, 31 Cretaceous eutherians, 20 extinct Tertiary placentals, and 11 extant placentals). Maelestes is identified as a member of Cimolestidae sensu Kielan- Jaworowska et al. (2004) along with the slightly younger and poorer known North American taxa Batodon Marsh, 1892, and Cimolestes Marsh, 1889. Cimolestidae, in turn, is grouped with Asioryctitheria sensu Archibald and Averianov (2006), which includes monophyletic Mongolian and Uzbekistani clades. The other principal Late Cretaceous clades are: a Laurasian Zhelestidae; Paranyctoides Fox, 1979 (North American and Uzbekistan) + Eozhelestes Nessov, 1997 (Uzbekistan); and an Asian Zalambdalestidae. In contrast to some previous analyses, but in common with Wible et al. (2007), no Cretaceous eutherians are identified as members of any placental group.
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    Morphology and relationships of Apternodus and other extinct, zalambdodont, placental mammals. Bulletin of the AMNH ; no. 273
    (New York, NY : American Museum of Natural History, 2002) Asher, Robert J.; McKenna, Malcolm C.; Emry, Robert J.; Tabrum, Alan R.; Kron, Donald G.
    We describe and illustrate new, middle Cenozoic fossils of dentally zalambdodont, North American placentals, including six relatively complete crania of Apternodus and two of Oligoryctes, as well as many partial skulls, mandibles, and teeth of these and other taxa. Several of the new Apternodus specimens are also associated with postcrania. We recognize seven species of Apternodus, three of which are new, formally propose the combination Oligoryctes altitalonidus, and recognize two other genera of small, North American, anatomically zalambdodont placentals, Parapternodus and Koniaryctes. We regard two other taxa previously associated with North American fossil zalambdodonts, one Bridgerian and the other Tiffanian, as valid but do not name them in this paper. In addition, we argue that dental zalambdodonty entails a primary occlusal relationship between the paracone and the ectoflexid, and the reduction or absence of the metacone and talonid basin. A phylogenetic analysis of cranial, dental, and postcranial characters of 30 fossil and Recent taxa leads us to conclude that (1) the Apternodontidae as defined in previous literature is not monophyletic and should be restricted to seven species of Apternodus, (2) the genus Oligoryctes contains at least two species and has a considerably longer geologic record than Apternodus, (3) neither Micropternodus nor currently known Paleocene taxa are closely related to Apternodus or Oligoryctes, and (4) a case can be made for a close relationship among modern soricids, Parapternodus, Koniaryctes, Oligoryctes and Apternodus to the exclusion of other insectivoran-grade taxa. With the use of ordered, multistate character transformations, Solenodon comprises the sister taxon to a soricid-fossil zalambdodont clade.
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    Neither a rodent nor a platypus : a reexamination of Necrolestes patagonensis Ameghino ; American Museum novitates, no. 3546
    (New York, NY : American Museum of Natural History, 2007) Asher, Robert J.; Horovitz, Inés.; Martin, Thomas, 1960-; Sánchez-Villagra, Marcelo R.
    We present new descriptions, figures, and interpretations of well-preserved cranioskeletal elements of the early Miocene, fossorial mammal Necrolestes patagonensis from Argentina. As previously noted, this animal is highly apomorphic and its phylogenetic affinities are difficult to interpret. Its derived features include hypsodont upper cheek teeth, a partially fused cervical spine, an unfused atlas consisting of separate right and left massae, and a distally ossified flexor tendon of the forearm. Characters that support its status as a therian mammal include a coiled cochlear housing of the inner ear. Consistent with its status as a metatherian is the presence of five upper incisors, transverse canal foramina, and a broad proximal fibula. However, we cannot confirm other characters claimed by previous researchers as evidence for affinity with marsupial or nonplacental mammals, such as the presence of an inflected mandibular angle and epipubic bones. Furthermore, Necrolestes shows similarities to eutherian mammals, such as small incisive foramina and possibly three molars. On biogeographic and some anatomical grounds, identification of Necrolestes as a metatherian remains a compelling option. However, pending a combined-data phylogenetic analysis encompassing Theria and accounting for the anatomical diversity of Necrolestes, possible membership in Eutheria should not be ruled out.