Browsing by Author "Rougier, Guillermo W."
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Item Basicranial anatomy of Priacodon fruitaensis (Triconodontidae, Mammalia) from the Late Jurassic of Colorado, and a reappraisal of mammaliaform interrelationships. American Museum novitates ; no. 3183(New York, N.Y. : American Museum of Natural History, 1996) Rougier, Guillermo W.; Wible, John R.; Hopson, James A.Item Cranial anatomy of Kryptobaatar dashzevegi (Mammalia, Multituberculata), and its bearing on the evolution of mammalian characters. Bulletin of the AMNH ; no. 247([New York] : American Museum of Natural History, 2000) Wible, John R.; Rougier, Guillermo W.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi.The cranial anatomy of the Mongolian late Cretaceous multituberculate Kryptobaatar dashzevegi is described based on exquisitely preserved specimens collected from Ukhaa Tolgod and Tugrugeen Shireh in the Gobi Desert by joint expeditions of the American Museum of Natural History and the Mongolian Academy of Sciences. Most sutural relationships are preserved, enabling a bone-by-bone description of the skull and lower jaws exclusive of the nasal fossa and paranasal sinuses. A reconstruction of the principal components of the cranial nervous, arterial, and venous systems is facilitated by specimens with exposed endocranial surfaces. Comparisons with previously described multituberculates, other Mesozoic mammaliaforms, and extant mammals allow an assessment of major topics in the evolutionary morphology of the multituberculate and mammaliaform skull, as well as identification of Kryptobaatar as an appropriate model regarding most aspects of the multituberculate skull for future phylogenetic studies. Elements previously unknown or poorly known in multituberculates are described. Included are a complete jugal on the internal surface of the zygoma; the orbital mosaic and foramina, including the optic foramen, the metoptic foramen, the transverse canal, and the foramen for the pituito-orbital vein; and the endocranium with an extensively ossified primary braincase wall formed by the pilae metoptica and antotica. The latter pila is very robust compared with its ossified remnants in non-mammalian cynodonts and monotremes, suggesting that it is a derived multituberculate condition. The co-occurrence of the pilae metoptica and antotica in multituberculates is thus far unique among mammaliaforms, but agrees with the morphology expected to be primitive for Mammalia. This in turn implies an independent loss of an ossified pila metoptica in monotremes, marsupials, and Vincelestes or the loss of the pila metoptica in the ancestry of multituberculates and therians combined with the independent reacquisition of a neomorphic pila metoptica in multituberculates and eutherians. The absence of several elements from the multituberculate skull, controversial in nature, is confirmed, including the prenasal process of the premaxilla, the septomaxilla, the ectopterygoid, and the orbital process of the palatine. Also confirmed is the presence of several controversial elements in the multituberculate skull, including an alisphenoid with a reduced contribution to the braincase and an anterior lamina expanded dorsal to the alisphenoid. Competing anatomical hypotheses for several elements are addressed, including the function of the lateral pterygopalatine trough as muscle attachment and not for the auditory tube, the homology of the postorbital process on the parietal with that on the frontal, the identity of foramina in the anterior lamina as for mandibular nerve branches and not for the mandibular and maxillary nerves, and the function of the jugular fossa as primarily having housed a diverticulum of the cavum tympani and not large cranial nerve ganglia. The cranial arterial system in Kryptobaatar generally resembled that restored for other multituberculates and for other mammaliaforms, in particular the prototribosphenidan Vincelestes. Both Kryptobaatar and Vincelestes had a transpromontorial internal carotid artery, a stapedial artery that ran through a bicrurate stapes, ramus inferior, ramus superior, and an arteria diploëtica magna. The cranial venous system in Kryptobaatar resembled that described for other Mongolian late Cretaceous multituberculates and for monotremes with the major exits of the dural sinuses having been the prootic canal and the foramen magnum. A revised diagnosis of Kryptobaatar distinguishes it from other djadochtatherians (the grouping that includes 10 of the 11 genera of Mongolian late Cretaceous multituberculates) by a pterygoid canal either confluent with or barely separated from the carotid canal and a separate hypoglossal foramen.Item Earliest eutherian ear region : a petrosal referred to Prokennalestes from the early Cretaceous of Mongolia. American Museum novitates ; no. 3322(New York, NY : American Museum of Natural History, 2001) Wible, John R.; Rougier, Guillermo W.; Novacek, Michael J.; McKenna, Malcolm C.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi.A right petrosal from the ?Aptian or Albian Khoobur locality is referred on the basis of size and morphology to Prokennalestes trofimovi, the earliest eutherian previously known only from dentigerous elements. The petrosal shows a mosaic of primitive and derived features, bearing on the purported therian and eutherian morphotypes. Among the primitive features shared with the early Cretaceous prototribosphenidan Vincelestes and other more basal taxa that are modified in later eutherians and metatherians are the pattern of basicranial arterial and venous circulation, including a prootic canal and an intrapetrosal inferior petrosal sinus; a vertical paroccipital process; and a fenestra semilunaris, an incomplete wall between the cavum epiptericum and cavum supracochleare. Among the derived features shared with therians is a cochlea coiled through a minimum of 360°, with Prokennalestes extending the range of the oldest occurrence of such a coiled cochlea by at least 10 million years. Shared with late Cretaceous eutherians is a shallow internal acoustic meatus with a thin prefacial commissure. The petrosal referred to Prokennalestes is intermediate in having a reduced anterior lamina and lateral flange, both of which are well developed in Vincelestes and essentially lacking in later eutherians and metatherians. Features previously held to be part of the therian and eutherian morphotypes, such as the absence of the anterior lamina and lateral flange, may have been lost independently in metatherians and in post-Prokennalestes eutherians.Item 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.Item First Jurassic triconodont from South America ; American Museum novitates, no. 3580(New York, NY : American Museum of Natural History, 2007) Rougier, Guillermo W.; Garrido, Alberto, paleontologist.; Gaetano, Leandro.; Puerta, Pablo.; Corbitt, Cynthia.; Novacek, Michael J.A new mammal from the Middle Jurassic CaŠnadon Asfalto Formation, Patagonia, Argentina, is reported. The specimen, an isolated lower? molariform, is erected as the type of a new genus and species of triconodont, Argentoconodon fariasorum. The molariform presents a peculiar combination of primitive and derived features that makes recognition of its affinities challenging. Argentoconodon shares similarities with poorly known triconodonts from the Jurassic of North America and Morocco and lacks the diagnostic traits of the triconodontid triconodonts. Argentoconodon resembles in general the paraphyletic "amphilestid" triconodonts. The specimen is too incomplete to warrant broader interpretations, but it suggests that at least this lineage of South American mammals was distinctly autapomorphic, perhaps with an origin in forms with a broader geographical distribution.Item Gobiconodonts from the early Cretaceous of Oshih (Ashile), Mongolia. American Museum novitates ; no. 3348(New York, NY : American Museum of Natural History, 2001) Rougier, Guillermo W.; Novacek, Michael J.; McKenna, Malcolm C.; Wible, John R.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi.We describe here the first discovered mammalian remains from the Mongolian early Cretaceous locality Oshih (Ashile). Four fragmentary, tooth-bearing specimens, probably corresponding to three individuals, have been recovered. All the fossils can be assigned to the family Gobiconodontidae (Chow and Rich, 1984). The specimens include three lower jaw fragments and one upper jaw fragment, and represent at least two different taxa. Gobiconodon hopsoni, n. sp., is described and diagnosed here. This new species is larger than G. ostromi (early Cretaceous Cloverly Formation, USA); thus, it is the largest triconodont and one of the largest Mesozoic mammals known. Gobiconodon sp., found also at Oshih, is slightly larger than G. borissiaki, from the early Cretaceous of Khoobur, Mongolia, but smaller than G. ostromi. The specimens of this second species are poorly preserved and provide insufficient data for a diagnosis. The status of the different species of Gobiconodon and the new gobiconodontid Hangjinia is reviewed. In gobiconodontids and Triconodontidae, the maxillae appear to make a significant contribution to the orbital rim, a condition unusual among basal mammals, in which the lacrimal and jugal are the main components. Other triconodonts such as Jeholodens, likely an "amphilestid", appear to show the primitive mammalian condition for this feature. We present a brief consideration of triconodont relationships and discuss alternative placements of Gobiconodon among Mammaliaformes.Item A late Campanian sphenodontid maxilla from northern Patagonia ; American Museum novitates, no. 3581(New York, NY : American Museum of Natural History, 2007) Apesteguía, Sebastián.; Rougier, Guillermo W.At the end of the early Cretaceous the once abundant sphenodontians vanished from the Laurasian record and were thought to have become virtually extinct, with the sole exception of Sphenodon, the living tuatara. Recent findings of large and abundant eilenodontine sphenodontids in the early late Cretaceous (Cenomanian-Turonian) and fragmentary material from other lineages from late Campanian outcrops of Patagonia, Argentina, have demonstrated that sphenodontids constituted an important component of the late Cretaceous terrestrial ecosystems in South America and possibly Gondwana. Although eilenodontine and possibly sapheosaurine sphenodontids are present in the late Cretaceous of Gondwana, they were only part of an unknown southern radiation. We report here on a new sphenodontid, Lamarquesaurus cabazai, n. gen. et sp., which is represented by an incomplete right maxilla that represents a previously unknown non-eilenodontine lineage and illustrates the diversity and role of sphenodontians in the tetrapod communities of the late Mesozoic of South America.Item A mammalian petrosal from the early Cretaceous of Mongolia : implications for the evolution of the ear region and mammaliamorph interrelationships. American Museum novitates ; no.3149(New York, N.Y. : American Museum of Natural History, 1995) Wible, John R.; Rougier, Guillermo W.; Novacek, Michael J.; McKenna, Malcolm C.; Dashzėvėg, Dėmbėrėliĭn.; Mongolyn Shinzhlėkh Ukhaany Akademi.Item Middle-ear ossicles of the multituberculate Kryptobaatar from the Mongolian late Cretaceous : implications for mammaliamorph relationships and the evolution of the auditory apparatus. American Museum novitates ; no. 3187(New York, N.Y. : American Museum of Natural History, 1996) Rougier, Guillermo W.; Wible, John R.; Novacek, Michael J.; Mongolyn Shinzhlėkh Ukhaany Akademi.Item New data on the skull and dentition in the Mongolian late Cretaceous eutherian mammal Zalambdalestes. Bulletin of the AMNH ; no. 281(New York, NY : American Museum of Natural History, 2004) Wible, John R.; Novacek, Michael J.; Rougier, Guillermo W.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi.Exquisitely preserved specimens of the late Cretaceous eutherian Zalambdalestes recently collected from the Djadokhta Formation (early Campanian) of the Gobi Desert by the Mongolian Academy of Sciences-American Museum of Natural History Expeditions are the centerpiece of a thorough redescription of this taxon's craniodental morphology. Resolved and amended are uncertainties and errors in prior descriptions based on poorer preserved specimens collected by earlier expeditions to the Gobi. Preserved and described for the first time in Zalambdalestes is the basicranium, including an ectotympanic bone and portions of the hyoid arch. Zalambdalestes with a skull length of nearly 50 mm is large compared with other Cretaceous eutherians. It is also highly specialized with a long, thin, tubular snout, large diastemata in the anterior upper dentition, and an elongated mesial lower incisor with restricted enamel. These specializations, though less extreme, are also present in the zalambdalestids Barunlestes from the slightly younger Barun Goyot Formation of the Gobi and Kulbeckia from the late Turonian and Coniacian of Uzbekistan and the Santonian of Tadjikistan. No phylogenetic analysis published to date includes enough taxonomic and morphological breadth to evaluate the relationships of Zalambdalestes. Nevertheless, we investigate the impact of our observations on seven phylogenetic analyses published since 1993 that include Zalambdalestes. A comprehensive phylogenetic analysis testing the relationships of Zalambdalestes is not included here, but it is expected to result from our ongoing efforts to produce a phylogeny of basal tribosphenic and therian mammals. Currently, zalambdalestids are viewed either as stem eutherians or as having affinities to Glires (lagomorphs and rodents). Our comparisons with other extinct and extant taxa support a position for Zalambdalestes within Eutheria but outside the crown-group Placentalia. Supporting this basal position for Zalambdalestes are such primitive features as the last upper incisor in the maxilla, nasals broadly expanded posteriorly to contact the lacrimals, pterygoids meeting on the midline, and the position of the glenoid fossa on the zygoma and not the braincase proper, in addition to the occurrence of epipubic bones reported previously. Zalambdalestes shares a number of apomorphies with Asioryctitheria, the clade including the Mongolian late Cretaceous Asioryctes, Ukhaatherium, and Kennalestes. Among the unusual specializations supporting a zalambdalestid-asioryctithere clade are: the postglenoid foramen anterior rather than posterior to the postglenoid process; the postglenoid and entoglenoid processes of the squamosal continuous; a fusiform ectotympanic expanded laterally and contacting the entoglenoid process; a suprameatal foramen in the squamosal; a crista interfenestralis connecting from the petrosal promontorium to a fingerlike tympanic process behind the round window; a large piriform fenestra in the anterior roof of the tympanic cavity, which transmitted the ramus inferior of the stapedial artery endocranially to the orbit; a foramen ovale between the alisphenoid and squamosal; and a medially positioned internal carotid artery. All but the last two of these specializations are reminiscent of those occurring in various extant lipotyphlans, including taxa placed by recent DNA sequence analyses within Afrotheria and Eulipotyphla, and may provide a link between the Mongolian Cretaceous eutherians and lipotyphlans. The available sample of Zalambdalestes exhibits a remarkable degree of individual variation, including the incidence of the upper maxillary incisor, the first upper premolar, and the second lower premolar. The possibility exists that more than a single species, Z. lechei, is represented.Item New Jurassic mammals from Patagonia, Argentina : a reappraisal of australosphenidan morphology and interrelationships ; American Museum novitates, no. 3566(New York, NY : American Museum of Natural History, 2007) Rougier, Guillermo W.; Martinelli, Agustín G.; Forasiepi, Analía M.; Novacek, Michael J.A new mammal, Henosferus molus, n.gen. and n.sp., from the Callovian-Oxfordian (latest middle to earliest late Jurassic) Cañadón Asfalto Formation from Chubut Province (Argentina) is described. This taxon corresponds to a new species clearly different from Asfaltomylos patagonicus from the same locality and stratigraphic level. This new species is based on three lower jaws with relatively well-preserved dentition. The lower jaw shows a primitive morphology having a Meckelian groove, a prominent medial flange associated with a lateral ridge of the dentary, and a deep dentary trough, which possibly indicates the presence, even though reduced, of postdentary bones still attached to the dentary. The lower dental formula is i4, c1, p5, m3. The premolars are simple, bearing a main cusp, while the molars appear to be tribosphenic, with an obtuse to right-angled trigonid and a basined talonid with three cusps. This association of plesiomorphic features in the jaw and derived features in the molars is documented in several taxa of the recently proposed Australosphenida. A phylogenetic analysis of mammaliaforms nests the new species with Asfaltomylos from the same locality and stratigraphic level; Henosferidae, new family, is recognized for Asfaltomylos and Henosferus, representing the basal radiation of Australosphenida. Henosferidae is the sister group to Ambondro from the Middle Jurassic of Madagascar, which, in agreement with previous phylogenies, is the sister taxon to the remaining australosphenidans. Additionally, our phylogenetic analysis does not support the inclusion of australosphenidans within eutherians. Henosferids likely retained some connection of the postdentary elements with the dentary; therefore, if the inclusion of Monotremata within Australosphenida is confirmed, final freeing of the postdentary elements and development of a triossicular middle ear would be convergent events in Monotremata and Theria. Finally, the distinctiveness of the yet sparse South American record of Jurassic mammals when compared with the slightly better documented Cretaceous data is emphasized. The clear faunistic break between the middle Jurassic and early/late Cretaceous underlies our rudimentary understanding of the evolution of Mesozoic mammals in Gondwana.Item A new multituberculate from the late Cretaceous locality Ukhaa Tolgod, Mongolia : considerations on multituberculate interrelationships. American Museum novitates ; no.3191(New York, N.Y. : American Museum of Natural History, 1997) Rougier, Guillermo W.; Novacek, Michael J.; Dashzėvėg, Dėmbėrėliĭn.; Mongolyn Shinzhlėkh Ukhaany Akademi.Item A new specimen of Eurylambda aequicrurius and considerations on "symmetrodont" dentition and relationships. American Museum novitates ; no. 3398(New York, NY : American Museum of Natural History, 2003) Rougier, Guillermo W.; Spurlin, Barton K.; Kik, Peter K.; Marsh, Othniel Charles, 1831-1899.A new specimen of the tinodontid "symmetrodont" Eurylambda (Simpson, 1925a, 1929) from the late Jurassic Como Bluff Quarry, Morrison Formation, is described. The specimen, a complete upper left molariform, is probably an M1. The major crown cusps of Eurylambda show similarities to those of triconodontids on the one hand and to spalacotherioids on the other. Cusp B of basal mammaliaforms is tentatively proposed as homologous with the cusp traditionally described as a stylocone in Eurylambda and with cusp Bʹ of Peralestes. These homologies imply that the stylocone is ancestrally a small cusp in the lineage leading to Theria and that the development of a parastylar lobe or "hook" is a derived feature of post-tinodontid mammals. If accepted, this scenario results in a more complex origin for the therian upper molar than previously recognized. Wear facet 1 (Crompton, 1971) of holotherians would not be homologous between Kuehneotherium-Eurylambda-Zhangheotherium, on the one hand, and the therians, on the other.