Browsing by Author "Ni, Xijun."
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Item Discovery of the first early Cenozoic euprimate (Mammalia) from Inner Mongolia ; American Museum novitates, no. 3571(New York, NY : American Museum of Natural History, 2007) Ni, Xijun.; Beard, K. Christopher.; Meng, Jin (Paleontologist); Wang, Yuan-qing.; Gebo, Daniel Lee, 1955-Although it is widely thought that euprimates originated in Asia, the fossil record of early euprimates remains sparse there. We describe herein a new omomyid euprimate, Baataromomys ulaanus, n. gen. et sp., based on an isolated right lower m2 from Bumbanian strata at Wulanboerhe in the Erlian Basin of Inner Mongolia, China. In terms of the size and proportions of m2, Baataromomys ulaanus is intermediate between Eurasian and North American species that are usually assigned to Teilhardina. Morphologically, m2 of Baataromomys differs from that of Teilhardina and North American small-bodied omomyids (including Anemorhysis, Tetonoides, Trogolemur, and Sphacorhysis) in having a smaller paraconid that is less fully connate with the metaconid, a lower entoconid, a weaker crest connecting the metaconid with the entoconid, and a weaker buccal cingulid. The new taxon is much smaller and lower crowned than Steinius, a genus commonly regarded as a basal omomyid. Despite the substantial difference in size, the m2s of Baataromomys and Steinius share some important features, including a very broad talonid basin and a relatively low hypoconid and cristid obliqua. Given its early occurrence and primitive anatomy, Baataromomys may eventually help to clarify the phylogenetic relationships among basalomomyids, but more complete specimens will be required to test this possibility. Baataromomys brandti from the basal Wasatchian zone Wa-0 in the northern Bighorn Basin, Wyoming, was previously allocated to Teilhardina. However, several dental features shared by B. brandti and B. ulaanus suggest that they are closely related. The co-occurrence of Baataromomys in Asia and North America indicates that small-bodied euprimates were able to dispersal across the Beringian region near the Paleocene-Eocene boundary.Item Eucricetodon (Rodentia, Mammalia) from the late Oligocene of the Junggar Basin, northern Xinjiang, China. (American Museum novitates, no. 3665)(New York, NY : American Museum of Natural History., 2009) Maridet, Olivier.; Wu, Wenyu.; Ye, Jie.; Bi, Shundong.; Ni, Xijun.; Meng, Jin (Paleontologist).New specimens of Eucricetodon are described from the late Oligocene Tieersihabahe Formation of the Junggar basin, northern Xinjiang, China. The relatively abundant material documents the morphological variation within Asian species of the genus. The taxon, identified as E. aff. E. caducus, is similar to E. caducus from the Oligocene of Kazakhstan and China and E. occasionalis from the Early Miocene of Kazakhstan. It also shows noticeable resemblances to E. longidens from the Late Oligocene of Europe whose origin is currently in debate. The study confirms the strong morphological affinity between Asian and European species of Eucricetodon and suggests that the evolutionary trends among paracricetodontines are probably more complex than previously assumed, especially with the new forms discovered from the last decade. A systematic revision of Eurasian paracricetodontines at species level is needed to understand their evolutionary history.Item New distylomyid rodents (Mammalia, Rodentia) from the early Miocene Suosuoquan Formation of northern Xinjiang, China. (American Museum novitates, no. 3663)(New York, NY : American Museum of Natural History., 2009) Bi, Shundong.; Meng, Jin (Paleontologist); Wu, Wenyu.; Ye, Jie.; Ni, Xijun.Three new distylomyid species, Distylomys burqinensis, Prodistylomys wangae, and P. lii, are described from the Suosuoquan Formation, early Miocene, of Xinjiang Province, northwestern China. Previously unknown cranial materials and upper dentitions add new information for the higher-level taxonomy of distylomyid rodents. Based on these new discoveries, the family Distylomyidae is resurrected. These fossils demonstrate that distylomyids have a combination of primitive "ctenodactylid" characters and derived hystricognathous ones, possibly indicating a close affinity with South American caviomorph rodents and thereby offering new evidence to challenge the hypothesis that the traditional "Ctenodactyloidea" are monophyletic. Prodistylomys lii was recovered from Suosuoquan mammal assemblage III (magnetostratigraphically dated as 21.69-21.16 Mya) at the Chibaerwoyi locality. Distylomys burqinensis and Prodistylomys wangae were collected from a new fossiliferous locality, Locality XJ200601 of Burqin County. The composition of the fauna from this new locality suggests that it represents an assemblage younger than Suosuoquan mammal assemblage III. Preliminary comparison with other faunas suggests that the assemblage is of early Miocene age, approximately 20 Mya old, and is a new fossil level within the Suosuoquan Formation.Item A new Eocene rodent from the lower Arshanto Formation in the Nuhetingboerhe (Camp Margetts) area, Inner Mongolia ; American Museum novitates, no. 3569(New York, NY : American Museum of Natural History, 2007) Meng, Jin (Paleontologist); Li, Chuan-Kuei.; Ni, Xijun.; Wang, Yuan-qing.; Beard, K. Christopher.A new miniscule rodent represented by isolated cheek teeth is reported from the lower part of the late early Eocene Arshanto Formation, Nuhetingboerhe (Camp Margetts) area, Inner Mongolia. A new family, based on the new genus and species, is proposed. The new taxon resembles alagomyids but differs from early rodents in having a partial buccal cingulum, a distinct metaconule that merges posteriorly with the postcingulum, a transversely oriented trigon basin that widely separates the paracone and metacone, a prominent hypoconulid on lower molars, and in lacking the hypocone and protocristid. It differs from alagomyids in having a greater length/width ratio of upper cheek teeth, a neomorphic cusp termed as the preprotoconule, a preprotoconule crista that projects anteriorly, an anteroconid on dp4, an oblique cristid obliqua bearing a distinct mesoconid, and the hypoconid more posteriorly extended (or hypoconulid less posteriorly extended) on m3. The dental morphology of the new taxon is derivable from analagomyid dental pattern and is intermediate between alagomyids and rodents of modern aspect; it casts new light on the evolution of dentition of early rodents.Item New material of Alagomyidae (Mammalia, Glires) from the late Paleocene Subeng locality, Inner Mongolia ; American Museum novitates, no. 3597(New York, NY : American Museum of Natural History, 2007) Meng, Jin (Paleontologist); Ni, Xijun.; Li, Chuan-Kuei; Beard, K. Christopher.; Gebo, Daniel Lee, 1955-; Wang, Yuan-qing.; Wang, Hongjiang.Newly discovered specimens of alagomyids, mostly isolated teeth collected by screenwashing at the Gashatan (late Paleocene) Subeng locality in Inner Mongolia, document considerable intraspecific variation in Tribosphenomys minutus that has not been appreciated previously because of limited sample sizes. P4s of Tribosphenomys are described for the first time, which helps to clarify the posterior premolar identification of alagomyids. Some of the alagomyid specimens are referred to Tribosphenomys cf. T. secundus and Neimengomys qii gen. and sp. nov. Based on the new data, Tribosphenomys borealis from the Bumban Member of the Naran Bulak Formation, Mongolia, is considered to be a junior synonym of Alagomys inopinatus, and T. tertius from the Zhigden Member of the Naran Bulak Formation is regarded as a junior synonymof T. minutus. Alagomyidae, consisting of Tribosphenomys, Alagomys and Neimengomys, is maintained as a valid family. The presence of a diversity of alagomyids and other recently obtained fossils and stratigraphic evidence from the Erlian Basin suggest that the Gashatan and Bumbanian of Asia are probably correlative to the late Tiffanian-early Wasachian of North America. The faunal turnover during the Gashatan and Bumbanian in Asia is probably related to the late Paleocene-early Eocene global warming, but current evidence is insufficient to link any specific event with the Paleocene-Eocene Thermal Maximum.Item A new species of Gomphos (Glires, Mammalia) from the Eocene of the Erlian Basin, Nei Mongol, China. (American Museum novitates, no. 3670)(New York, NY : American Museum of Natural History., 2009) Meng, Jin (Paleontologist); Kraatz, Brian P.; Wang, Yuan-qing.; Ni, Xijun.; Gebo, Daniel Lee, 1955-; Beard, K. Christopher.Dental and postcranial specimens of Gomphos shevyrevae, sp. nov., from the lower part of the Irdin Manha Formation at the Huheboerhe locality, Erlian Basin, Nei Mongol (Inner Mongolia), are described. The new species differs from G. elkema and G. ellae in having more robust teeth with inflated cusps and stronger lophs and a calcaneus with extra articulation for the astragalus and navicular. The new species is stratigraphically well constrained and probably represents the youngest known species of the genus, extending its geological record into the Middle Eocene. It also shows that mimotonids coexisted for millions of years as a side branch of duplicidentates with the earliest stem lagomorphs, including Dawsonolagus.Item New stratigraphic data from the Erlian Basin : implications for the division, correlation, and definition of Paleogene lithological units in Nei Mongol (Inner Mongolia) ; American Museum novitates, no. 3570(New York, NY : American Museum of Natural History, 2007) Meng, Jin (Paleontologist); Wang, Yuan-qing.; Ni, Xijun.; Beard, K. Christopher.; Sun, Chengkai.; Li, Qian (Paleontologist); Jin, Xun (Paleontologist); Bai, Bin, 1981-Newly measured stratigraphic sections are reported for Paleogene rocks in the Nuhetingboerhe-Huheboerhe (Camp Margetts) area of Nei Mongol (Inner Mongolia), China. The composite sequence in this region is 82.4 m thick, encompassing three lithological units separated by important depositional hiatuses. In stratigraphic order, these rock units correspond to the Nomogen, Arshanto and Irdin Manha formations. The sequence contains faunas from four Asian land-mammal "ages", the Gashatan, Bumbanian, Arshantan, and Irdinmanhan, which together span the interval from late in the late Paleocene to early in the middle Eocene. Comparisons with localities and sections documented since the time of the Central Asiatic Expeditions (CAE) show that the so-called Houldjin gravels of the CAE from this area are mostly Irdin Manha Formation and that the "Irdin Manha beds" of the CAE belong to the Arshanto and/or Nomogen formations. These findings reveal that previous concepts of the Irdin Manha and Arshanto faunas from the Camp Margetts area probably include fossils of different ages, so that the corresponding Asian land-mammal "ages" based on these faunas are problematic and need systematic revision. The Nomogen, Arshanto, and Irdin Manha formations are redefined.Item Propalaeocastor (Rodentia, Mammalia) from the early Oligocene of Burqin Basin, Xinjiang. American Museum novitates ; no. 3461(New York, NY : American Museum of Natural History, 2004) Wu, Wenyu.; Meng, Jin (Paleontologist); Ye, Jie.; Ni, Xijun.A new species of castorids, Propalaeocastor irtyshensis, n.sp., from the Burqin Basin of Xinjiang Uygur Autonomous Region, China, is described. The new species, represented by a right maxilla with well-preserved P4-M3, is the earliest and northernmost occurrence of castorids in China. It is characterized mainly by the cheek tooth crown being higher than that of P. butselensis but lower than that of Steneofiber aff. dehmi (probably a new species of Propalaeocastor), and by lingual confluence of the mesoflexus to the lingual fossette of the premesoflexus. Comparison with known species previously assigned to Steneofiber from Europe and Kazakhstan leads to the conclusion that the early Oligocene forms previously assigned to the genus, such as "S. butselensis" and "S. kazachstanicus", differ significantly from those represented by S. eseri from the late Oligocene and early Miocene of Europe. We consider Propalaeocastor a valid genus, provide an emended diagnosis for it, and discuss its evolutionary trend in relation to Steneofiber. Preliminary analysis of Burqin fauna suggests an age of early early Oligocene. Faunal transformations across the Eocene-Oligocene boundary in the Burqin region are comparable to those of Europe and the Mongolian Plateau and suggest linkage of faunal turnovers and global climate changes.