Table of Content

15 December 2010, Volume 48 Issue 4

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MINCHEN CHOW’S ACADEMIC MARATHON FROM THE BIGHORN BASIN TO THE NANXIONG BASIN

MIAO De-Sui, LI Chuan-Kui, WANG Yuan-Qing

2010, 48(4):  281-284. 

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Russell and Zhai(1987:21) point out that,"Although Eocene and Oligocene localities were known in China south of the Gobi in the 1920's, very little augmentation of the collections occurred until approximately the 1960's, when increased field activity on the part of crews directed by Minchen Chow was responsible for much new material collected and described."Minchen Chow's own report of the late Eocene to early Oligocene mammals from Yunnan and Guangxi provinces began to appear in 1957(Chow,1957). In the following three years, Chow published more than half a dozen papers on Paleogene mammals from Yunnan, Henan, Jiangxi, and Xinjiang. These works set the stage for the discoveries mentioned above by Russell and Zhai. Paradoxically, this sudden surge of interest in Chinese Paleogene mammals was not accidental, given the fact that during the 1950s and early 1960s, the Chinese government promoted geological investigations and Chinese vertebrate paleontologists seized this opportunity to expand their scope of exploration and research. It is, however,a historical accident that Minchen Chow, the principal organizer and a major player in these increased research activities, learned his trade in the Bighorn Basin, Wyoming from Glenn Jepsen,a vertebrate paleontologist at Princeton University. Chow spent the summer of 1950 with Jepsen's Princeton field crew, where he familiarized himself with North American Paleogene mammalian faunas. Before that, Chow had focused on the Pennsylvanian freshwater bivalves of Pennsylvania, as his PhD dissertation at Lehigh University. Thus, the seeds of passion for mammalian paleontology were sowed in remote Wyoming, and the harvest began only a few years later across the Pacific.

WERE IMMIGRANTS A SIGNIFICANT PART OF THE EARLIEST PALEOCENE MAMMALIAN FAUNA OF THE NORTH AMERICAN WESTERN INTERIOR?

William A. CLEMENS

2010, 48(4):  285-307. 

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The roles of immigration and endemic radiation of survivors of the extinctions marking the Cretaceous/Tertiary (K/T) boundary in evolution of the earliest Paleocene (Puercan) mammalian fauna of the North American Western Interior have been debated. Continued field and laboratory research has significantly expanded and refined knowledge of the compositions of North American latest Cretaceous (Lancian North American Land Mammal Age) and Puercan 1 (Pu1) local faunas. It has also revealed limitations in biochronological correlations of these local faunas. In general, Pu1 local faunas of the northern Western Interior reflect the extinction or extirpation of lineages of Lancian marsupials and consist primarily of multituberculate and eutherian mammals. The majority of Pu1 mammals were immigrants, many dispersing into the area soon after the K/T boundary. Testing the hypothesis of Asian origins of the immigrants is hampered by lack of latest Cretaceous or earliest Paleocene mammalian local faunas particularly from high North American paleolatitudes and Pacific coastal areas of Asia. Another working hypothesis, that most, if not all, of the Pu1 immigrant mammals entering the northern Western Interior could have dispersed from other areas of the North American continent has increasing support and has yet to be falsified.

MAMMALIAN FAUNAL SUCCESSION THROUGH THE PALEOCENE−EOCENE THERMAL MAXIMUM (PETM) IN WESTERN NORTH AMERICA

Philip D. GINGERICH 

2010, 48(4):  308-327. 

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The late Professor Minchen Chow started his career in vertebrate paleontology with a team of scholars working to clarify the biostratigraphy and paleogeography of Paleocene–Eocene change in mammalian faunas. This is the time of first appearance of artiodactyls, perissodactyls, and primates (APP taxa) in the fossil record. Recognition of the Paleocene as an epoch separate from the Eocene started to be accepted in 1911 following discovery of a new Clarkforkian latest–Paleocene mammalian fauna at Polecat Bench in western North America. Later the Paleocene–Eocene boundary was shown to include an interval with dwarfed mammalian lineages. A Paleocene–Eocene carbon isotope excursion (CIE) was discovered coincident with both mammalian dwarfing and the first appearance of APP taxa. This enabled global generalization of the CIE, which is linked in turn to the Paleocene–Eocene thermal maximum (PETM). The PETM was a global greenhouse warming event with transient effects on the earth’s climate and biota, but also profound lasting effects on the biota. Much of what we know about mammals in relation to the CIE and PETM we have learned through high-resolution study of the exceptional stratigraphic record flanking Polecat Bench, where Professor Chow worked early in his career and where his ashes now lie.

THE DIATOMYIDAE (MAMMALIA, RODENTIA) AND BILOPHODONTY IN MIDDLE EOCENE ASIAN RODENTS

Mary R. DAWSON, LI Chuan-Kui, QI Tao

2010, 48(4):  328-335. 

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 The Asian endemic rodent family Diatomyidae is known to have inhabited eastern and southern Asia since the Oligocene. Its current distribution is limited to karstic regions of Laos. So far as known these hystricomorphous-sciurognathous rodents have some degree of transverse bilophodonty of the cheek teeth. The earliest recognized diatomyids, which are from the Oligocene of Pakistan, retain some traces of cusps on the cheek teeth, overlying the basically bilophodont tooth structure. By the end of the Oligocene there is some dental diversity within the family. Miocene and later diatomyids are relatively rare in the fossil record. Molecular evidence unites the diatomyids in the Ctenohystrica, an assignment that receives some support from the molar morphology of Eocene ctenodactyloids. Other than this connection, little is clear regarding the origin of the diatomyids. The middle Eocene Asian Hydentomys exhibits a slight degree of bilophodonty, but is otherwise unlike diatomyids. Another taxon of bilophodont rodent, Dolosimus n. gen. from the middle Eocene of Jiangsu Province, has still more precocious development of bilophodonty, especially in the lower molariform teeth. The incomplete record of this new taxon as well as its morphology cannot answer the question of whether this taxon is allied to such later appearing, strongly bilophodont rodents as diatomyids and pedetids, or is an early experiment of this striking morphological development that left no successors.

PSEUDOTRIBOSPHENIC: THE HISTORY OF A CONCEPT

Thomas H. RICH, Patricia VICKERS-RICH

2010, 48(4):  336-347. 

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Palaeontology is for the most part a postdictive science. That is, its central task is for the most part to explain existing data. A rare instance of palaeontology being a predictive science is to be found in the history of the development of the pseudotribosphenic concept. Based on the structure of the lower molars in a single dentary of a pseudotribosphenic mammal, the structure of the then unknown upper molars was hypothesized. The subsequent discovery first of an isolated upper molar regarded as likely to be a pseudotribosphenic mammal and later, a specimen of a pseudotribosphenic mammal with its upper and lower molars in occlusion, rigorously corroborated the original hypothesis. The acceptance of the pseudotribosphenic concept was instrumental in the recognition that the tribosphenic condition, a key innovation in the history of mammals, could well have arisen more than once, despite its complexity. Living languages evolve through time. As the term “pseudotribosphenic” was utilised after being originally coined, its usage by some subsequent workers departed significantly from the original concept. The term has been used both to describe teeth of docodonts which do not occlude in the pseudotribosphenic manner as originally defined as well as teeth that were clearly tribosphenic as that term was originally defined rather than pseudotribosphenic. As a result, its definition as understood by the paleontological community became less precise, and thus the utility of the concept was significantly reduced. Consequently, a return to the original definition would be appropriate.

OLIGOCENE STRATIGRAPHY BASED ON A SEDIMENT-BASALT ASSOCIATION IN CENTRAL MONGOLIA (TAATSIIN GOL AND TAATSIIN TSAGAAN NUUR AREA, VALLEY OF LAKES): REVIEW OF A MONGOLIAN-AUSTRIAN PROJECT

Gudrun DAXNER-HÖCK, Demchig BADAMGARAV, Margarita ERBAJEVA

2010, 48(4):  348-366. 

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The Oligocene sedimentary sequence of the Taatsiin Gol and Taatsiin Tsagaan Nuur area is of unique stratigraphic importance: here, the exposed sediments of the Hsanda Gol and the Loh Formations display multiple fossil horizons and interbedded basalt layers. In the frame of a Mongolian–Austrian project, 289 fossil taxa (11 Gastropoda, 2 Amphibia, 9 Reptilia and 267 Mammalia) were collected from 85 fossil horizons of 33 sections/fossil sites of the study area. The taxa were identified by an international team of specialists. This contribution presents comprehensive mammal lists of all localities. By integrating the new data on large and small mammals, the Mongolian informal biozones A, B, C, C1 were updated. 40Ar/39Ar-datings provide at least two groups of basalt ages, the Early Oligocene basalt I group around 31.5 Ma and the Late Oligocene basalt II group around 28 Ma. They serve as chronological tie points in the Oligocene mammalian stratigraphy. From the Early to the Late Oligocene the mammal associations underwent remarkable changes involving a significant decrease of species numbers in the Late Oligocene. This trend was most striking in creodont, carnivore and ruminant communities.

PALEOGENE AVIFAUNA OF THE HOLARCTIC

Larry D. MARTIN

2010, 48(4):  367-374. 

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China occupies a unique position in studies of Holarctic biogeography by having rich and accessible fossil deposits at relatively high latitudes. It provides a connection between the early Cenozoic deposits of Europe and North America. These faunas contain a diverse avifauna that is only now receiving adequate attention. The Early Eocene was a time of world-wide tropical forests, even at high latitudes (Martin, 1994), and the Green River Lakes in Wyoming preserve the fossil leaves of palm trees. It is no surprise that the avifauna of Messel, Germany shows affinity with the tropical forests of Africa and that of the Green River in Wyoming with Tropical South America. In fact, the signature feature of the Paleogene was a universal distribution of warm moist ecosystems resulting in a reduction of the effectiveness of high latitude barriers to distribution. The Late Eocene−Oligocene drop in global temperatures resulted in increased continental isolation and precipitated the ecological changes that characterize the Neogene and resulted in the modern taxonomic diversity of birds.

PALEOCENE HAPALODECTES (MAMMALIA: MESONYCHIA) FROM SUBENG, NEI MONGOL: FURTHER EVIDENCE OF “EAST OF EDEN” DISPERSAL AT THE PALEOCENE−EOCENE BOUNDARY

K. Christopher BEARD, WANG Yuan-Qing, MENG Jin, NI Xi-Jun, Daniel L. GEBO, LI Chuan-Kui

2010, 48(4):  375-389. 

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A new species of the mesonychian mammal genus Hapalodectes is described from the Gashatan (late Paleocene) site of Subeng in Nei Mongol (Inner Mongolia). This is the first Paleocene record ofHapalodectes from China, and the second Gashatan species of Hapalodectes to be recorded from Asia. Available phylogenetic and biostratigraphic evidence supports an Asian origin for Hapalodectes (and Hapalodectidae). Hapalodectes apparently dispersed across Beringia coincident with PETM warming to colonize North America, thereby conforming to the “East of Eden” biogeographic pattern. Reconstructing the historical biogeography of Hapalodectes is facilitated by its restricted (i.e., non-European) geographic distribution. “East of Eden” dispersal such as that shown by Hapalodectes qualifies as an excellent example of geo-dispersal, whereby a major perturbation of the physical environment allows multiple clades to exhibit similar biogeographic and phylogenetic patterns. Purported examples of intercontinental mammalian dispersal at or near the Paleocene−Eocene boundary that conflict with the “East of Eden” pattern are critically examined and found to be wanting. The “East of Eden” biogeographic pattern adequately explains mammalian faunal turnover and Laurasian mammalian biogeography during the PETM.

NEW RODENTS FROM THE EARLIEST EOCENE OF NEI MONGOL, CHINA

MENG Jin, LI Chuan-Kui

2010, 48(4):  390-401. 

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New rodent material is described from the Bumbanian Gomphos bed in Earlian Basin,Nei Mongol (Inner Mongolia), China. A new genus and species, Yuanomys zhoui, is named. The new species differs from other Early Eocene rodents in having slim and isolated cusps and conules on cheek teeth and transverse paracone and metacone with steep surfaces facing a broad trigon basin. These features of Y. zhoui to some degree resemble those of alagomyids. Constrained magneto- and biostratigraphically, the occurrence of these rodents indicates that the earliest radiation of rodents with modern aspect probably took place during the period of mid-Paleocene to early Eocene.