Table of Content

15 March 2011, Volume 49 Issue 1

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ASIAN EARLY PALEOGENE CHRONOLOGY AND MAMMALIAN FAUNAL TURNOVER EVENTS

TING Su-Yin, TONG Yong-Sheng, William C. CLYDE, Paul L. KOCH, MENGJin, WANG Yuan-Qing, Gabriel J. BOWEN, LI Qian, Kathryn E. SNELL

2011, 49(1):  1-28. 

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Biostratigraphic, chemostratigraphic, and magnetostratigraphic studies of the Paleocene and early Eocene sediments in the Nanxiong Basin of Guangdong, Chijiang Basin of Jiangxi, Qianshan Basin of Anhui, Hengyang Basin of Hunan, and Erlian Basin of Nei Mongol, China, provide the first well-resolved geochronological constraints on stratigraphic framework for the early Paleogene of Asia. Asian Paleocene and early Eocene strata are subdivided into four biochronological units (Land Mammal Ages). From oldest to youngest, they are the Shanghuan, the Nongshanian, the Gashatan, and the Bumbanian Asian Land Mammal Ages (ALMA). Paleomagnetic data from the Nanxiong Basin indicate that the base of the Shanghuan lies about 2/3 the way up Chron C29r. Nanxiong data and recent paleomagnetic and isotopic results from the Chijiang Basin show that the Shanghuan-Nongshanian ALMA boundary lies between the upper part of Chron C27n and the lower part of Chron C26r, close to the Chron C27n-C26r reversal. This record favors a correlation of Shanghuan-Nongshanian ALMA boundary to the Torrejonian-Tiffanian North American Land Mammal Age (NALMA) boundary and to the Danian-Selandian stage boundary in the marine record. The paleomagnetic and isotopic data from the Erlian Basin show that typical Gashatan faunas persist into Chron C24r and may range into Chron C25r and possibly C26n, and the records from the Nanxiong Basin indicate that both Nongshan and Guchengcun formations may correlate to the upper part of Chron C26r. These results would imply that the Nongshanian-Gashatan ALMA boundary may correlate within the Tiffanian NALMA. The paleomagnetic and isotopic evidence from the Hengyang Basin indicates that the transient carbon isotope excursion that marks the Paleocene-Eocene boundary is present between the Limuping and Lingcha formations, and the boundary is placed at the uppermost reversed polarity interval correlated to Chron C24r and to the Thanetian-Ypresian stage boundary in the marine record. The Bumbanian Lingcha fauna seems to correlate with the Wasatchian-0 faunal zone of North America to within ~104 yr. Both Shanghuan and Nongshanian faunas are mainly composed of Asian endemic taxa. The coincidence of faunal turnover at the Shanghuan-Nongshanian boundary with the Torrejonian-Tiffanian boundary and Danian-Selandian stage boundary in far separated ecosystems may indicate independent ecologic and/or evolutionary response to climatic changes. The Gashatan fauna shows less endemism and has taxa shared with those of the Clarkforkian NALMA in North America at the generic level. The Bumbanian fauna is cosmopolitan. A sudden appearance of modern mammalian orders at the Gashatan-Bumbanian boundary is the same pattern as observed in North America and Europe, indicating the faunal turnover is related to the transient global warming event at the Paleocene-Eocene boundary known as the Paleocene-Eocene Thermal Maximum (PETM).

An updated mammalian biochronology and biogeography for the Early Paleogene of Asia

Pieter MISSIAEN

2011, 49(1):  29-52. 

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Recent research has greatly increased the information available on Asian Paleocene and early Eocene mammal faunas, creating the need to update the existing Asian biochronological and biogeographical framework. Based on a quantitative and qualitative analysis, biochronological boundaries are refined to correspond to major faunal turnovers, and an improved age correlation and biogeography of the Paleocene and early Eocene Asian Land Mammal Ages (ALMAs) is proposed. The poorly known Shanghuan ALMA is characterised as an assemblage dominated by primitive gliriforms and pantodonts. The following Nongshanian ALMA shows an endemic diversification of Asian mammals. Gliriforms radiated, with the appearance of new basal gliriforms and the first appearance of true Glires. The Shanghuan/Nongshanian boundary has been correlated to the Torrejonian/Tiffanian boundary in North America, and it is suggested here that the faunal turnover was possibly triggered by the start of a period of global cooling. The following Gashatan ALMA witnesses a further diversification and an abrupt reduction of the endemism of Asian mammals. Multituberculates, nyctitheriids, cimolestids and carpolestids appeared in the Gashatan faunas and represent North American immigrants. Conversely, a first wave of Asian mammals consisting of arctostylopids and prodinoceratids invaded North America at the start of Tiffanian-5a, and a second wave consisting of rodents, tillodonts and coryphodontids arrived in North America at the beginning of the Clarkforkian. The start of the Gashatan is therefore correlated with the start of North American Tiffanian-5a. The start of the Bumbanian ALMA is marked by the first appearance of artiodactyls, perissodactyls and true primates, similar to their appearance in North America and Europe at the start of the Eocene, and is correlated to the Paleocene-Eocene boundary. Contrasting with dispersal at the start of the Gashatan, dispersal during the Bumbanian seems to have been possible during a more extended period, and was also possible directly between Asia and Europe.

EOCENE MAMMALS FROM THE AKASAKI AND NAKAKOSHIKI FORMATIONS, WESTERN KYUSHU, JAPAN: PRELIMINARY WORK AND CORRELATION WITH ASIAN LANDMAMMAL AGES

MIYATA Kazunori, TOMIDA Yukimitsu, K. Christopher BEARD, Gregg F. GUNNELL, UGAI Hiroaki, HIROSE Koji

2011, 49(1):  53-68. 

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The earliest known Paleogene mammals from Japan are reported from the Eocene Akasaki Formation, Amakusa area, Kumamoto Prefecture and from the stratigraphically equivalent Nakakoshiki Formation, Koshiki Islands, KagoshimaPrefecture, western Kyushu. Preliminary work has revealed a high diversity of mammals from these formations, including at least 18 different species from nine orders. The Akasaki fauna is represented by three trogosine tillodonts, two coryphodontid pantodonts, an isectolophid perissodactyl, two dichobunoid artiodactyls, a hyopsodontid condylarth, a sivaladapid primate, an unidentified insectivoran, and two possible ctenodactyloid rodents. The mammal fauna from the Nakakoshiki Formation includes a coryphodontid pantodont, two small brontotheriid perissodactyls, a hypsodont hyopsodontid condylarth, two rodents, and a miacid carnivoran. These Japanese mammal assemblages are from near the Early/Middle Eocene boundary, which is previously poorly known in Asia. Given the occurrences of trogosine tillodonts and brontotheriid perissodactyls, the Akasaki and Nakakoshiki faunas are younger than Bumbanian faunas and are most likely correlated with Arshantan faunas on the Asian mainland. The Japanese faunas contain several new taxa unknown from the Asian mainland, and there are unique faunal combinations in the mammal assemblages.

ACRODONT IGUANIANS (SQUAMATA) FROM THE MIDDLE EOCENE OF THE HUADIAN BASIN OF JILIN PROVINCE,CHINA, WITH A CRITIQUE OF THE TAXON “TINOSAURUS”

Krister T. SMITH, Stephan SCHAAL, SUN Wei, LI Chun-Tian

2011, 49(1):  69-84. 

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Two acrodont iguanians from the middle Eocene Huadian Formation, Jilin Province, China, highlight the diversity of Acrodonta early in the Tertiary. The first is characterized by a high number (six) of anterior pleurodont tooth loci and by unicuspid, labiolingually compressed cheek teeth. These teeth, however, show no special similarity to those of major acrodontan clades in which the accessory cusps are absent (e.g., Hydrosaurus, Agaminae). Its relationships are poorly constrained. The dentition of the second taxon is similar to that of a number of living tricuspid agamids (viz., Leiolepis and Draconinae) and species of the fossil taxon Tinosaurus; one osteological feature suggests it may be related to a clade including Agaminae, Hydrosaurinae, Draconinae and Amphibolurinae, but more numerous and complete specimens are required before conclusions are drawn. A comparative examination of living agamids demonstrates that tricuspid teeth similar to those of Tinosaurus spp.are probably characteristic of some 200 living species in Leiolepis and Draconinae.Tinosaurus is inadequately diagnosed with respect to these clades. Because Acrodonta is thought to have been diversifying in the early Cenozoic, fossils from eastern Asiahave great potential to elucidate the evolutionary history of the clade, particularly in combination with molecular-genetic methods. However, the multiplication of new taxon names based only on jaw fragments brings us no closer to this goal.Considerable effort must first be dedicated to the collection and study of modern comparative skeletal material.

A new anthracotheriid artiodactyl from the Eocene Pondaung Formation of Myanmar

TSUBAMOTO Takehisa, ZIN-MAUNG-MAUNG-THEIN, EGI Naoko, NISHIMURATakeshi, THAUNG-HTIKE, TAKAI Masanaru

2011, 49(1):  85-113. 

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We describe a new bunodont anthracothere (Mammalia; Artiodactyla),Myaingtherium kenyapotamoides gen. et sp. nov., discovered from the upper middle Eocene Pondaung Formation of Myanmar. The specimens consist of upper and lower dentitions with fragmentary jaws. Myaingtherium is one of the basal anthracotheres and is comparable in size and overall morphology to a small-sized Pondaung anthracothere,Anthracokeryx tenuis. However, Myaingtherium is more similar in dental morphology to Anthracotherium and Anthracohyus rather than to Anthracokeryx in having more bunodont dentition. Myaingtherium is characterized particularly by having a very reduced molar paraconule among bunodont anthracotheres. Some dental characteristics of Myaingtherium, such as a reduced molar paraconule with bunodont dentition and a median accessory cusplet on the lower molars, are reminiscent of those of the Kenyapotaminae (most primitive fossil hippopotamuses) and hippo-like anthracotheriidKulutherium from the Miocene of Africa, implying a possibility that Myaingtheriummight be phyletically related to the Kenyapotaminae. Although more evidences are necessary to test the phyletic relationships of Myaingtherium, this discovery reinforces that the Pondaung anthracotheres are an important fauna for testing and understanding the phyletic relationships and early evolution of the hippo-anthracothere clade.

A NEW FOSSIL SITE WITH A RE-WORKED PALEOGENE ASSEMBLAGE AT BAOGEDA ULA, CENTRAL NEI MONGOL

WANG Xiao-Ming, LI Ping

2011, 49(1):  114-122. 

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We report a small Paleogene fossil assemblage in a predominantly Neogene basin in the Baogeda Ula area. A small pocket of fluvial sediments rests unconformably above fine-grained red beds. Fragmentary dental and postcranial materials are recovered from the fluvial beds. Many of the fossils show signs of having been reworked. The limited collection contains Breviodon minutus, Rhinocerotidae gen. et sp. indet., Brontotheriidae gen. et sp. indet., and others. This assemblage has a Paleogene characteristic, but the age of the fossil-producing sediments is uncertain. Although the possibility exists that this is an unaltered Paleogene deposit, we suspect the Paleogene fossils were reworked into the Neogene Baogeda Ula Formation.

EARLY EOCENE PERISSODACTYLS (MAMMALIA) FROM THE UPPER NOMOGEN FORMATION OF THE ERLIANBASIN, NEI MONGOL, CHINA

WANG Yuan-Qing, MENG Jin,  JIN Xun, K. Christopher BEARD, BAI Bin, LI Ping, NI Xi-Jun, LI Qian, Daniel L. GEBO

2011, 49(1):  123-140. 

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Two species of perissodactyls from the upper part of the Nomogen Formation (Bumbanian, Early Eocene) are described: the lophialetid tapiroidMinchenoletes erlianensis gen. et sp. nov., and the hyracodontid rhinocerotoidPataecops parvus. M. erlianensis differs from the known lophialetids in having smaller size, lower crowned cheek teeth, less developed lophs, smaller length/width ratio in M1–2, and proportionally longer M3. Both taxa extend the fossil records of the Lophialetidae and the Rhinocerotoidea to the earliest Eocene. Recent stratigraphic data shows that Minchenoletes is only found from the upper part of the Nomogen Formation (Bumbanian), while Schlosseria and Lophialetes occurred respectively in the Arshanto and the Irdin Manha formations, enhancing their significance in biostratigraphic correlations and understanding of early evolution of perissodactyls. Based on the new stratigraphic data and review of the fieldnote of the CAE we consider that the Mongolian specimens of Pataecops parvus probably came from a lower stratigraphic level than most taxa of the Kholobolchi fauna, possibly correlative to the Bumbanian age.