Takehisa Tsubamoto

QUANTITATIVE ANALYSES OF BIOGEOGRAPHY AND FAUNAL EVOLUTION OF MIDDLE TO LATE EOCENE MAMMALS IN EAST ASIA

Abstract The biogeography and faunal evolution of middle to late Eocene mammals throughout East Asia is assessed. Appearance Event Ordination was used to get a reliable temporal ordination of 92 Paleogene faunas from East Asia. Results from this analysis are generally consistent with the faunal sequence of traditional East Asian Land Mammal “Ages” (EALMAs). Exceptions are that the Arshantan Fauna fell within Irdinmanhan EALMA faunas, and three latest middle to late Eocene faunas from southern East Asia are misaligned due to high degrees of endemism. Comparison of 30 major middle/late Eocene mammalian faunas at the generic level, using Simpsons Faunal Resemblance Index and the ordinal composition of each fauna indicate that: (1) the differentiation in faunal similarity and composition between northern and southern East Asia started near the middle Eocene-late Eocene boundary; (2) this differentiation is reflected by the decline of perissodactyls and radiation of several artiodactyl clades in the later Eocene of southern East Asia; and (3) in southern East Asia, faunal endemism increased in the later Eocene. The latest middle to late Eocene faunas of the southern area do not fit within the EALMA system, which was primarily established with northern faunas, because of their endemism. Mammalian faunal changes actually seem to have begun much earlier in the southern region of East Asia than in the northern part, so the faunal changes toward the end of the Eocene in East Asia were not synchronous. Faunal changes during the Eocene-Oligocene transition in southern East Asia seem not to have been controlled by global climatic changes.

Cranial osteology of a juvenile specimen of Tarbosaurus bataar (Theropoda, Tyrannosauridae) from the Nemegt Formation (Upper Cretaceous) of Bugin Tsav, Mongolia

ABSTRACT A juvenile skull of the tyrannosaurid Tarbosaurus bataar found in the Bugjn Tsav locality in the Mongolian Gobi Desert is described. With a total length of 290 mm, the present specimen represents one of the smallest skulls known for this species. Not surprisingly, it shows various characteristics common to juvenile tyrannosaurids, such as the rostral margin of the maxillary fenestra not reaching that of the external antorbital fenestra and the postorbital lacking the cornual process. The nasal bears a small lacrimal process, which disappears in adults. Lacking some of the morphological characteristics that are adapted for bearing great feeding forces in adult individuals, this juvenile specimen suggests that T. bataar would have changed its dietary niches during ontogeny. The numbers of alveoli in the maxilla (13) and dentary (14 and 15) are the same as those in adults, suggesting that they do not change onto genetically in T. bataar and thus are not consistent with the hypothesis that the numbers of alveoli decreases ontogenetically in tyrannosaurids.

Body mass estimates for Eocene eosimiid and amphipithecid primates using prosimian and anthropoid scaling models

We estimated body masses for middle to late Eocene East Asian eosimiids and amphipithecids from the crown areas of cheek teeth. First, we calculated body mass estimate equations via an extant primate sample of 11 prosimian and 30 anthropoid species, and compared the reliability of the resulting body mass estimate regressions. M1–2 and M1–2 are better body mass estimators, especially for fossils with few samples, because of their low intraspecific variations in dimensions. Moreover, body masses derived from M1–2 tend to indicate lower estimate error than those from other cheek teeth. The relationships between tooth crown areas and body mass differ between prosimians and anthropoids; the estimated body mass from crown area of P4 or any molar will be larger if anthropoids, instead of prosimians, are used as a reference taxon. Second, We applied the regressions to the fossil primates. The estimated body masses in kg are as follows: Eosimias centennicus, 0.16; E. sinensis, 0.14; Eosimiidae indet. from the Pondaung Formation, ≤0.41; Bahinia pondaungensis, 0.57; Myanmarpithecus yarshensis, 1.8; Amphipithecus mogaungensis, 6.8; Pondaungia cotteri, 5.9; Pondaungia savagei, 8.8; Siamopithecus eocaenus, 5.9. Eosimiids fit the prosimian model better than the anthropoid model. Amphipithecids do not fit one model particularly better than the other, as the estimates vary considerably according to the tooth used and the reference taxon. The anthropoid model gives smaller differences between upper- and lower-molar-based body mass estimates, but premolars are relatively much smaller in amphipithecids than in extant prosimians and anthropoids.

Endocranial cast and morphology of the olfactory bulb of Amphipithecus mogaungensis (latest middle Eocene of Myanmar)

A detailed endocranial cast of the olfactory bulb of Amphipithecus mogaungensis, a latest middle Eocene primate from the Pondaung Formation (Myanmar), was studied in comparison with some Paleogene primates, the olfactory bulb of which has been reported. The olfactory bulb of Amphipithecus is located just anterior to the postorbital constriction, that is, within the interorbital septum. It is relatively large and pedunculate, not overlapped by the frontal lobe, and consists of two parallell aligned bodies. The relative volume of the olfactory bulb shows the same pattern as in adapiforms, but the location and bilobed form are more similar to those of omomyoids than of adapiforms.

Reevaluation of some ungulate mammals from the Eocene Pondaung Formation, Myanmar

Abstract We reevaluate some fossil specimens of ungulate mammals from the uppermost middle Eocene Pondaung Formation (central Myanmar), describing some new materials. The taxa studied in this paper are Hsanotherium parvum (Ungulata), Asiohomacodon myanmarensis gen. et sp. nov. (Artiodactyla; Dichobunidae; Homacodontinae), Indomeryx (Artiodactyla; Ruminantia), Indolophus guptai (Perissodactyla; Tapiromorpha; Indolophidae), and Ceratomorpha fam., gen. et sp. indet. (Perissodactyla). (1) The lower molars of Hsanotherium show a similarity to those of Gobiohyus pressidens (Artiodactyla; Helohyidae), and its mesiodistally elongated and trilobed dP4 morphology recalls that of artiodactyls and macroscelideans. However, the unique molar and P4 morphologies of Hsanotherium indicate that Hsanotherium cannot confidently be classified into any present ungulate order, although it can be identified as belonging to the Ungulata because of its large, elongated, and posteriorly projecting hypoconulid on M3. (2) The molar size and morphology of Asiohomacodon recall primitive protoreodontine agriochoerids (Oreodontoidea) such as Protoreodon parvus and derived and agriochoerid-like homacodontine dichobunids such as Pentacemylus, both of which occur in Eocene North America. Asiohomacodon is classified not into the Protoreodontinae but into the Homacodontinae because of the lack of molar metastylid. The lower molar morphology of Asiohomacodon also resembles that of an unusual and agriochoerid-like anthracotheriid, Atopotherium, from Eocene Thailand, although the affinity between these two genera cannot be tested because of the lack of the P4 material of Asiohomacodon. (3) The Pondaung Indomeryx consists of large and small species, I. cotteri (including I. pilgrimi) and I. arenae (including I. minus). Dental morphology in each species of the Pondaung Indomeryx indicates relatively high variation, and the two species are not separable based on their dental morphology. Indomeryx shows many primitive characteristics among ruminants and lacks any critical derived features referable to any ruminant family. (4) Indolophus is referable to primitive tapiromorphs in having a somewhat lophodont dentition and in lacking lingual and buccal cingula and molar metaconule, paraconule, and metastylid. It differs from other tapiromorphs in having a smaller parastyle on the upper dentition and a unique P2–4 morphology with large protocone, high and acute preprotocristid, and no postprotocristid. (5) Although the material of the indeterminate ceratomorph is poorly preserved, its preserved tooth is not identical to any other ceratomorph from the Pondaung Formation, indicating an occurrence of an additional ceratomorph species in the Pondaung fauna.

Proviverrine hyaenodontids (Creodonta: Mammalia) from the Eocene of Myanmar and a phylogenetic analysis of the proviverrines from the Para-Tethys area

SYNOPSIS Recent expeditions in the Pondaung Formation have revealed an assemblage of hyaen‐odontid creodonts from the late middle Eocene of Myanmar. Among the three proviverrines known from the fauna, Kyawdawia lupina gen. et sp. nov. is represented by the most complete dental materials. Kyawdawia is similar to the proviverrines known from the Eocene and middle Miocene of India‐Pakistan and from the late Eocene to middle Miocene of Africa, in that it has a short protocone and strong buccal cingulum on M1–2, a small metaconid on m2–3 and a well‐basined talonid on p4‐m2. In addition, it lacks an anterior accessory cusp on p4 and the distinction between the hypoconulid and entoconid on the lower molars. It is unique among the Afroasian proviverrines in lacking a protocone lobe on P4 and in having a broader paracone relative to the metacone on M1–2. This species is one of the largest proviverrines and was estimated to be the size of a red wolf. The type specimen includes postcranial materials. The well‐developed deltopectoral crest, supracondylar ridge and medial epicondyle of the humerus and the relatively short gracile tibia suggest some digging adaptations, while the two well preserved caudal vertebrae indicate the presence of a long tail. The cladistic analysis of 14 proviverrines from Europe and Afroasia based on dental morphologies supports the monophyly of proviverrines from Africa and South and Southeast Asia. This group must have originated from the European forms by the early Eocene and dispersed into South and Southeast Asia. Kyawdawia is phylogenetically closest to Masrasector from the late Eocene to early Oligocene of Egypt and Oman, and the second closest to Paratritemnodon from the middle Eocene of India‐Pakistan. The other two Pondaung proviverrines, Yarshea cruenta and an indeterminate proviverrine, are also close to these genera.

Hyaenodon chunkhtensis and the hyaenodontid fauna from the upper Eocene Ergilin Dzo Formation of Mongolia

Hyaenodon Laizer and Parieu, 1838 is one of the most speciose genera of the Hyaenodontidae (Mammalia; Creodonta) and is widely distributed in the late middle Eocene to Oligocene of North America (Mellett, 1977; Gunnell, 1998), in the late Eocene to Oligocene of Europe (Lange-Badré, 1979; Schmidt-Kittler, 1987), and in the late middle Eocene to early Miocene of Asia (Russell and Zhai, 1987; Lange-Badré and Dashzeveg, 1989; Huang et al., 2001; Wang et al., 2005). Hyaenodon chunkhtensis Dashzeveg, 1985 is one of the six smallest species of Hyaenodon and is the smallest among the Asian species of Hyaenodon (Lavrov and Emry, 1998). So far, H. chunkhtensis had been reported only from the lower Oligocene Hsanda Gol ‘svita’ at the Shunkht locality of southern Mongolia (Dashzeveg, 1985). The upper Eocene Ergilin Dzo Formation of southeastern Mongolia has been famous for yielding many vertebrate fossils including several species of Hyaenodon (Matthew and Granger, 1923; Belyayeva et al., 1974; Dashzeveg, 1974, 1993; Yanovskaya et al., 1977). The mammals of this formation are the type fauna of the Ergilian (late Eocene) Asian Land Mammal Age (Russell and Zhai, 1987; McKenna and Bell, 1997; Meng and McKenna, 1998). Although in this formation several species of hyaenodontid creodonts have been reported (Matthew and Granger, 1925; Gromova, 1952; Dashzeveg, 1964, 1985; Lange-Badré and Dashzeveg, 1989; Lavrov, 1999), the number of taxa and generic and species names of the hyaenodontids from the formation are confused (Russell and Zhai, 1987; Polly, 1993; Wang et al., 2005; Morlo and Nagel, 2006; Egi et al., 2007). In this short article, we report H. chunkhtensis from the Ergilin Dzo Formation at the Khoer Dzan locality and briefly review the hyaenodontid fauna of the formation to clarify its current status. The specimen described here is a left mandible with p4–m3 discovered by the Hayashibara Museum of Natural Sciences and Mongolian Paleontological Center Joint Paleontological Expedition in 2004 (Tsubamoto, Watabe et al., 2006). The specimen was found by surface prospecting at a lower part of a slope of the locality, so that the precise stratigraphic horizon of the specimen within the formation cannot be determined. This discovery adds one more species to the hyaenodontid fauna of the formation. Institutional Abbreviations—AMNH, American Museum of Natural History, New York, USA; BDMAS, Biological Department of the Mongolian Academy of Sciences, Ulaanbaatar, Mongolia; HMNS, Hayashibara Museum of Natural Sciences, Okayama, Japan; MPC, Mongolian Paleontological Center, Ulaanbaatar, Mongolia; MPC-M, mammalian fossil collections stored in MPC; PIN, Paleontological Institute, Russian Academy of Sciences, Moscow, Russia; PSS and PST, Paleontology and Stratigraphy Section, Geological Institute, Ulaanbaatar, Mongolia; SHG, specimens from the Shand Gol locality of central Mongolia stored in Vienna Museum, Vienna ( Wien), Austria. Anatomical Abbreviations—c, lower canine; M/m, upper/ lower molar; P/p, upper/lower premolar.

A NEW GENUS AND SPECIES OF HYAENODONTID CREODONT FROM THE PONDAUNG FORMATION (EOCENE, MYANMAR)

NAOKO EGI1*, PATRICIA A. HOLROYD2, TAKEHISA TSUBAMOTO1, NOBUO SHIGEHARA1, MASANARU TAKAI1, SOE THURA TUN3, AYE KO AUNG4, and AUNG NAING SOE4, 1Primate Research Institute, Kyoto University, Inuyama, Aichi 484-8506 Japan, egi@anthro.zool.kyotou.ac.jp; 2Museum of Paleontology, University of California, Berkeley, California 94720 U.S.A.; 3Department of Geology, University of Yangon, Yangon, Myanmar; 4Department of Geology, Dagon University, Yangon, Myanmar

New specimens of anthracotheriid artiodactyls from the upper Eocene Ergilin Dzo Formation of Mongolia

Abstract We describe fossil specimens of two taxa of anthracotheriid artiodactyls (Mammalia) discovered in the upper Eocene Ergilin Dzo Formation of southeastern Mongolia and briefly review the late Eocene anthracotheriids of northern East Asia. The specimens described here are: (1) an upper molar, an astragalus, and a calcaneum of a small bunodont anthracotheriid; and (2) upper and lower postcanine dentitions, an astragalus, and a distal tibia of a Bothriodon/Aepinacodon-like selenodont anthracotheriid. This paper provides the first description and figures of the Anthracotheriidae from the formation, which were hitherto poorly understood. The anthracotheriid fauna of the formation currently consists of two species, an indeterminate bunodont anthracotheriid and cf. Bothriodon sp. This is the first discovery of a bunodont anthracotheriid in the late Eocene of the northern part of East Asia. The anthracotheriids are mainly represented by selenodont and bunoselenodont species and are rare faunal elements in the late Eocene of northern East Asia; in contrast, they are mainly represented by bunodont and bunoselenodont species and are predominant faunal elements in the late Eocene of southern East Asia. This implies a paleobiogeographical separation between the northern and the southern parts of East Asia during the late Eocene.

SYSTEMATIC STATUS OF ASIAN “PTERODON” AND EARLY EVOLUTION OF HYAENAELURINE HYAENODONTID CREODONTS

Abstract We establish a new genus of a hyaenaelurine hyaenodontid (Creodonta: Mammalia), Orienspterodon for “Pterodon” dahkoensis, which is known from three late middle Eocene localities in central and southern China and Myanmar. This paper provides a full description of the species and a comment on the early evolution of Hyaenaelurinae. Some features of Orienspterodon (p2–p3 without an anterior accessory cuspulid, lesser reduction of the m3 talonid relative to m1–m2 talonids, double-rooted P3, and better fusion of the paracone and metacone on M1) confirm that O. dahkoensis is distinct from Pterodon. Orienspterodon differs from the other specialized hyaenodontids from the Paleogene of Asia in being a hyaenaelurine, in being unrelated to Hyaenodon, and in having a geographical distribution in the southern part of the continent. Orienspterodon represents the earliest fossil records of Hyaenaelurinae, and some features (small metaconid on m3, basined talonid on all lower molars, a short and more diagonally oriented metastyle, large size, better fused paracone and metacone) indicate an early branching of this genus from the other hyaenaelurines.