Naoko Egi

Body Mass Estimates in Extinct Mammals from Limb Bone Dimensions: the Case of North American Hyaenodontids

The body mass estimation of several limb bone dimensions (shaft cross-sectional properties, articular sizes, and bone lengths) were examined using bivariate linear regression analyses. The sample included taxonomically and behaviourally diverse small to medium-sized Recent carnivorans and carnivorous marsupials. All examined limb bone dimensions indicated low errors (percentage standard error of estimate, 8–13) for the body mass estimations. Among them, humeral and femoral shaft properties correlated best with body weight, while limb bone lengths gave larger errors. Both humeral and femoral head dimensions have relatively large individual variations, and distal humeral articular dimensions seem to be influenced more by phylogenetic differences. The regressions based on each locomotor group gave slightly lower errors than those based on the total pooled sample. The results were then applied to hyaenodontid creodonts from the Eocene–Oligocene of North America. The estimated body masses (kg) are: Arfia, 5.4–9.5; Prototomus, <6.0; Pyrocyon, 2.6; Sinopa, 1.3–1.4; Tritemnodon, 7.6–13; Prolimnocyon, 1.6; Thinocyon, 0.7–2.5; Machaeroides, 12; Limnocyon, 7.8– 16; Hyaenodon, 9.1–43. The various limb bone dimensions give different body mass values, but the variation in estimates is smaller compared to those derived from dental or cranial measurements.

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.

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.

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

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.

A revision of Tetraconodon (Mammalia, Artiodactyla, Suidae) from the Miocene of Myanmar and description of a new species

ABSTRACT We describe five new dentognathic specimens of Tetraconodon, a genus of Miocene tetraconodontine suid (Mammalia, Artiodactyla), discovered in Myanmar (= Burma). In Myanmar, we recognized three distinct species of Tetraconodon (T. minor, T. intermedius and T. malensis sp. nov.) and one specifically undetermined specimen, which is here named Tetraconodon sp. cf. T. intermedius. The new species, T. malensis, has characteristics of Tetraconodon, such as extremely enlarged P4 and simple and relatively small M3. It is distinct from the other Tetraconodon species in being much smaller, suggesting that it is the most primitive known Tetraconodon species. The dental size and characteristics of T. malensis suggest that Tetraconodon was derived during the late middle Miocene from the early middle Miocene Conohyus sindiensis, which was discovered in the Siwalik Group of Indo-Pakistan and Nepal and has also been found in the middle Miocene deposits of Thailand, or a close relative. The discovery of the most primitive form in Myanmar suggests that Tetraconodon may have originated in Myanmar.

New Amphicyonid (Mammalia: Carnivora) from the Upper Eocene Ergilin Dzo Formation, Mongolia

Abstract. A mammal tooth discovered from the upper Eocene Ergilin Dzo Formation of southeastern Mongolia is identified as an upper second molar of a small amphicyonid (Mammalia: Carnivora). It is similar to Cynodictis, which is a primitive amphicyonid from the late Eocene to early Oligocene of Europe, in overall size, relative size of the trigon cusps, and smooth lingual cingulum. However, it differs from Cynodictis and other amphicyonids in having an extremely thick lingual cingulum that bulges posterolingually and a parastyle that positions anterior to the paracone, indicating that it belongs to a new genus of the family. Reappraisals of previously reported “Cynodictis” materials from the Paleogene of Asia imply that none of them belong to the Amphicyonidae, and only the present material confirms the existence of an amphicyonid in the Eocene of northern East Asia. This opens questions on the previously proposed existence of Cynodictis and migration of amphicyonids in the Paleogene of Asia.