Masanaru Takai

New fossil materials of the earliest new world monkey, Branisella boliviana, and the problem of platyrrhine origins.

Branisella boliviana, from the Late Oligocene of Salla, Bolivia, is the oldest fossil platyrrhine monkey discovered. To date, several fossil specimens of Branisella have been obtained, but most of them are fragmentary dentitions, so the animals craniodental morphology is still obscure. During the 1996 field season a pair of upper and lower jaw fragments and another nearly complete mandible were recovered. These new fossil materials reveal the following morphological features in Branisella: 1) P(2) is much smaller than P(3,4), whereas P(2) is relatively small but probably sexually dimorphic; 2) the zygomatic arch protrudes smoothly posterolaterally from the maxillary bone, as in extant Callicebus; 3) the mandibular arcade is nearly V-shaped and the symphysial angle, which is formed by the horizontal plane and the anterior face of mandibular symphysis, is about 40 degrees, i.e., it neither leans as far anteriorly as in callitrichines nor does it stand as vertically as Cebus; 4) upper and lower molars wore down rapidly in life, suggesting a herbivorous diet and the possibility of terrestriality; and 5) dental eruptive sequence is the same as in extant Aotus. As a whole, the dentition of Branisella is very similar to that of Proteopithecus from the Late Eocene of Fayum, Egypt, except in the lower canine morphology, suggesting a close phyletic relationship between them. The origin and early diversification of platyrrhine monkeys might have occurred on the African continent before crossing the Atlantic Ocean.

Anthropoid origins : a phylogenetic analysis

Living Anthropoidea—the group that includes monkeys, apes, and humans—has long been recognized as a monophyletic group among primates diagnosed by a suite of features of the skull, dentition, and postcranium. Likewise it is agreed that there are two monophyletic groups of living anthropoids—the Central and South American Platyrrhini (New World monkeys) and African and Eurasian Catarrhini (Old World monkeys, “apes,” and humans). As well, most paleontologists and neontologists agree that Tarsius is the closest living relative of anthropoids and that strepsirrhines, lemurs and lorises, are more distantly related (but see Eizirik et al., this volume for a different view). Paleontologists also generally accept the following “facts”: The oldest Tarsius relatives occur in the Asian middle Eocene. The oldest undisputed fossil record of anthropoids is from the late Eocene localities in Afro-Arabia. Platyrrhines first appear in the late Oligocene in South America and the catarrhine record is acknowledged by all to include Propliopithecidae from the early Oligocene of Egypt and Oman.

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.

Dental variability inSaimiri and the taxonomic status ofNeosaimiri fieldsi, an early squirrel monkey from La Venta, Colombia

Neosaimiri fieldsi, from the South American middle Miocene locality of La Venta, is represented by a relatively complete mandible and dentition that strongly resembles that of extantSaimiri. Comparison with a large sample of mandibles ofSaimiri indicates that this specimen cannot be distinguished from modern populations on the basis of any reportedly diagnostic feature, such as cingulid development, molar length ratio, trigonic/talonid ratio, or mandibular depth. The fossil is best considered an extinct species of the modern genusSaimiri until further material indicates otherwise.

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.

The Pondaung Primates, Enigmatic “Possible Anthropoids” from the Latest Middle Eocene, Central Myanmar

The first mammal fossils were reported from the Pondaung area, Central Myanmar (Burma), at the beginning of the 20th century (Pilgrim and Cotter, 1916). The fossil specimens included not only large mammals, such as anthracotheres, amynodontids, and brontotheres ( = titanotheres), but also a primate, Pondaungia cotteri which was collected in 1914 and described by Dr G. E. Pilgrim in 1927. Following this discovery of many fossil specimens, Dr Barnum Brown of the American Museum of Natural History visited Burma to collect vertebrate fossils in 1923. Although Brown’s collection was not studied for many years after his return to the United States, Colbert 1937, 1938) described several mammal fossils from it, including a new primate, Amphipithecus mogaungensis.

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.

Ecogeographical and Phylogenetic Effects on Craniofacial Variation in Macaques

The widespread and complex ecogeographical diversity of macaques may have caused adaptive morphological convergence among four phylogenetic subgroups, making their phylogenetic relationships unclear. We used geometric morphometrics and multivariate analyses to test the null hypothesis that craniofacial morphology does not vary with ecogeographical and phylogenetic factors. As predicted by Bergmanns rule, size was larger for the fascicularis and sinica groups in colder environments. No clear size cline was observed in the silenus and sylvanus groups. An allometric pattern was observed across macaques, indicating that as size increases, rounded faces become more elongated. However, the elevation was differentiated within each of the former two groups and between the silenus and sylvanus groups, and the slope decreased in each of the two northern species of the fascicularis group. All allometric changes resulted in the similar situation of the face being more rounded in animals inhabiting colder zones and/or in animals having a larger body size than that predicted from the overarching allometric pattern. For non-allometric components, variations in prognathism were significantly correlated with dietary differences; variations in localized shape components in zygomatics and muzzles were significantly correlated with phylogenetic differences among the subgroups. The common allometric pattern was probably influenced directly or indirectly by climate-related factors, which are pressures favoring a more rounded face in colder environments and/or a more elongated face in warmer environments. Allometric dissociation could have occurred several times in Macaca even within a subgroup because of their wide latitudinal distributions, critically impairing the taxonomic utility of craniofacial elongation.