New Eocene primate from Myanmar shares dental characters with African Eocene crown anthropoids

Maxilla of Siamopithecus eocaenus (Anthropoidea, Primates) from the Paleogene of Krabi, Thailand, and its taxonomic status

Detailed descriptions of the maxillae of Siamopithecus eocaenus, discovered from the latest Eocene/earliest Oligocene lignite mine in the Krabi basin of Peninsular Thailand, are presented. They include the morphology of P3-M3, the palate, a partial orbital region, and the zygomatic root. The specimen exhibits distinctive dental features including a single-rooted P2 alveolus, a protocone on the P3 and P4, and a true hypocone on the upper molars, indicating its derived anthropoid dentition. Comparative studies and virtual reconstructions of the facial anatomy reveal close affinities with diurnal anthropoids rather than the notharctid strepsirrhines. The reconstructed facial morphology of Siamopithecus displays a short and subvertically oriented face, significant orbital convergence (72.1°), and frontation (81.6°), distinguishing it from both fossil and extant strepsirrhines. Moreover, the presence of a thin bony lamina extending from the distal part of the upper preserved area of the zygomatic suggests partial or complete postorbital closure. Phylogenetic analyses suggest an affiliation with amphipithecids, but recent morphological observations challenge this, leading to the proposal of an elevated family-group ranking, Siamopithecidae. Comparison with the most primitive known Afro-Arabian propliopithecid, the Taqah propliopithecid from Oman, reveals similarities in their molar structure but differences in dental formula (retention of P2) and premolar structure. The abrupt appearance of propliopithecids in the early Oligocene of Afro-Arabia, without a local ancestor, contributes to the debate on whether catarrhine origins were in Asia or Africa. However, alternative views, based on sister-group relationships with oligopithecids, support an African origin of propliopithecids from an undocumented Afro-Arabian region. This research provides new insights into the evolutionary history of early anthropoids, suggesting a complex biogeographical scenario involving both Asian and African lineages.

Early anthropoid primates: New data and new questions

Although the evolutionary history of anthropoid primates (monkeys, apes, and humans) appears relatively well-documented, there is limited data available regarding their origins and early evolution. We review and discuss here the earliest records of anthropoid primates from Asia, Africa, and South America. New fossils provide strong support for the Asian origin of anthropoid primates. However, the earliest recorded anthropoids from Africa and South America are still subject to debate, and the early evolution and dispersal of platyrhines to South America remain unclear. Because of the rarity and incomplete nature of many stem anthropoid taxa, establishing the phylogenetic relationships among the earliest anthropoids remains challenging. Nonetheless, by examining evidence from anthropoids and other mammalian groups, we demonstrate that several dispersal events occurred between South Asia and Afro-Arabia during the middle Eocene to the early Oligocene. It is possible that a microplate situated in the middle of the Neotethys Ocean significantly reduced the distance of overseas dispersal.

Tooth chipping patterns and dental caries suggest a soft fruit diet in early anthropoids

OBJECTIVES

Fossils from the Fayum Depression, Egypt, are crucial for understanding anthropoid evolution due to the abundance of taxa and the time interval they represent (late Eocene to early Oligocene). Dietary and foraging behavioral interpretations suggest fruits were their dominant food source, although hard foods (e.g., seeds and nuts) and leaves could have been important dietary components for particular groups. In this study, we compare dental chipping patterns in five Fayum primate genera with chipping data for extant primates, to assess potential hard object feeding in early anthropoids.

MATERIALS AND METHODS

Original specimens were studied (Aegyptopithecus: n = 100 teeth; Parapithecus: n = 72, Propliopithecus: n = 99, Apidium: n = 82; Catopithecus: n = 68); with the number, severity, and position of chips recorded. Dental caries was also recorded, due to its association with soft fruit consumption in extant primates.

RESULTS

Tooth chipping was low across all five genera studied, with a pooled chipping prevalence of 5% (21/421). When split into the three anthropoid families represented, chipping prevalence ranged from 2.6% (4/154) in Parapithecidae, 6% (12/199) in Propliopithecidae, and 7.4% (5/68) in Oligopithecidae. Three carious lesions were identified in Propliopithecidae.

DISCUSSION

The chipping prevalence is low when compared to extant anthropoids (range from 4% to 40%) and is consistent with a predominantly soft fruit diet, but not with habitual hard food mastication. The presence of caries supports consumption of soft, sugary fruits, at least in Propliopithecidae. Our results add support for low dietary diversity in early anthropoids, with soft fruits as likely dominant food sources.

Total evidence phylogeny of platyrrhine primates and a comparison of undated and tip-dating approaches

There have been multiple published phylogenetic analyses of platyrrhine primates (New World monkeys) using both morphological and molecular data, but relatively few that have integrated both types of data into a total evidence approach. Here, we present phylogenetic analyses of recent and fossil platyrrhines, based on a total evidence data set of 418 morphological characters and 10.2 kilobases of DNA sequence data from 17 nuclear genes taken from previous studies, using undated and tip-dating approaches in a Bayesian framework. We compare the results of these analyses with molecular scaffold analyses using maximum parsimony and Bayesian approaches, and we use a formal information theoretic approach to identify unstable taxa. After a posteriori pruning of unstable taxa, the undated and tip-dating topologies appear congruent with recent molecular analyses and support largely similar relationships, with strong support for Stirtonia as a stem alouattine, Neosaimiri as a stem saimirine, Cebupithecia as a stem pitheciine, and Lagonimico as a stem callitrichid. Both analyses find three Greater Antillean subfossil platyrrhines (Xenothrix, Antillothrix, and Paralouatta) to form a clade that is related to Callicebus, congruent with a single dispersal event by the ancestor of this clade to the Greater Antilles. They also suggest that the fossil Proteropithecia may not be closely related to pitheciines, and that all known platyrrhines older than the Middle Miocene are stem taxa. Notably, the undated analysis found the Early Miocene Panamacebus (currently recognized as the oldest known cebid) to be unstable, and the tip-dating analysis placed it outside crown Platyrrhini. Our tip-dating analysis supports a late Oligocene or earliest Miocene (20.8-27.0 Ma) age for crown Platyrrhini, congruent with recent molecular clock analyses.

Ethics, law, and politics in palaeontological research: The case of Myanmar amber

Fossil material in amber from Myanmar can provide important insights into mid-Cretaceous forest ecosystems. However, Myanmar amber has been receiving increased international attention due to reported links between amber mining and the ongoing humanitarian crisis in northern Myanmar, as well as the legal issues associated with its exportation. Here, we conduct a bibliometric analysis of Myanmar amber publications (1990-2021) and demonstrate how research interest in Myanmar amber is explicitly linked to major political, legal, and economic changes. An analysis of the authorship networks for publications on amber inclusions reveals how current research practices have excluded Myanmar researchers from the field. In addition, the international trade of Myanmar amber with fossil inclusions falls into a legal 'grey-zone' which continues to be exploited. This case study vividly demonstrates that systemic changes, alongside an increased awareness of inequitable research practices amongst the broader scientific and allied communities, are urgently needed to curb illegal practices in palaeontology.

Rodent faunas, their paleogeographic pattern, and responses to climate changes from the early Eocene to the early Oligocene in Asia

Rodents are an important component in Paleogene terrestrial ecosystems. Their evolution and faunal turnover have likely been influenced and triggered by global climate change. Here, we compiled rodent faunas from the early Eocene to the early Oligocene in Asia to discuss rodent faunal turnover and its correlation with paleogeographic and paleoclimate changes. Successive rodent faunas from the early Eocene to the early Oligocene are recorded in East Asia, and rodent faunal turnover is obviously affected by paleoclimatic changes. During the Ulangochuian (after the middle Eocene climatic optimum), when temperatures declined slowly, the East Asian rodent fauna showed a clear decline in generic diversity and a transformation from ctenodactyloid-dominant to cricetid–dipodid-dominant faunas. During the Eocene–Oligocene transition (EOT) and global cooling, the East Asian rodent fauna exhibited a considerably high generic diversity of cricetids, dipodids, and ctenodactylids. The low temperatures during the Ulangochuian and Ergilian in East Asia served as a habituation ground for the cricetids and dipodids, which became preadapted for the EOT, successfully helping rodents become dominant faunas after EOT. The rodent faunas in South Asia formed a relatively unique group in much of the Eocene and early Oligocene; sometimes, they were closer to European or African than to Asian rodents. The greatly different paleoenvironment probably caused striking differences between the rodent faunas in South Asia and East Asia.

Extant species fail to estimate ancestral geographical ranges at older nodes in primate phylogeny

A clade's evolutionary history is shaped, in part, by geographical range expansion, sweepstakes dispersal and local extinction. A rigorous understanding of historical biogeography may therefore yield insights into macroevolutionary dynamics such as adaptive radiation. Modern historical biogeographic analyses typically fit statistical models to molecular phylogenies, but it remains unclear whether extant species provide sufficient signal or if well-sampled phylogenies of extinct and extant taxa are necessary to produce meaningful estimates of past ranges. We investigated the historical biogeography of Primates and their euarchontan relatives using a novel meta-analytical phylogeny of over 900 extant (n= 419) and extinct (n = 483) species spanning their entire evolutionary history. Ancestral range estimates for young nodes were largely congruent with those derived from molecular phylogeny. However, node age exerts a significant effect on ancestral range estimate congruence, and the probability of congruent inference dropped below 0.5 for nodes older than the late Eocene, corresponding to the origins of higher-level clades. Discordance was not observed in analyses of extinct taxa alone. Fossils are essential for robust ancestral range inference and biogeographic analyses of extant clades originating in the deep past should be viewed with scepticism without them.

Amphipithecine primates are stem anthropoids: cranial and postcranial evidence

Since their discovery in 1927, the phylogenetic status of the Myanmar amphipithecines has been highly debated. These fossil primates are recognized either as anthropoids or as adapiform strepsirrhines. This uncertainty was largely the consequence of a limited fossil record consisting mostly of jaw fragments but lacking the critical cranial elements that might resolve this debate. We report here cranial remains associated with an ulna from a single individual pertaining to the amphipithecine Ganlea megacanina. In addition to anthropoid-like dentognathic characters, Ganlea displays several ulna and skull features that testify to its anthropoid affinities (e.g. short subvertically oriented lacrimal duct, lacrimal foramen and bone inside the orbit, maxillary contribution to the lower orbital rim, fused metopic suture). By contrast to crown anthropoids, however, Ganlea lacks postorbital closure, confirming that postorbital closure appeared later than many anthropoid dentognathic characters and evolved convergently in extant tarsiers and anthropoids. Thus, amphipithecines must now be recognized as stem anthropoids offering a unique window on the early evolution of cranial and skeletal features in anthropoids, and reinforcing the hypothesis of an origin and early diversification of anthropoids in Asia.