Xijun Ni

A euprimate skull from the early Eocene of China

The debut of undoubted euprimates (primates of modern aspect) was in the early Eocene, about 55 Myr ago. Since their first appearance, the earliest euprimates can be distinguished as Cantius, Donrussellia and Teilhardina. Nonetheless, the earliest euprimates are primarily known from isolated teeth or fragmentary jaws. Here we describe a partially preserved euprimate skull with nearly complete upper and lower dentition, which represents a new species of Teilhardina and constitutes the first discovery of the genus in Asia. The new species is from the upper section of Lingcha Formation, Hunan Province, China, with an estimated age of 54.97 Myr ago. Morphology and phylogeny analyses reveal that the new species is the most primitive species of Teilhardina, positioned near the root of euprimate radiation. This discovery of the earliest euprimate skull known to date casts new light on the debate concerning the adaptive origin of euprimates, and suggests that the last common ancestor of euprimates was probably a small, diurnal, visually oriented predator.

A new tarkadectine primate from the Eocene of Inner Mongolia, China: phylogenetic and biogeographic implications

Tarka and Tarkadectes are Middle Eocene mammals known only from the Rocky Mountains region of North America. Previous work has suggested that they are members of the Plagiomenidae, an extinct family often included in the order Dermoptera. Here we describe a new primate, Tarkops mckennai gen. et sp. nov., from the early Middle Eocene Irdinmanha Formation of Inner Mongolia, China. The new taxon is particularly similar to Tarka and Tarkadectes, but it also displays many features observed in omomyids. A phylogenetic analysis based on a data matrix including 59 taxa and 444 dental characters suggests that Tarkops, Tarka and Tarkadectes form a monophyletic group—the Tarkadectinae—that is nested within the omomyid clade. Within Omomyidae, tarkadectines appear to be closely related to Macrotarsius. Dermoptera, including extant and extinct flying lemurs and plagiomenids, is recognized as a clade nesting within the polyphyletic group of plesiadapiforms, therefore supporting the previous suggestion that the relationship between dermopterans and primates is as close as that between plesiadapiforms and primates. The distribution of tarkadectine primates on both sides of the Pacific Ocean basin suggests that palaeoenvironmental conditions appropriate to sustain primates occurred across a vast expanse of Asia and North America during the Middle Eocene.

Synchronous turnover of flora, fauna, and climate at the Eocene–Oligocene Boundary in Asia

The Eocene–Oligocene Boundary (~34 million years ago) marks one of the largest extinctions of marine invertebrates in the world oceans and of mammalian fauna in Europe and Asia in the Cenozoic era. A shift to a cooler climate across this boundary has been suggested as the cause of this extinction in the marine environment, but there is no manifold evidence for a synchronous turnover of flora, fauna and climate at the Eocene–Oligocene Boundary in a single terrestrial site in Asia to support this hypothesis. Here we report new data of magnetostratigraphy, pollen and climatic proxies in the Asian interior across the Eocene–Oligocene Boundary; our results show that climate change forced a turnover of flora and fauna, suggesting there was a change from large-size perissodactyl-dominant fauna in forests under a warm-temperate climate to small rodent/lagomorph-dominant fauna in forest-steppe in a dry-temperate climate across the Eocene–Oligocene Boundary. These data provide a new terrestrial record for this significant Cenozoic environmental event.

Comparative study of notoungulate (Placentalia, Mammalia) bony labyrinths and new phylogenetically informative inner ear characters

The phylogenetic relationships of notoungulates, an extinct group of predominantly South American herbivores, remain poorly resolved with respect to both other placental mammals and among one another. Most previous phylogenetic analyses of notoungulates have not included characters of the internal cranium, not least because few such features, including the bony labyrinth, have been described for members of the group. Here we describe the inner ears of the notoungulates Altitypotherium chucalensis (Mesotheriidae), Pachyrukhos moyani (Hegetotheriidae) and Cochilius sp. (Interatheriidae) based on reconstructions of bony labyrinths obtained from computed tomography imagery. Comparisons of the bony labyrinths of these taxa with the basally diverging notoungulate Notostylops murinus (Notostylopidae), an isolated petrosal from Itaboraí, Brazil, referred to Notoungulata, and six therian outgroups, yielded an inner ear character matrix of 25 potentially phylogenetically informative characters, 14 of them novel to this study. Two equivocally optimized character states potentially support a pairing of Mesotheriidae and Hegetotheriidae, whereas four others may be diagnostic of Notoungulata. Three additional characters are potentially informative for diagnosing more inclusive clades: one for crown Placentalia; another for a clade containing Kulbeckia, Zalambdalestes, and Placentalia; and a third for Eutheria (crown Placentalia plus stem taxa). Several other characters are apomorphic for at least one notoungulate in our study and are of potential interest for broader taxonomic sampling within Notoungulata to clarify currently enigmatic interrelationships. Measures of the semicircular canals were used to infer agility (e.g. capable of quick movements vs. lethargic movements) of these taxa. Agility scores calculated from these data generally corroborate interpretations based on postcranial remains of these or closely related species. We provide estimates of the low‐frequency hearing limits in notoungulates based on the ratio of radii of the apical and basal turns of the cochlea. These limits range from 15 Hz in Notostylops to 149 Hz in Pachyrukhos, values comparable to the Asian elephant (Elephas maximus) and the California sea lion (Zalophus californianus) when hearing in air, respectively.

Discovery of the First Early Cenozoic Euprimate (Mammalia) from Inner Mongolia

Abstract Although it is widely thought that euprimates originated in Asia, the fossil record of early euprimates remains sparse there. We describe herein a new omomyid euprimate, Baataromomys ulaanus, n. gen. et sp., based on an isolated right lower m2 from Bumbanian strata at Wulanboerhe in the Erlian Basin of Inner Mongolia, China. In terms of the size and proportions of m2, Baataromomys ulaanus is intermediate between Eurasian and North American species that are usually assigned to Teilhardina. Morphologically, m2 of Baataromomys differs from that of Teilhardina and North American small-bodied omomyids (including Anemorhysis, Tetonoides, Trogolemur, and Sphacorhysis) in having a smaller paraconid that is less fully connate with the metaconid, a lower entoconid, a weaker crest connecting the metaconid with the entoconid, and a weaker buccal cingulid. The new taxon is much smaller and lower crowned than Steinius, a genus commonly regarded as a basal omomyid. Despite the substantial difference in size, the m2s of Baataromomys and Steinius share some important features, including a very broad talonid basin and a relatively low hypoconid and cristid obliqua. Given its early occurrence and primitive anatomy, Baataromomys may eventually help to clarify the phylogenetic relationships among basal omomyids, but more complete specimens will be required to test this possibility. Baataromomys brandti from the basal Wasatchian zone Wa-0 in the northern Bighorn Basin, Wyoming, was previously allocated to Teilhardina. However, several dental features shared by B. brandti and B. ulaanus suggest that they are closely related. The co-occurrence of Baataromomys in Asia and North America indicates that small-bodied euprimates were able to dispersal across the Beringian region near the Paleocene–Eocene boundary.

New primate hind limb elements from the middle Eocene of China

The continued washing, sorting, and identification of middle Eocene ( approximately 45Mya) primates from the Shanghuang fissure-fillings (Jiangsu Province, China) have produced additional hind limb elements. All are isolated elements. The strepsirhine hind limb elements include a first metatarsal and a talus, which are appropriate in size and morphology to pertain to Adapoides troglodytes. Adapoides is interpreted as a quadrupedal-climbing (nonleaping) primate with similarities to living lorises and the fossil primate Adapis. The haplorhine hind limb elements are estimated to span a range of adult body sizes from tiny (17g) to small (200g). Included among the new sample of haplorhine hind limb specimens is the smallest primate talus reported thus far. These new postcranial specimens expand our understanding of early haplorhine hind limb anatomy and demonstrate additional similarities between Shanghuang eosimiids and other anthropoids.

New Stratigraphic Data from the Erlian Basin: Implications for the Division, Correlation, and Definition of Paleogene Lithological Units In Nei Mongol (Inner Mongolia)

Abstract Newly measured stratigraphic sections are reported for Paleogene rocks in the Nuhetingboerhe-Huheboerhe (Camp Margetts) area of Nei Mongol (Inner Mongolia), China. The composite sequence in this region is 82.4 m thick, encompassing three lithological units separated by important depositional hiatuses. In stratigraphic order, these rock units correspond to the Nomogen, Arshanto and Irdin Manha formations. The sequence contains faunas from four Asian land-mammal “ages”, the Gashatan, Bumbanian, Arshantan, and Irdinmanhan, which together span the interval from late in the Late Paleocene to early in the Middle Eocene. Comparisons with localities and sections documented since the time of the Central Asiatic Expeditions (CAE) show that the so-called Houldjin gravels of the CAE from this area are mostly Irdin Manha Formation and that the “Irdin Manha beds” of the CAE belong to the Arshanto and/or Nomogen formations. These findings reveal that previous concepts of the Irdin Manha and Arshanto faunas from the Camp Margetts area probably include fossils of different ages, so that the corresponding Asian land-mammal “ages” based on these faunas are problematic and need systematic revision. The Nomogen, Arshanto, and Irdin Manha formations are redefined.

Oligocene primates from China reveal divergence between African and Asian primate evolution

Climate filters dominant species The transition between the Eocene and Oligocene periods was marked by distinct cooling. Because primate species are particularly susceptible to cold, this change in climate drove a retraction of primates globally. After this transition, anthropoid primates were dominant in Afro-Arabian regions, but little has been known about primate reestablishment in Asia. Ni et al. describe 10 previously unknown primates found in Yunnan Province in China that show that primates took a different path in Asia. Instead of anthropoids, strepsirrhine (lemur-like) primates were dominant. It is still unknown whether this difference was due to the environment or chance. Science, this issue p. 673 Fossil evidence suggests that primate evolution followed different paths in Asia and Africa. Profound environmental and faunal changes are associated with climatic deterioration during the Eocene-Oligocene transition (EOT) roughly 34 million years ago. Reconstructing how Asian primates responded to the EOT has been hindered by a sparse record of Oligocene primates on that continent. Here, we report the discovery of a diverse primate fauna from the early Oligocene of southern China. In marked contrast to Afro-Arabian Oligocene primate faunas, this Asian fauna is dominated by strepsirhines. There appears to be a strong break between Paleogene and Neogene Asian anthropoid assemblages. Asian and Afro-Arabian primate faunas responded differently to EOT climatic deterioration, indicating that the EOT functioned as a critical evolutionary filter constraining the subsequent course of primate evolution across the Old World.

NEW MATERIAL OF ALAGOMYIDAE (MAMMALIA, GLIRES) FROM THE LATE PALEOCENE SUBENG LOCALITY, INNER MONGOLIA

Abstract Newly discovered specimens of alagomyids, mostly isolated teeth collected by screenwashing at the Gashatan (Late Paleocene) Subeng locality in Inner Mongolia, document considerable intraspecific variation in Tribosphenomys minutus that has not been appreciated previously because of limited sample sizes. P4s of Tribosphenomys are described for the first time, which helps to clarify the posterior premolar identification of alagomyids. Some of the alagomyid specimens are referred to Tribosphenomys cf. T. secundus and Neimengomys qii gen. and sp. nov. Based on the new data, Tribosphenomys borealis from the Bumban Member of the Naran Bulak Formation, Mongolia, is considered to be a junior synonym of Alagomys inopinatus, and T. tertius from the Zhigden Member of the Naran Bulak Formation is regarded as a junior synonym of T. minutus. Alagomyidae, consisting of Tribosphenomys, Alagomys and Neimengomys, is maintained as a valid family. The presence of a diversity of alagomyids and other recently obtained fossils and stratigraphic evidence from the Erlian Basin suggest that the Gashatan and Bumbanian of Asia are probably correlative to the late Tiffanian–early Wasachian of North America. The faunal turnover during the Gashatan and Bumbanian in Asia is probably related to the Late Paleocene–Early Eocene global warming, but current evidence is insufficient to link any specific event with the Paleocene-Eocene Thermal Maximum.

An early Oligocene fossil demonstrates treeshrews are slowly evolving “living fossils”

Treeshrews are widely considered a “living model” of an ancestral primate, and have long been called “living fossils”. Actual fossils of treeshrews, however, are extremely rare. We report a new fossil species of Ptilocercus treeshrew recovered from the early Oligocene (~34 Ma) of China that represents the oldest definitive fossil record of the crown group of treeshrews and nearly doubles the temporal length of their fossil record. The fossil species is strikingly similar to the living Ptilocercus lowii, a species generally recognized as the most plesiomorphic extant treeshrew. It demonstrates that Ptilocercus treeshrews have undergone little evolutionary change in their morphology since the early Oligocene. Morphological comparisons and phylogenetic analysis support the long-standing idea that Ptilocercus treeshrews are morphologically conservative and have probably retained many characters present in the common stock that gave rise to archontans, which include primates, flying lemurs, plesiadapiforms and treeshrews. This discovery provides an exceptional example of slow morphological evolution in a mammalian group over a period of 34 million years. The persistent and stable tropical environment in Southeast Asia through the Cenozoic likely played a critical role in the survival of such a morphologically conservative lineage.