[Show abstract][Hide abstract] ABSTRACT: Microtoid cricetids are widely considered to be the ancestral form of arvicoline rodents, a successful rodent group including voles, lemmings and muskrats. The earliest previously known microtoid cricetid is Microtocricetus molassicus Fahlbusch and Mayr 1975 from the MN9 (about 10-11 Ma) of Europe. Here we report a new microtoid cricetid, Primoprismus fejfari, gen. et sp. nov., discovered from locality XJ 200604 in the Junggar basin of Xinjiang, northwest China. The rodent assemblage found in association with this specimen indicates a late Early Miocene age, roughly estimated at 18–17 Ma, and thus more than 6 million years
earlier than the record of M. molassicus. While morphological comparisons suggest that the new taxon is most closely related to M. molassicus, it also presents a striking combination of primitive characters compared to the latter, including its relatively lower crown, smaller size, differentiated posterolophid and hypolophid, faint anterolophid, and the absence of an ectolophid, as well as the presence of a stylid on the labial border of the tooth. Arid conditions prevailing across the mid-latitude interior of Eurasia during the Early Miocene, enhanced by the combined effects of the Tibetan uplift and the gradual retreat of the Tethys Ocean, likely played a role in the appearance of grasslands which triggered the evolution of microtoid cricetids and, ultimately, the origin of arvicoline rodents.
[Show abstract][Hide abstract] ABSTRACT: Mammalian bipedalism has long been thought to have arisen in response to arid and open environments. Here we tested whether bipedalism coevolved with environmental changes using molecular and paleontological data from the rodent superfamily Dipodoidea and statistical methods for reconstructing ancestral characteristics and past climates. Our results show that the post-Late Miocene aridification exerted selective pressures on tooth shape, but not on leg length of bipedal jerboas. Cheek tooth crown height has increased since the Late Miocene, but the hind limb/head-body length ratios remained stable and high despite the environmental change from humid and forested to arid and open conditions, rather than increasing from low to high as predicted by the arid-bipedalism hypothesis. The decoupling of locomotor and dental character evolution indicates that bipedalism evolved under selective pressure different from that of dental hypsodonty in jerboas. We reconstructed the habitats of early jerboas using floral and faunal data, and the results shows that the environments in which bipedalism evolved were forested. Our results suggest that bipedalism evolved as an adaptation to humid woodlands or forests for vertical jumping. Running at high speeds is likely a by-product of selection for jumping, which became advantageous in open environments later on. This article is protected by copyright. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: Tree-building with diverse data maximizes explanatory power. Application of molecular clock models to ancient speciation events risks a bias against detection of fast radiations subsequent to the Cretaceous-Paleogene (K-Pg) event. Contrary to Springer et al., post-K-Pg placental diversification does not require "virus-like" substitution rates. Even constraining clade ages to their model, the explosive model best explains placental evolution.
[Show abstract][Hide abstract] ABSTRACT: Reconstructing the earliest phases of primate evolution has been impeded by gaps in the fossil record, so that disagreements persist regarding the palaeobiology and phylogenetic relationships of the earliest primates. Here we report the discovery of a nearly complete and partly articulated skeleton of a primitive haplorhine primate from the early Eocene of China, about 55 million years ago, the oldest fossil primate of this quality ever recovered. Coupled with detailed morphological examination using propagation phase contrast X-ray synchrotron microtomography, our phylogenetic analysis based on total available evidence indicates that this fossil is the most basal known member of the tarsiiform clade. In addition to providing further support for an early dichotomy between the strepsirrhine and haplorhine clades, this new primate further constrains the age of divergence between tarsiiforms and anthropoids. It also strengthens the hypothesis that the earliest primates were probably diurnal, arboreal and primarily insectivorous mammals the size of modern pygmy mouse lemurs.
[Show abstract][Hide abstract] ABSTRACT: To discover interordinal relationships of living and fossil placental mammals and the time of origin of placentals relative to the Cretaceous-Paleogene (K-Pg) boundary, we scored 4541 phenomic characters de novo for 86 fossil and living species. Combining these data with molecular sequences, we obtained a phylogenetic tree that, when calibrated with fossils, shows that crown clade Placentalia and placental orders originated after the K-Pg boundary. Many nodes discovered using molecular data are upheld, but phenomic signals overturn molecular signals to show Sundatheria (Dermoptera + Scandentia) as the sister taxon of Primates, a close link between Proboscidea (elephants) and Sirenia (sea cows), and the monophyly of echolocating Chiroptera (bats). Our tree suggests that Placentalia first split into Xenarthra and Epitheria; extinct New World species are the oldest members of Afrotheria.
[Show abstract][Hide abstract] ABSTRACT: A new genus and species of aplodontid rodent, Proansomys dureensis, from the late Oligocene of the northern Junggar Basin of China is described. The new genus is referred to as Ansomyinae because the ectoloph on the upper cheek teeth, although not fully crested, has attained the same characteristic bucket-handle-shaped configuration as other members of the subfamily. It represents the earliest record of the subfamily yet discovered in Asia and is more plesiomorphic than species of the genus Ansomys in having a partly crested ectoloph, a lower degree of lophodonty, and less complex tooth basins (lacking accessory lophules). Proansomys has transitional features between Prosciurus and Ansomys, suggesting that the Ansomyinae derived from a group of aplodontids related to Prosciurus, as did other advanced aplodontid rodents. This provides new light on the paleobiogeography of the Ansomyinae.
PLoS ONE 01/2013; 8(1):e52625. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Here we report a new early Oligocene cricetid, Paracricetops virgatoincisus, gen. et sp. nov., discovered from the Caijiachong locality in Yunnan Province, China. This new cricetid shows a peculiar combination of characters, such as massive and transversely positioned cusps, crenulated cheek tooth enamel, and a deep fossette enclosed between protocone and paracone. These characters are also present in Cricetops, a cricetid rodent of which the phylogenetic relationship with other cricetids remains debatable. Our phylogenetic analysis based on a data matrix including 37 taxa and 67 morphological characters reveals that Paracricetops and Cricetops are sister groups. Paracricetops, Cricetops, Deperetomys, Meteamys, Selenomys, Melissiodon, Mirrabella, Enginia, Muhsinia, and Aralocricetodon constitute a monophyletic group. This result suggests that these genera should all be grouped in the subfamily Cricetopinae. Our phylogenetic analysis also casts new lights on the origin and early radiation of the family Cricetidae. The subfamily Pappocricetodontinae is a polyphyletic group. Pappocricetodon and Raricricetodon, two basal cricetid genera, are also polyphyletic. A thorough systematic revision of these basal cricetids is needed. Chronological distribution of Eucricetodontinae, Paracricetodontinae, Pseudocricetodontinae, and Cricetopinae indicates that the establishment of these cricetid clades should be in the late Eocene at least. We therefore deduced that the first diversification and dispersal of the family Cricetidae across Eurasia must have occurred well before the Eocene-Oligocene transition.
Journal of Vertebrate Paleontology 01/2013; 33(1):185–194. · 2.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The timing of the origin and diversification of rodents remains controversial, due to conflicting results from molecular clocks and paleontological data. The fossil record tends to support an early Cenozoic origin of crown-group rodents. In contrast, most molecular studies place the origin and initial diversification of crown-Rodentia deep in the Cretaceous, although some molecular analyses have recovered estimated divergence times that are more compatible with the fossil record. Here we attempt to resolve this conflict by carrying out a molecular clock investigation based on a nine-gene sequence dataset and a novel set of seven fossil constraints, including two new rodent records (the earliest known representatives of Cardiocraniinae and Dipodinae). Our results indicate that rodents originated around 61.7-62.4 Ma, shortly after the Cretaceous/Paleogene (K/Pg) boundary, and diversified at the intraordinal level around 57.7-58.9 Ma. These estimates are broadly consistent with the paleontological record, but challenge previous molecular studies that place the origin and early diversification of rodents in the Cretaceous. This study demonstrates that, with reliable fossil constraints, the incompatibility between paleontological and molecular estimates of rodent divergence times can be eliminated using currently available tools and genetic markers. Similar conflicts between molecular and paleontological evidence bedevil attempts to establish the origination times of other placental groups. The example of the present study suggests that more reliable fossil calibration points may represent the key to resolving these controversies.
PLoS ONE 01/2012; 7(10):e46445. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We document the morphology of the bony labyrinth of Chilecebus carrascoensis, one of the best preserved early platyrrhines known, based on high resolution CT scanning and 3D digital reconstruction. The cochlea is low and conical in form, as in other anthropoids, but has only 2.5 spiral turns. When the allometric relationship with body mass is considered, cochlear size is similar to that in extant primates. The relative size of the semicircular canals, which is well within the range of other primates, indicates that Chilecebus carrascoensis was probably not as agile in its locomotion as other small-bodied platyrrhines such as Leontopithecus rosalia, Saguinus oedipus, and Callithrix jacchus, but it probably was not a suspensory acrobat or a slow climber. The proportion, shape, and orientation of the semicircular canals in Chilecebus carrascoensis also mirror that typically seen in extant primates. However, no single variable can be used for predicting the locomotor pattern in Chilecebus carrascoensis. Based on Principle Component Analysis (PCA) scores we calculated rescaled Euclidean distances for various taxa; primates with similar locomotor patterns tend to share shorter distances. Results for Chilecebus carrascoensis underscore its general resemblance to living quadrupedal primate taxa, but it is not positioned especially near any single living taxon.
Journal of Human Evolution 10/2010; 59(6):595-607. · 4.09 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Paleogene strata in the Huheboerhe area, Erlian Basin, Inner Mongolia, China have been subdivided into three lithological
units: the Nomogen Formation, the Arshanto Formation, and the Irdin Manha Formation. At least 12 mammal-bearing horizons have
been recognized in these formations, of which 4 in the Nomogen Formation, 6 in the Arshanto Formation, and 2 in the Irdin
Manha Formation. Recent investigation proved that the “Houldjin Formation” recognized in this area by the Central Asiatic
Expeditions (CAE) of the American Museum Natural History in the 1920s is actually the Irdin Manha Formation, while the “Irdin
Manha Formation” of CAE is the Arshanto Formation. A recent paleomagnetic study suggests that the upper part of the Nomogen
Formation is early Eocene in age and the Arshanto Formation is mainly early Eocene rather than middle Eocene as previously
thought. The Gashatan, Bumbanian, and Arshantan land mammal ages are correlated respectively to the Thanetian, the early Ypresian,
and the middle Ypresian through earliest Lutetian of the Geological Time Scale. These land mammal ages are also correlated
with the late Tiffanian through Clarkforkian, the early Wasatchian, and the middle-late Wasatchian and most of the Bridgerian
of the North American Land Mammal Ages. During the early Paleogene, the mammalian history of the Erlian Basin was dominated
by the appearance of new mammalian families and the replacement of a variety of genera and species, corresponding to the gradual
climatic changes during this time period. The abrupt emergence of several modern mammalian orders at the beginning of the
Eocene is probably related to extreme climatic warming in relation to the Paleocene-Eocene Thermal Maximum.
KeywordsErlian Basin-Paleogene-mammal-faunal turnover-biochronology-environmental response
Science China Earth Science 01/2010; 53(12):1918-1926. · 1.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: New specimens of Eucricetodon are described from the Late Oligocene Tieersihabahe Formation of the Junggar basin, northern Xinjiang, China. The relatively abundant material documents the morphological variation within Asian species of the genus. The taxon, identified as E. aff. E. caducus, is similar to E. caducus from the Oligocene of Kazakhstan and China and E. occasionalis from the Early Miocene of Kazakhstan. It also shows noticeable resemblances to E. longidens from the Late Oligocene of Europe whose origin is currently in debate. The study confirms the strong morphological affinity between Asian and European species of Eucricetodon and suggests that the evolutionary trends among paracricetodontines are probably more complex than previously assumed, especially with the new forms discovered from the last decade. A systematic revision of Eurasian paracricetodontines at species level is needed to understand their evolutionary history.
American Museum Novitates 12/2009; · 1.69 Impact Factor