Chuankui Li

A new symmetrodont mammal from China and its implications for mammalian evolution

A new symmetrodont mammal has been discovered in the Mesozoic era (Late Jurassic or Early Cretaceous period) of Liaoning Province, China. Archaic therian mammals, including symmetrodonts, are extinct relatives of the living marsupial and placental therians. However, these archaic therians have been mostly documented by fragmentary fossils. This new fossil taxon, represented by a nearly complete postcranial skeleton and a partial skull with dentition, is the best-preserved symmetrodont mammal yet discovered. It provides a new insight into the relationships of the major lineages of mammals and the evolution of the mammalian skeleton. Our analysis suggests that this new taxon represents a part of the early therian radiation before the divergence of living marsupials and placentals; that therians and multituberculates are more closely related to each other than either group is to other mammalian lineages; that archaic therians lacked the more parasagittal posture of the forelimb of most living therian mammals; and that archaic therians, such as symmetrodonts, retained the primitive feature of a finger-like promontorium (possibly with a straight cochlea) of the non-therian mammals. The fully coiled cochlea evolved later in more derived therian mammals, and is therefore convergent to the partially coiled cochlea of monotremes.

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 Mesozoic gliding mammal from northeastern China

Gliding flight has independently evolved many times in vertebrates. Direct evidence of gliding is rare in fossil records and is unknown in mammals from the Mesozoic era. Here we report a new Mesozoic mammal from Inner Mongolia, China, that represents a previously unknown group characterized by a highly specialized insectivorous dentition and a sizable patagium (flying membrane) for gliding flight. The patagium is covered with dense hair and supported by an elongated tail and limbs; the latter also bear many features adapted for arboreal life. This discovery extends the earliest record of gliding flight for mammals to at least 70 million years earlier in geological history, and demonstrates that early mammals were diverse in their locomotor strategies and lifestyles; they had experimented with an aerial habit at about the same time as, if not earlier than, when birds endeavoured to exploit the sky.

Laonastes and the "Lazarus effect'' in recent mammals

The living Laotian rodent Laonastes aenigmamus, first described in early 2005, has been interpreted as the sole member of the new family Laonastidae on the basis of its distinctive morphology and apparent phylogenetic isolation from other living rodents. Here we show that Laonastes is actually a surviving member of the otherwise extinct rodent family Diatomyidae, known from early Oligocene to late Miocene sites in Pakistan, India, Thailand, China, and Japan. Laonastes is a particularly striking example of the “Lazarus effect” in Recent mammals, whereby a taxon that was formerly thought to be extinct is rediscovered in the extant biota, in this case after a temporal gap of roughly 11 million years.

Cranial anatomy and relationships of a new ctenodactyloid (Mammalia, Rodentia) from the Early Eocene of Hubei Province, China

ABSTRACT Two remarkably complete skulls and associated mandibles from the late early Eocene of the Yuhuangding Formation of Hubei Province, central China, are described as a new genus and species of rodent, Exmus mini, and referred to the early ctenodectyloid family Cocomyidae. This is a small rodent in the size range of the early Eocene Asian Cocomys. Dental characters that link Exmus with other cocomyids include: non-molariform P4; cheek teeth increasing in size posteriorly; lower molar ectolophid weak or absent; and lower molar hypoconulid distinct, enlarged on m3. Cranial characters linking Exmus and Cocomys include: skull shape and proportions, including a short rostrum and large orbit; sagittal crest absent; large optic canal, confluent between the orbits; and no petrosal shelf posterior to the caudal tympanic process of the petrosal. Differences from Cocomys are numerous and include: absence of conules on P4 and loss of the protoconule on the upper molars; tiny meta-cone and hypocone on P4; molariform p4: and auditory bulla tightly attached, rather than loose as in Cocomys. Exmus also displays a number of autapomorphies that distinguish it from all other Eocene rodents examined in this study, such as substantial orbital roof formed by lacrimal and frontal, and a suture between the parietals that is nearly completely fused. A phylogenetic analysis based on characters of the skull, mandible, and dentition supports the concept of two clades within the ingroups, one composed of Eocene paramyids, sciuravids, and theridomyids and the other composed of Bandaomys, Exmus, Cocomys, Tamquammys, Advenimus, and Yuomys as stem taxa to ctenodactylids and hystricognaths. This dichotomy, which has been suggested by others prior to the discovery of Exmus, is here considered to represent an accurate assessment of Eocene rodent evolution and makes good paleogeographic sense. However, the desirability of adding more taxa to a phylogenetic analysis of early rodents is clearly recognized.

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.

A new species ofGobiconodon (Triconodonta, Mammalia) and its implication for the age of Jehol Biota

A new species ofGobiconodon is found from the Yixian Formation of western Liaoning, China. The new taxa,G. zofiae sp. nov., has a confluent opening for branches II and III of the trigeminal nerve on the anterior lamina of the petrosal.G. zofiae sp. nov. is similar toRepenomamus in having an ossified Meckel’s cartilage connecting the lower jaws and ear region. The new species, with enlarged I1/I1, posteriorly located infraorbital foramen and four mental foramina, distinctly differs from the other species ofGobiconodon. The new material indicates thatGobiconodon has four, not five, upper molariforms. The presence ofGobiconodon in Jehol Biota makes it possible to correlate Jehol Biota with faunas in eastern Asia and North America, and suggests the age of the Yixian Formation to be Early Cretaceous.

A new spalacotheriid symmetrodont from the Early Cretaceous of northeastern China

Abstract Symmetrodonts are Mesozoic mammals having lower molars with nearly symmetrical trigonids but lacking talonids. They appear to be stem members of the mammalian clade that led to extant tribosphenic mammals, but the fossil record of symmetrodonts is poor. Here we report a new genus and species of an acute-angled spalacotheriid symmetrodont, Heishanlestes changi, n.gen. and n.sp., represented by well-preserved lower jaws with teeth from the Early Cretaceous of northeastern China. The new mammal has four tightly spaced premolars and three morphological groups of lower molars, in which the first molar has an obtuse trigonid angle and the last two molars have a large neomorphic cusp in the center of the trigonid, a feature not seen in other mammals. Heishanlestes appears to be a specialized member of the spalacotheriid subfamily, Spalacolestinae, which is otherwise only known from North America. The animal probably used the premolars to crush its prey before shearing it with the molars.

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.

Novel dental pattern in a Mesozoic mammal

1. Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China; 2. Division of Paleontology, American Museum of Natural History, New York 10024, USA; 3. Biology Program, Graduate School and City College of New York, City University of New York, New York 10016, USA; 4. Laboratory for Vertebrate Paleontology, Department of Biological Sciences, University of Alberta, Edmonton T6G 2E9, Canada Correspondence should be addressed to Hu Yaoming (email: yhu@amnh. org)