Mary R. Dawson

Earliest complete dentition of an anthropoid primate from the late middle Eocene of Shanxi Province, China

The complete lower dentition of a new species of the basal anthropoid genus Eosimias shows a combination of primitive and derived traits unknown in other living or fossil primates. Although certain dental traits are decidedly more primitive in Eosimias than in other basal anthropoids, numerous derived aspects of jaw and dental morphology support the anthropoid affinities of Eosimiidae. Eosimiids document an early structural phase in the evolution of higher primates. Phylogenies that derive early anthropoids from cercamoniine adapiforms are inconsistent with eosimiid anatomy. Because early fossil anthropoids are known from both Asia and Africa, the fossil record is presently insufficient to specify the continent on which this clade originated.

Arctic terrestrial biota: paleomagnetic evidence of age disparity with mid-northern latitudes during the late cretaceous and early tertiary.

Magnetostratigraphic correlation of the Eureka Sound Formation in the Canadian high Arctic reveals profound difference between the time of appearance of fossil land plants and vertebrates in the Arctic and in mid-northern latitudes. Latest Cretaceous plant fossils in the Arctic predate mid-latitude occurrences by as much as 18 million years, while typical Eocene vertebrate fossils appear some 2 to 4 million years early.

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.

Paleogene terrestrial vertebrates: northernmost occurrence, ellesmere island, Canada.

Recently discovered Paleogene land vertebrates from the Eureka Sound Formation at about latitude 78� north in Arctic Canada include fish, turtles, an alligatorid, and several taxa of mammals. The assemblage, which is probably early or middle Eocene in age, adds to previously known paleobotanical evidence in suggesting temperate to warm-temperate climatic conditions.

A semi-aquatic Arctic mammalian carnivore from the Miocene epoch and origin of Pinnipedia

Modern pinnipeds (seals, sea lions and the walrus) are semi-aquatic, generally marine carnivores the limbs of which have been modified into flippers. Recent phylogenetic studies using morphological and molecular evidence support pinniped monophyly, and suggest a sister relationship with ursoids (for example bears) or musteloids (the clade that includes skunks, badgers, weasels and otters). Although the position of pinnipeds within modern carnivores appears moderately well resolved, fossil evidence of the morphological steps leading from a terrestrial ancestor to the modern marine forms has been weak or contentious. The earliest well-represented fossil pinniped is Enaliarctos, a marine form with flippers, which had appeared on the northwestern shores of North America by the early Miocene epoch. Here we report the discovery of a nearly complete skeleton of a new semi-aquatic carnivore from an early Miocene lake deposit in Nunavut, Canada, that represents a morphological link in early pinniped evolution. The new taxon retains a long tail and the proportions of its fore- and hindlimbs are more similar to those of modern terrestrial carnivores than to modern pinnipeds. Morphological traits indicative of semi-aquatic adaptation include a forelimb with a prominent deltopectoral ridge on the humerus, a posterodorsally expanded scapula, a pelvis with relatively short ilium, a shortened femur and flattened phalanges, suggestive of webbing. The new fossil shows evidence of pinniped affinities and similarities to the early Oligocene Amphicticeps from Asia and the late Oligocene and Miocene Potamotherium from Europe. The discovery suggests that the evolution of pinnipeds included a freshwater transitional phase, and may support the hypothesis that the Arctic was an early centre of pinniped evolution.

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.

Fission-Track Dating of Haughton Astrobleme and Included Biota, Devon Island, Canada

Haughton Astrobleme is a major extraterrestrial impact structure located on Devon Island in the Canadian Arctic Archipelago, Northwest Territories. Apatite grains separated from shocked Precambrian gneiss contained in a polymict breccia from the center of the astrobleme yielded a fission-track date of 22.4 million � 1.4 million years before the present or early Miocene (Aquitanian). This provides a date for the impact event and an upper limit on the age of crater-filling lake sediments and a flora and vertebrate fauna occurring in them. A geologically precise date for these fossils provides an important biostratigraphic reference point for interpreting the biotic evolution of the Arctic.

The Origin of Rodents and Lagomorphs

Although the two major groups of gliriform mammals, the rodents and lagomorphs, are frequently grouped together by nonspecialists, the opinion of both paleontologists and neomammalogists has long been that the two orders are not closely related. Now, new evidence on this question has come from recent fossil discoveries in China and from reevaluation of other evidence, especially developmental. After a review of the past interpretations and new evidence, we return to the view that the Lagomorpha and Rodentia can be traced to a common ancestral group and that the Cohort Glires is a valid taxonomic unit.

Early Wasatchian Mammals of the Red Hot Local Fauna, Uppermost Tuscahoma Formation, Lauderdale County, Mississippi

ABSTRACT Fossil mammals comprising the early (and perhaps earliest) Wasatchian Red Hot local fauna from the Gulf Coastal Plain of Mississippi are described. As currently understood, the fauna consists of 33 species of mammals, including the following new taxa: Mimoperadectes sowasheensis, new species; Apatemys pygmaeus, new species; Palaeosinopa aestuarium, new species; Naranius americanus, new species; Colpocherus mississippiensis, new genus and species; Diacocherus dockeryi, new species; Wyonycteris primitivus, new species; Choctawius foxi, new genus and species; Haplomylus meridionalis, new species; Ectocion nanabeensis, new species; Miacis igniculus, new species; Eogale parydros, new genus and species; Viverriscus omnivorus, new genus and species; Paramys dispar, new species; Corbarimys? nomadus, new species; and Franimys? actites, new species. New combinations proposed here include Plagioctenodon dormaalensis (Quinet, 1964), Plagioctenodon rosei (Gingerich, 1987), Choctawius mckennai (Szalay, 1969), and Paramys wutui (Tong and Dawson, 1995). The Red Hot local fauna derives from an estuarine sand unit that also yields fossil spores, pollen, dinoflagellate cysts, fishes, and snakes. The fauna is taphonomically biased against the preservation of mammals having medium to large body mass. The Red Hot local fauna provides a rare opportunity to gauge the significance of biotic provincialism within North America near the Paleocene-Eocene boundary, a time of dynamic climate change. Faunal endemism with respect to the Rocky Mountain Interior of North America is high at the species level, consistent with evidence for substantive differences in the physical environment and flora. Several lines of evidence, including mammalian biostratigraphy, sequence stratigraphy, and dinoflagellate zonation, suggest that the Red Hot local fauna correlates with earliest Wasatchian (Wa-M) faunas from the Bighorn Basin of Wyoming. Latitudinal shifts in taxon ranges coincident with global warming provide an alternative explanation for seemingly transient episodes of phyletic dwarfing among mammals during the PETM in the Bighorn Basin.

Arctic plant diversity in the Early Eocene greenhouse

For the majority of the Early Caenozoic, a remarkable expanse of humid, mesothermal to temperate forests spread across Northern Polar regions that now contain specialized plant and animal communities adapted to life in extreme environments. Little is known on the taxonomic diversity of Arctic floras during greenhouse periods of the Caenozoic. We show for the first time that plant richness in the globally warm Early Eocene (approx. 55–52 Myr) in the Canadian High Arctic (76° N) is comparable with that approximately 3500 km further south at mid-latitudes in the US western interior (44–47° N). Arctic Eocene pollen floras are most comparable in richness with todays forests in the southeastern United States, some 5000 km further south of the Arctic. Nearly half of the Eocene, Arctic plant taxa are endemic and the richness of pollen floras implies significant patchiness to the vegetation type and clear regional richness of angiosperms. The reduced latitudinal diversity gradient in Early Eocene North American plant species demonstrates that extreme photoperiod in the Arctic did not limit taxonomic diversity of plants.