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Docodonts are a Mesozoic mammal group (Synapsida: Mammaliaformes) with a fossil record from the Middle Jurassic to the late Early Cretaceous. With highly distinctive molars for both shearing and grinding functions, docodonts are inferred to have diverse dietary adaptations, including insectivory, omnivory, and even carnivory. This group also offers the earliest-known case of mammalian swimming adaptation; at least two docodonts are inferred to have occupied a semi-aquatic niche. Here we present a phylogenetic analysis of 31 dental characters of docodonts (12 genera), plus six outgroups, including the taxa considered by some to be close relatives to docodonts. Our analysis recognizes a clade of Itatodon and Krusatodon and a clade of Tashkumyrodon and Borealestes, both of the Middle Jurassic. There is also a well-supported Late Jurassic Euroamerican clade (Dsungarodon, Docodon, and Haldanodon) and an Asiatic clade (Sibirotherium and Tegotherium). The Late Jurassic and Early Cretaceous clades are nested in a paraphyletic series of plesiomorphic taxa from the Middle Jurassic of Eurasia. Our re-analysis of Gondtherium from the Kota Formation of India confirms its docodont affinity and supports a prior hypothesis that this group dispersed to Gondwana during the Middle Jurassic. We hypothesize that docodonts and Late Triassic Tikitherium are sister taxa, and that the Tikitherium-docodont clade, in turn, is related to the mammaliaforms Woutersia and Delsatia. Contingent on the current scheme of cusp homology, docodonts are related to some Late Triassic mammaliaforms with triangular molar cusps, a paraphyletic group commonly known as “symmetrodonts.”
Here I attempt to weave together a few strands of knowledge about the Cretaceous–Tertiary asteroid collision and its biological effects. The sheer enormity of kinetic energy involved in the collision and the immediate conversion of the energy to infrared radiation upon worldwide reentry of suborbitally lofted debris is not adequately appreciated by most paleontologists who deal with nonmarine organisms. Consideration of the physics of such a collision leads to the conclusion that there should have been no live Paleocene nonavian dinosaurs, but a view that nonavian dinosaurs survived into the Paleocene has been accepted by some students on the basis of “Paleocene pollen” found stratigraphically beneath specimens of nonavian dinosaurs. However, investigation of the biostratigraphic basis of dating “Paleocene” dinosaurs points to flaws in palynological dating of Late Cretaceous and early Paleocene strata in Rocky Mountain basins of deposition. The argument for “Paleocene” pollen occurring with or stratigraphically beneath non-reworked nonavian dinosaurs is not acceptable because palynological zone P1 and most or all of zone P2 occur in Upper Cretaceous strata in the Hell's Half Acre area of central Wyoming where the palynological scheme of zonation originated, not in Paleocene strata. Although said to conflict, palynological occurrences are actually compatible with results from dinosaurs. Finding P1 and/or P2 pollen stratigraphically beneath nonavian dinosaur remains does not push those dinosaurs up into Tertiary strata. Populations of sheltering organisms, provided that they were of small enough individuals, would have survived the K–T calamity easily. However, manifestations of Mayr's “founder effect” would have altered the equilibria of genetic composition of populations forever. “Molecular clocks” would have temporarily run fast, giving the impression that phylogenetic branch points lie deeper in the Cretaceous than was actually the case.
Malfelis badwaterensis, gen.et sp. nov., represented by a nearly complete juvenile skull, isolated I1–2, P1, DP2, and a fragment of the dentary from the same individual (CM 62590), is described from the early middle Eocene (Gardnerbuttean, early Bridgerian) of the Wind River Formation, Wyoming in North America. M. badwaterensis preserves a unique combination of characters that set it apart from all other creodonts including the presence of a P1 and reduced M2, a carnassial complex from DP3–4–M1 with reduced protocones, simplified trenchant P2–3, and M1 with conjoined metacone and paracone, and metastylar blade. M. badwaterensis is referred to the Oxyaenidae based on the well-developed metastylar blade of M1, a reduced M2, and loss of M3. This new creodont was perhaps the largest of all animals from the type locality, which has yielded nearly 80 species of mammals.
A new lagomorph, Dawsonolagus antiquus, gen. et sp. nov., collected from the possible late early Eocene Arshanto Formation of Nei Mongol (Inner Mongolia), China, is described. The material includes a partial skull with P4-M2 on both sides, two fragmentary mandibles, several isolated teeth, three calcanei and an astragulus. The new genus is characterized by a mosaic combination of features similar to mimotonids and lagomorphs, presenting a morphotype intermediate between a mimotonid and a typical lagomorph.
The early Bridgerian (early middle Eocene) myomorph rodent Elymys complexus, from the Sheep Pass Formation near Ely, Nevada, is more variable in its dental morphology than originally described. Its similarity to Aksyiromys and other middle Eocene myomorphs from China and Central Asia suggests close relationships, which requires intercontinental interchange of these small rodents during the middle Eocene. At present, the biogeographic scenario for the origin and early evolution of Myomorpha that best fits the known record of occurrences is: evolution of Myomorpha from Sciuravidae in North America at least as early as the beginning of the middle Eocene, emigration of an Elymys-like myomorph from North America to Asia in the early middle Eocene, diversification of dipodoids and muroids in the later Eocene of Asia, emigration of Eucricetodon-like cricetids from Asia to North America (eumyine cricetids) in the latest Eocene, followed later by dipodids in the Miocene.
<p class="first" id="ID0EF">The Diatomyidae (Rodentia, Mammalia) are a group of medium to large rodents restricted to southern and eastern Asia. The skull, characterized by hystricomorphous musculature, a 4/4 cheek tooth formula, a sciurognathous jaw, and other features, places the Diatomyidae in a phylogenetic position near, but not within, Hystricognathi. Like living Ctenodactylidae, they are a product of the early radiation of Rodentia that includes, ultimately, the hystricognaths. The oldest fossil Diatomyidae occur in Oligocene terrestrial sediments of the Indian subcontinent. Younger sediments in Pakistan near the Oligocene/Miocene boundary produce a quite different diatomyid that presents unique, derived conditions, and demonstrates early diversification of the family. This diatomyid, described here as <b><span class="genus-species">Marymus dalanae</span>, new genus and species</b>, has cuspate anterior cheek tooth morphology interpreted as specialized, possibly for predation on invertebrates. All early diatomyids are relatively abundant components of their fossil assemblages. Later Diatomyidae from Thailand, China, and Japan suggest a clade characterized by increased body size, simplified dentition, greater molar crown height, and bilophodonty with planar wear indicating herbivory. Most of these later diatomyids are rare and infrequently recorded as fossils. This suggests a shift in habitat preference, with consequent under-representation in fluvial settings, or a new bias against preservation at sites where they do occur. That the habitat preferred by later diatomyids was different from that of early species and was peripheral to fluvial systems would be consistent with the recognition that <span class="genus-species">Laonastes</span> of rocky terrain in central Laos is a living diatomyid.
At least four individuals of desmostylian are described from a single locality on Unalaska Island, Alaska. Desmostylians are known only from the North Pacific region from Japan to Mexico, but this form is currently unique to Unalaska. It retains certain primitive features, such as relatively low-crowned columnar (desmostylodont) cusps with remnants of cingula, that are shared with Cornwallius. However, it is derived in having additional cusps on lower molars. It also has well-developed upper and lower tusks and a narrow mental symphysis, so far as can be determined. The age of the desmostylian sample is either late Oligocene or (more likely) earliest Miocene. Although the representation of skeletal elements of individuals is low, the presence of a neonate dentary implies that a breeding population of this taxon inhabited, rather than simply dispersed through, the Aleutian Chain during the mid-Cenozoic.
The Section of Mammals, Carnegie Museum of Natural History houses skulls from seven genera of extant lagomorphs (one ochotonid and six leporids). Described and illustrated are the external surfaces of the bones of the skull of the North American pika Ochotona princeps (Richardson, 1828) and also illustrated is the volcano rabbit Romerolagus diazi (Ferrari-Pérez, 1893). Comparisons of selected craniomandibular features are made between O. princeps, R. diazi, and the following additional leporids: Pronolagus crassicaudatus (I. Geoffroy, 1832), Lepus capensis Linnaeus, 1758, Oryctolagus cuniculus (Linnaeus, 1758), Sylvilagus nuttallii (Bachman, 1837), and Brachylagus idahoensis (Merriam, 1891). Also included in the comparisons based on published descriptions are the following extinct taxa: Prolagus, the Sardinian pika, a Quaternary ochotonid; Palaeolagus, a late Eocene-Oligocene stem lagomorph; Mimolagus, an early Oligocene mimotonid; Mimotona, a Paleocene mimotonid; Gomphos, an early Eocene stem lagomorph; and Rhombomylus, an early Eocene eurymylid. Characters are identified that support various hypotheses of phylogenetic relationships among the studied taxa.
Between 1973 and 2002, Mary Dawson and team spent 11 field seasons searching for vertebrate fossils on Ellesmere, Axel Heiberg, Devon, Ellef Ringnes, Bylot, and Banks Islands in Canada's Arctic Archipelago. Their pioneering efforts resulted in one of the greatest discoveries in vertebrate paleontology of the twentieth century—the first, and best, record of Paleogene terrestrial vertebrates from within the Arctic Circle. Here we provide a history of the field research and discoveries by Dawson and collaborators in the Canadian High Arctic. Discovery of Eocene vertebrate faunas in the Eureka Sound Group on Ellesmere and Axel Heiberg Islands supports the former existence of a high-latitude land connection between Europe and North America, provides insight into the origin of certain mammalian taxa such as microparamyine rodents, and yields evidence for a warm, temperate High Arctic climate at that time. Moving up in the section, Dawson's discoveries in Haughton Astrobleme on Devon Island include the only known High Arctic Miocene terrestrial vertebrate fauna and sparked many other studies ranging from dating the impact crater to palynological and paleoclimatic studies. Dawson's legacies include a large body of literature on High Arctic paleontology and geology by herself, her colleagues, and those she inspired and mentored. Just as important, Dawson's pioneer discoveries provide the impetus and inspiration for further exploration of the High Arctic.
We provide a brief synopsis of Mary Dawson's contributions to vertebrate paleontology in China through her fieldwork, research, and repeated fostering of international collaborations, some of which are ongoing. Dawson and her Chinese and American colleagues carried out a series of successful expeditions during the 1990s, notably including work at the middle Eocene Shanghuang fissure-fillings in southern Jiangsu Province and in the middle Eocene Heti Formation, Yuanqu Basin, Shanxi and Henan Provinces. Dawson's research on Chinese fossil vertebrates focused on reconstructing the origin and evolution of Glires, although she also made important contributions to our knowledge of other mammalian taxa and to biogeographic relationships among Holarctic mammals in general. Her efforts continue to bear fruit, both in terms of her own research and that of her numerous colleagues and students.
Fossil primates from the late middle Eocene Pondaung Formation of Myanmar have figured prominently in recent efforts to reconstruct the early evolutionary history of anthropoids. The anthropoid affinities of Amphipithecidae, the most abundant fossil primates currently known from the Pondaung Formation, have proven to be particularly controversial. Here we describe two new genera and species, Paukkaungia parva and Kyitchaungia takaii, of sivaladapid primates from the Pondaung Formation. Tarsal elements that are appropriate in size and morphology to belong to Kyitchaungia takaii are also described. These are the first undoubted adapiforms—and the first fossil primates other than anthropoids—to be reported from the Eocene of Myanmar. The discovery of sivaladapids in the Pondaung Formation enhances the taxonomic and paleoecological diversity of the late middle Eocene primate fauna of Myanmar. In this respect, the fossil primate community from the Pondaung Formation appears to have resembled roughly contemporaneous assemblages from China, Thailand, and Pakistan. The newly discovered sivaladapid tarsal elements help to resolve conflicting interpretations regarding the taxonomic allocation of large-bodied primate postcranial elements from the Pondaung Formation. The NMMP 20 partial skeleton from the Pondaung Formation, which has often been regarded as that of an amphipithecid, is more plausibly interpreted as pertaining to a third Pondaung sivaladapid. Recognizing the sivaladapid affinities of the NMMP 20 partial skeleton solidifies the anthropoid status of amphipithecids, further constraining temporal, phylogenetic, and biogeographic hypotheses regarding anthropoid origins.
Two distal humeral fragments are described from the middle Eocene Shanghuang fissures (southern Jiangsu Province, China). These specimens provide the first evidence of forelimb morphology among Shanghuang primates. One specimen belongs to an adapiform strepsirhine primate that is morphologically similar to European adapines, while the other pertains to a small haplorhine primate having numerous features in common with North American omomyids. Both fossils exhibit classic primate elbow adaptations that are functionally related to arboreality and climbing.
Pipestoneia douglassi, a new genus and species of selenodont artiodactyl, is known from the middle Chadronian part of the Climbing Arrow Member of the Renova Formation exposed in the classic Pipestone Springs area along the extreme western margin of the Jefferson River Basin, Jefferson County, Montana. Specimens of P. douglassi are moderately common at the Pipestone Springs localities but have sometimes been mistaken for specimens of either “Leptotragulus” profectus or “Leptomeryx” mammifer, both of which are of about the same size and occur at the same localities. Although Pipestoneia is tentatively assigned to the Leptomerycidae, it exhibits some characters that make this assignment problematic, and the genus may well pertain to some other group of selenodont artiodactyls.
A sample of upper and lower dentitions of a large paramyid is described from the upper part of the Willwood Formation of the Bighorn Basin (late Wasatchian biozone Wa-6, = “Lysitean”). The specimens are referred to Notoparamys costilloi, originally described from the Lysitean of the Huerfano Formation of southern Colorado. The sample shows considerable variation, interpreted here to represent one highly variable species. This leads to the conclusion that many characters that have been used to distinguish species and even genera among paramyids might in some cases reflect intraspecific variability.
“Pseudotomus” coloradensis and Leptotomus loomisi are probably junior synonyms of Notoparamys costilloi. The incisor enamel of N. costilloi is pauciserial, as in other paramyids. The enamel of P4 (and presumably the molars) has three zones: outer and inner zones of radial enamel and a middle zone of multiserial Hunter-Schreger bands. This constitutes the S-type schmelzmuster, a condition more derived than in some other paramyids but characteristic of sciuromorphs, sciuravids, hystricognaths, and various other rodents. Occlusal study reveals a relatively continuous mesiolingual movement of the lower molars across the uppers during phases I and II, as in Paramys.
Incisor enamel microstructure analysis does not support a rodent suborder Sciuravida (most recent common ancestor of Ivanantoniidae, Sciuravidae, Chapattimyidae, Cylindrodontidae, Ctenodactylidae and all its descendants) as proposed by McKenna and Bell (1997). Early to middle Eocene Ivanantonia, Sciuravidae, and Prolapsus have the plesiomorphic rodent schmelzmuster with pauciserial Hunter-Schreger bands (HSB). Within the Cylindrodontidae a schmelzmuster with uniserial HSB evolved: early Eocene Dawsonomys and middle Eocene Jaywilsonomyinae possess a schmelzmuster with pauciserial HSB, and middle to late Eocene Cylindrodontinae have more derived schmelzmuster with uniserial HSB. Chapattimyidae and Ctenodactylidae represent a clade with the potential to evolve multiserial schmelzmuster. Early Eocene Chapattimyinae, Yuomyinae, and Cocomyinae have plesiomorphic schmelzmuster with pauciserial HSB, whereas middle Eocene Cocomyinae, Yuomyinae, late Eocene Protophiomys, early Miocene Baluchimyinae, and the Ctenodactylidae possess derived schmelzmuster with multiserial HSB. Uniserial and multiserial HSB are derived but represent different pathways of evolution. Schmelzmuster distribution supports the hypothesis of a basal dichotomy of Rodentia suggested by Luckett and Hartenberger (1985) characterized by an ischyromyoid clade with the potential to evolve schmelzmuster with uniserial HSB and a ctenodactyloid plus hystricognath clade with the potential to evolve schmelzmuster with multiserial HSB.
A new genus and species of paramyine ischyromyid, Metaparamys dawsonae, is described from the Chadronian of Wyoming. The new genus is distinguished from other paramyines in having the ectolophid on lower molars complete between protoconid and hypoconid and without a mesoconid, hypocone and metaconule on upper molars relatively larger than in Paramys, lower incisor wide with convex anterior surface, and masseteric scar on mandible more anterior than in other paramyines. The Uintan species Paramys compressidens Peterson is also assigned to Metaparamys. The Bridgerian P. delicatior Leidy appears to be a likely ancestor for Metaparamys based on the cross-sectional shape of the lower incisor. The occurrence of M. dawsonae is one of the latest records of a paramyine rodent in North America.
We report here the first discovery of microvertebrates from the Mae Moh coal mine, Lamphang Province, northern Thailand. This discovery sheds new light on the age and paleoenvironments of the Miocene basins of northern Thailand. Previous investigations of paleomagnetic stratigraphy in the Mah Moh Basin demonstrated that the fossiliferous Q and K coal seams there date between 13.12–13.3 Ma. The microvertebrate fauna from the Q and K coal seams includes Tarsius sp., erinaceid insectivores and rodents, the last being represented by the monospecific genera Prokanisamys and Neocometes. These microvertebrate fossils are extremely similar to elements of the Mae Long fauna from the Li Basin, which had been estimated to date between 16–18 Ma. Accordingly, the Mae Long fauna in the Li Basin appears to be contemporaneous with the fauna from the Q and K coal seams in the Mae Moh Basin, suggesting that previous estimates of the age of the Mae Long fauna were 3–5 Ma too old. The discovery of numerous fragments of the primitive deer Stephanocemas cf. rucha and the pig Conohyus thailandicus in the Mae Moh Basin confirms the correlation suggested by the microvertebrates. As a result, there is no longer any reason to advocate a west-east chronological gradient for the opening of the intermontane basins of northern Thailand. Alternatively, dating of other Tertiary basins in Thailand suggests a south-north gradient. The Krabi Basin, located in peninsular Thailand, is of latest Eocene age, the Nong Ya Plong Basin in central Thailand dates to the late Oligocene, and basins in northern Thailand are middle Miocene in age. Analysis of mammalian faunas and pollen indicate that the middle Miocene was a period of dramatic climatic fluctuations in northern Thailand. The Q and K coal seams in the Mae Moh Basin show a temperate-tropical vegetation, whereas the uppermost coal layers testify to warmer tropical vegetation. Based on magnetostratigraphic data, these climatic fluctuations were synchronous with those observed in Antarctic deep waters. Climatic fluctuations during the middle Miocene cannot be used for purposes of correlation, because they appear to have occurred in an iterative fashion.
The cranium of the Hemingfordian beaver Anchitheriomys nanus Korth differs from the previously described skull of the Barstovian A. fluminis (Matthew) in being smaller and having less procumbent incisors, grooves on the palate, and the ethmoid and optic foramina more posterior in position on the skull. These features are viewed as being primitive in A. nanus relative to A. fluminis. The basicranium of A. nanus is preserved (unknown for A. fluminis) and demonstrates the derived castorid character of lacking the stapedial foramen in the auditory bulla, but has the apomorphic features of an elongated anterior process and a concave external meatus of the bulla (evidently a functioning part of the glenoid fossa). The paroccipital process is greatly broadened, another unique feature among castorids.
The cranial morphology of the earlier A. nanus suggests that the anchitheriomyines are more closely related to the advanced castorids (Castorinae and Castoroidinae) than the primitive agnotocastorines, with which they were previously allied. Anchitheriomys is part of a Miocene dispersal episode from Eurasia, in concert with numerous other rodents and insectivores.
The Miocene Mammal Mapping Project (MIOMAP), a relational database of all published mammalian vertebrate localities between 30 and 5 million years old from the western United States, is now online for use by the paleontological community. The database is housed at the University of California at Berkeley, served through the Berkeley Natural History Museums, and accessible via the University of California Museum of Paleontology website. Here we outline the salient features of the database to facilitate its use and provide the information needed for users to adapt the data to their own needs. Online queries of the database can be accessed via http://www.ucmp.berkeley.edu/miomap and made through HTML forms or an interactive map created using open source MapServer 4.0 software and Google Earth™. We also highlight past work done using the database and some of its potential applications.
Although the tundra muskox (Ovibos moschatus) is not often included in discussions of late Quaternary megafaunal extinctions, ancient DNA (aDNA) evidence indicates that this species lost a considerable portion of its genetic diversity sometime after the Last Glacial Maximum but before the mid-Holocene. Ovibos originally arose in Asia and enjoyed a Holarctic distribution during the late Pleistocene. It was previously believed that the tundra muskox disappeared in Asia near the end of that epoch. However, new evidence establishes that Ovibos expressing modern haplotypes “reappeared” for a brief period along the Arctic periphery of northeastern Asia between 3700–2800 yrbp. Where Ovibos managed to survive during the early and middle Holocene is unknown; it may have been North America or Asia (or both). In this there are certain parallels to the extinction dynamics of the woolly mammoth, Mammuthus primigenius. Most populations of woolly mammoth (including all known mainland populations) had disappeared by 9000 yrbp. However, peripheral populations on Wrangel Island in the Chukchi Sea and St. Paul Island in the Pribilofs managed to survive much later (until ca. 3700 yrbp in the case of the Wrangel population). This pattern of end-Pleistocene range collapse, followed by short-term “recovery” in the Holocene, has also been detected in the radiocarbon record for the giant Irish deer, Megaloceros giganteus. This may signify that the late Quaternary extinction process took place over a much longer interval than imagined heretofore. However, whether these megafaunal collapses occurred in truly close correlation with one another will have to be tested more rigorously with a much better 14C database than exists currently.