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The extremely well-preserved tarsus of the tapejarid Tapejara sp. and the anhanguerid Anhanguera piscator (Pterosauria, Pterodactyloidea) are described and regarded as representative of the ankle structure of Pterosauria. The pterosaur ankle joint (PAJ) shows the following features: astragalus mediolaterally elongated forming a hemicylinder; proximal part of the astragalocalcaneal contact characterized by a ridge bordered on each side by a depression on the astragalus that has a perfect counterpart in the calcaneum, and distal part that is concavo-convex, with the concavity present in the astragalus; calcaneum extremely reduced not reaching the posterior portion of the tarsus; absence of an astragalar posterior groove, perforating foramen, calcaneal tuber, and astragalar ascending process; proximal tarsals fusing very early in ontogeny, forming a tibiotarsus.
The main movement between the crus and foot in the PAJ occurs between the proximal and distal tarsals as in the advanced mesotarsal-reversed joint (AM-R). The main differences from the latter are the lack of an ascending process and the extreme reduction of the calcaneum that make the PAJ unique. The absence of an astragalar groove and the reduction of the calcaneum reinforce the hypothesis that pterosaurs are basal ornithodirans and closely related to the Dinosauromorpha. As has been demonstrated by this and other studies, the ankle structure (a complex of characters) is phylogenetically informative and, in the light of characters from other parts of the animal's body, can contribute to a better understanding of archosaur relationships.
At least six different taxa are represented among the 21 specimens of mammals found at the Early Cretaceous Flat Rocks site in southeastern Australia. Analysis of these fossils reveals that, although the yield of mammalian specimens per person-year of effort at this locality is remarkably low, it is reasonable to expect that with further effort this assemblage will ultimately prove to be as diverse as any Early Cretaceous mammal assemblage known. By contrast, the two mammalian specimens collected thus far from the Early Cretaceous Dinosaur Cove locality in southeastern Australia are all that are likely to ever be recovered there.
Specimens from the Brushy Basin Member, Morrison Formation (Upper Jurassic), Dinosaur National Monument, Utah, provide new information on the anterior dentition of the early multituberculate Ctenacodon. An upper canine, previously thought to be lacking in Ctenacodon, is present as a simple, single-rooted tooth immediately mesial to the first premolar. The I3 has a strongly mesiodistally compressed principal cusp with a small, but distinct cusp placed low on the distobuccal corner of the tooth. The principal cusp bears vertical crests and ridges; wear results in a transverse apical wear facet that resembles that described in some paulchoffatiids. This pattern may have been produced by wear against the tip of the lower incisor at some phase of mastication.
Two small, isolated, teeth similar in morphology to the I3 may be deciduous incisors of Ctenacodon. Other possible deciduous teeth of that taxon are some small four-cusped premolars from the same locality.
The Mussentuchit local fauna, upper Cedar Mountain Formation (Cretaceous: Albian–Cenomanian), Utah, includes the geologically oldest marsupials: Kokopellia juddi, described previously, and three new taxa named herein. Adelodelphys muizoni, new genus and species, and Sinbadelphys schmidti, new genus and species, both unassignable to family, are among the smallest of Cretaceous marsupials; Pariadens mckennai, new species, tentatively assigned to Stagodontidae, is among the largest. The three are morphologically similar: they bear certain dental specializations of Marsupialia (e.g., presence of labial postcingulid and “twinning” of hypoconulid and entoconid on lower molars), but are plesiomorphic with respect to most or all Late Cretaceous marsupials in other features (e.g., relatively lingual position of conules, lack of stylar cusps C or D on upper molars). Compared to Late Cretaceous (Cenomanian– Maastrichtian) assemblages of North America, the marsupials of the Mussentuchit local fauna are rare and low in morphologic and taxonomic diversity. Biogeographic origin of Marsupialia and their antiquity in North America remain unknown. However, patterns of diversification and differentiation suggest that the taxa from the Cedar Mountain Formation lie near the base of North America's Cretaceous marsupial radiation.
The Abanico (= Coya-Machalí) Formation of the Chilean Andes Cordillera continues to yield beautifully preserved fossil mammals of a variety of Cenozoic ages, with previously documented faunas spanning at least the Eocene to early Miocene. We describe here a new species of polydolopine marsupial, Polydolops mckennai, based on a skull preserving most of the upper dentition or alveoli. This, only the second polydolopid cranium known, provides important information on dental homologies and phylogeny for the group. The specimen on which this taxon is based is the first reported from new localities in the Río Cachapoal drainage. These localities appear to be early Oligocene or older in age (at least in part), expanding the geographic and temporal distribution of mammalian faunas from the Abanico Formation and bearing on models of the tectonic evolution of the central Chilean Andes.
Phylogenetic analyses based on morphological data support monophyly of Glires, but not a link between Glires and zalambdalestids. Glires are more closely related to several Tertiary taxa, including primates, leptictids, pseudictopids, anagalids, and macroscelideans. Phylogenetically constrained distributions of Glires support the conventional view for a post K-T boundary radiation of modern orders of placental mammals and disagree with conclusions of some molecular studies that divergence of Rodentia and Lagomorpha at infraordinal, ordinal, and certain supraordinal levels occurred in the Cretaceous. Current hypotheses employed to explain the discrepancy between the fossil record and the molecular clock hypothesis are not supported by phylogenetic and distributional evidence of Glires. There is no compelling evidence that close relatives of Glires were present in the Cretaceous.
To the extent now possible, I trace out what appear to be the adaptive changes involved in the origin of rodents. This requires, as a preliminary, a critical analysis of the existing evidence that bears on their phylogenetic relationship to other groups. Part of the paper provides such an analysis, from an unusual perspective. The evidence for a phylogenetic association of rodents and lagomorphs is weaker than is usually claimed but may nevertheless reflect reality. In particular, the precursors of rodents are not yet adequately identified. The initial adaptations of rodents were for the most part quite different from those of lagomorphs, despite their similar gnawing. There is evidence that the Myomorpha constitute the earliest diverging branch of extant rodents. Conapomorphy and spermativore are new terms.
Sixteen dental measurements in nineteen species of the extant rodent genus Dipodomys were examined to determine which techniques commonly used to identify the presence of multiple species in qualitatively homogeneous fossil samples are reliable. Each technique was tested using a simulation approach whereby samples created from a sympatric pooled-species group were compared with those of a single-species referent to determine the power of each technique. The type-I error rate of each method was assessed by comparing simulated pooled samples created from a single species to the same referent. Most techniques, including all range-based methods, performed poorly. Only the coefficient of variation using a 1% significance level and Levene's test of relative variation using a 2.5% significance level were reliable. The most useful dental variables were the widths of the upper and lower first and second molars.
The previously unknown preorbital part of the skull of Patriomanis americanus shows that by the end of the Eocene, this North American pangolin was already like all extant pangolin species in being completely edentulous. The skull, like the postcranial skeleton, has defining pangolin characters imposed on a morphology that is otherwise quite generalized and primitive. The absence of teeth in Patriomanis reinforces its close relationship to living pangolins, but also means that some morphologic information that might have shed light on the question of pangolin origins is absent.
Taxon ranges of larger mammalian carnivores can be grouped into seven temporal intervals during the later Cenozoic. These intervals are of varied duration and seem to correspond to periodic faunal reorganizations that accompanied the progressive climatic deterioration occurring from the late Eocene to the Pleistocene. Recent oxygen isotope records from deep-sea cores serve as proxy for the pattern of global climate during the Cenozoic and compare reasonably well with the large carnivore intervals. Intervals A, B, and the early part of C characterize a time of cooler global climate (δ18O: 1.3 to 3.0‰) following the early Eocene climatic optimum. The later part of Interval C, following the mid-Miocene climatic optimum, and Intervals D through F record a gradual climatic deterioration (δ18O: 2.0 to 3.8‰) from the mid-Miocene to early Pliocene. Interval G (δ18O: 3.8 to 5.0‰) corresponds to the extreme global cooling of the later Pliocene and Pleistocene. Glacioeustatic decline in sea level during these intervals probably made possible the entrance of migrant Eurasian carnivores and other mammals into the New World via the Bering route. The periodic emergence of this land bridge and the effect of the climatic oscillations of the later Cenozoic on the mammalian fauna appear responsible for the faunal shifts.
Herein I describe new felid material from the early Miocene, Ulaan Tologoi locality of Mongolia. A dentary fragment and a metapodial are the first large felid fossils to be recovered from the early Miocene of Asia. Both specimens are referred to the genus Pseudaelurus. Comparisons of these Asian specimens to previously described European, Asian, and North American species provide insights into the size and form of this cat. I review the Asian literature on early felids and discuss possible causes for fossil felid scarcity in the early Miocene of Asia.
Four humeri of Oligoscalops are described from the early Oligocene Hsanda Gol Formation of Central Mongolia, extending the known range of Proscalopidae from North America to Asia. Several characters support allocation of the humeri to Proscalopidae, including a prominent deltoid process that is situated on the middle of the humeral shaft and a partial fusion of the medial epicondyle and teres tubercle. Like those of North American Oligoscalops, the Mongolian humeri are small in size and have a partially, but not completely, fused teres tubercle and medial epicondyle. Several hypotheses to explain the occurrence of Oligoscalops in Asia are discussed. Although none of the hypotheses are convincingly supported by existing data, efforts to determine the sister-group of Proscalopidae may yield insights into its biogeographic history.
The basicranial and posterior cranial anatomy of the extinct suborder Toxodontia (order Notoungulata) is described using representatives from the five constituent families, Isotemnidae, Homalodotheriidae, Leontiniidae, Notohippidae, and Toxodontidae. New traits of intratympanic anatomy in toxodontians are identified. Based on observations presented here, some previous anatomical interpretations are clarified or corrected. The morphology of the bulla does not imply a compound bony origin; it is apparently comprised solely of ectotympanic bone. Additionally, previous osteological evidence offered to support the presence of an internal carotid artery could not be confirmed, leaving open the question of the source of intracranial blood supply.
Moropus merriami Holland and Peterson (1914), an early Barstovian schizotheriine chalicothere from North America, is rediagnosed and redescribed on the basis of additional material. While originally recognized from the Virgin Valley and High Rock Canyon local faunas of northwest Nevada, M. merriami can also be identified from the Lower Snake Creek fauna preserved in the Olcott Formation of northwest Nebraska. It represents a derived species of Moropus in which the astragalus and metatarsals have become relatively broad and short. The large claw associated with digit II of the manus is laterally compressed, and proximal and middle phalanges of digit II of the pes are uniformly fused. In northwest Nebraska, M. merriami is the early Barstovian faunal replacement for the dome-skulled chalicothere Tylocephalonyx skinneri, which is found in the Sheep Creek Formation. The early Barstovian appearance on the Great Plains of a species best known from the Great Basin and Columbia Plateau is a significant event at a time when specific-level faunal differences between these regions were pronounced.
A revised nomenclature for the description of fossil horse teeth is proposed. Wherever possible, names used exclusively by horse paleontologists are abandoned in favor of terms that enjoy wide usage by most mammalian paleontologists. Each of the names adopted is defined in terms of the three-dimensional structure represented.
Body size is of fundamental importance in understanding macroevolutionary patterns, both for extant taxa and for those with a fossil record. In this paper we describe four different kinds of body-size evolution: autapomorphic giantism, autapomorphic nanism, phyletic giantism, and phyletic nanism. The terms giantism and nanism are preferred here rather than the frequently, although incorrectly used equivalents, gigantism and dwarfism, respectively. We assert that without a known phylogeny, it is difficult or impossible to differentiate these four different kinds of body-size evolution. Case examples are presented for two groups: varanid lizards (family Varanidae) and fossil horses (family Equidae).
Previous hypotheses of body-size evolution within the Varanidae suggested that there were several cladogenic events in which some groups and isolated species became large. The most recent phylogeny of Varanidae based on mtDNA suggests otherwise. Mapping the known total body lengths onto the phylogeny indicates that varanids were already getting large early in their evolutionary history, with the crown group, Odatria, becoming secondarily small on mainland Australia. Although hypothesized as a giant island varanid, the komodo dragon (Varanus komodoensis) is discovered to be nested within a clade in which the basalmost taxon (V. salvadorii), also endemic to an island, reaches body lengths similar to those of the komodo dragon. Review of the Varanidae suggests that caution should be taken when characterizing taxa as island giants/dwarfs without first reviewing a phylogeny.
Fossil horses (family Equidae) are frequently cited in the literature, as well as depicted in museums, as prime examples of Cope's rule, i.e., a gradual trend toward body-size increase over time. Several recent parsimony analyses have resolved many of the phylogenetic interrelationships of North American fossil horses and have elucidated their patterns of body-size evolution. In light of these new analyses, there is no evidence for Cope's rule in fossil horses. In fact, the evolution of large body size occurred multiple times in fossil horses and exemplifies autapomorphic giantism. Body-size decrease, oftentimes considered the exception to Cope's rule, is actually widespread within multiple clades of fossil horses and is characterized by both autapomorphic and phyletic nanism.
The result of our analysis suggests that studies of body-size evolution must be intimately tied to a phylogeny before distinct patterns, if any, can be discerned. Cope's rule is not applicable to the two case examples presented herein, calling into question the most frequently cited mode of body size evolution.
Mentored by Don Savage at the University of California, Berkeley, in the 1950s, Malcolm C. McKenna was instrumental in bringing about a revolutionary change in dating the North American mammalian time scale. In 1973, he became involved with the revision of the Eocene part of the Wood et al. (1941) land mammal “ages”. Finally published in 1987 (Krishtalka et al., 1987), this revision laid the foundation for our modern understanding of Eocene mammalian stratigraphy. McKenna was, and still is, one of the most interdisciplinary of mammalian paleontologists, constantly synthesizing disparate data sources and integrating new developments (such as K-Ar dating and magnetic stratigraphy) into the poorly understood Cenozoic chronostratigraphy of North America. Through his work, and that of his students and several other Berkeley-trained paleontologists, the North American mammalian time scale has been radically revised, so that many events can now be dated to the nearest 100,000 years and reliably correlated to the Lyellian epochs based in Europe and to the global time scale.