Phalangeal morphology of the Paromomyidae (?Primates,Plesiadapiformes): The evidence for gliding behavior reconsidered

A comparative morphometric analysis of isolated proximal and intermediate phalanges attributed to the paromomyids Ignacius graybullianus and Phenacolemur simonsi was undertaken to test the hypothesis that these fossil phalanges exhibit evidence of a dermopteran-like interdigital patagium. Linear dimensions were collected for the fossil phalanges and a comparative sample of associated proximal and intermediate phalanges representing extant tree squirrels, tree shrews, dermopterans (colugos), gliding rodents and marsupials, and prosimian primates. Quantitative data indicate that the proximal and intermediate phalanges of paromomyids are most similar in their overall shape to those of the dermopteran Cynocephalus. The proximal phalanges of paromomyids and colugos possess well-developed flexor sheath ridges and broad, high shafts, whereas the intermediate phalanges of these taxa are most similar to one another in their trochlear morphology. Discriminant analysis indicates that all of the paromomyid intermediate phalanges resemble those from colugo toes more so than those from colugo fingers. Moreover, the relative length and midshaft proportions of both the proximal and intermediate phalanges of paromomyids closely resemble those of several squirrels that lack an interdigital patagium. The following conclusions are drawn from this study: 1) paromomyids share a number of derived phalangeal features with modern dermopterans that may be indicative of a phylogenetic relationship between them, 2) existing intermediate phalanges of paromomyids are inconsistent with the “mitten gliding” hypothesis because they do not possess the distinctive length and midshaft proportions characteristic of colugo manual intermediate phalanges, and 3) paromomyids share with colugos and the scaly-tailed squirrel Anomalurus several aspects of phalangeal morphology functionally related to frequent vertical clinging and climbing on large-diameter arboreal supports. Am J Phys Anthropol 109:397–413, 1999. © 1999 Wiley-Liss, Inc.     

Primate origins: evolutionary change in digital ray patterning and segmentation

This study presents evidence that the first primates share with extant lemurs, tarsiers, and anthropoids hand proportions unlike those of their close relatives, the tree shrews (Scandentia), colugos (Dermoptera), and plesiadapiforms. Specifically, early primates as well as modern strepsirhines and haplorhines have relatively short metacarpals and long proximal phalanges giving them a grasping, prehensile hand. Limb development was studied in the primate Microcebus murinus and a comparative sample of rodents, artiodactyls, and marsupials to investigate the role of embryonic patterning in the morphogenesis and evolution of primate hand proportions. Comparative analysis shows that the derived finger proportions of primates are generated during the early phases of digital ray patterning and segmentation, when the interzone cells marking the presumptive metacarpo- and interphalangeal joints first appear. Interspecific variation in relative digit and metapodial proportions therefore has high developmental penetrance; that is, adult differences are observed at early ontogenetic stages. The paleontological, comparative, and developmental data are therefore consistent with the hypothesis that the early Cenozoic origin of primates involved an evolutionary change in digital ray pattern formation ultimately yielding a grasping, prehensile hand.     

The head and neck muscles of the Philippine colugo (Dermoptera: Cynocephalus volans), with a comparison to tree‐shrews,primates, and other mammals

The colugos, or flying lemurs (Dermoptera), are arboreal gliding mammals that are commonly grouped with tree‐shrews (Scandentia) and Primates in the superorder Euarchonta. However, little is known about the head and neck muscles of these gliding mammals. This raises difficulties for the discussion of not only the functional morphology and evolution of colugos, but also the origin, evolution, functional morphology, and phylogenetic relationships of the Euarchonta as a whole, and thus also of our own clade, the Primates. In this work, I describe the head and neck muscles of the colugo Cynocephalus volans, and compare these muscles with those of other mammals, either dissected by me or described in the literature. My observations and comparisons indicate that, with respect to the number of muscles, the plesiomorphic condition for euarchontans as well as for primates is more similar to that found in extant tree‐shrews than in extant colugos. This is because various muscles that were probably plesiomorphically present in the euarchontan and primate clades, as, e.g., the stylohyoideus, mandibulo‐auricularis, cleido‐occipitalis, omohyoideus, and sternohyoideus, are not present as independent elements in extant colugos. These observations and comparisons also indicate that various laryngeal and facial muscles that are present in modern humans were absent in the last common ancestor of extant primates. J. Morphol., 2009. © 2008 Wiley‐Liss, Inc.     

Cranial anatomy of the Paleocene plesiadapiform Carpolestes simpsoni (Mammalia, Primates) using ultra high-resolution X-ray computed tomography, and the relationships of plesiadapiforms to Euprimates

Central to issues surrounding the origin of euprimates, affinities of Paleocene Carpolestidae have been controversial. Carpolestids have been classified as plesiadapoid primates, tarsiiform euprimates, dermopterans, or the sister taxon of euprimates to the exclusion of other plesiadapiforms, based exclusively on dental or postcranial data. Newly discovered crania of Carpolestes simpsoni from the latest Paleocene of the Clarks Fork Basin, Wyoming, are the first described for the family Carpolestidae. The two best preserved skulls were studied using ultra high-resolution X-ray computed tomography. Comparison of these specimens to those of other stem primates (Plesiadapiformes) demonstrates that the diversity of cranial morphology in this group is greater than previously thought. Carpolestes differs from euprimates and is similar to other plesiadapiforms (Ignacius and Plesiadapis) in lacking a postorbital bar and having a relatively long rostrum. Carpolestes is similar to fossil euprimates and Plesiadapis in having a bullar morphology consistent with a petrosal origin, and differs from Ignacius, in which the bulla is composed of the entotympanic. Carpolestes differs from primitive euprimates and all other known plesiadapiforms in possessing a two-chambered auditory bulla, similar to that of modern Tarsius. However, Carpolestes had an internal carotid artery (ICA) that took a transpromontorial route from a posteromedially positioned posterior carotid foramen (pcf), unlike Tarsius, in which this artery takes a perbullar route from an anterolaterally positioned pcf. Carpolestes has clear grooves on the promontorium for both the promontorial and stapedial arteries, indicating that it had an unreduced internal carotid circulation, similar to that of early euprimates. Carpolestes differs from primitive euprimates and some specimens of Ignacius in not having bony tubes surrounding the branches of the ICA. Cladistic analysis of cranial data fails to support a close relationship of Carpolestidae to either tarsiiform euprimates or extant Dermoptera, but suggests a close relationship between Carpolestidae, Plesiadapidae, and Euprimates.     

A resampling approach and implications for estimating the phalangeal index from unassociated hand bones in fossil primates

Primate fossil assemblages often have metacarpals and phalanges from which functional/behavioral interpretations may be inferred. For example, intrinsic hand proportions can indicate hand function and substrate use. But, estimates of intrinsic hand proportions from unassociated hand elements can be imperfect due to digit misattribution. Although isolated metacarpals can be identified to a specific digit, phalanges are difficult to assign to a specific ray. We used a resampling approach to evaluate how estimates of intrinsic hand proportions are affected by such uncertainty. First, the phalangeal index—intermediate phalanx length plus proximal phalanx length divided by metacarpal length—for the third digit was calculated for associated specimens of terrestrial, semiterrestrial, and arboreal taxa. We then used resampling procedures to generate distributions of “composite digits” based on resampled ratios in which phalanges from the second, fourth, and fifth rays, and from different individuals, were chosen randomly. Results confirm that the phalangeal index for associated third digits significantly discriminates groups. We also found that resampled ratios had significantly lower means, indicating that using composite digits is prone to systematic underestimation. Resampled ratios also generated distributions with greater variance around the means that obscured distinctions between groups, although significant differences between the most arboreal and terrestrial taxa are maintained. We conclude that using unassociated phalanges to calculate a phalangeal index is prone to sampling bias. Nevertheless, a resampling approach has the potential to inform estimates of hand proportions for fossil taxa, provided that the comparative sample is constrained to mimic the fossil composition. Am J Phys Anthropol 151:280–289, 2013. © 2013 Wiley Periodicals, Inc.     

Hominoid phalanges from the middle Miocene site of Paşalar, Turkey

Eleven proximal and ten intermediate partial or complete hominoid phalanges have been recovered from the middle Miocene site of Pa?alar in Turkey. Based on species representation at Pa?alar, it is likely that most or all of the phalanges belong to Griphopithecus alpani rather than Kenyapithecus kizili, but both species may be represented. All of the complete or nearly complete phalanges appear to be manual, so comparisons to extant and other fossil primate species were limited to manual phalanges. Comparisons were made to extant hominoid and cercopithecoid primate genera expressing a variety of positional repertoires and varying degrees of arboreality and terrestriality. The comparisons consisted of a series of bivariate indices derived from previous publications on Miocene catarrhine phalangeal morphology. The proximal phalanges have dorsally expanded proximal articular surfaces, which is characteristic of cercopithecoids and most other Miocene hominoids, and indicates that the predominant positional behaviors involved pronograde quadrupedalism. Among the extant primates, many of the proximal and intermediate phalangeal indices clearly distinguish more habitually terrestrial taxa from those that are predominantly arboreal, and especially from taxa that commonly engage in suspensory activities. For nearly every index, the values of the Pa?alar phalanges occupy an intermediate position-most similar to values for Pan and, to a lesser extent, Macaca-indicating a generalized morphology and probably the use of both arboreal and terrestrial substrates. At least some terrestrial activity is also compatible with reconstructions of the Pa?alar habitat. Most proximal and intermediate phalanges of other middle and late Miocene hominoids have similar index values to those of the Pa?alar specimens, revealing broadly similar manual phalangeal morphology among many Miocene hominoids.     

Primates: cladistic diagnosis and relationships

The morphological evidence for the phylogenetic relationships of euprimates, archaic primates, and related eutherian orders is reviewed following the methods of Hennigian phylogenetic systematics. Euprimates, the group including living primates and their closest common ancestor, is diagnosed by a suite of shared derived characters of the cranium and posteranium exhibiting relatively unique distributions among Eutheria. Plesiadapiformes, the group of archaic primates generally held to be the sister group to Euprimates, is not demonstrably monophyletic (with or without Microsyopidae). The Superorder Archonta (primates, tree shrews, bats, and colugos) is the only higher-level grouping including Euprimates that is based on uniquely derived morphological characters. Hypotheses of relationships within Archonta ally Euprimates with either tree shrews or some plesiadapiforms (paromomyids and plesiadapids), but the eurprimate-tree shrew clade receives more support from the distribution of derived characters among the taxa studied. Because the higher-level affinities of Euprimates are not well resolved, we advocate equating the Order Primates with the taxon Euprimates.     

辽宁西部早白垩世义县组一新的手盗龙类(英文)

我国辽西早白垩世热河群义县组和九佛堂组近年来产出大量恐龙化石 ,已知兽脚类恐龙包括 8属 1 0种 ,其中 6属 8种保存有原始羽毛或者羽毛结构。已经报道的属种均产自朝阳地区。 2 0 0 1年 ,中国科学院古脊椎动物与古人类研究所辽西野外考察队在邻近朝阳的锦州地区义县头台乡王家沟义县组下部采集到一件恐龙标本。这一标本保存了较为完整的肩带和前肢 ,在骨骼化石附近还保存了皮肤结构。通过研究对比 ,我们建立了手盗龙类的一个新属种 :长掌义县龙 (Yixianosauruslongimanusgen .etsp .nov .)。依据以下特征将长掌义县龙归入手盗龙类 :肩胛骨明显短于肱骨、肩臼窝的乌喙骨部分小、乌喙骨近四方形、尺骨向后弯曲以及挠骨细。长掌义县龙手部的相对长度以及手指各指节的相对比例不同于已知手盗龙类。原始兽脚类恐龙的手部一般短于肱骨 ;手盗龙手部加长 ,长于肱骨 ;原始鸟类的手部相对更长 ,但进步鸟类出现反转 ,手部次生变短。长掌义县龙手部的相对长度在非鸟兽脚类恐龙当中仅比原始祖鸟 (Protarchaeopteryx) (Jietal.,1 998)和树息龙 (Epidendrosaurus) (Zhangetal.,2 0 0 2 )短。次末端指节加长是兽脚类恐龙的一个进步特征 ,长掌义县龙具有这一特征。比如 ,长掌义县龙的手指指节Ⅱ 2长于掌骨Ⅱ ,在已知兽?     

Autopodial skeletal diversity in hystricognath rodents: Functional and phylogenetic aspects

Metapodials and phalanges of the second to fourth digital ray were measured for the hands and feet of 214 specimens belonging to 45 extant species of hystricognath rodents, encompassing members of all major clades of the radiation. Principal components analysis (PCA), the phalangeal index of the third digital ray in the hands and feet, and the relationship between second and fourth digital ray were used to investigate intrinsic autopodial proportions as well as to provide a base for comparisons between hands and feet. PCA separated cursorial Hystricognathi from arboreal ones, but lead to little distinction in other locomotory modes. Cursors have longer metapodials and shorter phalanges, particularly in their hind limb, while arboreal species have relatively longer manual and pedal phalanges. Terrestrial, scansorial, fossorial, and semi-aquatic species were not clearly distinguished, but there is a tendency towards elongated manual digits and relatively short feet in most fossorial species. Closely related species with similar locomotory habits tend to group together in PCA morphospace, and also have similar phalangeal indices. The results are in agreement with current hypotheses on locomotory adaptations of the hand and foot, and concur with many previous findings on autopodial proportions in arboreal, cursorial, and fossorial species. They also highlight the limited use of autopodial proportions for inferring systematic affinities. The lack of distinction in the majority of species is likely related to the lack of highly specialized locomotory types in Hystricognathi.     

A comparison of primate, carnivoran and rodent limb bone cross-sectional properties: are primates really unique?

The cross-sectional properties of mammalian limb bones provide an important source of information about their loading history and locomotor adaptations. It has been suggested, for instance, that the cross-sectional strength of primate limb bones differs from that of other mammals as a consequence of living in a complex arboreal environment (Kimura, 1991, 1995). In order to test this hypothesis more rigorously, we have investigated cross-sectional properties in samples of humeri and femora of 71 primate species, 30 carnivorans and 59 rodents. Primates differ from carnivorans and rodents in having limb bones with greater cross-sectional strength than mammals of similar mass. This might imply that primates have stronger bones than carnivorans and rodents. However, primates also have longer proximal limb bones than other mammals. When cross-sectional dimensions are regressed against bone length, primates appear to have more gracile bones than other mammals. These two seemingly contradictory findings can be reconciled by recognizing that most limb bones experience bending as a predominant loading regime. After regressing cross-sectional strength against the product of body mass and bone length, a product which should be proportional to the bending moments applied to the limb, primates are found to overlap considerably with carnivorans and rodents. Consequently, primate humeri and femora are similar to those of nonprimates in their resistance to bending. Comparisons between arboreal and terrestrial species within the orders show that the bones of arboreal carnivorans have greater cross-sectional properties than those of terrestrial carnivorans, thus supporting Kimura's general notion. However, no differences were found between arboreal and terrestrial rodents. Among primates, the only significant difference was in humeral bending rigidity, which is higher in the terrestrial species. In summary, arboreal and terrestrial species do not show consistent differences in long bone reinforcement, and Kimura's conclusions must be modified to take into account the interaction of bone length and cross-sectional geometry.     

Evidence at hand: Diversity, functional implications, and locomotor prediction in intrinsic hand proportions of diprotodontian marsupials

Knowledge about the diversity, locomotor adaptations, and evolution of the marsupial forelimb is limited, resulting in an underrepresentation of marsupials in comparative anatomical literature on mammalian forelimb anatomy. This study investigated hand proportions in the diverse marsupial order Diprotodontia. Fifty-two measurements of 95 specimens representing 47 species, as well as 6 non-diprotodontian specimens, were explored using principal components analysis (PCA). Bootstrapping was used to assess the reliability of the loadings. Phylogenetically independent contrasts and phylogenetic ANOVA were used to test for correlation with size and functional adaptation of forelimbs for locomotor habit, scored as arboreal vs. terrestrial. Analysis of first principal component (PC1) scores revealed significant differences between arboreal and terrestrial species, and was related to relative slenderness of their phalangeal elements. Both locomotor groups displayed allometry along PC1 scores, but with different intercepts such that PC1 discriminated between the two locomotor habits almost completely. PC2 separated some higher-level clades and burrowing species. Analysis of locomotor predictors commonly applied by palaeontologists indicates that ratios between proximal and intermediate phalanges were unsuitable as predictors of arboreality/terrestriality, but the phalangeal index was more effective. From PCA results, a phalangeal slenderness ratio was developed which proved to be a useful discriminator, suggesting that a single unallocated phalanx can be used for an impression of locomotor mode in fossils. Most Diprotodontia are laterally paraxonic or ectaxonic, with the exception of digging species whose hands are medially paraxonic. Our results complement those of studies on placental mammals, suggesting that the demands of arboreality, terrestriality, or frequent digging on intrinsic hand proportions are met with similar anatomical adaptations in marsupials.     

Evaluating the Phylogenetic Position of Chinese Tree Shrew （Tupaia belangeri chinensis） Based on Complete Mitochondrial Genome： Implication for Using Tree Shrew as an Alternative Experimental Animal to Primates in Biomedical Research

Tree shrew(Tupaia belangeri) is currently placed in Order Scandentia and has a wide distribution in Southeast Asia and Southwest China.Due to its unique characteristics,such as small body size,high brain-to-body mass ratio,short reproductive cycle and life span,and low-cost of maintenance,tree shrew has been proposed to be an alternative experimental animal to primates in biomedical research.However,there are some debates regarding the exact phylogenetic affinity of tree shrew to primates.In this study,we determined the mtDNA entire genomes of three Chinese tree shrews(T.belangeri chinensis) and one Malayan flying lemur(Galeopterus variegatus).Combined with the published data for species in Euarchonta,we intended to discern the phylogenetic relationship among representative species of Dermoptera,Scandentia and Primates.The mtDNA genomes of Chinese tree shrews and Malayan flying lemur shared similar gene organization and structure with those of other mammals.Phylogenetic analysis based on 12 concatenated mitochondrial proteinencoding genes revealed a closer relationship between species of Scandentia and Glires,whereas species of Dermoptera were clustered with Primates.This pattern was consistent with previously reported phylogeny based on mtDNA data,but differed from the one reconstructed on the basis of nuclear genes.Our result suggested that the matrilineal affinity of tree shrew to primates may not be as close as we had thought.The ongoing project for sequencing the entire genome of Chinese tree shrew will provide more information to clarify this important issue.     

The limb musculature of the Tupaiidae

The limb musculature of the tree shrews,Tupaia glis, Tupaia nicobarica, Lyonogale (Tupaia) tana, andUrogale everetti, is described and compared with published accounts. Although these species show preferences for different forest levels, i.e., arboreal (T. nicobarica), semiarboreal (T. glis), and terrestrial (L. tana, U. everetti) niches, their musculoskeletal contrasts present no consistent patterns attributable to locomotor adaptations. However, a re-examination of the myological evidence bearing on the much discussed question of the relationship of tree shrews to primates suggests that those features shared by these forms are retentions from their basal mammalian heritage, and supports the view that tree shrews possess a primitive rather than a progressive insectivoran limb morphology.     

The evolutionary radiation of plesiadapiforms

Very shortly after the disappearance of the non‐avian dinosaurs, the first mammals that had features similar to those of primates started appearing. These first primitive forms went on to spawn a rich diversity of plesiadapiforms, often referred to as archaic primates. Like many living primates, plesiadapiforms were small arboreal animals that generally ate fruit, insects, and, occasionally, leaves. However, this group lacked several diagnostic features of euprimates. They also had extraordinarily diverse specializations, represented in eleven families and more than 140 species, which, in some cases, were like nothing seen since in the primate order. Plesiadapiforms are known from all three Northern continents, with representatives that persisted until at least 37 million years ago. In this article we provide a summary of the incredible diversity of plesiadapiform morphology and adaptations, reviewing our knowledge of all eleven families. We also discuss the challenges that remain in our understanding of their ecology and evolution.     

New partial skeletons of Palaeocene Nyctitheriidae and evaluation of proposed euarchontan affinities

Small-bodied, insectivorous Nyctitheriidae are known in the Palaeogene fossil record almost exclusively from teeth and fragmentary jaws and have been referred to Eulipotyphla (shrews, moles and hedgehogs) based on dental similarities. By contrast, isolated postcrania attributed to the group suggest arboreality and a relationship to Euarchonta (primates, treeshrews and colugos). Cretaceous–Palaeocene adapisoriculid insectivores have also been proposed as early euarchontans based on postcranial similarities. We describe the first known dentally associated nyctitheriid auditory regions and postcrania, and use them to test the proposed relationship to Euarchonta with cladistic analyses of 415 dental, cranial and postcranial characteristics scored for 92 fossil and extant mammalian taxa. Although nyctitheriid postcrania share similarities with euarchontans likely related to arboreality, results of cladistic analyses suggest that nyctitheriids are closely related to Eulipotyphla. Adapisoriculidae is found to be outside of crown Placentalia. These results suggest that similarities in postcranial morphology among nyctitheriids, adapisoriculids and euarchontans represent separate instances of convergence or primitive retention of climbing capabilities.     

Allometric patterning in the limb skeleton of bats: Implications for the mechanics and energetics of powered flight

Allometric analysis was employed to compare linear dimensions of forelimb and hindlimb bones (humeri, radii, third and fifth metacarpals, third and fifth manual phalanges, femora, and tibiae) of 227 species of bats and 105 species of nonvolant mammals of varying degrees of phylogenetic affinity to bats. After accounting for body size, all forelimb bones are longer in bats than in nonvolant species, with the exception of humeri and radii of a few highly arboreal primates. Hindlimb bones are generally, but not uniformly, shorter in bats than in other mammals. For the humerus, radius, and metacarpals, midshaft diameters are greater in bats than in their comparably sized relatives. Proximal phalangeal midshaft diameters are statistically indistinguishable from those of other mammals, and distal phalanges show significantly reduced outer diameters. The pattern of relative reduction in wing bone diameters along the wing's proximodistal axis parallels the reduction in bone mineralization along the same axis, and a similar pattern of change in cortical thickness from the smallest wall thicknesses among mammals in the humerus and radius to the greatest wall thicknesses among mammals in the phalanges. The combination of altered cross-sectional geometry and mineralization appears significantly to reduce the mass moment of inertia of the bat wing relative to a theoretical condition in which elongated bones preserve primitive mammalian mineralization levels and patterns of scaling of long bone diameters. This intercorrelated suite of skeletal specializations may significantly reduce the inertial power of flight, contributing significant energetic savings to the total energy budgets of the only flying mammals. J. Morphol. 234: 277–294, 1997. © 1997 Wiley-Liss, Inc.     

Substrate alters forelimb to hindlimb peak force ratios in primates

It is often claimed that the walking gaits of primates are unusual because, unlike most other mammals, primates appear to have higher vertical peak ground reaction forces on their hindlimbs than on their forelimbs. Many researchers have argued that this pattern of ground reaction force distribution is part of a general adaptation to arboreal locomotion. This argument is frequently used to support models of primate locomotor evolution. Unfortunately, little is known about the force distribution patterns of primates walking on arboreal supports, nor do we completely understand the mechanisms that regulate weight distribution in primates. We collected vertical peak force data for seven species of primates walking quadrupedally on instrumented terrestrial and arboreal supports. Our results show that, when walking on arboreal vs. terrestrial substrates, primates generally have lower vertical peak forces on both limbs but the difference is most extreme for the forelimb. We found that force reduction occurs primarily by decreasing forelimb and, to a lesser extent, hindlimb stiffness. As a result, on arboreal supports, primates experience significantly greater functional differentiation of the forelimb and hindlimb than on the ground. These data support long-standing theories that arboreal locomotion was a critical factor in the differentiation of the forelimbs and hindlimbs in primates. This change in functional role of the forelimb may have played a critical role in the origin of primates and facilitated the evolution of more specialized locomotor behaviors.     

The Late Permian herbivore Suminia and the early evolution of arboreality in terrestrial vertebrate ecosystems

Vertebrates have repeatedly filled and partitioned the terrestrial ecosystem, and have been able to occupy new, previously unexplored habitats throughout their history on land. The arboreal ecospace is particularly important in vertebrate evolution because it provides new food resources and protection from large ground-dwelling predators. We investigated the skeletal anatomy of the Late Permian (approx. 260 Ma) herbivorous synapsid Suminia getmanovi and performed a morphometric analysis of the phalangeal proportions of a great variety of extant and extinct terrestrial and arboreal tetrapods to discern locomotor function and habitat preference in fossil taxa, with special reference to Suminia. The postcranial anatomy of Suminia provides the earliest skeletal evidence for prehensile abilities and arboreality in vertebrates, as indicated by its elongate limbs, intrinsic phalangeal proportions, a divergent first digit and potentially prehensile tail. The morphometric analysis further suggests a differentiation between grasping and clinging morphotypes among arboreal vertebrates, the former displaying elongated proximal phalanges and the latter showing an elongation of the penultimate phalanges. The fossil assemblage that includes Suminia demonstrates that arboreality and resource partitioning occurred shortly after the initial establishment of the modern type of terrestrial vertebrate ecosystems, with a large number of primary consumers and few top predators.     

Aquatic Adaptation and Swimming Mode Inferred from Skeletal Proportions in the Miocene Desmostylian Desmostylus

Desmostylians are enigmatic, extinct, semiaquatic marine mammals that inhabited coastlines of the northern Pacific Rim during the late Oligocene through middle Miocene. Principal components analysis (PCA) of trunk and limb proportions provides a rational multivariate context for separating living semiaquatic mammals on three orthogonal axes: a size axis (PC-I), a degree of aquatic adaptation axis (PC-II), and a forelimb- versus hind-limb-dominated locomotion axis (PC-III). The necessary skeletal measurements are available for Desmostylus hesperus but not for other desmostylians. Among species similar in size to Desmostylus in the study set, the one most similarly proportioned is the polar bear. Projection of Desmostylus on PC-II shows it to have been more aquatic than a polar bear (indicated by its relatively short ilium and femur, combined with relatively long metapodals and phalanges). Projection of Desmostylus on PC-III suggests that its aquatic locomotion was even more forelimb-dominated than that of a bear (indicated by its relatively long metacarpal III and corresponding proximal phalanx, combined with a relatively short metatarsal III and corresponding proximal phalanx). Desmostylians were different from all living semiaquatic mammals, and desmostylians are properly classified in their own extinct order, but their skeletal proportions suggest that bears provide an appropriate baseline for imagining what desmostylians were like in life.