Three species of sexually-dimorphic opossums are broadly distributed across South America: the habitat generalist Didelphis albiventris, the Atlantic forest-dweller D. aurita, and the Amazonian forest-dweller D. marsupialis. We used 2D geometric morphometrics to quantify skull size and shape variation in the three opossum species and test the hypothesis that degrees of sexual dimorphism and morphological

Commerson’s dolphin (Cephalorhynchus commersonii), Peale’s dolphin (Lagenorhynchus australis), dusky dolphin (Lagenorhynchus obscurus), and hourglass dolphin (Lagenorhynchus cruciger) are closely related species occurring in the Southern Hemisphere. Even though they are partially sympatric, they have evolved towards diverse foraging strategies, prey, and habitat preferences. Size variation occurs both

Rodents and carnivorans constitute two diverse clades with variable life habits. To analyze the common ecomorphological aspects of their limbs in relation to their different substrate uses, the shape of humerus and femur was explored using 3-D geometric morphometrics. The principal components and MANOVA analyses show that the shape of the humerus is similarly related to the substrate use and taxonomy

Lower Miocene outcrops from Patagonia (Gaiman Formation, Burdigalian) may reveal more clues for the yet unknown aspects for this period in the evolution of odontocetes. Here, we present the first toothless platanistoid dolphin from the lower Miocene of Patagonia, Dolgopolis kinchikafiforo, gen. et sp. nov. The specimen includes an incomplete skull, with no mandibles or earbones, but sufficiently different

Variation in the dentition yields insight into the evolutionary history of Mammalia. However, to date, there has been limited research on the dental variation in Pteropodidae, a family of bats found throughout sub-Saharan Africa, Southeast Asia, and Oceania. Most species are large, diurnal, non-echolocating, and eat fruit or nectar. Pteropodids are of significant concern in conservation due to rapidly

The adaptations for a particular locomotor type (e.g., fossorial or saltatorial) could affect limb bone morphology throughout ontogeny. We explore how the measurements of the forelimbs and functional indices change along the postnatal ontogeny of 92 specimens of sigmodontines belonging to four genera (Akodon, Eligmodontia, Oligoryzomys, and Oxymycterus) with different locomotor types (ambulatory,

Understanding feeding ecology of extinct kangaroos is fundamental to understanding the evolution of kangaroos and the Australia paleoenvironment during the Oligo-Miocene. Comparisons with extant species have suggested that the macropodiforms of the Oligo/Miocene (kangaroos and allies) from the Riversleigh World Heritage Area, northern Australia, were predominantly folivorous browsers or fungivores

Caviomorphs are a mainly South American rodent clade with high taxonomic and ecomorphological diversity. In this study, we combine geometric morphometric, functional, ancestral reconstruction, and macroevolutionary analyses to quantify the magnitude, direction, and rates of shape diversification of the caviomorph mandible, and to explore the morpho-functional implications and potential ecological catalysts

The mammalian neck adopts a variety of postures during daily life and generates numerous head trajectories. Despite its functional diversity, the neck is constrained to seven cervical vertebrae in (almost) all mammals. Given this low number, an unexpectedly high degree of modularity of the mammalian neck has more recently been uncovered. This work aims to review neck modularity in mammals from a developmental

The Yucatan Peninsula (YP) is a biotic province located in southeastern Mexico, delimited mainly by climatic variables. One endemic species of the YP is the Yucatan deer mouse Peromyscus yucatanicus. It is considered a member of the P. mexicanus species group, but some morphological characters and habitat preferences separate it from them. Herein, the DNA barcoding identification of P. yucatanicus

The late Miocene was a period of great radiation for the subfamily Caninae in North America. During this time, the early taxa of the two tribes of this subfamily, Vulpini and Canini, arose. Among them, Eucyon is one of the most important elements of the latest Miocene-Pliocene Canidae guild of both North America and Eurasia as they rapidly spread worldwide. The earliest member of the genus Canis, Canis

The dormice (Gliridae) represent a relatively small family of rodents, but exhibit considerable variation in their cranial anatomy. The skull morphology of almost all genera of dormice was described from osteological specimens in an earlier publication. However, the rare desert dormouse, Selevinia betpakdalaensis, was only assessed using previous descriptions and photographic images, resulting in difficulties

Understanding the interplay between morphological integration and modularity is considered an important topic in the study of the evolution of the form of complex structures. The mandible is a complex structure that can be shaped by diverse factors such as ontogeny, ecology, and evolutionary history. In canids, this is particularly interesting because they have a large diversity in feeding behavior

The dynamics of species diversification have attracted significant scientific attention in recent decades. Many lineages tend to maintain their niche characteristics over evolutionary time, a phenomenon known as phylogenetic niche conservatism (NC), which can slow the processes of ecological speciation by diversification selection. NC can, however, promote speciation through neutral evolution, favoring

Xenarthra, one of the major clades of placentals, comprises two different lineages (sloths and anteaters, and armadillos) with extant representatives showing strongly different morphologies and life habits. Sloths are arboreal herbivores, anteaters are insectivores with digging/climbing abilities, and armadillos are terrestrial diggers with varied diets. The ulna is one of the forelimb elements that

South American cervids have a relatively recent evolutionary history in the Neotropics. Present taxonomical richness includes six genera and 17 species grouped in at least two clades, Blastocerina and Odocoileina. With few exceptions, functional morphology or ecomorphological approaches have not been rigorously applied to the masticatory apparatus of Neotropical deer. In order to understand the relationship

Monotremes are a group of egg-laying mammals, possessing a mosaic of ancestral and derived anatomical features. Despite much interest in monotremes from phylogenetic, morphological, and ecological perspectives, they have been the subject of relatively few biomechanical studies. In this study, we examined shoulder and proximal forelimb muscle anatomy and architecture in the short-beaked echidna, Tachyglossus

The anthropic effect associated with worldwide European settlements over the last 500 years has caused dramatic environmental changes, modified regional patterns of biodiversity, and often led to local or complete extinctions. The sigmodontine rodents of Bahía Samborombón (Humid Pampas, central-eastern Argentina) constitute a good case study: a late Holocene archaeological site allowed us to compare

Understanding species distributions and the variation of assemblage structure in time and space are fundamental goals of biogeography and ecology. Here, we use an ecological niche modeling and macroecological approach in order to assess whether constraints patterns in carnivoran richness and composition structures in replicated assemblages through time and space should reflect environmental filtering

The Stagodontidae include the largest metatherians known from the Cretaceous of North America. Of the recognized species of the stagodontid genus Eodelphis, E. cutleri is larger and has a more robust dentary, more inflated premolars, and third premolars specialized for crushing, as opposed to the more gracile E. browni. These differences have led to the hypothesis that an E. cutleri-like ancestor gave

Different living mammals have developed a carnivorous habit (e.g., Carnivora, Dasyuridae, Thylacinidae, some Didelphidae). They exhibit different specializations for carnivory; however, they share some characters such as a carnassial molar. Previous studies have correlated the shape of molars with diet using morphometric indices or surface scans. In this work, we used 3D geometric morphometrics to

Despite its clear functional role in hock (ankle) plantarflexion, the bovid calcaneus has been understudied with respect to the functional constraints imposed by locomotion in differing habitats, the allometric influence of inter-specific body size differences, and phylogenetic signal. This study uses a comparative sample of extant bovid species to shed light on the evolution of bovid calcaneal morphology

We describe new dental remains of the genus Iberictis (Carnivora: Mustelidae) from the late early Miocene of the Iberian Peninsula. The new fossils of Iberictis azanzae from Artesilla (16.5–16.3 Ma, MN4; Calatayud-Teruel Basin, Zaragoza, Spain) add important morphological information about this species. Material from another species, Iberictis buloti, is described from els Casots (16.5–16.3 Ma, MN4;

A new Paleogene metatherian from locality IAA 1/90, Marambio (Seymour) Island in the Antarctic Peninsula is described. Pujatodon ektopos, gen. et sp. nov., is recognized on the basis of a tiny lower left molar recovered from early Eocene (late Ypresian) levels of the Cucullaea I Allomember, La Meseta Formation. The tooth is characterized by its small size, bunoid aspect, short trigonid with closely

The genus Ctenomys comprises approximately 70 recognized living species of subterranean rodents endemic to South America. Phylogenetic studies to date, based on mitochondrial DNA data, place 44 recognized species in eight species groups and provide evidence for a burst of speciation early in the history of the genus. Species from Argentina, Uruguay, Bolivia, and southern Brazil are well studied at

The Sparassodonta (Mammalia: Metatheria) were the principal group of carnivorous mammals in Cenozoic South America and an important component of this continent’s terrestrial predator guild for nearly 60 million years. However, knowledge of the evolutionary history of this group is biased towards species larger than 1.5 kg from extra-tropical latitudes. Here, we describe a new, small sparassodont from

The internal cranial morphology of the terrestrial sloth Glossotherium robustum is described here based on a neurocranium from the late Pleistocene of the Pampean region of Buenos Aires, northeastern Argentina. The first published data on the morphology of the brain cavity of this species date back to the latest nineteenth century. The novel techniques of CT scanning and digital reconstructions enable

Bats are atypical small mammals. Size is crucial for bats because it affects most aerodynamic variables and several key echolocation parameters. In turn, scaling relationships of both flight and echolocation have been suggested to constrain bat body size evolution. Previous studies have found a large phylogenetic effect and the inclusion of early Eocene fossil bats contributed to recover idiosyncratic

Neotropical cricetid rodents of the subfamily Sigmodontinae constitute an incredibly diverse and ubiquitous clade of mammals in South America. In spite of recent advances in sigmodontine systematics, a variable collection of genera from eastern South America with no clear tribal affiliations and well-differentiated morphologies has been pervasive in most classification attempts, being generally listed

The diversification of anatomical structures with functional importance during the branching process of a clade is a widely studied phenomenon in evolutionary biology. In recent years, there is a growing interest in the study of the inner ear, a structure associated with hearing, locomotion, and indirectly, with body size. These studies have been particularly important in primates. The platyrrhine

Processes such as climate fluctuations together with recent volcanism have driven the diversification and local persistence of biodiversity within the Mexican highlands. We reconstruct the phylogeographic pattern and historical demography of the volcano rabbit, Romerolagus diazi, an endemic lagomorph in central Mexico, to elucidate the effect of the climate-volcanism interaction on its evolutionary

Although didelphid marsupials are considered to have a conservative body shape, they show a considerable amount of size variation. They also have different diets (from frugivore to animalivore), but none of the species are specialized. Didelphid marsupials also have a certain degree of specialization in vertical habitat use, from ground-dwellers to canopy-dwellers. Several authors have shown in other

Sthenurine kangaroos, extinct “giant kangaroos” known predominantly from the Plio-Pleistocene, have been proposed to have used bipedal striding as a mode of locomotion, based on the morphology of their hind limbs. However, sthenurine forelimb morphology has not been considered in this context, and has important bearing as to whether these kangaroos employed quadrupedal or pentapedal locomotion as a

The Tetonius-Pseudotetonius (T-P) transition is an often-cited example of phyletic gradualism, but rates of evolution and the roles of neutral and adaptive processes across this lineage remain unclear. Linking Tetonius and Pseudotetonius, two omomyid primates, are a series of stratigraphic and morphologic intermediates revealing trends suggestive of a functional and developmental reorganization of

The Old World fossil record of the family Camelidae is patchy, but a new partial cranium and some other remains of Camelus grattardi from the Mille-Logya Project area in the Afar, Ethiopia, greatly increase the fossil record of the genus in Africa. These new data – together with analysis of unpublished and recently published material from other sites, and reappraisal of poorly known taxa – allow for

Recently, dental microwear analysis has been successfully employed to xenarthran teeth. Here, we present new data on use wear features on 16 molariforms of Orophodon hapaloides and Octodontotherium grande. These taxa count among the earliest sloths and are known from the Deseadan SALMA (late Oligocene). Modern phylogenetic analyses classify Octodontotherium and Orophodon within Mylodontoidea with whom

Eutherian mammals-placentals and their closest extinct relatives-underwent a major radiation following the end-Cretaceous extinction, during which they evolved disparate anatomy and established new terrestrial ecosystems. Much about the timing, pace, and causes of this radiation remain unclear, in large part because we still know very little about the anatomy, phylogenetic relationships, and biology

The skull of the polydolopimorphian marsupialiform Epidolops ameghinoi is described in detail for the first time, based on a single well-preserved cranium and associated left and right dentaries plus additional craniodental fragments, all from the early Eocene (53-50 million year old) Itaboraí fauna in southeastern Brazil. Notable craniodental features of E. ameghinoi include absence of a masseteric

The biotic and geologic dynamics of the Great American Biotic Interchange are reviewed and revised. Information on the Marine Isotope Stage chronology, sea level changes as well as Pliocene and Pleistocene vegetation changes in Central and northern South America add to a discussion of the role of climate in facilitating trans-isthmian exchanges. Trans-isthmian land mammal exchanges during the Pleistocene

PSEUDOCHEIRIDAE (MARSUPIALIA: Diprotodontia) is a family of endemic Australasian arboreal folivores, more commonly known as ringtail possums. Seventeen extant species are grouped into six genera (Pseudocheirus, Pseudochirulus, Hemibelideus, Petauroides, Pseudochirops, Petropseudes). Pseudochirops and Pseudochirulus are the only genera with representatives on New Guinea and surrounding western islands

We describe and discuss the morphology and functional anatomy of the thoracolumbar and sacrocaudal regions of the vertebral column of the late Miocene amphicyonid Magericyon anceps. These regions are essential for body support, and very relevant for locomotion and prey capture, and thus their study provides interesting insights on the paleobiology and biomechanics of this top predator. Magericyon anceps

“Sparassocynids” are small, carnivorously-adapted marsupials known from the late Miocene and Pliocene of South America, thought to be relatives of living didelphid opossums but of otherwise uncertain phylogenetic relationships. Here, we describe a nearly complete juvenile skull of the “sparassocynid” Sparassocynus derivatus, from the Pliocene (~5–3 million years old) Chapadmalal Formation, Argentina

Diversification and adaptive radiations are tied to evolvability, which in turn is linked to morphological integration. Tightly integrated structures typically evolve in unison, whereas loosely integrated structures evolve separately. Highly integrated structures are therefore thought to constrain evolutionary change by limiting morphological disparity. Mounting evidence suggests that high integration

Comparative morphometric study of recently recovered fossil elephant molars from Natodomeri, Kenya identifies them as belonging to Elephas jolensis and confirms the presence of this species in Members I and II of the Kibish Formation. Improved datation of these geological units constrains them between 205 and 130 ka. Elephas jolensis is also reported from localities in northern, northwestern, eastern

The sand cat, Felis margarita Loche, 1858, is a small desert cat with a fragmented distribution across the Sahara, Arabian Peninsula, and Central Asia. It is currently listed as Least Concern by the IUCN; however, its status in many countries is unknown. Sand cats are generally classified into four subspecies: F. m. margarita (North Africa and Sahara), F. m. harrisoni (Arabia), F. m. thinobia (Central

Chiroptera is the only group of mammals capable of powered flight. The mechanical basis of bat flight is well established, but evolution of its constituent aerodynamic variables remains poorly understood. Here, we determine the macroevolutionary patterns of traditional aerodynamic variables (wing loading, aspect ratio, tip shape index) in a comprehensive phylogeny of Chiroptera using an extensive dataset

As molecularly derived phylogenies have become more prominent in determining evolutionary relationships, researchers have developed multiple methods of time-calibration to estimate ages of speciation or dispersal events. These methods, however, do not always arrive at congruent node ages. Fossil evidence is one of the most common forms of calibration for phylogenies, but age estimates can vary greatly

Argyrolagus constitutes, both for its craniodental and postcranial anatomy, one of the most notably specialized South American Neogene metatherians. Differentiating it from any other South American mammal, bipedal jumping has been proposed for Argyrolagus, even though this hypothesis was not supported by morphofunctional studies. Here, we describe the postcranium of A. scaglai (from the Pliocene of

We describe here a new small bunodont metatherian from Priabonian deposits of the Geste Formation exposed in the Puna of Catamarca Province (Argentina). The material, an isolated right M2?, was recovered by screen-washing techniques and allows us to erect the new species Apeirodon sorianoi. The combination of diagnostic characters includes triangular occlusal pattern, bunoid, with an equally developed

In this contribution we describe a partial dentary with teeth and an astragalus referred to the ancient megatheriine Megathericulus patagonicus Ameghino, 1904 (Xenarthra, Tardigrada) recovered from the Collón Curá Formation (Miocene) at Chubut Province, Argentina. Referral of the new specimens is based on metric and morphological similarities with the holotype and specimens that have been referred

In mammals, the infraorbital canal provides a passage for the infraorbital ramus of the maxillary branch of the trigeminal nerve. The infraorbital nerve ensures tactile sensitivity of the upper teeth and face between the eye and upper lip and, more significantly, the innervation of mystacial vibrissae (whiskers). In contrast, most non-mammalian synapsids display a more “reptilian-like” ancestral condition

Diversification of animal vocalizations plays a key role in behavioral evolution and speciation. Vocal organ morphology represents an important source of acoustic variation, yet its small size, complex shape, and absence of homologous landmarks pose major challenges to comparative analyses. Here, we use a geometric morphometric approach based on geometrically homologous landmarks to quantify shape

Xenarthra (sloths, anteaters, and armadillos) are the quintessential South American mammals. Among the xenarthrans, sloths constitute the most diverse paleontologically with almost 100 fossil genera recorded. However, this abundant sloth fauna in the Americas became extinct around 10,000 years ago. Only six species belonging to two genera, Bradypus (four three-toed sloth species) and Choloepus (two

X-ray computed tomography of the cladotherian Henkelotherium guimarotae from the Kimmeridgian Guimarota coal mine (Portugal) adds new information on its postcranial skeleton. Contrary to earlier description, the humerus of Henkelotherium shows a plesiomorphic cladotherian condition similar to that seen in Dryolestes leiriensis in having individual radial and ulnar condyles on the anterior aspect of

The pigmentation patterns of many carnivorous mammals comprise contrasting white patches of hair in different parts of the body whose evolution remains largely misunderstood. Some felids (Felidae) exhibit conspicuous white spots on the posterior part of the ears, while the ear color of others is uniform. On the basis that ear movement in felids has a role in intraspecific communication and that color

Notoungulates are an extinct clade of South American mammals, comprising a large diversity of body sizes and skeletal morphologies, and including taxa with highly specialized dentitions. The evolutionary history of notoungulates is characterized by numerous dental convergences, such as continuous growth of both molars and incisors, which repeatedly occurred in late-diverging families to counter the

This study tests whether three species of fossorial, scratch-digging mammals – Dasypus novemcinctus, Ictidomys tridecemlineatus, and Taxidea taxus – show commonality in pelvic anatomies inferred to be adaptive for this behavior and, correspondingly, divergence in these anatomies from nonfossorial species. The fossorial and nonfossorial species are in the same superorder or family; the comparative sets

Tapirs have historically been considered as ecologically analogous to several groups of extinct perissodactyls based on dental and locomotor morphology. Here, we investigate comparative functional morphology between living tapirs and endemic Eocene European perissodactyls to ascertain whether tapirs represent viable analogues for locomotion in palaeotheres and lophiodontids. Forelimb bones from 20

The evolution of subterranean and fossorial rodents has been linked to the Neogene climatic shift to xeric conditions leading to open vegetation, like prairies and grasslands; most modern subterranean rodents occur in arid and open areas. Among South American spiny rats (family Echimyidae), the subfamily Euryzygomatomyinae includes both fossorial (Clyomys and Euryzygomatomys) and ambulatorial (Trinomys)

We have analyzed the internal structure of the brain of the microbiotherian marsupial Dromiciops gliroides and compared it with the brains of American and Australian marsupials. Dromiciops does not have a fasciculus aberrans, but does exhibit other features of brain structure that are similar to diprotodontid metatherians (e.g., lamination of the lateral geniculate nucleus of the dorsal thalamus).