Search

In mammals, sexual size dimorphism often reflects the intensity of sexual selection, yet its connection to genomic evolution remains unexplored. Gene family size evolution can reflect shifts in the relative importance of different molecular functions. Here, we investigate the associate between brain development gene repertoire to sexual size dimorphism using 124 mammalian species. We reveal significant changes in gene family size associations with sexual size dimorphism. High levels of dimorphism correlate with an expansion of gene families enriched in olfactory sensory perception and a contraction of gene families associated with brain development functions, many of which exhibited particularly high expression in the human adult brain. These findings suggest a relationship between intense sexual selection and alterations in gene family size. These insights illustrate the complex interplay between sexual dimorphism, gene family size evolution, and their roles in mammalian brain development and function, offering a valuable understanding of mammalian genome evolution. Sexual size dimorphism in mammals, often linked to sexual selection, can impacts genome evolution. This study finds sexual dimorphism in body size is associated with expanded gene families for olfactory functions and contracted gene families for brain development. [ABSTRACT FROM AUTHOR]

Cancer is a disease that many multicellular organisms have faced for millions of years, and species have evolved various tumour suppression mechanisms to control oncogenesis. Although cancer occurs across the tree of life, cancer related mortality risks vary across mammalian orders, with Carnivorans particularly affected. Evolutionary theory predicts different selection pressures on genes associated with cancer progression and suppression, including oncogenes, tumour suppressor genes and immune genes. Therefore, we investigated the evolutionary history of cancer associated gene sequences across 384 mammalian taxa, to detect signatures of selection across categories of oncogenes (GRB2, FGL2 and CDC42), tumour suppressors (LITAF, Casp8 and BRCA2) and immune genes (IL2, CD274 and B2M). This approach allowed us to conduct a fine scale analysis of gene wide and site-specific signatures of selection across mammalian lineages under the lens of cancer susceptibility. Phylogenetic analyses revealed that for most species the evolution of cancer associated genes follows the species' evolution. The gene wide selection analyses revealed oncogenes being the most conserved, tumour suppressor and immune genes having similar amounts of episodic diversifying selection. Despite BRCA2's status as a key caretaker gene, episodic diversifying selection was detected across mammals. The site-specific selection analyses revealed that the two apoptosis associated domains of the Casp8 gene of bats (Chiroptera) are under opposing forces of selection (positive and negative respectively), highlighting the importance of site-specific selection analyses to understand the evolution of highly complex gene families. Our results highlighted the need to critically assess different types of selection pressure on cancer associated genes when investigating evolutionary adaptations to cancer across the tree of life. This study provides an extensive assessment of cancer associated genes in mammals with highly representative, and substantially large sample size for a comparative genomic analysis in the field and identifies various avenues for future research into the mechanisms of cancer resistance and susceptibility in mammals. [ABSTRACT FROM AUTHOR]

Modern views on the origin and early evolution of mammals are presented. The material accumulated by the author on the morphology of modern and fossil monotremes, marsupials, and placentals are used. Data on Mesozoic mammals, including those obtained in recent years, are summarized. A model of the mechanism of morphogenetic transformations during the evolutionary development of Mammalia is proposed. An overview of the main directions of the formation of mammals from the Late Triassic to the Cenozoic is given. [ABSTRACT FROM AUTHOR]

The genetic basis underlying adaptive physiological mechanisms has been extensively explored in mammals after colonizing the seas. However, independent lineages of aquatic mammals exhibit complex patterns of secondary colonization in freshwater environments. This change in habitat represents new osmotic challenges, and additional changes in key systems, such as the osmoregulatory system, are expected. Here, we studied the selective regime on coding and regulatory regions of 20 genes related to the osmoregulation system in strict aquatic mammals from independent evolutionary lineages, cetaceans, and sirenians, with representatives in marine and freshwater aquatic environments. We identified positive selection signals in genes encoding the protein vasopressin (AVP) in mammalian lineages with secondary colonization in the fluvial environment and in aquaporins for lineages inhabiting the marine and fluvial environments. A greater number of sites with positive selection signals were found for the dolphin species compared to the Amazonian manatee. Only the AQP5 and AVP genes showed selection signals in more than one independent lineage of these mammals. Furthermore, the vasopressin gene tree indicates greater similarity in river dolphin sequences despite the independence of their lineages based on the species tree. Patterns of distribution and enrichment of Transcription Factors in the promoter regions of target genes were analyzed and appear to be phylogenetically conserved among sister species. We found accelerated evolution signs in genes ACE, AQP1, AQP5, AQP7, AVP, NPP4, and NPR1 for the fluvial mammals. Together, these results allow a greater understanding of the molecular bases of the evolution of genes responsible for osmotic control in aquatic mammals. [ABSTRACT FROM AUTHOR]

Same-sex sexual behaviour has attracted the attention of many scientists working in disparate areas, from sociology and psychology to behavioural and evolutionary biology. Since it does not contribute directly to reproduction, same-sex sexual behaviour is considered an evolutionary conundrum. Here, using phylogenetic analyses, we explore the evolution of same-sex sexual behaviour in mammals. According to currently available data, this behaviour is not randomly distributed across mammal lineages, but tends to be particularly prevalent in some clades, especially primates. Ancestral reconstruction suggests that same-sex sexual behaviour may have evolved multiple times, with its appearance being a recent phenomenon in most mammalian lineages. Our phylogenetically informed analyses testing for associations between same-sex sexual behaviour and other species characteristics suggest that it may play an adaptive role in maintaining social relationships and mitigating conflict. There is still no consensus on the factors favouring the evolution of same-sex sexual behaviour in mammals. This study presents evidence that it is a widespread behaviour that has evolved repeatedly in mammals, and that may play an adaptive role in bonding and conflict resolution. [ABSTRACT FROM AUTHOR]

Tooth classes are an innovation that has contributed to the evolutionary success of mammals. However, our understanding of the mechanisms by which tooth classes diversified remain limited. We use the evolutionary radiation of noctilionoid bats to show how the tooth developmental program evolved during the adaptation to new diet types. Combining morphological, developmental and mathematical modeling approaches, we demonstrate that tooth classes develop through independent developmental cascades that deviate from classical models. We show that the diversification of tooth number and size is driven by jaw growth rate modulation, explaining the rapid gain/loss of teeth in this clade. Finally, we mathematically model the successive appearance of tooth buds, supporting the hypothesis that growth acts as a key driver of the evolution of tooth number and size. Our work reveal how growth, by tinkering with reaction/diffusion processes, drives the diversification of tooth classes and other repeated structure during adaptive radiations. Despite their key role in the evolution of mammals, the origin and diversification of tooth classes (incisors, canines, premolars and molars) remain relatively obscure. Here the authors use integrative approaches to explain the independent evolution and rapid diversification of two tooth classes, premolar and molars, in noctilionoid bats. [ABSTRACT FROM AUTHOR]

Aquaporins (AQPs) are integral membrane proteins responsible for water transport across cellular membranes in both prokaryotes and eukaryotes. A subfamily of AQPs, known as aquaglyceroporins (AQGPs), facilitate the transport of small solutes such as glycerol, water, and other solutes across cellular membranes. These proteins are involved in a variety of physiological processes, such as organogenesis, wound healing, and hydration. Although AQPs have been studied extensively in different species, their conservation patterns, phylogenetic relationships, and evolution in mammals remain unexplored. In the present study, 119 AQGP coding sequences from 31 mammalian species were analysed to identify conserved residues, gene organisation, and most importantly, the nature of AQGP gene selection. Repertoire analysis revealed the absence of AQP7, 9, and 10 genes in certain species of Primates, Rodentia, and Diprotodontia, although not all three genes were absent in a single species. Two Asparagine-Proline-Alanine (NPA) motifs located at the N- and C-terminal ends, aspartic acid (D) residues, and the ar/R region were conserved in AQP3, 9, and 10. Six exons encoding the functional MIP domain of AQGP genes were found to be conserved across mammalian species. Evolutionary analysis indicated signatures of positive selection in AQP7, 9, and 10 amongst different mammalian lineages. Furthermore, substitutions of certain amino acids located close to critical residues may alter AQGP functionality, which is crucial for substrate selectivity, pore formation, and transport efficiency required for the maintenance of homeostasis in different mammalian species. [ABSTRACT FROM AUTHOR]

In recent years, highly pathogenic avian influenza H5 subtype (HPAI H5) viruses have been prevalent around the world in both avian and mammalian species, causing serious economic losses to farmers. HPAI H5 infections of zoonotic origin also pose a threat to human health. Upon evaluating the global distribution of HPAI H5 viruses from 2019 to 2022, we found that the dominant strain of HPAI H5 rapidly changed from H5N8 to H5N1. A comparison of HA sequences from human- and avian-derived HPAI H5 viruses indicated high homology within the same subtype of viruses. Moreover, amino acid residues 137A, 192I, and 193R in the receptor-binding domain of HA1 were the key mutation sites for human infection in the current HPAI H5 subtype viruses. The recent rapid transmission of H5N1 HPAI in minks may result in the further evolution of the virus in mammals, thereby causing cross-species transmission to humans in the near future. This potential cross-species transmission calls for the development of an H5-specific influenza vaccine, as well as a universal influenza vaccine able to provide protection against a broad range of influenza strains. [ABSTRACT FROM AUTHOR]

The origin of embryo implantation in mammals ~148 million years ago was a dramatic shift in reproductive strategy, yet the molecular changes that established mammal implantation are largely unknown. Although progesterone receptor signalling predates the origin of mammals and is highly conserved in, and critical for, successful mammal pregnancy, it alone cannot explain the origin and subsequent diversity of implantation strategies throughout the placental mammal radiation. MiRNAs are known to be flexible and dynamic regulators with a well-established role in the pathophysiology of mammal placenta. We propose that a dynamic core microRNA (miRNA) network originated early in placental mammal evolution, responds to conserved mammal pregnancy cues (e.g. progesterone), and facilitates species-specific responses. Here we identify 13 miRNA gene families that arose at the origin of placental mammals and were subsequently retained in all descendent lineages. The expression of these miRNAs in response to early pregnancy molecules is regulated in a species-specific manner in endometrial epithelia of species with extreme implantation strategies (i.e. bovine and human). Furthermore, this set of miRNAs preferentially target proteins under positive selective pressure on the ancestral eutherian lineage. Discovery of this core embryo implantation toolkit and specifically adapted proteins helps explain the origin and evolution of implantation in mammals. Here 13 conserved miRNAs are identified that arose at the origin of placental mammals. Their expression is triggered by early pregnancy cues in a species-specific way, providing insights into the origin and evolution of implantation in mammals [ABSTRACT FROM AUTHOR]

The pattern of dental replacement in marsupial mammals has received much attention for its derived nature and potential relationship to the life history of the group. However, few species have been studied thoroughly, and little is known about the embryonic structures and their use in addressing issues of homology and dental evolution in general. We studied a developmental series of ten individuals of pouch young Caluromys philander to thoroughly document dental development with histological sections and 3D models of dental series. We report that the successor P3 arises from a lingual successional lamina from its predecessor dP3. The germs of vestigial, unerupted deciduous incisors and canines are present alongside their respective permanent successors. These discoveries demonstrate significant differences from the developmental patterns reported for Didelphis and Monodelphis and illustrate that an unsuspected diversity of dental ontogeny is not reflected in the adult pattern of mineralised, erupted or almost erupted teeth. [ABSTRACT FROM AUTHOR]

From the evolutionary point of view, the priority problem for an individual is not longevity, but adaptation to the environment associated with the need for survival, food supply, and reproduction. We see two main vectors in the evolution of mammals. One is a short lifespan and numerous offspring ensuring reproductive success (r-strategy). The other one is development of valuable skills in order compete successfully (K-strategy). Species with the K-strategy should develop and enhance specific systems (anti-aging programs) aimed at increasing the reliability and adaptability, including lifespan. These systems are signaling cascades that provide cell repair and antioxidant defense. Hence, any arbitrarily selected long-living species should be characterized by manifestation to a different extent of the longevity-favoring traits (e.g., body size, brain development, sociality, activity of body repair and antioxidant defense systems, resistance to xenobiotics and tumor formation, presence of neotenic traits). Hereafter, we will call a set of such traits as the gerontological success of a species. Longevity is not equivalent to the evolutionary or reproductive success. This difference between these phenomena reaches its peak in mammals due to the development of endothermy and cephalization associated with the cerebral cortex expansion, which leads to the upregulated production of oxidative radicals by the mitochondria (and, consequently, accelerated aging), increase in the number of non-dividing differentiated cells, accumulation of the age-related damage in these cells, and development of neurodegenerative diseases. The article presents mathematical indicators used to assess the predisposition to longevity in different species (including the standard mortality rate and basal metabolic rate, as well as their derivatives). The properties of the evolution of mammals (including the differences between modern mammals and their ancestral forms) are also discussed. [ABSTRACT FROM AUTHOR]

Life underground has constrained the evolution of subterranean mammals to maximize digging performance. However, the mechanisms modulating morphological change and development of fossorial adaptations in such taxa are still poorly known. We assessed the morpho-functional diversity and early postnatal development of fossorial adaptations (bone superstructures) in the appendicular system of the African mole-rats (Bathyergidae), a highly specialized subterranean rodent family. Although bathyergids can use claws or incisors for digging, all genera presented highly specialized bone superstructures associated with scratch-digging behavior. Surprisingly, Heterocephalus glaber differed substantially from other bathyergids, and from fossorial mammals by possessing a less specialized humerus, tibia and fibula. Our data suggest strong functional and developmental constraints driving the selection of limb specializations in most bathyergids, but more relaxed pressures acting on the limbs of H. glaber. A combination of historical, developmental and ecological factors in Heterocephalus are hypothesized to have played important roles in shaping its appendicular phenotype. Morphological and developmental analyses demonstrated that the naked mole-rats are the least anatomically specialized bathyergid for scratch-digging. Developmental, ecological and historical factors may be involved in such peculiar phenotype [ABSTRACT FROM AUTHOR]

The abundance of domesticable mammals in Eurasia facilitated its early transition from hunter–gatherer to agricultural economies, with dramatic consequences for human history. This paper empirically examines the origins of these biogeographical advantages and finds that the extinction of large mammals during the past 100,000 years was a decisive force in the evolution of mammal domestication. In Eurasia's domestication cradles, humans had sufficient incentives to continually practice herd management as a hunting strategy to prevent the depletion of their vital common resources. These strategies changed some targeted species and made them more receptive to human domination. The absence of these conditions (human incentive and animal receptivity) in other regions resulted in the paucity of domestication. The paper presents the most comprehensive empirical analysis of the origins of animal domestication and the roots of global inequalities to date and unearths a critical channel for the influence of deep history on comparative economic development. [ABSTRACT FROM AUTHOR]

Teeth act as tools for acquiring and processing food, thus holding a prominent role in vertebrate evolution. In mammals, dental-dietary adaptations rely on tooth complexity variations controlled by cusp number and pattern. Complexity increase through cusp addition has dominated the diversification of mammals. However, studies of Mammalia alone cannot reveal patterns of tooth complexity conserved throughout vertebrate evolution. Here, we use morphometric and phylogenetic comparative methods across fossil and extant squamates to show they also repeatedly evolved increasingly complex teeth, but with more flexibility than mammals. Since the Late Jurassic, multiple-cusped teeth evolved over 20 times independently from a single-cusped common ancestor. Squamates frequently lost cusps and evolved varied multiple-cusped morphologies at heterogeneous rates. Tooth complexity evolved in correlation with changes in plant consumption, resulting in several major increases in speciation. Complex teeth played a critical role in vertebrate evolution outside Mammalia, with squamates exemplifying a more labile system of dental-dietary evolution. Tooth morphology has provided many insights into the tempo and mode of dietary evolution in mammals. A study of fossil and extant squamates shows that this group also repeatedly evolved increasingly complex teeth with more flexibility than mammals, and that higher tooth complexity and herbivory likely led to higher speciation rates. [ABSTRACT FROM AUTHOR]

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, intraspecific relationships, and the level of genetic differentiation among its geographical distribution were examined. Sequences of the mitochondrial cytochrome c oxidase subunit 1 gene were used for the phylogenetic, demographic history, and genetic structure analysis. In addition, an ecological niche model was built and transferred to 6000 years ago in order to explore the current and past environmental suitability of the species. Results showed that P. yucatanicus was monophyletic and its phylogenetic relationships unresolved. Intraspecific analyses showed signatures of a scenario of demographic stability followed by population growth, and three genetic haplogroups were identified. Paleontological, paleoclimate, and the results presented here are useful to hypothesize that P. yucatanicus likely diverged in the Pleistocene and invaded the south of YP after the Last Glacial Period with the arrival of the current vegetation in the late Pleistocene—early-middle Holocene, and its demographic population was stable during the remaining Holocene epoch with slight growth at the late-middle Holocene resulting in the major precipitation changes that provided more plant coverage. [ABSTRACT FROM AUTHOR]

Anatomy of bat genital organs has been conventionally studied by gross and microscopic observations to date. Here, we employ both histological observation and diceCT (diffusible iodine-based contrast-enhanced computed tomography) to study the detailed three-dimensional morphological structure of the male genital organs in bats, using the greater horseshoe bat, Rhinolophus ferrumequinum. This is the first study to three-dimensionally describe the whole reproductive organs of bats in detail. Our highly resolved three-dimensional reconstruction reveals that the male organs of R. ferrumequinum consist of paired testes, epididymides, deferent ducts, and five accessory genital glands. The boundary between the ampullary and vesicular glands has been difficult to identify in previous observations, but our diceCT imaging allowed us to clearly differentiate the two. We found that the ampullary gland is located at the terminal part of the deferent ducts, and the vesicular gland lies distal to the ampullary glands. This species possesses a single and carrot-shaped urethral gland, which is not found in most chiropteran families. The presence of the urethral gland in this species and its secretions suggest that after copulation this species is capable of forming a vaginal plug, which can seal the female's vaginal orifice to block the entrance of spermatozoa from other males. The presence of the urethral gland and elongated epididymal tail and the fact that some individuals can terminate their hibernation and reactivate imply forced copulation on hibernating females can occur in R. ferrumequinum. [ABSTRACT FROM AUTHOR]

Previous studies have demonstrated the pliability and adaptability of mammalian mandibles in response to different ecological demands such as food availability. The dwarf gerbil Gerbillus nanus has a wide distribution in Asia in which it encounters varied environments. These varied environments can house different food resources and it would be adaptively advantageous for the opportunistic rodents to have mandibles best suited for the most prevalent food resource. Geometric morphometric analysis was used to test this hypothesis by examining mandibular variation in 436 G. nanus specimens sampled from 44 localities. Based on this sample, mandibular morphology seems to be highly conserved in this species, with both size and shape being non-significantly different between pairs of geographic groups (i.e., locality clusters) and ecoregions. Mandibular size and shape are both not strongly predicted by 48 examined environmental variables. Despite this, the most variable aspect of mandibular shape was associated with its caudal regions, spanning from the coronoid process to the ventral mandibular border. These are regions of temporalis and masseter muscle attachments and thus mandibular variation could be associated with differential (potentially plastic) masticatory adaptations. [ABSTRACT FROM AUTHOR]

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, unlike the majority of extant species. To further test this hypothesis, we investigate the relationship between variation in cranial and mandibular shape of extant and extinct macropodiforms and ecological factors such as diet, locomotion, and body mass using 3D geometric morphometric analysis of 42 living species and eight extinct species from two radiations (the extinct clade of Balbaridae and some early representatives of the extant Macropodidae. Dietary class (fungivore, browser, grazer, and mixed feeder) correlated strongly with variation in cranial shape (20–25% of variance explained). There was also significant association between cranial shape, and both locomotor mode and body mass. In a principal component analysis of shape variation for crania (including the shape of the molar row), Riversleigh macropodiforms cluster with extant folivorous browsers on principal components (PC) 1 and 3, providing support for previous interpretations of these species as browsing kangaroos. However, as a group and regardless of phylogenetic association, the shape centroid of extinct species differs significantly from that of extant species. Riversleigh macropodiforms cluster with regular hoppers or arboreal tree kangaroos, but this may be a result of the correlation between diet and locomotor mode in kangaroos. Their similarity to extant browsers supports previous interpretations of rainforest and woodland environments at Riversleigh during the early and middle Miocene, respectively. Procrustes ANOVA Analysis of the full shape dataset and diet also shows that diet accounts for a significant portion of variation; however, when phylogeny is taken into account these results become nonsignificant. In analyses of dentary shape, some balbarid species cluster with extant mixed feeders, although this may reflect phylogenetic differences rather than ecological signal. [ABSTRACT FROM AUTHOR]

The relationship between muscle architectural properties and hind foot drumming of African mole-rats has yet to be determined using established methodology. Therefore, the internal structure of 32 hind limb muscles was evaluated in two drumming and one non-drumming species of Bathyergidae. The muscle mass (MM), fascicle length (Lf), and angle of pennation were measured to calculate the physiological cross-sectional area (PCSA) as well as estimate the maximum isometric force of contraction (Fmax). The most significant differences for the various muscle architecture parameters analyzed in synergistic muscle groups and individual muscles were observed between the rapid drumming Georychus capensis and the non-drumming Cryptomys hottentotus natalensis. The PCSA values of the hip extensors, hip adductors, knee extensors, and knee flexors of G. capensis were significantly larger than that of C. h. natalensis. Additionally, the hip extensors and knee flexors of both the drumming species (G. capensis and Bathyergus suillus) were shown to be capable of higher power output compared to the non-drumming species, and the hip adductors of G. capensis capable of faster contraction. M. gracilis anticus may play a key role in facilitating hind foot drumming as it was the only muscle to be significantly different in G. capensis and C. h. natalensis for all three muscle architecture parameters analyzed. Furthermore, it features in the high shortening capacity quadrant of the functional space plot of both G. capensis and B. suillus but not the non-drumming C. h. natalensis. [ABSTRACT FROM AUTHOR]

Paramyine ischyromyids are one of the first ancestral rodent groups to appear in North America. Studying ecological indicators of these extinct animals enables us to better understand how they integrated into North American mammalian communities. In this study we reassess the locomotor behavior of a nearly complete skeleton of a paramyine, Paramys delicatus (AMNH FM 12506), using functional limb indices and living squirrels as extant analogues. We then used the results of the functional limb index study to select an appropriate locomotor group for body mass estimations of Paramys delicatus and other early North American (Wasatchian-Bridgerian) paramyines. This was done because body mass is strongly tied to locomotor patterns and more reliable body mass estimates can be generated from an extant sample that functionally resembles the fossils being studied. Functional limb indices were calculated for three locomotor groups (arboreal, semifossorial, and gliding) of living sciurids. Comparisons among arboreal, semifossorial, and gliding sciurids show that the functional indices related to mechanical advantage of muscles and limb robusticity enable distinction among locomotor groups; however, there is considerable overlap between arboreal and semifossorial taxa. Paramys delicatus was found to have generally greater mechanical advantages and limb robusticity than most living squirrels, including semifossorial taxa. As these traits are associated with semifossorial squirrels that frequently use scratch-digging, this suggests that Paramys delicatus and perhaps other early paramyines were likely proficient scratch-diggers. However, indices reflecting limb proportions of paramyines suggest that these early rodents may have used more hind limb dominated locomotion than do living squirrels. Body mass estimations for early paramyines were therefore derived from a semifossorial squirrel sample. Statistical comparisons suggest that many of the most reliable estimators for body mass in Paramys delicatus and other paramyines are those derived from humeral dimensions, with the most reliable estimate being humeral head superoinferior breadth. Using these estimators, individual body mass estimates of early paramyines range from 3391 to 4005 g for Paramys delicatus, 1137–1329 g for Paramys copei, 1291 g for Paramys taurus, and 3357 g for Notoparamys costilloi. All body mass estimations derived from postcranial elements are substantially larger than previously published estimates derived from the dentition, which may be because postcranial elements play a larger role in supporting body weight. [ABSTRACT FROM AUTHOR]

Dental and craniomandibular data have been predominantly used to infer relationships among mylodontid ground sloths. Recent studies indicate the osteology of the manus also provides useful data to test phylogenetic relationships in mylodontine mylodontids. Here we provide new comparative data from the study of the manus of a member of the Scelidotheriinae, Scelidotherium Owen, 1839, based on specimens from the Province of Córdoba that provide information on the variation and systematic relationships of the genus. The Scelidotherium material from the Province of Córdoba in central Argentina presents several morphological differences with material of the genus from northwestern Argentina. The manus of Scelidotherium shares several traits with Catonyx Ameghino, 1891, but not with Valgipes Gervais, 1874. These include: trapezoid with a sharp ridge on the articular surface for metacarpal II; magnum with at least half of articular surface for metacarpal II located on the dorsal half of the medial and distal aspects of the bone; metacarpal II with a notch on the axial border of its distal articular surface; and ungual process of the distal phalanx of the second digit markedly dorsopalmarly flattened. A phylogenetic analysis that includes osteological characters of the manus indicates that within the family Scelidotheriinae, Scelidotherium is more closely related to Catonyx than to Valgipes or Proscelidodon gracillimus Rovereto, 1914. [ABSTRACT FROM AUTHOR]

The Miocene-Pliocene (Turolian-Ruscinian) transition represents a fundamental interval in the evolution of Euro-Mediterranean paleocommunities. In fact, the paleoenvironmental changes connected with the end of the Messinian salinity crisis are reflected by a major renewal in mammal faunal assemblages. An important bioevent among terrestrial large mammals is the dispersal of the genus Sus, which replaced all other suid species during the Pliocene. Despite its possible paleoecological and biochronological relevance, correlations based on this bioevent are undermined by the supposed persistence of the late surviving late Miocene Propotamochoerus provincialis. However, a recent revision of the type material of this species revealed an admixture with remains of Sus strozzii, an early Pleistocene (Middle Villafranchian to Epivillafranchian) suid, questioning both the diagnosis and chronological range of P. provincialis. Here we review the late Miocene Suidae sample recovered from the Casino Basin (Tuscany, central Italy), whose taxonomic attribution has been controversial over the nearly 150 years since its discovery. Following a comparison with other Miocene, Pliocene, and Pleistocene Eurasian species, the Casino Suidae are assigned to P. provincialis and the species diagnosis is emended. Moreover, it is recognized that all the late Miocene (Turolian) European Propotamochoerus material belongs to P. provincialis and that there is no compelling evidence of the occurrence of this species beyond the Turolian-Ruscinian transition (MN13-MN14). [ABSTRACT FROM AUTHOR]

The caudal cranium and occipito-cervical region, although usually overlooked, are informative about the paleobiology of fossil mammals, allowing inquiry into vision and hearing abilities, as well as head and neck postures. Particularly for Pachyrukhinae, some related features remain unexplored. In this contribution, 22 specimens of Paedotherium and Tremacyllus were analyzed in a mainly qualitative and comparative framework. Pachyrukhines are characterized by having large orbits and hearing cavities, moderate to short necks with generalized morphologies, and S-shape postures. These features allow rejecting some types of specialized digging habits, and support the preference of open or low-humidity environments. Paedotherium typicum is distinguished by the presence of laterally oriented eyes, marked vaulted cranium and predominant short extensor and stabilizing neck muscles, and cervico-occipital-hyoid configurations suitable for ventro-flexed resting posture. These features indicate accentuated frontation and panoramic-vision, upward head postures enhancing substrate perception, and the resistance of impacts during leaping-cursorial locomotion. Conversely, P. bonaerense, and to lesser degree Tremacyllus spp., show less frontation and probably adopted more horizontal head postures. More particularly, stronger ventral and lateral neck and head flexors and extrinsic arm musculature are reconstructed for P. bonaerense, compatible with generalist or scratch-digging habits. Its smaller auditory cavities and stronger ear musculature, compared to the contemporary P. typicum and especially Tremacyllus spp., would indicate larger ears and microhabitat segregation. The integrative analysis proposed here and in the accompanying contribution aims to shed light on convergences with extant models, paleobiology, niche partitioning, and external appearance of the latest rodent-like ungulates. [ABSTRACT FROM AUTHOR]

Several recent studies have suggested past gene flow between the Przewalski's horse and modern domestic horse and questioned the wild origin of the Przewalski's horse. Mitochondrial DNA has placed representatives of the Przewalski's horse into three among the eighteen haplogroups detected from the modern horse. Of these, two haplogroups have so far been found exclusively in the Przewalski's horse, while the one shared with the domestic horse includes captive individuals that have uncertain pedigrees. We recently found five domestic horse individuals of North European horse breeds to carry a mitochondrial haplogroup that was previously confined only to the Przewalski's horse. These individuals were sequenced for 6039 bp of mitochondrial DNA and used, together with domestic and Przewalski's horse sequences presenting all horse haplogroups, to examine the phylogenetic relationships and to date the divergence time between Przewalski's and domestic horse clusters within this haplogroup. The divergence was dated to have likely occurred about 13,300–11,400 years ago, which coincides with the time of the Younger Dryas. [ABSTRACT FROM AUTHOR]

Inquiring into the paleoecology of extinct forms is always a challenge, particularly when the taxa under study correspond to derived ecomorphs of ancient and completely extinct clades. In this contribution, the configuration of the masticatory apparatus and associated features of the Neogene pachyrukhines Paedotherium and Tremacyllus are studied in a detailed, mainly qualitative, comparative analysis of 36 specimens. Tooth morphology and the reconstructed muscular configuration of pachyrukhines indicate an important mediolateral component during chewing, and predominant crushing over grinding, as well as anteroposterior movements for the coupling and action of stronger gnawing incisors. These actions are more compatible with hard and brittle or turgid fruit food consumption than specialized folivorous, and particularly grazing, habits. The infraorbital and palatal foramina morphology and other rostral features indicate increased touch sensibility for object recognition and are congruent with the presence of infoldings of the lips protecting the gingiva during gnawing on hard foods. Additionally, there was a morphological gradient between Tremacyllus and P. bonaerense, from high selection of relatively soft and small food items, to specialized hard item consumption and higher resistance for abrasion and masticatory efforts (e.g., in eventual association with digging habits), respectively. Paedotherium typicum presents intermediate characteristics, with incisors designed for better cropping action or poorer selectivity during feeding. This more profound understanding of the feeding habits of pachyrukhines further allows the suggestion of paleoecological factors that could have contributed to niche segregation between these long-term coexisting rodent-like taxa. [ABSTRACT FROM AUTHOR]

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 variation should follow a cline across different South American environments. We first detected a strong impact of allometry on skull shape variation especially in males of the three species that tend to show stronger bite force, which is thought to be related to sexual selection. The degree of sexual dimorphism varies in relation to environmental seasonality. The skull of the plastic species, D. albiventris, showed the strongest ecogeographical pattern, showing conformity to Bergmann's rule. In this species, size increase and shape changes are associated with colder climates and stronger bite force. Skulls of D. marsupialis are moderately impacted by climate, following productivity patterns of tropical regions associated with fruit availability. The most territorial species, D. aurita, has the strongest allometric effect and shows no clinal variation. Our results also support a degree of evolutionary constraint on the skull morphology of the three South American opossums. The black-eared opossums clade exhibits a weak (D. marsupialis) or nonexistent (D. aurita) association between skull morphology and climate. Skull shape changes of D. aurita are allometrically driven while those of the white-eared opossums clade (D. albiventris) vary in relation to the environment. [ABSTRACT FROM AUTHOR]

We provide detailed morphological description, including enamel microstructure, of the earliest known embrithopod mammals (Afrotheria, Paenungulata), Stylolophus minor and S. major, n. sp., recently discovered in the early Eocene of the Ouled Abdoun phosphate basin, Morocco. Stylolophus minor and S. major, n. sp., show close morphological affinity, and the enamel microstructure supports their congeneric status. Stylolophus major, which comes from an upper level (middle Ypresian) of the Ouled Abdoun phosphate series, has more derived features than S. minor in addition to a larger size. This argues that S. minor and S. major are chronospecies. This new mammal lineage recognized in the Ouled Abdoun phosphate series is characterized by a rapid size increase, as for the proboscideans and probably in correlation with early-middle Ypresian global climatic warming events. We investigated relationships of Stylolophus in a new cladistic analysis based on an extended and revised matrix that includes new enamel microstructural features studied in Stylolophus. Resulting MPTs recover 1) basal relationships of Stylolophus within the Embrithopoda; 2) sister-group relationship of the Embrithopoda to the crown Tethytheria (Proboscidea, Sirenia); and 3) the clades Tethytheria and Paenungulata. It supports in particular that the order Embrithopoda is a basal tethytherian offshoot that rapidly evolved and specialized in parallel to the splitting and early evolution of extant tethytherian orders. Stylolophus shows that the ancestral embrithopod morphotype was already well specialized in the early Eocene and quite distinctive with respect to other paenungulates (e.g., hyperdilambdodonty, lingual hypoconulid, cristid obliqua very lingual on the trigonid, small and lingual hypoconulid lobe on M3, large paranasal sinuses, concave palate), even with respect to their earliest representatives. Stylolophus minor was larger than the contemporary proboscidean Phosphatherium escuilliei. Together with the stem tethytherian relationship of the Embrithopoda, it supports an old origin of the order, at least early in the Paleocene. This relationship is also most consistent with the evolution of the embrithopod hyperdilambdodont pattern from the dilambdodont and selenodont ancestral morphotype of the paenungulates, which is known in early hyracoids but not in proboscideans and sirenians, which have reduced the ectoloph. The most specialized embrithopods evolved hyperdilambdodonty in a pseudolophodont state in parallel to the true lophodonty of crown tethytherians. The Ouled Abdoun embrithopods further help indeed to show that the early Tertiary herbivorous niches of the African island favored convergent evolution of the folivorous diet in several paenungulate and tethytherian clades. At higher scale, convergence of African and Laurasian "ungulates" is supported by enamel microstructure of Stylolophus. The early and basalmost embrithopods S. minor and S. major, n. sp., are new evidence of the Arabo-African origin of the order. [ABSTRACT FROM AUTHOR]

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 declining populations resulting from habitat loss, climate change, and their impacts on agriculture and disease. We collected dental metrics from the mandibular postcanine teeth of 101 pteropodid specimens spanning six species within the family to test three hypotheses: H1) dental metrics are significantly different across pteropodid species; H2) variation in pteropodid dental metrics is associated with variation in body size; and H3) variation in pteropodid dental proportions is associated with phylogenetic relatedness. We find that dental linear metrics vary significantly across pteropodids and are significantly associated with body size. In contrast, dental proportions of pteropodids reflect phylogenetic relationships. We propose that the combination of approaches for quantifying postcanine dental variation can elucidate and refine our understanding of the various selective forces that shaped the Pteropodidae radiation. [ABSTRACT FROM AUTHOR]

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 from other named odontocetes to propose a new genus and species. Phylogenetic analyses indicate it is a platanistoid of uncertain position within the group, and that it shares some homoplastic characters with physeteroids and ziphioids. Given the absence of defined alveoli and teeth and an inferred moderately short and wide rostrum, we interpreted this new species as most likely a capture suction feeder. Based on our phylogenetic hypothesis, the optimization of feeding strategies recovered raptorial feeding as the plesiomorphic method, and convergent evolution of capture suction feeders in at least four lineages. Platanistoids recorded all feeding strategies during the late Oligocene-early Miocene, although raptorial is the predominant method. This suggests a partitioning of the ecological niches in the early phases of platanistoid evolution, as well as a high diversification of feeding methods previously underestimated for this period. Thus, ecological adaptations have a strong evolutionary pressure in odontocete communities and should be further explored. [ABSTRACT FROM AUTHOR]

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, morpho-functional, and paleontological perspective and how high functional diversity evolved in the mammalian neck after the occurrence of meristic limitations. The fixed number of cervical vertebrae and the developmental modularity of the mammalian neck are closely linked to anterior Hox genes expression and strong developmental integration between the neck and other body regions. In addition, basic neck biomechanics promote morpho-functional modularity due to preferred motion axes in the cranio-cervical and cervico-thoracic junction. These developmental and biomechanical determinants result in the characteristic and highly conserved shape variation among the vertebrae that delimits morphological modules. The step-wise acquisition of these unique cervical traits can be traced in the fossil record. The increasing functional specialization of neck modules, however, did not evolve all at once but started much earlier in the upper than in the lower neck. Overall, the strongly conserved modularity in the mammalian neck represents an evolutionary trade-off between the meristic constraints and functional diversity. Although a morpho-functional partition of the neck is common among amniotes, the degree of modularity and the way neck disparity is realized is unique in mammals. [ABSTRACT FROM AUTHOR]

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 a comprehensive phylogenetic analysis showing that C. grattardi is the earliest (2.2–2.9 Ma) and most basal species of the genus. We also show that the lineages leading to the extant taxa C. dromedarius and C. bactrianus diverged much higher in the tree, suggesting a recent age for this divergence. A late divergence date between the extant species is consistent with the absence of any fossil forms that could be ancestral, or closely related, to any of the extant forms before the late Pleistocene, but stands in contrast to molecular estimates which place the divergence between the dromedary and the Bactrian camel between 8 and 4 million years ago. [ABSTRACT FROM AUTHOR]

Cytochrome c (cyt c) is widely used as a model protein to study (i) folding and stability aspects of the protein folding problem and (ii) structure–function relationship from the evolutionary point of view. Databases of cyts c now contain 285 cyt c sequences from different organisms. A sequence alignment of all these proteins with respect to horse cyt c led to several important conclusions. One of them is that Leu94 is always conserved in all 30 mammalian cyts c. It is known that mutation L94G of the wild type (WT) horse cyt c is destabilizing and mutant exists as molten globule under the native condition (buffer pH 6 and 25 °C). We have expressed and purified uniformly labeled (13C and 15N) and unlabeled WT horse cyt c and its L94G mutant. We report that labeling does not affect the thermodynamic stability of proteins. To support this conclusion, the secondary and tertiary structure of each protein in labeled and unlabeled forms was determined by conventional techniques (UV–Vis absorption and circular dichroism spectroscopy). [ABSTRACT FROM AUTHOR]

Jaw morphology is closely linked to both diet and biomechanical performance, and jaws are one of the most common Mesozoic mammal fossil elements. Knowledge of the dietary and functional diversity of early mammals informs on the ecological structure of palaeocommunities throughout the longest era of mammalian evolution: the Mesozoic. Here, we analyse how jaw shape and mechanical advantage of the masseter (MAM) and temporalis (MAT) muscles relate to diet in 70 extant and 45 extinct mammals spanning the Late Triassic-Late Cretaceous. In extant mammals, jaw shape discriminates well between dietary groups: insectivores have long jaws, carnivores intermediate to short jaws, and herbivores have short jaws. Insectivores have low MAM and MAT, carnivores have low MAM and high MAT, and herbivores have high MAM and MAT. These traits are also informative of diet among Mesozoic mammals (based on previous independent determinations of diet) and set the basis for future ecomorphological studies. Nuria Melisa Morales-García et al. analyze jaw shape and mechanical advantage of 70 small modern mammals and 45 Mesozoic mammals and find that these metrics can be used to distinguish dietary groups for most extant mammals, and to infer diet in Mesozoic taxa. [ABSTRACT FROM AUTHOR]

Chromosome structural change has long been considered important in the evolution of post-zygotic reproductive isolation. The premise that karyotypic variation can serve as a possible barrier to gene flow is founded on the expectation that heterozygotes for structurally distinct chromosomal forms would be partially sterile (negatively heterotic) or show reduced recombination. We report the outcome of a detailed comparative molecular cytogenetic study of three antelope species, genus Raphicerus, that have undergone a rapid radiation. The species are largely conserved with respect to their euchromatic regions but the X chromosomes, in marked contrast, show distinct patterns of heterochromatic amplification and localization of repeats that have occurred independently in each lineage. We argue a novel hypothesis that postulates that the expansion of heterochromatic blocks in the homogametic sex can, with certain conditions, contribute to post-zygotic isolation. i.e., female hybrid incompatibility, the converse of Haldane's rule. This is based on the expectation that hybrids incur a selective disadvantage due to impaired meiosis resulting from the meiotic checkpoint network's surveillance of the asymmetric expansions of heterochromatic blocks in the homogametic sex. Asynapsis of these heterochromatic regions would result in meiotic silencing of unsynapsed chromatin and, if this persists, germline apoptosis and female infertility. [ABSTRACT FROM AUTHOR]

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 dentition. Notable changes involved the P3, which reduced size and became indistinguishable from the canine and I2, and the P4, which became a robust tall-cusped tooth comparable to a molar. We test two hypotheses: (1) neutral evolution can explain the observed phenotypic differences in the lineage, and (2) P4 lost developmental association with P3 and became integrated with the molars. First, we calculate the rate of evolutionary differentiation, based on the ratio between inter- and intra-species variation in length and width of P3, P4, M1, and M2 teeth, between lineage segments and over the entire lineage. We test the second hypothesis by comparing bivariate correlations between teeth within individual lineage segments. As the lineage evolved, correlations between P3 and the molars diminished, whereas correlations between P4 and the molars increased. We found evidence of varying degrees of stabilizing selection in the lengths and widths of all cheek teeth and evidence of neutral evolution in the width of P4. These results support a trend towards P4 becoming integrated into the molar morphogenetic field, and demonstrates that morphological rates of evolution, and consequently the degree of selective pressures, vary through time and between teeth. [ABSTRACT FROM AUTHOR]

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 the geographic isolation of populations. Among the mega-diverse Rodentia group, the low species richness of the family Caviidae stands out. Here, we analyzed if the processes of climatic NC are related to the slow diversification observed in the Caviidae family. Locality data for 13 species and nine climatic variables were used to generate ecological niche models. Niche similarity was quantified using the Schoener D index and used to examine correlations between the times of species divergence and niche similarities, thus characterizing their niche occupation profiles (NOP). The NOP were subsequently used to perform phylogenetic niche reconstructions for these species. Niche models accurately described known distributions of species. The greatest niche overlap documented was between Kerodon rupestris and Galea spixii (0.86). The niche and species divergence times showed a negative correlation (beta = -0.013; p = 0.01). These results support the existence of NC, with phylogenetically closer species occupying similar niches, and emphasize the importance of NC in diversification processes at continental scales in a slowly diversifying group. [ABSTRACT FROM AUTHOR]

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 aculeatus, through contrast-enhanced computed tomography and gross dissection. Muscle architecture is a major determinant of muscle function and can indicate specialized muscle roles, such as the capacity for generating large forces (through large physiological cross-sectional area, PCSA) or working ranges (through long fascicle lengths). We hypothesized that some muscles would exhibit architectural specializations convergent with other fossorial and/or sprawling animals, and that other muscles would reflect the echidna's unusual anatomy and locomotor style. Instead, we found the shoulder and proximal forelimb muscles in echidna to have little variation in their architecture. The muscles generally had long fascicles and small-to-intermediate PCSAs, consistent with force production over a wide working range. Further, muscles did not show overt differences in architecture that, in therian mammals, have been linked to increased forelimb mobility and the transition from sprawling to parasagittal posture. Our measures of architectural disparity placed the echidna closer to the tegu lizard than other sprawling fossorial mammals (e.g., mole). The low architectural diversity found in the echidna's shoulder and proximal forelimb muscles is interpreted as a lack of functional specialization into distinct roles. We hope our study will contribute to greater understanding of monotreme anatomy and biomechanical function, and to the reconstruction of musculoskeletal evolution in mammals. [ABSTRACT FROM AUTHOR]

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 a pre-European settlement assemblage (12 species) with the extant one (nine species). We used linear morphometrics (16 cranial and ten mandibular measurements) to assess interspecific morphological variations of the masticatory apparatus in relation to dietary habits for each assemblage. Even though sigmodontines have a tendency towards omnivory, groups based on dietary preference only overlapped partially. Size was one of the main variables involved in niche segregation, and shape characteristics such as rostrum elongation or mandible robustness were linked to different diets. We found that a combination of dietary preference and size was associated with extinctions. The main morphospace change between the two assemblages was related to the local extinction of the three greater insectivores and the smallest graminivore, located towards the center of the assemblage's morphospace. An insectivore was incorporated, involving no significant changes in the general morphospace. Graminivores and larvivores were not affected. Our study sheds light on the causes of local extinctions of small mammals at the Humid Pampas, a phenomenon that had never been studied from an ecomorphological approach. [ABSTRACT FROM AUTHOR]

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 slow gait, as in extant kangaroos. Study of the correlation of morphology of the proximal humerus in a broad range of therian mammals shows that humeral morphology is indicative of the degree of weight-bearing on the forelimbs during locomotion, with terrestrial species being distinctly different from arboreal ones. Extant kangaroos have a proximal humeral morphology similar to extant scansorial (semi-arboreal) mammals, but sthenurine humeri resemble those of suspensory arboreal taxa, which rarely bear weight on their forelimbs, supporting the hypothesis that they used bipedal striding rather than quadrupedal locomotion at slow gaits. The humeral morphology of the enigmatic extinct "giant wallaby," Protemnodon, may be indicative of a greater extent of quadrupedal locomotion than in extant kangaroos. [ABSTRACT FROM AUTHOR]

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 history. We sequenced two mtDNA regions for 152 individuals from 45 sample sites located at the volcanic fields Sierra Chichinautzin and Sierra Nevada. We surveyed the genetic diversity, and reconstructed and dated an intraspecific phylogeny. The effective population size trough time was estimated, and an Ecological Niche Model was projected onto the past. Results showed a well-supported phylogeny with five monophyletic lineages with a north to south geographic pattern at Sierra Nevada, and east to west at Sierra Chichinautzin. Dating estimates indicated that those lineages might have started their diversification ca. 1.4 Ma, which agrees with the geological dating reported for the volcanic fields rising. We detected changes in demographic history and potential distribution, with a global population expansion during the Last Glacial Maximum and a retraction during the Last Interglacial period. The molecular evidence showed that the volcano rabbit had a dynamic evolutionary history molded by geological and climatic events during the Pleistocene. The volcanic events that shaped Sierra Chichinautzin and Sierra Nevada generated regions that allowed the colonization, isolation and posterior in-situ diversification of their populations. Additionally, the climatic fluctuations of the latest glacial-interglacial cycles promoted altitudinal populations shifts, with a sky-island dynamic that allowed their persistence. [ABSTRACT FROM AUTHOR]

Enamel microstructure of 34 species in eight odontocete families is described and categorized according to structural complexity (from no or prismless enamel to highly arranged enamel in decussating layers), then correlated with parameters of ecology, life history, and occlusal function. Overall, more complex dental structure in extant and extinct cetaceans is associated with smaller, more numerous teeth in taxa that bite or grasp smaller, harder prey with longer, narrower jaws and have more oral processing. Enamel complexity loosely correlates with mechanical properties, but measurement of compressive strength is complicated by the presence of cementum overlying or in place of crown enamel. Given the presence of Hunter-Schreger bands and other indices of high microstructural complexity in archaic cetaceans (with presumed plesiomorphic characters), the absence of complex enamel, as well as more generally of gross dental form, signals a loss of complexity in various cetacean lineages. Nonetheless, it is difficult to draw robust or reliable inferences regarding either cetacean phylogeny or dental function given the pattern of presumed loss of tooth complexity, and the confounding presence of numerous exceptions (taxa with complex teeth despite limited use, or with thin, weakly developed enamel and soft, simple teeth despite high occlusal function). Although retention of a complex feature implies its continued adaptive value, and thus selection for the underlying genetic and developmental bases for that complexity, loss of complexity can simply follow absence of function. Loss of complex traits presumably relates to accumulated mutations and economic efficiency, but unfolds with no distinct pattern of distribution. [ABSTRACT FROM AUTHOR]

In the transition from a terrestrial to an aquatic environment, sirenian marine mammals reduced and lost their hind limbs and developed a horizontal caudal fin, the main propulsive organ in extant sirenians. Quadrupedal forms are only known from the Eocene and are represented by three different clades: the amphibious "prorastomids," the aquatic quadrupedal protosirenids, and Sobrarbesiren cardieli, a four-legged sirenian from the middle Eocene of Spain, considered the sister taxon of the fully aquatic Dugongidae. This ecological shift from terrestrial to an aquatic environment was naturally associated with adaptations, among others, of the skeleton. However, sirenian hind limb bones have been poorly studied because of the scarce material available in the fossil record. Here, we describe in detail the hind limb bones of Sobrarbesiren, analyzing their functional morphology and comparing them with other basal sirenians and cetaceans, and with related terrestrial mammals such as proboscideans and hyracoids. The hind limbs of Sobrarbesiren were capable of a great variety of movements. Based on the presence of a strong sacroiliac articulation, we propose that it swam by dorsoventral pelvic undulation combined with pelvic paddling analogous to extant otters and the "prorastomid" Pezosiren. We also conduct the first microanatomical analysis of hind limb bones of an Eocene sirenian. Data reveal extreme inner compactness in the Sobrarbesiren innominate and femur, with the first description of osteosclerosis in an amniote innominate combined with the highest degree of osteosclerosis observed in amniote femora. The results confirm that the microanatomical changes precede the external morphological changes in such ecological transitions. The process of adaptation of sirenians to an aquatic life was thus a more complex process than previously thought. [ABSTRACT FROM AUTHOR]

Five multituberculate species have been reported to date from the upper Lower Cretaceous (Aptian–Albian) Shahai and Fuxin formations in Liaoning Province, northeastern China. We herein describe an additional species of eobaatarid multituberculate from the Fuxin Formation, Dolichoprion lii, gen. et sp. nov., with a long (relative to height) crown of the fourth lower premolar, which is unique among eobaatarids. We also describe the upper dentition possibly referable to another eobaatarid genus previously known only from lower jaws, Liaobaatar, based on a newly discovered specimen. The new species is the sixth multituberculate (and the fourth eobaatarid) species described from the Shahai and Fuxin formations. These species suggest that multituberculates, especially eobaatarids, were taxonomically quite diverse in the mammalian fauna of East Asia at that time. [ABSTRACT FROM AUTHOR]

New material of Agriotherium from the late Hemphillian (~6 Ma) Quiburis Formation in Arizona, North America is reported. These specimens represent a new species, Agriotherium hendeyi, sp. nov., of small size and with a bucco-lingually narrow lower dentition distinguishing it from North American "Agriotherium" schneideri as well as the genotype and other Old World species of Agriotherium. Strikingly, the m1 metaconid-entoconid complex of the new species exhibits a morphologically transitional state between the pattern observed in Indarctos (three cusps) and the typical Agriotherium pattern (two cusps). Together with a review of the variation in A. africanum, a geometric morphometric analysis permits identification and discussion of a proposed transformation pathway from the Indarctos pattern to the Agriotherium pattern. It is shown that the two cusps in the metaconid-entoconid complex in Agriotherium correspond to the two entoconids in Indarctos, whereas the ancestral metaconid is reduced or lost in Agriotherium. From a developmental perspective, the metaconid fused to the anterior entoconid as a result of the shortening of the talonid, rather than via replacement of the metaconid by a posterior shift of the entoconid, presumably under selective pressure towards a more typically hypercarnivorous tooth morphology and carnivorous diet. [ABSTRACT FROM AUTHOR]

Xenarthra is unique in having striking features in the axial skeleton, usually very different from the rest of the eutherian clades. Some of these features are widely spread among the members of the group (e.g., the presence of xenarthrales in most cingulates and all pilosans, and the synsacrum with sacroischial union to the pelvis in almost all xenarthrans) and others are restricted to some taxa (e.g., deviated number of cervical vertebrae in Bradypus and Choloepus). In this study, we aim to explore the great diversity of vertebral elements composing the xenarthran synsacrum within a phylogenetic framework. Vertebral counts of the adult synsacrum was obtained from almost all extant genera, with the exception of Calyptophractus, and several fossils. The modal number of vertebrae from the adult synsacrum was mapped onto a composite phylogeny of Xenarthra. The ancestral number of synsacrals for Xenarthra was recovered as ambiguous, although one of the optimizations recorded a number of six synsacrals, probably three iliac and three post-iliac vertebrae. The clade Cingulata is characterized by a high number of vertebrae forming the synsacrum (eight synsacrals), which is fused to the ischium through the tip of the transverse processes of the most posterior vertebrae. In pilosans, the ancestral number of synsacral vertebrae seems to be lower, probably formed by five or six vertebrae, and the union with the ischium is achieved through the base of the transverse processes of the most posterior vertebrae. Two exceptions stand out, one involving the extant suspensory sloths and Megalocnus, and the other involving a family of ground sloths, the Mylodontidae. A probable relationship of the synsacral number in the different taxa to the lifestyles is discussed. [ABSTRACT FROM AUTHOR]

New dental and dentary fossils collected in the Upper Cretaceous La Colonia Formation in central Patagonia provide new evidence on the morphology, feeding ecology, and relationships of the enigmatic mammal Reigitherium. The newly discovered specimens described here include elements of the upper dentition and several partial dentaries, elucidating fundamental questions of serial homology and postcanine dental formula (four premolars and three molars). This new evidence supports a nested position of Reigitherium within the advanced meridiolestidan clade Mesungulatoidea. Apomorphic features of the upper and lower molariform elements include intense enamel crenulation circumscribed within the primary trigon and trigonid, elevated cingulids, and the neomorphic appearance of cusps/cuspulids, all of which increase overall crown complexity. A Dental Topography Analysis comparing Reigitherium and its sister taxon Peligrotherium to Cretaceous and Cenozoic therians demonstrates functional similarity between the mesungulatoids and South American marsupial taxa that succeed them in the small-to medium-sized herbivore niche during the Paleocene. Previous taxonomic attributions of Reigitherium are discussed and comparisons with other meridiolestidans highlight the remarkable radiation of this group in the Cretaceous of South America. [ABSTRACT FROM AUTHOR]

Identifying the genomic changes that underlie phenotypic adaptations is a key challenge in evolutionary biology and genomics. Loss of protein-coding genes is one type of genomic change with the potential to affect phenotypic evolution. Here, we develop a genomics approach to accurately detect gene losses and investigate their importance for adaptive evolution in mammals. We discover a number of gene losses that likely contributed to morphological, physiological, and metabolic adaptations in aquatic and flying mammals. These gene losses shed light on possible molecular and cellular mechanisms that underlie these adaptive phenotypes. In addition, we show that gene loss events that occur as a consequence of relaxed selection following adaptation provide novel insights into species’ biology. Our results suggest that gene loss is an evolutionary mechanism for adaptation that may be more widespread than previously anticipated. Hence, investigating gene losses has great potential to reveal the genomic basis underlying macroevolutionary changes. [ABSTRACT FROM AUTHOR]

Programmed (adaptive) aging refers to the idea that mammals, including humans and other complex organisms, have evolved mechanisms that purposely cause or allow senescence or otherwise internally limit their lifespans in order to obtain an evolutionary advantage. Until recently, programmed aging had been thought to be theoretically impossible because of the mechanics of the evolution process. However, there is now substantial theoretical and empirical support for the existence of programmed aging in mammals. Therefore, a comprehensive approach to medical research on aging and age-related diseases must consider programmed aging mechanisms and the detailed nature of such mechanisms is of major importance. Theories of externally regulated programmed aging suggest that in mammals and other complex organisms, genetically specified senescence mechanisms detect local or temporary external conditions that affect the optimal lifespan for a species population and can adjust the lifespans of individual members in response. This article describes why lifespan regulation in response to external conditions adds to the evolutionary advantage produced by programmed aging and why a specific externally regulated programmed aging mechanism provides the best match to empirical evidence on mammal senescence. [ABSTRACT FROM AUTHOR]

Programmed aging theories contend that evolved biological mechanisms purposely limit internally determined lifespans in mammals and are ultimately responsible for most instances of highly age-related diseases and conditions. Until recently, the existence of programmed aging mechanisms was considered theoretically impossible because it directly conflicted with Darwin's survival-of-the-fittest evolutionary mechanics concept as widely taught and generally understood. However, subsequent discoveries, especially in genetics, have exposed issues with some details of Darwin's theory that affect the mechanics of the evolution process and strongly suggest that programmed aging mechanisms in humans and other mammals can and did evolve, and more generally, that a trait that benefits a population can evolve even if, like senescence, it is adverse to individual members of the population. Evolvability theories contend that organisms can possess evolved design characteristics (traits) that affect their ability to evolve, and further, that a trait that increases a population's ability to evolve (increases evolvability) can be acquired and retained even if it is adverse in traditional individual fitness terms. Programmed aging theories based on evolvability contend that internally limiting lifespan in a species-specific manner creates an evolvability advantage that results in the evolution and retention of senescence. This issue is critical to medical research because the different theories lead to dramatically different concepts regarding the nature of biological mechanisms behind highly age-related diseases and conditions. [ABSTRACT FROM AUTHOR]

Episodes of rapid faunal turnover in the fossil record are often used to examine processes driving macroevolutionary changes, such as competitive exclusion. The sudden appearance in the earliest Eocene of North America of artiodactyls and perissodactyls, and subsequent decline of endemic 'condylarths' constitutes such an episode. It has been suggested that the specializations for high speed locomotion (cursoriality) that are present in artiodactyls and perissodactyls were key innovations of these orders accounting for their success in the Eocene and onwards. A quantitative geometric morphometric analysis of distal femoral articular morphology was used to examine changes in locomotor specializations in North American ungulates across the Paleocene-Eocene boundary. 'Condylarths' were found to have displayed a broad range of locomotor adaptions, including cursoriality. The early Eocene had the broadest disparity in terms of taxonomic and locomotor contributions to morphological diversity. Changes in locomotor variety were associated with the disappearance of arboreal taxa, primarily 'condylarths.' The initial impact of artiodactyls and perissodactyls in North America on existing locomotor diversity was limited and does not support a competitive exclusion hypothesis. [ABSTRACT FROM AUTHOR]