Evolution in coyotes (Canis latrans) in response to the megafaunal extinctions

Living coyotes modify their behavior in the presence of larger carnivores, such as wolves. However, little is known about the effects of competitor presence or absence on morphological change in coyotes or wolves over long periods of time. We examined the evolution of coyotes and wolves through time from the late Pleistocene, during which many large carnivorous species coexisted as predators and competitors, to the Recent; this allowed us to investigate evolutionary changes in these species in response to climate change and megafaunal extinctions at the end of the Pleistocene. We measured postcranial skeletal morphologies of wolves (Canis lupus) and coyotes (C. latrans) from Pleistocene-aged tar deposits, as well as early, mid, and recent Holocene populations of both. We found few morphological differences between Pleistocene and Holocene wolf populations. Conversely, we found many differences in coyotes: Pleistocene coyotes were larger and more robust than Holocene populations. However, within 1,000 y of the megafaunal extinctions, coyotes are morphologically indistinguishable from modern populations. We cannot attribute these differences directly to climate change because modern coyotes do not follow Bergmann’s rule, which states body size increases with decreasing temperature. Instead, we suggest that Pleistocene coyotes may have been larger and more robust in response to larger competitors and a larger-bodied prey base. Although we cannot separate competition from predator-prey interactions, this study indicates that the effects of biotic interactions can be detected in the fossil record

Cryptic complexity in felid vertebral evolution: shape differentiation and allometry of the axial skeleton

Members of the mammalian family Felidae (extant and extinct cats) are grossly phenotypically similar, but display a 300-fold range in body size, from less than 1 kg to more than 300 kg. In addition to differences in body mass, felid species show dietary and locomotory specializations that correlate to skull and limb osteological measurements, such as shape or cross-sectional area. However, ecological correlates to the axial skeleton are yet untested. Here, we build on previous studies of the biomechanical and morphological evolution of the felid appendicular skeleton by conducting a quantitative analysis of morphology and allometry in the presacral vertebral column across extant cats. Our results demonstrate that vertebral columns of arboreal, scansorial and terrestrial felids significantly differ in morphology, specifically in the lumbar region, while no distinction based on dietary specialization was found. Body size significantly influences vertebral morphology, with clear regionalization of allometry along the vertebral column, suggesting that anterior (cervicals and thoracics) and posterior (lumbar) vertebrae may be independently subjected to distinct selection pressures

Long-Term Psychological Outcomes And Awareness Of Deficit In Persons With Traumatic Brain Injury And Their Significant Others: The Role Of Physiological And Neuroendocrine Reactivity To Stress

This study investigated the relationships between physiological/neuroendocrine reactivity to stress and long-term psychological outcomes among persons with TBI and their significant others. In addition, this study examined the potential moderating role of patient AOD in characterizing these relationships. The findings indicate that physiological stress reactivity predicts poor psychosocial functioning in survivors of TBI and their significant others. Chronic stress (reflected in high baseline values) and stress reactivity were generally adversely associated with psychological distress and life satisfaction. Among significant others of TBI survivors, this pattern was also observed for sense of caregiving mastery and burden. However, there were also some counterintuitive relationships that emerged as well. For instance, among TBI survivors, baseline systolic blood pressure was favourably associated with life satisfaction. Similarly, among significant others, baseline cortisol level was favourably associated with life satisfaction, psychological distress, and perceived caregiving burden. The construct of survivor awareness of deficits helped to elucidate this intriguing pattern of results. In general, and as predicted, stress responses were larger among survivors with intact awareness of their deficits and significant others of survivors with impaired awareness of their deficits than among survivors with impaired awareness and significant others of survivors with intact awareness of deficits. Moreover, counterintuitive findings were only observed among survivors with impaired awareness of deficits and their significant others

The scaling of postcranial muscles in cats (Felidae) I: forelimb, cervical, and thoracic muscles

The body masses of cats (Mammalia, Carnivora, Felidae) span a ~300‐fold range from the smallest to largest species. Despite this range, felid musculoskeletal anatomy remains remarkably conservative, including the maintenance of a crouched limb posture at unusually large sizes. The forelimbs in felids are important for body support and other aspects of locomotion, as well as climbing and prey capture, with the assistance of the vertebral (and hindlimb) muscles. Here, we examine the scaling of the anterior postcranial musculature across felids to assess scaling patterns between different species spanning the range of felid body sizes. The muscle architecture (lengths and masses of the muscle‐tendon unit components) for the forelimb, cervical and thoracic muscles was quantified to analyse how the muscles scale with body mass. Our results demonstrate that physiological cross‐sectional areas of the forelimb muscles scale positively with increasing body mass (i.e. becoming relatively larger). Many significantly allometric variables pertain to shoulder support, whereas the rest of the limb muscles become relatively weaker in larger felid species. However, when phylogenetic relationships were corrected for, most of these significant relationships disappeared, leaving no significantly allometric muscle metrics. The majority of cervical and thoracic muscle metrics are not significantly allometric, despite there being many allometric skeletal elements in these regions. When forelimb muscle data were considered in isolation or in combination with those of the vertebral muscles in principal components analyses and MANOVAs, there was no significant discrimination among species by either size or locomotory mode. Our results support the inference that larger felid species have relatively weaker anterior postcranial musculature compared with smaller species, due to an absence of significant positive allometry of forelimb or vertebral muscle architecture. This difference in strength is consistent with behavioural changes in larger felids, such as a reduction of maximal speed and other aspects of locomotor abilities

Measures of Relative Dentary Strength in Rancho La Brea Smilodon fatalis over Time

The late Pleistocene megafaunal extinction of approximately 12,000 years ago, included the demise of Smilodon fatalis, a hypercarnivore from the Rancho La Brea deposits, which has been studied across time by looking at different deposits or pits to determine morphological size and shape changes and trends during this time. To better understand functional aspects of these changes, this study focused on a measure of jaw strength over time, which can give an indication of morphological changes within the jaw that cannot be seen using surface morphometrics. By radiographing dentaries, cortical bone can be seen, which provides an estimate of resistance to bending forces while biting, and can be measured and used as an indicator of jaw strength. Measurements were taken at repeatable locations on the dentary of the depth of the cortical bone, and of a standardized measure of cortical bone, which allows for the comparison between different individuals. Specimens included those of five different pits ranging from about 37 Kybp to 13 Kybp (just before the extinction of S. fatalis). No significant difference was found in the depth of jaws at any of the measurement points from any of the pits. However, significant differences were found in both the actual thickness of cortical bone, and the standardized thickness of cortical bone at the lower P4 between pit 13 (which had the lowest amount of bone) and pit 61/67 (which had the highest). These conclusions support other studies that have shown that individuals in pit 13 were under physiological and perhaps dietary stress, which may be reflected in the deposition of cortical bone, while the opposite trend is seen in the individuals in pit 61/67. Our results further support findings suggesting Smilodon did not appear to be morphologically most vulnerable right before its extinction

The fossil record of phenotypic integration and modularity: A deep-time perspective on developmental and evolutionary dynamics

Variation is the raw material for natural selection, but the factors shaping variation are still poorly understood. Genetic and developmental interactions can direct variation, but there has been little synthesis of these effects with the extrinsic factors that can shape biodiversity over large scales. The study of phenotypic integration and modularity has the capacity to unify these aspects of evolutionary study by estimating genetic and developmental interactions through the quantitative analysis of morphology, allowing for combined assessment of intrinsic and extrinsic effects. Data from the fossil record in particular are central to our understanding of phenotypic integration and modularity because they provide the only information on deep-time developmental and evolutionary dynamics, including trends in trait relationships and their role in shaping organismal diversity. Here, we demonstrate the important perspective on phenotypic integration provided by the fossil record with a study of Smilodon fatalis (saber-toothed cats) and Canis dirus (dire wolves). We quantified temporal trends in size, variance, phenotypic integration, and direct developmental integration (fluctuating asymmetry) through 27,000 y of Late Pleistocene climate change. Both S. fatalis and C. dirus showed a gradual decrease in magnitude of phenotypic integration and an increase in variance and the correlation between fluctuating asymmetry and overall integration through time, suggesting that developmental integration mediated morphological response to environmental change in the later populations of these species. These results are consistent with experimental studies and represent, to our knowledge, the first deep-time validation of the importance of developmental integration in stabilizing morphological evolution through periods of environmental change

The scaling of postcranial muscles in cats (Felidae) II: hindlimb and lumbosacral muscles

In quadrupeds the musculature of the hindlimbs is expected to be responsible for generating most of the propulsive locomotory forces, as well as contributing to body support by generating vertical forces. In supporting the body, postural changes from crouched to upright limbs are often associated with an increase of body mass in terrestrial tetrapods. However, felids do not change their crouched limb posture despite undergoing a 300-fold size increase between the smallest and largest extant species. Here, we test how changes in the muscle architecture (masses and lengths of components of the muscle-tendon units) of the hindlimbs and lumbosacral region are related to body mass, to assess whether there are muscular compensations for the maintenance of a crouched limb posture at larger body sizes. We use regression and principal component analyses to detect allometries in muscle architecture, with and without phylogenetic correction. Of the muscle lengths that scale allometrically, all scale with negative allometry (i.e. relative shortening with increasing body mass), whereas all tendon lengths scale isometrically. Only two muscles' belly masses and two tendons' masses scale with positive allometry (i.e. relatively more massive with increasing body mass). Of the muscles that scale allometrically for physiological cross-sectional area, all scale positively (i.e. relatively greater area with increasing body mass). These muscles are mostly linked to control of hip and thigh movements. When the architecture data are phylogenetically corrected, there are few significant results, and only the strongest signals remain. None of the vertebral muscles scaled significantly differently from isometry. Principal component analysis and manovas showed that neither body size nor locomotor mode separate the felid species in morphospace. Our results support the inference that, despite some positively allometric trends in muscle areas related to thigh movement, larger cats have relatively weaker hindlimb and lumbosacral muscles in general. This decrease in power may be reflected in relative decreases in running speeds and is consistent with prevailing evidence that behavioural changes may be the primary mode of compensation for a consistently crouched limb posture in larger cats

Evidence for Pleistocene gene flow through the ice-free corridor from extinct horses and camels from Natural Trap Cave, Wyoming

Natural Trap Cave (Bighorn Mountains, Wyoming) preserves an abundance of fossil remains from extinct Late Pleistocene fauna and is situated near a past migration route that likely connected populations in Eastern Beringia and the contiguous US—the ice-free corridor between the Cordilleran and Laurentide icesheets. Some palaeontological evidence supports a correspondingly high affinity between fauna recorded in Natural Trap Cave and Eastern Beringia versus elsewhere in the contiguous US, but this hypothesis has not yet been extensively tested using genetic data. In the present study, we analysed 16 horse specimens and one camel specimen from Natural Trap Cave. Of the horse specimens we analysed, we obtained 10 unique and previously unreported mitochondrial haplotypes belonging to two distinct (extinct) genetic clades—two haplotypes corresponded to a caballine horse (Equus sp.) and eight corresponded to the stilt-legged horse (Haringtonhippus francisci). With only one exception, it appears these newly sequenced individuals all shared a common ancestor more recently with Eastern Beringian individuals than with others from the contiguous US. In addition, mitochondrial data from a specimen assigned to Camelops sp. revealed that it shares a closer affinity with specimens from the Yukon Territory than those from Idaho or Nevada, though all appear to belong to a single species (“yesterday''s camel”; Camelops cf. hesternus). Together, these results are consistent with a high level of genetic connectivity between horse and camel populations in the Bighorn Mountains and Eastern Beringia during the Pleistocene. © 2021 Elsevier Ltd and INQU

Radiographs Reveal Exceptional Forelimb Strength in the Sabertooth Cat, Smilodon fatalis

Background: The sabertooth cat, Smilodon fatalis, was an enigmatic predator without a true living analog. Their elongate canine teeth were more vulnerable to fracture than those of modern felids, making it imperative for them to immobilize prey with their forelimbs when making a kill. As a result, their need for heavily muscled forelimbs likely exceeded that of modern felids and thus should be reflected in their skeletons. Previous studies on forelimb bones of S. fatalis found them to be relatively robust but did not quantify their ability to withstand loading. Methodology/Principal Findings: Using radiographs of the sabertooth cat, Smilodon fatalis, 28 extant felid species, and the larger, extinct American lion Panthera atrox, we measured cross-sectional properties of the humerus and femur to provide the first estimates of limb bone strength in bending and torsion. We found that the humeri of Smilodon were reinforced by cortical thickening to a greater degree than those observed in any living felid, or the much larger P. atrox. The femur of Smilodon also was thickened but not beyond the normal variation found in any other felid measured. Conclusions/Significance: Based on the cross-sectional properties of its humerus, we interpret that Smilodon was a powerful predator that differed from extant felids in its greater ability to subdue prey using the forelimbs. This enhanced forelimb strength was part of an adaptive complex driven by the need to minimize the struggles of prey in order to protec