Comparative anatomy of the caudate nucleus in canids and felids: Associations with brain size, curvature, cross-sectional properties, and behavioral ecology

The evolutionary history of canids and felids is marked by a deep time separation that has uniquely shaped their behavior and phenotype toward refined predatory abilities. The caudate nucleus is a subcortical brain structure associated with both motor control and cognitive, emotional, and executive functions. We used a combination of three-dimensional imaging, allometric scaling, and structural analyses to compare the size and shape characteristics of the caudate nucleus. The sample consisted of MRI scan data obtained from six canid species (Canis lupus lupus, Canis latrans, Chrysocyon brachyurus, Lycaon pictus, Vulpes vulpes, Vulpes zerda), two canid subspecies (Canis lupus familiaris, Canis lupus dingo), as well as three felids (Panthera tigris, Panthera uncia, Felis silvestris catus). Results revealed marked conservation in the scaling and shape attributes of the caudate nucleus across species, with only slight deviations. We hypothesize that observed differences in caudate nucleus size and structure for the domestic canids are reflective of enhanced cognitive and emotional pathways that possibly emerged during domestication.

Neuropil Variation in the Prefrontal, Motor, and Visual Cortex of Six Felids

INTRODUCTION

Felids have evolved a specialized suite of morphological adaptations for obligate carnivory. Although the musculoskeletal anatomy of the Felidae has been studied extensively, the comparative neuroanatomy of felids is relatively unexplored. Little is known about how variation in the cerebral anatomy of felids relates to species-specific differences in sociality, hunting strategy, or activity patterns.

METHODS

We quantitatively analyzed neuropil variation in the prefrontal, primary motor, and primary visual cortices of six species of Felidae (Panthera leo, Panthera uncia, Panthera tigris, Panthera leopardus, Acinonyx jubatus, Felis sylvestris domesticus) to investigate relationships with brain size, neuronal cell parameters, and select behavioral and ecological factors. Neuropil is the dense, intricate network of axons, dendrites, and synapses in the brain, playing a critical role in information processing and communication between neurons.

RESULTS

There were significant species and regional differences in neuropil proportions, with African lion, cheetah, and tiger having more neuropil in all three cortical regions in comparison to the other species. Based on regression analyses, we find that the increased neuropil fraction in the prefrontal cortex supports social and behavioral flexibility, while in the primary motor cortex, this facilitates the neural activity needed for hunting movements. Greater neuropil fraction in the primary visual cortex may contribute to visual requirements associated with diel activity patterns.

CONCLUSION

These results provide a cross-species comparison of neuropil fraction variation in the Felidae, particularly the understudied Panthera, and provide evidence for convergence of the neuroanatomy of Panthera and cheetahs.

A new large pantherine and a sabre-toothed cat (Mammalia, Carnivora, Felidae) from the late Miocene hominoid-bearing Khorat sand pits, Nakhon Ratchasima Province, northeastern Thailand

We describe two large predators from the hominoid-bearing Khorat sand pits, Nakhon Ratchasima Province, northeastern Thailand: a new genus of pantherine, Pachypanthera n. gen., represented by partial mandible and maxilla and an indeterminate sabre-toothed cat, represented by a fragment of upper canine. The morphological characters of Pachypanthera n. gen., notably the large and powerful canine, the great robustness of the mandibular body, the very deep fossa for the m. masseter, the zigzag HSB enamel pattern, indicate bone-cracking capacities. The genus is unique among Felidae as it has one of the most powerful and robust mandibles ever found. Moreover, it may be the oldest known pantherine, as other Asian pantherines are dated back to the early Pliocene. The taxa we report here are the only carnivorans known from the late Miocene of Thailand. Although the material is rather scarce, it brings new insights to the evolutionary history of Neogene mammals of Southeast Asia, in a geographic place which is partly "terra incognita."

Rapid evolution of the primate larynx?

Tissue vibrations in the larynx produce most sounds that comprise vocal communication in mammals. Larynx morphology is thus predicted to be a key target for selection, particularly in species with highly developed vocal communication systems. Here, we present a novel database of digitally modeled scanned larynges from 55 different mammalian species, representing a wide range of body sizes in the primate and carnivoran orders. Using phylogenetic comparative methods, we demonstrate that the primate larynx has evolved more rapidly than the carnivoran larynx, resulting in a pattern of larger size and increased deviation from expected allometry with body size. These results imply fundamental differences between primates and carnivorans in the balance of selective forces that constrain larynx size and highlight an evolutionary flexibility in primates that may help explain why we have developed complex and diverse uses of the vocal organ for communication.

Iliac auricular surface morphofunctional study in felidae

Felids show remarkable phenotypic similarities and are conservative in behavioral and ecological traits. In contrast, they display a large range in body mass from around 1kg to more than 300kg. Body size and locomotory specializations correlate to skull, limb and vertebral skeleton morphology. With an increase in body mass, felids prey selection switches from small to large, from using a rapid skull or spine lethal bite for small prey, to sustained suffocating bite for large prey. Dietary specialization correlates to skull and front limbs morphology but no correlation was found on the spine or on the hind limb. The morphology of the sacroiliac junction in relation to ecological factors remained to be described. We are presenting a study of the overall shape of the iliac auricular surface with qualitative and quantitative analyses of its morphology. Our results demonstrate that body mass, prey selection, and bite type, crucially influence the auricular surface, where no significant effect of locomotor specialization was found. The outline of the surface is significantly more elevated dorso-caudally and the joint surface shows an irregular W-shape topography in big cats whereas the surface in small cats is smoother with a C-shape topography and less of an elevated ridge. Biomechanically, we suggest that a complex auricular surface increases joint stiffness and provides more support in heavier cats, an advantage for subduing big prey successfully during a sustained bite.

Comparing hair-morphology and molecular methods to identify fecal samples from Neotropical felids

To avoid certain problems encountered with more-traditional and invasive methods in behavioral-ecology studies of mammalian predators, such as felids, molecular approaches have been employed to identify feces found in the field. However, this method requires a complete molecular biology laboratory, and usually also requires very fresh fecal samples to avoid DNA degradation. Both conditions are normally absent in the field. To address these difficulties, identification based on morphological characters (length, color, banding, scales and medullar patterns) of hairs found in feces could be employed as an alternative. In this study we constructed a morphological identification key for guard hairs of eight Neotropical felids (jaguar, oncilla, Geoffroy's cat, margay, ocelot, Pampas cat, puma and jaguarundi) and compared its efficiency to that of a molecular identification method, using the ATP6 region as a marker. For this molecular approach, we simulated some field conditions by postponing sample-conservation procedures. A blind test of the identification key obtained a nearly 70% overall success rate, which we considered equivalent to or better than the results of some molecular methods (probably due to DNA degradation) found in other studies. The jaguar, puma and jaguarundi could be unequivocally discriminated from any other Neotropical felid. On a scale ranging from inadequate to excellent, the key proved poor only for the margay, with only 30% of its hairs successfully identified using this key; and have intermediate success rates for the remaining species, the oncilla, Geoffroy's cat, ocelot and Pampas cat, were intermediate. Complementary information about the known distributions of felid populations may be necessary to substantially improve the results obtained with the key. Our own molecular results were even better, since all blind-tested samples were correctly identified. Part of these identifications were made from samples kept in suboptimal conditions, with some samples remaining outdoors for up to seven days, simulating conditions in the field. It appears that both methods can be used, depending on the available laboratory facilities and on the expected results.

Morphological modularity in the vertebral column of Felidae (Mammalia, Carnivora)

BACKGROUND

Previous studies have demonstrated that the clear morphological differences among vertebrae across the presacral column are accompanied by heterogeneous functional signals in vertebral shape. Further, several lines of evidence suggest that the mammalian axial skeleton is a highly modular structure. These include its composition of serial units, a trade-off between high shape variance and strong conservation of vertebral count, and direct association of regions with anterior expression sites of Hox genes. Here we investigate the modular organisation of the presacral vertebral column of modern cats (Felidae, Carnivora, Mammalia) with pairwise comparisons of vertebral shape covariation (i.e. integration) and evaluate our results against hypotheses of developmental and functional modularity. We used three-dimensional geometric morphometrics to quantify vertebral shape and then assessed integration between pairs of vertebrae with phylogenetic two-block partial least square analysis (PLS).

RESULTS

Six modules were identified in the pairwise analyses (vertebrae included are designated as 'C' for cervical, 'T' for thoracic, and 'L' for lumbar): an anterior module (C1 to T1); a transitional module situated between the last cervicals and first thoracics (C6 to T2); an anterior to middle thoracic set (T4 to T8); an anticlinal module (T10 and T11); a posterior set composed of the last two thoracics and lumbars (T12 to L7); and a module showing covariation between the cervicals and the posterior set (T12 to L7). These modules reflect shared developmental pathways, ossification timing, and observed ecological shape diversification in living species of felids.

CONCLUSIONS

We show here that patterns of shape integration reflect modular organisation of the vertebral column of felids. Whereas this pattern corresponds with hypotheses of developmental and functional regionalisation in the axial skeleton, it does not simply reflect major vertebral regions. This modularity may also have permitted vertebral partitions, specifically in the posterior vertebral column, to be more responsive to selection and achieve higher morphological disparity than other vertebral regions.

Using a Novel Absolute Ontogenetic Age Determination Technique to Calculate the Timing of Tooth Eruption in the Saber-Toothed Cat, Smilodon fatalis

Despite the superb fossil record of the saber-toothed cat, Smilodon fatalis, ontogenetic age determination for this and other ancient species remains a challenge. The present study utilizes a new technique, a combination of data from stable oxygen isotope analyses and micro-computed tomography, to establish the eruption rate for the permanent upper canines in Smilodon fatalis. The results imply an eruption rate of 6.0 millimeters per month, which is similar to a previously published average enamel growth rate of the S. fatalis upper canines (5.8 millimeters per month). Utilizing the upper canine growth rate, the upper canine eruption rate, and a previously published tooth replacement sequence, this study calculates absolute ontogenetic age ranges of tooth development and eruption in S. fatalis. The timing of tooth eruption is compared between S. fatalis and several extant conical-toothed felids, such as the African lion (Panthera leo). Results suggest that the permanent dentition of S. fatalis, except for the upper canines, was fully erupted by 14 to 22 months, and that the upper canines finished erupting at about 34 to 41 months. Based on these developmental age calculations, S. fatalis individuals less than 4 to 7 months of age were not typically preserved at Rancho La Brea. On the whole, S. fatalis appears to have had delayed dental development compared to dental development in similar-sized extant felids. This technique for absolute ontogenetic age determination can be replicated in other ancient species, including non-saber-toothed taxa, as long as the timing of growth initiation and growth rate can be determined for a specific feature, such as a tooth, and that growth period overlaps with the development of the other features under investigation.

Evolutionary allometry of the thoracolumbar centra in felids and bovids

Mammals have evolved a remarkable range of body sizes, yet their overall body plan remains unaltered. One challenge of evolutionary biology is to understand the mechanisms by which this size diversity is achieved, and how the mechanical challenges associated with changing body size are overcome. Despite the importance of the axial skeleton in body support and locomotion, and much interest in the allometry of the appendicular skeleton, little is known about vertebral allometry outside primates. This study compares evolutionary allometry of the thoracolumbar centra in two families of quadrupedal running mammals: Felidae and Bovidae. I test the hypothesis that, as size increases, the thoracolumbar region will resist increasing loads by becoming a) craniocaudally shorter, and b) larger in cross-sectional area, particularly in the sagittal plane. Length, width, and height of the thoracolumbar centra of 23 felid and 34 bovid species were taken. Thoracic, prediaphragmatic, lumbar, and postdiaphragmatic lengths were calculated, and diameters were compared at three equivalent positions: the midthoracic, the diaphragmatic and the midlumbar vertebra. Allometric slopes were calculated using a reduced major axis regression, on both raw and independent contrasts data. Slopes and elevations were compared using an ANCOVA. As size increases the thoracolumbar centra become more robust, showing preferential reinforcement in the sagittal plane. There was less allometric shortening of the thoracic than the lumbar region, perhaps reflecting constraints due to its connection with the respiratory apparatus. The thoracic region was more robust in bovids than felids, whereas the lumbar region was longer and more robust in felids than bovids. Elongation of lumbar centra increases the outlever of sagittal bending at intervertebral joints, increasing the total pelvic displacement during dorsomobile running. Both locomotor specializations and functional regionalization of the axial skeleton appear to have influenced its response to increasing size.

Jaw function in Smilodon fatalis: a reevaluation of the canine shear-bite and a proposal for a new forelimb-powered Class 1 Lever Model

The jaw function of Smilodon fatalis has long been a source of debate. Although modern-day lions subdue large prey through the use of a suffocating throat bite, the dramatically elongated maxillary canines of S. fatalis suggest an alternative bite mechanism. The current literature favors a "canine shear-bite," in which the depression of the cranium by the ventral neck flexors assists the mandibular adductors in closing the jaws. Although the model makes intuitive sense and appears to be supported by scientific data, the mechanical feasibility of "neck-powered" biting has not been experimentally demonstrated. In the present study, the computer-assisted manipulation of digitized images of a high-quality replica of an S. fatalis neck and skull shows that a rotation of the cranium by the ventral neck flexors will not result in jaw closure. Instead, the cranium and mandible rotate ventrally together (at the atlantooccipital joint), and the jaws remain in an open configuration. The only manner by which rotation of the cranium can simultaneously result in jaw closure is by an anterior rotation at the temporomandibular joint. Based on this finding, the author proposes a new Class 1 lever mechanism for S. fatalis jaw function. In this model, the mandible is immobilized against the neck of the prey and a dorsally directed force from the extension of the forelimbs rotates the cranium anteriorly at the temporomandibular joint. The maxillary canines pierce the prey's neck and assist in clamping the ventral neck structures. The model is based on a maximum gape angle of approximately 90° and incorporates a secondary virtual point of rotation located slightly anteroventral to the temporomandibular joint. The Class 1 Lever Model is mechanically feasible, consistent with current data on S. fatalis anatomy and ecology, and may provide a basis for similar studies on other fossil taxa.

Himalayan fossils of the oldest known pantherine establish ancient origin of big cats

Pantherine felids ('big cats') include the largest living cats, apex predators in their respective ecosystems. They are also the earliest diverging living cat lineage, and thus are important for understanding the evolution of all subsequent felid groups. Although the oldest pantherine fossils occur in Africa, molecular phylogenies point to Asia as their region of origin. This paradox cannot be reconciled using current knowledge, mainly because early big cat fossils are exceedingly rare and fragmentary. Here, we report the discovery of a fossil pantherine from the Tibetan Himalaya, with an age of Late Miocene-Early Pliocene, replacing African records as the oldest pantherine. A 'total evidence' phylogenetic analysis of pantherines indicates that the new cat is closely related to the snow leopard and exhibits intermediate characteristics on the evolutionary line to the largest cats. Historical biogeographic models provide robust support for the Asian origin of pantherines. The combined analyses indicate that 75% of the divergence events in the pantherine lineage extended back to the Miocene, up to 7 Myr earlier than previously estimated. The deeper evolutionary origin of big cats revealed by the new fossils and analyses indicate a close association between Tibetan Plateau uplift and diversification of the earliest living cats.

Comparative Biomechanical Modeling of Metatherian and Placental Saber-Tooths: A Different Kind of Bite for an Extreme Pouched Predator

Questions surrounding the dramatic morphology of saber-tooths, and the presumably deadly purpose to which it was put, have long excited scholarly and popular attention. Among saber-toothed species, the iconic North American placental, Smilodon fatalis, and the bizarre South American sparassodont, Thylacosmilus atrox, represent extreme forms commonly forwarded as examples of convergent evolution. For S. fatalis, some consensus has been reached on the question of killing behaviour, with most researchers accepting the canine-shear bite hypothesis, wherein both head-depressing and jaw closing musculatures played a role in delivery of the fatal bite. However, whether, or to what degree, T. atrox may have applied a similar approach remains an open question. Here we apply a three-dimensional computational approach to examine convergence in mechanical performance between the two species. We find that, in many respects, the placental S. fatalis (a true felid) was more similar to the metatherian T. atrox than to a conical-toothed cat. In modeling of both saber-tooths we found that jaw-adductor-driven bite forces were low, but that simulations invoking neck musculature revealed less cranio-mandibular stress than in a conical-toothed cat. However, our study also revealed differences between the two saber-tooths likely reflected in the modus operandi of the kill. Jaw-adductor-driven bite forces were extremely weak in T. atrox, and its skull was even better-adapted to resist stress induced by head-depressors. Considered together with the fact that the center of the arc described by the canines was closer to the jaw-joint in Smilodon, our results are consistent with both jaw-closing and neck musculature playing a role in prey dispatch for the placental, as has been previously suggested. However, for T. atrox, we conclude that the jaw-adductors probably played no major part in the killing bite. We propose that the metatherian presents a more complete commitment to the already extreme saber-tooth 'lifestyle'.

Big cats in our backyards: persistence of large carnivores in a human dominated landscape in India

Protected areas are extremely important for the long term viability of biodiversity in a densely populated country like India where land is a scarce resource. However, protected areas cover only 5% of the land area in India and in the case of large carnivores that range widely, human use landscapes will function as important habitats required for gene flow to occur between protected areas. In this study, we used photographic capture recapture analysis to assess the density of large carnivores in a human-dominated agricultural landscape with density >300 people/km² in western Maharashtra, India. We found evidence of a wide suite of wild carnivores inhabiting a cropland landscape devoid of wilderness and wild herbivore prey. Furthermore, the large carnivores; leopard (Panthera pardus) and striped hyaena (Hyaena hyaena) occurred at relatively high density of 4.8±1.2 (sd) adults/100 km² and 5.03±1.3 (sd) adults/100 km² respectively. This situation has never been reported before where 10 large carnivores/100 km² are sharing space with dense human populations in a completely modified landscape. Human attacks by leopards were rare despite a potentially volatile situation considering that the leopard has been involved in serious conflict, including human deaths in adjoining areas. The results of our work push the frontiers of our understanding of the adaptability of both, humans and wildlife to each other’s presence. The results also highlight the urgent need to shift from a PA centric to a landscape level conservation approach, where issues are more complex, and the potential for conflict is also very high. It also highlights the need for a serious rethink of conservation policy, law and practice where the current management focus is restricted to wildlife inside Protected Areas.

[Mechanical buffering characteristics of feline paw pads]

In the long time of natural evolution, the bodies of some animals, such as feline, that live in the wild and complicate surroundings have evolved to possess outstanding buffering characteristics, which make the animals adapt to the environment perfectly. These animals generally have well-developed paw pads under their soles to play an important role in attenuating the intensity of impact when they land on the ground. Investigating the buffering characteristics of these animals' paw pads could help us to design "bionic" buffering and energy-absorption devices. In this paper, based on observations of animal jumping test, a simple mass-spring-buffer model was proposed to explore the buffering characteristics of the animals' paw pads. By analytically solving the differential equations of this model, the parameters concerned with paw pads functions were discussed and some significant results were obtained.

Variation in craniomandibular morphology and sexual dimorphism in pantherines and the sabercat Smilodon fatalis

Sexual dimorphism is widespread among carnivorans, and has been an important evolutionary factor in social ecology. However, its presence in sabertoothed felids remains contentious. Here we present a comprehensive analysis of extant Panthera and the sabertoothed felid Smilodon fatalis. S. fatalis has been reported to show little or no sexual dimorphism but to have been intraspecifically variable in skull morphology. We found that large and small specimens of S. fatalis could be assigned to male and female sexes with similar degrees of confidence as Panthera based on craniomandibular shape. P. uncia is much less craniomandibularly variable and has low levels of sexual size-dimorphism. Shape variation in S. fatalis probably reflects sexual differences. Craniomandibular size-dimorphism is lower in S. fatalis than in Panthera except P. uncia. Sexual dimorphism in felids is related to more than overall size, and S. fatalis and the four large Panthera species show marked and similar craniomandibular and dental morphometric sexual dimorphism, whereas morphometric dimorphism in P. uncia is less. Many morphometric-sexually dimorphic characters in Panthera and Smilodon are related to bite strength and presumably to killing ecology. This suggests that morphometric sexual dimorphism is an evolutionary adaptation to intraspecific resource partitioning, since large males with thicker upper canines and stronger bite forces would be able to hunt larger prey than females, which is corroborated by feeding ecology in P. leo. Sexual dimorphism indicates that S. fatalis could have been social, but it is unlikely that it lived in fusion-fission units dominated by one or a few males, as in sub-Saharan populations of P. leo. Instead, S. fatalis could have been solitary and polygynous, as most extant felids, or it may have lived in unisexual groups, as is common in P. leo persica.

Convergence and divergence in the evolution of cat skulls: temporal and spatial patterns of morphological diversity

BACKGROUND

Studies of biological shape evolution are greatly enhanced when framed in a phylogenetic perspective. Inclusion of fossils amplifies the scope of macroevolutionary research, offers a deep-time perspective on tempo and mode of radiations, and elucidates life-trait changes. We explore the evolution of skull shape in felids (cats) through morphometric analyses of linear variables, phylogenetic comparative methods, and a new cladistic study of saber-toothed cats.

METHODOLOGY/PRINCIPAL FINDINGS

A new phylogenetic analysis supports the monophyly of saber-toothed cats (Machairodontinae) exclusive of Felinae and some basal felids, but does not support the monophyly of various saber-toothed tribes and genera. We quantified skull shape variation in 34 extant and 18 extinct species using size-adjusted linear variables. These distinguish taxonomic group membership with high accuracy. Patterns of morphospace occupation are consistent with previous analyses, for example, in showing a size gradient along the primary axis of shape variation and a separation between large and small-medium cats. By combining the new phylogeny with a molecular tree of extant Felinae, we built a chronophylomorphospace (a phylogeny superimposed onto a two-dimensional morphospace through time). The evolutionary history of cats was characterized by two major episodes of morphological divergence, one marking the separation between saber-toothed and modern cats, the other marking the split between large and small-medium cats.

CONCLUSIONS/SIGNIFICANCE

Ancestors of large cats in the 'Panthera' lineage tend to occupy, at a much later stage, morphospace regions previously occupied by saber-toothed cats. The latter radiated out into new morphospace regions peripheral to those of extant large cats. The separation between large and small-medium cats was marked by considerable morphologically divergent trajectories early in feline evolution. A chronophylomorphospace has wider applications in reconstructing temporal transitions across two-dimensional trait spaces, can be used in ecophenotypical and functional diversity studies, and may reveal novel patterns of morphospace occupation.

Scaling and mechanics of the felid calcaneus: geometric similarity without differential allometric scaling

Six mechanically significant skeletal variables were measured on the calcanei from 60 Felidae specimens (22 species) to determine whether these variables were scaled to body mass, and to assess whether differential scaling exists. The power equation (y = a · x(b) ) was used to analyse the scaling of the six variables to body mass; we compared traditional regression methods (standardised major axis) to phylogenetically independent contrasts. In agreement with previous studies that compared these methodologies, we found no significant differences between methods in the allometric coefficients (b) obtained. Overall, the scaling pattern of the felid calcaneus conformed to the predictions of the geometric similarity hypothesis, but not entirely to those of the elastic similarity hypothesis. We found that the moment arm of the ankle extensors scaled to body mass with an exponent not significantly different from 0.40. This indicated that the tuber calcanei scaled to body mass faster than calcaneus total length. This explained why the effective mechanical advantage of the ankle extensors increased with body mass, despite the fact that limb posture does not change in felid species. Furthermore, this finding was consistent with the hypothesis of the isometric scaling of ground reaction forces. No evidence for differential scaling was found in any of the variables studied. We propose that this reflected the similar locomotor pattern of all felid species. Thus, our results suggested that the differences in allometric coefficients for 'large' and 'small' mammals were in fact caused by different types of locomotion among the species included in each category.

3D Morphometric and posture study of felid scapulae using statistical shape modelling

We present a three dimensional (3D) morphometric modelling study of the scapulae of Felidae, with a focus on the correlations between forelimb postures and extracted scapular shape variations. Our shape modelling results indicate that the scapular infraspinous fossa becomes larger and relatively broader along the craniocaudal axis in larger felids. We infer that this enlargement of the scapular fossa may be a size-related specialization for postural support of the shoulder joint.

The making of a monster: postnatal ontogenetic changes in craniomandibular shape in the great sabercat Smilodon

Derived sabercats had craniomandibular morphologies that in many respects were highly different from those of extant felids, and this has often been interpreted functionally as adaptations for predation at extreme gape angles with hypertrophied upper canines. It is unknown how much of this was a result of intraspecific postnatal ontogeny, since juveniles of sabercats are rare and no quantitative study has been made of craniomandibular ontogeny. Postnatal ontogenetic craniomandibular shape changes in two morphologically derived sabercats, Smilodon fatalis and S. populator, were analysed using geometric morphometrics and compared to three species of extant pantherines, the jaguar, tiger, and Sunda clouded leopard. Ontogenetic shape changes in Smilodon usually involved the same areas of the cranium and mandible as in extant pantherines, and large-scale modularization was similar, suggesting that such may have been the case for all felids, since it followed the same trends previously observed in other mammals. However, in other respects Smilodon differed from extant pantherines. Their crania underwent much greater and more localised ontogenetic shape changes than did the mandibles, whereas crania and mandibles of extant pantherines underwent smaller, fewer and less localised shape changes. Ontogenetic shape changes in the two species of Smilodon are largely similar, but differences are also present, notably those which may be tied to the presence of larger upper canines in S. populator. Several of the specialized cranial characters differentiating adult Smilodon from extant felids in a functional context, which are usually regarded as evolutionary adaptations for achieving high gape angles, are ontogenetic, and in several instances ontogeny appears to recapitulate phylogeny to some extent. No such ontogenetic evolutionary adaptive changes were found in the extant pantherines. Evolution in morphologically derived sabercats involved greater cranial ontogenetic changes than among extant felids, resulting in greatly modified adult craniomandibular morphologies.

Why the leopard got its spots: relating pattern development to ecology in felids

A complete explanation of the diversity of animal colour patterns requires an understanding of both the developmental mechanisms generating them and their adaptive value. However, only two previous studies, which involved computer-generated evolving prey, have attempted to make this link. This study examines variation in the camouflage patterns displayed on the flanks of many felids. After controlling for the effects of shared ancestry using a fully resolved molecular phylogeny, this study shows how phenotypes from plausible felid coat pattern generation mechanisms relate to ecology. We found that likelihood of patterning and pattern attributes, such as complexity and irregularity, were related to felids' habitats, arboreality and nocturnality. Our analysis also indicates that disruptive selection is a likely explanation for the prevalence of melanistic forms in Felidae. Furthermore, we show that there is little phylogenetic signal in the visual appearance of felid patterning, indicating that camouflage adapts to ecology over relatively short time scales. Our method could be applied to any taxon with colour patterns that can reasonably be matched to reaction-diffusion and similar models, where the kinetics of the reaction between two or more initially randomly dispersed morphogens determines the outcome of pattern development.

Supermodeled sabercat, predatory behavior in Smilodon fatalis revealed by high-resolution 3D computer simulation

The American sabercat Smilodon fatalis is among the most charismatic of fossil carnivores. Despite broad agreement that its extraordinary anatomy reflects unique hunting techniques, after >150 years of study, many questions remain concerning its predatory behavior. Were the "sabers" used to take down large prey? Were prey killed with an eviscerating bite to the abdomen? Was its bite powerful or weak compared with that of modern big cats? Here we quantitatively assess the sabercat's biomechanical performance using the most detailed computer reconstructions yet developed for the vertebrate skull. Our results demonstrate that bite force driven by jaw muscles was relatively weak in S. fatalis, one-third that of a lion (Panthera leo) of comparable size, and its skull was poorly optimized to resist the extrinsic loadings generated by struggling prey. Its skull is better optimized for bites on restrained prey where the bite is augmented by force from the cervical musculature. We conclude that prey were brought to ground and restrained before a killing bite, driven in large part by powerful cervical musculature. Because large prey is easier to restrain if its head is secured, the killing bite was most likely directed to the neck. We suggest that the more powerful jaw muscles of P. leo may be required for extended, asphyxiating bites and that the relatively low bite forces in S. fatalis might reflect its ability to kill large prey more quickly, avoiding the need for prolonged bites.

Interspecific scaling of the morphology and posture of the limbs during the locomotion of cats (Felidae)

For phylogenetically diverse mammals, ranging from small rodents to large ungulates, the generalization that limb erectness increases with increased size is supported by some size-dependent scaling relationships of appendicular skeletal anatomy as well as a limited number of direct observations of limb posture during locomotion. If size alone is the causal basis for different limb posture, then the erectness of limbs should increase significantly with increased size within a phylogenetically narrow lineage, but such data are sparse. Thus, to better establish the correlation between size and posture of mammalian limbs, we quantified the scaling relationships between mass and limb dimensions and kinematics during walking of nine species within the felid(cat) clade, which has qualitatively similar limb design. We studied the domestic cat, serval, ocelot, lynx, leopard, cheetah, cougar, lion and tiger,which had masses ranging from <4 kg to nearly 200 kg. Apart from variation associated with overall size, the lengths of the appendicular skeletal structures of most of the felid species were morphologically very similar in multivariate space. The kinematics of the limbs were also relatively uniform,and size had little predictive value for limb posture among felid species. Only three out of a total of 24 angular variables at footfall and midstance changed significantly (0.02<P<0.05) with increased mass. Thus,in contrast to previous broadly comparative studies of mammals, larger species of felids did not have more upright limbs than smaller species.

Geographical Variation in the Clouded Leopard, Neofelis nebulosa, Reveals Two Species

The clouded leopard, Neofelis nebulosa, is an endangered semiarboreal felid with a wide distribution in tropical forests of southern and southeast Asia, including the islands of Sumatra and Borneo in the Indonesian archipelago. In common with many larger animal species, it displays morphological variation within its wide geographical range and is currently regarded as comprising of up to four subspecies. It is widely recognized that taxonomic designation has a major impact on conservation planning and action. Given that the last taxonomic revision was made over 50 years ago, a more detailed examination of geographical variation is needed. We describe here the results of a morphometric analysis of the pelages of 57 clouded leopards sampled throughout the species' range. We conclude that there are two distinct morphological groups, which differ primarily in the size of their cloud markings. These results are supported by a recent genetic analysis. On that basis, we give diagnoses for the distinction of two species, one in mainland Asia (N. nebulosa) and the other in Indonesia (N. diardi). The implications for conservation that arise from this new taxonomic arrangement are discussed.

Sabertooth characters in the clouded leopard (Neofelis nebulosa Griffiths 1821)

The clouded leopard (Neofelis nebulosa) is an unusual medium-sized felid whose ecology in the wild is poorly known. Mainly famous for its large canines, it has often been an overlooked taxon in analyses of felid morphology and systematics or has proven aberrant and difficult to interpret. In this article I report on a number of unusual features in the clouded leopard skull hitherto considered characteristic of sabertooth felids exclusively, and, accordingly, universally believed to be absent in extant felids. The skull morphology of the clouded leopard sets it apart from other extant felids, and in a number of respects it approaches the morphology of primitive sabertooths. This indicates convergence of several characters in machairodontine felids and the clouded leopard, mainly as adaptations for attaining a large gape. This raises doubts about the characters hitherto considered as distinguishing sabertoothed from nonsabertoothed predators, and since no evidence at present suggests a different functional killing and feeding ecology in Neofelis, regardless of its unusual skull morphology, also whether primitive sabertoothed felids were functionally similar to advanced forms such as Homotherium, Megantereon, or Smilodon.

Body size of Smilodon (Mammalia: Felidae)

The body masses of the three large saber-toothed machairodontines, Smilodon gracilis, S. fatalis, and S. populator, were estimated on the basis of 36 osteological variables from the appendicular skeleton of extant felids. A new model is introduced that takes the reliability of the predictor equations into account, since mass estimates are more reliable when computed from multiple variables per bone. At a body mass range of 55-100 kg, S. gracilis was comparable in size to extant jaguars, and S. fatalis was found to be somewhat lighter than previously assumed, with a body mass range of 160-280 kg, similar to that of the largest extant felid, the Siberian tiger. Smilodon populator was substantially heavier and larger than any extant felid, with a body mass range of 220-360 kg. Particularly large specimens of S. populator almost certainly exceeded 400 kg in body mass. The differences from previous estimates are most likely caused by differences in the databases used for mass estimation.

Cementum onSmilodon sabers

The maxillary canines of Smilodon californicus Bovard, 1907 have a deeply curved cementoenamel junction. The gingiva of modern cats is attached to the tooth at the cementoenamel junction and provides tactile and other dental information to the animal. The presence of cementum at the cervix of the maxillary canines, also called sabers, would indicate that the gingiva in Smilodon was attached in this region. Such an attachment would be advantageous, providing stability and sensory input for the large tooth. Also, gingiva at the cervix would impact the manner in which the teeth were used. Previous study using scanning electron microscopy of dental casts was indirect. The purpose of this study was to confirm by direct methods the presence of cementum at the cervix of Smilodon californicus sabers. Parts of three Smilodon californicus sabers were sectioned and examined with light and scanning electron microscopy (EDS). In addition, percent weight of calcium and phosphorus was measured in enamel, dentin, and cementum using electron dispersive spectroscopy. Cementum was identified in the cervical region of each saber. Spectroscopy confirmed that the tissue is calcified and the mineral is hydroxyapatite. Percent calcium and percent phosphorus of individual tissues were highly variable between specimens. However, the ratios of calcium to phosphorus were not significantly different from the hydroxyapatite standard. In the future, bite models will have to take the presence of soft tissues into account.

Renal ultrasonographic evaluation in the oncilla (Leopardus tigrinus)

Ultrasonography is currently used in veterinary medicine to examine the anatomy and physiology of internal organs and to establish normal standards for exotic animal species. Specifically, the kidneys may be evaluated and measured in length, width, and height. The kidneys in 33 oncilla (Leopardus tigrinus), including 20 males and 13 females, were opportunistically located, characterized, and measured by ultrasound using a 7.5-MHz linear transducer at two different zoologic facilities in São Paulo, Brazil. Renal volume was calculated from these linear measurements. The mean linear measurements and volume of the right and left kidneys were not significantly different.