The trend of global cooling across the Cenozoic transformed the North American landscape from closed forest to more open grasslands, resulting in dietary adaptations in herbivores in response to shifting resources. In contrast, the material properties of the predator food source (muscle, skin, and bone) have remained constant over this transition, suggesting a corresponding lack of change in predator dietary adaptations. We investigated the North American mammalian predator fossil record using a tooth-shape metric and body mass, predicting that the former would exhibit stability. Instead, we found that mean molar morphology became more blade-like, with our tooth-shape metric sharply increasing in the late Eocene and remaining high from the Oligocene onward. Subsequent tests in extant carnivorans reveal taxa with more bladelike teeth are prevalent in more open environments. Our results reveal an unexpected functional shift among North American predators in response to large-scale environmental changes across the Cenozoic.

Theropod dinosaurs were, and mammalian carnivores are, the top predators within their respective communities. Beyond that, they seem distinct, differing markedly in body form and ancestry. Nevertheless, some of the same processes that shape mammalian predators and their communities likely were important to dinosaurian predators as well. To explore this, we compared the predatory adaptations of theropod dinosaurs and mammalian carnivores, focusing primarily on aspects of their feeding morphology (skulls, jaws, and teeth). We also examined suites of sympatric species (i.e., ecological guilds) of predatory theropods and mammals, emphasizing species richness and the distribution of body sizes within guilds. The morphological comparisons indicate reduced trophic diversity among theropods relative to carnivorans, as most or all theropods with teeth appear to have been hypercarnivorous. There are no clear analogs of felids, canids, and hyaenids among theropods. Interestingly, theropods parallel canids more so than felids in cranial proportions, and all theropods appear to have had weaker jaws than carnivorans. Given the apparent trophic similarity of theropods and their large body sizes, it was surprising to find that species richness of theropod guilds was as great as or exceeded that observed among mammalian carnivore guilds. Separation by body size appears to be slightly greater among sympatric theropods than carnivorans, but the magnitude of size difference between species is not constant in either group. We suggest that, as in modern carnivoran guilds, smaller theropod species might have adapted to the threats posed by much larger species (e.g., tyrannosaurs) by hunting in groups, feeding rapidly, and avoiding encounters whenever possible. This would have favored improved hunting skills and associated adaptations such as agility, speed, intelligence, and increased sensory awareness.

Sabertooths exhibit one of the most extreme feeding adaptations seen in mammals. The functional consequences of accommodating extremely elongate upper canine teeth are severe, resulting in a well-documented suite of cranial modifications. We used geometric morphometric methods to study the evolution of overall shape in the skulls of extant and extinct feline and machairodontine felids, as well as extinct nimravids. Trends in skull evolution were evaluated by using relative warps analysis and tested for association with body size and canine tooth length. Primitive sabertooths from all lineages exhibit cranial shapes more similar to conical-toothed cats, despite the presence of moderately developed saberteeth. More-derived forms in both nimravids and felids diverge in skull morphospace to form two distinct sabertooth types (dirk-toothed and scimitar-toothed) that differ in canine shape. Skull shape in conical-toothed cats is strongly associated with body size, but not canine length. However, within each sabertooth lineage, skull shape is significantly correlated with canine length, suggesting that gape-related demands drove the evolution of sabertooth skull morphology.

The asphalt deposits of Rancho La Brea are well known for preserving a prolific and diverse Late Pleistocene fauna. However, little taphonomic research has been done on these collections. To better understand the formation of this impressive assemblage, a taphonomic study of the bones of the large mammals from one asphalt deposit, Pit 91, was carried out, and results are presented here. The predominance of carnivore specimens in the Rancho La Brea deposits has long been explained by a scenario in which a prey animal was trapped in asphalt and attracted large numbers of carnivores who became trapped in turn. Hypotheses generated from this scenario were tested by collecting taphonomic data on over 18,000 specimens. Weathering data indicate that elements were deposited fairly rapidly. However, patterns of skeletal part representation for the seven most common species demonstrate that complete skeletons are not present. Water transport is ruled out as the primary process responsible for removing skeletal elements based on abrasion data. Instead, the feeding activity of carnivores (ravaging) appears to have been an important factor in the formation of the assemblage.

The impact of environment, interspecific competition, and, to a lesser extent history, on the structure of the guild of large predatory mammals is explored in one fossil and four Recent communities. Two aspects are emphasized: (1) the number of species within each guild and (2) the extent of locomotor convergence as inferred from morphology among the constituent species. Locomotor behavior reflects habitat choice, hunting mode, and escape strategy, all of which appear to be important avenues of adaptive divergence among coexisting predators.

Locomotor behavior in extinct and extant predators is determined from body weight and five measured characteristics of the postcranial skeleton, including ungual shape, elbow shape, and limb proportions. Results indicate that levels of morphologic and inferred ecologic similarity between large predators are higher in the tropical grassland guild of East Africa than in the equivalent guilds of either tropical or temperate forest. This may be due to the great density and diversity of terrestrial herbivores in the productive grasslands. The fossil guild, from the Late Chadron–Orellan (Oligocene) of North America, appears most similar to the tropical forest guilds, but the predators seem to have been slower and more robust than their modern counterparts. Since the Orellan represents an early stage in the evolution of large, fissiped carnivores, both ancestry and time could have influenced Orellan guild structure.

Trophic diversity within guilds of terrestrial predators is explored in three modern and two ancient communities. The modern communities span a range of environments including savannah, rainforest, and temperate forest. The paleocommunities are North American, Orellan (31–29 Ma), and late Hemphillian (7–6 Ma), respectively. The predator guilds are compared in terms of: 1) species richness; 2) the array of feeding types; and 3) the extent of morphological divergence among sympatric species. Feeding type is determined from dental measurements that reflect the proportion of meat, bone, and non-vertebrate foods in the diet. Measurements include estimates of canine shape, tooth size, cutting blade length, and grinding molar area. Morphological divergence among sympatric predators is measured by calculating Euclidean distances among species in a six-dimensional morphospace. Results indicate that the number of predator and prey species are roughly correlated in both ancient and modern communities. Two of the predator guilds, the late Hemphillian and modern Yellowstone, contain relatively few species and appear to be the result of extinction without replacement. Despite differences in history, age, and environment, the extent of morphological divergence within guilds does not differ significantly for the sampled communities. It is clear that the basic pattern of adaptive diversity in dental morphology among coexisting carnivores was established at least 32 million years ago. It appears that interspecific competition for food has acted similarly to produce adaptive divergence among sympatric predators in communities that differ widely in time, space, and taxonomic composition.

Convergent evolution of hypercarnivorous adaptations in canids has occurred a number of times in the last 40 m.y. among distantly related taxa. The adaptations include an increase in carnassial blade length, reduction or loss of post-carnassial molars, and transformation of the talonid of the lower first molar from a basinlike depression into a trenchant, bladelike cusp. Although the diversity of these specialized canids is typically low in past and present communities, it was unusually high during the Late Oligocene of North America and the Pleistocene of South America. These two comparable events provide an opportunity for exploring possible causes of the evolution of hypercarnivory in canids. Plots of generic diversity against time for North American predators reveal a roughly inverse relationship between the number of hypercarnivorous canid taxa and the numbers of other hypercarnivores, such as creodonts, nimravids, mustelids, and amphicyonids. Similarly, the radiation of hypercarnivorous canids in South America occurred at a time of relatively low diversity of other hypercarnivores. Analysis of trophic diversity within the North American carnivore paleoguild before, during, and after the Late Oligocene reveals considerable taxonomic turnover among carnivores because of immigration and speciation. Late Oligocene hypercarnivorous canids appear to have been replaced first by amphicyonids and large mustelids, and then by felids.

Despite the repeated tendency of canids to evolve adaptations for hypercarnivory, a canid has yet to appear that is completely catlike, that is, without any post-carnassial molars. This possible constraint on morphological evolution in canids is argued to have resulted, paradoxically, in increased flexibility over evolutionary time and a great potential for rapid diversification and clade survivorship. Finally, it is suggested that the iterative pattern of specialization of the lower molars for meat-slicing that is seen in all families of carnivores, past and present, is probably a result of intraspecific competition for food, perhaps among littermates. This intraspecific selective force is countered by competition among species, since there are limits on the number of sympatric hypercarnivorous species within a single community.

The respiratory turbinates of mammals are complex bony plates within the nasal chamber that are covered with moist epithelium and provide an extensive surface area for the exchange of heat and water. Given their functional importance, maxilloturbinate size and structure are expected to vary predictably among species adapted to different environments. Here the first quantitative analysis is provided of maxilloturbinate structure based on high-resolution computed tomography (CT) scans of the skulls of eight canid and seven felid species. The key parameters examined were the density of the maxilloturbinate bones within the nasal chamber and how that density varied along the air pathway. In both canids and felids, total maxilloturbinate chamber volume and bone volume increased with body size, with canids having c. 1.5–2.0 times the volume of maxilloturbinate than felids of similar size. In all species, the volume of the maxilloturbinates varies from rostral to caudal, with the peak volume occurring approximately midway, close to where airway cross-sectional area is greatest. Interspecific differences among canids or felids in maxilloturbinate density were not consistent with adaptive explanations, i.e. the densest maxilloturbinates were not associated with species living in arid or cold habitats. Some of the observed variation in maxilloturbinate form might reflect a need for both low- and high-resistance pathways for airflow under alternative conditions.

Patterns of morphological variation in the skulls of extant bears were studied as they relate to diet and feeding behaviour. Measurements of craniodental features were used to compute indices that reflect dietary adaptations of the dentition and biomechanical properties of the skull, jaw and related musculature. Species were classified as either carnivores, omnivores, herbivores or insectivores. Differences among dietary groups were assessed with analysis of variance and discriminant factor analysis. Results demonstrated significant morphological separation among all four groups. Carnivores were distinguished by, among other features, molar size reduction, flexible mandibles and, most surprisingly, relatively small carnassial blades. In contrast, herbivores displayed, among other features, large molar grinding areas, rigid mandibles and large carnassial blades. The insectivorous sloth bear was characterized by extreme reduction of the post-canine teeth. As expected, omnivores tended to have morphology intermediate between that of carnivorous and herbivorous ursids. Comparison with previous studies revealed that bears exhibit a different set of morphological specializations for diet than other carnivoran groups. Carnivorous ursids, for example, were found to share aspects of craniodental morphology with omnivorous canids. The relatively weak adaptations for carnivory observed in bears may be the result of selection for the ability to cope with temporal fluctuations in dietary components. The giant panda Ailuropoda melanoleuca was found to have a relatively stiff jaw and great mechanical advantage of the jaw-closing muscles, features previously observed in carnivorous canids and unexpected in this herbivorous bear. Comparison of patterns of morphological variation and patterns of phylogenetic relationships among species revealed surprisingly strong congruence between morphology and phylogenetics.

Synapsids include modern mammals and their fossil ancestors, the non-mammalian synapsids, or ‘mammal-like reptiles' of old classifications. The synapsid fossil record extends from the Late Carboniferous to the present, a span of nearly 300 million years. However, it can be broken into two distinct phases of diversification, separated by about 150 million years. The first phase extends from the Late Carboniferous to the mid-Triassic, includes the first large land predators on Earth, and is almost entirely non-mammalian. The second phase begins about 65 million years ago after the demise of the dinosaurs, includes only mammals, and extends to the present. In this overview of synapsid predators, we emphasize terrestrial species of large size, and their adaptations for killing and feeding, rather than locomotion. Despite fundamental differences in jaw mechanics and tooth morphology, there are significant parallels in the non-mammalian and mammalian radiations of synapsid predators. Both groups evolve sabertooth forms more than once, and both evolve short-snouted, powerful biting forms. In addition, both the Late Carboniferous—Triassic and Cenozoic phases are characterized by repeated patterns of clade replacement, in which one or a few clades evolve large size and seem to dominate the carnivore guild for several million years, but then decline and are replaced by new taxa. Moreover, within both ancient and Cenozoic predator clades, there are parallel trends over time toward increased body size and hypercarnivory that likely result from a combination of interspecific competition and energetic constraints.

Bite strength is of great importance to carnivores, as their jaws must produce forces of sufficient magnitude to kill and consume their prey. Spotted hyenas, well known for crushing and consuming bones, were studied to determine how tooth and jaw growth affect bite strength and feeding behaviour. Nine captive individuals, aged 6 months to 2 years of age, were sampled as they grew. At 8- to12-week intervals, morphological measurements that estimated jaw muscle mass, tooth size and skull size were taken. Using a force transducer, bite force was measured directly for these juveniles as well as other captive individuals of different ages. In addition, feeding behaviour and performance were quantified periodically by bone tests in which individuals were offered a sheep femur for 15 min. Behaviour and performance were expected to change with the shift from juvenile to adult dentition. Results were not entirely as expected. Morphological measurements of growth reached a plateau at about 20 months, whereas bite strength increased in a linear fashion up to 5 years of age. A fundamental change in tooth use during bone cracking followed the replacement of deciduous teeth with permanent teeth; the primary area of tooth use moved from anterior to rearmost premolars, increasing the mechanical advantage of the jaw adductors. The timing of this shift seemed to be a function of a decrease in gape limitation as a result of growth as well as caudal movement of the premolars. Our data demonstrated that juvenile hyenas had not achieved adult feeding performance levels at 12 months of age, when they are typically weaned in the wild. This suggests that recently weaned cubs may be at an increased risk of starvation and that selection might favour later weaning times.

The Florida panther, Puma concolor coryi, is a subspecies on the verge of extinction. Recent field studies have shown the dwindling population to be suffering from numerous physical problems manifest in their soft tissues. Here we explore the skulls and skeletons of more than 50 P. concolor coryi for corroborative evidence of poor condition such as tooth fracture, arthritis, infection, trauma, and lines of arrested growth (Harris lines). Results are compared with those for an osteological collection of presumed healthy pumas from outside Florida. Although the two samples did not differ significantly in the relative prevalence of most of the pathologies, the Florida cats fractured their teeth more often and exhibited significantly more lines of arrested growth in their long bones. The greater number of teeth broken in life is associated with heavier tooth wear among Florida panthers and a diet depauperate in large prey. The elevated incidence of Harris lines is probably a result of more regular episodes of poor nutrition in the Florida population. Our results demonstrate that the study of osteopathologies is a new tool for the conservation biologist and highlight the value of preserving entire skeletons, as has been done for P. concolor coryi.