Blaire Van Valkenburgh

Skeletal indicators of locomotor behavior in living and extinct carnivores

ABSTRACT In this paper, I assess the correspondence between locomotor function (climbing, digging, and running) and skeletal morphology in living carnivores. Published behavioral observations are used to assign fifty-three extant carnivore species to four broad locomotor categories: arboreal, scansorial, terrestrial, and semi-fossorial. Body weight and measurements of claw shape, relative size of fore and hind claws, olecranon size and orientation, astragalar shape, and manus and hindlimb proportions are presented for each species. The correspondence between locomotor type and morphologic indices is examined with bivariate and multivariate (discriminant function) analyses. Results demonstrate that osteological indices are good predictors of locomotor behavior among extant carnivores. Arboreal and scansorial carnivores exhibit relatively more curved claws, longer proximal phalanges, and shorter metatarsals than do terrestrial taxa; semi-fossorial carnivores differ from other locomotor types in having relat...

Trophic diversity in past and present guilds of large predatory mammals

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 sa- vannah, 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 Hemp- hillian 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 commu- nities. 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 com- munities that differ widely in time, space, and taxonomic composition.

The Ecological Role of the Mammalian Mesocarnivore

Large mammalian carnivores are ecologically important because relatively few individuals can cause strong predation-driven direct effects or fear-driven indirect effects that can ripple through communities and, ultimately, influence ecosystem structure and function. Most mammalian carnivores are not large, however, but are small to midsized species collectively termed “mesocarnivores.” Mesocarnivores are more numerous and more diverse than larger carnivores, and often reside in closer proximity to humans, yet we know little about how they influence communities and ecosystems. In this article we review the ecological role of the mesocarnivore and present examples where mesocarnivores drive community structure and function in roles similar to, or altogether different from, their larger brethren. Together, these examples substantiate the need for an assessment of the ecological role of mammalian carnivores beyond an examination of only the largest species. In particular, we emphasize the need to study the trophic penetrance of mesocarnivores and examine how ecological context modulates their functional role.

INCIDENCE OF TOOTH BREAKAGE AMONG LARGE, PREDATORY MAMMALS

Data on the frequency of tooth breakage among nine, large carnivorous mammals suggest that the probability of an individual predators breaking at least one tooth in its lifetime is greater than 0.25. This figure is similar to published estimates of bone-fracture incidence in primates and viverrid carnivores and indicates that the safety factors of teeth and bone are similar. Given that bones heal and teeth do not, the equivalent rates of fracture are surprising. It suggests that the cost of tooth fracture is slightly less than that of bone fracture. The highest incidences of tooth breakage (0.35, 0.40) were found in the habitual bone eaters (hyenas), and the lowest (0.15-0.24) in the felids and the African wild dog. The gray wolf, a moderately frequent bone eater, was intermediate (0.29). Eating bone appears to increase the risk of accidental fracture because it produces relatively high, unpredictable loads. The most commonly broken teeth are canines, followed by premolars, carnassial molars, and incisor...Data on the frequency of tooth breakage among nine, large carnivorous mammals suggest that the probability of an individual predators breaking at least one tooth in its lifetime is greater than 0.25. This figure is similar to published estimates of bone-fracture incidence in primates and viverrid carnivores and indicates that the safety factors of teeth and bone are similar. Given that bones heal and teeth do not, the equivalent rates of fracture are surprising. It suggests that the cost of tooth fracture is slightly less than that of bone fracture. The highest incidences of tooth breakage (0.35, 0.40) were found in the habitual bone eaters (hyenas), and the lowest (0.15-0.24) in the felids and the African wild dog. The gray wolf, a moderately frequent bone eater, was intermediate (0.29). Eating bone appears to increase the risk of accidental fracture because it produces relatively high, unpredictable loads. The most commonly broken teeth are canines, followed by premolars, carnassial molars, and incisors. Canines are more likely to break because their shape and function tend to subject them to significant bending stresses that are unpredictable in magnitude and direction. The evolution of canine teeth with higher safety factors is probably constrained by the necessity of maintaining a functional shape and the material properties of dentine and enamel. Finally, it is suggested that mammalian predators of large prey are likely to fracture their teeth much more often than consumers of small prey or plant material because of a much greater risk of accidental fracture during the killing of large prey.

Feeding Behavior in Free-Ranging, Large African Carnivores

Carnivores exhibit a diverse array of teeth, including peg-like incisors, elongate canines, blade-like carnassials, and rounded, bunodont molars, all of which are presumed to be adapted for particular functions, such as slicing flesh or cracking bones. The validity of these presumed correlations between form and function was explored in a field study of feeding behavior in four sympatric species of free-ranging African carnivores; African lion ( Panthera led ), cheetah ( Acinonyx jubatus ), spotted hyena ( Crocuta crocuta ), and wild dog ( Lycaon pictus ). Based on videotapes of feeding behavior on carcasses of ungulates, the associations among use of teeth, motion of jaw, action of neck, use of paws, and type of food were compiled. There were significant interactions between use of teeth and type of food, and use of teeth and action of neck, in all species. Skin tended to be cut with the carnassials in association with a slight pull, whereas muscle was more likely to be pulled from the carcass by the incisors. Bones usually were cracked with the premolars in hyenas and the postcarnassial molars in wild dogs. Repeated chewing motions were most common in all species when eating the toughest foods, i.e., skin or muscle in combination with bone. The association between use of teeth and type of food was not perfect; sometimes skin was cut with incisors and bones were cracked with carnassials. This apparent lack of precision in use of teeth suggests that selection will likely favor specializations for particular functions in teeth other than those that are the primary tools for that purpose.

Forelimb indicators of prey‐size preference in the Felidae

The forelimbs, along with the crania, are an essential part of the prey‐killing apparatus in cats. Linear morphometrics of the forelimbs were used to determine the morphological differences between felids that specialize on large prey, small prey, or mixed prey. We also compared the scaling of felid forelimbs to those of canids to test whether prey capture strategies affect forelimb scaling. Results suggest that large prey specialists have relatively robust forelimbs when compared with smaller prey specialists. This includes relatively more robust humeri and radii, relatively larger distal ends of the humerus, and relatively larger articular areas of the humerus and radius. Large prey specialists also had relatively longer olecranon processes of the ulna and wider proximal paws. These characters are all important for subduing large prey while the cat positions itself for the killing bite. Small prey specialists have relatively longer distal limb elements for swift prey capture, and mixed prey specialists had intermediate values with relatively more robust metacarpals. Arboreal felids also had more robust limbs. They had relatively longer proximal phalanges for better grip while climbing, and a relatively short brachial index (radius to humerus ratio). Additionally, we found that felids and canids differ in forelimb scaling, which emphasizes the dual use of forelimbs for locomotion and prey capture in felids. This morphometric technique worked well to separate prey‐size preference in felids, but did not work as well to separate locomotor groups, as scansorial and terrestrial felids were not clearly distinguished. J. Morphol. 2009.

Long in the tooth: evolution of sabertooth cat cranial shape

Abstract 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.

Aquatic adaptations in the nose of carnivorans: evidence from the turbinates

Inside the mammalian nose lies a labyrinth of bony plates covered in epithelium collectively known as turbinates. Respiratory turbinates lie anteriorly and aid in heat and water conservation, while more posterior olfactory turbinates function in olfaction. Previous observations on a few carnivorans revealed that aquatic species have relatively large, complex respiratory turbinates and greatly reduced olfactory turbinates compared with terrestrial species. Body heat is lost more quickly in water than air and increased respiratory surface area likely evolved to minimize heat loss. At the same time, olfactory surface area probably diminished due to a decreased reliance on olfaction when foraging under water. To explore how widespread these adaptations are, we documented scaling of respiratory and olfactory turbinate surface area with body size in a variety of terrestrial, freshwater, and marine carnivorans, including pinnipeds, mustelids, ursids, and procyonids. Surface areas were estimated from high‐resolution CT scans of dry skulls, a novel approach that enabled a greater sampling of taxa than is practical with fresh heads. Total turbinate, respiratory, and olfactory surface areas correlate well with body size (r2u2003≥u20030.7), and are relatively smaller in larger species. Relative to body mass or skull length, aquatic species have significantly less olfactory surface area than terrestrial species. Furthermore, the ratio of olfactory to respiratory surface area is associated with habitat. Using phylogenetic comparative methods, we found strong support for convergence on 1u2003:u20033 proportions in aquatic taxa and near the inverse in terrestrial taxa, indicating that aquatic mustelids and pinnipeds independently acquired similar proportions of olfactory to respiratory turbinates. Constraints on turbinate surface area in the nasal chamber may result in a trade‐off between respiratory and olfactory function in aquatic mammals.

Saving the World's Terrestrial Megafauna

From the late Pleistocene to the Holocene, and now the so called Anthropocene, humans have been driving an ongoing series of species declines and extinctions (Dirzo et al. 2014). Large-bodied mammals are typically at a higher risk of extinction than smaller ones (Cardillo et al. 2005). However, in some circumstances terrestrial megafauna populations have been able to recover some of their lost numbers due to strong conservation and political commitment, and human cultural changes (Chapron et al. 2014). Indeed many would be in considerably worse predicaments in the absence of conservation action (Hoffmann et al. 2015). Nevertheless, most mammalian megafauna face dramatic range contractions and population declines. In fact, 59% of the world’s largest carnivores (≥ 15 kg, n = 27) and 60% of the world’s largest herbivores (≥ 100 kg, n = 74) are classified as threatened with extinction on the International Union for the Conservation of Nature (IUCN) Red List (supplemental table S1 and S2). This situation is particularly dire in sub-Saharan Africa and Southeast Asia, home to the greatest diversity of extant megafauna (figure 1). Species at risk of extinction include some of the world’s most iconic animals—such as gorillas, rhinos, and big cats (figure 2 top row)—and, unfortunately, they are vanishing just as science is discovering their essential ecological roles (Estes et al. 2011). Here, our objectives are to raise awareness of how these megafauna are imperiled (species in supplemental table S1 and S2) and to stimulate broad interest in developing specific recommendations and concerted action to conserve them.

Respiratory turbinates of canids and felids: a quantitative comparison

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.