Feline leukemia virus in a captive bobcat

An 11-mo-old captive-bred male neutered bobcat (Felis rufus) presented with lethargy, anorexia, leukopenia, neutropenia, lymphopenia, and nonregenerative anemia. The animal was diagnosed as feline leukemia virus (FeLV) positive by immunofluorescent antibody and enzyme-linked immunosorbant assay (ELISA) testing. It died despite supportive care. Pathologic examination revealed multifocal non-suppurative encephalitis, diffuse interstitial pneumonia, multifocal hepatocellular necrosis, non-suppurative peritonitis, and lymphoid depletion. FeLV was isolated from peripheral blood mononuclear cells, bone marrow, spleen, and lymph node. FeLV-specific gag sequences were amplified by DNA polymerase chain reaction (PCR) and aligned with known domestic cat FeLV's. The source of the virus was speculated to be a domestic cat that was a surrogate nurse. Case reports of FeLV in nondomestic felids are few, and FeLV does not appear to be enzootic in wild felids, except European wildcats (Felis silvestris) in France and Scotland. Introduction of FeLV into free-living and captive nondomestic felid populations could have serious consequences for their health and survival. Measures to prevent the introduction of this virus to nondomestic felids are warranted.     

Comparative endocrinology of domestic and nondomestic felids

The ability to track gonadal and adrenal activity via hormones is key to optimizing health and reproduction. Through decades of study, a great deal has been learned about the biology of female domestic cats, including endocrine function. More recently, comparative endocrine studies have greatly expanded our knowledge base of nondomestic felids as well. The latter has been possible largely through the development of noninvasive fecal steroid metabolite analysis techniques, which currently is the method of choice for monitoring endocrine function in wildlife species, including felids. It now is well-recognized that a range in endocrine patterns exists among Felidae, with many traits and mechanisms being uncommon, if not unique. There is a high degree of variability in the type of ovulation (spontaneous versus induced) expressed across the taxon. Even within species, some individuals exhibit ovulation that is only induced, whereas others ovulate spontaneously as well. Steroid metabolism also differs in that metabolites are excreted almost exclusively in feces, with very little steroid found in urine. Across species there are marked differences in seasonal and social influences on reproduction, adrenal responses to husbandry practices, and ovarian responses to assisted reproductive procedures. This means that developing strategies to improve health and reproduction of felids must be done on a species by species basis. This paper summarizes current knowledge on the reproductive endocrinology of female domestic and nondomestic cats, and describes how the rapidly growing endocrine database is aiding ex situ management efforts.     

Isolation of preantral follicles from nondomestic cats—viability and ultrastructural investigations

Large scale isolation of small preantral follicles (40–90 μm) from nondomestic cats (lion, puma, cheetah, jaguar, and three kinds of tigers) is described and compared with domestic cats. The viability of preantral follicles was estimated by trypan blue staining of granulosa cells and/or by 5-bromo-2′-deoxy-uridine (BrdU) incorporation into oocytes and granulosa cells during short term culture. Native and isolated preantral follicles were compared ultrastructurally. In nondomestic cats the mechanical dissection of ovaries provided 0–12 500 follicles per ovary with a viability of 20–50%, estimated by trypan blue staining. Even the follicles recovered from domestic cats, whose ovaries are considerable smaller than ovaries from all other felids, are characterised by only 28.7% viable follicles. The follicles from one Siberian tiger and three Indian lions were cultivated and their in vitro viability assessed by BrdU labelling. Lion follicles were comparable to domestic cat follicles with respect to BrdU incorporation. Tiger follicles were characterised by a decreased staining of granulosa cells.The ultrastructure of feline oocytes appears similar to that of most mammalian species and was only slightly affected during the isolation procedure. A central vesicular body was only observed in tiger oocytes.     

Female reproductive cycles of wild female felids

Many felid species are endangered because of destructive human activities. As a result, zoos are being tasked with sustaining genetically healthy populations in case of catastrophic extinctions. Unfortunately, with the exception of a few species, most felids do not reproduce well in captivity. The ability to track reproductive activity via hormones is key to developing successful ex situ breeding programs. Through the development of noninvasive fecal hormone monitoring techniques, a high degree of variability in estrous cycle characteristics has been found to exist across the taxon, including the type of ovulation. For example, although all felids have induced ovulations, the occurrence of spontaneous ovulations varies across species, and even between individuals within a species. Clouded leopards, fishing cats and margays frequently have spontaneous ovulations, whereas these are rarely observed in the cheetah, tigrina and ocelot. There are marked species differences in the impact of season on reproductive function, with some being exquisitely sensitive to photoperiod (e.g., Pallas' cat), some moderately affected (tiger, clouded leopard, snow leopard), and others that are not influenced at all (e.g., ocelot, tigrina, margay, lion, leopard, fishing cat). One of the greatest challenges remaining is overcoming the problems associated with highly variable ovarian responses to ovulation induction therapies used with assisted reproductive procedures, like artificial insemination (AI). Success is relatively high in the cheetah and ocelot, but few pregnancies have resulted after AI in clouded leopard, fishing cat and tiger. Current knowledge of the reproductive physiology of nondomestic felids, including aspects of the anatomy, behavior and ovarian cycles will be presented, and how the rapidly growing endocrine database is aiding ex situ management efforts.     

Disseminated toxoplasmosis in a captive ring-tailed lemur (Lemur catta)

A 3-yr-old secundiparous female ring-tailed lemur presented to the Auburn University Small Animal Clinic with signs of dyspnea, lethargy, and anorexia. The animal died before she could be examined, and a full necropsy was immediately performed. Provisional necropsy findings included moderate pneumonia and hepatopathy. Acute interstitial pneumonia and focal hepatocellular necrosis were confirmed histologically. Lung impression smears, histopathology, electron microscopy, immunohistochemistry, and tissue culture isolation resulted in a diagnosis of acute disseminated Toxoplasma gondii infection, which was confirmed by polymerase chain reaction. The isolate of T. gondii was avirulent for mice and was named AU Tgl and genetically is type II. The source of the infection remains unclear, but speculation suggests contaminated fruit or blackbirds (Passeriformes: Icteridae) acting as transport hosts for oocysts from nondomestic felids and feral cats on the property.     

Development, validation, and application of a urinary relaxin radioimmunoassay for the diagnosis and monitoring of pregnancy in felids

Many nondomestic felids are highly endangered, and captive breeding programs have become essential components of holistic conservation efforts for these species. The ability to diagnose pregnancy early in gestation is fundamental to developing effective breeding programs. The purpose of this study was to develop a radioimmunoassay (RIA) for the detection of urinary relaxin in felids and assess its applicability for early, noninvasive pregnancy diagnosis in domestic cats (Felis silvestris catus) and leopards (Panthera pardus). Urine was collected from pregnant and nonpregnant domestic cats and leopards at mating, and then weekly thereafter for the duration of gestation. Paired serum samples were also collected from the domestic cats. A RIA for relaxin that uses an antiserum against synthetic canine relaxin was validated for felid urine and shown to detect relaxin immunoreactivity in pregnant cat urine subjected to acid-acetone extraction. In the cat, urinary relaxin was first detected between Days 21 and 28 of gestation; levels peaked at 42-49 days, and the concentrations then declined over 2 wk prior to parturition. The urinary relaxin profiles of the cat mirrored those in serum. In the leopard, urinary relaxin was first detected at Day 25-28 of gestation; levels peaked at Day 60-64 and declined in the last 3-4 wk of pregnancy. These results indicate that measurement of urinary relaxin in the cat and leopard provides a reliable method for pregnancy determination from as early as 3-4 wk of gestation. This method of pregnancy diagnosis and monitoring may prove useful in the breeding management of domestic cats and other felid and canid species, and provides a foundation for future studies on pregnancy in captive exotic carnivores.     

Exposure to FIV and FIPV in wild and captive cheetahs

Two RNA-containing viruses, feline infectious peritonitis virus (FIPV) and feline immunodeficiency virus (FIV), have been observed to infect cheetahs. Although both viruses cause lethal immunogenetic pathology in domestic cats, only FIPV has documented pathogenesis in cheetahs. We summarize and update here a worldwide survey of serum and plasma from cheetah and other nondomestic felids for antibodies to FIV and FIPV, based on Western blot and immunofluorescence assays. FIPV exposure shows an acute pattern with recognizable outbreaks in several zoological facilities, but is virtually nonexistent in sampled free-ranging populations of cheetahs. FIV is more endemic in certain natural cheetah populations, but infrequent in zoological collections. FIV exposure was also seen in lions, bobcats, leopards, snow leopards, and jaguars. FIV causes T-cell lymphocyte depletion and associated diseases in domestic cats, but there is little direct evidence for FIV pathology in exotic cats to date. Because of the parallels with a high incidence of simian immunodeficiency virus in free-ranging African primates without disease, the cat model may also reflect historic infections that have approached an evolutionary balance between the pathogen and immune defenses of their feline host species. Published 1993 Wiley-Liss, Inc.     

Ovarian response to repeated administration of alternating exogenous gonadotropin regimens in the ocelot (Leopardus pardalis) and tigrinus (Leopardus tigrinus)

Exogenous gonadotropins are used to stimulate ovarian follicular growth and ovulation in mammalian species, including wild cats. However, successes in application of assisted reproduction techniques in nondomestic felids have been sparse. Our objectives were to assess the effectiveness of alternating gonadotropin regimens on ovarian responses. Five adult female ocelots and four adult female tigrinus were treated four to six times, using alternating eCG/hCG and pFSH/pLH at 4-month intervals. Laparoscopies were done to assess follicular development and to collect oocytes from matures follicles. The average number of follicles and corpus luteum (CL) per stimulation was higher in ocelots (7.0 +/- 0.8; mean +/- S.E.M.) than in tigrinus (2.5 +/- 0.4; P < 0.05), but the percentage of mature oocytes did not differ between the two species (mean range, 54-55%). Within species, both gonadotropin regimens were equally effective in inducing follicular growth and oocyte maturation. The total number of ovarian structures and oocyte maturation percentages did not decrease in either species with sequential stimulations. In summary, female ocelots and tigrinus continued to respond to repeated alternating ovarian stimulation protocols. In conclusion, the use of alternating gonadotropin regimens may permit more intensive reproductive management in these endangered cats.     

Susceptibility of Domestic Cats to Chronic Wasting Disease

Domestic and nondomestic cats have been shown to be susceptible to feline spongiform encephalopathy (FSE), almost certainly caused by consumption of bovine spongiform encephalopathy (BSE)-contaminated meat. Because domestic and free-ranging nondomestic felids scavenge cervid carcasses, including those in areas affected by chronic wasting disease (CWD), we evaluated the susceptibility of the domestic cat (Felis catus) to CWD infection experimentally. Cohorts of 5 cats each were inoculated intracerebrally (i.c.) or orally (p.o.) with CWD-infected deer brain. At 40 and 42 months postinoculation, two i.c.-inoculated cats developed signs consistent with prion disease, including a stilted gait, weight loss, anorexia, polydipsia, patterned motor behaviors, head and tail tremors, and ataxia, and the cats progressed to terminal disease within 5 months. Brains from these two cats were pooled and inoculated into cohorts of cats by the i.c., p.o., and intraperitoneal and subcutaneous (i.p./s.c.) routes. Upon subpassage, feline CWD was transmitted to all i.c.-inoculated cats with a decreased incubation period of 23 to 27 months. Feline-adapted CWD (Fel^CWD) was demonstrated in the brains of all of the affected cats by Western blotting and immunohistochemical analysis. Magnetic resonance imaging revealed abnormalities in clinically ill cats, which included multifocal T2 fluid attenuated inversion recovery (FLAIR) signal hyperintensities, ventricular size increases, prominent sulci, and white matter tract cavitation. Currently, 3 of 4 i.p./s.c.- and 2 of 4 p.o. secondary passage-inoculated cats have developed abnormal behavior patterns consistent with the early stage of feline CWD. These results demonstrate that CWD can be transmitted and adapted to the domestic cat, thus raising the issue of potential cervid-to-feline transmission in nature.     

Comparative bite forces and canine bending strength in feline and sabretooth felids: implications for predatory ecology

The sabretooth felids were widespread across much of the world in the Late Tertiary, and appear to have been an important group of large predators. Owing to the substantially different skull morphology of derived sabretooths compared with extant felids, there has been considerable debate over the killing mode, bite forces, and bending strength of the large upper canines, and over the implications of these characteristics on feeding ecology. Debates have, however, usually been based on indirect comparisons of force vectors. In this paper, I provide assessments of the estimated force output from the jaw adductor muscles, based on estimates of muscle cross-sectional areas and force vectors, along with canine bending strengths, in a variety of sabretooth felids, in comparison with extant felids. In general, sabretoothed felids had moderately powerful bites, albeit with less jaw adductor power for their body sizes compared with extant felids, sometimes markedly so. Less derived sabrecats appear to have had proportionally higher bite forces than derived forms. The length of the upper canines seemingly compromised their bending strength at any given body size, and again this was most marked in derived forms. However, compared with estimated jaw adductor forces, the canines of sabrecats appear, if anything, to have been stronger than those of extant conical-toothed felids. It has previously been suggested that large sabretoothed felids hunted large prey with a canine shearing bite, powered in part by the jaw adductors and in part by the muscles of the upper neck–occipital region. The present results of canine bending strengths versus the predicted bite force from the jaw adductors supports this suggestion.  © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 151 , 423–437.     

Contraception in felids

Contraceptives are used for reversible reproductive control in genetically valuable wild felids, as permanent reproductive control in generic wild felids, and as an economically practicable means to control feral cats. The progestin contraceptives, megestrol acetate, melengesterol acetate, medroxyprogesterone acetate, and levonorgestrol (administered orally, in implants, or as depot injections), are effective in preventing pregnancy. However, long-term use is associated with endometrial hyperplasia, endometrial cancer, and mammary cancer. Gonadotropin releasing hormone analogs or luteinizing hormone vaccines that achieve contraception by suppressing ovarian or testicular function, do not have the adverse health effects of progestins. However, reliable reversibility has not been demonstrated, and male secondary sex characteristics may be suppressed. Bisdiamines also inhibit spermatogenesis and lower circulating testosterone concentrations in treated male cats. Porcine zona pellucida vaccines are ineffective contraceptives in felids and may cause serious health problems when combined with some adjuvants. Because of the limited availability of non-progestin contraceptives and side effects associated with some agents, widespread application of contraception to felids has been curtailed. More non-steroidal methods of contraception should be tested in the future to provide alternatives for controlling reproduction in felids. Furthermore, all empirical information on contraceptive safety and efficacy should be assembled in a database to provide the knowledge needed by veterinarians and managers to determine benefits/risks of currently available contraceptives in felids, both domestic and wild.     

Research in nondomestic species: experiences in reproductive physiology research for conservation of endangered felids

Tremendous strides have been made in recent years to broaden our understanding of reproductive processes in nondomestic felid species and further our capacity to use this basic knowledge to control and manipulate reproduction of endangered cats. Much of that progress has culminated from detailed scientific studies conducted in nontraditional laboratory settings, frequently at collaborating zoological parks but also under more primitive conditions, including in the field. A mobile laboratory approach is described, which incorporates a diverse array of disciplines and research techniques. This approach has been extremely useful, especially for conducting gamete characterization and function studies as well as reproductive surveys, and for facilitating the development of assisted reproductive technology. With continuing advances in assisted reproduction in rare felids, more procedures are being conducted primarily as service-related activities, targeted to increase effectiveness of species propagation and population management. It can be a challenge for both investigators and institutional animal care and use committees (IACUCs) to differentiate these service-based procedures from traditional research studies (that require IACUC oversight). For research with rare cat species, multi-institutional collaboration frequently is necessary to gain access to scientifically meaningful numbers of study subjects. Similarly, for service-based efforts, the ability to perform reproductive procedures across institutions under nonstandard laboratory conditions is critical to applying reproductive sciences for managing and preserving threatened cat populations. Reproductive sciences can most effectively assist population management programs (e.g., Species Survival Plans) in addressing conservation priorities if these research and service-related procedures can be conducted "on the road" at distant national and international locales. This mobile laboratory approach has applications beyond endangered species research, notably for other scientific fields (e.g., studies of hereditary disease in domestic cat models) in which bringing the laboratory to the subject is of value.     

Cats under cover: Habitat models indicate a high dependency on woodlands by Atlantic Forest felids

Four Neotropical small and medium felids—the ocelot, jaguarundi, margay, and southern tiger cat—have overlapping geographic distributions in the endangered Atlantic Forest. Local studies show that these felids avoid areas with high human impact, but the three smaller ones use human‐modified areas more frequently than do ocelots. To understand how landscape changes affect the habitat distribution of these four felids in the Atlantic Forest of Argentina, we used maximum entropy models to analyze the effect of environmental and anthropogenic factors. We estimated niche breadth and overlap among these felids. The conversion of the native forest to land uses without trees was the most important variable that determined the habitat distribution of the four species. For all four species, the optimal habitat covered about 1/3 of the study area and corresponds mainly to the native forest areas. Nearly 50% of these areas had some level of protection. The niche width was higher for the small felids than for ocelots. Niche overlap was high for all species pairs, but higher among the small felids and lower for each of these with the ocelot. The four felids were negatively affected by native forest loss, with ocelots being more sensitive than the smaller felids. The conversion of unprotected forest areas to other types of land uses would imply a greater habitat loss for these felids. The protection of current remnants of Atlantic Forest in Argentina is important for the long‐term conservation of the four felids. Abstract in Spanish is available with online material.     

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.     

Previously undescribed features in the temporalis and masseteric musculature of several large felids raised in captivity

Although the anatomy of the domestic housecat has been examined in meticulous detail, comparative observations on the anatomy of the larger wild cats is scant and information about particularities in their cranial complexes rarer still. In the course of dissecting sets of masticatory muscles in five large felids, all older zoo animals, we had the opportunity to note muscular attachments in the head and jaw apparatus that appeared significantly broader and more distal in their insertion sties than expected. Further investigation may determine whether these masticatory peculiarities are functional adaptations of felids, or instead are associated in some manner with the specialized diets large felids receive in captive environments. Zoo Biol 16:187–191, 1997. © 1997 Wiley-Liss, Inc.     

Fecal androgen metabolite analysis for noninvasive monitoring of testicular steroidogenic activity in felids

Limited data are available on long-term, seasonal changes in testicular steroidogenic activity in nondomestic felids, primarily because of the difficulties associated with longitudinal blood sampling (e.g., handling, restraint, anesthesia). Therefore, a noninvasive approach for assessing testicular androgen production was developed using the domestic cat (Felis catus) as a model. Two adult males were injected i.m. with 4 μCi¹⁴-testosterone to determine the time course and relative proportions of androgen metabolites excreted in urine and feces. Peak urinary radioactivity was detected 13 and 19 hr postinjection and accounted for ∼8% of the total radioactivity recovered. High performance liquid chromatography (HPLC) analysis detected multiple polar urinary metabolites, none of which eluted with the ³H-testosterone reference tracer. The majority of urinary testosterone metabolites consisted of nonenzyme-hydrolyzable, water-soluble (presumably conjugated) forms. In feces, radioactivity was detected in the first sample collected at 22 hr postinjection for both males, although peak metabolite excretion in one male was not observed until 61 hr postinjection. HPLC analysis detected several fecal metabolites consisting primarily of nonhydrolyzable, water-soluble forms (84.4 ± 0.9%) with some ether-soluble forms (15.6 ± 0.9%). None of the fecal androgen metabolites were associated with free testosterone. However, one or more of the water-soluble fecal metabolites was quantifiable using a commercially available testosterone radioimmunoassay. The biological relevance of this immunoactivity was confirmed in the domestic cat; concentrations were high in adult, intact males and nondetectable in intact females and castrated males and females. In addition, fecal androgen concentrations in a male Pallas' cat (Felis manul) exhibited seasonal fluctuations that corresponded with parallel changes in serum testosterone and ejaculate quality. These data indicate that testicular steroidogenic activity can be monitored non invasively in felids, providing a potentially valuable tool for endangered felid management to: (1) assess pubertal status, (2) determine the influence of season on reproduction, and (3) diagnose possible causes of sub- or infertility. © 1996 Wiley-Liss, Inc.     

An ontological crisis? A review of large felid conservation in India

The need for a solid knowledge base to inform conservation activity is now universally recognised. We critically scrutinised the scientific knowledge of large felids in India located in peer-reviewed research papers to assess the information available to make landscape-level management decisions that aid conservation, which is a stated goal of both the Indian government and the international community. We found two striking patterns: the biological sciences dominate in the published literature, and nearly all the research has been carried out in protected areas, though a substantial number of large felids also live outside protected areas. We argue that these patterns are not incidental, but the result of the dualistic ontology of science that uses processes of ‘purification’ and ‘translation’ to fit complex realities into disciplinary prerogatives organised around creating dichotomies (like nature–culture). In addition, since this body of scientific knowledge locates large felids in ‘pure’ biological landscapes, there is little or no insight from multi-use landscapes. These findings, we believe, highlight important knowledge gaps in our present research-based knowledge of large felids in India, which urgently need to be addressed if progress is to be made in conservation.     

A dynamic model for the evolution of sabrecat predatory bite mechanics

The ability of sabretoothed felids to achieve sufficiently high bite forces for predation at extreme gape angles has been the subject of decades of debate. Previous studies have indicated that bite forces in derived sabretoothed felids would have been low, but that they were probably augmented by head depressing muscles. However, bite mechanics is a dynamic process, and mechanical properties change with changes in gape angles. In this study, I present the first comprehensive model of bite mechanics, vector angles, and forces about the temporomandibular joint at gape angles from occlusion to maximal inferred gape in sabretoothed felids. Primitive sabrecats (Machairodus, Paramachairodus) appear broadly comparable to extant large felids (Panthera, Puma), but derived sabrecats in the groups Homotherini (Amphimachairodus, Homotherium, Xenosmilus) and Smilodontini (Megantereon, Smilodon) are often substantially different from either of the former. The ability of the mandibular adductors to generate torque changes with gape angle, indicating that previous models fail to capture potentially important differences in bite function. Inferred muscle sizes and the angles of effective torque from individual adductor fibres in derived sabrecats are different from those of primitive sabrecats and extant large felids, but they had evolved a number of compensatory adaptations for maximizing force output at the canine and carnassial, primarily changes in muscle fibre angles and more compact crania. Inferred outforces at the canines and carnassials were comparable amongst all groups at low gape angles, but at extreme gape angles outforces would have been low, supporting previous hypotheses of head flexor contribution during initial stages of the killing bite in sabrecats. Mandibular adduction in extant carnivores is a complicated pattern of differences in twitch tension and electromyographical activity at different gape angles, and inference of maximal isotonic bite forces from reconstructed mandibular adductor sizes in fossils will give estimates primarily suitable for comparative purposes. Potentially, derived sabrecats could have evolved differences from extant felids in adductor histochemistry or pinnation angle of individual fibres. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 162 , 220–242.     

Comparative Scaling of Humeral Cross-Sections of Felids and Canids Using Radiographic Images

The cortical thickness of long bones can be an effective indicator of locomotor modes and other stresses encountered by bone. Felids and canids are two carnivoran families that have similar levels of phylogenetic diversity and overlap in body size, but differ in their locomotor habits. Many canids and felids are cursorial, but felids also climb more frequently than canids. Felids also display a secondary use for their forelimbs not observed in any canids: they use their forelimbs to grasp and subdue prey. Large felids use their forelimbs much more extensively to subdue prey than do large canids and, therefore, should have proportionately greater forces applied to their forelimbs. This study uses a non-invasive radiographic approach to examine the differences in cortical thickness in the humerus between the Felidae and Canidae, as well as between size groups within these two families. Results show few significant differences between the two families, with a slight trend toward more positive allometry in the felids. Overall, radiographic measurements were found to be better predictors of body mass than either prey killing behavior or locomotor mode in these two carnivoran families. One canid that demonstrated exceptionally high cortical area was the bush dog, Speothos venaticus. The rarely observed bush dog has been postulated to swim and dig regularly, and it may be that the thickened cortical bone reflects these behaviors.     

Canine tooth strength and killing behaviour in large carnivores

Bending strength of upper canine teeth is examined among living canids, felids, hyaenids and several extinct species including sabretooth cats, borophagine dogs and the dire wolf, Canis dirus. The tooth is modelled as a cantilever with an elliptical cross-section. Using beam theory, the bending strength of the upper canine is calculated given a constant force applied to the canine tip. Results indicate that felids and hyaenids have relatively stronger canines than canids, particularly in bending about the anteroposterior (AP) rather than the mediolateral axis. It is suggested that canine shape reflects the forces produced during killing and feeding. As shown by an analysis of jaw muscle moment arms, felids and hyaenids have relatively stronger bites than canids. Moreover, the canines of hyaenids and felids are perhaps more likely to contact bone during feeding and killing and consequently may be subjected to larger and more frequent bending moments about the AP axis. The canines of sabretooth cats are shown to be more similar in shape and strength characteristics to those of living canids than felids, whereas those of the borophagine dogs and the dire wolf are closer to modern hyaenas.