Post by Infinity Blade on Sept 27, 2022 6:31:36 GMT 5
Cats grapple with strong, flexible forelimbs and retractable claws, while dogs run after prey and only use their jaws to capture and kill. There are certainly forms in both families that deviate or break from this convention (cheetahs and homotheres in felids, at least some borophagines in canids), but in general, you could say cats are grapplers, and dogs are head-hunters.
That said, there are also significant differences between the two families in their feeding apparata: i.e. the skull and neck. While anyone can tell you the differences between cat and dog limbs, I feel their differences in cranial, dental, and neck anatomy are not discussed enough or widely known online. The fact that all the information I found discussing these differences comes from academic sources is testament to this. So the purpose of this review is to highlight differences in the functional morphology of felid and canid feeding apparata, and how it ties in with their hunting behavior. I could have probably made this a post in the thread dedicated to animal feeding mechanisms, but I felt I had enough information and things to explain to make it its own review thread.
DISCLAIMER: Both canids and felids displayed a diversity of cranial and dental morphologies throughout their evolutionary histories. So when I say “felids” and “canids” here, I’m really just referring to modern felids and canids, especially their large prey specialists. Not everything I say will necessarily be true for some fossil canids and felids, or to small prey specialists.
Teeth:
In mammalian carnivores in general, the canines are the killing teeth. Modern felids and canids actually have differences in canine tooth shape that reflect their killing behaviors. First, felid canines are more rounded in cross section than those of canids. Instead, canid canines are actually lateromedially compressed (i.e. more knife-like in cross section).
(Generalized cross sections of the canines of a felid (Panthera pardus) and canid (Canis lupus). Notice how the cat’s canines are rounded in cross section. Source: Biknevicius & van Valkenburgh (2019).)
Why is this so? Felids deliver deeply-penetrating killing bites that hold onto prey for a prolonged period of time. During this time, their prey struggles, which results in stresses along the canine teeth that can be unpredictable in direction and magnitude. They are also more likely to get into incidental contact with bone. As a result, felids need canines that are relatively rounded in cross section, allowing them to withstand force from any direction (Biknevicius & van Valkenburgh, 2019).
On the other hand, canids kill prey with multiple shallow slashing bites. The elliptical cross sections of their canines make them better suited for this method of killing than the more rounded canines of cats (Ruff & van Valkenburgh, 1987). It is also indicative of forces acting primarily in the anteroposterior (front to back) direction; think of a wolf pulling back a chunk of flesh or being dragged along by running prey (Mech & Boitani, 2010). Because the canines are wider fore-and-aft than side-to-side, they are not as resistant to lateral bending forces as the canine teeth of felids. However, they don’t need to be, as the canines are used for shallow, slashing bites. That way, the canines are not only less prone to incidental contact with bone, but they’re also in contact with prey for a much shorter period of time (Biknevicius & van Valkenburgh, 2019).
(It should be noted that felid canines being stronger than canid canines only holds true when actual bite forces at the canines are ignored. Because felids have some of the strongest bites at the canines relative to other similar-sized carnivorans, and because their canines are long (which compromises bending strength), their canines are no stronger than those of other carnivorans in the context of biting (Christiansen & Adolfssen, 2005).)
(Interesting side note: if you’re a theropod enthusiast, this should sound familiar to you. You might think of a cat’s canines as similar to a tyrannosaurid’s teeth, while a dog’s canines are more like a typical theropod’s teeth. Tyrannosaurids had pachydont teeth that were used to violently struggle with prey and to crush bone, although they were more osteophagous than most felids. Most carnivorous theropods had blade-like ziphodont teeth used to create slashing wounds, although their teeth were more specialized for this function than canid canines.)
Additionally, canid upper canines are more curved and hook-like than felid upper canines. This helps canids grip and hold onto prey, while also pushing their teeth further into prey/food (since the tip of the tooth points in the direction opposite to the pull force). By contrast, felids need straighter canines that penetrate deeply and have a central axis that matches the direction of their biting force (Pollock et al., 2019).
(© @ Tahlia Pollock)
Bite force:
Previous studies have suggested that felids have relatively stronger bites than canids (Radinsky, 1981; Ruff & van Valkenburgh, 1987; Christiansen & Adolfssen, 2005). Felids possess relatively longer moment arms of the temporalis muscle than canids, which proves advantageous for bite force (Ruff & van Valkenburgh, 1987).
Additionally, the short snout of cats increases the mechanical advantage of the jaw muscles. Because the canines are closer to the fulcrum of the lever (in this case the jaw joint), the moment arm of resistance is decreased, and increases bite force at the canines (Kitchener et al., 2010).
One study, interestingly, found extant canids to have higher mean bite force quotient (i.e. ratio of actual bite force compared to bite force expected for size) than in felids. However, it also found that relative to skull length, bite force at the canines was stronger in felids than in canids, possibly due to greater skull width relative to length (Wroe et al., 2005).
Neck strength:
Analysis of occipital width in carnivorans suggests that felids (and to a greater extent, mustelids) have relatively stronger neck muscles than canids (Radinsky, 1981).
Additionally, most species of modern canid have relatively longer, straighter necks than felids (which have relatively shorter, more S-curved necks). Since shorter muscles contract more powerfully than longer muscles, this helps to make the necks of felids stronger than those of canids. Canids also have smaller muscle insertion areas on their cervical vertebrae than do felids, further indicating less powerful neck muscles (Wang & Tedford, 2010).
Cranial and mandibular strength:
All felids possess a dorsoventrally and labiolingually strong mandibular symphysis compared to canids and hyaenids (Therrien, 2005).
The shorter skulls of cats might be more resistant to forces produced by violently struggling prey than those of canids (Wroe et al., 2005).
Conclusions:
Screen capture taken from Biknevicius & van Valkenburgh (2019).
It is apparent that many aspects of the craniodental and cervical anatomy of felids is more powerfully constructed than that of canids. Modern cats have structurally stronger canine teeth (at least in the context of forces other than actual bite force), stronger bite forces at the canines (certainly so when adjusting for skull length), stronger mandibular symphyses, (possibly) stronger crania, and stronger neck muscles compared to modern dogs.
Why do extant, large prey-specialist dogs seem so deficient in many of these regards compared to cats? The answer is simple (and alluded to in some of the works I cite): dogs hunt in packs, while most cats don’t. Because wolves, African wild dogs, and dholes usually work together to kill large prey, they do not need any of the adaptations felids possess to perform this same feat. They do not need jaw bones as strong as those of felids because multiple individuals are absorbing the stress of a violently struggling prey item. They do not need bite forces as strong at the canine because multiple other individuals are causing damage elsewhere on the body.
It is important to remember context when comparing animal adaptations to each other. To some, a canid might seem “inferior” to a felid in predatory ability for lacking the same kind of power the latter has in its jaws, neck, and limbs/claws. But this ignores the evolutionary context that modern large prey specialist canids (and the spotted hyena) evolved within; that is, as cooperative pack hunters. Judging a wolf for not possessing the grappling limbs, retractable claws, or the same cranial, dental, and cervical myological properties as the cougar it rubs shoulders with is akin to judging a human hunter-gatherer for lacking the same sharp teeth and claws either of these two predators has. It simply performs the same task (i.e. hunting large prey) in a different way that is effective all the same.
That said, there are also significant differences between the two families in their feeding apparata: i.e. the skull and neck. While anyone can tell you the differences between cat and dog limbs, I feel their differences in cranial, dental, and neck anatomy are not discussed enough or widely known online. The fact that all the information I found discussing these differences comes from academic sources is testament to this. So the purpose of this review is to highlight differences in the functional morphology of felid and canid feeding apparata, and how it ties in with their hunting behavior. I could have probably made this a post in the thread dedicated to animal feeding mechanisms, but I felt I had enough information and things to explain to make it its own review thread.
DISCLAIMER: Both canids and felids displayed a diversity of cranial and dental morphologies throughout their evolutionary histories. So when I say “felids” and “canids” here, I’m really just referring to modern felids and canids, especially their large prey specialists. Not everything I say will necessarily be true for some fossil canids and felids, or to small prey specialists.
Teeth:
In mammalian carnivores in general, the canines are the killing teeth. Modern felids and canids actually have differences in canine tooth shape that reflect their killing behaviors. First, felid canines are more rounded in cross section than those of canids. Instead, canid canines are actually lateromedially compressed (i.e. more knife-like in cross section).
(Generalized cross sections of the canines of a felid (Panthera pardus) and canid (Canis lupus). Notice how the cat’s canines are rounded in cross section. Source: Biknevicius & van Valkenburgh (2019).)
Why is this so? Felids deliver deeply-penetrating killing bites that hold onto prey for a prolonged period of time. During this time, their prey struggles, which results in stresses along the canine teeth that can be unpredictable in direction and magnitude. They are also more likely to get into incidental contact with bone. As a result, felids need canines that are relatively rounded in cross section, allowing them to withstand force from any direction (Biknevicius & van Valkenburgh, 2019).
On the other hand, canids kill prey with multiple shallow slashing bites. The elliptical cross sections of their canines make them better suited for this method of killing than the more rounded canines of cats (Ruff & van Valkenburgh, 1987). It is also indicative of forces acting primarily in the anteroposterior (front to back) direction; think of a wolf pulling back a chunk of flesh or being dragged along by running prey (Mech & Boitani, 2010). Because the canines are wider fore-and-aft than side-to-side, they are not as resistant to lateral bending forces as the canine teeth of felids. However, they don’t need to be, as the canines are used for shallow, slashing bites. That way, the canines are not only less prone to incidental contact with bone, but they’re also in contact with prey for a much shorter period of time (Biknevicius & van Valkenburgh, 2019).
(It should be noted that felid canines being stronger than canid canines only holds true when actual bite forces at the canines are ignored. Because felids have some of the strongest bites at the canines relative to other similar-sized carnivorans, and because their canines are long (which compromises bending strength), their canines are no stronger than those of other carnivorans in the context of biting (Christiansen & Adolfssen, 2005).)
(Interesting side note: if you’re a theropod enthusiast, this should sound familiar to you. You might think of a cat’s canines as similar to a tyrannosaurid’s teeth, while a dog’s canines are more like a typical theropod’s teeth. Tyrannosaurids had pachydont teeth that were used to violently struggle with prey and to crush bone, although they were more osteophagous than most felids. Most carnivorous theropods had blade-like ziphodont teeth used to create slashing wounds, although their teeth were more specialized for this function than canid canines.)
Additionally, canid upper canines are more curved and hook-like than felid upper canines. This helps canids grip and hold onto prey, while also pushing their teeth further into prey/food (since the tip of the tooth points in the direction opposite to the pull force). By contrast, felids need straighter canines that penetrate deeply and have a central axis that matches the direction of their biting force (Pollock et al., 2019).
(© @ Tahlia Pollock)
Bite force:
Previous studies have suggested that felids have relatively stronger bites than canids (Radinsky, 1981; Ruff & van Valkenburgh, 1987; Christiansen & Adolfssen, 2005). Felids possess relatively longer moment arms of the temporalis muscle than canids, which proves advantageous for bite force (Ruff & van Valkenburgh, 1987).
Additionally, the short snout of cats increases the mechanical advantage of the jaw muscles. Because the canines are closer to the fulcrum of the lever (in this case the jaw joint), the moment arm of resistance is decreased, and increases bite force at the canines (Kitchener et al., 2010).
One study, interestingly, found extant canids to have higher mean bite force quotient (i.e. ratio of actual bite force compared to bite force expected for size) than in felids. However, it also found that relative to skull length, bite force at the canines was stronger in felids than in canids, possibly due to greater skull width relative to length (Wroe et al., 2005).
Neck strength:
Analysis of occipital width in carnivorans suggests that felids (and to a greater extent, mustelids) have relatively stronger neck muscles than canids (Radinsky, 1981).
The high OCPW' in mustelids and felids (Table 1) could reflect either relatively large brains (resulting in wider braincases) or powerful neck muscles. For biomechanical considerations of the latter, with respect to resisting lateral loadings, it is the distance from the occipital condyle to the lateral border of the occiput (i.e. maximum moment arm of head turning muscles) that is important and that distance was estimated by subtracting bi-occipital condyle width from 0 CPW. When that measurement is analysed, felids are still significantly higher than viverrids and canids, while mustelids stand out even further from the other families (see modified OCPW’ at bottom of Table 1). This suggests that mustelids, and to a lesser degree felids, have relatively more powerful neck musculature than do canids and viverrids.
Additionally, most species of modern canid have relatively longer, straighter necks than felids (which have relatively shorter, more S-curved necks). Since shorter muscles contract more powerfully than longer muscles, this helps to make the necks of felids stronger than those of canids. Canids also have smaller muscle insertion areas on their cervical vertebrae than do felids, further indicating less powerful neck muscles (Wang & Tedford, 2010).
Cranial and mandibular strength:
All felids possess a dorsoventrally and labiolingually strong mandibular symphysis compared to canids and hyaenids (Therrien, 2005).
Although the strength of the symphysis varies among species, all felids possess a dorsoventrally and labiolingually strong symphyseal region (Zx/L and Zy/L respectively) compared to canids and hyaenids (see below). This adaptation reflects the powerful canine bite used by felids to kill their prey (Ewer, 1973). Because felids are generally solitary predators, the success of a hunt depends on the ability of a single individual to restrain its prey. Retractile claws, used in combination with a powerful canine bite, enable the predator to subdue prey without the help of a conspecific (Gonyea & Ashworth, 1975). In addition to the dorsoventral stresses generated during the bite, the mandible must also be able to withstand the labiolingual and torsional stresses generated by struggling prey or when the canines encounter bone (Van Valkenburgh & Ruff, 1987). Indeed, when biting an unsecured, struggling prey, the direction of loading at the canine can vary unpredictably, putting the mandible at high risks of fracture (Alexander, 1981). To decrease the probability of accidental failure owing to unpredictable loads, the anterior region of the mandible must, thus, be strong labiolingually.
In canids, small dorsoventral force (Zx/L) at the canine indicates a relatively weak canine bite. Indeed, canids are known to hunt in packs and subdue their prey by delivering rapid, shallow bites (Ewer, 1973). Since prey capture does not depend on the action of a single individual, for which subduing prey rapidly and efficiently is essential, but on the collaboration of several individuals, canids do not need to deliver powerful canine bites. Instead, canids weaken their prey by inflicting numerous superficial wounds (Ewer, 1973; Biknevicius & Ruff, 1992a).
The dorsoventral mandibular force profiles (Zx/L) of hyaenids seem to be intermediate between the felid and canid conditions. The relatively lower Zx/L values at the canine than at the carnassial reflect, as in canids, pack hunting behaviour where prey is subdued through rapid, shallow bites delivered by the several individuals rather than by a single animal. However, the mandibular force profiles also indicate that the mandible at the canine is relatively stronger than in canids. This feature presumably reflects the buttressing of the symphyseal region against large dorsoventral stresses, as hyaenids are known to occasionally crack bones with their anterior dentition (Rensberger, 1995; Van Valkenburgh, 1996).
The shorter skulls of cats might be more resistant to forces produced by violently struggling prey than those of canids (Wroe et al., 2005).
Although extant canids and dasyuromorphians have higher mean BFQ than felids, the shorter skull of cats may confer greater resistance to forces produced by struggling prey.
Conclusions:
Screen capture taken from Biknevicius & van Valkenburgh (2019).
It is apparent that many aspects of the craniodental and cervical anatomy of felids is more powerfully constructed than that of canids. Modern cats have structurally stronger canine teeth (at least in the context of forces other than actual bite force), stronger bite forces at the canines (certainly so when adjusting for skull length), stronger mandibular symphyses, (possibly) stronger crania, and stronger neck muscles compared to modern dogs.
Why do extant, large prey-specialist dogs seem so deficient in many of these regards compared to cats? The answer is simple (and alluded to in some of the works I cite): dogs hunt in packs, while most cats don’t. Because wolves, African wild dogs, and dholes usually work together to kill large prey, they do not need any of the adaptations felids possess to perform this same feat. They do not need jaw bones as strong as those of felids because multiple individuals are absorbing the stress of a violently struggling prey item. They do not need bite forces as strong at the canine because multiple other individuals are causing damage elsewhere on the body.
It is important to remember context when comparing animal adaptations to each other. To some, a canid might seem “inferior” to a felid in predatory ability for lacking the same kind of power the latter has in its jaws, neck, and limbs/claws. But this ignores the evolutionary context that modern large prey specialist canids (and the spotted hyena) evolved within; that is, as cooperative pack hunters. Judging a wolf for not possessing the grappling limbs, retractable claws, or the same cranial, dental, and cervical myological properties as the cougar it rubs shoulders with is akin to judging a human hunter-gatherer for lacking the same sharp teeth and claws either of these two predators has. It simply performs the same task (i.e. hunting large prey) in a different way that is effective all the same.
