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Post by brobear on Mar 22, 2017 12:02:20 GMT -5
One interesting phenomenon that potentially links to dietary meat relates to the fact that brown bears seem to have diminished in size over the course of the last ice age (the Pleistocene). This was observed early in the research on evolution of bear body size (during 1950s) by researchers such as N.K. Vereshshagin and Bjorn Kurten, the one famous in Russia, the other in Europe as pioneering paleontologists.
More recently, Adrian Marciszak and associates published results, based on measures of bear skulls found in Europe, that seem to have pretty much nailed this trend. These results are summarized at left, arrayed according to time, from left to right, differentiating males from females and measures of skull length from skull width. (The acronym MP refers to "middle Pleistocene," progressing in time to the recent, "R"). One feature of these results is the suggestion that males dwarfed more substantially than did females.
This begs the question: Why? There was certainly a lot of meat around during the Pleistocene, perhaps in the form of carrion able to be obtained from the carcasses of the numerous large herbivores dying from any number of causes (see History). According to Herve Bocherens, at expert on reconstructing diets from the analysis of ancient tissues, brown bears were especially carnivorous during the Ice Age, especially in the steppe tundra of Eurasia. This is all consistent with the larger size of Ice Age brown bears being a consequence of ingesting more meat. Even the differences between trends in male and female sizes (see below) is consistent with a meat effect given that males tend to eat comparatively more meat whenever it is available, which means they would have been comparatively more affected by the rapid decline of the meat resource caused by widespread extinctions of the large herbivores towards the end of the last Ice Age.
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Post by brobear on Mar 22, 2017 12:02:38 GMT -5
Sexual dimorphism
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Post by brobear on Mar 22, 2017 12:04:34 GMT -5
As I noted at the beginning of this page, male brown/grizzly bears are, on average, consistently larger in size than females, especially as they grow beyond cub-hood. Beyond this baseline there are several interesting trends. One (illustrated in the graph above left) is that the enlarging of males relative to females (i.e., deviation above the 1:1 line) increases with average size of bears in the population. The rate of this increase is denoted by the power value attached to the X-coefficient above (1.44, with indicates a rapid rate of increase, in contrast to a value of 1, which would denote parity of increase in the sizes of males and females).
As to the driver of this difference? The graph at upper right again suggests that dietary meat plays a role. As you can see, the ratio of male to female body size increases with an increase in percentage of meat in the averaged population diet. The rate of this increase seems to be greater for populations consuming terrestrial meat than for populations in coastal areas that consume primarily salmon. Remember that, by contrast, the increase in overall body size of bears is greater in fish-eating versus ungulate-eating populations. The difference could simply be a mathematical artifact in that the denominator of this ratio (female body size) tends to be greater at any given level of meat consumption among fish-eating versus ungulate-eating populations. That said, the overall trend in this ratio (increase with increasing consumption of meat) defies this bias, and strongly suggests that males do, indeed, get larger at a more rapid rate compared to females with each increment of meat consumption.
Again (as noted above), this divergence could have something to do with the greater ability of the larger less-security-conscious males to dominate concentrated sources of meat. Plus it could have something to do with the extent to which, compared to females, males more efficiently convert dietary protein into lean body mass. Although such a phenomenon has not been definitively shown for bears, it has been well-documented in swine and humans, two other large-bodied omnivore.
As a parting note, the graph at the left places the sexual dimorphism of bears in context of other carnivores, thanks, again, to the work of Per Christiansen. The height of each bar denotes canine (and skull) size as the ratio of males to females for each of the carnivore families comprised of larger-bodied species (excluding, for example, weasels and mongooses). Ursids are denoted by the dark brown bar.
So, the main points here are that: cats (Felids) tend to be the most dimorphic of all families; that the greater differences between males and females of all families are found in canine strength; and that bears are not exceptional in the degree of expressed dimorphism, at as expressed by key skeletal indicators such as skull length and canine size and strength. Parenthetically, it is interesting to note that hyaenas are truly exceptional in being one of the few families of terrestrial mammals in which females are larger than males.
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Post by brobear on Mar 22, 2017 12:04:56 GMT -5
Sexual dimorphism
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Post by brobear on Mar 22, 2017 12:06:30 GMT -5
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Post by brobear on Mar 22, 2017 12:10:04 GMT -5
journals.plos.org/plosone/article?id=10.1371/journal.pone.0102457
The “Bear” Essentials: Actualistic Research on Ursus arctos arctos in the Spanish Pyrenees and Its Implications for Paleontology and Archaeology
Abstract
Neotaphonomic studies of large carnivores are used to create models in order to explain the formation of terrestrial vertebrate fossil faunas. The research reported here adds to the growing body of knowledge on the taphonomic consequences of large carnivore behavior in temperate habitats and has important implications for paleontology and archaeology. Using photo- and videotrap data, we were able to describe the consumption of 17 ungulate carcasses by wild brown bears (Ursus arctos arctos) ranging the Spanish Pyrenees. Further, we analyzed the taphonomic impact of these feeding bouts on the bones recovered from those carcasses. The general sequence of consumption that we charted starts with separation of a carcass’s trunk; viscera are generally eaten first, followed by musculature of the humerus and femur. Long limb bones are not broken open for marrow extraction. Bears did not transport carcasses or carcass parts from points of feeding and did not disperse bones appreciably (if at all) from their anatomical positions. The general pattern of damage that resulted from bear feeding includes fracturing, peeling, crenulation, tooth pitting and scoring of axial and girdle elements and furrowing of the upper long limb bones. As predicted from observational data, the taphonomic consequences of bear feeding resemble those of other non-durophagus carnivores, such as felids, and are distinct from those of durophagus carnivores, such as hyenids. Our results have paleontological and archaeological relevance. Specifically, they may prove useful in building analogical models for interpreting the formation of fossil faunas for which bears are suspected bone accumulators and/or modifiers. More generally, our comparative statistical analyses draw precise quantitative distinctions between bone damage patterns imparted respectively by durophagus (modelled here primarily by spotted hyenas [Crocuta crocuta] and wolves [Canis lupus]) and non-durophagus (modelled here by brown bears and lions [Panthera leo]) carnivorans.
Introduction
A major focus of neotaphonomic research is to understand the cause-and-effect relationships that are involved when modern carnivores act as bone-modifying agents. From paleontological and archaeological perspectives, a major objective of this kind of research is to use what we learn about the taphonomic impact of carnivores in order to, in stepwise fashion, isolate evidence of non-carnivore, presumably hominin-induced effects in fossil fauna palimpsests. It is from that point that hypotheses of carcass foraging by ancient human ancestors can proceed.
Much of previous paleontologically and archaeologically directed neotaphonomic research has concentrated on durophagus carnivorans, including especially hyenids (e.g., [1]–[7]). But there are exceptions to this generalization, which include important work on bone-modifying felids (e.g., [8]–[15]), birds (e.g., [16]–[18]), crocodiles (e.g., [19]–[20]) and even bacteria (e.g., [21]), among other taxa. Ursids have also been occasional taphonomic subjects of paleontologists and archaeologists. Here we add to this last body of research, presenting the results of our study of the taphonomy of ungulate carcasses consumed and modified by free-ranging brown bears (Ursus arctos arctos) in the Spanish Pyrenees.
Fossils of the genus Ursus (including the extinct cave bear species Ursus deningeri and Ursus spelaeus) are very common in assemblages from European Pleistocene sites–including those that also contain hominin remains and hominin-produced stone artifacts. These regular paleontological associations of cave bear fossils and especially Neanderthal (Homo neanderthalensis) fossil and archaeological remains formed the basis of dramatic and influential hypotheses that Neandertals both hunted and worshipped cave bears (e.g., [22]–[27]).
In contrast to their prominent role in scenarios of ancient European life, from a neotaphonomic perspective, ursids are among the least studied of all common, large carnivores. Given that most experts recognize that bears were very likely significant taphonomic agents in past (especially in karst contexts, where their hibernation-related activities and probable cannibalistic inclinations held great potential to modify the spatial distribution and condition of the bones of their conspecifics and other animals (e.g., [28]–[40]), this imbalance is doubly unfortunate. We acknowledge that Ursus arctos arctos is obviously not an exact match for its prehistoric congeners (e.g., [41]–[43]). For instance, unlike Pleistocene bears, extant Pyrenean brown bears face little to no feeding competition for large carcasses (see below) and, depending on their exact distribution on the landscape, have access to different arrays and quantities of other foods. These differences probably impact the relative intensity of bear feeding behaviors, as well as condition their decision making processes about whether to transport (or not transport) carcass parts to sheltered feeding sites. We do not believe, however, that these differences disqualify modern brown bears as suitable taphonomic referents for extinct cave bears. Instead, we highlight relevant continuities between the two types of bear: modern brown bears are about the same size as were cave bears [41]; the skulls of both taxa have “domed” frontals and prominent, similarly placed sites for the attachments of large temporalis and masseter muscles [44]–[46], imbuing both with powerful bite forces [43], [45]; both–based on behavioral observations for modern brown bears and on isotopic [37], [47], [48] and occlusal microwear [49] evidence for cave bears–are/were omnivorous.
Couturier’s [50] work in the Cantabrian Mountains (northern Spain) was the first study to describe the sequence by which modern brown bears consumed large vertebrate carcasses, but his observations were also unsystematic and lacked a contemporary taphonomic focus. It was almost thirty years later that Haynes [51]–[53] became the first researcher to describe modifications of selected skeletal elements of cattle (Bos taurus) fed to captive bears; Haynes then used these results to interpret taphonomic damage on carcass remains of wild North American ungulates. Haynes’s observations and conclusions–that bears usually abandon feeding on a carcass once it has been defleshed and eviscerated, and that this behavior produces only minimal taphonomic damage, including minor tooth pitting, scoring, furrowing, crushing and perforating of cortical bone (see below)–have often been recruited in analogical models that assert ursid involvement in the accumulation and/or modification of some Pleistocene fossil faunas (e.g., [54], [32], [33], [36], [37]).
More recently, Saladié et al. [55] fed fleshed, but disarticulated, limb segments of young cattle, pigs (Sus scrofa) and sheep (Ovis aries) to captive brown bears in the Barcelona Zoo and in the Hosquillo Natural Park (Spain). In contrast to the general patterns of bear-induced taphonomic damage documented by Haynes [51]–[53], Saladié et al. [55] found that bears generated bone surface destruction and modification patterns very comparable to those produced by other, better-studied large carnivores. Such patterns include: a high degree of bone breakage; the abundant production of “diaphyseal cylinders” (i.e., long limb bone [LLB] specimens that lack epiphyses, which were chewed-off, but that retain intact, full-circumferenced shafts); the furrowing, and scooping-out of trabeculae from LLB epiphyses. Saladié et al. [55] also showed that the metric range of individual bear-produced tooth marks overlaps with that previously documented for African lions (Panthera leo).
Confusing these apparently clear taphonomic patterns were the conclusions of Sala and Arsuaga [56], who tracked the modification of nine domestic equid carcasses consumed by free-ranging brown bears in the Cantabrian Mountains. In addition to the interesting behavioral data that Sala and Arsuaga [56] phototrap study yielded (e.g., the Cantabrian bears often moved carcasses before feeding on them, but never into caves or other secluded refuges; observations that are obviously relevant to models that prehistoric bears collected carcasses and bony residues in shelter sites), their taphonomic results, in contrast to those of Saladié et al. [55], included much reduced intensities of tooth-marking and fracturing of bones and clustering of most tooth marks on axial, rather than on appendicular, skeletal elements. Sensibly, Sala and Arsuaga [56] attribute the stark difference in the taphonomic patterns that emerged from their study and those documented by Saladié et al. [55] to the fact that the former was conducted with free-ranging subjects and whole carcasses and the latter with captive animals and selected carcass portions of much smaller ungulates.
In summary, each study in the development of research on brown bears as taphonomic agents has been an incremental improvement to its predecessor(s); each has also proven of great value in the interpretation of fossil faunas suspected to have been (at least partially) formed and/or modified by prehistoric bears. By presenting new data and conclusions on the taphonomic behaviors and consequences of free-ranging brown bears in the Pyrenees of Lleida (Spain), here we contribute to the evolving research program on this critically important but understudied large carnivore. Importantly, our study advances the state of knowledge about brown bears as taphonomic agents because our study group is composed of free-ranging bears who were granted unfettered access to complete, fresh carcasses of seventeen ungulates. In addition, we contextualize our results by presenting a cross-species, multivariant analysis, comparing our taphonomic data to those generated in other studies on other major large carnivore taphonomic agents, including spotted hyenas (Crocuta crocuta), lions and wolves (Canis lupus). (Taphonomic data on brown hyenas [Parahyaena brunnea] and striped hyenas [Hyaena hyaena] are utilized more restrictively in selected analyses.) In doing so, this analysis achieves a broader goal of further refining those taphonomic signatures that are respectively diagnostic of durophagus (modelled here by spotted hyenas and wolves) and non-durophagus (modelled here by brown bears and lions) carnivorans. These results will prove useful to paleontologists and archaeologists investigating questions about Pleistocene large mammal terrestrial ecosystems.
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Post by brobear on Mar 22, 2017 12:10:28 GMT -5
Front limbs Of all the morphologic features that typify bears, the front limbs and associated skeletal infrastructure are the most distinctive. They are also diagnostic of the bear life strategy (see Life strategy). No other terrestrial vertebrate of its size--certainly no other large carnivore--has front limbs that are as flexible, powerfully built, and mounted with such dexterous paws. Nor do any comparable-sized carnivores have such out-sized claws...claws which are clearly "designed" to be powered by the muscular arms and shoulders to either climb trees, extract food from a durable matrix (i.e., dig), or grapple with and subdue large prey such as seals, moose, and elk. What follows is a summary of the evidence produced over the years elaborating on and substantiating the preceding thumbnail sketch. You will have to forgive me for the abundance that follows, but it is reflective of the extent to which I see this aspect of bear morphology as key to understanding the overall bear life strategy--as well as niche.
Ihe results at left come from a seminal paper published by Alberto Martin-Serra and his colleagues in 2014. His analyses delve into patterns of variation in post-cranial skeletal structure among carnivores. Some of the results are relatively arcane, as is often the case in morphology. But the overall results insofar as bears are concerned are pretty straight-forward.
Each of the graphs at left represents major coordinated trends in the shape of two important front-limb bones--the radius at top, and the scapula (or shoulder blade) in the bottom two graphs. This variation is after accounting for the effects of body size, as such. Each dot represents an individual specimen, with those of bears denoted by brown dots and those of all other carnivore species by gray dots. The bones illustrated along each axis portray the shape that is associated with extreme values along each gradient. "PC I" invariably represents the dominant theme of variation, "PC II" the secondary theme, and "PC III" the tertiary theme. The typifying characteristics of the quadrant occupied by the bear specimens are described in the corresponding corner.
The key results here are: first, that bears are clearly differentiated from all other carnivores when it comes to shape of the radius and scapula, especially so for the scapula; and, second, that the main differentiating theme is captured by the term "robust." In other words, even after controlling for the effects of body size, bears have stout and strongly built front limb bones, most remarkably so in the case of the scapula. Which implies that these robust bones are built to support disproportionately strong front-limb muscles. Which further implies that the "bear niche" is typified by activities that require deployment of strong front legs anchored to a strong scapula.
The graphic above (thanks to a 1949 paper by Dwight Davis) emphasizes the concluding point made at left, more specifically that the stout skeletal infrastructure of the front limbs in bears--most especially the scapula--is host to proportionately robust muscles. Each color in the bars above corresponds to the proportion of all muscle mass in the shoulder and arms of lions (Panthera), wolves (Canis), and bears (Ursus) consisting of the muscle group identified to the right of the three bars. The key point here is that scapular muscles (anchored to the scapula) account for a disproportional amount of muscle mass in bears. This is especially true for the brown or grizzly bear, which accounts, in part, for the "hump" that typifies this species.
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Post by brobear on Mar 22, 2017 12:11:33 GMT -5
Continued from post #22 - *Note: Graphs can be viewed on site given here: www.allgrizzly.org/front-limbs Dexterity The figures above illustrate the flexibility (or dexterousness) of the forelimb in bears. The bar-shaped summary values at upper left derive from the work of Andy Iwaniuk, who devised a scheme for scoring dexterity and then applied it to a number of carnivore species through direct observations of zoo animals. The result of his work is pretty obvious. Bears (i.e., Ursids) are by far the most dextrrous of large carnivores, whether reckoned in terms of "distal" or "total" forepaw dexterity--comparable to the dexterity of the much smaller procyonids (e.g., raccoons). This is remarkable given that the bears have to support much more weight on their front legs and paws than do raccoons and their relatives. The results above right relate pretty directly to the idea of "dexterity." Here, based on the work of Ki Andersson, main themes in variation of the shape of the ulna (upper arm bone) where it intersects the elbow joint are plotted against body mass, again restricted to carnivores. Each dot represents a species, with bears denoted by brown dots, canids (dogs) by dark red dots, and felids (or cats) by the orange dots. "GB" denotes "grizzly bears" (Ursus arctos). The key distinction noted in this graph is between the "cursors" and "grapplers"--the cursors being those that are built to run long distances efficiently and the grapplers those built to grab and subdue large prey after a short rush. Or, perhaps, simply dig roots. Bears are clearly among the grapplers, which is wholly consistent with a dexterous forelimb and paw. Olecranon process of the ulna Size and shape of the olecranon process have been singled out by morphologists as being especially indicative of how animals move and, related to that, the basic configuration of their posture. The olecranon process is at the end of the ulna, where it is an integral part of the elbow as well as the anchor for the triceps muscles (the ulna is paired with the radius in the lower arm). The relationship of the olecranon process to the "semilunar notch" and to the main axis of the ulnar bone are particularly signifying. The semilunar notch is the half-sphere hollow in the side of the ulna that hosts the end of the humerus. This is where the radius and ulna pivot around the end of the humerus, which is the upper arm bone. A lesser capacity for sustained speed and a greater capacity for bearing the load of a heavy body are indicated by: (1) a relatively short olecranon process; and (2) a wide angle between the main axis of the ulna below the notch and the main axis of the olecranon process--which indicates a rearward facing process. The basic difference is characterized as either "cursorial" (built for sustained speed) or "ambulatory" (built to ambulate). The figure above again draws on the work of Martin-Serra, but focused here on the shape of the ulna. This shape-related variation is what remains after accounting for the effects of body size. As you can see, the bears (dark brown dots) are differentiated from all other carnivores primarily by the shape of the olecarnon process (along PC II). More specifically, bears have relatively the shortest and most rearward (or caudal)-facing process, which signifies a less important role for the triceps (versus the biceps)...which signifies, in turn, a design to hold up under various load stresses rather than to efficiently move about over long distances. The figures above, left, show how the various bear species (each denoted by an orange dot) plot relative to other carnivores when comparing body mass to proportional length (top) and orientation (bottom) of the olecranon process. These data come mostly from Blaire van Valkenbugh, but also from other researchers. Orientation is measured in terms of degrees of inclination toward the tail-end (caudal end) of the body. These results contrast with the results shown in the figure to the immediately above, which depict variation left over after controlling for the dominant effect of body size. Considering all of the carnivores, the basic theme is one of an increasing backward angle (but at a decreasing rate) and increasing relative length (at an increasing rate) as body mass increases. Generally speaking, the bears cluster with other carnivores of the same size. They tend to have a similar configuration of the olecranon process, roughly of the sort you would expect given how big they are. The one exception, though, is the brown or grizzly bear (Urar, Ursus arctos). The grizzly bear has a lesser backward orientation to the olecranon relative to what you would expect by its body size, and the longest olecranon process relative to the ulnar shaft length of any carnivore. This last feature is noteworthy given that long olecrana have been associated with animals who spend a lot of time digging--which is consistent with the notion that adaptations for digging are a key feature of the grizzly bear niche. Which is consistent with the robust scapula and well-developed scapular muscles of most bears (see above), which also seem designed for activities such as digging. The results from Martin-Serra's work (above right) could be read as suggesting that all bears have a short olecranon--in contrast to the result just described above for grizzly bears. Reconciliation of this apparent discrepancy could involve the considerable statistical gymnastics that Martin-Serra went through to "control for" effects of body size and evolutionary relatedness. It could also have something to do with the brown dot in his graph denoting the bear species with the lowest score on his PC II axis. Although the species associated with this dot was not identified, it may represent brown/grizzly bears and, if so, be an outlier for this family, at least in the context of Martin-Serra's work.
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Post by brobear on Mar 22, 2017 12:11:56 GMT -5
Running speed The comparatively slow running speed of bears lends additional support to the theme that bears have heavily built forelimbs and highly flexible paws that are "designed" to facilitate activities such as climbing or digging rather than moving long (or even short) distances efficiently and rapidly.
The slow speed of bears is illustrated graphically immediately above. Maximum running speed of numerous terrestrial mammals is plotted relative to body features that have previously been correlated with speed: total mass (or overall size) and length of the fore- and hind-limbs. The general relationship is one of increasing absolute speed with size, and then a decline. Increasing limb length would likely produce a longer stride--and, hence, speed--but only up to a point. That point being where increasing bulk would (1) mandate that bones accommodate load stresses rather than deliver speed, as well as (2) slow the gait because of the inertia of increasingly massive limbs.
But notice the bears (brown dots). They fall well below the trend line in all three relationships, suggesting that at least the three bear species represented here are slow given their size (roughly 50 kph [30 mph], maximum speed). This is not surprising in light of the information summarized above, all of which paints a picture of limbs that provide ample strength and flexibility for climbing, digging, and grappling, rather than ample stored and released energy for rapid and efficient movement. If you watch a bear run (albeit faster than most people), you will probably be struck by how inefficient the whole process seems, especially compared to a deer or an elk.
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Post by brobear on Mar 22, 2017 12:12:18 GMT -5
Claws The final topic that I cover here under "forelimbs" is claws (or the ungal: highly-modified terminal phalanges). As a general point, bear claws are not retractable like those of cats--they are more like the non-retractable claws of dogs and the larger members of the weasel family. Looking at the graph immediately to the upper left (again, thanks to Blaire van Valkenburgh), bears fall out in a distinctive quadrant when you plot the characteristic depth of a claw against its curvature--which signifies how stout versus elongate it is. Considering all of the carnivores, there is a general trend from deep slightly curved claws, characteristic of the cats (the orange dots), to elongate claws (curved, but less deep) more common of canids (dark red dots) and bears (brown dots). The inset profiles of various claw shapes illustrate the extremes.
So...notice, again, the brown or grizzly bear (Uar, U. arctos). Next to the badger (the gray dot farther to the right and below), grizzlies have the most elongate claws of all the carnivores shown here. The graph identifies the realm of "scratch diggers"--animals that live aboveground but dig for a significant part of their food, whether rodents, squirrels, or roots. Grizzly bears fall within this type. Added to the evidence presented above, this bit of data pretty conclusively establishes that Ursus arctos is well-built to excavate roots and rodents--that, in fact, the ability to excavate such foods probably defined a significant part of the evolutionary imperative that led to the emergence of this species (more on this under Foods and History).
Parenthetically, relative claw length seems to systematically vary among brown bear genetic lineages (clades; see Evolution). The map above shows the length of claws relative to the length of skulls for various populations of brown bears in Eurasia. The claw profiles are scaled to this value, which is presented in numeric form immediately above. This information is overlain on a map of brown bear clades and skull sizes (see Body size) for reference. The data come from publications by Bjorn Kurten and Sergei Ognev that date to the middle part of the last century--when biologists were interested in compiling such arcana. Brown bears in Europe, the Caucasus, and among the salmon-eating bears along the Pacific coast had the smallest claws. Everywhere else the claws were relatively larger.
But the key pattern in this map relates to the exceptionally large claws of the bears living on and near the Tibetan Plateau, part of the relatively limited Clades 5 and 6. These clades were apparently isolated at high elevations during the late Pleistocene, which may explain why they are so distinct in appearance--including claw size. But there is also a likely link to diet. Brown bears on the Tibetan Plateau rely to an exceptional degree on excavated foods, including the Plateau pika, the Tibetan marmot, as well as various roots (see Foods). On the other hand, brown bears living in Europe and among salmon along the Pacific coast don't dig much at all--other than into fairly soft sand (the coast) or ant hills (Europe). So...the importance of claws for digging is potentially evident even in variation of these appendages among brown bear populations in Eurasia.
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Post by brobear on Mar 22, 2017 12:13:42 GMT -5
jeb.biologists.org/content/218/19/3102
RESEARCH ARTICLE Grizzly bear (Ursus arctos horribilis) locomotion: gaits and ground reaction forces Catherine L. Shine, Skylar Penberthy, Charles T. Robbins, O. Lynne Nelson, Craig P. McGowan Journal of Experimental Biology 2015 218: 3102-3109; doi: 10.1242/jeb.121806
Locomotion of plantigrade generalists has been relatively little studied compared with more specialised postures even though plantigrady is ancestral among quadrupeds. Bears (Ursidae) are a representative family for plantigrade carnivorans, they have the majority of the morphological characteristics identified for plantigrade species, and they have the full range of generalist behaviours. This study compared the locomotion of adult grizzly bears (Ursus arctos horribilis Linnaeus 1758), including stride parameters, gaits and analysis of three-dimensional ground reaction forces, with that of previously studied quadrupeds. At slow to moderate speeds, grizzly bears use walks, running walks and canters. Vertical ground reaction forces demonstrated the typical M-shaped curve for walks; however, this was significantly more pronounced in the hindlimb. The rate of force development was also significantly higher for the hindlimbs than for the forelimbs at all speeds. Mediolateral forces were significantly higher than would be expected for a large erect mammal, almost to the extent of a sprawling crocodilian. There may be morphological or energetic explanations for the use of the running walk rather than the trot. The high medial forces (produced from a lateral push by the animal) could be caused by frontal plane movement of the carpus and elbow by bears. Overall, while grizzly bears share some similarities with large cursorial species, their locomotor kinetics have unique characteristics. Additional studies are needed to determine whether these characters are a feature of all bears or plantigrade species.
Within terrestrial animals a continuum of foot postures exists, from plantigrade species with their entire foot on the ground, to unguligrade animals that stand on the tips of their toes (Ginsburg, 1961; Carrano, 1997). The plantigrade posture is ancestral for mammals and it is generally agreed that digitigrade and unguligrade postures evolved as adaptations for speed and endurance. Because of this, numerous studies have examined the gait mechanics of digitigrade and unguligrade species (Budsberg et al., 1987; Hutchinson et al., 2006; Robilliard et al., 2007; Hudson et al., 2012). However, relatively few studies have examined the links between the plantigrade posture and locomotor mechanics. Plantigrade species are considered locomotor generalists, and because of the lack of cursorial specialisations, their limb movements are less restricted to the sagittal plane (Liem et al., 2001). Within mammals, plantigrade species include raccoons, badgers, weasels, as well as all rodents and primates. All of these animals are small compared with most digitigrade and especially unguligrade species; however, bears also retain the plantigrade stance. The goal of this study was to determine whether the locomotor mechanics of a stereotypical plantigrade quadruped, the grizzly bear (Ginsburg, 1961), differ from those of more extensively studied cursorial quadrupeds.
The selection of gaits used by plantigrade and cursorial species could represent some of the locomotor differences observed between these postures. Analysis of gaits, through footfall patterns, has been applied broadly to a wide range of terrestrial species (e.g. Gray, 1968; Hildebrand, 1976, 1977). Within quadrupedal animals, a lateral walk, in which the placement of the hindfoot is followed by the placement of the ipsilateral forefoot, is the gait used at slow speeds by the majority of species, including bears (Hildebrand, 1976). But, there is variation in terms of intermediate and faster gaits. The most common intermediate gait is the trot, defined by diagonal couplets, as this is seen in digitigrade (e.g. dogs and cats) and unguligrade (e.g. horses) animals, although these animals will also use a pace (ipsilateral couplets; Alexander, 1984). Interestingly, plantigrade carnivorans have not been shown to trot, but there have been a few observations of a pace (McClearn, 1992). Faster gaits include canters and gallops. Canters can be considered a slow gallop; however, they are characterised as being a three beat gait with one diagonal couplet (Hildebrand, 1976). Rotary gallops, as described above for the lateral walk, and transverse gallops, with the leading hindfoot placement being followed by the contralateral forefoot, can both be observed in the same species (Vilensky and Larson, 1989; Walter and Carrier, 2007), although there may be energetic differences between them (Bertram and Gutmann, 2009). Gallops are the fastest gait used by quadrupedal animals and studies have demonstrated that galloping occurs in species representing all three foot postures – unguligrade, digitigrade and bears within plantigrade species (Hildebrand, 1989; Renous et al., 1998; Robilliard et al., 2007; Walter and Carrier, 2007). Within carnivorans, bears are the most plantigrade along the posture continuum (Ginsburg, 1961). The specific morphological features defining plantigrady include: well-developed digits on both forefeet and hindfeet; different sizes of the metapodials, e.g. metapodials 3 and 4 are rarely the same length in plantigrade species; and a substantial angle produced between the ulna and the humerus during elbow extension (20 deg in bears; Ginsburg, 1961). Ursidae is considered a generalist family; yet, the individual species exhibit substantial differences in diet, habitat and ecology. Grizzly bears have the broadest range of behaviours in Ursidae and are able to climb (particularly as juveniles), swim and have been reported to run as fast as 13.3 m s−1 (Garland and Janis, 1993; Brown, 2009). There has been very limited research into the locomotion and biomechanics of Ursidae (Gambaryan, 1974; Inuzuka, 1996; Renous et al., 1998); however, it is likely that differences in limb morphology and locomotor behaviour may exist within Ursidae (Irschick and Garland, 2001), as well as between bears and other quadrupeds.
Previous studies have shown that locomotion by cursorial animals over a large size range can be described as dynamically similar across all speeds (Farley et al., 1993; Alexander, 2005). Locomotion is considered to be dynamically similar if, at a given dimensionless speed (Froude number), parameters can be made identical by multiplying forces, linear dimensions and time intervals by constant factors (Alexander and Jayes, 1983). In their seminal study, Alexander and Jayes (1983) characterised cursorial animals as those that stand with the humerus and femur closer to vertical than horizontal, which excludes other morphological characteristics that are considered cursorial in other studies (described above).
Relative to cursorial species, bears appear to have substantial movement in the frontal plane during locomotion. For example, bears have an unusual carpal movement, which manifests as a medial rotation during swing (Davis, 1949; Gray, 1968; Inuzuka, 1996). Further, grizzly bears have a medially directed forefoot position during stance, relative to the direction of travel. This differs from most cursorial species, which limit movement to the frontal plane to enhance efficiency and restrict forces to the direction of travel (Liem et al., 2001). Because of this, the mediolateral forces generated by cursorial animals are comparatively small and frequently ignored in the analysis of locomotion (Budsberg et al., 1987). However, some primates walking bipedally and animals with sprawling gaits have been shown to produce mediolateral ground reaction forces equal to or greater than the magnitude of their anterior–posterior forces (Willey et al., 2004). Currently, it is unclear to what extent the forces generated by bears during locomotion are similar to or differ from those of well-studied groups of terrestrial mammals, particularly considering the angle of the forefoot during stance.
In addition to terrestrial locomotion, the forelimbs may be involved in a wide range of other activities, especially in non-predatory carnivorans that may forage for food or exhibit escape behaviours such as climbing. The requirement of predators to chase down vertebrate prey overcomes the need for dexterity upon capture; therefore, forelimb dexterity in carnivores is negatively correlated with vertebrate predation. Bears and other plantigrade carnivores (i.e. generally omnivorous species) have higher dexterity scores than digitigrade carnivorans (Iwaniuk et al., 2000). Contributing to this dexterity is the morphology of the forelimbs, such that the ulna and radius are separate in plantigrade animals, resulting in the ability to supinate and pronate (rotate the forearm to point the palm up or down). In cursorial animals, the ulna and radius are fused to increase stability and therefore speed (Liem et al., 2001). Additionally, pentadactyly is only retained in plantigrade species as loss of digits is characteristic of digitigrade and unguligrade postures; this is associated with the reduction of distal limb mass that, along with elongation of the distal limbs, increases speed in cursorial animals (Garland and Janis, 1993). The difference in forelimb bone anatomy, as well as the differences in ecology, between cursorial and plantigrade species of the Carnivora is likely to have resulted in differences in locomotion.
The overall goal of this study was to determine whether locomotion by grizzly bears differs from that of other large quadrupedal animals, which tend to be digitigrade or unguligrade. We hypothesised that the gaits used by grizzly bears would be similar to those used by smaller plantigrade animals, as opposed to similarly sized cursorial animals, because of the differences in morphology of the distal limb. Further, we predicted that the mediolateral ground reaction forces would be higher in forelimbs of bears, compared with other species, as a result of their medially directed stance. These hypotheses were addressed by examining the footfall patterns and stride parameters of grizzly bears to identify gaits, and characterising the magnitude, time-varying shape and relative distribution of three-dimensional ground reaction forces generated by the forelimbs and hindlimbs over a range of speeds.
*Go to the site posted for more info.
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Post by brobear on Mar 22, 2017 12:14:09 GMT -5
grizzlybrain.webs.com/
Grizzly Bear Brain Atlas Special gratitude to John and Frank Craighead
Concept: Ursus horribilis The neuroscience that forms the basis of the central nervous system and autonomic nervous system in grizzly and black bears has been correlated with gross brain and spinal cord anatomy. Explicit attention has been directed to the special senses, particularly olfaction. We analyze the neuro-physiological function of the Grizzly Bear brain using MRIs, CT Scans, and arteriograms. In addition, we include histological staining of grizzly bear brain sections.
Histological sections corresponding with the coronal, horizontal, and sagittal views of magnetic resonance imaging (MRI) and computerized tomography (CT) have delineated the exact status of the bear’s (1) cerebral cortex, (2) thalamus, (3) midbrain, (4) pons and medulla, (5) and cerebellum.
The structures referred to above as well as the hypothalamus and pituitary gland control the bear’s actions. These include avoidance, aggression, learning and memory, hibernative, and reproductive behaviors.
From a comparative morphology standpoint, the work depicted in a neuroanatomical atlas is suggestive of all current species of bear, as well as ancestral ursoidea, e.g.: Indarctos oreganenis and Agriotherium schneiden.
Research involves further analysis of histological sections as well as depiction of all arteries (MRA) involved in the bear neuroanatomy. The atlas will be valuable in veterinary schools and hospitals around the world.
A special thank you to Montana Fish, Wildlife, and Parks research facility in Bozeman, MT, Los Angeles Museum of Natural History, The Field Museum of Chicago, and the Denver Museum of Natural History for materials from bear skulls, and the Department of the Interior, Fish and Wildlife in Florida, as well as The British Museum, London, UK, Smithsonian in Washington, D.C., and the American Museum of Natural History in NYC, and Chris Servheen of University of Montana, which have facilitated these studies and research.
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Post by brobear on Mar 22, 2017 12:14:31 GMT -5
Posted by Polar.... Skull-Based Method of Age Determination for the Brown Bear Ursus arctos Linnaeus, 1758
Abstract: Due to the lack of a proper technique for determining the ages of brown bears, a simple and straightforward method that is based on published data and our own observations is proposed. This method is based on the simultaneous use of the following different skull parameters to more accurately determine the ages of brown bears: size and weight parameters, degree of obliteration of the joints, degree of wear of the teeth, and development of the flanges. The proposed method contributes to non-destructive age determination, allows for the discrimination of immature and adult bears and also classifies the skulls of adult animals into one of the five selected age groups.
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Post by brobear on Mar 22, 2017 12:14:50 GMT -5
www.sciencedirect.com/science/article/pii/S2078152015000139 Correspondences of axial skull and mandible parameters with age in brown bears. Characteristics Age groups Less than 3 years old ... 4–6 years old ... 6–11 years old ... 12–14 years old ... 15–18 years old ... 18 or more years old. ( in my own words )... In the book, "The Grizzly Years" by Doug Peacock, he divided the male grizzlies into three age groups: Juvenile, sub-adult, and fully-adult ( 10+ years old ). It has irked me ever since I first began studying the grizzly, that when biologists capture, tag, measure, and weigh male grizzlies, any bear of sexual maturity is listed as adult ( 4.5 years old ). The weights of bears this young are "in the mix" when the weights are averaged out to determine the average weight of adult male grizzlies within any given population. To be more precise, each bear should be weighed in the summer months only and grizzlies 10 years old and up ( only ) should be accepted to determine the average weight of mature male grizzlies. I doubt that 11 and 12 year old boys are weighed when determining the average weight of men within any given population.
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Post by brobear on Mar 22, 2017 12:15:14 GMT -5
*I have no idea what this means: bmcevolbiol.biomedcentral.com/articles/10.1186/s12862-015-0521-z
Growth trajectories in the cave bear and its extant relatives: an examination of ontogenetic patterns in phylogeny
Background The study of postnatal ontogeny can provide insights into evolution by offering an understanding of how growth trajectories have evolved resulting in adult morphological disparity. The Ursus lineage is a good subject for studying cranial and mandibular shape and size variation in relation to postnatal ontogeny and phylogeny because it is at the same time not diverse but the species exhibit different feeding ecologies. Cranial and mandibular shapes of Ursus arctos (brown bear), U. maritimus (polar bear), U. americanus (American black bear), and the extinct U. spelaeus (cave bear) were examined, using a three-dimensional geometric morphometric approach. Additionally, ontogenetic series of crania and mandibles of U. arctos and U. spelaeus ranging from newborns to senile age were sampled.
Results The distribution of specimens in morphospace allowed to distinguish species and age classes and the ontogenetic trajectories U. arctos and U. spelaeus were found to be more similar than expected by chance. Cranial shape changes during ontogeny are largely size related whereas the evolution of cranial shape disparity in this clade appears to be more influenced by dietary adaptation than by size and phylogeny. The different feeding ecologies are reflected in different cranial and mandibular shapes among species.
Conclusions The cranial and mandibular shape disparity in the Ursus lineage appears to be more influenced by adaptation to diet than by size or phylogeny. In contrast, the cranial and mandibular shape changes during postnatal ontogeny in U. arctos and U. spelaeus are probably largely size related. The patterns of morphospace occupation of the cranium and the mandible in adults and through ontogeny are different.
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Post by brobear on Mar 22, 2017 12:15:57 GMT -5
Dr. Blaire Van Valkenburgh shaggygod.proboards.com/Introduction Bears are unusual members of the order Carnivora, an order which also includes cats, dogs, weasels, civets, and hyenas on land, and seals, sea lions, and walruses in the sea. With the exception of the highly predacious polar bear, bears tend to be the most herbivorous of the carnivores, feeding on fruits and tubers more often than prey. Moreover, all eight species are large, with the smallest of them, the sun bear, weighing more than the wolf, the largest of the canids. Indeed, the polar bear and Kodiak brown bear are currently the largest of all carnivores. Males of these species occasionally weigh in at up to 800 kilograms (1,760 pounds), nearly the size of an adult male bison. Surprisingly, the large size of bears is not achieved through the rapid growth of cubs. In comparison with other carnivores, newborn bear cubs are tiny relative to their mothers and grow slowly. SPEED AND STRENGTH All bears have a large head with small ears followed by massive shoulders and a short back and | tail, all of which are supported on thick limbs and broad paws. Compared with big cats, bears have longer snouts and shorter, stiffer backs. Relative to large dogs, bears have bulky legs and much more spreading feet. Unlike these other carnivores, and more like humans, bears walk on the soles of their hindfeet, with their ankle joint positioned just above the ground. This condition is called plantigrade, and differs from the digitigrade posture of cats and dogs, in which the “soles” of the feet are elevated, along with the ankle, and only the toes touch the ground. To understand why bears are built so differendy from cats and dogs, it is essential to explain the benefits of digitigrade feet. Running around on your toes in a digitigrade posture is advantageous if speed is important. Speed is the product of stride length and stride frequency. Raising the ankle adds length to the part of the limb that determines stride length, that is from the shoulder or hip to the point of contact with the ground. Longer limbs take bigger strides, and digitigrade posture is therefore typical of mammals designed to run. Digitigrade animals also tend to have relatively long bones, or metapodials, making up the sole of the foot, adding further to total limb length. In addition, their limb muscles are much thicker close to the hip or shoulder joint, and taper towards the toes as long, elastic tendons. This construction reduces muscle mass near the ankles and feet, where the limb travels farthest during locomotion, and thus reduces inertial effects. A The skeletons of a bear and a domestic dog illustrate the difference between plantigrade and digitigrade postures. The dog is digitigrade, standing on its toes with the soles of its feet (metapodials) off the ground. By contrast, the soles of the bear's hindfeet are flat to the ground, as in humans, giving it a plantigrade posture. If one imagines the additional energy required to walk or run with ankle weights or heavy shoes, then the drawbacks of heavy feet become clear. There are yet further benefits to runners in having long tendinous muscle attachments. Tendons are elastic and act as energy-saving springs when running. They are stretched as the limb is flexed under the weight of the animal and then rebound, propelling the body forward and upward. So, digitigrade posture, long metapodials, and compact muscles with stretchy tendons are typical of carnivores built for speed. Bears are clearly not built for speed. Although their forefeet are semi-digitigrade, their hind-feet are plantigrade. Moreover, their metapodials are short and their muscles thick throughout the length of the limb. In many ways, bears are built more like badgers than other similar-sized carnivores, such as tigers, and it shows in their speed. The top speed recorded for both black and brown bears is 50 kilometers (30 miles) per hour, whereas the range for the fully digitigrade lion and wolf is 55 to 65 kilometers (35 to 40 miles) per hour. If bears are not built for speed, then what does the combination of massive limbs, plantigrade hindfeet, cumbersome paws, and a short back provide? Strength and mobility of limb movement are the answers. The stout limbs of bears are capable of producing large forces over a much greater range of motion than those of dogs or even cats. Bears use these capabilities when digging for food or shelter, fishing for salmon, climbing to escape danger, and battling with members of their own species as well as other predators. Imagine a wolf trying to perform a bear hug or climb a tree. Dogs have forfeited these abilities in favor of speed. Cats are more like bears in their range of possible movements, but lack strength. Bears may not be able to outrun danger, but can successfully defend themselves through brute force.
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Post by brobear on Mar 23, 2017 18:31:32 GMT -5
California Grizzly by Tracy I. Storer and Lloyd P. Tevis, Jr.
The bodily framework of the grizzly is substantial, to support the weight of the animal; yet the bear has a greater degree of flexibility in its movements than is possible in many other sturdily built mammals. This freedom of motion is a correlated function of the bones, ligaments, and muscles. The skeleton of a bear - grizzly or other kind - is much like that of related carnivores, but there are many small differences.
A noticeable massiveness is evident in all the bones. The neck vertebrae are large but are capable of much rotation movement, the spinous processes along the back on the dorsal vertebrae are heavy, and the shoulder blade is ample. The limbs are of nearly equal length. Both fore and hind feet are fully plantigrade: the entire surface of each foot comes in contact with the ground as the bear walks. The bones used in lifting or extending the feet ( the pisiform on the fore foot, the calcaneum on the hind ) are larger than in some other carnivores. All bones of the legs, both front and rear, are separate. In the front leg, the radius and ulna are of nearly equal size for easy and powerful rotation of that member; and in the hind leg, the fibula, which is involved in twisting movements, is free and larger in relation to the tibia than in mammals unable to make such movements. These skeletal features, together with the muscles attached to them, give the bears dexterity in using their limbs - more or less in the manner of human beings.
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Post by brobear on Mar 23, 2017 18:35:34 GMT -5
California Grizzly by Tracy I. Storer and Lloyd P. Tevis, Jr.
The bodily framework of the grizzly is substantial, to support the weight of the animal; yet the bear has a greater degree of flexibility in its movements than is possible in many other sturdily built mammals. This freedom of motion is a correlated function of the bones, ligaments, and muscles. The skeleton of a bear - grizzly or other kind - is much like that of related carnivores, but there are many small differences.
A noticeable massiveness is evident in all the bones. The neck vertebrae are large but are capable of much rotation movement, the spinous processes along the back on the dorsal vertebrae are heavy, and the shoulder blade is ample. The limbs are of nearly equal length. Both fore and hind feet are fully plantigrade: the entire surface of each foot comes in contact with the ground as the bear walks. The bones used in lifting or extending the feet ( the pisiform on the fore foot, the calcaneum on the hind ) are larger than in some other carnivores. All bones of the legs, both front and rear, are separate. In the front leg, the radius and ulna are of nearly equal size for easy and powerful rotation of that member; and in the hind leg, the fibula, which is involved in twisting movements, is free and larger in relation to the tibia than in mammals unable to make such movements. These skeletal features, together with the muscles attached to them, give the bears dexterity in using their limbs - more or less in the manner of human beings ( fig. 11 ).
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Post by brobear on Mar 24, 2017 2:39:44 GMT -5
Physical Characteristics
Grizzly bears are among the largest land carnivores in the world. Males are 38% larger than females and typically reach a weight of 300 to 800 pounds depending on where they live. Females grow from 200 to 400 pounds. The heaviest recorded grizzly was 1496 pounds (Brown, 1993). Grizzlies grow to an average size of 6-7 feet when standing up and 3-4 feet to the top of their shoulders when on all fours. The large hump found on their shoulders is mainly composed of muscle and fat. This provides them with exceptional digging power useful when carving out dens or searching for food. Grizzlies are avid swimmers and very fast runners, reaching speeds of up to 56km/h (35mph) in a sprint. Like most other bears, grizzlies have short, stubby tails.
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Post by brobear on Mar 24, 2017 2:40:46 GMT -5
Fur The fur of a grizzly bear can be anywhere from a cream colour to a nearly black, dark brown coat (Brown, 1993) Cubs usually have a lighter coat The tips of their fur is white or silver which gives them a grizzled look, and led to their name, the grizzly bear Their pelt is highly insulating and protects bears from insects and the environment Their colour helps grizzly bears blend in with their surroundings to avoid enemies and remain unknown to prey Teeth Grizzly bears have 42 teeth (Brown, 1993) Several longer, sharp teeth are located towards the front of their mouth for tearing meat As they are omnivores, they have large, flat molars used for grinding Cubs begin losing their juvenile teeth at 5-6 months of age and have a full set of adult teeth at 1.5 years old (Zavatsky, 1974) Head Large head in relation to body size Skull length ranges from 30-40 cm Cubs have nearly round heads, which lengthen and change shape as they reach sexual maturity to assume the adult structure (Zavatsky, 1974) Adults have a forehead with a steep slope leading into a long muzzle, giving them a concave or dish shaped skull (Brown, 1993) Very wide nasal opening Paws Large paws with five digits Grizzlies walk flat on their paws, or plantigrade Long claws, can grow from 2.5-5 inches (5-12 cm) Foreclaws are longer and straighter than hindclaws Claws come in a variety of colours including black and brown but are usually white or yellowish and can be striped Lifespan Grizzlies in the wild live to an average of 25 years, which is close to the life expectancy of most other bear species The oldest grizzly found in the wild was an Alaskan bear of 35 years Sensory Function Excellent sense of smell is their main tool for detecting and locating food as well as evading conflict Short, round ears provide good hearing which is helpful in locating prey (French and French, 1989) Their eyes are forward, tiny and closely spaced Eyesight is generally thought to be poor and comparable to that of humans
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