Bone Density/Robusticity among extant Ursids

[brobear]

The word density in the medical term bone density is used to quantify only the mineral content of the bone (bone mineral). It's not intended to describe the total mass density of the bone like we are used to from physics.

[theundertaker45]

Hello everyone, this will be my first thread on this forum and the focus is set on comparing bone density/robusticity between extant ursids and other carnivores. 

This is the abstract from the study I will attach below:

"We measured the lengths and diameters of four long bones from 118 terrestrial carnivoran species using museum specimens. Though intrafamilial regressions scaled linearly, nearly all intraordinal regressions scaled non-linearly. The observed non-linear scaling of bone dimensions within this order results from a systematic decrease in intrafamilial allometric slope with increasing body size. A change in limb posture (more upright in larger species) to maintain similar peak bone stresses may allow the nearly isometric scaling of skeletal dimensions observed in smaller sized mammals (below about 100 kg). However, strong positive allometry is consistently observed in a number of large terrestrial mammals (the largest Carnivora, the large Bovidae, and the Ceratomorpha). This suggests that the capacity to compensate for size increases through alteration of limb posture is limited in extremely large-sized mammals, such that radical changes in bone shape are required to maintain similar levels of peak bone stress."

So the aim was to determine the capacity to withstand pressure/stress; they created two values using different approaches of measuring: the ML-diameter (related to the stress during motions similar to those when grappling) and the AP-diameter (related to the stress during locomotory motions, running in general). The more interesting thing for me here is the ML-diameter as they are always is a lot of discussion on the grappling ability of bears compared to other species. I will list the ML-diameters of all four major limb bones below, ranking them from highest to lowest (note that this value isn't perfectly proportional and will increase with gaining size)

1. Sloth Bear - 42.42% 
2. Brown Bear - 40.97%
3. Asian Black Bear - 40.23% 
4. Polar Bear - 39.81% 
5. Sun Bear - 39.38% 
6. Giant Panda - 37.43% 
7. American Black Bear - 35.60% (should definitely be higher as the individuals used in the sample were rather small)
8. Spectacled Bear - 34.64% 




Here are some measurements of various other species:

Jaguar - 40.38% 
River Otter - 40.25% 
American Badger - 37.13%
Lion - 36.86%
Spotted Hyena - 36.55%
Leopard - 36.29%
Cougar - 35.66%
Tiger - 34.35%
Grey Wolf - 30.34%
Cheetah - 28.41%


Some comments from my side:

- Sloth bears are extremely robust bears and I believe that's mainly due to the fact that they have a very aggressive nature and will stand their ground against enemies. This includes much larger tigers in India and the leopards in Sri Lanka who may overlap with sloth bears in size as Sri Lankan leopards are a rather big subspecies and Sri Lankan sloth bears are much smaller than their mainland cousins. They have to be able to survive next to big cats rivalling/trumping them in size and I believe that's one of the key reasons for their adaptions regarding bone density.
- It's no wonder that brown bears also have extremely dense bones; it matches their spectacular hump of muscles which needs to be suppored by strong and thick bones in order to function properly.
- The difference regarding Asiatic black bears and American black bears did surprise me, however, I looked up the size of both bears and realized that they are similar in weight with the Asian black bear being smaller in frame (length and shoulder height). This may explain why he edges out his American cousin by a fair margin; another reason could be that the Asiatic black bears used in the sample were decently larger than the American black bears. I would personally consider the Asian black bear more robust as they seem to be more compact than American black bears at similar weights, however, I do also think that the relatively low value of Ursus americanus is partly attributed to the small size in the samples.
- The polar bear and the sun bear take their place in the middle; I am actually impressed by the polar bear reaching an exceptionally high value despite being rather slender in his built compared to other ursids, that's definitely noteworthy. 
- The spectacled bear is a little bit off regarding bone density due to his comparatively long limbs (related to the short-faced bear); that also is/was the common consensus among various bear communities/debaters and is therefore factually correct.


Comparing the bone density of ursids to other species shows that they are among the most robust creatures on earth and equipped with extremely strong limbs that are able to withstand a lot of stress. If we had to pick the most robust bear on earth, it would probably be one of the giant Alaskan grizzlies/Kodiak brown bears who may rival and even surpass modern day polar bears in size. If we went by average weights, the polar bears from Foxe Basin (averaging ~1300lbs) would be the most robust ursids alive and if we assumed a comparison at parity, then the sloth bear or sun bear would probably come out on top in terms of bone density.

Leave your comments/opinions/thoughts here, I hope I could provide some interesting information.

Carnivores Robusticity Study.pdf (932.57 KB)

[OldGreenGrolar]

The polar bear is actually more robust than both the tiger and lion. While a jaguar seems to have more robust limbs pound to pound than most bears, I believe these bears have stronger shoulder muscles, more flexible forearms, and longer stronger claws.
Other than that good data available 😁.
Welcome to the forum theundertaker45

[theundertaker45]

OldGreenGrolar

Thank you very much; you are right about bears having more flexible limbs, I will analyse and post another study tomorrow which includes forelimb dexterity/flexibility among extant carnivores and I can tell you that bears literally wipe the floor with all other species.

[OldGreenGrolar]

While I believe that pantherines are very powerful pound to pound (cougars despite being non pantherines are on par with them in terms of strength), bears bulkier built and more powerful forearms as well as superior grappling skills would enable them to basically control the fight.

[theundertaker45]

I added the cougar and the leopard to the table above and we all know that the forelimbs are particularly involved when grappling so I just added the data for the humerus and radius and these were the results:




1. Sloth Bear - 22.3%
2. Brown Bear - 22.14%
3. Asiatic Black Bear - 21.75%
4. Polar Bear - 20.87%
5. Sun Bear - 20.13%
6. Giant Panda - 18.42%
7. American Black Bear - 18.30%
8. Spectacled Bear - 18.14%

Other species:

Jaguar - 21.41%
River Otter - 19.24%
American Badger - 19.05%
Lion - 18.82%
Leopard - 19.03%
Cougar - 19.72%
Tiger - 17.46%

[King Kodiak]

Thanks for posting this study Undertaker. We already had a similar robusticity study, i wonder if its the same, take a look...

domainofthebears.proboards.com/post/17692/thread

[King Kodiak]

So the tiger has the less robust forelimbs pound for pound, what a surprise, lmao.

[theundertaker45]

I didn't see that, it was the same study indeed. I just thought of analysing it specifically in terms of the different ursids so that we can have a clear ranking in terms of bone density.

[King Kodiak]

Mar 22, 2020 21:27:12 GMT -5 theundertaker45 said:

I didn't see that, it was the same study indeed. I just thought of analysing it specifically in terms of the different ursids so that we can have a clear ranking in terms of bone density.

Definitely yeah, you have done a great job bro. Everything is very clear.

[brobear]

Mar 22, 2020 19:57:41 GMT -5 OldGreenGrolar said:

While I believe that pantherines are very powerful pound to pound (cougars despite being non pantherines are on par with them in terms of strength), bears bulkier built and more powerful forearms as well as superior grappling skills would enable them to basically control the fight.

I agree 100% with all said Green One. As for the cougar ( IMHO ) he is a big cat in all but lineage.

[brobear]

Mar 22, 2020 21:27:12 GMT -5 theundertaker45 said:

I didn't see that, it was the same study indeed. I just thought of analysing it specifically in terms of the different ursids so that we can have a clear ranking in terms of bone density.

Great information here 'taker. In looking at this study, which of the living bears would you say has the strongest limbs considering both muscles and bones pound-for-pound?

[theundertaker45]

Pinpointing the fact that bone density tends to increase with size, especially among large carnivores I do think that would be the ranking at hypothetical parity:

1. Sun Bear
2. Sloth Bear
3. Brown Bear
4. Asiatic Black Bear
5. Polar Bear/Giant Panda
6. American Black Bear
7. Spectacled Bear

However, I have to make clear that this is just related to pure bone density and there are two other major factors coming into play when talking about forelimb capability: dexterity/flexibility and muscularity attached to the bones. Taking this into account I would personally rate the brown bear as the most impressive species on a lbs for lbs basis.
I have to ask you a question, brobear, the brown bear in your profile pic is the most impressive individual I have ever seen so far, is it the famous Van starring in the "Great Bear Stakeout"?

[brobear]

No; at first I had thought so too. But comparing the pictures; no. It is a rather old photo. I do remember though that this bear was a dominant boar of the Alaskan peninsula - maybe Van's Daddy

[tom]

So are we talking in terms of pound for pound?  Example, a Sloth bear pound for pound is more robust than a Brown Bear even though the Brown Bear carries much more weight and muscle?


Using Robust to describe bone density?

By the way undertaker we have another member here (maybe you know of him) Verdugo who has a strong interest mophology. If you search for his posts you will undoubtedly see where his interests are. 

[brobear]

Mar 23, 2020 7:58:45 GMT -5 tom said:

So are we talking in terms of pound for pound?  Example, a Sloth bear pound for pound is more robust than a Brown Bear even though the Brown Bear carries much more weight and muscle?


Using Robust to describe bone density?

By the way undertaker we have another member here (maybe you know of him) Verdugo who has a strong interest mophology. If you search for his posts you will undoubtedly see where his interests are. 

Found here at "Bears in General" topic: Strength and Girth Comparison of Bears and Big Cats. 

[King Kodiak]

So all species of bears have more robust front limbs than tigers. No wonder they need to ambush a bear or run away. 

On the other hand, the lion has more robust front limbs than Pandas, American black bears, and spectacled bears. No wonder they are more of a face to face fighters. It all makes sense.

[OldGreenGrolar]

How bears keep their bones strong during hibernation
.
By Emily DeMarcoJul. 8, 2015 , 6:00 PM



Tucked into its den, the slumbering black bear hibernates, barely stirring throughout the winter months. Such sedentary behavior in humans would lead to weakened, brittle bones, but when the bear emerges in the spring, its skeleton is little worse for the little wear. How black bears (Ursus americanus) accomplish the feat has puzzled scientists for years. Now, a new study suggests that the creature’s ability to suppress and balance bone remodeling—the lifelong, two-step process by which mature bone tissue is removed from the skeleton (called resorption) and new tissue is created (called formation)—may provide the elusive explanation. For their research, scientists captured 13 black bears over four hibernation seasons and collected blood samples every 10 days before releasing the animals back into the wild. They found that the levels of a bone formation marker known as bone-specific alkaline phosphatase (BSALP) and a bone resorption marker known as tartrate-resistant acid phosphatase (TRACP) fell during hibernation, suggesting that overall bone turnover had decreased, the team reports online today in The Journal of Experimental Biology. The scientists also found that the bears’ levels of calcium—of which bone is made—in the blood did not change during hibernation, meaning that even though bone remodeling is suppressed, it remains balanced, which helps limit bone loss. A closer look at one of the hormones known to reduce bone resorption called the cocaine- and amphetamine-regulated transcript showed that it surged to levels 15 times higher than normal in the dozing bears, which suggests that it may play a role in regulating the ways bears have evolved to protect their skeleton from the long periods of stillness. Continued efforts to understand the protective measures could lead to new ways of treating degenerative bone problems or diseases in humans, the scientists say.


www.sciencemag.org/news/2015/07/how-bears-keep-their-bones-strong-during-hibernation

[OldGreenGrolar]

He wondered how the Ursus americanus, which hibernates for up to seven months a year, can wake with bones that are just as strong as they were when it first settled down for a snooze. Taking a long nap might sound like a great plan, but if a human were to do the same for only two weeks, its bones would begin to wear down from disuse.


curioussciencewriters.org/2013/01/23/what-black-bears-can-teach-us-about-bone-strength/

[brobear]

Jun 16, 2020 9:19:08 GMT -5 OldGreenGrolar said:

He wondered how the Ursus americanus, which hibernates for up to seven months a year, can wake with bones that are just as strong as they were when it first settled down for a snooze. Taking a long nap might sound like a great plan, but if a human were to do the same for only two weeks, its bones would begin to wear down from disuse.


curioussciencewriters.org/2013/01/23/what-black-bears-can-teach-us-about-bone-strength/

Equally as fantastic; after sleeping for up to six months, the bear wakes up just as strong as when he first laid down. Bears do not lose muscle tissue during their long Winter's nap. These are just two of the bear's amazing super-powers.