Limb bone data (Extant Bears)

[grrraaahhh]

For several of us, interest in limb bone data for extant bears is strong, however, current literature provides limited data. Whatever information can be found, please post here (for sure, I will do my part). Data for mature bears are especially coveted. Here again, outside assistance is also welcomed. Thanks.


~ Grrraaahhh

[Ursus arctos]

There is large variation in measurements.
Unfortunately, some of them I am posting may be inaccurate.
-Average measure/average measure. Even if both are of the same sample, biases results.
-Measure taken via pixel counting a graph.
-Biased presentation, selection, and focus. Focus on diameter or circumference/length ratios of the humerus of brown bears. I will improve this, but right now my aim is just to post something quickly.
-Measurements may differ between authors

"Scaling Patterns and Ecological Correlates of Postcranial Skeletal Robusticity in Canis and Ursus: Implications for Human Evolution"



One brown bear's value lies far from that of the others included in this article.

Trying to measure pixels using GIMP:
log(AP diameter): 1.728
AP diameter: 10^1.728= 53.5 mm
log(ML diameter): 1.717
ML diameter= 10^1.717 = 52.1 mm
log(length)= 2.594
Humerus length= 10^2.594 = 393 mm

AP humerus robusticity= 13.6%
ML humerus robusticity= 13.3%
Total humerus robustness= 26.9%


This struck my interest as these values are high. For comparison, the sample of Smilodon fatalis used in "Radiographs Reveal Exceptional Forelimb Strength in the Sabertooth Cat, Smilodon fatalis":
AP%; ML%; Combined%
15.2%; 11.5%; 26.6%
15.0%; 10.8%; 25.8%
15.0%; 9.9%; 24.8%
16.8%; 11.4%; 28.2%
15.0%; 12.2%; 27.2%
14.5%; 10.5%; 25.1%
13.6%; 11.1%; 24.7%
14.0%; 10.9%; 25.0%
15.0%; 11.2%; 26.3%
16.0%; 11.6%; 27.6%

While similar in the combined value, that individual bear was much smaller in the anteroposterior direction, and much greater in mediolateral.

From "Morphofunctional analysis of the postcranium of Amphicyon major (Mammalia, Carnivora, Amphicyonidae) from the Miocene of Sansan (Gers, France) compared to three extant carnivores: Ursus arctos, Panthera leo, and Canis lupus":

Variation in diameter/length ratios is interesting. Compare AP/length and MP length of 8.8% and 8.6% respectively with the maximum of the bear from the above article.

High variation, probably due to high variation in body mass relative to leg length in bears.

"Differential Scaling of Limb Bones in Terrestrial Carnivores and Other Mammalia" by Biewner includes average values for a large sample of Carnivora. I will add values for a large variety of ungulates within the next week.




The article "What size were Arctodus simus and Ursus spelaeus (Carnivora: Ursidae)?" by Per Christiansen also includes graphs of fore and hindlimb least circumference and body length.
Here is the graph, and here is the key.

From using GIMP to pixel count, these are the values I got for brown bears and the "slender legged" Arctodus simus. If there is interest in compiling info in a table more species could be added.
Humerus 1:
785,211
Roughly 145 mm least circumference, and 447 mm long.
Least circumference/length= 0.324

Humerus 2:
806, 207
Humeral least circumference of about 146 mm, and about 457 mm long.
Least circumference/length= 0.319

Humerus 3:
890,177.5
Least circumference of about 154 mm, and about 497 mm long.
Least circumference/length= 0.311


Humerus 4:
1086, 50
Least circumference of about 190 mm, and about 590 mm long.
Least circumference/length= 0.322


Non-Kodiak brown bears:
Humerus 1:
337, 447
Least circumference: 77.3
Length: 234 mm
Least circumference/length= 0.330

Humerus 2:
375, 461
Least circumference: 73.3
Length: 252 mm
Least circumference/length= 0.290

Humeri 1 and 2 belong to the two smallest brown bears. Weight estimates based on their humeri lengths. least circumferences, and average of both respectively are:
Humerus 1: 53, 89, 71 kg
Humerus 2: 70, 77, 73 kg

Humerus 3:
385.5, 415.5
Least circumference: 86.4
Length: 257 mm
Least circumference/length= 0.335

Humerus 4:
412, 465
Least circumference: 72.1
Length: 270 mm
Least circumference/length= 0.267

Humerus 5:
413, 433
Least circumference: 81.3
Length: 270 mm
Least circumference/length= 0.301

Humerus 6:
423, 415.5
Least circumference: 86.4
Length: 275 mm
Least circumference/length= 0.314

Humerus 7:
463, 419
Least circumference: 85.3
Length: 294 mm
Least circumference/length= 0.290

Humerus 8:
538, 307
Least circumference: 117
Length: 330 mm
Least circumference/length= 0.356

Weight estimates based on humerus length, least circumference, and the average respectively for the two largest regular brown bears included:
Humerus 7: 123, 115, 119 kg
Humerus 8: 187, 268, 228 kg

Kodiak bears:
Humerus 1:
580, 279
Least circumference: 125
Length: 350 mm
Least circumference/length= 0.358

Humerus 2:
731, 191
Least circumference: 151
Length: 422 mm
Least circumference/length= 0.357

Weights of the two Kodiak bears based on humerus lengths, least circumference, and average of the two respectively:
Humerus 1: 233, 320, 276 kg
Humerus 2: 463, 518, 490 kg


The two Kodiak bears and the largest of the brown bears (but still only modest) had large least circumference to length ratios.
Arctodus simus specimens were far from slender.


For reference, "Osteology and ecology of Megantereon cultridens SE311 (Mammalia; Felidae; Machairodontinae), a sabrecat from the Late Pliocene – Early Pleistocene of Senéze, France" has average values for felines. Remember though that felines have humeri far more oval in cross section than those of bears however.

As in other derived sabrecats, the humerus of
Megantereon is very similar to those of extant big
cats, albeit with exaggerated robustness overall.
The ratio of humerus least circumference of the dia-
physis relative to articular length in Megantereon
(0.356; Fig. 15A) is distinctly higher than in Panthera
leo (0.318 ± 0.005; P < 0.001), P. onca (0.322 ± 0.008;
P < 0.001), P. pardus (0.290 ± 0.005; P < 0.001),
P. tigris (0.303 ± 0.005; P < 0.001), Neofelis nebulosa
(0.298 ± 0.010; P = 0.009) and Puma concolor
(0.291 ± 0.009; P < 0.001), and even than in Smilodon
gracilis (0.330 ± 0.011; P = 0.047) and S. fatalis
(0.337 ± 0.008; P = 0.027). Only the very robust
S. populator has a higher circumference/length ratio
than Megantereon (0.401 ± 0.011; P = 0.003).

Note again the very high variation from brown bear to brown bear- the brown bear's standard deviation, at ± 0.02896, was much higher than those of any of these members of Felidae.


Smilodon populator had an extremely robust humerus.


On the reliability of my "pixel counting": questionable. I got 385 kg instead of 389 kg from the table in "Morphometric characteristics of brown bears on the central Alaska Peninsula". Mistakes are amplified when converting from log graphs.

Per Christiansen used the same sample of bones in his article "Scaling of mammalian long bones: small and large
mammals compared".

Average least circumference value of the two Kodiak bears: 138.5 mm, vs 138 I got from the graph.
Average humerus length: 386.0 vs 386. Cool!

Actual average vs one I got for:
Brown bear humeral least circumference: 85.6 vs 84.8875
Length: 272.8 vs 272.75

Not perfect, but IMO it is reasonable.


Small sample from supporting info of "A universal scaling relationship between body mass and proximal limb bone dimensions in quadrupedal terrestrial tetrapods":
Common name Specimen Body mass H length H circumference F length F least circumference
Black bear ROM 71435 204000 296 101.5 302 96.5
Grizzly bear ROM 35699 435500 400.5 146.25 445.5 126.25
Polar bear AHR1985 447695 158 135

Measurements are g and mm.

The grizzly included in the above article's humerus least circumference/length ratio was 0.365.

[grrraaahhh]

Abstract


The hindlimbs of the Malayan sun bear (Helarctos malayanus), the polar bear (Ursus maritimus), the brown bear (Ursus arctos) and the giant panda (Ailuropoda melanoleuca) have been anatomically and osteometrically studied. The Musculus tibialis cranialis of the Malayan sun bear and the giant panda possessed a well-developed rich fleshy portion until the distal end of the tibia. In the polar bear and the brown bear, however, the fleshy portion of the M. tibialis cranialis was not developed until the distal end of the tibia. The tendon of the M. tibialis cranialis inserting on the proximal end of the Ossa metatarsalia was shorter in the Malayan sun bear and the giant panda than in the polar bear and the brown bear. In the Malayan sun bear and the giant panda, moreover, the M. popliteus was attached more distally to the tibia than in the polar bear and the brown bear. The stable dorsiflexion and supination of the foot and the efficient pronation of the crus are important for skillful tree climbing. The present study suggests that the Malayan sun bear and the giant panda have hindlimbs especially adapted to tree climbing by the well-developed fleshy portion of the M. tibialis cranialis reaching the distal end of the tibia, its short tendon, and the M. popliteus inserting near the distal end of the tibia.

Sasaki M, Hideki E, Wiig Ø, Derocher AE, Tsubota T, et al. (2005) Adaptation of the hindlimbs for climbing in bears. Ann Anat 187: 153–160.
www.sciencedirect.com/science/article/pii/S0940960205000038

[grrraaahhh]

Abstract

The mechanical properties of the bone material of femora of five wild polar bears, ranging in age from three months to seven and three-quarter years, were compared with those of humans and axis deer. There are changes in mechanical properties in all three species with age, but their time course and extent vary greatly between species. The age-related changes in mechanical properties are attributable mainly to changes in mineralization. At any age, the properties of the polar bear's bones lie between those of humans and the deer. The architecture of the bear's bones, and the mechanical properties of their bone material, were related to the weight of the bears. The calculated stresses in the bones, and their deflection under load, were relatively constant compared with the very large differences in the weights of the bears and the sizes of their bones.

Brear, K., Currey, J. D. and Pond, C. M. (1990), Ontogenetic changes in the mechanical properties of the femur of the polar bear Ursus maritimus. Journal of Zoology, 222: 49–58.

onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.1990.tb04028.x/abstract

[grrraaahhh]

FWIW, I am sure more relating data can be found in veterinary and anatomy literature.

[Ursus arctos]

datadryad.org/resource/doi:10.5061/dryad.77tm4
Includes extensive data on multiple limb bones for all eight extant bear species.

[grrraaahhh]

Abstract


Cross-sectional geometric properties (areas, second moments of area) of ursid femoral diaphyses were calculated using formulae for a hollow ellipse. Inner bone contours were obtained from biplanar radiographs. The species included are Ursus spelaeus, Ursus arctos, Ursus deningeri and Ursus sp. from Deutsch-Altenburg 4B. Midshaft femoral bending rigidity is markedly increased in the mediolateral plane in U. spelaeus, while it is more equally distributed in U. arctos. This relationship is not correlated with size. The Early and Middle Pleistocene species investigated exhibit intermediate properties. Along with other skeletal traits, femoral cross-sectional shape in U. spelaeus is interpreted as being indicative of a limb structure designed primarily for static stability.



Kunst G.K. Femoral morphology of some Quaternary bears. Acta Zoologica Cracoviensia year: 1996, vol: 39, number: 1, pages: 269-278.

[grrraaahhh]

Abstract


The morphological study and biometrical analysis presented in this paper revealed that the two European Middle and Late Pleistocene bear species, U. spelaeus and U. arctos, can be distinguished not only through teeth and skull features but also through limb bone ones. The phyletical relationships between the various European Pleistocene bear species are also discussed. A phyletical sketch based on the biochronological occurrences, on the migration pathways followed by bears during the Pleistocene and on the palaeobiological opportunities that determined the evolutive trend from U. etruscus to U. deningeri and to U. spelaeus is proposed. The modern brown bears evolved in Asia from archaic U. arctos and occurred in the Italian peninsula during the Fontana Ranuccio Faunal Unit. The coexistence with U. spelaeus was biologically compatible because of the two species' lived in different ecological niches.


PETRONIO, C., CANZIO, E. DI & STEFANO, G. DI (2003): Morphological and biometrical differences in the limb bones of Ursus arctos and Ursus spelaeus and phylogenetical considerations on the two species. Palaeontographica Abt. A, 269 (4-6): 137-152; Stuttgart.

[Ursus arctos]

Data from Christiansen 1999 figures 1 and 2.
Look at columns J and K.

I think the correlations are deceptively high, however. Comparing data with tables where they are actually listed reveals that error is not negligible.

One tab per graph.