Biggest of the Biggest Bears

[brobear]

In a contest of size - for the biggest short-faced bear and - for the biggest bear of the Genus Ursus. This is two separate contests.
    
1 - Arctodus simus vs Arctotherium angustidens.  
 
2 - Ursus maritimus tyrannus vs Ursus ingressus.

 

[brobear]

As for skulls: Length:
Actodus simus - 521 mm ( 20.51 inches ).
Ursus ingrssus - 57.14 cm ( 22.5 inches ).

I have found no info on the Arctotherium skull. No U. maritimus tyrannus skull has ever been found.

[brobear]

Skull of Arctotherium angustidens 

[brobear]

dinopedia.wikia.com/wiki/Arctotherium

Arctotherium was the largest bear, known at this time. Compared with Arctodus simus, it had a more powerful physique with the same linear dimensions and was also very much robustly build. Representatives of this species reached 4.7 m ( 15 feet 5 inches ) in length and weighed about 2,200 kg. ( 4,850 pounds ). The calculations were made ​​on the basis of seven different measurements of animal bones. Arctotherium angustidens lived during the Pleistocene, the Argentine plains. At one time (2 million - 500 thousand years ago) it was the largest predator on the planet. It appeared to have been omnivorous, but large herbivores were the basis of its diet. Some competition it could make is with the sabre-toothed cats, who were also at the top of the food chain. The closest relative of A. angustidens is that of the living spectacled bear, which is significantly lost in size compared to its distant ancestor.

[brobear]

wiseaboutbears.org/bears-of-yesterday-prehistoric/

Giant bears once dominated the mega-fauna.
Ursus spelaeus – the giant cave bear – roughly 1000 pounds.
Arctodus simus – the giant short-faced bear – roughly 2000 pounds.
*Agriotherium africanum – primitive short-faced bear – roughly 1400 pounds.
Arctotherium angustidens – South American short-faced bear – roughly 3000 pounds.
Ursus maritimus tyrannus – giant brown bear – roughly 2500 pounds.

[Polar]

Some of those weights are a bit exaggerated:

Cave Bear - 1000 pounds
Arctodus simus - 1300 to 1600 pounds
Arctotherium - 2000 pounds
Agriotherium - 1400 pounds
Ursus maritimus tyrannus - 1800 to 2000 pounds

So a battle between the polar bear's ancestor and the South American short-faced bear!

[brobear]

It's a contest of size; and thank you for adding the picture.
But no. Ursus ingressus was a mostly-carnivorous cave bear. 

[brobear]

According to tigerluver ( Bioligist ) - normal maximum size:

Arctotherium angustidens - 1100 kg ( 2,425 pounds ). vs arctodus simus - 1100 kg ( 2,425 pounds ).

Ursus maritimus tyrannus - 700 kg ( 1,543 pounds ). vs Ursus ingressus - 740 kg ( 1,631 pounds ).

[brobear]

shaggygod.proboards.com/

sus maritimus tyrannus (B.M. 24361 Kew Bridge specimen)

L, total length of the ulna.

PD, greatest proximal diameter, measured anteroposteriorly from the tip of the coronoid process to Margo dorsalis.

SD, inner diameter of the semilunar notch, measured vertically.

BS, minimum transverse breadth of shaft. This is in the distal portion of the shaft, at some distance above the capitulum. The extreme constriction lies close to the capitulum in the Brown Bear and the spelaeids, but higher on the shaft in the Polar Bears, including the Kew specimen.

1 L, length; PD, maximum proximal diameter; SD, inner diameter of semilunar notch; BS, minimum shaft diameter.

Ulna measurements

L: e485
PD: a95
SD: 44
BS1: 27.6

Ursus maritimus tyrannus (Plate # 2 Ulnae)

Kurten, Bjorn 1964, The evolution of the Polar Bear Ursus maritimus Phipps.

[brobear]

shaggygod.proboards.com/    
   
Arctotherium angustidens





Ulna measurements



Greatest length: Right; Left, 570.



Greatest width of olecranon processWidth from posterior border to tip of coronoid process: Right, 108; Left, 109.



Least distance from sigmoid notch to posterior

border: Right, 66; Left, 70.



Greatest diameter of distal epiphyses: Right, 63; Left, 62.5.

[brobear]

shaggygod.proboards.com/

The specimen described here has an estimated body mass ranging from 983 to 2,042 kg depending on the equations considered (Tables 3 and 4). The highest predicted value is probably unrealistic, although the size of this individual is much higher than other known specimens (see Table 5). All predicted body masses based on humeral measurements are shown in Table 3. The mean and median (considering all equations) are 1,588 and 1,749 kg respectively. Thus, we suggest that the body mass of this gigantic bear was between these two values. To our knowledge, this makes the A angustidens described here the largest known bear, and probably the most powerful terrestrial carnivoran of the late Cenozoic (Soibelzon & Schubert 2011).

[brobear]

Above post: shaggygod gives the weight of Arctotherium angustidens a weight ranging somewhere between 983 kg ( 2,167 pounds ) and 2,042 kg ( 4,502 pounds ).
I averaged this lowest number with the highest estimate and came up with the weight of 3,334 pounds - which sounds realistic.

[brobear]

Also from shaggygod: Good news everyone. Collection of materials on the Americas GSFB HEAVYWEIGHTS have met with good success. Many of us have been following with strong interest the latest material covering Arctotherium angustidens. The new data on the giant South American specimen inspired me to double check and dig around for material on its comparable sized North American cousins; the Giant Short Faced Bear (A. simus). By my count, there are a handful of fossil specimens that are comparable in scope, however, the heavier build advantage goes to the South American bear. They include a northern Californian specimen with a record size ulna measurement of 591 mm; the Lake Bonville, Utah specimen with a record size femur measurement of 723 mm; a Kansas specimen with a record size humerus measuring 646 mm; a Cass County (Nebraska) specimen with a humerus measurement of 633 mm, and another large Nebraska specimen from Hay Springs.

As the data reveals, although there are North American A.simus specimens that produce longer humerus values, a review of the mid shaft width values tell us that A.angustidens is the heavier built bear. Comparable femoral data suggest a similar conclusion.


The closest North American specimen to approach A.angustidens relative to robusticity is the specimen from Kansas. In the North American theater, the Kansas River specimen produced a higher mid shaft width femoral values than both the Lake Bonneville and Hay Springs bears. Moreover, the Kansas specimen produces a longer humerus than the Cass County, Nebraska GSFB.

[brobear]

Also from shaggygod:
Per Christiansen's 1999 paper on A.simus & Cave bear body mass:



What size were Arctodus simus and Ursus spelaeus (Carnivora: Ursidae)?

Abstract

Body masses of the giant short-faced bear (Arctodus simus Cope) and the cave bear (Ursus spelaeus Rosenmueller & Heinroth) were calculated with equations based on a long-bone dimensions:body mass proportion ratio in extant carnivores. Despite its more long-limbed, gracile and felid-like anatomy as compared with large extant ursids, large Arctodus specimens considerably exceeded even the largest extant ursids in mass. Large males weighed around 700-800 kg, and on rare occasions may have approached, or even exceeded one tonne. Ursus spelaeus is comparable in size to the largest extant ursids; large males weighed 400-500 kg, females 225-250 kg. Suggestions that large cave bears could reach weights of one tonne are not supported.  

 400 kg to 500 kg = 882 pounds to 1,102 pounds.  /  700 kg to 800 kg = 1,543 pounds to 1,764 pounds.

[brobear]

From the book, Ice Age Cave Bear by Barbara Hehner.
Cave bear paws were enormous - the paw prints they left behind in caves measure as much as seven inches ( 18 cm ) across. Most brown bear prints are only about four inches ( 10 cm ) across.

[brobear]

dinopedia.wikia.com/wiki/Ursus_maritimus_tyrannus

Ursus maritimus tyrannus is an extinct subspecies of the polar bear, known from a single fragmentary ulna found in the gravels of the Thames at Kew Bridge, London. It was named by the Finnish paleontologist Björn Kurtén in 1964 and is interpreted to represent a relatively large subadult individual: the ulna is estimated to have been 48.5 cm (19 in) long when complete. For comparison, modern subadult polar bear ulnae are 36–43 cm (14–17 in) long.
An unpublished reinvestigation of the fossil suggests that the fossil is actually a brown bear.

[brobear]

I had to look up "ulna" as I have next-to-no knowledge of medical anatomy terminology. 

www.innerbody.com/image_skelfov/skel21_new.html

The ulna is the longer, larger and more medial of the lower arm bones. Many muscles in the arm and forearm attach to the ulna to perform movements of the arm, hand and wrist. Movement of the ulna is essential to such everyday functions as throwing a ball and driving a car.
The ulna extends through the forearm from the elbow to the wrist, narrowing significantly towards its distal end. At its proximal end it forms the elbow joint with the humerus of the upper arm and the radius of the forearm. The ulna extends past the humerus to form the tip of the elbow, known as the olecranon.

[brobear]

Polar - In knowing that family and school are keeping you frantically busy these days ( completely understood ) when you can find some much-needed leisure time, please see if you can research the length of the ulna of both the Kodiak bear and the polar bear and - if at all possible - a cave bear ulna. -Thankz.

[brobear]

About Ursus speleaus and Ursus ingressus: Acording to GrizzlyClaws ( very knowledgeable ) it is viable that speleaus and ingressus were not separate species but that ingressus was more likely a subspecies of speleaus. That would mean that a more appropriate name would be: Ursus speleaus ingressus.
Ursus speleaus speleaus was ( probably ) completely vegetarian whereas Ursus speleaus ingressus was an omnivore who leaned more towards meat. This meat-eating habit would explain his slightly larger size.

I will edit and add: I have two books on cave bears and ingressus is not even mentioned in either. This further convinces me that both are of the same species. Therefore, bone comparisons, other than skulls, can come from either subspecies.   

[brobear]

True or False information: The Ursus maritimus tyrannus ulna is from a sub-adult specimen?
dinopedia.wikia.com/wiki/Ursus_maritimus_tyrannus

Ursus maritimus tyrannus is an extinct subspecies of the polar bear, known from a single fragmentary ulna found in the gravels of the Thames at Kew Bridge, London. It was named by the Finnish paleontologist Björn Kurtén in 1964 and is interpreted to represent a relatively large subadult individual: the ulna is estimated to have been 48.5 cm (19 in) long when complete. For comparison, modern subadult polar bear ulnae are 36–43 cm (14–17 in) long.
An unpublished reinvestigation of the fossil suggests that the fossil is actually a brown bear.