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South American Giant Short-faced Bear v Andrewsarchus
Topic Started: Jan 13 2012, 10:33 PM (14,643 Views)
Taipan
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Andrewsarchus mongoliensis
Andrewsarchus mongoliensis was a giant mammalian predator of Central Asia and the largest, and most famous member of the mesonychids, a wholly extinct group of prehistoric mammals. The mesonychids were the only known group of ungulates to become carnivorous, and looked vaguely like wolves, with blunt, hoof-like nails instead of claws. Andrewsarchus (Andrews + Greek ἀñ÷üò, "ruler") was named for the famous explorer and fossil hunter Roy Chapman Andrews, who led the expedition on which it was discovered in 1923.
Andrewsarchus is known only from an enormous skull (83 cm long and 56 cm wide) and pieces of bone, but the skull's similarity to that of smaller mesonychids suggests that Andrewsarchus had the same wolf-like body on a larger scale. Extrapolating from the body proportions of similar mesonychids, as well as large land mammals in general, Andrewsarchus was most likely about 4–6 metres (13–18 feet) long, standing nearly 2 metres (6 feet) at the shoulder, and weighing well over 1,500 pounds,[1] making it the largest terrestrial carnivorous mammal known to have ever existed. Based on the proportion comparisons to mesonychids and modern day ursids, it is believed that the largest of the Andrewsarchus may have weighed nearly a ton (close to 2,000 pounds, or 907 kg). It is open to debate whether the animal was gracile or robust in build. It should be noted that modern white rhinoceros specimens are much heavier than these figures, though rhino bodies are about as long.

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South American Giant Short-faced Bear - Arctotherium angustidens
Arctotherium is an extinct genus of South American short-faced bears within Ursidae of the late Pliocene through the end of the Pleistocene. They were endemic to South America living from ~2.0–0.01 Ma, existing for approximately 1.99 million years. Their closest relatives were the North American short-faced bears of genus Arctodus (A. pristinus and A. simus). The closest living relative would be the Spectacled bear (Tremarctos ornatus).
Based on measurements of the fossil's leg bones and equations used to estimate body mass, the researchers say the bear would have stood at least 11 feet tall (3.3 meters) on its hind legs and would have weighed between 3,500 and 3,855 pounds (1,588 and 1,749 kilograms). In comparison, "the largest record for a living bear is a male polar bear that obtained the weight of about 2,200 pounds (1,000 kg)," said researcher Leopoldo Soibelzon, a paleontologist at the La Plata Museum.

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Edited by Taipan, Sep 3 2012, 09:02 PM.
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HyperNova
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Ausar
Apr 2 2015, 01:38 AM
Posted Image

That puts Arctotherium's weight at 590 kilograms. On the other hand, Andrewsarchus appears to be ~660 kilograms.

That's a ~12% size advantage. I'm not so sure if I'd really call that significant. With that said, that the artiodactyl is, if anything, heavier doesn't really help the bear, considering what the former has going for it. It's pretty safe to assume that the bear was a much better grappler, but attempting to grapple with a head and jaws this proportionately (and absolutely) large would be a very dangerous task. It's not the same as grappling with something armed with horns or tusks. Case in point, lions never attack the head of a crocodile or hippo, they go behind them. In the case of Arctotherium & Andrewsarchus though, nothing suggests the former would be more agile than the latter.

Because of this, I favor Andrewsarchus.
Arctotherium was really that small? If that's the case would't arctodus simus be bigger?
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Ausar
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I guess?

I wonder if there are remains indicating larger animals than the individual above though.
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blaze
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MACN 5132 is not the large specimen that made the news a couple of years ago, that's MLP 35-IX-26 which is 14% larger than MACN 5132 so about 900kg but yes, the largest fossils of Arctodus simus are bigger than those of MLP 35-IX-26.
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Ausar
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^Wait, 14% larger? Then wouldn't it be ~673 kilograms?

590*0.14=82.6+590=672.6
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Spartan
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He probably meant in linear dimensions.
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Ursus arctos
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Ausar
Jun 18 2016, 06:55 AM
^Wait, 14% larger? Then wouldn't it be ~673 kilograms?

590*0.14=82.6+590=672.6
Blaze meant around 14% longer, which translates to about 50% heavier (assuming isometry). Think: if one cube is 14% longer than another, it is also about 50% heavier (1.14*1.14*1.14 = roughly 1.48). Isometry means the same shape (like two cubes are both cubes).

MACN 5132's humerus was 54 cm long.
MLP 35-IX-26's (the big one's) humeri were 61.5 and 62 cm long (left and right, respectively). That makes about 13.9% and 14.8% longer.

An example of what I mean on positive allometry:
Humerus least circumference is a better predictor of weight than humerus length.
MACN 5132's humerus least circumference was 22 cm.
MLP 35-IX-26's two humeri least circumference were 26.5 and 26.2 cm (left and right, respectively).



Humerus least circumference shouldn't be exagerated by the bone growth of the right humerus (probably triggered by deep injuries and infections):
Posted Image

The injury on the right doesn't cover much length, and judging from the 64.6 cm long Arctodus simus humeri, the least circumference comes just above the distal Humeral epicondyle. I recall reading earlier that it generally occurs about 1/3rd up from the distal end, rather than at midshaft.

The fact that the left's value is extremely similar makes me expect it is fairly appropriate.


The reason I draw attention to the humerus circumference (besides being better predictors of body mass): they're massively wide!

HLC (humerus least circumference)/HL (humerus length) ratio averaged 0.318 (n=17) for lions and 0.303 (n=19) for tigers. Smilodon fatalis averaged at 0.337 (n=7).

MLP 35-IX-26's values?
0.423 and 0.431.

As far as bigger Arctodus simus go, you can see 63.6 and 64.6 cm long Arctodus simus humeri in the above image.

These are clearly among the largest humeri in the world -- of any animal (note: bears have big upper arms).
1264 kg hippo: 18.25 cm HLC, 42.25 cm HL
1900 kg white rhino: 25.7 cm HLC, 45.7 cm HL
1435 kg Javan rhino: 21.3 cm HLC, 42.5 cm HL
990 kg giraffe: 21.8 cm HLC, 49.5 cm HL
3534 kg Indian elephant: 31 cm HLC, 83 cm HL
6435k kg African elephant: 41.63 HLC, 103.5 cm HL
[Warning: these numbers (Campione and Evans) are from captive zoo animals.]

You have to actually get to elephants before you finally start seeing bigger humeri in modern animals!

To be fair, hippos and rhinos are tanks on tiny legs, while giraffe front legs are mostly radius and metacarpals:
Posted Image
Note: the elbows are at about chest height, the joint you see about half way down the leg is actually the wrist!

Still, make no mistake: MLP 35-IX-26 was massive.
Also, most Arctodus simus specimens were much smaller than MLP 35-IX-26. I only know of those two that weren't, so a member of A. simus does indeed hold the mantle of biggest bear (and terrestrial carnivoran) yet discovered.

Anyway, as far as the matchup goes:
Stating Andrewsarchus is more agile is totally missing the meaning of the word in the context of a fight.
You have to actually get to bite the other animal for an advantage in jaws to be worth a flip.
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blaze
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Yes, I meant 14% larger in línear dimensions/longer.

Ursus, Soibelzon and Schubert describe the measurement as mid shaft circumference which is not the same as least/minimum circumference, the latter, in the case of these bears, as you point out should be just above the distal condyles so clearly not at the middle and a much smaller measurement.
Edited by blaze, Jun 18 2016, 09:04 AM.
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Ursus arctos
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From table 3:
"HMSC Humerus mid shaft circumference."

Oops, you're correct.
That also means these measurements are not directly comparable with those I reported on cats. I will have to check Campione & Evans to see their details on the circumference measurement.

EDIT:
Campione & Evans state:
"Following the Anderson method, we use minimum circumference (thinnest region along the diaphysis) as a proxy for limb robusticity. "

So they followed the method of Christiansen as well.

That Soibelzon and Schubert did not is odd, given that they used Christiansen's formulas to estimate body mass.

Final edit:
Double checking, Christiansen 1999 did indeed use least circumference to develop his circumference formula.
Then, Soibelzon and Schubert take a midshaft circumference measurement, and use it for his formula (H5) in their article? Heh. No comment.
Edited by Ursus arctos, Jun 18 2016, 09:39 AM.
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blaze
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Yeah, they were careless in that regard and not only when it comes to Christiansen (1999) they also got wrong Anyonge (1993), he writes that circumference and transverse and anteroposterior diameters of the shaft were taken at 35% of the length of the humerus starting from the distal end, in the Arctotherium humerus that point coincidentally falls exactly were you said the minimum circumference should be, just above the distal condyles, here the humerus is ~70mm wide.

Soibelzon and Schubert write that the transverse diameter of shaft at middle of the left humerus is 90mm, the only points in the shaft where it is that wide is at ~45% and ~55% of the total length.

Posted Image

So they did try to avoid the effect of the pathology and didn't exactly measure at the very middle but they didn't follow the procedures required for the equations they used.
Edited by blaze, Jun 18 2016, 10:07 AM.
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Ursus arctos
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Those two points are still clearly exaggerated by the pathology.

For example, the proximal part of the 63.3 cm A. simus humerus looks more robust than the corresponding region in the A. angustidens humerus, yet it looks much thinner at the 45% and 55% marks you indicated with a red line.


Anyway, I'm a little frustrated with that because it all just seems so ridiculous.
Neither Christiansen nor (as you point out also) Anyonge call for measurements from the injured regions. So, Soibelzon and Schubert use the wrong measurements in the first place, choosing to instead measure the gross bone deformity.
I digress.

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For fun, here is a figure from Sorkin's 2008 bear ecomorphology article, with the left A. angustidens humerus from Soibelzon and Schubert overlain. Unfortunately, they're anterior and caudal views respectively (so I had to flip the A. angustidens humerus so the curve lines up).
Gives some idea of the thickness.
Sorkin's white ruler is 15 cm long, while the black bar from Soibelzon and Schubert is supposed to be 10 cm.

The pictured A. simus, U. a. gyas, and P. tigris humeri were 58, 44.4 cm, and 30.34 cm respectively.

The distal region of the left humerus looks particularly massive, although interestingly its maximum distal epicondylar width to humerus length ratio was almost identical to that of a sample of 23 male brown bears from Morris and Carrier (0.299 vs 0.298).
Its right humerus has a more typical appearance; is the length over which the left distal humerus maintains its width the result of another injury?

Interestingly, MACN 5132's distal humeral epicondyle was 20.5 cm wide. This results in a ratio of 0.38, the highest I've ever seen.
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blaze
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I said that they tried not that they were successful haha

btw, in the photos from Sorkin (2008), did you account that the lengths were functional lengths? ignoring the lesser and greater tubercles and the trochlea?

Perhaps it is the result of the same injury, it must have had effects elsewhere, the distal region of the right one looks more "normal" even though that one is also pathologic.

I've had the feeling for a good while that there's something wrong with the humerus of MACN 5132, it's distal end is just way too wide to be normal.

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Ursus arctos
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blaze
Jun 19 2016, 12:43 AM
btw, in the photos from Sorkin (2008), did you account that the lengths were functional lengths? ignoring the lesser and greater tubercles and the trochlea?


I scaled them to be roughly similar pixel lengths, so take them as rather imprecise comparisons.

blaze
Jun 19 2016, 12:43 AM
Perhaps it is the result of the same injury, it must have had effects elsewhere, the distal region of the right one looks more "normal" even though that one is also pathologic.

I've had the feeling for a good while that there's something wrong with the humerus of MACN 5132, it's distal end is just way too wide to be normal.


Agreed on both accounts; I would also doubt 0.37 is a functionally accurate HEI until I see a photo of its humerus.
Browsing google scholar for "MACN 5132", I don't one in any of the articles.
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Carcharadon
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Ausar
Apr 2 2015, 01:38 AM
Posted Image

That puts Arctotherium's weight at 590 kilograms. On the other hand, Andrewsarchus appears to be ~660 kilograms.

Edit: read blaze's subsequent post. Seems this can be at parity.

It's pretty safe to assume that the bear was a much better grappler, but attempting to grapple with a head and jaws this proportionately (and absolutely) large would be a very dangerous task. It's not the same as grappling with something armed with horns or tusks. Case in point, lions never attack the head of a crocodile or hippo, they go behind them. In the case of Arctotherium & Andrewsarchus though, nothing suggests the former would be more agile than the latter.

Because of this, I favor Andrewsarchus.
^ My opinion here reflects this.
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Warsaw2014
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blaze
Jun 18 2016, 06:49 AM
MACN 5132 is not the large specimen that made the news a couple of years ago, that's MLP 35-IX-26 which is 14% larger than MACN 5132 so about 900kg but yes, the largest fossils of Arctodus simus are bigger than those of MLP 35-IX-26.
Largest brown bears have access to meat,; Bears with vegetable diet are smaller.

Though it seems that A. simus did not overlap temporallyand spatially with A. pristinus in the southeast during the latePleistocene, A. simus would have co-occurred with bothTremarctos floridanus and Ursus americanus Pallas, 1780 inthis region. The earliest record of these two species in Floridais late Pleistocene (Hulbert, 2001), and they occur together atsome localities (Kurte´n and Anderson, 1980). Tremarctosfloridanus is the more common of the two in Florida andknown from far more localities (Kurte´n, 1966; Hulbert, 2001).While T. floridanus went extinct at the end of the Pleistocene,U. americanus survived and is the only bear still living in thestate. From a dietary perspective, U. americanus is a generalistand omnivore while T. floridanus is thought to have beenprimarily herbivorous (e.g., Kurte´n and Anderson, 1980;Emslie, 1995). This proposed dietary separation may haveallowed the two to co-exist without marked ecologicalcompetition (Kurte´n and Anderson, 1980).The addition of A. simus to the southeastern ursid faunaadds yet another potential competitor for existing bears. Thedietary behavior of A. simus has been considered by a numberof researchers (e.g., Kurte´n, 1967; Emslie and Czaplewski,1985; Matheus, 1995; Bocherens et al., 1995; Matheus, 2003;Barnes et al., 2002; Sorkin, 2006), which has resulted in somedebate. While all of the hypotheses and associated researchwill not be repeated here (for review see Schubert and Wallace,2009), the results of the C/N isotopic studies are pertinent forthis discussion. These isotopic analyses confirm that A. simusfrom Beringia consumed high proportions of meat (Matheus,1995; Bocherens et al., 1995; Barnes et al., 2002). Whether ornot this animal protein was primarily acquired from predationor scavenging is not known. Further, isotopic analyses on A.simus from the contiguous United States and Mexico have notbeen reported, so it is possible that diet varied geographically.Despite these uncertainties we hypothesize that A. simus wouldhave been more carnivorous than other southeastern bearsand therefore filled a different ecological niche than did T.floridanus and U. americanus.
https://www.researchgate.net/publication/250071137_Giant_Short-faced_Bears_Arctodus_simus_in_Pleistocene_Florida_USA_a_Substantial_Range_Extension
Warsaw2014
Jul 11 2016, 03:01 AM
blaze
Jun 18 2016, 06:49 AM
MACN 5132 is not the large specimen that made the news a couple of years ago, that's MLP 35-IX-26 which is 14% larger than MACN 5132 so about 900kg but yes, the largest fossils of Arctodus simus are bigger than those of MLP 35-IX-26.



Yes largest fossils of Arctodus simus (humerus) are bigger (longer) than those of MLP 35-IX-26.620 mm vs 647 mm ,but MLP 35 have more massive bone IMO.

Posted Image

BTW Humerus of the spectacled bear dated at 30,000 years old.(length c .50 cm)

http://www.infoban.com.ar/despachos.asp?cod_des=47427&ID_Seccion=2
Compared to MLP 35-IX-26
Posted Image

https://www.facebook.com/139565012790803/photos/a.469871199760181.1073741901.139565012790803/469871549760146/?type=3&theater
Edited by Warsaw2014, Jul 11 2016, 04:23 AM.
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HyperNova
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@Warsaw2014
Who do you think was eavier between MLP 35-IX-26 and the largest specimen of arctodus simus?
Edited by HyperNova, Jul 11 2016, 07:20 AM.
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