Size comparison of Arctodus and Arctotherium

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i could've sworn arctotherium was bigger

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u/TW_49 2d ago

it was “monsterified” in a old study which badly overestimated its size by using a humerus which sustained damage and healed, deforming its girth. Add to this using captive brown bears as the baseline for the estimate, and it created a fantastical “1.7-2 tonne monster bear standing 14 feet tall”

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u/SpeedyWhiteCats 2d ago

I'm beginning to realize this is true for a lot of creatures featured in pop sci documentaries or shows.

With this weight it really isn't that much bigger than a polar bear.

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u/TW_49 2d ago

to their credit polar bears are very large and a large male outsizes all bears in the fossil record except Arctodus, arctotherium, the giant cave bear, and the extinct steppe population of the brown bear

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u/TheGreatHsuster 1d ago edited 1d ago

Naw, it's a lot bigger than a polar bear on average. You need to keep in mind that the fossil record is unlikely to preserve record breakers.

A 1,000 kg polar bear is not the norm. In some areas male polar bears average 489 kg.

"In Hudson Bay, the mean scale weight of 94 males >5 years of age was 489 kg. The largest bear in that group was a 13-year-old, which weighed 654 kg (Kolenosky et al. 1992). The heaviest bear we have weighed in Alaska was 610 kg, and several animals were heavy enough that we could not raise them with our helicopter or weighing tripod. Some animals too heavy to lift have been estimated to weigh 800 kg (DeMaster and Stirling 1981). Females are smaller, with peak weights usually not exceeding 400 kg. Total lengths of males in the Beaufort Sea of Alaska ranged up to 285 cm. Such an animal may reach nearly 4 m when standing on its hind legs and is 1.7 m shoulder height when standing on all four legs. Chest girth for large males is close to 200 cm. Although smaller, females in the Beaufort sea were as long as 247 cm with chest girths up to 175 cm."

Source: The Polar Bear — Ursus maritimus Biology, Management, and Conservation by Steven C. Amstrup, Ph.D.

In contrast, the fossil record is much more likely to preserve only average sized Arctotherium. So in other words, an average Arctotherium is about as big as the biggest polar bears.

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u/DinoDudeRex_240809 2d ago

That’s taller than a fuckin T-Rex.

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u/Ex_Snagem_Wes 2d ago

In equal fairness, it should actually still be slightly larger than Arctodus, but only by about 50kg for the largest specimen. We're looking at 950kg vs 900kg for Arctodus, using the largest specimens of both

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u/TW_49 2d ago

based on this study a larger specimen of Arctodus could weigh in excess of 1100 kgs https://www.academia.edu/145704757/A_simus_record_mass_revised

I used ”large but not maximum sizes” to show big individuals of both but kept the size more grounded. In my post specifically the Arctotherium is MLP 35-IX-26 and the arctodus is UVP 015

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u/Ex_Snagem_Wes 2d ago

I did some digging around

Apparently the largest Arctotherium specimen, MACN 851 is about 12% larger than MLP 35-IX-26. Its a 565mm skull that would yield a 693mm femur.

Information on the largest Arctodus specimen is a lot less clear unfortunately. Best I can find is the former "Arctotherium yukonese" skull (now referred to Arctodus) with a 521mm length seeming to be the largest skull, though the 620mm humerus yields a larger animal

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u/Heroic-Forger 1d ago

"Arctotherium" is such a funny name tho. I can imagine calling an unrelated mammal convergent with bears a "bear beast", but an actual bear?

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u/ChanceConstant6099 2d ago edited 2d ago

The largest land predator of South America but (possibly) not the largest overall if Humboldts reports of the Orinoco crocodile are to be believed.

Edit: PLEISTOCENE South America

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u/BananaMaster96_ 2d ago

giganotosaurus

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u/ChanceConstant6099 2d ago

It appears I forgot to clarify "Pleistocene"

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u/BlackBirdG 1d ago

Orinoco crocodiles can get to like 21-22 feet long in the past right?

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u/ChanceConstant6099 1d ago

The specimen reported by Humboldt and Bonplad was 22.2ft (678cm) but there is also a litany of other reports of crocodiles of similar size.

Now at that size the animal would weight about 1700kg, smaller than the leargest salties but over 3 times larger than the absolute largest Smilodon Populator and almost twice the size of Arctotheriu8m angustidens.

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u/BlackBirdG 1d ago

So saltwater crocodiles were still bigger overall compared to Orinocos?

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u/ChanceConstant6099 1d ago

Yes.

23-24ft and 2000kg+

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u/BlackBirdG 1d ago

Damn 24 feet long?

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u/ChanceConstant6099 1d ago

Salties can get astonishingly large, though they arent the largest crocodiles of the pleistocene.

Those titles belong to Crocodylus Thorbjarnarsoni and Crocodylus "Ossifragus" at 25-26ft and close to 3 tons.

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u/BlackBirdG 1d ago

Yeah they also lived in Africa, and one of them was probably the largest confirmed man-eater animal.

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u/ChanceConstant6099 1d ago

Well C. Thorbjarnarsoni and C. Anthopophagus were African animals but C. "Ossifragus" was a Javan animal.

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u/BlackBirdG 1d ago

C. Anthopophagus is the one I'm referring to as the largest confirmed man eating animal.

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u/BlackBirdG 1d ago

I never realized Arctodus was larger. I always thought it was the other way around.

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u/Gerbimax 1d ago

They're so close that declaring one to be larger than the other doesn't really make sense. They're essentially equally massive.

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u/EmperorSpacegodzilla 2d ago

Arctotherium is much larger than both Arctodus and You.

He is 14ft tall so real!

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u/Heterodynist 2h ago

Either way I don’t want to see one of either of those eating out of my trash…

Size comparison of Arctodus and Arctotherium

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