Spectacular counterpart of hyenas in South America

 The role of bone-crunching scavenger is taken

  • in Africa and Asia by hyenas, and
  • in Australia (in a minor way because its body mass is only about 6.5 kg) by Sarcophilus.

I assume that, in the Pleistocene, Sarcophilus extended to New Guinea. And for now I will exclude any gaps presented by southeast Asia.

I have already covered Madagascar (https://www.inaturalist.org/journal/milewski/67599-which-animal-scavenged-bones-in-madagascar#).
This raises the question: why do we not hear of any bone-crunching scavengers in South America?
Here, I suggest that not only was there a bone-crunching scavenger in South America, but it was exceptionally large.
As a preamble, let me point out that assessment of the fauna of South America is complicated by two factors. These are

  • the megafaunal extinctions at the start of the Holocene, and
  • the unrivalled proliferation of rodents in the Neotropics.

Rodents, although gnawing bones only incidentally, are numerous, diverse, and in some cases large-bodied, in South America. So much so that it is easy to imagine them consuming any large bones available, without even being noticed doing this.
While I still think the current absence of any obvious bone-crunching scavengers (apart from, perhaps, peccaries) in South America is puzzling, let us put this puzzle aside, and ask ourselves: which animals filled this niche just before the megafaunal extinctions?
The obvious candidates are the genus Arctotherium of the tremarctine bears.
One way to think of Arcotherium is as a ‘superhyena’, with body mass an order of magnitude more than that of any living hyena, and extremely long legs suited to great mobility.
His may lead to the realisation that, at least until the end of the Pleistocene, South America not only had a bone-crunching scavenger, but had the ‘ultimate’ bone-crunching scavenger.

For, just as the sabretooth felid of the Pampas, Smilodon imperator, was the largest cat ever to live on Earth, so Arctotherium was probably the largest bear ever to live on Earth.

And it seems reasonable to assume that the latter scavenged the bones left by the former – a wonderful thing to ponder when we consider the extreme differences and the extreme specialisations in the jaws and dentitions of the two genera.

While Smilodon was ‘the ultimate sabretooth’ with teeth extremely specialised for slicing, but at the same time extremely vulnerable to fracture, Arctotherium complemented this by evolving a dentition that could hardly be more durable in processing large, hard objects by blunt, brute force.
By comparison with this bear, all other known bone-crunching scavengers show a kind of compensation for their limited size.

Crocuta has a skull of modest size, even relative to its body, but relies on an extremely ‘dexterous’ use of its teeth, breaking large bones not with its molars but with one conical premolar on each side.

Sarcophilus relies on uncomplicated force (which is inadequate for breaking bones even as large as the largest bones of kangaroos) and compensates for the inevitable fracturing of its unspecialised teeth by having a naturally short lifespan of about 6 years – which means that it runs out of life and becomes senescent before it runs out of teeth.
Although the existence of Arctotherium is well-known (and as you can see from the artwork below prominent in the imaginations of those who study such matters), there are two points, emerging from this, which I think have been underplayed.
Firstly, Arctotherium is usually portrayed as a predator first and a scavenger second.

I see no particular reason to frame it this way. It seems as logical, and more biogeographically meaningful, to assume that it was a scavenger first, and a predator second.

And, if so, the way we should think of Arctotherium is as ‘the ultimate megafaunal scavenger’ among the mammals.

Arctotherium angustidens:

Posted on September 02, 2022 07:01 AM by milewski milewski


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