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In a world where man entered North and South America without causing a mass extinction, all of the paleofauna which became extinct ~10,000 BC in the Americas are still around. There are several families of giant ground sloths, mammoth and mastodons, horses, many llamas, glyptodonts, sabretooths, scimitar cats, short-faced bears and more.

South America is a wet continent and has many freshwater aquatic environments. Two of the biggest river systems in the world, the Orinoco and Parana, run through savanna, along with many smaller rivers.

In Africa, there is a niche occupied by the hippo, a large, aquatic grazer of both water plants and grass (usually by night). It thrives in rivers that run through the savanna. What animal in the Americas, particularly in South America, is most likely to have filled this niche?

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  • $\begingroup$ Well, the pre-human fauna of the Americas died for reasons beyond that of human settlement. $\endgroup$ – ifly6 Dec 30 '16 at 1:43
  • $\begingroup$ @ifly6 Arguable, but that's not what this question is about. $\endgroup$ – kingledion Dec 30 '16 at 1:57
  • $\begingroup$ There is no way man could have done such obvious damage to the Pleistocene environment. The timing just was never in sync. $\endgroup$ – JohnWDailey Dec 30 '16 at 2:50
  • $\begingroup$ Here is a Biology.SE question about Pleistocene extinctions. $\endgroup$ – kingledion Dec 30 '16 at 2:58
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    $\begingroup$ @JohnWDailey: But there's no way anything else could have made such changes to the fauna. A change in climate wouldn't work, when you consider that the horse was eliminated from the Americas, yet reintroduced horses now flourish in the wild in that changed climate. $\endgroup$ – jamesqf Dec 30 '16 at 4:30
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You ask what animal in the Americas would fill the niche? Not hippos. Or anything as agressive. More like a Dugong or Manatee-like creature. They are day eaters, but they fit into the aquatic grazer mold.

See this on where they came from, where they went, and how they have changed (early models had legs). They first developed during the Eocene, and have been around ever since in various iterations. Anywhere the water is warm and there's aquatic stuff to munch. They can swim the ocean, and do, but prefer to swim up rivers where they can.

They would have had time to develop by the pleistocene. Here's the wiki on Sirenian evolution.

Apparently at various times there were multiple models of sea cows swimming around, filling various niches. And there were a lot of them during the Pleistocene:

Pleistocene-age manatee bones have been excavated from over 24 sites in Florida, and men hunted them as soon as Indians arrived in the region. link to source

Here's a link to a scientific paper regarding the various kinds around the world. Notice that the ones in Florida that were found, were linked to a period just before what you are looking for.

See this handy link for the current ranges of the species in South America and some of the fossil records of it for the area. It's pretty extensive and likely that they were there, by the time period you are seeking.

An earlier version might have been less docile, and there's plenty of extinct versions to choose from.

Anyway. it's a place to start and they do, at least somewhat, fit what you are looking. Only a hippo is a hippo. As far as I can find, a specifically night feeding, aggressive aquatic feeder is a pretty specific niche--hard to find something exactly the same that isn't a hippo--but some of the early evolution pictures of the sea cow look a bit hippoish, from before they lost the legs. Problematically, by the era you indicate they would have lost the legs again, but maybe you can tinker with that--evolutionarily they've been in and out of the water a bit...

Early model:

Early model

Latest model:

enter image description here

Quite a bit smaller, but still reaching into this niche: the capybara. During this time and in this place, they reached about 100 pounds. Not huge but still interesting.

Capybaras graze in meadows, bed down in the woods, and spend much of their time in water. They require habitat that offers all 3 of these environments. They use water to escape from predators and to cool down during the heat of the day. They are not as helpless as they look for they are fast runners and swimmers, and they have thick hides. Nevertheless, jaguars were likely their most dangerous enemy in North America during the Pleistocene. The extinction of capybaras here probably contributed to the extirpation of jaguars in this region. link to source

Here's a modern photo of these guys, which are about 1/4 the size they would be in the Pleistocene. enter image description here

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    $\begingroup$ Interestingly the Afrikaans word for Hippo is "seekoei". Which directly translated is "sea cow". $\endgroup$ – Lu22 Dec 30 '16 at 7:35
  • $\begingroup$ Capybaras are good. Regarding the manatees, I'm looking for creatures that did actually exist 10,000 years ago, so while manatees were around they are strictly aquatic and not quite the hippos I am looking for. $\endgroup$ – kingledion Dec 30 '16 at 13:17
  • $\begingroup$ the not having legs thing--yeah, thought that might be a problem.... $\endgroup$ – Erin Thursby Dec 30 '16 at 14:36
  • $\begingroup$ @kingledion you didn't say that it had to have legs, though--you said: " large, aquatic grazer of both water plants and grass" which DOES fit the sea cow even without legs. If you want your niche-filler to have certain characteristics (like being able to go on land) probably should edit. $\endgroup$ – Erin Thursby Jan 2 '17 at 0:22
  • $\begingroup$ @kingledion there were sea cows around during that era--all kinds--that's what I found, and for sure they'd be sharing the water with capybaras, although the number of sea cows at the time was pretty prodigious... $\endgroup$ – Erin Thursby Jan 2 '17 at 0:24
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Giant Sloth

enter image description here

There were at least 4 different families of giant sloths living in the Americas at the end of the Pleistocene. In those families, there were something like 8 different genera, with some larger number of species. In short, there was a lot of sloth variety at that time.

There is one genus of sloth, Thalassocnus, that is suspected of being a semi-aquatic marine (as in salt water) sloth. This genus has such specialized adaptations as heavier bones to provide neutral buoyancy and an extended flattened radius (forearm bone) to act more like a paddle.

Thalassocnus was extinct, but the fact that it appears to be aquatic makes the many varieties of sloths a good bet for a hippo-like grazer. The closest relatives to Thalassocnus alive in the Pleistocene were the Nothrotheriidae, like the Shasta Ground Sloth. however, these various Nothrotheriid sloths all seem to come from rather mountainous and dry areas.

The next most distant branch of the sloth tree are the Megatheriidae. of these there were two living genuses, Megatherium and Eremotherium. These two are distinguished as the largest Pleistocene ground sloths, being up to 6m long and with estimated weights at 3 tons or more.

These two sloths are traditionally seen as more of a giraffe analogue, being able to prop up on two hind legs and a tail to reach as high as giraffes can into trees. But since the two sloths coexisted, and overlapped in range, what if they filled fundamentally different niches? Megatherium is present in places that were projected to have been parkland and semi-arid regions. Its range corresponds closely with the places a giraffe would be comfortable in the Americas. Eremotherium is only present in tropical rainforests and the wet southeast United States.

Conclusion: Eremotherium has the attributes to replace a hippo in tropical american ecosystems.

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  • $\begingroup$ Didn't these guys go extinct before the end of the Pliocene? And they were mostly salt water and not fresh? I know hippos can go in the ocean, but mostly stick to fresh water. I don't know much about giant sloths--were they aggressive? Really unusual species! Sorry for all the questions, just really find them interesting! $\endgroup$ – Erin Thursby Jan 14 '17 at 2:00
  • $\begingroup$ @ErinThursby Thalassocnus was extinct, but I'm using it as an example that it is not outrageous to imagine some sloths being mostly aquatic. $\endgroup$ – kingledion Jan 14 '17 at 16:48
  • $\begingroup$ I see that sloths are nocturnal, so it fits there. I never knew sloths could be aquatic. $\endgroup$ – Erin Thursby Jan 14 '17 at 18:52

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