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Here is all you need to know about the creodonts:

  1. They were a group of carnivorous mammals that, despite having carnassials, had no relation to Carnivora.
  2. They were a global force, occupying territories all across North America, Eurasia and Africa.
  3. They lived a long life, from 63 all the way to 11 million years ago.

Apparently, this clade became extinct not because of some dramatic environmental catastrophe, but because of competition with the carnivorans. But here's the deal--Carnivora did not occupy all the niches at once. The pinnipeds (seals, sea lions and walruses) did not debut until as recently as 24 million years ago.

So, in an alternate Earth, the creodonts managed to occupy the pinniped niche earlier in the Oligocene, millions of years before the carnivorans could. That way, by the time we get to the deadline of their extinction, those who were finfooted and semiaquatic would survive because there was nobody for them to compete with, indeed to as recently as the Holocene. Plausible or Not?

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    $\begingroup$ What exactly is your question? You created a scenario for an alternate history. As such it can't be true or false, it is fiction. What do you want to know? $\endgroup$ – quarague Nov 14 '19 at 12:02
  • $\begingroup$ @quarague, he's asking for validation of an alternate world hypothesis. With John the fine details are important, it may help to have reasonable expertise of the period in question to be able to answer it. $\endgroup$ – Separatrix Nov 14 '19 at 13:51
  • $\begingroup$ @Separatrix I still feel he could improve the question by expanding the 'True or False?' a little bit. 'Is this plausible?' would already be an improvement, something that explains what he wants beyond a yes or no answer would be even better. $\endgroup$ – quarague Nov 14 '19 at 13:54
  • $\begingroup$ Giving that Creodonts have limited limb mobility compared to Carnivora, I doubt they would make excellent swimmers like seals are. $\endgroup$ – Tardigreat Nov 14 '19 at 15:14
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there was nobody for them to compete with

This is false. There are plenty of fishes in the sea, battling their daily fight for a meal, even without pinnipeds on the dance floor.

Sharks, tuna and so on and so forth down the size ladder. If there were no mammals to compete with, also carnivorous fishes would have evolved to occupy the available slots.

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  • $\begingroup$ Do sharks and tuna crawl onto land? $\endgroup$ – JohnWDailey Nov 14 '19 at 3:44
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    $\begingroup$ @JohnWDailey, no, but neither do pinnipeds hunt for food on land, except those in entertainment parks. $\endgroup$ – L.Dutch - Reinstate Monica Nov 14 '19 at 3:47
  • $\begingroup$ Bottom line is, you are detracting from the real point of the question. $\endgroup$ – JohnWDailey Nov 14 '19 at 3:54
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    $\begingroup$ No, his point is well made. The niche is not necessarily about the animal in it, it's about the prey. Get chased off land, and water only works if you can beat the competition there. $\endgroup$ – Halfthawed Nov 14 '19 at 4:15
  • $\begingroup$ @Halfthawed That was not what I asked. $\endgroup$ – JohnWDailey Nov 15 '19 at 0:45
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Impossible to say. Perhaps they might have survived, if they filled their niche well enough, perhaps they would have gone extinct. Perhaps they would share the niche with pinnipeds. There certainly would still have been competition for resources from other creatures regardless of whether pinnipeds died out or not, just as there are other predators (birds, fish) that prey on the same species as seals do. This is your alternative history, so you can play it however you want.

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I would not bet against the carnivorans.

  1. The creodonts were established in the various niches before there were carnivorans, and creodonts were outcompeted from all of those niches. Being established in a niche ahead of the competition did not save them. There is no reason to think the pinniped niche is different. Pinniped-analog creodonts will be ousted just as their contemporaries were ousted from terrestrial niches.

  2. Carnivorans probably outcompete other carnivores because of their brains. On the Australia side of Wallace’s line, marsupial carnivores persist. On the mainland side they were outcompeted. Carnivora as an order also have outcompeted other orders of placental mammals that might eat meat – those nonCarnivora carnivores that exist today occupy extreme niches not amenable to the carnivore body plan: the shrews, bats and whales. Head to head, carnivores have something going on that gives them an edge against older groups.

  3. The one way pinniped creodonts might survive to modern times is geographic isolation – the same way the Tasmanian devils and thylacines made it. You could start your pinniped creodonts in Australia or maybe some place like the Great Lakes. Pinniped carnivorans evolving on the mainland would not oust the creodont seals from their refuges until some human brought some there to see what would happen..

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