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Okay, now this question is a bit random.

But, I'm planning for a possible book project about a 2019 expedition to an undiscovered island. The island is near the northern tip of the Ninetyeast Ridge in the Indian Ocean. I think the book will be in a similar format to James Gurney's Dinotopia, existing as both a story and a "scientific journal" of the protagonist.

The only thing is, the fauna on this island includes descendants of tigers and various south Asian small cats, rhinoceroses and other fauna typical of Indonesia, Malaysia and nearby regions. However, other animals on the island hail from African ancestors - notably the last surviving members of the Protelinae or "dog-like hyena" subfamily* (Excluding the aardwolf**.), as well as other bone-crushing hyena species.

The last biogeographical obstacle is the presence of earless seals on the island. The only seal that favours tropical climates are the monk seals - With one extinct species*** in the Caribbean, one in Hawaii, and one in the Mediterranean. To me, the Hawaiian monk seal looks like the best candidate for a migrator, but there's still a massive distance between Hawaii and Ninety East. However, anyone who's heard of a Baikal seal will know that seals are very good at overcoming geographical obstacles.

So, this sounds like a lot of zoology, and a lot of paleontology too. But really, I don't need a zoology or a paleontology expert to answer. The main thing I need in a respondant is someone who is versed in geography and knows how an island the size of Ireland**** (The country, not the whole island) could end up on the Ninety East Ridge with East African fauna dating from 800,000 BC as well as more recent South Asian animals. My basic theory is that the island could have split off from East Africa, and the Asian wildlife could have colonised it somehow, but I'm no geographer. I doubt that it would be possible for it to join up with Sundaland (I believe it was a thing fairly recently, again, not a geographer.) Also, if anybody knows how earless seals could get from Hawaii, past Indonesia and to my island, then I'd love to hear from you.

Note: I know that this question may raise the hackles of some people who don't like science/what-if questions, but really this is the only SE site that relates to this. It's a mixture of geography and biology and involves heavy speculation. So, if it's voted to be closed, then there's nothing I can do about that, but please understand that this is the best site, as far as I know, to ask this question.

*The large members of this subfamily didn't go extinct like their mainland counterparts due to the absence of large canids on the island - when dholes and other small canids arrived at the island, the Protelinaeans were dominant and could not be out-competed.

** If the whole 800,000 BC thing doesn't fit into a plausible timescale, I could potentially have more recent aardwolves evolve into large running hyenas.

*** Just because it's extinct now doesn't mean it could have colonised the island before it went extinct, but as said, I think that the Hawaiian seals are a more plausible option anyway.

**** I can change the size if it's necessary.

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  • $\begingroup$ Northern Ireland is only about 15% of the landmass of the island of Ireland, if the distinction is significant for the purposes of the question I'd give the size of your island to be approx 72,000 square kilometers $\endgroup$
    – Binary Worrier
    Apr 5, 2018 at 11:16
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    $\begingroup$ Your question currently is very long and includes a lot of debating if this is a good question or not and you being modest in general and in a way feeling sorry for even asking. Either check out the sandbox in the meta if you are unsure if this is the right place and way to ask or clean up your question. Currently I personally find it very bothersome to read your question and trying to extract what you want to know and what you already know. Usually people asking here show no sign of awareness or self-reflection, you went a bit too much into the other direction $\endgroup$
    – Raditz_35
    Apr 5, 2018 at 11:19
  • $\begingroup$ If we can find penguins all the way North to the Galapagos islands, your fauna of african ascendancy can be found on your island. $\endgroup$
    – The Square-Cube Law
    Apr 5, 2018 at 13:00
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    $\begingroup$ @Renan Yes, animals can emigrate very far, but there's always a reason why, and I'd like to include that reason in the project. $\endgroup$
    – SealBoi
    Apr 5, 2018 at 16:32
  • $\begingroup$ Small cats and rhinoceros also hail from Africa... $\endgroup$
    – John
    Apr 29, 2021 at 17:39

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It seems impossible to find an island that have split off from Africa and moved that far in the east of Indian Ocean. You're far beyond the limits of somali plate.

So it would be more plausible to explain the presence of african species by an ancient migration.

Your island seems to be very close to Andaman islands. Indigenous people from Adaman, like the Jarawas, look more like African than Asian people.

Jarawa kids

The Adamans appears to be a milestone in the great coastal migration of Humans along the shores of Indian Ocean.

Black tribes came from Africa via the Arabian peninsula, and then they migrate toward India, South-East Asia and Oceania.

enter image description here

So we can imagine that other african species may have followed the same road, and reached your island when the sea was lower, during the ice age. Even if your island was never directly linked to the continent, it may have been close enough to allow terrestrial animals to end up there.

After the sea rises they would have been definitively trapped on the island, but they found a way to survive.

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    $\begingroup$ Thanks, I wasn't sure about the whole "splitting off from Africa" thing and if it would work. This actually seems really likely, since there are a good few Africa-originating animals in Asia. EDIT: I looked it up and this did actually happen. African animals such as elephants spread through Africa then emigrated to Southern Asia, according to Wikipedia. Thanks for the great answer! $\endgroup$
    – SealBoi
    Apr 5, 2018 at 12:48
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Biogeographically, you shouldn't have a problem. It can be an island with really odd fauna due to rafting events. Just make sure your African animals had a Eurasian distribution at least once. Your island is pretty far for them to survive the voyage.

https://en.wikipedia.org/wiki/Oceanic_dispersal

As a geographer, you might want to consider how to explain the geological origin of your island. If you want to go with a chunk of Gondwana breaking off, then I'd suggest this site

http://www.hhmi.org/biointeractive/earthviewer

to get a better understanding of how India, Africa, Australia, and Antarctica fit together and subsequently broke apart. It's not unheard of for remnants of Gondwana to become "sunken continents" (hello, New Zealand and Kerguelen) but right now all the former parts of Gondwana are accounted for. So you might want to think about what part of Gondwana you want to cut your island out of.

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  • $\begingroup$ Well, I was thinking that the African fauna would have been there before the island split off from Africa, but rafting works too if the time frame is implausible. Also, thanks for the resources! $\endgroup$
    – SealBoi
    Apr 5, 2018 at 12:35
  • $\begingroup$ Yeah, the time frame is the problem. Gondwana started breaking up at the end of the dinosaur era, so it'd be difficult for Ice Age mammals to get there. $\endgroup$
    – KernelOfChaos
    Apr 6, 2018 at 0:12
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Based on the location of the island, I'd say it is somewhat plausible. Maybe the way the island formed is that the tectonic plates did something different in an alternate timeline. Some animals may have migrated there, that is possible. Species that are extinct elsewhere can survive there as it has happened in reality.

But there are some animals, like the tigers and rhinoceros, I don't agree could be there naturally. But maybe the island was connected to Africa and other places before lots of it sank somehow, like a lost continent. Or an ancient, now lost, civilization brought them there for hunting or living there purposes. It's really up to you. I hope I answered your question well!

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  • $\begingroup$ Well, another respondent has highlighted the fact that rafting could be possible with large animals. Perhaps that would work out. $\endgroup$
    – SealBoi
    Apr 5, 2018 at 12:37
  • $\begingroup$ I would agree. It's just that I find that having a tiger travel a gazillion miles across the ocean and surviving on a super large stick highly implausible. Or do you mean rafted on a raft by humans? That would make sense. $\endgroup$
    – Rewan Demontay
    Apr 5, 2018 at 20:58
  • $\begingroup$ “Rafting” often refers to a rather large chunk of floating tangled debris. Consider a seasonal Lake in a forested area that floods out to the ocean — a few dozen uprooted trees tangled together can plausibly carry a breeding population of larger mammals. $\endgroup$
    – arp
    Apr 6, 2018 at 3:14
  • $\begingroup$ Another respondent suggested the possibility of African animals migrating from Africa, through Arabia and into southern Asia, which gives them a far shorter distance to raft, and probably actually happened, since there are many animals of African origins in southern Asia. $\endgroup$
    – SealBoi
    Apr 6, 2018 at 8:12
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Not really

The thing is your fictional island is it is located at the tip of a mid-oceanic ridge as an oceanic island out in the middle of the ocean. There is a parallel in the form of Christmas Island, which is located near where you have your landmass but is much, much closer to the Indonesian mainland. And Christmas Island's native mammal fauna consists of...two bats, two rats, and a shrew. This is about what you'd expect for your fictional island assuming similar processes. Probably more if the island was the size of Ireland, but the fauna would be almost all rodents, bats, and shrews.

Carnivores in particular are terrible at dispersing to islands. The issue being that most of them are large, and thus cannot raft, because they exist at low population densities (and thus are less likely to disperse), and because they are carnivorous and have trouble finding enough food to sustain themselves. Most cases of carnivores on islands are on continental islands, in which the island was connecting to the mainland during the ice age and subsequently because isolated when sea levels rose. In fact, the region why IRL Indonesia has so many large mammals is because it was once one big land mass during the ice age and rhinoceroses and tigers could walk to most places that are now islands. Even many carnivores such as the Channel Island fox (Urocyon littoralis) are thought to have been originally introduced to the islands by humans thousands of years ago. Some carnivores have been known to cross oceanic boundaries, but they tend to be very small, omnivorous species like civets and raccoons that can survive the journey on rafts. Or otters. The only species you've listed that could potentially make the journey are tigers, which have been known to swim to islands, but nowhere near that far.

The other issue is an Ireland-sized island probably couldn't support the diversity of animals that you wanted. Island ecosystems are very fragile and often can't support a huge diversity of megafauna all together at once because they can only support small populations. Ireland did have a number of large mammals, but this is because it was a continental island and the fact that wolves, bears, Irish elk, and many other large mammals were rapidly wiped out by human arrival shows how fragile these ecosystems can be.

Big animals in general also don't raft very well. The only big mammals which are known to disperse across oceans reliably are hippos, elephants, and tigers, and a lot of that is because they swim the distance rather than rafting. Hyenas would be completely out of luck.

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This might be what you're looking for...

https://en.wikipedia.org/wiki/Lemuria

Lemuria is a hypothetical landmass, that of course never existed... but it was located between Africa and Asia. The Ninety East Ridge was pretty much its center. That's of course not a geographically correct answer, because we pretty much know that this landmass never existed, but your island is fictional... so a fictional explanation might help.

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Thousands of years ago, Austronesians from Indonesia sailed to Madagascar and settled there. Later on, Bantus from Southeast Africa came to Madagascar and mixed with the locals. The point is that an ancient connection between Indonesia and Africa is possible. Other ancient fauna migrations include the voyage of Old World Monkeys to the New World.

So if humans or some other force caused Indonesian animals to sail to Madagascar (or caused African animals to sail to Indonesia), that could work. If you're willing to change geography, this event is much more plausible if there was a vary large island or a chain of islands between East Africa and Indonesia.

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