If Rodents evolve

[ttyo888]

Hi I am here for some scientific backing on a novel I am working on.

 

My novel involved rodents that have evolved into larger forms that can rival that of other mammalian groups.

 

They evolved on an island like New Zealand and Gough Island which had no mammalian predators but lots of naive bird species. Soon after the rodents found the island, they increased in size and supplanted the native avians and became the dominant species. Provided that there are no humans to stop the rodents and there is plenty of bugs and plants to sustain the ecosystem, how possible is this scenario that rodents evolve into creatures that I suggest?

 

I sincerely wish for some scientific minds to share their opinions as how the rodents here can evolve?

[Moontanman]

Hmmm, don't mammals generally get smaller on islands and reptiles get bigger? Dwarf elephants, hippos, rhinos, even humans?

[ttyo888]

Well moontanman, there are some trends that big animals shrink on islands but small animals enlarge.

 

Gough Island for example had house mouse bigger than their ancestors introduced in the 19th century. If they can change their size in a century, imagine what they can become in a million years time if nothing was done to stop them.

[Moontanman]

The islands limited resources is what would limit their size. a very small animals with no predators might get bigger but there is a very real limit the resources an island can provide so no matter how long they evolve I would expect them to stay smaller than say a rodent population on a continent sized body would get with the necessary environmental pressures.

[ttyo888]

I understand

 

My rodent will not be reaching dinosaur size despite the temptation but they will be much bigger than the little rodents scurrying up the tree definitely

 

I would say the size of an elephant is the limit of my rodents. The largest of them is only the size of an Asian elephant at 3 metres at the shoulder. The predators are smaller and the biggest of them is only the size of the tiger. But despite so I think the suspense and fear of them is still there right?

[Moontanman]

It would have to be a very big island dude but the idea sounds interesting

[ttyo888]

is 710.2 km square enough?

 

Btw is that a mimic octopus in your avatar?

[Moontanman]

almost certainly not

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No it's a stomatopod

[ttyo888]

Okay I have some theories on how the rodents got onto my islands and then evolved in isolation.

 

So there are two theories

How the rodents got to the Gnaw Islands

 

Theory 1: Drift Wood Migration= based on New Zealand environmental tragedy and Madagascar

The rodents drifted from the earthquake prone Sunda Shelf which included Indonesia in the past. Perhaps in the past, a Kratatoa like eruption or another natural disaster had send a substantial amount of rodents onto the "virgin" Gnaw Island via driftwood like the lemurs reaching Madagascar. "Virgin" Gnaw Island probably like New Zealand had an avian-dominated ecosystem. But once the rodents drifted there, being rodents they ate all of the native avian fauna to extinction. It is suspected that the rodents that drift there were from the Sciuridae[squirrels] stock as even the flying species of avians were not spared either.

[squirrels have been known to eat insects, eggs, small birds, snakes and rodents].

 

Theory 2: Part of the Sunda Shelf or Zealandia= New Caledonia

Taking from the Sunda Shelf map, it is possible that the island was once like New Caledonia, part of the super continent Gondwana. But then it's more likely that the island might have mammalian fauna instead of merely reptile and avian fauna of New Caledonia. It's possible that the rodents took over as the original carnivoran or ungulate inhabitants died off. This absence of carnivorans and ungulates, rodent adaptability and island gigantism can account for the large size of the rodents.

[YT2095]

Rabits and Beavers can get quite large, but there would need to be some driving force that made being bigger than that an advantage.

[D H]

The islands limited resources is what would limit their size. a very small animals with no predators might get bigger but there is a very real limit the resources an island can provide so no matter how long they evolve I would expect them to stay smaller than say a rodent population on a continent sized body would get with the necessary environmental pressures.

Not necessarily. Think Komodo dragon.

 

Dwarf elephants are an example of island dwarfism. Komodo dragons are an example of the flip side of island dwarfism, island gigantism.

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Even better than Komodo dragons: http://en.wikipedia.org/wiki/Flores_Giant_Rat.

[YT2095]

you may find this interesting (I did): http://en.wikipedia.org/wiki/Capybara

[CDarwin]

you may find this interesting (I did): http://en.wikipedia.org/wiki/Capybara

 

See, capybaras are heavily herbivorous, as are beavers and rabbits. I think that tends to be the trend in rodents. The whole rodent adaptive system is geared toward processing low grade foods that need a lot of chewing. The smaller ones can supplement their diets with a wider variety of foods, but I don't see a large rodent ever becoming, say, an ace predator, ttyo888. If you want big rodents, you'd better have lots of low grade plant material on your island for them feed on. Capyburas graze, I believe, so it wouldn't be unreasonable to imagine herding rodents feeding off of grasses. Incidentally, they would have to reingest their feces. All herbivorous rodents do, because they ferment their cellulose in a large sac at the beginning of their large intestine, the caecum, which means most of it misses the small intestine the first time through, where most of the energy and nutrients of food are taken up.

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Theory 1: Drift Wood Migration= based on New Zealand environmental tragedy and Madagascar

The rodents drifted from the earthquake prone Sunda Shelf which included Indonesia in the past. Perhaps in the past, a Kratatoa like eruption or another natural disaster had send a substantial amount of rodents onto the "virgin" Gnaw Island via driftwood like the lemurs reaching Madagascar. "Virgin" Gnaw Island probably like New Zealand had an avian-dominated ecosystem. But once the rodents drifted there, being rodents they ate all of the native avian fauna to extinction. It is suspected that the rodents that drift there were from the Sciuridae[squirrels] stock as even the flying species of avians were not spared either.

[squirrels have been known to eat insects, eggs, small birds, snakes and rodents].

 

Actually, that's how rodents got to South America across the Atlantic, so that's not a stretch at all.

Edited May 25, 2009 by CDarwin
Consecutive posts merged.

[ttyo888]

The selection pressures; existence of carnivorans and other predators, prevent the evolution of predatory rodents.

 

But if lets say there are no such selective pressures....

 

What do you guys think?

[Mokele]

Ok, there's several issues here.

 

First, IMHO, dispersal vs. vicariance (drifting with the splitting continents) will only make a difference in terms of which rodents are present and which natural fauna you start with.

 

However, if you want a big island, you should probably go with vicariance - most volcanic islands are far too small to support large mammalian carnivores. Big mammal carnivores need HUGE areas to roam, and even bigger areas to maintain a suitably large population.

 

As far as rodent diet, while they are well adapted to low-quality plant matter, that doesn't necessarily preclude evolving into a more predatory lifestyle - after all, crocodiles have evolved herbivorous, clam-eating and filter-feeding forms in the past. On the other hand, there are suspiciously few rodent carnivores, and no known large rodent predators, so maybe there is some constraint on them? Given that this is fiction, though, I'd embrace the possibility - if fiction stuck too close to fact, it'd be pretty boring.

 

Size is the main issue. Rodent-sized things can reach elephant sizes - after all, that's exactly what happened after the dinosaurs died out, and where elephants come from. But on an island? Truly huge endotherms almost never occur on islands. Even the giant ground sloths that used to live in Cuba were small compared to their massive continental bretheren.

 

Would it be possible to set your novel after a mass extinction, rather than on an island? That way, you could wipe out all the big animals, predators included, and have rodents radiate on a continent.

[ttyo888]

ah, Mokele I have been expecting your input on this subject.

 

hmm I have made a thread here about carnivorous rodents out of curiosity sometime ago.

 

I am thinking the thylacoleo, the marsupial lion from Australia has the design for the rodent carnivore as it looks almost rodent like.

 

In fact, after getting bitten by hamsters in the past. I think there is little modification on rodent dentition in order to feed on flesh. The case is more on the body anatomy to get meat from living herbivores.

 

Also I have some size limits on my creatures. the biggest ones on my island are only as big as asian elephants and the biggest carnivores are big as tigers only. So no dinosaur rodents on my island but even at this kinda of size, I think most people with the fear of mice would be running for their lives.

[YT2095]

it May also help to remember that a Rodent simply means a mammal that`s teeth continue to grow (a bit like our fingernails do), the "dent" (dentia, dental etc...) in the name is a bit of a give-away

so you Could have them evolve into all manner of creatures if you wanted to, even Giraffe like if there was a reason to reach higher for food.

[ttyo888]

Oh but the rate which the teeth grow varies from species to species right?

[YT2095]

I don`t know enough about it to answer that, all I know is what qualifies them for the name and that I used to breed Gerbils.

[CDarwin]

it May also help to remember that a Rodent simply means a mammal that`s teeth continue to grow (a bit like our fingernails do), the "dent" (dentia, dental etc...) in the name is a bit of a give-away

so you Could have them evolve into all manner of creatures if you wanted to, even Giraffe like if there was a reason to reach higher for food.

 

There are other important features. Rodents are distinguished form lagomorphs like rabbits, for example, by only having two upper incisors (rabbits have four). And the incisors are the only teeth that grow continuously.

 

 

 

Dentition is an interesting angle actually. Rodents don't have canines, so they would have to co-opt some of their other teeth to grasp pray and chunks of flesh in a carnivorous manner. They are limited in their number of incisors, so I imagine they would probably modify their first premolar into something caniniform (sort of like in your marsupial lion; lemurs also have caniniform premolars).

 

Modifying rodent incisors would seem tricky to me, since they only have dentin on the inside surface and grow continuously. They might have to lose that ability and encase the whole tooth in enamel. Elephant tusks are modified incisors that grow continuously, but I don't imagine those would be very useful for tearing into flesh.

[Moontanman]

 

Actually, that's how rodents got to South America across the Atlantic, so that's not a stretch at all.

 

Really? Can you provide any evidence for this?

[Mokele]

Really? Can you provide any evidence for this?

 

http://books.google.com/books?hl=en&lr=&id=uogzJvYSQHoC&oi=fnd&pg=PA8&dq=rodent+biogeography+gondwana&ots=-h9dlQGRdY&sig=J7A4O8Z_h-wInZx3ko5owSGyZs4#PPA12,M1

[ttyo888]

Is it possible maybe there will be a "true" flying rodent? We have gliding ones already so......

[Sisyphus]

Why would an elephant-sized rodent be any more frightening than an elephant?

[Mokele]

Is it possible maybe there will be a "true" flying rodent? We have gliding ones already so......

 

Very possible, though they'd have to abandon the typical rodent diet of low-grade plant matter for something more energy rich, such as fruit or insects, like bats.

Edited May 28, 2009 by Mokele
Major typo