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I have a speculative evolution project regarding giraffes. For those unfamiliar, giraffes are ruminants and rumination is not viable for carnivory according to every site I have wandered upon in my research. Ignoring any of the other issues of giraffes evolving to become carnivorous, my question here is how rumination could be adapted to a carnivorous diet.

There are no animals in our world that are ruminating carnivores and from my research, it simply isn't necessary. To me, it seems like there would be a firm pressure to remain an herbivore rather than make the leap to carnivory.

Now for some small but important details. The only animals besides giraffes in this project are paper wasps, the particular species of which prefers nectar and would be unlikely to decide it is a good idea to predate giraffes. The ecosystem is a series of islands, so contact with meat would be frequent through dead giraffes. I would like any answers to apply to scavengers and active hunters, if there are any differences between the two. And finally, while some handwavium is allowed as I do not need the exact chemical composition of their stomach acid, I want to be able to stick as close to realism as I can.

So, would rumination disable the path of carnivory in evolution?

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    $\begingroup$ This is bewildering: "The only animals besides giraffes in this project are paper wasps" $\endgroup$
    – Daron
    Jul 2, 2022 at 15:37
  • $\begingroup$ @Daron That's the magic of seed world projects. In technicality other creatures exist, but they aren't the focus of the project. $\endgroup$
    – King of the Hounds
    Jul 2, 2022 at 15:42
  • $\begingroup$ The thing about meat is that everything wants to eat it right now, because it's so much more jam-packed with accessible nutrients than plant matter, that the only way the microorganisms get an edge is by spoiling it. If a ruminating species has a routine, viable path to eating meat, I think it would probably evolve towards deprecating rumination instead of abandoning carnivory. $\endgroup$
    – notovny
    Jul 2, 2022 at 17:10
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    $\begingroup$ The cetaceans (including the carnivorous dophins and orcas) are closely related to the ruminants. And deer routinely engage in carnivorous activity, eating fish when they can catch them and the meat of dead animals when they can find them. $\endgroup$
    – AlexP
    Jul 2, 2022 at 20:29
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    $\begingroup$ @AlexP I researched this, and it unfortunately doesn't work too well. Cetaceans are not ruminants to my knowledge despite being closely related and deers have a simple-chambered stomach and do not ruminate. $\endgroup$
    – King of the Hounds
    Jul 2, 2022 at 23:15

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They might not need to evolve.

Many real-world ruminants are actually opportunistic carnivores, even if we call them herbivores. This means that they are able to eat meat and will do so of their own accord (i.e. they're not starving), but usually they can't or don't for whatever reason.

For example, cows will occasionally eat small animals such as mice, chicks, or even chickens. They will scavenge from carrion when the opportunity presents itself, and cows in particular also eat their own placental afterbirth.

Biologists debate why this occurs. Some think that this signals a nutrition defect, like lack of protein or calcium in diet, and the animal is attempting to secure diverse nutrients. Others think that the ruminant is simply trying to be a generalist, so they take the food when it's easy and ignore it otherwise. Despite some claims to the contrary- cows are capable of digesting meat. The last of their four stomachs, the abomasum, is similar in function to traditional omnivores or carnivores- it secretes hydrochloric acid like our own and is perfectly capable of breaking down meat protein. However, some other chambers of the cow's stomach are not good at handling meat and they can develop health problems or die if they eat too much meat.

You might have it backwards.

Interestingly, in cows there is evidence to suggest that the abomasum is evolutionarily the oldest stomach of the four. This could mean that the cow was originally a carnivore or an omnivore that evolved into a herbivore, rather than the other way around.

This makes a lot of sense if you think about it- the four-chamber stomach is a highly specialized organ designed to get the most out of plant matter. Each chamber optimizes one or more different functions- moving food between different chambers, fermentation, microbe growth, water absorption, enzyme application, acid breakdown, and others. However, only the fourth stomach closest to an omnivore stomach, the abomasum, can function independently. Thus, an animal with a traditional omnivore stomach could evolve specialized organs for dealing with commonly available food, but an animal with only a fermentation stomach might not even be biologically workable.

So- maybe there were other animals in your history's past that were hunted to extinction and the giraffes had to make do with the remaining plants. Or maybe they are opportunistic cannibals that will sometimes kill and eat other giraffes. Or maybe they eat giraffe carrion when they find it.

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You might begin with the evolution of a plant with more protein that attracts protein-rich insects; and the giraffe preferentially eats this plant as well. Along with the insects, which are even more protein-rich than the plant. The insects could be your paper wasps, maybe they build their nests in the plants, and the giraffe eats them wholesale, crunching down whole nests at a time. Like other animals, it can evolve an immunity to their sting, so it is a minor irritation at best.

All animals, even crickets, are protein-seekers, proteins are necessary for life biochemistry. (It is why even grazers have meaty bodies).

Then the giraffe's digestive system evolves to lean toward richer protein digestion, and then to almost exclusively seeking the nests of the wasps.

But they are still giraffes, the long neck lets them eat from the ground or the trees or anywhere the wasps may hide.

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    $\begingroup$ This is a fantastic concept, thank you! This works well as the plants on the islands such as acacias and mimosas are rich in protein, giving me a boosting point to begin with. $\endgroup$
    – King of the Hounds
    Jul 2, 2022 at 23:17
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No it does not preclude evolving into a carnivore.

If its literally the only large animal it is going to diversify into a whole load of niches, carnivory will be one of them, it will take a long time and radically change the animals anatomy, but it will happen eventually unless all megafauna go extinct.

Will it still be a ruminant by then, unlikely, digesting meat is far far easier than cellulose, a ruminant gut offers no benefit to carnivore, and it is using a lot of resources that could be spend making it a better carnivore or just making it better at getting a mate. What type of predator will split off from it is impossible to guess, there has never been a vertebrate extinction that eliminated all vertebrate predators and I can't imagine a worse starting anatomy for a predator than a giraffe so the path is pure speculation.

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It would make sense for a ruminant to transition to becoming an omnivore first before it becomes a carnivore. Maybe a fast ruminant like gazelles can hunt small animals. Overall though, it would be unlikely to occur since ruminant lifestyle is about going for food sources that are easy to access (grass) but hard to digest. Meat on the other hand is hard to access (prey runs away) but easy to digest. A ruminant carnivore would have to eat small animals that cannot really run away but are hard to digest for some reason. Maybe something like poison dart frogs.

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  • $\begingroup$ This is a useful mention but sadly isn't the answer I am looking for. I am aware that it is unlikely to occur, but evolution is known to barge its way into every ecological niche it can without asking if it should. I am more or less trying to find the biological processes that would lead to a carnivorous lifestyle, as I would consider a giraffe eating another giraffe to qualify as easy to access but hard to digest for a ruminant. I'll keep this in mind for the project later on, though! $\endgroup$
    – King of the Hounds
    Jul 2, 2022 at 18:13
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    $\begingroup$ @KingoftheHounds evolution get get from one point to almost any other point but it can't do it in one jump, it has to follow a path of viable intermediates. Can a ruminant evolve into a carnivore absolutely can it do it without any intermediaries, no. $\endgroup$
    – John
    Jul 2, 2022 at 21:44
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The trouble with a giraffe as a carnivore is not its digestive system, but the fact it is enormous, really tall and very specialised at feeding on high tree branches. Think about how awkward it is for a giraffe to get a drink of water: it has to splay its front legs wide apart, or sort of crouch, to get its mouth low enough to touch the water surface. Being a giraffe is all about getting your food from right up in the tree tops.

So the question you need to ask yourself is this: do you want your giraffe-carnivores to remain giraffe-shaped?

If you don't mind them drastically altering their body shape, then you can invent a scenario where some sort of environmental change favoured low scrub over tall trees and the giraffes' long legs and long necks gradually reduced in size through natural selection. A smaller, more 'camel-like' or deer-like' body shape is a better bet for ending up as the sort of carnivore that chases zebras or rabbits. Have a look at Andrewsarchus or the Entelodonts to inspire you with ideas of omnivorous/scavenging creatures which are related to ruminants.

If you want your giraffes to stay recognisably 'giraffe-shaped', you need to think of ways the giraffe can catch and eat animals in the tree tops.

Some things are relatively easy. If it is eating mouthfuls of leaves, it probably accidentally eats caterpillars, aphids, scale bugs and other insects. So invent a seasonal glut of one or more of these creatures, and have your giraffes switch to eating them at that time of year. For instance they could eat gregarious caterpillars, such as Mopane worms in summer. Or perhaps there is plague of locusts every autumn.

The giraffe's mobile lips and dextrous tongue could be good for picking eggs or chicks out of the birds' nests it can reach. Perhaps it could grab the occasional angry parent bird trying to defend its nest. So spring/wet season could be a feast of eggs and birds.

If there is enough slow and nutritious animal food in the tree tops all year round, the giraffe gradually adapts its digestion and dentition to a more carnivore pattern.

If you want the giraffes eating more nimble tree-dwelling animals, such as monkeys or squirrels or fruit bats, you might have to invoke pack tactics. One giraffe batters at branches with its thick, strong neck. Other giraffes wait to grab monkeys fleeing to the other side of the tree, squirrels trying to leap to the next tree, or fruit bats launching themselves into the air.

There will, of course, be a portion of the tree that the giraffes can't reach: in the middle and top of the canopy.

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