I am designing a rather sizable (~ 2000 kg) carnivorous predatory species and I want it to expel all the waste it produces in the form of dry, compacted pellets (similar to owl pellets, except of course it would contain more than simply undigestable bones and feathers, and be much larger) that it regurgitates from its mouth.

Is this feasible? How would the digestive and waste management system need to be changed to facilitate this?

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    No need to complicate things. Model the creature on any species that do not excrete wet urine, but where the nitrogen cycle instead leads to dry waste. Then combine that with the concept of cloaca animals, where the urethra and colon combine to form a single orifice (like birds and reptilians). Both of these things exist in real life. Then all you need to do is to let this cloaca not end up as an orifice near the rear of the animal but somewhere near its esophagus. And there you go. – MichaelK Aug 28 '17 at 13:29
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    All bilaterally symmetric animals except the very primitive and obscure Xenacoelomorpha have digestive tracts in the form of a tube with one input opening and one output opening. This species must have diverged from the other bilaterans some 600 million years ago, deep in the Precambrian... – AlexP Aug 28 '17 at 13:30
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    @MichaelK Thats probably the start of a good answer, you should write it up – James Aug 28 '17 at 14:18
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    @MichaelK - can you elaborate also on "nitrogen cycle" part - would it enable this animal to bound all excess water? – Alexander Aug 28 '17 at 16:40

Here on Earth there are several Classes of animals which have a "sack" digesting system, but they tend to be fairly low on evolution scale (e.g. Coelenterates).

These gastrointestinal systems are much simpler and less efficient than ours.

OTOH it would be quite easy to devise an animal whose excreting orifice is quite near to mouth, perhaps because the whole body is encased in some kind of bone armor. with just one opening.

The "pellets" is not really a problems, there are animals (mainly in very dry climate) e.g. some Australian parrots, that deliver some soft pellets, as dry as they could make them (can be picked up with your fingers without dirtying them) as their only escretion.

You can get inspiration from the Komodo dragon

After digestion, the Komodo dragon regurgitates a mass of horns, hair, and teeth known as the gastric pellet, which is covered in malodorous mucus. After regurgitating the gastric pellet, it rubs its face in the dirt or on bushes to get rid of the mucus, suggesting it does not relish the scent of its own excretions.

However keep in mind that regurgitating the ingested material means that the animal is not even trying to extract nutrients from it. Therefore it makes sense only for hardly digestible substances like horns, hair and teeth. All the rest, once gone through the digestive apparatus, would take too much effort to go all the way back and would not be evolutionarily advantageous, in particular for a 2000 kg animal, with large energy needs.

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