I am working on a world where giant tortoise-like animals wiped out the majority of the planet's ecosystem. The planet has on large continent near the equator that once was covered in lush rainforests. However, an animal evolved to take full advantage of this lush environment. These creatures formally named Magnus Clydeus (Courtesy of fellow Worldbuilding user @StephenG). These animal's bodies were so efficient that their waste was unusable for any decomposers currently on that planet. This lead to Magnus Clydeus eating the entirity of the rainforsts save for any places which they could not traverse such as bowl craters. This resulted in the continent becoming a massive dustbowl dessert. Without their constant supply of food, Magnus Clydeus went extinct. These animals had no natural predators past their juvinille stage, giving them free reign. However, oce these animals die, they simply drop to the ground, leaving behind massive cadavers. Could stable ecosystems arise within the sheltered sanctuary that the shells of these rotting giants provide?.

The shells and overall skeleton would be sturdy enough to persist for thousands of years after death. Once the body is decomposed enough, the shell would be hollow and jam packed full of nutrient rich remains. This would be converted into soil by later decomposers which would allow for plant life to thrive.

  • $\begingroup$ I'd like to once again give credit to @StephenG for their naming of Magnus Clydeus, common name Clyde. $\endgroup$ Sep 21 '20 at 13:41
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    $\begingroup$ If they are tortoise-like then presumably there are lots of dome-shaped giant shells. How big are these in metres approximately? 10 metres across? 100 metres? Also they sound like they would be the equivalent of hot caves with little or no light. Is that the case? $\endgroup$ Sep 21 '20 at 13:45
  • $\begingroup$ @chasly-reinstateMonica The total length of the shell is roughly 16.25 m and the total height is 8.75 m. The total width is 18 m. This can vary between individuals with some being larger or smaller but for the sake of the question, I will use these measurements. As for openings in the shell, there is one large opening at the front where the forelimbs and neck would be accommodated(7m high, 8.6m wide) and another smaller opening at the rear which would accommodate the rear end of the animal (5 by 8 meters across). These opening might be somewhat obstructed by the limb bones and vertebrae. $\endgroup$ Sep 21 '20 at 14:12
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    $\begingroup$ Can light penetrate the shells or is it dark in there? $\endgroup$ Sep 21 '20 at 14:17
  • $\begingroup$ @chasly-reinstateMonica the shells are completely opaque. $\endgroup$ Sep 21 '20 at 14:34

In theory, I suppose it could develop into something like a cave ecosystem. You have some potential problems though.

The decomposition is going to provide you with plenty of nutrients and even moisture, but it is not an renewable set of resources. Since the ecosystem has effectively been turned into a desert you have a problem with water getting to where it is needed. There is no vegetation left to hold the ground soil together so erosion is going to happen at least until grasses can grow. That is going to let water drain away from the shells. This creates the problem of water getting inside to replenish whatever life is going on inside. You can't have life (on earth, anyway) without water.

Next you have a time scale problem. Even though we are talking about Megafauna, How long will the nutrient bath last inside the shell? Yes, these things are huge, but the carcasses are going to rot pretty fast. It might take a hundred years, but when you are talking about specializing an ecosystem, that's not any time at all.

You also have a problem with just plain old size. These creatures were huge, but not quite enough to create space for an entirely new ecosystem.

What could happen would be similar to shallow cave ecosystems. Some trees would grow, especially closer to the openings. Smaller plant might grow a little farther back inside. Fungi, mushrooms and such much deeper inside. If enough started to grow soon enough after the creature died, when decompisition started to take place but before it was all gone, the materials from the plant life might create a cycle of composting material sustaining the nutrient bath for a while.

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    $\begingroup$ I believe the water drainage problem might be solved by the shell. The lower portions of the opening could stick out enough that they act as a water catcher. And with the shell being rounded, water would pool at the bottom. $\endgroup$ Sep 22 '20 at 11:43

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