Ridge-bellied hippopototortoise, by Alex Kirk

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This extraordinary creature was a hybrid remnant that showcased remarkable traits from both the hippopotamus and the tortoise, with subtle hints of the rhinoceros and walrus. The story of its life cycle reveals the intense evolutionary pressures that ultimately led to the downfall of Choeropelonoidensis kirkimus. Today's hippos and tortoises are plant-eaters because their last common meat-eating ancestor, a diminutive hippopotortoise, failed miserably in its bid as a semi-aquatic egg-eater and fish-hunter. Its feeble legs and massive armored shell made it woefully inefficient at hunting, and its large crocodile predators were far more skilled at safeguarding their eggs than the hippopotortoise was at snatching them up. This led to a split into two herbivorous populations: one in the presence of its predator, which retained its protective shell, and another in a peaceful pond without predators, where it lost its shell and evolved into modern hippos and tortoises.