A hairy crocodile
The clam newnewotter

Crocodiles have been absent from Antarctica since the Cambiocene, and it's not surprising given their inability to withstand the freezing temperatures of the continent. In the absence of these reptiles, some endothermic species have attempted to occupy a similar ecological niche, with varying degrees of success. One notable example of this evolutionary radiation is the clam newnewotter (Malacolutra antarctica), which stands as the largest known geotter species aside from the smoky beaster. With nearly 3 meters in length and weighing up to 200 kg (440 lbs), these massive carnivores inhabit wetlands of the coldvanna and the northernmost regions of the trample steppe.

During the early spring, clam newnewotters undertake anadromous migrations from their wintering grounds along the coast to the inland waters of the continent. There, they prey upon any animal approaching rivers, lakes, or bogs. Webrumbles and alphabetabrumbles, due to their preference of wet and shrub-rich habitats, are among the most common prey, along with stottmice and other small-to-medium rodents. To hide themselves from their unsuspecting prey, clam newnewotters often float on the water's surface, camouflaging their bodies with mud when near the coast. Their bite force is considerable thanks to their short, robust skulls designed to withstand substantial pressure, but more remarkable is the speed with which they can close their jaws, like a true crocodile.
To minimize energy consumption, clam newnewotters spend much of their day basking on the coast. Given their endothermic metabolism, these mammals require significantly more food daily than crocodiles. Over their evolutionary history, they have developed various behavioral and physiological adaptations to mitigate this challenge; their metabolic rate, for example, can lower by 50% when resting. As a result, clam newnewotters can consume up to a quarter of their body weight in meat and then sustain themselves for more than three weeks without food. Additionally, they scavenge on dead animals carried by river currents to maintain their relatively active lifestyle.

Challenges arise with the onset of winter, as water begins to freeze and the biomass of megafauna diminishes due to seasonal mortality. To avoid food shortages, clam newnewotters migrate back to the coast, where the presence of salt prevents freezing, at least in the coldvanna. Here, they adapt their diet, shifting to hard-shelled mollusks and sea urchins, akin to the feeding habits of the Holocenic sea otter. While prey may be smaller, they are sufficient to sustain the species until the arrival of spring, when rivers thaw once more.