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Description
Another speculative evolution critter. From a suggestion by Titanomonstrus (feline in a crocodile niche)

River cat, or León del lago (lion of the lake)

Genus & species: Gyrinopuma ripicola
Meaning of: Tadpole puma, river-dweller
Ancestral creature: Jaguarundi (Puma yagouaroundi)
Size: 300-400 lbs
Activity cycle: diurnal
Habitat: northern American rivers, lakes, ponds, streams
Social structure: solitary, territorial
Diet: fish, large mammals

River cats evolved from the jaguarundi (Puma yagouaroundi), a small, otter-like feline of the Americas which was an accomplished fisher. River cats have become even more well adapted to an aquatic life, and fill a niche similar to crocodilians in environments too cold for the reptiles to be active year round. In the south where their ranges overlap river cats have been known to actively seek out and attack crocs and gators and seem to particularly enjoy digging up and devouring their eggs.

The body is long and flexible, with short, heavily built limbs and a flattened, muscular tail. The head is quite uncatlike, long, narrow and deep with no forehead and eyes set high on the skull. The ears are small and can clamp completely shut, and the nostrils are directed backwards (which keeps water from flowing in them when the animal swims). The lower limbs and tail are covered with thick, scaly skin, and the guard hairs of the pelt are oily and waterproof. Typically colored seal brown with rosettes of light gold, there is considerable individual and regional variation in coloring. Southern animals tend to be smaller and “red phase” with more distinct patterning, and northerners are usually larger and “gray phase” with heavier coats and blurred or entirely absent markings. Males are roughly 20% larger than females.

Swift and graceful in the water, the river cat will actively hunt fish and is able to take even quite large specimens several times its own weight. They swim with an up-and-down undulating movement like an otter, sculling with the tail and using their limbs to change direction. Their digits are webbed, and the pads are rough, giving them an excellent grip on slippery rocks and wriggly prey. The claws are retractable, but the tips remain visible even when fully retracted because they’re not covered with the usual hood of loose skin.

The cat’s preferred method of hunting land-dwelling prey is to lurk in the shallows by the bank of a lake or pond or the edges of a river, crouched down so that only the eyes and nostrils break the water’s surface. When an unwary animal lowers its head to drink, the huge cat pounces. If the prey manages to leap back in time or break free, it is safe, as the river cat is a poor runner and disinclined to pursue.

Smaller prey is killed with a swift bite to the throat that severs the carotid artery, causing death in seconds. Larger prey will be dragged backwards into the water to drown. The cats will cache a carcass in cold running water to preserve it, feasting for several days. Many species of fish have taken to hovering nervously near a hunting river cat, waiting for a chance to feed off its scraps but running the risk of becoming hors d'oeuvres themselves.

River cats are solitary and highly territorial. Females have large home ranges centering on a den which they build from sticks and mats of vegetation on a small island or rocky outcropping in the middle of a body of water. The interior of the den is warm and watertight, lined with leaves, dry grass and her own shed fur. This is where her 1-4 cubs are born after a 70-day gestation period. The cubs remain in the den for the first month, and are able to swim competently after another month. They hunt alongside the mother for several months before striking out on their own, but it takes two years (four for males) for them to reach their full growth.

Males have much larger territories which encompass the territories of several females, and no fixed home base. The male is peripatetic, wandering through his territory re-establishing his scent marks and scratching warnings to other males on trees, sleeping for a few days in one spot before moving on. During the mating season he attempts to visit every female in his range, barely stopping to eat, which leaves him dangerously exhausted at the end. This is the time when upstart young males usually attempt to drive an older male off his land. The usual lifespan of a male is about 12 years, while females can live into their late twenties.

Description
Another speculative evolution critter. From a suggestion by Titanomonstrus (feline in a crocodile niche)

River cat, or León del lago (lion of the lake)

Genus & species: Gyrinopuma ripicola
Meaning of: Tadpole puma, river-dweller
Ancestral creature: Jaguarundi (Puma yagouaroundi)
Size: 300-400 lbs
Activity cycle: diurnal
Habitat: northern American rivers, lakes, ponds, streams
Social structure: solitary, territorial
Diet: fish, large mammals

River cats evolved from the jaguarundi (Puma yagouaroundi), a small, otter-like feline of the Americas which was an accomplished fisher. River cats have become even more well adapted to an aquatic life, and fill a niche similar to crocodilians in environments too cold for the reptiles to be active year round. In the south where their ranges overlap river cats have been known to actively seek out and attack crocs and gators and seem to particularly enjoy digging up and devouring their eggs.

The body is long and flexible, with short, heavily built limbs and a flattened, muscular tail. The head is quite uncatlike, long, narrow and deep with no forehead and eyes set high on the skull. The ears are small and can clamp completely shut, and the nostrils are directed backwards (which keeps water from flowing in them when the animal swims). The lower limbs and tail are covered with thick, scaly skin, and the guard hairs of the pelt are oily and waterproof. Typically colored seal brown with rosettes of light gold, there is considerable individual and regional variation in coloring. Southern animals tend to be smaller and “red phase” with more distinct patterning, and northerners are usually larger and “gray phase” with heavier coats and blurred or entirely absent markings. Males are roughly 20% larger than females.

Swift and graceful in the water, the river cat will actively hunt fish and is able to take even quite large specimens several times its own weight. They swim with an up-and-down undulating movement like an otter, sculling with the tail and using their limbs to change direction. Their digits are webbed, and the pads are rough, giving them an excellent grip on slippery rocks and wriggly prey. The claws are retractable, but the tips remain visible even when fully retracted because they’re not covered with the usual hood of loose skin.

The cat’s preferred method of hunting land-dwelling prey is to lurk in the shallows by the bank of a lake or pond or the edges of a river, crouched down so that only the eyes and nostrils break the water’s surface. When an unwary animal lowers its head to drink, the huge cat pounces. If the prey manages to leap back in time or break free, it is safe, as the river cat is a poor runner and disinclined to pursue.

Smaller prey is killed with a swift bite to the throat that severs the carotid artery, causing death in seconds. Larger prey will be dragged backwards into the water to drown. The cats will cache a carcass in cold running water to preserve it, feasting for several days. Many species of fish have taken to hovering nervously near a hunting river cat, waiting for a chance to feed off its scraps but running the risk of becoming hors d'oeuvres themselves.

River cats are solitary and highly territorial. Females have large home ranges centering on a den which they build from sticks and mats of vegetation on a small island or rocky outcropping in the middle of a body of water. The interior of the den is warm and watertight, lined with leaves, dry grass and her own shed fur. This is where her 1-4 cubs are born after a 70-day gestation period. The cubs remain in the den for the first month, and are able to swim competently after another month. They hunt alongside the mother for several months before striking out on their own, but it takes two years (four for males) for them to reach their full growth.

Males have much larger territories which encompass the territories of several females, and no fixed home base. The male is peripatetic, wandering through his territory re-establishing his scent marks and scratching warnings to other males on trees, sleeping for a few days in one spot before moving on. During the mating season he attempts to visit every female in his range, barely stopping to eat, which leaves him dangerously exhausted at the end. This is the time when upstart young males usually attempt to drive an older male off his land. The usual lifespan of a male is about 12 years, while females can live into their late twenties.