Lutrats

As the Time of Hunger drove a population exodus, many rats found themselves on the beaches of the continents. The shoreline provided excellent food sources for those able to exploit them; the Time of Hunger saw the seabed littered with fish corpses, invertebrates abounded in rock pools, and meadows of sea plants flourished in the bright shallows. Although excellent swimmers, rats are not suited for ocean life, as their little bodies struggle against powerful tides and waves. However, the sheltered bays and inlets of Western Whiskiia provided an excellent nursery to hone their aquatic skills, leading to the evolution of saltwater amphibious rats.

The Lutrats (pronounced lute-rats) are now a common sight along the shorelines, steadily spreading further along the coast as their adaptations improve over the generations. Superficially they resemble otters, with a long, thick body plan, enlarged tail and legs tucked directly under the body. The fur has become increasing dense to both better increase heat retention and resist water penetration.

Lutrats are still bound to the land, but actively forage in the oceanic shallows. Retaining their omnivorous diets, lutrats will eat anything they can find, though their diets consist mainly of larger invertebrates, carrion, and easily digestible plant matter. Slow moving or trapped fish are also taken, though lutrats currently lack the adaptations to enable active hunting of fast, open water fishes. Populations are increasingly beginning to show specialisations for particular food sources, such as molluscs and underwater vegetation, which will lead to further speciation in the future.

Compared to other mammalian vertebrates lutrats have an unusual form of swimming. In rats swimming is usually carried out by the back legs; however, this form of locomotion provides insufficient power when fighting against the ocean’s currents. Instead, lutrats swim by using their entire back end, with most of the stroke provided by the tail. What makes this unusual is the movement itself. Mammalian spines flex in a sagittal manner- that is, up-and-down- compared to the lateral (side-to-side) flexing of reptilian spines. In aquatic animals this flexing can clearly be seen by comparing how such animals move: in dolphins the tail is moved in an up-and-down motion whereas in ichthyosaurs- who are otherwise remarkably similar due to convergent evolution- moved theirs in a side-to-side motion. As rats use their tails for balance purposes, their tails are capable of rotating in a wide 360 degree arc (known as ‘windmilling’ when done rapidly). The lutrats have adapted this ability and turned their tail into a paddle which- when powered by their entire body movement- gives them enough power to push against strong currents. For now it is a simple development, but one with much potential to evolve further.

Due to the open nature of the shoreline luterats do not make burrows. Instead, mothers will make a scrape far above the tideline and remain with their litters. Populations living close to vegetated shorelines will make scrapes a fair distance apart, relying on the grass for camoflague. Those living on exposed beaches will instead lie closer together in makeshift colonies, relying on numbers for protection. A predator seeking a vulnerable pup will have to face the gauntlet of perhaps hundreds of snapping jaws, causing many to seek an easier meal elsewhere.

As the mothers must remain with their pups for protection, they rely on the male to keep them fed. As rats cannot vomit (and thus cannot regurgitate food), males must gather as much food as possible in their mouths before returning to their family, depositing the material at the scrape before returning to hunt. To facilitate this lutrats display an unusual form of sexual dimorphism: males have developed expanded cheek pouches similar to hamsters, in which they can store more food. The flesh area on the lower jaw beneath the tongue is also becoming increasingly hollow, forming an extra pouch for food storage. A male with full pouches presents an extraordinary sight as it waddles up the beach to its mate.

To facilitate this arrangement male and female lutrats form strong partner bonds. Attentive males ensure the increased survival rates of their pups, as the mother can remain on shore to protect them from predators. Pairs are monogamous as- quite simply- the male simply does not have the time or resources to provide for multiple mates. Paired couples reinforce their bond via reciprocal grooming. Due to the energy-intensive effort of raising their young, lutrats only breed once a year. However, as they lack predators in the ocean once able to swim juveniles enjoy a higher survival rate than their fully terrestrial peers.

Once the young gain their sea legs the mother will take over feeding duties (much to the relief of the exhausted male), teaching her children how to forage in the shallows and hunt their own food. After around two months of this education juveniles are sufficiently independent enough to make their own way in the world, becoming full adults by the time of the next breeding season.