Tetra-whale

Tetra-whales are a group of cetaceans that, unlike aquatic cetaceans and the airborne skycetaceans, have legs as opposed to flippers/fins. Most species of tetra-whales live in the shorelines, swamplands, and marshlands, with some thriving in forests, grasslands, and all species thrives in human settlements. There are around 48 extant species, which are divided into two groups or parvorders, the Tetrodontoceti or tetra-toothed whales, a group of more than 70 species that includes the tetra-dolphins and tetra-porpoises, and the Tetramysticeti or tetra-baleen whales, of which there are now 28 species.

Tetra-whales range in size from the 1 m (3 ft 3 in) and 50 kg (110 lb) Maui's tetra-dolphin to the 8.9 m (79 ft) and 100,000 kg (200,000 lb) blue tetra-whale, which is also the largest land mammal ever known to have existed. Several species exhibit sexual dimorphism. They have streamlined bodies and four walking limbs. Though not as flexible or agile as hippopotamuses (which also lives on land and is also amphibious), tetra-whales can swim very quickly, with the killer tetra-whale able to travel at 41 kilometres per hour (26 mph) in short bursts and the fin tetra-whale able to cruise at 29 kilometres per hour (18 mph). On land, different species of tetra-whales can walk/run at different speeds, for example, the killer tetra-whale can run in high speeds up to about 21 kilometres per hour (13 mph) and the fin tetra-whale running in high speeds up to about 17 kilometres per hour (10 mph).

Baleen tetra-whales have short hairs on their mouth, unlike the toothed tetra-whales. Just like cetaceans and skycetaceans, tetra-whales have well-developed senses—their eyesight and hearing are adapted for both air and water, and baleen tetra-whales have a tactile system in their vibrissae. They have a layer of fat, or blubber, under the skin to maintain body heat in cold environments.

Although tetra-whales are widespread, most species prefer the colder habitats of the Northern and Southern Hemispheres. They spend their lives in the cold forests, swamps, shorelines, or grasslands, having to mate, give birth, molt or escape from predators, like killer tetra-whales, on land. This has drastically affected their anatomy to be able to do so. They feed largely on fish, aquatic invertebrates, frogs, lizards, birds, and small mammals (rats, mice, etc); but a few, like the killer tetra-whale, feed on large mammals and birds, such as ostriches, wild pigs, deer, some species of dylanusids, etc. Some baleen tetra-whales (mainly gray tetra-whales and right tetra-whales) are specialised for feeding on small swampland creatures (fish, frogs, etc).

Male tetra-whales typically mate with more than one female (polygyny), although the degree of polygyny varies with the species. Tetra-whales are not shown to have pair bonds. Male tetra-whales strategies for reproductive success vary between herding females, defending potential mates from other males, or whale song which attracts mates. Calves are typically born in the fall and winter months, and females bear almost all the responsibility for raising them. Mothers of some species fast and nurse their young for a relatively short period of time, which is more typical of baleen tetra-whales as their main food source (insects, small birds, etc) aren't found in their breeding and calving grounds (tropical grasslands). Tetra-whales produce a number of vocalizations, notably the clicks and whistles of dolphins and the moaning songs of the humpback tetra-whale.

Unlike aquatic cetaceans and like the skycetaceans, none of the known species of tetra-whales are endangered or threatened with extinction, as it is against the law to hunt any species of tetra-whales. All of the tetra-whale species can flourish in human settlements, so they are all classed as Least Concern

Evolution
They were once thought to be a group of cetaceans that re-developed legs by magic, but we now all know that this didn't happened. Instead, they evolved from a group of Ambulocetuses that have evolved into two groups, cetaceans (which some evolved to skycetaceans) and, of course, the tetra-whales.