Land Shark
The Hitchhiker's Guide to the Multiverse has this to say about the Land Shark:
It is widely held by sentients in most dimensions that Land Sharks are cool. They're sharks, except on land. Such a prospect should fill any sane being with a sense of dread, yet instead the appearance of one of these beasts is frequently accompanied by squeals of excitement and enthusiasm (frequently shortly followed by shrieks of pain). According to the philosopher Ly Tin Wheedle of Earth-TRN420 this is why they seem to exist in so many dimensions, despite the fundamental unlikeliness of such a piscine/mammalian hybrid existing at all. In some less stable and predictable dimensions they are naturally occurring, but frequently they are the product of mad scientists of deranged wizards; Wheedle's claim is that the idea of Land Sharks is too good for them not to exist, and thus through some process of morphic resonance, they tend to.
The exact nature of Land Sharks varies somewhat from universe to universe and dimension to dimension. While they are, universally, legged sharks that inhabit the land rather than the sea, the details of their life cycle and behavior vary widely. In some places the land sharks roam majestically in vast hordes, depleting the local area of anything and everything edible. In others, lone nocturnal land sharks stalk the unwary down dingy back alleys. In a few instances, notably those from Wonderland, land sharks have evinced the remarkable ability to swim in land as if it is sea. However it is speculated that this is primarily because Wonderland is a very silly place, and that a land shark taken from there to another, saner dimension will rapidly lose this ability.
Amongst all breeds of Land Shark, a peculiar genetic disorder causes a small but significant proportion to suffer from an antigeriatric syndrome. Individual specimens have been known to retain an infantile appearance as land shark 'puppies' for decades. Such land sharks are widely sought-after as pets due to an almost disgusting degree of cuteness, and it is speculated that this may represent an evolutionary survival strategy. Keeping a baby land shark as a pet can be rewarding as they tend to be extremely loyal, but also expensive, as they consume fearsome amounts of food (as well as anything else that takes their fancy).
For reasons that nobody has ever adequately explained but possibly involving some kind of complicated and obscure psychic influence, one of the more unusual properties of the baby land shark is that many sentient beings come to the conclusion that they look like a Jeff. This is undoubtedly why both Kate Bishop and Gwendolyn Poole independently chose that name for their Land Sharks.
