In 2044, wallabies have mutated to have the personality and dentition of sharks and “land pirahna is a colloquial term.
Lord Howe Island was discovered in 1788. https://simple.wikipedia.org/wiki/Lord_Howe_Island
The Doctors Ruby have taken advantage of this wildlife mutation to import and breed them to roam the island. Not good for the local fauna, but they soon deal with any unsuspecting visitors in an environmentally friendly manner.
Land Pirahnas are particularly good at detecting methane.
AC 12, HD 2, Bite: 2d4, Kick: 1d4, Tail:1d3
Can use claws for minor effect or tails like cudgels if wanting to leap away, which is not very likely in a kill frenzy. Add morale modifiers for that.