Which animal's fingerprints are so similar to ours that they have confused crime-scene investigators?

Answer

Koalas have ridged fingertip patterns that are very close to human prints, even though the two groups evolved them separately.

Context

The observation comes from Maciej Henneberg, a biological anthropologist and forensic scientist who noticed the prints while working with koalas at a wildlife park near Adelaide in the mid-1990s. According to PBS NOVA, under a microscope he found the ridge patterns could not be reliably told apart from human ones, and he published a paper shortly after a 1996 newspaper interview.

Koalas are described as the only non-primates with true fingerprints. Their close relatives, wombats and kangaroos, lack them, which indicates the trait arose recently and independently, a case of convergent evolution. Henneberg suggested they help koalas grip handfuls of eucalyptus leaves and branches while climbing, in line with the general view that ridges improve friction and fingertip sensitivity. Koalas also have two opposable digits on each forepaw, which fits a strongly grasping hand.

The crime-scene claim needs care. Henneberg himself said it is extremely unlikely that koala prints would ever turn up at a crime scene, and I found no documented case of an investigation actually misled by one. The story is best read as a vivid way to say the patterns look alike.

Primates have fingerprints through shared ancestry, and the koala example shows that the same useful structure can evolve independently in unrelated lineages.