Some of Jack Pettigrew's peers regard the former director of the Vision, Touch and Hearing Centre at the University of Queensland as an eccentric, and some consider his hypothesis that bats are our distant cousins as somewhat, well, batty.

In 1992, for example, a news article in the international journal Science caricatured his ideas with an image of the flying monkeys from the Wizard of Oz.

But the neuroanatomist Wizard of Oz was not the first to conclude that the Megachiroptera - fruit bats and flying foxes - are flying primates.

Nearly 250 years ago the great Swedish naturalist Carl von Linne, inventor of the modern system of classifying living species, grouped bats and south-east Asia's colugo or flying lemur (Cynocephalus volans) with primates, because they shared key characteristics common to all primates.

By an accident of history, Linnaeus chose the world's only echo-locating fruit bat, the Egyptian rousette (Rousettus aegyptiacus), as his holotype, when he could have used any one of Europe's 40-plus insectivorous microbats.

The Egyptian rousette roosts in caves, using the echoes of its rapid tongue clicks - not ultrasonic squeaks - to find its way around in the dark. On a number of key characters, Linnaeus was unable to exclude it as a primate.

In a paper published in Philosophical Transactions of the Royal Society 1989, Pettigrew drew attention to more than 50 characters that he believes separate megabats from microbats.

His opponents, however, invoked evolution's parsimony principle: what chance that nature would invent flapping flight twice in mammals?

Their knockout punch was DNA sequencing experiments, which in the early 1990s grouped megabats with microbats. For Pettigrew to be right, DNA - the ultimate arbiter on taxonomic issues - had to be wrong. Morphology may mislead, but DNA tells no lies.

But if the DNA evidence is right, fruit bats must have made some highly improbable changes to the design specifications for the common ancestor of all bats - assuming that insect-eating, echo-locating bats, the second most diverse group of mammals on the planet, appeared first on the evolutionary stage.

Indeed, on any number of physical, physiological and behavioural characteristics, they've made a sport of vaulting over Richard Dawkins' lofty evolutionary peak, Mt Improbable, from their ancestral home in the Vale of Microbats, to reach Primate Plain.

Pettigrew's critics invited him to explain what fruit bats had evolved from, if not microbats. (The question can be reversed, however: the paucity of fossils from both groups has led a few to argue for a scheme in which microbats evolved from a megabat ancestor like R. aegypticus).

Pettigrew's answer, 20 years ago, paid homage to Linnaeus: fruit bats evolved from south-east Asia's flying lemur, the colugo - or, more accurately, megabats and colugos diverged from a colugo-like gliding primate.