Scientists at the University of New South Wales (UNSW) in Australia have discovered the fossilized remains of an ancient species of bat in New Zealand, which they believe could have roamed the earth on four limbs.

The newly discovered bat species, known as Mystacina miocenalis, lived around 16 million years ago and was endemic in a subtropical rainforest. It is related to the modern-day New Zealand lesser short-tailed bat (Mystacina tuberculate), but the prehistoric bat is three times larger compared to its living relatives.

Suzanne Hand, a vertebrate paleontologist at UNSW and chief author of the study, explained that the discovery proves for the first time that bats of the Mystacina family have existed in New Zealand for more than 16 million years, and that they had resided in habitats with similar plant life and sources of food.

The only other terrestrial mammals native to New Zealand are three bat species, which includes two that belong to Mystacina genus.

One of these bats was the burrowing bat which was last seen during the 1960s. The bat earned its name because it was known to forage on the ground under snow and leaf-litter. It also does this in the air by scuttling on its wrists and its feet facing backward, while also keeping its wings furled tightly.

Researchers have believed the bats were long been part of New Zealand's history, but until the recent discovery, the oldest known fossil of a Mystacina bat in the country was one recovered from a South Island cave that dated back to around 17,500 years in the past.

The UNSW findings provides evidence to investigate further when these walking bat species had first crossed the ditch and from which particular part of Australia did they originate.

"This helps us understand the capacity of bats to establish populations on islands and the climatic conditions required for this to happen," Hand said.

"Bats are important pollinators and seed dispersers that keep forests healthy. Understanding the connectivity between the bat faunas of different landmasses is important for evaluating biosecurity threats and conservation priorities for fragile island ecosystems."

The dental structure of the Mystacina miocenalis bat is similar to that of its present day cousin. This means that the ancient bat's diet could have included insects, spiders, nectar, fruits and pollen.

The limb bones on the bat fossil also had similar structures that suggest that it had the ability to walk.

The primary difference the ancient bat had on its cousin is its body size, which was estimated at 40 grams. The fossilized bat species would have been almost thrice as heavy as its living relative and the average weight of over 900 other present day bats.

Hand added that the sizes of bats are often constrained due to the physical demands of echolocation and flight. They need to be small in order to be accurate and quick to chase its prey in the dark.

The unusual size of the ancient bat, however, suggests that it did not spend much time hunting in-flight, she said. The bat preferred to take heavier prey from the ground and larger fruits compared to its living cousin.

The UNSW researchers also discovered a diverse collection of animal, insect and plant fossils at the site. These provide considerable proof at how the subtropical ecosystem that New Zealand had 16 million years ago resembled the more temperate one the country has today.

The University of New South Wales study is published in the journal PLOS ONE.

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