two extinct relatives in northern Egypt suggests the unusual creatures, which evolved sticky footpads to roost on slick surfaces, are primitive members of a group of bats that evolved in Africa and ultimately went on to flourish in South America.
A team of researchers described the two bat species from several sets of fossilized jawbones and teeth unearthed in the Sahara. The findings, reported in the journal PLOS ONE, represent the first formal description of the family in the fossil record and show the sucker-footed bat family to be at least 36 million years older than previously known.
"We've assumed for a long time that they were an ancient lineage based on DNA sequence studies that have placed them close to very old groups in the bat family tree," said Nancy Simmons, co-author on the study and a curator in the Department of Mammalogy.
But until now, scientists lacked any fossil evidence to confirm it.
Today, the sucker-footed bats consist of two species, Myzopoda aurita and M. schliemanni, endemic to Madagascar. In contrast to almost all other bats, they don't cling upside-down to cave ceilings or branches. Sucker-footed bats roost head-up, often in the furled leaves of the traveler's palm, a plant in the bird-of-paradise family. To stick to such a smooth surface, the bats evolved cup-like pads on their wrists and ankles. Scientists previously suspected the pads held the bats up by suction, but recent research has demonstrated the bats instead rely on wet adhesion, like a tree frog.
The two extinct species, Phasmatonycteris phiomensis and P. butleri, date to 30 and 37 million years ago, respectively, when the environment was drastically different. Northern Africa was more tropical, said Dr. Simmons, and home to a diverse range of mammals, including primates and early members of the elephant family.
"The habitat was probably fairly forested, and there was likely a proto-Nile River, a big river that led into the ancient Tethys Ocean," said Gregg Gunnell, director of the Duke University Lemur Center's Division of Fossil Primates and a co-author on the paper.
The fossilized teeth imply that, like their living relatives, the ancient bats fed on insects. It's impossible to know from the fossils if the extinct species had already evolved their characteristic sucker-feet, but the teeth shed light on another aspect of bat evolution. The presence of sucker-footed bats in Africa at least 37 million years ago supports the theory that this family is one of the most primitive members of a lineage that now dominates South America.
From vampires to fruit- and nectar-eaters to carnivores, the majority of South America’s bats belong to one large superfamily, known as Noctilionoidea.
"We think that the superfamily originated in Africa and moved eastward as Gondwana was coming apart," Gunnell said. "These bats migrated to Australia, then actually went through Antarctica and up into South America using an ice-free corridor that connected the three continents until about 26 million years ago."
According to this hypothesis, the sucker-footed bat fossils showed up right where scientists expected to find them: at the literal and figurative base of the Noctilionoidea family tree.
"Now, we can unambiguously link them through Africa," Simmons said.