The flight-adapted fragile bones of the bats are hard to fossilize. That's why scientists have been complaining about the scarce number of bat fossils, for obtaining clues about how mammals evolved for flight.
After the description of the oldest known bat species, Onychonycteris finneyi, 52.5 million years old, encountered in Wyoming's fossil-rich Green River formation, which was fully adapted to flight, a new bonanza of fossil bat species has been encountered in Egypt.
Six new 35 million-year-old species of bats have been discovered in
El Faiyum, an oasis 50 mi (80 km) southwest of Cairo. The scientists analyzed 33 fossils, including teeth and jawbones, that had been unearthed, and the new fossils will be described in the "Journal of Vertebrate Paleontology." All the new species belonged to families of modern-day microbats, who use ultrasound echolocation. They are opposed to the large megabats, or fruit bats, tropical species that use smell and sight for orientation.
"They are all pretty primitive members of modern groups, which is a little bit odd. Generally in [this period in the fossil record], you tend to [find] archaic bats but nothing very modern, … but these animals are all members of living families," said lead researcher Gregg F. Gunnell, a paleontologist at the University of Michigan.
It appears that modern bat groups evolved in Africa rather than in the Northern Hemisphere, as the common concept says. Fossil bats found in the Northern Hemisphere belonged to extremely primitive species, very different from modern bats.
"A primitive bat species made its way to Africa some 50 million years ago, then differentiated into these more modern forms," said Gunnell.
One of the new species was a "giant" amongst microbats, the largest so far encountered. The largest living microbat is the Ghost Bat or Australian False Vampire Bat (Macroderma gigas), which has a wingspan of 50 cm (1.6 ft).
"The larger microbat could have had a wingspan close to 2 feet (0.6 meter). Modern-day megabats, by comparison, have wingspans as wide as three feet (about a meter). It would have been loud-it would have been obnoxious. Just going by the large echolocating bats that I know that live today … many are very loud and very pushy and very boisterous. … I am assuming these bats would have been, too," said Gunnell.
Bats from Eocene (56 to 34 million years ago) are rare in Africa, and just a few bone fragments have been recovered so far from Egypt, Morocco, Tanzania, and Tunisia.
"Egypt, particularly el Faiyum, holds the best fossil records in Africa from the period between 37 million and 27 million years ago. [This ten-million-year span] is a big slice of Earth history as far as Africa is concerned. [Africa] is a high-standing continent-that means it doesn't have a lot of sedimentary basins [with deposits that yield] ancient mammals-but Egypt does," said Duke University paleontologist Elwyn L. Simons, who found these fossils and has been working in El Faiyum since the 1960s (this oasis is famous for having revealed fossils of one of the most primitive elephant ancestors).
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