The oldest bat skeletons yet discovered were discovered in southwest
Wyoming, and their discovery caused the bat family tree to be
rearranged.
Researchers have discovered the oldest bat bones yet discovered—two
exquisitely preserved specimens discovered in Wyoming—which belonged to a
previously unknown species. They are 52 million years old.
The unusual fossils were found in the state's southwest in the Green River
Formation.
The newly discovered species, which could easily fit into a human palm with
its wings folded against its body, was somewhat smaller than the closest
known related bat species, Icaronycteris index.
Lead author
Tim Rietbergen, a bat paleontologist and collection manager at the Naturalis Biodiversity
Center in Leiden, the Netherlands, told Live Science in an email, "When I
first saw the first skeleton, I instantly felt it was strange. These are the
oldest skeletons because they are found further down in the stratigraphy
(sediment layers) than other fossilized bats.
The Eocene era saw the origin of bats (56 million to 36 million years ago).
The more than 50 million-year-old fossil bones of I. index and another
extinct species known as Onychonycteris finneyi, which paleontologists also
described from Green River Formation deposits, were the oldest bat skeletons
known up to this point. The best-preserved skeletons may be found, according
to Rietbergen, in the Green River Formation.
The new discoveries have led to a revision in the categorization of early
bats to include the newly discovered species in the family tree. The new
discoveries are detailed in a paper that was published on Wednesday, April
12 in the journal
PLOS One.
The researchers compared the new fossils with whole skeletons from six
Eocene bat species, as well as with single teeth from two additional extinct
species and with skeletons of extant bats, in order to ascertain the
evolutionary history, or phylogeny, of the bats. They dubbed the new species
of Icaronycteris I. gunnelli in honor of the late bat researcher
Greg Gunnell
after their findings, which showed that the recently discovered bat
skeletons belong to a previously undiscovered species .
"It obviously stood out as being a new species after comparing the
measurements with other bats," Rietbergen added. "I became really thrilled
and thought maybe the bat variety from the early Eocene was far more than we
realized," the author said.
The only other Icaronycteris species known to exist in North America is I.
index, and the researchers also found that these two species have a sister
connection, making them each other's closest living relatives.
I. index was presumably significantly bigger than I. gunnelli, although
detailed scans of the fossils indicate that the latter weighed less than an
ounce (22.5 to 28.9 grams), which is around the same body mass. According to
the study, the mismatch between the reconstructed weight and wingspan may be
the result of bone distortion during fossilization.
Emma Teeling, a professor of zoology at University College Dublin in Ireland who was
not involved in the study, told Live Science in an email: "This newly
described species is considered to be one of the oldest known articulated
bat skeletons, providing novel insight into the phylogeny of our earliest
bat fossils. However there are still phylogenetic issues that can only be
answered by finding more complete and well-defined fossils of bats.
The researchers' study leads them to believe that Green River bats diverged
from other Eocene bats. We still don't know a lot, according to Rietbergen.
If we have a clear picture of the variety of bats, we may look at
evolutionary adaptations and potentially uncover clues that will help us
determine the origin of bats.
