Giant toothless
pterosaurs with wingspans stretching 39 feet (12 meters) across ruled
the skies 60 million years ago, and new research suggests that these
ancient flying creatures once had a worldwide presence, and likely
played an important role in the Late Cretaceous ecosystem.
Despite their formidable size, the pterosaurs
in the Azhdarchidae family had no teeth. The new research suggests they
replaced their toothed relatives as the dominant species when high
levels of carbon dioxide killed off important microscopic marine
creatures, leading to a mass extinction about 90 million years ago.
"This shift in dominance from toothed to toothless pterodactyloids
apparently reflects some fundamental changes in Cretaceous ecosystems,
which we still poorly understand," Alexander Averianov, from the Russian
Academy of Sciences, wrote in a new study of this type of pterosaur.
Fossil records show that pterosaurs were likely the first airborne vertebrates and they took to the skies around 220 million years ago. Some were so large they likely had to get a running start before taking off and
had a hard time landing, according to research presented at the 2012
Geological Society of America meeting. The name Azhdarchidae comes from
the Persian word "aždarha," which means dragon.These toothless creatures
lived during the Late Cretaceous Period, about 70 million years ago.
Scientists know little about pterosaurs, since their fossil record
is largely incomplete. Pterosaur bones are more fragile than other
dinosaur bones and there are few that have survived. Most Azhdarchidae
pterosaur fossils are preserved in soft sediment deposits called
Konservat-Lagerstätten. These kinds of fossils are rare for the Late
Cretaceous, so paleontologists have a hard time piecing together the
pterosaur lineage.
"Azhdarchidae currently represents a real nightmare for pterosaur taxonomists," Averianov wrote in the paper.
In a 2008 review of
Azhdarchidae, scientists examined 32 bones, but Averianov examined 54
known Azhdarchidae fossils: 51 bones and three fossilized tracks. The
giant birds likely lived in a variety of environments, but after closely
examining the sediments in which the fossils were discovered, Averianov
discovered that most of the toothless pterosaurs probably lived near
lakes and rivers and along coastlines.
About 13 percent of the pterosaur fossils were found in lake sediments,
17 percent from river sediments, 17 percent from coastal plains, 18
percent from estuaries and 35 percent from marine sediments.
Most Azhdarchidae species are only defined based on a few fragmented
bones. The more complete skeletons scientists have discovered are not
very well preserved. This lack of fossils led researchers to create an
"inflated" number of pterosaur species, according to Averianov. After
reviewing the taxonomy, Averianov found that paleontologists created
separate species of Azhdarchidae based on sparse fossil evidence and may
have misclassified some of the bone fragments.
In an effort to learn more about the evolution of pterosaurs, scientists created an online database of fossils called PteroTerra,which maps out the distribution of these ancient creatures using Google Earth.
The new taxonomy research was published Aug. 11 in the journal ZooKeys.
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