Gabriel Lio
An artist's reconstruction of the newly discovered, and newly named, theropod dinosaur Bonapartenykus ultimus.
By Jeanna Bryner
Managing editor
A mysterious birdlike dinosaur was about to lay her eggs when
she perished some 70 million years ago in what is now Patagonia,
researchers have found.
The scenario is based on the discovery of two dinosaur eggs lying near the partial skeletal remains of an alvarezsaurid dinosaur, which was a type of small maniraptoran, a group of theropod dinosaurs believed to be the line that eventually led to modern-day birds.
Alvarezsaurids are bizarre among dinosaurs, scientists have said, due
to their short, massive forelimbs tipped with a single digit sporting a
gigantic claw. The dinosaurs also show highly birdlike skeletons, even
though they were flightless.
The team named the dinosaur Bonapartenykus ultimus in honor of Jose
Bonaparte, who in 1991 discovered the first alvarezsaurid in Patagonia.
Fernando Novas
One of the Bonapartenykus eggs showing its unique eggshell microstructure, which includes the tiny bumps covering its surface.
The dinosaur eggs
were found less than 7.9 inches (20 centimeters) from the partial
skeleton and seemed to belong to that individual dinosaur. The
researchers ruled out a postmortem mixing that brought the two together.
The partial skeleton was also articulated, which would likely not be
the case if they had been transferred there after death.
In addition, the researchers didn't find evidence of calcium
resorption, which happens in the later stages of embryonic development
when embryos suck up calcium for bone growth from the inner lining of
the egg, according to study researcher Martin Kundrat of Uppsala
University in Sweden.
After various microscopic analyses of the bones and eggs, along with
eggshells found in the area, the researchers speculate the two eggs,
each about 2.8 inches (7 cm) in diameter, may have been inside the
oviducts of the female Bonapartenykus when she died.
"So it looks like we have indirect evidence for keeping two eggs in
two oviducts," Kundrat told LiveScience. "They were close to being laid,
but the female didn't make it."
When analyzing eggshell fragments, found to belong to B. ultimus, the
researchers discovered fossilized fungi; such contamination affects bird eggs
today, Kundrat said. "It looks like at the very late stage the eggs
could suffer from the same contamination as in common birds," he said
during a telephone interview. "It doesn't mean it must kill the embryo,
because usually in the embryonic space or inner space it's still
protected by a very dense network of organic fibers called the shell
membrane."
This mama dinosaur
would have lived on Gondwana, the southern landmass in the Mesozoic
Era, which lasted from about 251 million to 65 million years ago. (The
era is split up into the Triassic, Jurassic and Cretaceous periods.)
The finding, which will be detailed in the June 2012 issue of the
journal Cretaceous Research, shows that early alvarezsaurids persisted
in what is now South America until latest Cretaceous times, Kundrat
said.
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