Huge meat-eating dinosaurs
that stalked a vast floodplain some 150 million years ago in what is now
Portugal left behind traces of their progeny: eggshells.
Some of the eggshells, which belonged to two Jurassic-Era theropods, or a group of carnivorous dinosaurs, once harbored embryos of Torvosaurus, the largest predator of its day.
"It was the equivalent of the T. rex in the Cretaceous," said study co-author Vasco Ribeiro, a paleontologist at the Universidade Nova de Lisboa in Portugal.
Ribeiro and his colleagues aren’t sure how the eggs came to be abandoned.
Delicate findsBecause they are so delicate, dinosaur eggs
are a relatively rare find. Paleontologists unearthed some of the most
primitive Torovosaurus embryos ever found earlier this year, and there
have been occasional dinosaur nursery finds, including a clutch of
hundreds of dinosaur egg fragments found in Spain. [Image Gallery: Dinosaur Daycare]
Ribeiro and his
colleagues found the eggshell fragments at two separate sites, both of
which were part of the Lourinhã Formation, a geological formation known
for its rich Jurassic dinosaur nest sites. During that time period, the
area was a floodplain that cycled through dry seasons and monsoon rains.
The eggshells were
shattered and there was no trace of the dinosaur embryos that once
coiled inside. But by analyzing the size, shape and texture of the
eggshells, the team was able to deduce which animals left those eggs so
long ago.
The shells found at one
site came from spherical eggs that were about 6 inches (15 centimeters)
in diameter. They likely belonged to a Torvosaurus, a massive, bipedal
dinosaur that grew up to 36 feet (11 meters) tall.
The eggs at the other
site were harder to identify. But the researchers believe the eggs may
have contained embryos of Lourinhanosaurus antunesi, a theropod that was
about 15 feet (4.5 m) long when full-grown. When intact, the eggs from
that site would have been about 5 inches (13 cm) along the long axis and
3.5 inches (9 cm) along the short axis.
Neglected or protected?The researchers don't know exactly how the eggs came to be abandoned.
One possibility is that
the ancient carnivores laid many eggs and simply left those eggs to
their own fates. Other researchers argue that these dinosaurs, like
crocodiles, were attentive parents during embryonic development,
guarding their clutches from predators.
Either way, once the hatchlings emerged, they were probably on their own, Ribeiro said.
"We have no evidence that mother dinosaur took food to the nest or protected the nest," Ribeiro told LiveScience.