Animals

Nests of Big-Clawed Dinosaurs Found in Mongolia

The huge-clawed, bird-like dinos appear to have gathered communally to nest.

A nursery of bizarre-looking dinosaurs known as therizinosaurs has been found in the Gobi Desert in Mongolia.

The nesting colony contained at least 17 clutches of eggs.

"Not only is this the largest colony of nonavian theropods, but this is the best documented site," said study co-author Yoshitsugu Kobayashi, a vertebrate paleontologist at Hokkaido University in Japan, who presented the findings here at the 73rd annual Society of Vertebrate Paleontology conference.

The finding suggests the odd little creatures were social animals.

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Oddball dinos Therizinosaurs, which lived about 70 million years ago, sported huge, round guts; stumpy legs; a long neck; and a turtlelike head and beak.

Despite being members of the carnivorous group known as theropods - which includes the deadly king of the predators Tyrannosaurus rex - the waddling dinosaurs were herbivores. They also had enormous Edward Scissorhands-like, three-digit claws that may have been used to grasp branches and scrape up plant material, similar to the way bamboo-eating pandas do today.

Kobayashi and his colleagues discovered the nest while in southeastern Mongolia in 2011. On the last day of their trip, they decided to leave the area they were excavating known for therizinosaur bones to instead examine another bone bed nearby.

"There aren't many bones from this formation, so we didn't expect to find anything good," Kobayashi told LiveScience.

As the sun was setting, a guide pointed out an eggshell, and the team soon found one nest site right next to their car. Further investigation revealed four more nest sites. The following year, they returned and excavated a total of 17 clutches, for a total of about 75 eggs.

Hatched youngsters The eggs were round, with about a 5-inch (13 centimeters) diameter and rough outer shells. Based on size analysis and the species found in nearby areas, the team concluded that therizinosaurs laid the eggs. The animals would have been about 220 lbs. (99 kilograms) when full-grown.

None of the eggs harbored dinosaur embryos. However, many of them had holes with eggshells inside, as if a baby dinosaur had poked a hole in the top of the egg and the broken shells had fallen back inside. The presence of eggshells inside the eggs suggested that most of the baby dinosaurs had hatched.

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That finding, in turn, indicated the adults must have guarded the eggs to protect them from predators, Kobayashi said.

Communal animals The finding bolsters the notion that therizinosaurs were social animals that hung out together.

"We have some very intriguing evidence of mass congregation in therizinosaurs," said Lindsay Zanno, director of the paleontology and geology research laboratory at the North Carolina Museum of Natural Sciences.

"We have several mass-death quarries," said Zanno, who was not involved in the study. "So the question for us is, what does that represent in terms of their ecology? Did they live in herds, or were they gathering periodically?"

The new finding suggests the animals at least gathered together for nesting, Zanno told LiveScience.

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Therizinosaurs lived about 70 million years ago, and despite being members of the carnivorous group known as theropods, the these odd-looking dinos were herbivores.

Jurassic Dino Nesting Site

Jan. 23, 2012

-- The oldest known dinosaur nesting site, dating to 190 million years ago, has been unearthed in Golden Gate Highlands National Park, South Africa. The extraordinary site, described in the latest Proceedings of the National Academy of Sciences, includes multiple dinosaur nests, eggs, hatchlings and the remains of adults for this species, Massospondylus. Project leader Robert Reisz, a professor of biology at the University of Toronto Mississauga, told Discovery News that the dinosaur was herbivorous. Like its sauropod relatives, it had a very small head and an extremely long neck. The hatchlings walked on all fours, but adults were bipedal. "The transition from four legs to two during an individual's lifetime is a very unusual growth pattern that we rarely see in animals, but we do see it in humans," Reisz said. "The largest articulated skeleton of this animal was about 6 meters (19.7 feet) in length, but they probably grew even larger."

Dinosaur Nest The discovery provides evidence for "nesting site fidelity," according to Reisz, "as it looks like these dinosaurs liked this place and returned to it repeatedly to lay their eggs." It's also the oldest evidence in the fossil record for a highly organized nest, with eggs carefully laid in a single layer. Reisz and co-author David Evans, an associate curator of vertebrate paleontology at the Royal Ontario Museum, are shown here standing next to a nest in plaster at the site. Plaster protects the excavated nest, just like the broken bone in a human. The plaster cover is later removed in the lab for research. Reisz said clues about the nest are difficult to interpret, but what's known so far is that "the nests seem to be fairly shallow because all the eggs are in one layer," he said. "We do not know if the nests were covered by vegetation or if they were buried because the nature of the sediments preclude the preservation of plant fossil remains. It is quite possible that the mother guarded the nests." Nest guarding today is fairly common among living reptiles, such as crocodiles. It's also now known "that the hatchlings stayed around the nesting area long enough to at least grow to double in size."

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Adult Massospondylus Skull, Complete Embryo This photo compares the size of the skull of an adult next to the skeleton of an entire tiny embryo. The researchers believe each Massospondylus mother laid a lot of small eggs, at least 35, which was a probable survival strategy. "There were large and small meat-eating theropod dinosaurs around at the time Massospondylus lived,” Evans told Discovery News. "The smaller, more agile predator called Coelophysis, was much smaller than adult Massospondylus, but would have been a threat to the hatchlings and juveniles." So far, the researchers have found 10 dinosaur nests at the site, but they suspect many more are still embedded within the South African cliff. They predict many other nests will be eroded out in time, as the natural weathering process continues.

Dinosaur Embryo Close-Up This close-up of a Massospondylus embryonic skeleton reveals that the head was pushed out of the egg after death. The scientists suspect gases produced by decay caused this to happen. They also think the site was so well preserved because the dinosaur moms chose to lay their eggs in what was then, back in the Early Jurassic Period, a wet spot at the edge of a river. Reisz explained, "Periodically there was an unusually wet season and this area was flooded, drowning the unhatched eggs and embryos, and covering the nests with very fine sediment. Yet this turned out not to be such a horrible disaster for paleontologists." South Africa appears to have been a hotspot for Massospondylus, with other possible nesting sites for this dinosaur probably in existence. So far, however, the one at Golden Gate Highlands National Park is the only nursery to yield complete clutches, with eggs containing embryos, Evans said. He added that similar evidence for large-scale nesting among dinosaurs exists, for dinos such as duck bills and sauropods, but that evidence is about 100 million years younger than this South African site.

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Baby Dinosaur Handprint The discovery provides the world's oldest clear evidence for baby dinosaur footprints at a nesting site. The handprint seen here, as well as the other excavated baby prints, indicates that the infants stayed near the nest site after hatching and walked on all four limbs at first. Reisz said, "The overall body shape of the hatchlings with a large, toothless head, relatively long neck, and general look of helplessness suggests that parental care was very likely in Massospondylus. We think that the mother may have guarded the nest and the hatchlings, but may have also fed the babies with plant material." The paleontologists are now in the process of testing this hypothesis by preparing more embryos from different nests, to see if any of them have teeth. This ongoing research would be the first study of different embryological stages in a dinosaur.

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