Cretaceous-era Korea was the site of a dinosaur baby boom that resulted in hundreds upon hundreds of dinos, ranging from giant plant eaters to bird-like, fleet-footed runners, two new studies suggest.
Based on the arrangements of dinosaur nests found there, it appears that the animals lived in densely populated groups, laid many eggs at a time and favored specific sites for their nurseries.
"This area may represent one of the world's largest (for) fossilized dinosaur eggs," Ihsan Al-Aasm, a co-author of one of the studies, told Discovery News.
"Other important areas are in China, India, Uruguay and Mongolia," added Al-Aasm, who is head of the Department of Earth and Environmental Sciences at the University of Windsor in Ontario, Canada.
He and his colleagues analyzed more than 200 eggs and 17 nests excavated at the Seonso Formation in South Korea. They were found along a two-mile stretch of scenic shoreline, suggesting to Al-Aasm and other researchers that the area supported "a nursery of herbivorous ornithopod and sauropod dinosaurs."
Many of the eggs are in good condition and even still have their breathing holes, which allowed oxygen and carbon dioxide to pass through the eggs before the dinosaurs hatched. It also appears that the parents may have buried the eggs during incubation, as many marine turtles do today.
Al-Aasm and his team studied some of the eggshell samples to determine the nature of their stable carbon and oxygen isotopes, which can provide information about the environmental conditions when the eggs were laid.
The findings indicate South Korea at the time experienced seasonal variations, with rainy periods followed by warmer, drier conditions. Based on the oxygen signatures within the eggshells, the scientists can even tell that dinosaurs drank ample fresh water during the rainy seasons and slightly evaporated water at other times.
Soil samples additionally reveal that hydrothermal fluids once washed into the dinosaur nursery area, adding extra carbon that wound up in the water and may have fueled the growth of abundant plants and trees.
The findings have been accepted for publication in the February issue of Cretaceous Research.
That same issue will also feature a study on yet another Cretaceous dinosaur nursery from the Sihwa Formation of mid-west Korea.
S.B. Kim of the Korea Polar Research Institute and colleagues identified approximately 140 dinosaur eggs within "gravelly" siltstones and channels.
"They are either isolated or clustered, forming a circular concentration in plain view," the researchers wrote. "The abundant yield of eggs, more than 20 eggs in 5 separate nests from a single depositional unit, suggests a dense population of parental dinosaurs."
The repetitive occurrence of eggs at specific spots suggests dinosaurs returned to certain sites each year to lay and to incubate their eggs, a practice that must have been repeated over and over again by later generations.