Psittacosaurus lujiatunensis
August 29, 2014

Dinosaur Nest And Young ‘Babysitter’ Fossilized In A Rock Slab From The Yixian Formation

April Flowers for - Your Universe Online

When we think of dinosaurs, we think of giant, scary reptiles that once ruled the Earth. But even giant monsters were babies at one point. And apparently, even dinosaur babies need a babysitter.

A new study, led by the University of Pennsylvania, examined a rock slab from northeastern China's Liaoning Province containing fossils of 24 very young dinosaurs and one older individual. This kind of grouping is suggestive of a group of hatchlings being watched by a caretaker — much like dinosaur daycare.

The 120 million year old fossils were discovered by amateur paleontologists in the Lujiatun beds of the Yixian Formation. The entire rock specimen is only 2 feet across, but it contains fossils from 25 Psittacosaurus lujiatunensis. These herbivorous dinosaurs are among the most abundant species every discovered.

Prior to this study, the find had only been described in a one page paper in 2004. The original location where the fossils were found and extracted was not recorded, a fact that has hampered the study to some degree. Penn’s Brandon P. Hedrick, a doctoral student in the School of Arts & Sciences' Department of Earth and Environmental Science, and Peter Dodson, professor of paleontology and animal anatomy, believed that there was much more to the specimen than had previously been reported, however.

“I saw a photo of it and instantly knew I wanted to explore it in more depth,” Hedrick said.

The research team used X-ray diffraction to analyze the thin slivers and ground-up rock material surrounding the fossils. X-ray diffraction works by capturing the unique ways different minerals bend light. They found that the rock was composed of volcanic material, suggesting that the animals were caught in flowing material ejected from an eruption — which was supported by the orientation of the fossils.

“If they were captured in a flow, the long axis — their spines — would be oriented in the same direction,” Hedrick said. “That was what we found. They were likely trapped by a flow, though we can’t say exactly what kind of flow.”

The researchers found no heat damage to the bones, which indicates that the flow might have been a slurry of water, mud, rock and other debris known as a lahar.

Because the younger fossils are quite similar in size, and no eggshell material was found, the researchers believe that they were fully hatched. The fact that smaller fossils of psittacosaurs have been identified supports this idea. Hendricks also notes that “the ends of their bones were well developed, which indicates they were capable of moving around.”

The older juvenile's skull was firmly embedded in the same layer of rock as the 24 young fossils. Two of the 24 were intertwined with the skull, leading the researchers to believe they were closely associated at the time of their death.

The older fossil's skull is about 4.5 inches long, and the scientists estimate its age at 4 to 5 years of age. The older dinosaur was probably not the parent of the hatchlings, however, as previous research has indicated that this species did not reproduce before age 8 or 9.

The team cautions that they cannot definitely call this assembly a nest, despite the fact that early studies have.

“It certainly seems like it might be a nest, but we weren’t able to satisfy the intense criteria to say definitively that it is,” Hedrick said. “It’s just as important to point out what we don’t know for sure as it is to say what we’re certain of.”

The researchers intend to continue their study of these fossils by examining the microstructure of the smaller animals' bones. This will allow them to establish whether they were all at the same stage of development. If so, it would lend credence to this being a singular clutch of dinosaurs.

The international group of scientists published their findings in the journal Cretaceous Research.