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Possible dinosaur nest and young 'babysitter'
This rock slab, which was found in the Lujiatun beds of the Yixian Formation in northeastern China's Liaoning Province, contains the remains of 24 very young dinosaurs and one older individual--suggestive of a group of hatchlings overseen by a caretaker. All of the species were Psittacosaurus lujiatunensis, which were plant eaters.
While the rock slab, which is about 120 million years old, was briefly described in a paper published in 2004, Brandon P. Hedrick and Peter Dodson of the University of Pennsylvania felt there was more to be gleaned from the specimen. Hedrick is a doctoral student in the School of Arts & Sciences' Department of Earth and Environmental Science, where Dodson is a professor of paleontology.
X-ray diffraction of samples of ground-up rock and magnification of thin slivers of rock suggested to the researchers that the slab in which the fossils were preserved was composed of volcanic material, an indication that the animals were caught in flowing material from an eruption, most likely from a lahar--a slurry of water, mud, rock and other debris associated with volcanic eruptions. In addition, the orientation of the fossils seemed to confirm this theory as well.
The 24 younger animals appeared to be similar in size, and while the team considered whether they might have been embryos still in their eggs, various observations such as the lack of eggshell suggested they had already hatched.
The skull of the larger animal was embedded in the same rock as the smaller animals and two of the younger ones were actually intertwined with the skull--a sign that the animals were closely associated at the time of their death. The researchers believe the close proximity of the older animal to the younger ones could indicate evidence of post-hatchling cooperation. Such behavior is exhibited by some species of modern-day birds. The older juvenile may have been a brother or sister helping care for its younger siblings.
Based on the size of the skull of the larger animal--about 4.5 inches long--its age is estimated to be between 4 and 5 years old. Past research has suggested that P. lujiatunensis did not reproduce until 8 or 9 years old, so this animal was probably not the parent of the younger dinosaurs.
Although earlier analyses of the specimen suggested it is a nest, Hedrick and Dodson say they cant definitively confirm this. "It certainly seems like it might be a nest, but we werent able to satisfy the intense criteria to say definitively that it is," Hedrick said.
This research was supported in part by a grant from the National Science Foundation (EAR 1024671).
To learn more, see the Penn news story Penn paleontologists describe a possible dinosaur nest and young 'babysitter'. (Date of Image: 2014)
Credit: Brandon Hedrick, University of Pennsylvania
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