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News: Mesozoic Babysitting?

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In 2004, a dinosaur nest was discovered in China. This nest contained the skeletons of thirty baby Psittacosaurus, along with a single skeleton of a much larger individual, long assumed to be an adult. Psittacosaurus, meaning “parrot lizard”, lived in the Gobi Desert of Mongolia and northern China during the middle Cretaceous Period. It was a dog-sized herbivore, a primitive member of the group called the ceratopsians – the same group that contains Triceratops, Styracosaurus, and Centrosaurus, among others. It was discovered during the Gobi Desert expeditions of Roy Chapman Andrews during the early 1920s and was officially named and described by Henry Fairfield Osbourn in 1923. The name was given to the parrot-like appearance of its head.

Psittacosaurus is nothing new, nor is the nest of individuals mentioned above, but what is new is an idea about who that larger individual is, and what role that individual was playing. Brandon Hendrick, a paleontology researcher at the University of Pennsylvania, saw a photo of the nest, and was a bit intrigued by the not-quite-fully-grown size of the large specimen. Paleontologists have found a lot of Psittacosaurus fossils over the years, so they have a pretty good grasp on the growth rate of this creature. Based upon the size of the babies’ bones and their development, these creatures had recently hatched. However, the larger specimen doesn’t seem to be an adult. Based upon the size of its skull, this creature was about four to five years old, but Psittacosaurus did not reach full-grown size until eight or nine years old. So, this creature was a juvenile. What would a juvenile be doing amidst a nest of babies?

It was here that Hendrick and his colleagues proposed something – could this be an example of “babysitting”? Many paleontologists had long assumed that one parent or the other was responsible for guarding the nest at any given time. However, this new discovery adds some more facets to that belief. Perhaps the entire family, not just the parents was responsible in raising and caring for the young. Furthermore, having juveniles guard the nest would serve as good training for when they became adults and had nests of their own, thereby making their offspring more likely to survive. Babysitting is also seen in some species of modern birds, and this adds further evidence to the argument that dinosaurs evolved into birds since they have some shared behaviors.

Brandon Hendrick and his colleagues have recently published their findings in the journal Cretaceous Research; their article is entitled “The osteology and taphonomy of a Psittacosaurus bonebed assemblage of the Yixian Formation (Lower Cretaceous), Liaoning, China”.

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