Paleontologists in China have unearthed the fossil of an Oviraptorosaurus sitting on a nest of eggs. That in itself is an amazing and rare discovery, but this fossil is unique because the eggs still contain evidence of unparalleled progeny. within.
Here we report the first [non-avian] dinosaur fossil known to maintain an adult skeleton on top of an egg clutch containing embryonic remains, “the authors of a Research paper published in Science Bulletin. Found in China, the fossil expands our understanding of oviraptorosaur behavior and physiology, while providing further evidence that non-avian dinosaurs used bird-like breeding behavior.
Oviraptorosaurs, also called oviraptors, were named as such because of an early paleontological misunderstanding of similar fossils. The name means “egg thief,” but these dinosaurs were not thieves, as oviraptorosaurs were later shown to be the rightful owners of fossilized eggs often found next to their buried skeletal remains.
Indeed, fossils of oviraptorosaurs nesting with their eggs have been found before. What’s new here is that the dino eggs still have evidence of the embryos in them. It is worth pointing out that embryos in oviraptor eggs have been found before, but only in isolation. A well-known example is the “Baby LouieFossil, discovered in Henan, China, in the 1990s.
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Oviraptorosaurs were a super successful Cretaceous theropod dinosaur. They varied wildly in size, with some of the largest weighing over 2,425 pounds (1,100 kilograms).Common features include feathers, a long neck, wings, and beaks. These non-avian dinosaurs looked very bird-like and resembled modern ostriches. When nesting, these animals laid their eggs in a near-perfect circle, layering their large claws eggs in a remarkably ordered manner.
The newly described fossil, named LDNHMF2008, was pulled from the Nanxiong Formation near the Ganzhou Railway in Jiangxi Province in southern China. The fossil dates back to the end of the Cretaceous, about 70 million years ago. It preserves the remains of an adult medium-sized Oviraptorosaurus, lacking the skull and other skeletal features. The animal appears to have died while in a nest position.
These fossilized bones were found alongside an “undisturbed clutch” of at least 24 eggs, “some of which are broken, exposing embryonic bones,” the authors wrote in the study. The researchers, led by Shundong Bi of Indiana University of Pennsylvania and Xing Xu of the Chinese Academy of Sciences, assigned the eggs to the fossil species Macroolithus yaotunensis
Oviraptorosaur nests containing so many eggs at once is not uncommon, and likely an adaptation to extreme poaching by true “egg thieves”.
Microscopic analysis of the fossils showed that some embryos were in the late stages of development and about to hatch. The authors took this as possible evidence that oviraptors were actively incubating their nests, and not just to monitor them, as some paleontologists have speculated.
“In the new specimen, the babies were almost ready to hatch, which tells us beyond a doubt that this oviraptorid has maintained its nest for quite some time,” Matthew Lamanna, a paleontologist at the Carnegie Museum of Natural History and co-author of the new study, said in a statement. “This dinosaur was a caring parent who eventually gave his life while nursing his young.”
Other evidence corroborated this interpretation, namely an oxygen isotope analysis that showed the eggs were incubated at high, bird-like temperatures around 97 to 100 degrees Fahrenheit (36 to 38 degrees Celsius). Interestingly, the eggs were in different stages of development, meaning they hatched at different times. This is referred to as incubate asynchrony a reproductive phenomenon seen in modern birds. The authors were unable to attribute a cause to the asynchronous hatching, but they presented a plausible scenario, as they wrote in their study:
As with ostriches, oviraptorosaurs would not have started incubating the nest until after all the eggs had been laid, so that the lower eggs, which had been laid earlier, would have hatched the same length of time as the upper eggs. However, the top eggs would have hatched earlier than the bottom eggs because, being closer to the brooding adult, they would have received more heat from this individual than the bottom eggs, and so the embryos in them would have developed more quickly. “
Finally, the scientists also discovered a handful of pebbles in the dino’s abdominal area. These rocks are likely gastroliths, which animals ingest to aid in digestion. This is the first time such a thing has been documented in an oviraptorosaur and a possible clue to their diet. Admittedly, that’s a lot of new insights for a single, albeit remarkable, fossil.
“It is extraordinary to consider how much biological information is contained in this one fossil alone,” said Xu. “We will learn from this specimen for many years to come.”