Paleontologists in China have unearthed the fossil of an oviraptorosaur sitting in a nest of eggs. By itself, this is a surprising and rare discovery, but this fossil is unique in that the eggs still retain evidence of unincubated offspring. inside.
“Here we report on the first [non-avian] dinosaur fossil known for preserving an adult skeleton on top of an egg clutch containing embryonic remains, ”say the authors of a research paper published in the Science Bulletin. Found in China, the fossil is broadening our understanding of the behavior and physiology of oviraptorosaurs, while providing additional evidence that non-avian dinosaurs used bird-like breeding behaviors.
Oviraptorosaurs, also known as 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 that are often found next to their buried skeletal remains.
In fact, fossils of oviraptorosaurs nesting with their eggs have been found before. The novelty here is that dino eggs still contain evidence of the embryos inside. It is worth noting that embryos had previously been found inside oviraptor eggs, but only isolated. A famous example is the “Baby Louie”Fossil, discovered in Henan, China, in the 1990s.
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Oviraptorosaurs were a highly successful Cretaceous theropod dinosaur. They varied greatly in size, with some of the largest weighing more than 2,425 pounds (1,100 kilograms).). Common features include feathers, long neck, wings and beaks. These non-avian dinosaurs looked very similar to the bird, similar to modern ostriches. When they nest, these animals lay their eggs in an almost perfect circle, laying their large claws in an extraordinarily orderly fashion.
The recently described fossil, named LDNHMF2008, was extracted from the Nanxiong Formation, near Ganzhou Railway in Jiangxi Province in southern China. The fossil dates to the end of the Cretaceous period, about 70 million years ago. It preserves the remains of a medium-sized adult oviraptorosaur, with the skull and other skeletal features missing. It appears that the animal died while in a nesting position.
These fossilized bones were found next to a “quiet clutch” of at least 24 eggs, “some of which are broken and expose embryonic bones,” the study authors wrote. The researchers, led by Shundong Bi of Indiana University in Pennsylvania and Xing Xu of the Chinese Academy of Sciences, assigned the eggs to the fossil species Macroolithus yaotunensis.
Oviraptorosaur nests that contain so many eggs at the same time are not uncommon and are likely to be adapted to extreme poaching by actual “egg thieves”.
Microscopic analysis of the fossils showed that some embryos were in the final stages of development and were about to hatch. The authors took this as potential evidence that oviraptors were actively incubating their nests and not just guarding them, as some paleontologists have speculated.
“In the new specimen, the babies were almost ready to hatch, which tells us, no doubt, that this oviraptoride had cared for the nest for a long time,” said Matthew Lamanna, a paleontologist at the Carnegie Museum of Natural History and co-author. of the new study, he said in a statement. “This dinosaur was a worried father who finally gave his life while caring for his cubs.”
Other tests supported this interpretation, namely an oxygen isotope analysis that showed that the eggs were incubated at bird-like high temperatures, between 36 and 38 degrees Celsius (97 to 100 degrees Fahrenheit). Interestingly, the eggs were found to be in various stages of development, i.e., they hatched at different times. This is known as hatching asynchrony, a reproductive phenomenon seen in modern birds. The authors could not attribute a cause to the asynchronous outbreak, but presented a plausible scenario, as they write in their study:
“As in ostriches, oviraptorosaurs would have begun incubating the nest only after laying all the eggs, so that the lower eggs, which had been laid earlier, would have been incubated proportionally at the same time as the upper eggs. However, the upper eggs would have hatched earlier than the lower eggs because, being closer to the adult cave, they would have received more heat from this individual than the lower eggs and therefore the embryos that were there. they would have developed faster.
Finally, the scientists also detected a handful of pebbles in the abdominal region of the dino. These rocks are probably gastroliths, which animals swallow to aid digestion. This is the first time such a thing has been documented in an oviraptorosaur and a potential clue to their diets. It’s true that it’s a lot of new ideas for a unique, albeit remarkable, fossil.
“It’s extraordinary to think how much biological information is captured just in this fossil,” Xu said. “We will learn from this specimen for many years to come.”