Fossil captures dinosaur nested next to unhatched hatchlings

Left: The new fossil preserving an adult oviraptorid dinosaur with eggs containing embryos.  Right: artist's rendering of a nested oviraptorid.

Left: The new fossil preserving an adult oviraptorid dinosaur with eggs containing embryos. Right: artist’s rendering of a nested oviraptorid.
Picture: Fossil: Shundong Bi; Artwork: Zhao Chuang

Paleontologists in China have unearthed the fossil of an oviraptorosaur sitting in a nest of eggs. In itself, it is a surprising and rare discovery, but this fossil is unique in that the eggs still retain evidence of unhatched progeny. within.

“Here we report the first [non-avian] dinosaur fossil known for preserving an adult skeleton over a clutch of eggs containing embryonic remains ”, state the authors of a research paper published in Science Bulletin. Found in China, the fossil is expanding our understanding of oviraptorosaur behavior and physiology, while providing further proof that non-avian dinosaurs employed bird-like breeding behaviors.

Oviraptorosaurs, also known as oviraptors, were named for an early paleontological misunderstanding of similar fossils. The name means “egg thief,” but these dinosaurs weren’t thieves, as oviraptorosaurs were later shown to be the rightful owners of fossilized eggs that are often found alongside their buried skeletal remains.

In fact, oviraptorosaur fossils have been found before nesting with their eggs. What’s new here is that dinosaur eggs still contain evidence of the embryos inside them. It’s worth noting that embryos within oviraptor eggs have been found before, but only in isolation. A famous example is the “Baby louie”Fossil, discovered in Henan, China, in the 1990s.

Oviraptorosaurs were a highly successful theropod dinosaur of the Cretaceous period. They vary greatly in size, with some of the largest weighing over 2,425 pounds (1,100 kilograms).). Common features include feathers, long necks, wings, and beaks. These non-avian dinosaurs had a very bird-like appearance, much like modern ostriches. When nesting, these animals laid their eggs in a near perfect circle, laying their large clutches of eggs in layers in a remarkably orderly fashion.

The newly described fossil, designated LDNHMF2008, was mined from the Nanxiong Formation near the Ganzhou Railway in southern China’s Jiangxi Province. The fossil dates from the late Cretaceous period, approximately 70 million years ago. Preserves the remains of a medium-sized adult oviraptorosaur, without its skull and other skeletal features. The animal appears to have died while in a nesting position.

These fossilized bones were found alongside an “intact clutch” of at least 24 eggs, “some of which are broken and expose the embryonic bones,” the study authors wrote. The researchers, led by Shundong Bi of the 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 the same time are not uncommon, and probably an adaptation to extreme poaching by true “egg thieves”.

Microscopic analysis of the fossils showed that some embryos were in the last stages of development and were about to hatch. The authors took this as potential evidence that the oviraptors were actively incubating their nests, and not just protecting them, as some paleontologists have speculated.

“In the new specimen, the babies were almost ready to be born, which tells us without a doubt that this oviraptorid had cared for its nest for quite some time,” Matthew Lamanna, paleontologist at the Carnegie Museum of Natural History and co-author. of the new study, he said in a sentence. “This dinosaur was a loving father who finally gave his life while caring for his young.”

Other evidence affirmed this interpretation, namely an oxygen isotope analysis showing that the eggs were incubated at high temperatures similar to those of birds, around 97 to 100 degrees Fahrenheit (36 to 38 degrees Celsius). Interestingly, the eggs were found to be in various stages of development, meaning that they hatched at different times. This is known as asynchrony to hatch, a reproductive phenomenon that is observed in modern birds. The authors could not attribute a cause to the asynchronous hatching, but presented a plausible scenario, as they write in their study:

As in ostriches, oviraptorosaurs would have started nest incubation only after all the eggs had been laid, so that the lower eggs, which had been laid earlier, would have incubated proportionally for the same amount of time as the upper eggs. However, the upper eggs would have hatched earlier than the lower ones because, being closer to the incubating adult, they would have received more heat from this individual than the lower eggs and, therefore, the embryos in them would have developed more rapidly ” .

Finally, the scientists also detected a handful of pebbles in the dinosaur’s abdominal region. These rocks are probably gastroliths, which animals swallow to help with digestion. This is the first time anything like this has been documented in an oviraptorosaur and a potential clue to their diets. Admittedly, that’s a ton of new information for a unique, albeit remarkable, fossil.

“It is extraordinary to think how much biological information is captured in this single fossil,” Xu said. “We will learn from this specimen for many years.”


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