About 70 million years ago, an ostrich-like dinosaur brooding atop a nest of blue-green eggs met its demise and perished with its nearly hatched babies in what is now southern China.
Now, the remains of that beast – an oviraptorosaur, or a giant feathered dinosaur that walked on two legs – represent the only recorded dinosaur fossil sitting on eggs that still contain dinosaur embryos, a new study finds.
“Dinosaurs kept on their nests are rare, and so are fossil embryos,” said lead researcher Shundong Bi, a paleontologist at the Center for Vertebrate Evolutionary Biology at Yunnan University in China. said in a statement“This is the first time a non-avian dinosaur has been found sitting on a nest of eggs containing embryos in a single spectacular specimen.”
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These eggs now join the ranks of another famous oviraptorid embryonic egg, known as Baby Louie, 90 million-year-old remains have also been found in China. (Baby Louie was not found in a nest with an adult on it.)
Oviraptorids, which are theropods – a group of mainly carnivorous biped dinosaurs including Tyrannosaurus rex and Velociraptor – bloomed during the Cretaceous Age (145.5 million to 65.5 million years ago). This brooding oviraptorid was discovered in rocks dating back to the last Cretaceous era, known as the Maastrichtian era (72 million to 65.5 million years ago), next to Ganzhou Railway Station in Jiangxi Province.
The fossil is not complete, as the adult’s skull and some of its bones, including parts of its vertebrae, are missing; but the nest is remarkably well preserved with the remains of at least 24 oval eggs. At least seven of those eggs, each about 21.5 inches long and just over 8.5 inches wide, contain bones or partial skeletons of embryonic dinosaurs.
The adult oviraptorid sat directly above the clutch, with its front legs (or arms) covering the edges of the nest, the researchers wrote in the study. Many of the embryos were about to hatch. This indicates that the adult was probably hatching its eggs, a behavior also seen in modern birds, the descendants of dinosaurs, rather than guarding its nest like a crocodile (crocodiles are archosaurs, meaning they are distant cousins. are from dinosaurs), the researchers said.
“This kind of discovery, essentially fossilized behavior, is the rarest of the rare in dinosaurs,” said study co-researcher Matt Lamanna, a paleontologist at the Carnegie Museum of Natural History in Pittsburgh, in the statement. “In the new specimen, the babies were almost ready to hatch, which tells us no doubt that this oviraptorid has maintained its nest for quite some time. This dinosaur was a caring parent who eventually gave its life while nursing its young.”
In addition, an analysis of the oxygen isotopes (atoms with varying numbers of neutrons in their nuclei) in the fossilized eggshells and embryonic dinosaur bones revealed that the eggs were incubated at high temperatures of about 54 to 68 degrees. Fahrenheit (30 to 38 degrees Celsius), the researchers said. The team found this by comparing the oxygen isotopes in the eggshells, which would match the mother’s oxygen isotopic makeup as she laid the eggs, with the chemistry of the embryonic bones, which would have changed over time due to the incubation heat applied to it. them. This finding adds another layer of evidence that the adult oviraptorid sat on the nest to keep the eggs warm. In contrast, reptiles tend to keep their eggs at cooler temperatures of about 47 to 58 F (26 to 32 C), the researchers said.
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Some of the embryos were more developed than others, indicating they likely lay at different times, the researchers noted. Such asynchronous hatching appears to have evolved independently in oviraptorids and some modern birds, including owls and pelicans, which may hatch eggs hours to weeks apart
The adult oviraptorid revealed another secret; the researchers found a cluster of pebbles near the abdominal area. These pebbles were likely gastroliths (“stomach stones” in Latin) that the dinosaur probably swallowed to help it grind and digest its food. This is the first instance of stones that are clearly gastroliths found in an oviraptoride specimen, the researchers said.
“It’s extraordinary to consider how much biological information is captured in just this one fossil,” senior researcher Xing Xu, a biologist at the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences, said in the statement. “We will learn from this specimen for many years to come.”
The study was published online in the journal in December 2020 as a peer-reviewed pre-print Science Bulletin
Originally published on Live Science.