About 70 million years ago, an ostrich-like dinosaur hatching on top of a nest of blue-green eggs, meets its doom and perishes with its nearly hatched babies in what is now south of China.
Now the remains of that animal – an oviraptorosaurus, or a giant-feathered dinosaur that walked on two legs – are the only dinosaur fossil recorded, found on top of eggs that still contain dinosaur embryos.
“Dinosaurs stored in 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-bird dinosaur has been found, sitting on a nest of eggs that preserve embryos, in a single spectacular specimen.”
Related: Photos: Petrified dino-embryo is a new oviraptorosaur species
These eggs now join the ranks of another famous oviraptoric embryonic egg, known as Baba Louie, of which the remains of 90 million years old have also been found in China. (Baby Louie was not found in a nest with an adult.)
Oviraptorids, which are teropods – a group of mostly carnivorous bipedal dinosaurs that include Tyrannosaurus rex and Velociraptor – thrives during the Chalk period (145.5 million to 65.5 million years ago). This breeding oviraptorid was discovered in rocks dating from the last century of the Cretaceous, known as the Maastrichtian era (72 million to 65.5 million years ago), next to the Ganzhou train station in Jiangxi province.
The fossil is not complete because the skull of the adult and some of the bones, including parts of the vertebrae, are missing; but its nest is remarkably well preserved with the remains of at least 24 oval-shaped eggs. At least seven of those eggs, each about 21.5 inches long and just over 8 inches wide, contain bones or partial skeletons of embryonic dinosaurs.
The adult oviraptoride sat directly over 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 probably raised his eggs, a behavior also seen in modern birds, the descendants of dinosaurs, rather than guarding his nest like a crocodile (crocodiles are argosaurs, meaning they are cousins of dinosaurs is).
“This kind of discovery, essentially petrified behavior, is the rarest of the rarest in dinosaurs,” said fellow researcher Matt Lamanna, a paleontologist at the Carnegie Museum of Natural History in Pittsburgh. “In the new specimen, the babies were almost ready to hatch, which no doubt tells us that this oviraptorid cared for its nest a long time ago. This dinosaur was a caring parent who eventually gave its life while raising its young.”
In addition, an analysis of the oxygen isotopes (atoms with a varying number of neutrons in their nuclei) in the petrified eggshells and the 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 out by comparing the oxygen isotopes in the eggshells, which would match the mother’s oxygen isotopic composition because she laid the eggs with the chemistry of the embryonic bones, which would change over time due to the incubation heat that on the them. This finding adds further evidence that the adult oviraptoride sat on the nest to keep the eggs warm. In contrast, reptiles keep their eggs at cooler temperatures of between 26 and 32 ° C, according to the researchers.
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Some of the embryos were more developed than others, suggesting that they were probably laid at different times, the researchers noted. Such asynchronous hatching appears to have evolved independently into oviraptorids and some modern birds, including owls and pelicans, in which eggs may hatch hours to weeks apart.
The adult oviraptoride has revealed another secret; the researchers found a group of pebbles near his abdomen. These pebbles were probably gastrolytes (“stomach stones” in Latin) that the dinosaur probably swallowed to help him grind and digest his food. This is the first time that stones that are clearly gastrolytes have been found in an oviraptorite sample, the researchers said.
“It’s extraordinary to think how much biological information is captured in just this single 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’ll be learning from this copy for many years to come.”
The study was published online in the journal in December 2020 as a peer-reviewed preface Science Bulletin.
Originally published on Live Science.