An international team of scientists has announced the discovery of an extraordinary fossilized nest in China, which preserves at least eight separate dinosaurs from 70 million years ago.
The clutch of ancient eggs belongs to a medium-sized adult oviraptator, and we know this because the father is part of the fossil. The skeleton of this ostrich-like theropod is positioned in a crouch over two dozen eggs, at least seven of which were on the verge of hatching and still contain embryos inside.
The ancient scene is unprecedented and provides the first evidence that dinosaurs were parents who pondered, laid eggs, and incubated them for a long time.
“This type of discovery (in essence, fossilized behavior) is the rarest of the rare in dinosaurs,” says paleontologist Matt Lamanna of the Carnegie Museum of Natural History (CMNH).
“Although some adult oviraptorids have previously been found in the nests of their eggs, no embryos have ever been found within those eggs.”
The 70 million year old fossil. (Shundong Bi / Indiana University of Pennsylvania)
Since the 1980s, paleontologists have unearthed numerous dinosaur nests containing fossilized eggs. Some rare ones have even been found with the skeleton of the parents sitting on top. Other oviraptor eggs suggest that they may have been blue-green in color.
However, inferring the behavior of these fossils has proven problematic. Although it appears that the parents of the oviraptor incubate their nests, it is also possible that these dinosaurs perished while laying or guarding the eggs, not necessarily by incubating them. This is more like how crocodiles treat their nests, not modern birds.
The new specimen was recovered from the Nanxiong Formation in Ganzhou, southern China, a region known for the world’s largest collection of fossilized dinosaur eggs, but it bears no resemblance to what scientists have found. before.
The relationship between the father and the embryo of the dinosaurs has never been closer than this. The body of the adult oviraptor is preserved “very close to the eggs,” with little or no intermediate sediment.
In at least seven of the eggs, exposed embryonic material was found, including ossified bones of identifiable shapes.
One of the eggs may contain a complete skeleton, with the vertebrae, dorsal ribs, a humerus, both iliac and femoral, and a tibia arranged in a curly position.
Analyzing the oxygen isotopes of these embryos, the researchers found that the estimated incubation temperature was consistent with the parents ’body temperature, sitting between 30 and 38 degrees Celsius (86 to 100 degrees Fahrenheit).
“In the new specimen, the babies were almost ready to hatch, which indicates to us, without any doubt, that this oviraptorid had cared for the nest for a long time,” Lamanna explains.
“This dinosaur was a worried father who finally gave his life while caring for his cubs.”
Oviraptor dinosaur artwork caving over a nest of blue-green eggs. (Zhao Chuang / PNSO)
Interestingly, however, not all embryos were in the same stages of development. This suggests that the clutch may have ended up hatching at different times, a feature that was thought to appear much later, only in some types of birds.
Although oviraptors are often considered an intermediate stage in this evolutionary process, they appear to have moved away independently of simultaneous hatching, suggesting that the evolution of bird reproduction was not a simple linear process. .
Most modern birds will wait until all the eggs have been laid before incubating them, sometimes with the help of both mother and father, and this causes synchronous hatching.
Although oviraptors may also have waited to incubate until all the eggs have been laid, the authors suggest that the upper eggs may have been closer to the incubating adult and therefore could have developed more. quickly. That, however, is just an idea. We will need more data to find out why some eggs would have hatched earlier than others.
In other ways, however, the oviraptor shares traits similar to modern birds. The sex of fossilized fathers, for example, may have been male, suggesting that the father may also have been involved in breeding, similar to ostrich mothers and fathers, who incubate their young in turns.
The sex of the adult oviraptor is still under debate (it could be a male or a female depending on available data), but the idea coincides with other analyzes of theropod nests, which suggest some level of paternal care.
Work of the skeleton of the adult oviraptor; preserved bones shown in white. (Andrew McAfee / Carnegie Museum of Natural History)
As if all this reproductive information wasn’t enough, this remarkable fossil has also given us an insight into the potential diet of the oviraptor. For the first time, scientists have found small stones in the stomach of this type of dinosaur, which would probably have been swallowed to aid digestion.
“It’s extraordinary to think how much biological information is captured only in this fossil,” says paleontologist Xing Xu of the Beijing Institute of Vertebrate Paleontology and Paleoanthropology.
“We will learn from this specimen for many years to come.”
The study was published in Science bulletin.