An international team of scientists has announced the discovery of an extraordinary fossilized nest in China, which keeps at least eight dinosaurs separated 70 million years ago.
The mating of ancient eggs belongs to a medium-sized adult oviraptor and we know this because the parent is actually part of the fossil. The skeleton of this ostrich-like theropod is positioned in a clump of over two dozen eggs, of which at least seven were on the verge of incubation and still contain embryos inside.
The ancient scene is unprecedented and provides the first clear evidence that dinosaurs were parents who flirted, laid their eggs and incubated them for a long time.
“This type of discovery – essentially fossilized behavior – is the rarest of the dinosaurs,” says paleontologist Matt Lamanna of the Carnegie Museum of Natural History (CMNH).
“Although several adult oviraptorids have been found in the nests of their eggs before, no embryos have ever been found inside these eggs.”
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 were even found with the skeleton of the father placed on top. Other oviraptor eggs suggest that it may have been blue-green.
However, the deduction of the behavior from these fossils proved problematic. While oviraptor parents appear to hatch their nests, it is also possible that these dinosaurs perished while laying or guarding their eggs, not necessarily incubating them. This is more like how crocodiles take care of their nests, not modern birds.
The new specimen was recovered from the Nanxiong Formation in Ganzhou in southern China – a region famous for the largest collection of fossilized dinosaur eggs in the world – but it is different from anything scientists have found before.
The relationship between the dinosaur parent and the embryo has never been closer. The body of the adult oviraptor is kept in “extremely close to the eggs”, with little or no sediment between them.
In at least seven of the eggs, embryonic material was found, including ossified bones in identifiable forms.
One of the eggs may actually contain a complete skeleton, with its vertebrae, dorsal ribs, a humerus, both iliac and femoral, and a tibia placed in a wavy position.
Analyzing the oxygen isotopes of these embryos, the researchers found that the estimated incubation temperature was consistent with the parent’s body temperature, standing somewhere between 30 and 38 degrees Celsius (86 to 100 degrees Fahrenheit).
“In the new specimen, the babies were almost ready to hatch, which no doubt tells us that this oviraptorid had cared for its nest for a long time,” explains Lamanna.
“This dinosaur was a caring parent who eventually gave his life while caring for his cubs.”
The work of art of an oviraptor dinosaur boiling on a nest of blue-green eggs. (Zhao Chuang / PNSO)
Interestingly, not all embryos were in the same stages of development. This suggests that the clutch may have finally come out at different times – a feature that was thought to appear much later, only in some types of birds.
While oviraptors are often considered an intermediate stage in this evolutionary process, it seems that they could have moved away independently of simultaneous hatching, and this suggests that the evolution of bird breeding 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 their mother and father – and this leads to synchronous hatching.
While oviraptors may also have waited to incubate until all the eggs had been laid, the authors suggest that the upper eggs may have been closer to the adult with the brood and therefore may have developed. faster. However, this is just an idea. We will need more data to figure out why some eggs would have hatched earlier than others.
In other ways, however, the oviraptor has similar features to modern birds. The sex of the fossilized parent, for example, could have been male, suggesting that the father may also have taken part in the brood, similar to ostrich mothers and fathers, who incubate their children in turn.
The sex of the adult oviraptor is still under debate (it could be a man or a woman based on available data), but the idea fits with other analyzes of theropod nests, which suggest a certain level of paternal care.
Illustration of the skeleton of the adult oviraptor; preserved bones shown in white. (Andrew McAfee / Carnegie Museum of Natural History)
As if all that reproductive information wasn’t enough, this remarkable fossil also gave us a look at 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 amazing to think how much biological information is captured in this single 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 The scientific bulletin.