Yeesh, what a holiday season. The looming threat of Omicron, the duplicity of Manchin, the pervasiveness of racism, and the discouraging feeling that our country is on the brink of utterly losing its mind. I feel like it’s necessary to stop periodically for a break, to be amazed and reassured by the enduring wonders of the natural world.
On December 21, a group of British and Chinese scientists teamed up to report, in the Cell open-access journal iScience, that they had found quite possibly the best-preserved fossil of a dinosaur embryo ever observed. The fossil itself, unearthed in 2000, had sat around for years as merely a “suspected egg” in a collection intended to be sorted through later by Yingliang Stone Nature History Museum, in the process of construction. When the eggshell was finally scraped away…
“This dinosaur embryo inside its egg is one of the most beautiful fossils I have ever seen,” said Prof Steve Brusatte of the University of Edinburgh, part of the research team, in a statement.
“It is one of the best dinosaur embryos ever found in history,” Fion Waisum Ma, a University of Birmingham researcher who co-authored [the paper], told AFP.
The fossil is of an oviraptorid theropod — not a bird, but a precursor of one — and its posture in the egg looks more like that of today’s birds than that of today’s reptiles.
In the late Cretaceous period (just before the you-know-what hit), large birdlike dinosaurs called oviraptorids thrived. Here is an approximation of what they looked like:
Some deduced profiles of known oviraptorids are shown below. They certainly look like pre-birds, don’t they?
The egg color you see in the picture above isn’t just fanciful; the blue-green pigment biliverdin has been found as the predominant pigment associated with fossilized eggshells of the oviraptorid Heyuannia huangi (“L” in the above diagram.)
Earlier this year, the first fossilized example of an oviraptorid dinosaur sitting atop a nest of its own eggs, thought to be about 70 million years old, was reported to have been discovered in Jiangxi Province, China. As often happens with fossils like this, the pieces are there, but they’re a bit displaced. Nevertheless, it was the clearest evidence yet of birdlike brooding behavior by oviraptorids:
Perhaps the most spectacular oviraptorid nest fossil is this one, found in the Guangdong Province of China in 1984. It gives a terrific nest layout, but as in many egg fossils, the embryo bones are not especially clear:
Other significant embryo finds include “Baby Louie”, from a nest of very large eggs, again with a lot of pieces, but somewhat-displaced ones:
… and 200-million-year-old fossils of Massospondylus carinatus eggs. Not a Cretaceous oviraptorid here, but an early-Jurassic sauropod, more like what we think of as a “plain old dinosaur”:
From what we can see of the exposed Massospondylus embryo, the posture looks reptilian, seated with the head not very near the limbs, like that of a modern-day lizard:
But a visual reconstruction of the new oviraptorid fossil find casts a different picture:
The authors make the case that this is similar to a modern bird embryo posture, where the head is enveloped by the limbs, and eventually gets “tucked” underneath the right wing:
That would certainly make sense, as oviraptorids are clear evolutionary precursors of birds. If you have a few minutes, take a really fun mini-tour of bird evolution with the American Museum of Natural History here.
Why does a bird embryo “tuck”, anyway? So that it can reach an air sac that forms within the egg, puncturing the sac with its beak, which gives it enough oxygen — over and above what diffuses in through the blood vessels that extend to pores in the shell — to allow it to make its foray out of the egg:
But regardless of the evolutionary implications, let’s just have one more look at the level of 3-D detail of this specimen:
How do you like that? An embryo is buried in mud before it can ever hatch from its egg, and yet 70 million years later, it is world-famous.