A tiny prehistoric chick that hatched 127 million years ago and promptly flopped over and died looks remarkably like a baby chicken, according to the artist’s impression. The chick, found in the Las Hoyas fossil deposits in Spain, belongs to a group of prehistoric birds called enantiornithes, explains the team in Nature Communications on Monday.
Enantiornithes looked a lot like today’s birds, differing mainly in having teeth in their beaks and clawed fingers on the wings. This one was about 5 centimeters (2 inches) long – smaller than your pinkie – said the team, led by Dr. Fabien Knoll of ARAID-Dinopolis and the University of Manchester. It would have weighed about 10 grams, a fraction of the weight of a newborn kitten.
"Our specimen is a true bird," Dr Knoll told Haaretz. "As birds are dinosaurs (theropod dinosaurs to be exact), it is also a dinosaur. The specimen contributes to our knowledge of bone formation in baby birds from the time of dinosaurs. It is not the oldest bird, which is Jurassic in age, but a little more recent. Still it is no less than 127 million years old."
We already knew that not all dinosaurs were monsters like the fearsome T-rex or the long-necked titanosaurs. We also realized that theropods, cousins of the notorious velociraptor, were the origin of birds. And we also recently began to suspect that all dinosaurs had feathers, much as all mammals have fur.
But it is a remarkable coup to find an animal so small, so well preserved from the early Cretaceous – about 150 million to 100 million years ago.
There are other examples of fossil baby birds – not least another enantiornithe encased in amber, no less, also from the Cretaceous, which was found in Myanmar in 2017 and dates to 99 million years ago. It also had teeth and is thought to have been be largely black, white and brown. That Myanmar infant had primitive flight feathers, which led to the theory that enantiornithes could fly from birth, and would have probably been quite independent from their parents.
But that may not have been so – or at least, not in all enantiornithes.
The team reporting this week was very excited about the chick dying and being preserved so soon after hatching, because it can shed light on the development and maturation of early birds, they explain. Whatever else it could do, fly it could not.
Happily, Las Hoyas, near the city of Cuenca, has been quite the hotbed of fossil finds, even of soft tissues, which are the holy grail for paleontologists. One of the more famous finds is the keratin crest on the back of an ornithomimosaur’s head (specifically a Pelecanimimus). Back in the day, the site was apparently lush land with lakes; fish fossils also abound in Las Hoyas. And now the scientists have found the baby bird.
The telltale missing bone
Humans are famously born with a hole on the top of the head, where the skull has not fully closed yet. Birds, from your canary to the enantiornithe, are not born with all their bones in place. As the scientists explain, upon hatching (akin to birth), ossification is not complete.
“What makes this fossil so important and unique is the fact it died not long after its birth. This is a critical stage in a bird’s skeletal formation,” writes the team.
Using state-of-the-art technology (synchrotron radiation, in France, the U.K. and the United States) to study the fossilized bones, the researchers could see where the chick had already ossified and where it had not.
The researchers decided that the chick’s breastplate bone (sternum) hadn’t developed into hard bone yet, which would have happened a bit later as the bird matured. Its sternum remained mostly cartilage, meaning it wouldn’t have been able to fly yet, they explain.
For one thing, the scientists concluded that the maturation of the skeleton is more varied than had been realized.
But they could not tell whether the soft breastbone and inability to fly necessarily meant the enantiornithes’ parents devotedly cared for its infant needs.
Many paleontologists agree that from the dinosaurs on, and certainly in birds, parental care – possibly even group care – was happening. Yet not all species are alike, even today: Baby owls, for instance, are altricial, which means they are profoundly dependent on parental nurturing. At the other end of the rainbow, baby chickens are an example of precocial behavior, pretty much managing on their own.
“This is not a black-and-white issue, but rather a spectrum, hence the difficulty in clarifying the developmental strategies of long gone bird species,” says the team. But at the end of the day, we laypeople look at the picture, think, “Oh my, that’s adorable,” and are left with the impression that birds haven’t changed much in 127 million years. Except for those beak teeth.