Early Cretaceous Bird Fossil Sheds New Light on Avian Evolution
The tiny fossil of a juvenile enantiornithe bird from the Early Cretaceous La Huérguina Formation of Spain is helping paleontologists understand how early birds came into the world in the age of dinosaurs.
The 127-million-year-old fossil is a chick from a group of prehistoric birds called Enantiornithes.
The specimen consists of a nearly complete skeleton; the feet, most of its hands, and the tip of the tail are the only missing parts.
It measures less than 2 inches (5 cm) and would have weighed just 10 g when it was alive. It is amongst the smallest known Mesozoic avian fossils ever discovered.
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. That means this bird’s extremely short life has given paleontologists a rare chance to analyze the species’ bone structure and development.
“Studying and analyzing ossification — the process of bone development — can explain a lot about a young bird’s life,” said University of Manchester researcher Dr. Fabien Knoll and colleagues.
“It can help us understand everything from whether it could fly or if it needed to stay with its parents after hatching or could survive on its own.”
“The evolutionary diversification of birds has resulted in a wide range of hatchling developmental strategies and important differences in their growth rates. By analyzing bone development we can look at a whole host of evolutionary traits,” Dr. Knoll said.
“With the fossil being so small we used synchrotron radiation to picture the tiny specimen at a ‘submicron’ level, observing the bones’ microstructures in extreme detail.”
The scientists found the baby bird’s sternum (breastplate bone) was still largely made of cartilage and had not yet developed into hard, solid bone when it died, meaning it wouldn’t have been able to fly.
The patterns of ossification observed in this and the other few very young enantiornithine birds known to date also suggest that the developmental strategies of this particular group of ancient avians may have been more diverse than previously thought.
“However, its lack of bone development doesn’t necessarily mean the hatchling was over reliant on its parents for care and feeding, a trait known as being ‘altricial’,” the study authors said.
“Modern day species like love birds are highly dependent on their parents when born. Others, like chickens, are highly independent, which is known as ‘precocial.’ Although, 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.”
“This new discovery, together with others from around the world, allows us to peek into the world of ancient birds that lived during the age of dinosaurs. It is amazing to realize how many of the features we see among living birds had already been developed more than 100 million years ago,” said Dr. Luis Chiappe, from the LA Museum of Natural History.
The research is published in the journal Nature Communications.
Fabien Knoll et al. 2018. A diminutive perinate European Enantiornithes reveals an asynchronous ossification pattern in early birds. Nature Communications 9, article number: 937; doi: 10.1038/s41467-018-03295-9