The fossil remains of a chick that lived around 127 million years ago offer new clues to avian evolution

The chick's phosphorous mapping and photo (Image Dr. Fabien Knoll)
The chick’s phosphorous mapping and photo (Image Dr. Fabien Knoll)

An article published in the journal “Nature Communications” describes the study of the fossil remains of a chick that lived about 127 million years ago and died shortly after its birth. A team of researchers led by Dr. Fabien Knoll of the University of Manchester examined this specimen that belongs to the Enantiornithes, a group of primordial birds that lived during the Cretaceous period. Its almost complete skeleton made it possible to analyze its bones’ structure and development, obtaining new data on those birds.

The specimen, cataloged as MPCM-LH-26189, was found in the Las Hoyas deposit in Spain. This site is dated to the Early Cretaceous and fossils in excellent condition were found there, especially dinosaurs but also some Enantiornithes. The chick consists of an almost complete skeleton and also some soft-tissue because in that type of deposit that too can fossilize at least partially.

This specimen is one of the smallest avian fossils of the Mesozoic era discovered so far with a length of less than 5 centimeters (2 inces) and a weight estimated around 10 grams (0.3 ounces) in the short period in which it was alive. What makes it extraordinary is the fact that it died at a crucial moment, shortly after birth, when ossification – it’s bones development process – was still taking place. Its study can provide important information about that chick and in general about primordial birds.

Dr. Fabien Knoll explained that the evolutionary diversification of birds produced a wide range of hatchling care strategies and important differences in their development rate. The consequence is that analyzing the ossification of the specimen MPCM-LH-26189 can provide information on a number of developmental traits, for example if it could fly or needed parental care.

The researchers exploited synchrotron radiation to perform an extremely accurate spectroscopic analysis of the fossil remains. Three different synchrotrons in France, the UK the USA made it possible to obtain details at levels levels under one micron – one thousandth of a millimeter – one of the increasingly common cases in which very advanced technologies are exploited in the field of paleontology.

The top image shows one of the results of the spectroscopic analysis with the fossil’s phosphorus mapping next to its photo. The bottom image shows a possible reconstruction of the chick with its silhouette in the inset compared to a cockroach. No traces of plumage were found so that part is the result of a hypothesis based on other Enantiornithes.

Regarding the chick’s skeleton, the analysis of its remains showed that at the time of its death it was still made above all by cartilage. This means that its species could fly only after a certain period, when their ossification was completed and their bones became solid.

It’s not clear how much its species’s chick were dependent on their parents. Even today there are various strategies for hatchling care and among the species in which they’re very dependent on their parents and the species in which hatchling already have some independence there’s a whole spectrum of possibilities. This makes it difficult to clarify extinct species strategies.

Despite the doubts still existing, the study of this chick is very interesting. Its species lived in an era when there were still dinosaurs and yet many characteristics of today’s birds were already developed. At the beginning of the Cretaceous period there were feathered dinosaurs and birds that show a notable diversification of a group of dinosaurs that paleontologists are slowly reconstructing.

The chick's reconstruction (Image Raúl Martín)
The chick’s reconstruction (Image Raúl Martín)

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