Mirarce eatoni was a bird that lived 75 million years ago with good flight capabilities

Skeletal reconstruction of Mirarce eatoni. The bones available are in white (Illustration courtesy Scott Hartman)
Skeletal reconstruction of Mirarce eatoni. The bones available are in white (Illustration courtesy Scott Hartman)

An article published in the journal “PeerJ” describes the study of some bones of a primitive bird that lived about 75 million years ago in today’s Utah. Nemed Mirarce eatoni, it belonged to the family of enantiornithines, primitive birds that lived in the Cretaceous period and then died out with dinosaurs. This species shows characteristics similar to those of modern birds that show flight skills equivalent to theirs but this makes it even more difficult to understand the reasons for the extinction of the enantiornithines.

In 1992, paleontologist Howard Hutchison of the University of Berkeley discovered the fossils that made up about 30% of the skeleton of a primitive bird in the Kaiparowits formation in Utah. However, the fossils remained in the palaeontology museum of the university for several years, almost untouched, until in 2009 the then student Jessie Atterholt discovered their existence and asked to study them. From there came a collaboration between the two of them that was extended to Jingmai O’Conner, the leading expert in enantiornithines, which led to a detailed analysis of those fossils.

Other known fossils indicate that the enantiornithines that lived between 115 and 130 million years ago were able to fly, although they probably weren’t yet adapted to flight as well as modern birds. Jessie Atterholt, now an assistant professor and instructor of human anatomy at the Western University of Health Sciences in Pomona, California, explained that the fossils studied show that that bird family developed some of the same adaptations to flight and as modern bird and were very successful spreading to all continents. Nevertheless, at the end of the Cretaceous the enantiornithines became extinct while modern birds survived.

A hypothesis proposed recently is that the enantiornithines were forest dwellers and when forests went up in smoke due to the consequences of the asteroid that caused a global devastation they too became extinct while modern birds lived in different habitats and their direct ancestors survived the catastrophe. According to the authors of an article published in the journal “Current Biology” in April 2016, the ancestors of modern birds fed on seed and survived that extinction.

Jessie Atterholt stated that the hypothesis about enantiornithine as forest dwellers is the most interesting to date but they need to study these birds’ ecology rigorously. That could be a key to understanding why only the ancestors of modern birds survived and could offer new information on the reactions of different species to an ecological collapse.

Reconstruction of Mirarce eatoni on a dinosaur Utahceratops gettyi (Illustration courtesy Brian Engh)
Reconstruction of Mirarce eatoni on a dinosaur Utahceratops gettyi (Illustration courtesy Brian Engh)

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