One-hundred-and-ten million years ago in the tops of early-cretaceous period trees, there were an early group of birds called enantiornithines. These animals were quite similar to modern birds, but looking back down the fossil record, we can see they didn’t become birds as we know them today.
A recent discovery of a vulture-sized bird in the dinosaur-rich state of Utah has deepened the mystery of the evolution of birds out from the age of the dinosaurs.
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The bird in question, Mirarce eatoni, and the fossils of other enantiornithines are very common and have been found all over the world.
Mirarce eatoni had an enlarged breastbone, allowing for much longer and stronger breast muscles – critical components for powerful wingbeats. The skeleton also featured “quill knobs”, which anchor large wing feathers to the bones, increasing their stability.
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These adaptations are seen today in vultures and other large birds. But it seems the entire enantiornithine lineage died off in the cataclysmic asteroid impact which wiped out the dinosaurs, further muddying the waters as to where birds came from.
Seeing that enanornithines were so expertly adapted to flying leads to some friction when discussing the ancestors of modern birds. The current theory is that birds evolved from Theropods, a group of dinosaurs which include celebrities like velociraptor and T-rex
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Modern birds have a lot more in common with enantiornithines than with these toothy land predators, which has led some paleontologists to ponder a little more about their origin. One theory involves the epoch-ending asteroid which struck the earth 65 million years ago. This impact would have set every tree on earth ablaze in a few hours, effectively vaporizing the entire ecosystem which enantiornithines evolved to inhabit; while microraptors, velociraptors, and archaeopteryx, the current stakeholders of the bird empire, managed to scrape by.