Why the bird brain is actually a dinosaur brain
A team of scientists has found that the enlarged brain once believed unique to birds actually predates the bird, complicating the bird's already murky evolutionary trajectory.
It’s a well-known tenet of paleontology: Those dinosaur-shaped chicken nuggets are actually dinosaur-shaped dinosaurs. That is to say, birds are dinosaurs.Skip to next paragraph
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Not just descended from dinosaurs. Birds genuinely are dinosaurs, since modern biology classifies any organism as belonging to the group from which it descended.
But pinpointing the moment at which some dinosaurs evolved into birds, and identifying the unique features that actually distinguish between the two, has been a vexing problem in paleontology.
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And it has just become more difficult. New research published in Nature suggests that one of the features once thought to be the exclusive domain of birds, the enlarged skull found in Archaeopteryx – often called the "first bird" – was in fact present in several other non-avian dinosaurs. That pushes back the evolution of the bird's complex, flight-supporting brain: non-avian dinosaurs, it seems, had similar brains and might have also been capable of flight.
In other words, the bird brain might just be a dinosaur brain.
“The flight-ready brain of Archaeopteryx does not represent a unique adaptation of birds for flight, but rather had evolved much earlier and was inherited by birds from their dinosaurian relatives,” says Gaberiel Bever, an assistant professor of anatomy at the New York Institute of Technology. “The large brain of birds predates birds themselves.”
The drama of bird evolution has for years turned on Archaeopteryx, an animal from the late Jurassic period some 150 million years ago. First discovered in 1861 in southern Germany, Archaeopteryx was initially considered a transitional fossil: its German name, Urvogel, means “first bird,” putting it squarely at that amorphous turning point when some dinosaurs became birds.
But over the last few years, the animal has been regularly un-pended from and then returned to its central evolutionary spot: Several studies have dismissed the animal from the avian tree altogether. Other studies have swept it back up into the tree again.
One data point in the debate has been Archaeopteryx’s brain. Birds are special among living reptiles for their enlarged brain case relative to their total body size. That disproportionate cranial size is critical to flight, which requires a complex nervous system. And Archaeopteryx’s brain, while a long way from the more evolved ones of modern birds, has long been known to be large enough to have supported flight.