A new paper published in Nature suggests that Archaeopteryx's flight-ready brain case was not unique but was found in non-avian dinosaurs, a find suggesting that the bird brain was actually received from the dinosaurs.
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.
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.
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.
But a team of scientists
has now found that the Archaeopteryx’s flight-ready skull size is not
unique among its relatives. CT scan data comparing Archaeopteryx’s brain
size to those of about 20 living birds and 10 non-avian dinosaurs show
that Archaeopteryx’s skull size is actually smaller than some of the
closely related dinosaur skulls to which it was compared.