New Feathered Dinosaur Discovery Raises Further Bird Evolution Questions

 @rpalmerscience on February 04 2013 6:01 PM

A newly discovered bird-like dinosaur is shaking up the family tree a little bit.

Scientists generally agree that birds arose from a group of dinosaurs called theropods during the Early Cretaceous period about 120 to 130 million years ago. But the finer details of this evolution are still being hashed out.

The fossilized skeleton of new species Eosinopteryx brevipenna was unearthed in China, and an international team of researchers detailed the discovery in the journal Nature Communications in January. Though Eosinopteryx had feathered wings, it was probably flightless, the researchers say.

Eosinopteryx had much more reduced plumage on its tail and lower legs compared to other feathered dinosaurs like the iconic Archaeopteryx. The dinosaur’s discoverers also hypothesize that, based on its bone structure, Eosinopteryx likely lacked the ability to flap its wings.

The researchers also claim that Eosinopteryx knocks Archaeopteryx off of its perch as a key transitional figure between dinosaurs and birds.

“This discovery sheds further doubt on the theory that the famous fossil Archaeopteryx  -- or "first bird" as it is sometimes referred to -- was pivotal in the evolution of modern birds,” coauthor and University of Southampton researcher Gareth Dyke said in a statement in January.

But other paleontologists take a bit of an issue with that claim, saying that Archaeopteryx hasn’t been really seriously considered a first bird for some time.

“For over 100 years, Archaeopteryx was the only feathered not-quite-modern-bird we had, and so every theory of bird origins HAD to talk about Archaeopteryx,” University of Chicago’s Jonathan Mitchell wrote in an email.

Since Archaeopteryx was discovered in 1861, scientists have found other feathered dinosaurs that have forced paleontologists to redraw the bird-dinosaur family tree. In 2011, a Chinese-led team detailed the discovery of a new bird-like dinosaur called Xiaotingia, which they say is closely related to Archaeopteryx and another feathered dinosaur, Anchiornis huxleyi.

Based on some of the shared traits between Xiaotingia, Archaeopteryx and Anchiornis, the team suggested that Archaeopteryx belongs in Deinonychosauria -- a group that includes the more familiar velociraptor -- and not in the bird group Avialae.

Yet neither the Eosinopteryx discovery nor the Xiaotingia find has truly undermined the idea that Archaeopteryx is an early branch off the line leading to modern birds, Mitchell says.

Both studies suggest that “Archaeopteryx is an ever-so-slightly earlier branch than we previously thought. However, it is still, ultimately, in the same spot: a fascinating and important twig on the grand bush of bird evolution,” Mitchell wrote.

Nick Longrich, a Yale University paleontologist who has discovered a number of new dinosaur species, including Mojoceratops, a hippo-sized cousin of  the triceratops with a towering, heart-shaped head frill -- think the fossils do show there’s still much scientists don’t understand about the evolution of flight.

Where Archaeopteryx, Eosinopteryx and other feathered dinosaurs sit on the family tree in relationship to each other and to modern birds is still something of a mystery. They may be near-direct ancestors of birds or distant cousins.

“It's a fascinating specimen and a provocative article, but I suspect we will be arguing about this for years to come,” Longrich says.

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