Archaeopteryx’s status as the forerunner of modern birds is crumbling in the face of a new, closely-related fossil.

The new discovery, a feathered, chicken-sized dinosaur named Xiaotingia, has prompted a fresh look at the dinosaur family tree, casting Archaeopteryx as a bird-like dinosaur rather than dinosaur-like bird.

Archaeopteryx has been fundamental to our understanding of birds’ origins but, if confirmed, this finding questions those assumptions.

“This result challenges the centrality of Archaeopteryx in the transition to birds,” write paleontologists led by Xing Xu in a July 28 Nature study.

Archaeopteryx. Digital Cat/Flickr

Since its initial discovery 150 years ago, Archaeopteryx, meaning “ancient wing,” has been a famed fossil.

The 150 million-year-old creature had many bird-like aspects, including its modern feathers, wings, wishbone  and cranial structure, as well as traits shared with dinosaurs, such as a long bony tail, teeth and claws on the front limbs.

Quite appropriately, the first specimenwas unearthed shortly after the publication of Charles Darwin’s Origin of Species. Archaeopteryx became a textbook example of a transitional fossil and a focus of ongoing debates over evolution, with some anti-evolutionists denying the creature’s transitional nature and even doubting the fossils’ authenticity.

For paleontologists and ornithologists, Archaeopteryx’s new status as a dinosaur may cause hand-wringing because, for the past century and a half, it’s been loved as the grandfather of birds.

“For ornithologists, Archaeopteryx is an icon,” said Jack Dumbacher, Curator of Birds and Mammals at the California Academy of Sciences in San Francisco, who was not involved in the new finding. “It’s something that kids know from grade-school.”

If Xu and his colleagues are right, it wasn’t Archaeopteryx that started modern birds, but little-known dinosaur-like birds Epidexipteryx, Jeholornis and Sapeornis instead. They are part of a procession of feathered dinosaurs and early birds that have appeared in recent years, slowly but steadily calling Archaeopteryx’s position into question.

Perhaps the time has come to finally accept that Archaeopteryx was just another small, feathered, bird-like theropod fluttering around in the Jurassic.

“It may seem heretical to say that Archaeopteryx isn’t a bird, but this idea has surfaced occasionally since as far back as the 1940s,” said paleontologist Lawrence Witmer of Ohio University in a commentary accompanying the finding. “Perhaps the time has come to finally accept that Archaeopteryx was just another small, feathered, bird-like theropod fluttering around in the Jurassic.”

The newly-discovered Xiaotingia, causing the hub-bub, was found in the hands of a fossil dealer but came originally from China’s Liaoning Province, a source of many proto-dino-bird fossils. Xiaotingia is itself a dinosaur, but when the researchers added it to their phylogenetic analysis — a statistical mapping to find a best-fit family tree for known traits and dates — of proto-dino-birds, Archaeopteryx flipped from the bird camp to dinos.

Xu’s team now place Archaeopteryx on new branch of dinosaurs, one which split from the trunk that brought us birds.

Since Archaeopteryx has been central to understanding bird origins, the new arrangement will shake things up. For starters, while Archaeopteryx has the sharp teeth of a carnivore, other dino-birds, including Epidexipteryx, have the high, boxy skulls of herbivores. It would appear that early birds ate plants, not meat.

However, as the authors freely admit, finding some new proto-bird fossil could again rework the avian family tree, push Archaeopteryx back into the flock.

“Being a scientist, you realize that these family trees are always flip-flopping,” said Dumbacher. “Every new discovery gives you a different way of looking at the world, and that’s a wonderful thing.”

Dumbacher continued, “That said, I wouldn’t be so quick to knock Archaeopteryx out of its perch.”

Xiaotingia skeleton. Xu et al./Nature

Top image: Artist’s depiction of Xiaotingia. (Xing Lida and Liu Yi)

Citation: “An Archaeopteryx-like theropod from China and the origin of Avialae.” By Xing Xu, Hailu You, Kai Du & Fenglu Han. Nature, July 28, 2011.