Scientists debate dinosaur-bird connection

From WSUEdu, RockDoc Column: Scientists debate dinosaur-bird connection

PULLMAN, Wash. - I’ve never met Ryan Carney of Brown University, but he is my kind of man. On his arm he has tattooed the image of a feather of the dino-bird known as Archaeopteryx. The feather is a famous feature of the animal that lived in the late Jurassic in what’s now southern Germany. And that animal was either an in-between species between dinosaurs and birds or was a cousin to that transitional animal.

You can check with any nine-year-old you know about the significance of Archaeopteryx. The feathered creature lived at the close of the age of the dinos. They were biggish creatures compared to modern birds, some a foot and a half long. A few of them were preserved in the shallow sediments of what’s known as the Solnhofen limestone in Europe.

The limestone in question is very fine-grained and preserved even the delicate structure of feathers. The fossils of Archaeopteryx are each worth a king’s ransom. They are sometimes cited as one of the most important set of fossils we have that show major evolutionary transitions.

The feather debate
Archaeopteryx’s feathers may have helped keep the animal warm or may have aided it in flight – or both.

There’s been a long discussion about whether Archaeopteryx came from earlier, tree-dwelling animals that could glide downwards – a hypothesis known as the "trees-down” model. Alternatively, Archaeopteryx may have lived on the ground where it ran quickly and made long leaps, launching itself into flight in what’s called the "ground-up” model.

Virtually all of the flesh and blood Archaeopteryx animals that lived and breathed in the late Jurassic died and rotted away. But a few fell into the shallow sea around which they lived and sank to the limey bottom. The bottom-most waters of the sea helped preserve them and then cover them with more layers of the sediment that became limestone.

Unearthing the fossils
In recent times, as Germans have quarried the Solnhofen limestone, the fossils have come to light in part because the rock breaks into flat sheets, revealing the fossils that lie mostly between the rocky beds of the limestone. Once in a while, quite out of the blue, the rock breaks open to reveal Archaeopteryx in all its glory.

There’s some technical dispute about whether it’s best to think of Archaeopteryx as a dino becoming a bird or as one of the first animals really and truly at the base of the bird family tree. It’s not surprising there’s such a debate.

In the first place, the fossil record is always incomplete compared to the full complexity of animal life through geologic time. And in the second place, as birds evolved from dinosaur stock there were "gray areas” where one researcher could legitimately think of a fossil as a specialized dinosaur while another scientist might understandably emphasize the bird-like features of a particular fossil find.

The most recent technical publication I’ve seen in the journal Nature is opposed to the notion that Archaeopteryx should be called the first bird on the planet.

But it’s clear that Archaeopteryx had features of both dinosaurs and birds. It had wings and feathers, on the one hand, but it also had features like sharp teeth and a long, bony tail that made it more like a dinosaur than a modern bird.

The black feathers
What’s interesting now is the news from the tattooed Mr. Carney and some of his colleagues that at least some of the feathers sported by Archaeopteryx were black. The evidence for color comes from the microscopic examination of pigment-bearing structures that are similar to those found in modern birds.

Today’s bird feathers have what the ScienceNews website calls "rod-shaped nubbins” that contain melanin pigments.

Carney and company compared the structures found in 87 kinds of modern birds with those of Archaeopteryx as it is preserved for us in the fine-grained limestone. The researchers found the fossil dino-bird had pigment-bearing structures that are more like black ones in modern birds than like those associated with brown or gray feathers.

But despite the recent news from the realm of scientific research, the jury is still out on the overall color of Archaeopteryx.

Still, I like to think Archaeopteryx looked good in basic black, just like our crows.