National Geographic

Archaeopteryx’s Evolutionary Humiliation Continues

Few extinct species have emerged from the Earth with more fanfare than Archaeopteryx. In 1861, workers in a limestone quarry in Germany discovered the impression of a single 145-million-year-old feather. Hermann von Meyer, the paleontologist who first studied, almost thought it was a forgery, until he compared the impressions of the feather on the upper and lower layers of limestone in which it was discovered. “No draughtsman could produce anything so real,” he declared.

Soon von Meyer was working on another fossil: the entire body of the animal that grew such feathers. It had some hallmarks of birds, such as feathered wings, but it also had more reptilian traits seen on no bird today, such as teeth and a long, bony tail. Von Meyer dubbed both fossils Archaeopteryx, meaning “ancient wing.” Darwin had just published the Origin of Species two years earlier, and he couldn’t ask for a better piece of evidence for evolution. “It is a grand case for me,” he confided to a friend.

For over a century Archaeopteryx stood as the crucial fossil for scientists wanting to understand how reptiles evolved into feathered flyers. But starting in the late 1900s, new fossils began to emerge, and, as I wrote in National Geographic in 2011, they revealed a gradual transformation of ground-running dinosaurs into birds.

Even with all the new company of feathered dinosaurs, Archaeopteryx still held an exceptional position in study of the origin of birds. It seemed to be the closest relative to living birds with an anatomy suited to flying, with traits such as long arms. In a very real sense, it was still the first bird.

Now Archaeopteryx is sinking back into the crowd of primitive birds and feathered dinosaurs. As Ed Yong has ably explained, a fresh wave of fossils are coming to light. They reinforce the argument that paleontologists have agreed on for a couple decades now: birds evolved from a lineage of dinosaurs called theropods. But it’s less clear now how exactly Archaeopteryx fits into that evolution. It might still be closely related to the ancestors of living birds, or there might be non-flying theropods that were more closely related. Combine this with the recent discoveries of heavily feathered dinosaurs–feathered down to their feet, in fact–and the possibility emerges that dinosaurs evolved into flyers more than once. We look up in the sky today and see the results of only one of those transitions.

Today comes a new study that gives Archaeopteryx a further push back into the crowd. A team of researchers at the American Museum of Natural History and the University of Texas have taken a look at Archaeopteryx‘s brain, and it’s pretty unexceptional.

Scientists have long known that the brains of living birds are quite exceptional. Compared to reptiles, birds have brains that are huge in proportion to their body. “Hyperinflated” is the word that scientists like to use to describe them.

Archaeopteryx brain reconstructed from a fossil. Colors mark brain regions: olfactory bulbs (orange), cerebrum (green), optic lobes (pink), cerebellum (blue) and brain stem (yellow). From Balanoff et al., Nature 2013

Archaeopteryx brain reconstructed from a fossil. Colors mark brain regions: olfactory bulbs (orange), cerebrum (green), optic lobes (pink), cerebellum (blue) and brain stem (yellow). From Balanoff et al., Nature 2013

When it first became clear that birds evolved from theropods, scientists took a look at dinosaur brains to trace this hyperinflation. They found that Archaeopteryx’s brain fell in between that of distantly related theropods, such as Tyrannosaurus rex, and living birds. What’s more, its structure resembled that of birds–at least compared to other dinosaurs. The visual centers were expanded, and the regions of the brain it used to process sound were big. Its brain was, it seemed, ready for flight.

With so many new bird-like dinosaur fossils to peruse, the American Museum team decided to make a more detailed comparison of brain cases from 28 species in total.

In this new study, Archaeopteryx no longer pops out. The researchers found, in fact, that several species of feathered dinosaurs, such as a troodontid called Zanabazar and an oviraptor called Conchoraptor, have brains that are bigger, relative to their body size, than Archaeopteryx.

The scientists also drilled down to look at the sizes of different regions of the brain and found that the only bird-like brain region in Archaeopteryx is the olfactory bulb, which it uses for smelling. But some other dinosaurs have bulbs that are just as big.

 A 3D rendering from CT scans of the troodontid dinosaur Zanabazar junior. In this image the endocast (brain) is rendered opaque and the skull transparent.  Amy Balanoff, AMNH

A 3D rendering from CT scans of the troodontid dinosaur Zanabazar junior. In this image the endocast (brain) is rendered opaque and the skull transparent.
Amy Balanoff, AMNH

It’s possible that the common ancestor of Archaeopteryx and other close relatives of birds had already evolved a more bird-like brain than other dinosaurs. It’s also possible that the different lineages of dinosaurs that were closely related to birds evolved even bigger brains in parallel. If a bird-like brain was essential for the mental challenge of flying through the air, then these other dinosaurs had what it took for flight. It will be up to future paleontologists and ornithologists to figure out how flight shapes the brain, and how well other feathered dinosaurs could fly. But Archeopteryx will only be one among many species that they consider when they tackle those questions.

[Update 7/31 2 pm: I fixed the etymology of Archaeopteryx, thanks to a commenter.]

There are 16 Comments. Add Yours.

  1. DB
    July 31, 2013

    “Archaeopteryx” doesn’t mean “first bird”: It means “ancient, primitive winged one.” It’s _reputation_ has been that it’s the first bird.

    [CZ: Thanks for pointing that out. I've corrected the piece accordingly.]

  2. Paul Braterman
    July 31, 2013

    How long, I wonder, until the DI quote-mines your heading?

  3. David Peters
    July 31, 2013

    Perhaps not such a good flyer. Good flyers came later, along with a bigger brain to handle flying and a larger sternum to anchor flight muscles. Archaeopteryx is still a grand transitional fossil, illuminating the changes and their order of appearance.

  4. DN
    July 31, 2013

    Apologies, but I had to point out that you spelt “lineages” as “linages”.

    [CZ: Thanks!]

  5. iconoclast2013
    August 1, 2013

    Perhaps paleontologists have been thinking about dinosaur/bird evolution backwards. Could it be that small bird-like theropods were actually the earliest dinosaurs, and all of the later forms (including large four-legged dinosaurs) evolved from them? If that were the case, one would expect vestigial bird organs/characteristics in some of the later/transitional species of theropods.

    I have often wondered whether the small arms of the Tyrannosaurs are a vestigial reminder of their evolution from winged theropods.

    [CZ: That's not supported by the evidence. There are a number of traits shared by Tyrannosaurus and birds that are not shared by more distantly related dinosaurs. And there are still more traits shared by birds and closer relatives, like Velociraptor. You can draw a series of concentric circles around birds based on the evolution of those traits. You wouldn't expect that if the first dinosaurs were feathered theropods.]

  6. Bob Montgomerie
    August 2, 2013

    A couple of small details about Archaeopteryx worth noting. First, that first skeleton that Von Meyer saw was a sketch of a skeleton that did not have a head so he could not have known that it had teeth. The first specimen with a head was not found until 1874/75. Second, it was really Richard Owen who did the first detailed study of that first skeleton, though he did make several key errors that were soon corrected by Thomas Henry Huxley.

  7. maxwello
    August 3, 2013

    Even if it becomes established that the Archaeopteryx is less exceptional link in the evolution of avian biology, it is still of monumental importance in the history of the human understanding. Whether or not it was the first true bird is an inconsequential point. It’s discovery provided the convincing argument for the evolution of dinosaurs into birds that has become the dominant theory.

    Evolution is constant, and therefore, no two generations are likely to be exactly the same. There are almost always minor mutations that either give an animal an edge or not. Selection occurs based on the environment in which it lives. The cutoffs we make defining exemplars of species are arbitrary, lalrgely based on the order in which we happen to dig up examples.

  8. lkr
    August 3, 2013

    As I recall, the solnhofen fauna was in a tropical archipelago of smallish islands… Any likelihood that brains would be down-sized in a “less competitive” environment [vs. mainland forms]?

  9. Jack Kalpakian
    August 3, 2013

    This is a story for the sake of creating a story. Archaeopteryx established the bird-theropod link, the other fossils will provide the fuller picture of the basic picture that Archaeopteryx helped us see. As time goes on, the line between theropod and bird will blur to nothing.

  10. tshenolo
    August 4, 2013

    i want to know what process formed the archaeopteryx fossil.

  11. Dan
    August 4, 2013

    I’m curious what was the initial evolutionary advantage that feathers gave early theropods? If modern bird behavior is any indication they could have played a role in species identification and sexual selection. But as with flight, it is quite possible that these behavioral adaptations came later and that feathers gave these theoropods another distinct survival advantage. What then was the purpose of the initial adaptation?

    [CZ: Sexual selection can be quite strong, and produce big anatomical traits (think horns).]

  12. Vaishnavi
    August 6, 2013

    Could the title BE more apt?!

  13. Wabisabi
    August 7, 2013

    Feathers, like fur, hold in heat. Perhaps they were an adaptation to climate change. When does fossil evidence show the first fur or hair? On what kind of animal? Feathers are very complex structures compared to hair.

  14. HugoHugo
    September 24, 2013

    The claim to the title ‘first bird’ probably comes from the German name for Archaeopteryx: ‘Urvogel,’ which means ‘Original bird.’

    Also, I love the Archaeopteryx tattoo over there on the right. I’ve been thinking about one myself!

  15. Refilwe
    September 27, 2013

    What processes realy formed the archaeopteryx

  16. thuto
    October 14, 2013

    What process formed archaeopteyx

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