I’ve been thinking a lot about Archaeopteryx lately, fueled partly by my 3-year-old son’s total obsession with all things dinosaur and partly by a months-old discussion about Randy Olson’s new movie Flock of Dodos on The Loom. One part of the discussion revolved around how to clearly explain the physical evidence supporting evolution to laypeople. And that started me thinking about Archaeopteryx, because it’s not just the earliest known bird – it’s been the quintessential transitional fossil for more than 150 years.
The first relatively complete Archaeopteryx was discovered in 1861, two years after Darwin published On the Origin of Species. It was immediately controversial. Richard Owen, already famous for describing a new group of extinct reptiles called dinosaurs, called Archaeopteryx a bird, pointing to its wishbone, bird-like shoulder and arm, and the feather impressions that surrounded it. Evolutionists like Thomas Huxley pointed to the fossil’s long tail and clawed hands as evidence that it was actually a transitional form – a reptile in the process of becoming a bird. Huxley went so far as to name the group of reptiles he thought Archaeopteryx had descended from – Owen’s own Dinosauria.
Archaeopteryx has been a subject of debate ever since. What were its closest relatives? Are birds really dinosaurs? It was hard to really answer these questions when there was only Archaeopteryx fossils to work with. But new discoveries have been filling in the gaps. Paleontologists have found bird fossils only 30 or 40 million years younger than Archaeopteryx with arms, tails, and feathers that are even more like modern birds. They’ve found fossils of theropod dinosaurs with primitive feathers, indicating that feathers aren’t unique to birds – they’re a feature of some dinosaurs that were co-opted for flight by their descendants.
And what about Archaeopteryx itself? Recent studies have shown that the hoary old bird is a real gimish of dinosaurian and birdlike characteristics. A three-dimensional model of the surface of its brain derived from a high-resolution x-ray scan of its skull (published in Science in 2004) shows that it had large optic lobes and enlarged semicircular canals in its inner ear, more like a bird than like a theropod. But a new specimen described in Nature in late 2005 had a foot that was far more like a small dromeosaur than like a modern bird, including a tiny version of the “killing claw” found in Deinonychus and Velociraptor.
So Archaeopteryx is a snapshot from a evolving lineage, a species that retained “old-style” theropod hands, feet, tail, and body feathers along with the modified wing feathers and brain that let it fly like a bird. And maybe it should be used to make the point that evolution is the reason every organism has both old and new characteristics. Humans have had huge brains for only a couple of million years. We’ve still got the same four limbs as our fishy ancestors.