Feb
25
2011

Archaeopteryx: Thermopolis specimen.
Archaeopteryx: Thermopolis specimen.Courtesy Mark Ryan
This year marks the 150th anniversary of the announced discovery of the first fossils of Archaeopteryx, a remarkable chimera of both bird and reptile traits. The first evidence identified was a single feather discovered at a limestone quarry in Solnhofen, Germany. This was in 1860. The German paleontologist Hermann von Meyer described the fossil in 1861, naming it Archaeopteryx lithographica. That same year, the first skeletal remains came to light, and although headless, the London specimen, as it became known, showed clearly both avian and reptilian characteristics.

The unique and iconic fossil appeared just two years after publication of Charles Darwin’s On the Origin of Species and helped bolster the naturalist’s theory of evolution through natural selection because its appeared to be a transitional fossil between reptile (dinosaur) and bird. Could Darwin have asked for any better evidence?

Since then nine other specimens have been found, including the Berlin specimen around 1877, which is considered one of most complete. For many years some Archaeopteryx specimens languished in collection drawers because they had been initially misidentified as another creature entirely. In 1970, Yale paleontologist John Ostrom was investigating a so-called pteradactyl fossil at a museum in the Netherlands, when he realized it had been misidentified and was actually an Archaeopteryx. The fossil had been found at Solhofen in 1855, five years prior to the feather! The museum curator was so shaken by Ostrom’s announcement, he clumsily wrapped the specimen in a paper bag and presented it to Ostrom so he could take it back to Yale for further study. Ostrom, by the way, re-ignited the “birds are dinosaurs” debate in the 1960s after his discovery of Deinonychus and his comparison of its structural features with those of birds.

The Thermopolis specimen, the latest Archaeopteryx fossil, became known around 2005 and was donated anonymously to the Wyoming Dinosaur Center in Thermopolis, Wyoming. I happened to visit the museum in June of 2007 during the first week the fossil went on public display, and was able to see the spectacular specimen firsthand. The small fossil (about 1.5 feet square) was displayed behind a small, glass opening in the wall. There was no crowd to speak of so I was able to take in and photograph the fossil for a long stretch of time by myself. Looking at it, your eye is immediately drawn to the distinct feather impressions evident on both its wings and tail. The head, arms, and legs are spread out across the slab, and even though it died 150 million years ago, it looks as flat and fresh as road kill on a modern highway.

About the size of a large crow, Archaeopteryx was an odd amalgam of both bird and reptile. It had slightly asymmetrical flight feathers, wings, and a furcula (wishbone) - all traits found in birds. But its pelvis, skull and sharp teeth were reptilian (although some skull features are bird-like), and it ha a long tail like a reptile. Its bones weren’t hollow, like the bones of modern birds are, nor is its sternum (breastbone) very pronounced; it’s flatter and without a large keel where, in birds, muscles flight are attached. And it also possesses gastralia (“belly ribs”), a feature found in reptiles and dinosaurs. The inner toe (the hallux) in the Thermopolis specimen doesn’t appear to be reversed so it couldn't grasp or perch and was probably more earth-bound than arboreal. Interestingly, its second toe was extensible – meaning it could be pulled back and elevated for tearing into flesh, just like the middle toes of such dinosaurs as Troodon and Velociraptor. Truth be told, if its feathers hadn’t been preserved, Archaeopteryx would have been classified a carnivorous bipedal dinosaur. In fact, one of the existing Archaeopteryx fossil was first identified as a Compsognathus until preparation revealed its feathers.

Solnhofen and much of Europe in the Late Jurassic: A cluster of islands off the coast of the North American continent.
Solnhofen and much of Europe in the Late Jurassic: A cluster of islands off the coast of the North American continent.Courtesy Ron Blakey, NAU Geology
So what kind of environment did Archaeopteryx live in, and why are its fossils so well preserved? Well, during the Late Jurassic, southern Germany and much of the rest of Europe were pretty much a group of large islands poking out of the Tethys Sea off the coast of North America. What is today the Solnhofen quarry was then part of an island lagoon protected by a barrier reef. Geological evidence in the strata suggests the lagoon dried up several times followed by periods of re-flooding with seawater. Mixed into a brackish soup of coral debris and mud, and in a warm climate conducive to rapid evaporation, the lagoon’s bottom water levels became anoxic, that is depleted of oxygen. Low oxygen meant less bacterial activity and subsequently slow decomposition of any organism that happened to die or get swept into the stagnant lagoon. Burial in the carbonate muck was swift, leaving fresh carcasses no time to be pulled apart by currents or scavengers.

Solnhofen limestone has been used for centuries as a building stone. Because the rock’s matrix is so fine and splits so evenly (sediment deposition likely occurred in very calm waters), the material was later quarried to produce stones for lithography, a printing technique first developed in 1796, and the source of Archaeoperyx’s species designation. Many early scientific illustrations, including some of the first images ofArchaeopteryx were preserved as lithographs created using Solnhofen limestone.

Archaeopteryx commorative coin: Germany will issue the 10 Euro coin in the summer of 2011
Archaeopteryx commorative coin: Germany will issue the 10 Euro coin in the summer of 2011Courtesy Federal Republic of Germany
Solnhofen’s fossil record shows that the lagoon’s biological population was diverse. Fish, turtles, lizards and insects, crocodiles, crustaceans, ammonites, squid and starfish, mollusks, pterosaurs, and even the soft remains of jellyfish are preserved in the fine-grained limestone. But the premiere creature is of course the Archaeopteryx, which remains the earliest bird (or most bird-like dinosaur, if you will) known to date. As research on existing specimens continues and new fossils appear it's exciting to imagine what advances will take place in the dinosaur-bird connection debate. Whatever happens, Archaeopteryx lithographica will remain one of the most significant and iconic fossils ever discovered. It's no wonder that later this year on August 11th, the Federal Republic of Germany will issue a 10 Euro silver coin to commemorate the 150th anniversary of the discovery of its most famous fossil.

SOURCES and LINKS

Witmer Lab Archaeopteryx blog
UCMP Archaeopteryx page
Solnhofen limestone of the Jurassic

Your Comments, Thoughts, Questions, Ideas

allan2's picture
allan2 says:

It is important that people have found so well preserved fossils.

posted on Mon, 02/28/2011 - 12:30am
Anonymous's picture
Anonymous says:

we never landed on the moon
lance armstrong is a liar

posted on Sat, 03/05/2011 - 2:35pm
Anonymous's picture
Anonymous says:

it was neil on the moon lance is the biker dude

posted on Sat, 03/05/2011 - 5:25pm

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