Courtesy Mark RyanChina has been producing some remarkable and groundbreaking dinosaur fossils in recent years that have caused paleontologists to reconsider long-held views. A recently described feathered dinosaur is no different. Xiaotingia zhengi, discovered in the Jurassic shales of the Liaoning Province, has been in the news lately because it supposedly knocked the well-known, so-called proto-bird Archaeopteryx from its perch as the earliest bird.
The study by paleontologist Xu Xing and his colleagues from the Chinese Academy of Sciences in Beijing appears in Nature. Their research, it seems, has determined that Xiaotingia and Archaeopteryx share many features that make the two of them more bird-like dinosaurs than dinosaur-like birds. Do you see the difference there? I guess I do. Anyway, essentially what it means is that Archaeopteryx has been pushed back a little and is just a bit more distantly related to birds than previously thought. The classification places both Xiaotingia and Archaeopteryx in with avian-like carnivorous dinosaurs such as deinonychosaurs, dromaeosaurids, and troodontids. The recent spate of fossils coming out of China can’t help but alter some our old views of the middle to late Jurassic fauna. Many dinosaurs (including non-avian ones) living during that time were equipped with bird-like features: e. g. long arms, feathers, wishbones, etc. They were all over the place.
But all you diehards out there in the Archaeopteryx-is-a-bird camp need not despair just yet. Dr. Xu himself admits that some of the conclusions in the study are based on pretty weak evidence. Archaeopteryx continues to rank as an exceptional transitional fossil (along with Xiaotingia). Its place in the transition has just shifted slightly, that’s all. Further studies and new fossils will no-doubt shake up the branches of the avian family tree again.
Courtesy Mark RyanThis 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.
Courtesy Ron Blakey, NAU GeologySo 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.
Courtesy Federal Republic of GermanySolnhofen’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
Courtesy Mark RyanWhen the first Archaeopteryx skeleton came to light in 1861 just two years after the publication of Charles Darwin’s On the Origin of Species, it was hailed as not only the earliest known bird but also as proof of evolution. The rare specimen (known as the London specimen) appeared to be somewhat of a chimera of both dinosaurian and bird features. Thomas Huxley, a fierce proponent of Darwin’s work, even suggested that birds were the descendents of small meat-eating dinosaurs. It took more than a century for the idea to become widely accepted. Today most paleontologists divide dinosaurs into two groups: avian dinosaurs (birds) and non-avian dinosaurs, the branch that died out at the end of the Cretaceous.
"For a long time, Archaeopteryx was considered the archetypical bird primarily because it had feathers, although it retained typical dinosaur features like a long tail and teeth,” said Mark Norell, Chair of the Division of Paleontology at the American Museum of Natural History. “But the discovery of classical bird features like feathers and wishbones have recently been found in many non-avian dinosaurs blurring the line of what constitutes a bird."
Now, a new study by Norell and co-author Gregory Erickson, a vertebrate paleontologist at Florida State University, shows that 150 million year-old Archaeopteryx (Greek for “ancient wing”) may have been much more like a non-avian dinosaur than a bird (avian dinosaur), at least in its bone structure and growth rate.
"Dinosaurs had a very different metabolism from today's birds,” Erickson said. “It would take years for individuals to mature, and we found evidence for this same pattern in Archaeopteryx and its closest relatives.”
For their research, the team removed tiny, 250-micron slivers of bone from the remains of several Archaeopteryx fossils, and from the bones of primitive but younger bird fossils (Jeholornis prima and Sapeornis chaochengensi, and Confuciornis sanctus) found recently in China. They also examined the bone structure of closely related non-avian dinosaurs such as Velociraptor mongoliensis.
Those samples from the Archaeopteryxes showed high bone-density, annual growth lines (a reptilian trait), and very small blood vessels similar to the bones sampled from the non-avian dinosaurs. The location of bone cells also appeared flattened and parallel – more like that of a velociraptor – and much different from the hollow, vascularized (i.e. filled with blood vessels), rapid growing bones found in younger-aged bird fossils, and most birds today. (Flightless birds such as ostriches and penguins have solid bones.)
"Although the genealogy of birds is well understood, the genesis of modern bird biology has been a huge mystery,” Norell said. “We knew that they are a kind of dinosaur, but we now know that the transition into true birds—physiologically and metabolically—happened well after Archaeopteryx."
What this implies is that Archaeopteryx was more of a dinosaur than it was a bird – at least in its metabolism and how fast it matured – and that the traits considered necessary for flight – such as light, hollow bone structure – evolved from a dinosaur body-plan sometime after Archaeopteryx.
"We show that avian flight was achieved with the physiology of a dinosaur," Erickson said.
The study can be found in a recent edition of the online journal PLoS ONE.
Courtesy Mark RyanRecently discovered fossils out of China add strong evidence to the theory that birds descended from dinosaurs. The fossil remains of a new feathered dinosaur, named Anchiornis huxleyi, were discovered in rock strata thought to be at least 10 million years older than that at Solnhofen, Germany. This is exciting news. Since the 19th century the quarries at Solnhofen have produced several skeletons of the feathered Archaeopteryx which has long been considered the first bird. But now it appears that feathers arose several millions of years before Archaeopteryx showed up in the fossil record. Professor Xu Xing of Chinese Academy of Science in Beijing reported his findings in the science journal Nature, and at the Society of Vertebrate Paleontology's annual convention being held this week at the University of Bristol in England.
What makes this fossil so special is that it is one of only ten described Archaeopteryx specimens in the entire world, and second only to the Berlin specimen in preservation. It’s also the only one that can be seen on this side of the Atlantic.
My brother and I happened to be in Wyoming on one of our annual geological excursions last week, so we made it part of our itinerary to head up to see this rare and unusual fossil. Thermopolis is located at the north end of the Wind River canyon about 220 miles from Yellowstone National Park. It’s not the most accessible site, but the drive offered both beautiful scenery and spectacular geology.
The magpie-sized Archaeopteryx (its name means “ancient wing”) is housed in the Wyoming Dinosaur Center, a privately owned museum containing an impressive array of fossils and mounted dinosaurs, including many found in right in the Thermopolis area. As you’d expect, a number of the skeletons on display are enormous, including a Tyrannosaurus rex, the bullish Triceratops, and a full-sized Supersaurus spanning an amazing 106 feet in length. But the new star of the show is the tiny, feathered dinosaur-bird preserved in about a foot-square slab of limestone from the famed Solnhofen limestone quarry in Bavaria, Germany. And let me tell you, it is truly something special to behold.
Since the discovery of the first Archaeopteryx back in 1861, the creature has long been considered as strong evidence of an evolutionary link between birds and dinosaurs, and the Thermopolis specimen adds greatly to that argument. Feathered impressions of its bird-like wings and long tail are clearly visible in the fossil, but so are ankles and foot bones that are nearly identical to those of velociraptors and other meat-eating therapod dinosaurs. The fossil shows the Archaeopteryx had a hyper-extendable second toe that could be raised off the ground perhaps for slashing or walking purposes, and a first toe (hallux) that isn’t reversed as it is in modern perching birds. The latter leads scientists to think that the protobird may not have spent much time in the trees when it was alive during the Late Jurassic period 150 million years ago. The fossil was described by Gerald Mayr, et al in the December 2005 issue of Science .
You might wonder how such a world-class fossil ended up in a tiny town in the middle of Wyoming. Well, when a private collector put the specimen up for sale a few years ago, a museum in Germany tried to purchase it but couldn’t come up with the funds. But then an anonymous donor came forward and purchased it for display at the Wyoming Dinosaur Center, with the understanding that it would be accessible to scientists and the public. That’s lucky for us.
Until now Thermopolis’s main claim to fame were the hot springs that percolate into the town from the nearby Owl Creek Mountains. But that’s all changed now that this very special fossil has come there to roost.
LINKS and MORE INFO
Wyoming Dinosaur Center
Description in the Zoological Journal of the Linnean Society
Article in the Casper Star-Tribune
Reproductions of Archaeopteryx by WDC’s Scott Hartman
Controversy about the Thermopolis specimen
One of the ongoing debates in science is: where the heck did birds come from? Bird bones are fragile and don't often become fossils, so there's not a lot of evidence. And when a new bird fossil is found, there's always a lot of debate over how it fits into the puzzle.