DINOS OF A FEATHER: The slab from which a tiny chip of the Munich Archaeopteryx was sampled to glimpse at how the 150-million-year-old creature grew
Image: MICK ELLISON/AMNH
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Just as Charles Darwin was proposing his radical theory of evolution, paleontologists discovered a curious fossil specimen in modern-day Germany: Archaeopteryx. The feathered specimen, pegged by many as the first bird, helped provide further evidence for the theory of evolution and the idea that modern birds evolved from dinosaurs.
Archaeopteryx's status as the first prehistoric bird has held for more than a century, but a new high-tech analysis of a rare sample of bones from a German specimen challenge that long-held presumption. It turns out that the 150-million-year-old Archaeopteryx appears to have matured to adulthood slowly, more like a dinosaur than a bird, pushing the appearance of more modern bird characteristics forward to the more recent past.
"Our research shows us that this is much more like a dinosaur than a modern bird," says Gregory Erickson of the Department of Biological Science at Florida State University in Tallahassee, and a lead author on the new report, which was published online yesterday in the journal PLoS ONE. By looking at the growth patterns in bone, Erickson and his colleagues were able to discover that Archaeopteryx had a slow and stilted growing period like other dinosaurs, and unlike modern birds, which "just explode into adult size," he explains.
The new data were obtained by studying tiny, 250-micron-long chips from the fossilized leg bones of Archaeopteryx and more than a dozen other species of birds and dinosaurs using polarizing microscopy. The researchers found features in Archaeopteryx's bones, including annual growth lines, small blood vessels and parallel bone cells, shared by other similar-size dinosaurs, such as the Jeholornis prima. Fragments from a more birdlike animal, the Ichthyornis dispar, which lived about 94 million years ago, revealed no annual growth lines, substantial vasculature and a more random distribution of bone cells—all characteristic of quick growth.
Researchers now estimate that Archaeopteryx would have taken a little more than two and a half years to mature—compared with just a few months for modern birds of similar size. The findings confirm the previous assumption that all 10 known Archaeopteryx specimens are, in fact, juveniles. The news also bumps the estimated size of an adult Archaeopteryx up to about the size of a raven, larger than had previously been estimated.
Despite the general similarities to modern birds—feathers, a beak and a wishbone—that led to its avian categorization in the first place, the Archaeopteryx "would be very foreign to bird-watchers today," Erickson says.
The distinction, however, that many casual observers have drawn between non-avian dinosaurs and modern birds is perhaps an exaggerated one. As Erickson points out, "We know that birds are dinosaurs," that is, even modern birds belong to the same lineage as dinosaurs. "Everybody would agree now that birds are really a kind of dinosaur, just like humans are a kind of primate," adds Mark Norell, chair of the Division of Paleontology at the American Museum of Natural History in New York City. Modern birds—or avian dinosaurs—share a different set of traits, such as hollow bones and rapid growth, than those exhibited by their prehistoric predecessors.
Research published by one of the co-authors (Dongyu Hu, of the Paleontological Institute at Shenyang Normal University in China) last month in Nature also moved a once-supposed avian species more firmly back into the dinosaur clan. (Scientific American is part of the Nature Publishing Group.) The well-feathered, 155-million-year-old Anchiornis huxleyi was shown to share more skeletal similarities with bona fide dinosaurs, despite its heavy plumage.
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6 Comments
Add CommentI believe all animals came from dinosaurs, somehow. There were primates, dinosaurs...was there another broader category? If birds and fish fall under dinosaurs, what else would there be? Where did the insects come from, or the bears?
Reply | Report Abuse | Link to thisAm I the only one that finds this a bit confusing?
fish shouldn't fall under dinosaurs, there were 'fish' long before the dinosaurs, after all the 'fish' had to leave the water to become land dwellers. i'm using inverted commas, because although they lived in the water and had backbones doesnt mean that they were necessarily fish, they may have not passed on their genes. mammals descended from the 'mammal-like reptiles' or synapsids who are the dinosaurs before real dinosaurs, animals like dimetrodon...they lived (mainly) until the end of the permian period, when an extinction event occured, allowing the sauropods to usurp their ecological niches. these sauropods are the true dinosaurs, and lived at a time when mammals were generally small creatures, and with the K-T extinction were then able to flourish into the niches left vacant. birds evolved from small dinosaurs, as is evident by similarities like hollow bones and the way that a bird's joints move. the ancestors of insects were among the first to leave the seas, and at a time when there was more oxygen in the air could grow larger (due to insects being able to 'breathe' through there chitin). bears come from the 'rat-like' mammals, who in turn come from synapsids, who came from amphibious creatures who came from fish-like creatures who evolved from insect like creatures who evolved from simple multi celled creatures (like sponges) who are in turn really just a colony of independant single celled organisms. as an interesting aside, the mitochondria (which allow us to convert oxygen (a poison) to energy) were a very early organism, who merged with other single celled organisms creating multi-cellular amoeba-ish things, which are still alive today. we call them 'cells'
Reply | Report Abuse | Link to thisPetriDishFan-
Reply | Report Abuse | Link to thisYou might want to take a look a look at Wikipedia. Depending on the classification system used, living things can be classified into three big groups: Archaea, Prokaryota, and Eukaryota. This Wikipedia chart might be of interest:
http://en.wikipedia.org/wiki/File:Tree_of_life_SVG.svg
The evolution of eukaryotes (with compartmentalized cells like plants, animals, fungi, and protozoans) is covered in detail on this phylogenetic tree:
http://tolweb.org/tree/
http://tellapallet.com/tree_of_life.htm
Dinosaurs, bears, and primates are branches from the category called tetrapods (four-limbed animals). Insects, spiders, and shrimp are branches from the category called arthropods (animals with a many-jointed shell).
Hey Stewie, pass me some of what you're smokin'
Reply | Report Abuse | Link to thisState of evolution that can be tested. We think, since the theory of evolution by Jean Lamarck (1809,) that milestones have to be used to put order in all the bones collected. The one presented for Archaeopteryx is of first importance in biology. If we prefer real treasures called missing lings , like the remains of Lucy, it is because they unveiled some complete organisms. For Lucy all Australopithecines, the genus that has preceded Homo, were concerned. Concerning bone histology, all vertebrates are involved. At last, the two forms of discoveries are of first importance to the understanding of our condition. Pierre Francois Puech
Reply | Report Abuse | Link to thisThe best and most readable book on this subject is The Ancestor's Tale by Richard Dawkins
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