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The Origin of Birds By: Shannon B. Carpenter The earliest known fossils, which were identified to be a type of bird, link their ancestry to reptiles, or small dinosaurs of the Triassic period. The fossilized birds from the Triassic/Jurassic Period have many characteristics in their skeletal structure that could suggest their derivation from reptiles; even living birds still show several similarities in skeletal makeup that can only otherwise be seen in long extinct reptiles. The Archaeopteryx, which means “ancient winged creature”, is the earliest fossil bird known. The first fossil of Archaeopteryx was discovered in 160 million year old limestone rocks of Southern Bavaria. There are many problems associated with the classification of Archaeopteryx as being a bird as this creature has traits typical of both dinosaurs and birds. Also discovered recently were a number of Chinese fossils of the same type of feathered dinosaurs; animals with down-covered bodies, strong legs, and stubby arms. These winged creatures are examples of some of the strongest evidence yet that birds evolved from dinosaurs. The Confuciornis, Protoarchaeopteryx, and the Caudipteryx were three species of these feathered dinosaurs that lived in the middle to late Jurassic Period of China. There is a difference in opinion as to whether the Archaeopteryx should be classified as a bird or a dinosaur. Sir Richard Owen of the British Museum of Natural History first declared that Archaeopteryx was a bird based on the presence of feathers and a specialized collarbone, found only in modern birds, called a furcula. Without its feathers, Archaeopteryx looks almost exactly like a small coelurosaur. In fact, one specimen of Archaeopteryx was misidentified as a coelurosaur for over 100 years until it’s feathers were noticed by pterosaur expert, Dr. Peter Wellnhofer. The Archaeopteryx was a land “bird” of limited flying powers (seen in the picture to the right). Researchers have calculated that Archaeopteryx could almost quadruple its running speed with thrust from flapping its wings. This “bird” was about the size of a raven, with a very compact skull structure. The skull has a large preorbital, narial and temporal fossae and a post temporal bar separating the orbit and temporal fossa. The Archaeopteryx also had short cylindrical teeth in both its upper and lower jaws. The compact skull structure and short cylindrical teeth are both characteristics of many fossil reptiles discovered from this time period, not of modern birds. Some other features that this creature had that were reptilian like were a long bony tail, claws on both its feet and on its feathered fore-limbs, and it’s bones were solid not hollow, making it seem even more like todays modern birds. The orbit of the Archaeopteryx’s skull has a ring of sclerotic plates. This skull is an intermediate form between that of Pseudosuchian reptiles and that of flying birds like the Pigeon. The brain, which has been reconstructed by many geologists, has been found to be similar in shape to that of reptiles, but different from that of all other known birds. The vertebrae of the Archaeopteryx have distinct reptilian traits. “ The vertebrae are certainty reptilian in structure for they are flat or slightly bioconcave on their articular ends and nowhere exhibit the saddle-shaped articulations found in other birds whether fossil or present.” (Swinton, Pg.21) The pectoral girdle is only one-third the length of the scapula, proving that the pectoral muscles were short and gave the creature poor flight capabilities. This creature is similar to modern birds because it has a “cupped-shaped joint between the coracoid and the scapula also houses the end of the clavicle, whose other end is joined distally to its fellow, the whole structure being known as the furcula (Latin for a ‘forked prop’) but more familiarly and generally called ‘the merrythought’ or wish-bone…” (Swinton, Pg. 22) The trait that stands out the most as being “bird-like” is the fact that the Archaeopteryx had distinct feathers, typical also to modern birds. These feathers can clearly be seen in the picture to the right. It is still unknown as to whether they were used for regulating its body temperature or for flight (because of the short pectoral muscles of this creature, the feathers were possibly used to glide not for flight). Feathers may have originally been intended for insulation, but as the creature evolved, become a more important device for it’s flight capabilities. Two models of the evolution of flight have been proposed. In the "trees-down" model, birds evolved from ancestors that lived in trees and could glide down, analogous to today's flying squirrels. In the "ground-up" model, the ancestors of birds lived on the ground and made long leaps. It is now believed that the Archaeopteryx more than likely fed on insects and other small animals. Most insects of the time could be found on plants, especially shrubs, and very few were found on the bare ground. While foraging there, the Archaeopteryx had to climb about on the branches and had to leap or fly from one bush to another. “In this activity it might have been used the claws of its forelimb for clinging to branches and its apposable hallux for perching.” (Hecht and Ostrom, Pg.42) Also, the Archaeopteryx probably fed on small animals that lived close to the shore (such as, worms, crayfish, and fishes) and climbed on the cliffs where it might have had its nesting-places. “The stimulus for flight was the new supply of insect food; in order to catch such food there would need to be a lengthening in the jaws, and with such feeding habits there could be associated that loss of teeth (no longer needed) and the slightly different means of jaw movement leading to snapping ability. These are precisely the changes that took place in the step from reptilian skull to the Archaeopteryx head and jaws.” (Swinton, 28) In the Liaoning province in northeast China, a number of feathered dinosaurs have recently been discovered (June of 1998) that date back more than 140 million years ago. Two species found here were the Caudipteryx and the Protoarchaeopteryx. Both animals closely resemble meat-eating dinosaurs called theropods. “The analysis showed that neither Caudipteryx nor Protarchaeopteryx was a true bird, but that both were dinosaurs that were very closely related to birds - indeed, Caudipteryx was determined to be one of the dinosaurs most closely related to true birds. Protarchaeopteryx (see below for diagram) was found to be more primitive, and may be a close relative to the Velociraptorinae, a group of dinosaurs that takes its name from its most famous member, Velociraptor…” (Chapman, web) Both of the creatures were fast runners and were probably unable to fly, judging from their short arms and long legs. Their feathers may have been for insulation or display, similar to the Archeopteryx. The Protoarchaeopteryx, which was about the size of a modern-day turkey, is the more primitive and earlier of the two fossils. There were feathers that covered its body but there is no fossilized evidence of wing feathers. The Caudipteryx, on the other hand, had more plumage, including and large tail fan. It stood about three feet tall. The Caudipteryx (see below for picture) had long, sharp teeth, which had deep, rounded roots. “These teeth were only in the front of the upper jaw, and pointed outward, giving it a bucktoothed look. (Enchanted Learning, web) When it was found, it had gizzard stones, gastroliths, in its gut that were used to grind up its food. Another feathered dinosaur that was found in the Liaoning province in northeast China was the Sinosauropteryx (see to the right for diagram). This creature dates back 125 million years ago. “It is early Cretaceous, its preservation is remarkable (despite the very crushed skull and scattered bones of the hands and feet). Soft tissue traces (including skin patches) and even the gut's contents are discernible.” (Neat School House, web) The most remarkable feature is that there seems to be a mane of hair-like or feather-like structures (downy feathers) that run all along the spine and tail. It was about 3 feet (1 m) long with 2mm long feathers and was bipedal, walking on two long legs. The longest featherfilaments were 1.5 inches long (3.8 cm). These filaments were probably used for heat insulation and were not used for flying. It had two short forelimbs, and many sharp teeth. It ate meat like other theropods, and probably preyed upon insects and small animals. It also had a very long tail, which had 64 vertebrate, the longest of any theropod. This tail was probably used for balance and for making quick turns. The feeding mode of the Sinosauropteryx was a meat-eater and it is the only dinosaur that has been found with a mammal in its stomach. (Only the jawbone of this unidentified mammal was found in the stomach of a Sinosauropteryx.) The most important thing about this finding is that the shoulder girdle of this dinosaur, allowed a wide range of up-and-down motion, like flapping. The shoulders of most dinosaurs enabled only more limited movement of the upper arms. “This is critical for the bird-kind of motion,” says Xiao-Chun Wu, a paleontologist at the University of Calgary in Alberta. “This anatomically shows this animal has the prerequisite for bird-type action of the forelimb.” Wu suggests the dinosaurs used the up-and-down motions to keep balance while running. (ABCNEWS, web) These findings show paleontologists that most likely, bird flight evolved from the ground up. “If feathers appeared first on ground-dwelling dinosaurs, then they must have originally served some purpose unrelated to flight. Some scientists speculate that down, like the Sinosauropteryx structures, evolved first and insulated the bodies of small theropods. Large plumes later may have served as a display for attracting mates.” (Science News, web) The existence of Protarchaeopteryx, Sinosauropteryx, and Caudipteryx lends scientists to believe that birds probably descended from theropod dinosaurs and not from four-legged tree-living reptiles. Some scientists do believe that these newfeathered fossils are from a time after that of the Archaeopteryx, which suggests that perhaps the fossils’ resemblance to birds could be a case of convergent evolution and that their feathers evolved for insulation, not flight, signifying a warm-blooded physiology. Two of the first birds to resemble today’s modern birds almost identically is the Ichthyornis (meaning "fish bird") and the Hesperornis. This creature was ternlike, that lived alongside dinosaurs like T. rex and the Triceratops. It lived in flocks, nested on shorelines, and hunted for fish in Cretaceous seas. Ichthyornis lived during the Cretaceous Period about 135-70 million years ago. Ichthyornis was about 8 inches (20 cm) long. It had a large head, toothed jaws, and a long beak. This powerful flyer is the oldest-known bird that had a keeled breastbone (sternum) similar to that of modern birds. The first Ichthyornis found was in 1872 in Kansas, USA, by a member of paleontologist Othniel C. Marsh's Yale University expedition. The Ichthyornis was named in Marsh of 1872. Similar fossils of this creature have also been found in Kansas and Texas, USA, and in Alberta, and Canada. More than a century ago, Yale paleontologist Othniel Charles Marsh (1880) clearly argued that three Mesozoic taxa, Archaeopteryx, Hesperornis, and Ichthyornis, differ so widely from one another that the evolution of birds must have taken place at a much earlier time, perhaps at the end of the Triassic. He predicted that Triassic birds with a freely movable quadrate bone would be found to fill the major morphological and evolutionary gaps in avian history. The Hespernis lived about 70 million years ago at the end of the age of dinosaurs. This creature had a long pointed bill, which contained teeth, like that of the Ichthyornis. From the tip of its beak to the end of its tail, the bird was about 1.8 meters long. The Hespernis (see right for diagram) had strong legs, which were adapted for swimming, but its forelimbs were only composed of small, nonfunctional wings. The best fossils of this creature come form the shallow seas that in Cretaceous times covered the region that is now Kansas. Hesperornis, Ichthyornis, and other Cretaceous diving birds, all had skeletons that were modified for flight, which includes fused pelvis bones, fused hand bones and a short, fused tail. These birds are greatly similar to modern day birds in physical appearance however, one characteristic that seems to remain from their reptilian ancestors is the fact that they still have true socketed teeth. There are many conjectures as to the origin of birds and their role in the development of today’s modern birds. No one knows for sure whether or not the Archaeopteryx is a direct ancestor of today’s living birds but there is a large amount of evidence, which suggests this may be true. Specific birds such as the Hesperornis, and Ichthyornis both are almost exact replicas of today’s birds with the exception that both have teeth. This is the last step in the evolutionary process that separates present day birds from latter day reptiles. Bibliography 1. M. K. Hecht, J.H. Ostrom, G. Viohl, & P.Wellnhofer (eds) 1985, The Beginnings of Birds: Proceedings of the International Archaeopteryx Conference, Eichstatt, Willibaldsburg. 2. Heilmann, G. 1927, Origin of Birds, D. Appleton and Company, New York. 3. Hoyle, F. & Wickramasinghe, C. 1986, Archaeopteryx THE PRIMORDIAL BIRD: A Case of Fossil Forgery, Christopher Davies Ltd., Swansea. 4. Swinton, W.E. 1965, Fossil Birds, Trustees of the British Museum (Natural History), London. 5. Chang, K. 1999, ABC News: Relating Dinos and Birds Available at: http://abcnews.go.com/sections/science/DailyNews/dinofeathers 990916.html 6. Enchanted Learning: Caudipteryx zoui Available at: http://www.enchantedlearning.com/subjects/dinosaurs/dinos/ Caudipteryx.shtml 7. Altman K. 1998, CNN News: Scientists: Fossils prove that birds evolved from dinosaurs Available at: http://cnn.com/TECH/science/9806/23/feathered.dinosaur /index.html 8. Goldman D. 2000, Dinosaur Illustrations Available at: http://www.geocities.com/CapeCanaveral/6930/a2d.htm 9. CNN, 1998, Researchers: Dinosaurs didn't die -- they flew away Available at: http://cnn.com/SPECIALS/1998/year.review/sci_tech/07.fossils.birds.dinos/ 10. Creation Science Facts, The Case of the Archaeopteryx-1 Available at: http://www.pathlights.com/ce_encyclopedia/20hist08.htm#Introduction 11. Nedin, C. 1999, All About Archaeopteryx Available at: http://www.talkorigins.org/faqs/archaeopteryx/info.html#conclusions 12. Chapman, E. 1998, International Research Team Announces Discovery Of Two Species Of Feathered Dinosaurs: Discovery Strengthens Evolutionary Link Between Birds And Dinosaurs Available at: http://www.eurekalert.org/releases/amnh-feadino.html 13. Moffet, B. 1998, National Geographic: Feathered Creatures From China Boost DinosaurBird Available at: http://www.nationalgeographic.com/society/ngo/events/releases/ pr980623.html 14. Rey, L., Sinosauropteryx Prima Available at: http://www.ndirect.co.uk/~luisrey/html/sinos256.htm