Jurassic Birds Study Resources

JURASSIC BIRDS This chapter examines flying creatures and includes the largest animals to ever inhabit Earth during the Jurassic period. The Jurassic, from 210 to 135 million years ago, was named for the limestone and limestone of the Jura Mountains in northwestern Switzerland. Early in the period, Pangaea began to break up into its current continents, forming the Atlantic, Indian, and Arctic Oceans.The mountains created by crustal upheaval during the previous period were flattened by erosion. Inland seas invaded the continent, providing additional offshore habitat for a bewildering assortment of marine species (Fig. 144). By this time, terrestrial fauna had reached a basic composition that they would have retained until the dinosaurs became extinct. Dinosaurs were very diverse during the Jurassic and reached their maximum size, becoming the largest land animals that ever lived. Widespread plant growth and coal formation indicate a warm and humid climate. The favorable climate and excellent growing conditions contributed to the gigantic size of several species of dinosaurs, many of which became extinct by the end of the period. Reptiles are very successful and occupy land, sea and air. Mammals are small, rodent-like, sparsely populated and almost unnoticed creatures. The first flightworthy birds appeared and shared the sky with flying reptiles called pterosaurs. EARLY BIRDS Birds first appeared in the Jurassic about 150 million years ago, though some accounts trace their origins as far back as the late Triassic 225 million years ago. About 135 million years ago, ancient birds began to diversify. They diverged into two bloodlines. One leads to ancient birds, and the other leads to modern birds. The birds are believed to have descended from diapsid reptiles called thecodonts, the common ancestor of dinosaurs and crocodiles. As a result, birds are often referred to as "glorified reptiles." Or, they could have descended from bipedal meat-eating dinosaurs known as theropods, from the Greek word for "ferocious foot." Indeed, birds are the only surviving relatives of dinosaurs. Except for having long tails, the skeletons of many species of small dinosaurs are very similar to birds, suggesting direct descendants of dinosaurs. Microraptor is by far the smallest adult dinosaur ever found and is about the size of a crow. The creature has fur on its body. It also had skeletal features linking it to birds, including bird-like clawed feet that may have been used to perch on branches. This animal is considered the closest dinosaur relative of birds and perhaps an agile tree climber. His ancestors may have lived on trees long enough to develop traits associated with arboreal lifestyles. Therefore, flying will be a simple matter of launching from the treetops back to the ground. Oviraptor (Fig. 145) was a dinosaur that incubated its eggs in communal nests. They are closely related to birds, which provides the strongest evidence of parental attention, suggesting birds inherited this behavior from dinosaurs. Oviraptors and birds probably evolved from a common ancestor that also exhibited brooding behavior. The animal appears to have lived before the earliest birds, which evolved alongside dinosaurs, mysteriously died while birds lived. Warm-blooded birds to obtain the maximum metabolic efficiency necessary for sustained flight but have maintained the reptile's mode of reproduction by laying eggs. The bones of some Cretaceous birds show growth rings, a common feature among cold-blooded reptiles. This suggests that ancient birds may not have yet fully developed warm-blooded bodies. The ability of birds to maintain high body temperatures has sparked controversy over whether some species of dinosaurs with similar skeletons were also warm-blooded. Archaeopteryx (Figure 146), from Greek meaning "ancient wing," is the earliest known fossil bird. It was about the size of a modern pigeon and appears to be a species in transition between a reptile and a true bird. Unlike modern birds, it did not have a faded sternum for attachment of flight muscles. Archaeopteryx was first thought to be a small dinosaur until fossils clearly showed the impression of feathers found in a unique limestone formation in Bavaria, Germany, in 1863. Eminent geologists of the 19th century claimed Archaeopteryx was a hoax and that feather impressions were simply etched into fossil-bearing rock. However, Archaeopteryx fossils discovered in 1950 from the same Bavarian formation yielded well-preserved specimens that clearly showed the impression of feathers. Although Archaeopteryx had many of the necessary supplies for flight, it was likely a bad flyer. It may only fly a short distance, similar to the current domesticated bird. It may achieve flight by running along the ground with its wings outstretched and gliding for a moment or jumping off the ground while flapping its wings to catch flying insects. Their ancestors may have flapped their wings to increase running speed while escaping predators, thus gaining pure flight by accident. Archaeopteryx had teeth, claws, a long bony tail, and many features of a small dinosaur skeleton but lacked hollow bones for lightweight. Its fur is the result of scales and may have originally served as insulation. Some species of birds retained their teeth until the end of the Cretaceous about 70 million years ago. The claws on the front edge of the wings may have helped the bird climb trees, from where it could launch itself into the air. Having mastered the skill of flying, the bird quickly spreads to all environments. Their superior adaptability allowed them to compete successfully with pterosaurs, possibly leading to the reptile's extinction. Giant flightless land birds appear at the beginning of the fossil record of birds. Their wide distribution is further evidence for the existence of Pangea, as these birds then had to travel from one corner of the world to another. After being propelled into the air by dinosaurs and kept there by hunting mammals, birds found life much easier on the ground once this threat was eliminated because they had to expend a lot of energy to stay in the air. Some birds also successfully adapt to life in the sea. Certain diving ducks are specially equipped to "fly" underwater to catch fish. Penguins, for example, are flightless birds that have lived in water and are well adapted to survive in the cold Antarctica