Birds: Dinosaurs Among Us

Overview

Recently, fossils of early birds and their most immediate predecessors have been collected at an unprecedented rate from Mesozoic-aged rocks worldwide. This wealth of new fossils has settled the century-old controversy of the origin of birds. Today, we can safely declare that birds evolved from a group of dinosaurs known as maniraptoran theropods--generally small meat-eating dinosaurs that include Velociraptors of Jurassic Park fame. Evidence that birds evolved from the carnivorous predators that ruled the Mesozoic ecosystems is plentiful and it comes from disparate lines of evidence. Traditionally, the primary source of evidence supporting this scientific view was the similar shape of the bones of birds and a variety of maniraptorans. However, spectacular recent discoveries have added other lines of evidence to the table. One of these involves a suite of features from the eggs of these dinosaurs. A host of fossils have shown that not only did maniraptoran dinosaurs resemble birds in the way they laid their eggs but that these eggs also looked like the eggs of birds. Another line of evidence involves the handful of snapshots that tell us about the behavior of the maniraptoran theropods. Fossils of animals in brooding poses or in resting postures also show a startling similarity with the behaviors we see among living birds. Yet, perhaps the most compelling new line of evidence comes from the discovery of soft tissues associated with the skeletons of these predatory dinosaurs, many fossils of these creatures are now known to have been covered by plumage. All this evidence has highlighted the fact that many features that were previously thought to be exclusively avian--from feathers to a wishbone--have now been discovered in the immediate dinosaur predecessor of birds. Even flight is likely to have been an attribute inherited by birds from their dinosaurian forebears! If the new wealth of fossils has clarified the old controversy of the origin of birds, many other fossils have provided a vivid testimony of the early phases of avian evolution. Hidden in these fossils are the clues to how birds perfected their flying abilities and how they evolved warm-bloodedness. As we know it today, the known history of birds starts with the spectacular Archaeopteryx, a jay-sized creature with toothed jaws, a long lizard-like tail, and flight feathers. Archaeopteryx lived 150 million years ago in today's southern Germany. Although Archaeopteryx stands alone in the fossil record of birds of the end of the Jurassic period, within the last decade a large number and variety of birds have been found in Cretaceous rocks ranging from 130 to 115 million years ago. Some of these fossils show that a great diversity of birds with long bony tails preceded the evolution of birds with the familiar short bony tail. Birds of the early Cretaceous blossomed in a range of shapes and sizes. The crow-sized, stout-beaked Confuciusornis sported enormous claws in its wings while the contemporaneous Sapeornis had very long and narrow wings like those of an albatross. These two birds were much larger than the sparrow-sized Eoenantiornis and Iberomesornis, which like most early birds had toothed jaws similar to those of Archaeopteryx. The different design of skulls, teeth, wings, and feet indicate that already at this early phase of their evolutionary history, birds had specialized into a variety of ecological niches, including seed-feeders, sap-eaters, insect-feeders, fish-eaters, and meat-eaters. At the same time, a host of novel features of the wings and ribcages suggests that soon after Archaeopteryx, birds evolved flying abilities not very different from the ones that amaze us today. As the rocks of the Cretaceous period become younger, the fossil record includes a great number of bird species with even more diverse lifestyles. The hesperornithiforms-large, flightless, foot-propelled divers-made their debut around 100 million years ago. A few million years later, these supreme fish-eaters would be crowned kings of the aquatic birds with the tiny-winged, 4-foot long, Hesperornis. The hesperornithiforms swam the waters of a warm sea dissecting North America from the Gulf of Mexico to the Arctic. On the shore of this shallow sea, over herds of duck-billed dinosaurs, soared the tern-sized Ichthyornis. Its large head with sharp teeth was designed to catch fish. Not all the birds that lived during the Mesozoic, the Age of Large Dinosaurs, may have looked as unfamiliar as Archaeopteryx, Confuciusornis, and Hesperornis. The early representatives of today's lineages of birds can also be traced back to this remote era of our geological past. In several continents, rocks from the last part of the Cretaceous period have started to provide the remains of early shore-birds, ducks, and other more familiar birds. Their descendants are the true heirs of the magnificent dinosaurs that ruled the Earth tens of millions of years ago.

Recommended Media

Web Resources: Print


Anchiornis
Gigantoraptor
Ornimithimus

Web Resources: Video

Geological Timeline
Evolutionary stages of feathers

Common Characteristics of Birds and Dinosaurs

Adapted from: https://en.wikipedia.org/wiki/Origin_of_birds and other Wikipedia pages
1. FEATHERS Archaeopteryx, the first good example of a "feathered dinosaur,” was discovered in 1861. The first specimen was found in the Solnhofen limestone in southern Germany, which is a lagerstätte, a rare and remarkable geological formation known for its superbly detailed fossils. Archaeopteryx is a transitional fossil, with features clearly intermediate between those of non-avian theropod dinosaurs and birds. Discovered just two years after Darwin's seminal Origin of Species, its discovery spurred the nascent debate between proponents of evolutionary biology and creationism. This early bird is so dinosaur-like that, without a clear impression of feathers in the surrounding rock, at least one specimen was mistaken for a non-avian theropod. Since the 1990s, a number of additional feathered dinosaurs have been found, providing even stronger evidence of the close relationship between dinosaurs and modern birds. The first of these were initially described as simple filamentous protofeathers, which were reported in dinosaur lineages such as tyrannosauroids. However, feathers indistinguishable from those of modern birds were soon after found in non-avian dinosaurs as well. We now know that most theropod dinosaurs possessed feathers of some kind--even T-rex and raptors. A small minority of researchers have claimed that the simple filamentous "protofeather" structures are simply the result of the decomposition of collagen fiber under the dinosaurs' skin or in fins along their backs, and that species with unquestionable feathers, such as oviraptorosaurs and dromaeosaurs are not dinosaurs, but true birds unrelated to dinosaurs. However, a majority of studies have concluded that feathered dinosaurs are in fact dinosaurs, and that the simpler filaments of unquestionable theropods represent simple feathers. Some researchers have demonstrated the presence of color-bearing melanin in the structures—which would be expected in feathers but not collagen fibers. Others have demonstrated, using studies of modern bird decomposition, that even advanced feathers appear filamentous when subjected to the crushing forces experienced during fossilization, and that the supposed "protofeathers" may have been more complex than previously thought. Detailed examination of the "protofeathers" of Sinosauropteryx showed that individual feathers consisted of a central quill (rachis) with thinner barbs branching off from it, similar to but more primitive in structure than modern bird feathers. 2. SKELETON Because feathers are often associated with birds, feathered dinosaurs are often touted as the missing link between birds and dinosaurs. However, the multiple skeletal features also shared by the two groups represent the more important link for paleontologists. Furthermore, it is increasingly clear that the relationship between birds and dinosaurs, and the evolution of flight, are more complex topics than previously realized. For example, while it was once believed that birds evolved from dinosaurs in one linear progression, some scientists, most notably Gregory S. Paul, conclude that dinosaurs such as the dromaeosaurs may have evolved from birds, losing the power of flight while keeping their feathers in a manner similar to the modern ostrich and other ratites. Comparisons of bird and dinosaur skeletons strengthens the case for the link, particularly for a branch of theropods called maniraptors. Skeletal similarities include the neck, pubis, wrist (semi-lunate carpal), arm and pectoral girdle, shoulder blade, clavicle, and breast bone.
A study comparing embryonic, juvenile and adult archosaur skulls concluded that bird skulls are derived from those of theropod dinosaurs by progenesis, which resulted in retention of juvenile characteristics of their ancestors.
3. LUNGS Large meat-eating dinosaurs had a complex system of air sacs similar to those found in modern birds, according to an investigation led by Patrick M. O'Connor of Ohio University. In theropod dinosaurs (carnivores that walked on two legs and had birdlike feet) flexible soft tissue air sacs likely pumped air through the stiff lungs, as is the case in birds. "What was once formally considered unique to birds was present in some form in the ancestors of birds,” O'Connor said.
4. HEART Computed tomography (CT) scans conducted in 2000 of the chest cavity of a specimen of the ornithopod Thescelosaurus found the apparent remnants of complex four-chambered hearts, much like those found in today's mammals and birds. The question of how this find reflects metabolic rate and dinosaur internal anatomy has not been resolved. Both modern crocodilians and birds, the closest living relatives of dinosaurs, have four-chambered hearts (albeit modified in crocodilians), so dinosaurs probably had them as well; the structure is not necessarily tied to metabolic rate.
5. SLEEPING POSTURE Fossils of the troodontids Mei and Sinornithoides demonstrate that the dinosaurs slept like certain modern birds, with their heads tucked under their arms. This behavior, which may have helped to keep the head warm, is also characteristic of modern birds.
6. REPRODUCTION When laying eggs, female birds grow a special type of bone in their limbs. This medullary bone forms as a calcium-rich layer inside the hard outer bone, and is used as a calcium source to make eggshells. The presence of endosteally derived bone tissues lining the interior marrow cavities of portions of a Tyrannosaurus rex specimen's hind limb suggested that T. rex used similar reproductive strategies, and revealed that the specimen is female. Further research has found medullary bone in the theropod Allosaurus and ornithopod Tenontosaurus. Because the line of dinosaurs that includes Allosaurus and Tyrannosaurus diverged from the line that led to Tenontosaurus very early in the evolution of dinosaurs, this suggests that dinosaurs in general produced medullary tissue.
7. BROODING AND CARE OF YOUNG Several different specimens of theropod dinosaurs have been found resting over the eggs in its nest in a position most reminiscent of brooding. Numerous dinosaur species, for example, Maiasaura, have been found in herds mixing both very young and adult individuals, suggesting rich interactions between them. A dinosaur embryo was found without teeth, which suggests some parental care was required to feed the young dinosaur, possibly the adult dinosaur regurgitated food into the young dinosaur's mouth. This behavior is seen in numerous bird species; parent birds regurgitate food into the hatchling's mouth.
8. GIZZARD STONES Both birds and ancient dinosaurs used gizzard stones. These stones are swallowed by animals to aid digestion and break down food and hard fibres once they enter the stomach. When found in association with fossils, gizzard stones are called gastroliths.
9. Molecular evidence On several occasions, the extraction of DNA and proteins from Mesozoic dinosaur fossils has been claimed, allowing for a comparison with birds. Several proteins have putatively been detected in dinosaur fossils, including hemoglobin. In the March 2005 issue of Science, Dr. Mary Higby Schweitzer and her team announced the discovery of flexible material resembling actual soft tissue inside a 68-million-year-old Tyrannosaurus rex leg bone of specimen MOR 1125 from the Hell Creek Formation in Montana. The seven collagen types obtained from the bone fragments, compared to collagen data from living birds (specifically, a chicken), suggest that older theropods and birds are closely related. The soft tissue allowed a molecular comparison of cellular anatomy and protein sequencing of collagen tissue published in 2007, both of which indicated that T. rex and birds are more closely related to each other than either is to Alligator. The successful extraction of ancient DNA from dinosaur fossils has been reported on two separate occasions, but upon further inspection and peer review, neither of these reports could be confirmed.
Lungs
Evolution of Wings

INTERESTING FACTS ABOUT REPRESENTATIVE NON-AVIAN AND AVIAN DINOSAURS

CRETACEOUS:• BEIPIAOSAURUS: https://web.archive.org/web/20240417201422/http://www.prehistoric-wildlife.com/species/b/beipiaosaurus.html• SINOSAUROPTERYX: https://web.archive.org/web/20240406193605/http://www.prehistoric-wildlife.com/species/s/sinosauropteryx.html• ZHENYUANLONG: https://www.nationalgeographic.com/science/phenomena/2015/07/16/paleo-profile-zhenyuanlong-suni/• EOCONFUCIUSORNIS (BIRD): http://www.sci-news.com/paleontology/melanosomes-beta-keratin-feathers-bird-eoconfuciusornis-04398.html• DEINONYCHUS: https://www.thoughtco.com/deinonychus-the-terrible-claw-1093783• ORNITHOMIMUS: https://www.thoughtco.com/things-to-know-ornithomimus-1093793• GIGANTORAPTOR https://www.thoughtco.com/things-to-know-gigantoraptor-1093788• OVIRAPTOR: https://www.thoughtco.com/oviraptor-the-egg-thief-dinosaur-1093794• STRUTHIOMIMUS: https://web.archive.org/web/20230609095124/http://www.prehistoric-wildlife.com/species/s/struthiomimus.html• VELOCIRAPTOR: https://www.thoughtco.com/things-to-know-velociraptor-1093806
Struthiomimus
Ornimegalonyx
Archaeopteryx

Partial List of birds of North America

Anseriformes: Geese, ducks, swans and screamersTinamiformes: TinamousGalliformes: Curassows, guans, guineafowls, quails, grouse and turkeysProcellariiformes: Albatrosses, shearwaters and petrelsSuliformes: Frigatebirds, boobies, gannets, cormorants and dartersPelecaniformes: Pelicans, bitterns, herons, egrets, ibises and spoonbillsAccipitriformes: Ospreys, hawks, eagles and kitesGruiformes: Rails, gallinules, coots, sungrebe, limpkin and cranesCharadriiformes: Thick-knees, lapwings, plovers, oystercatchers, stilts, avocets, jacanas, sandpipers, pratincoles, gulls, terns, skimmers, skuas, auks, murres and puffinsFalconiformes: Caracaras and falconsColumbiformes: Pigeons and dovesPsittaciformes: Lorikeets, parakeets, macaws and parrotsCuculiformes: Cuckoos, roadrunners and anisStrigiformes: OwlsCaprimulgiformes: Nightjars, potoos and oilbirdApodiformes: Swifts and hummingbirdsCoraciiformes: Todies, motmots and kingfishersPiciformes: Puffbirds, jacamars, barbets, toucans, woodpeckers, sapsuckers and flickersPasseriformes: Sapayoa, ovenbirds, antbirds, antpittas, tapaculos, flycatchers, tityras, cotingas, manakins, shrikes, vireos, jays, crows, magpies, ravens, larks, swallows, martins, chickadees, titmice, tits, nuthatches, treecreepers, wrens, gnatcatchers, dippers, bulbuls, kinglets, warblers, thrushes, mockingbirds, thrashers, starlings, mynas, accentors, wagtails, pipits, waxwings, longspurs, bananaquit, tanagers, saltators, sparrows, towhees, juncos, cardinals, grosbeaks, blackbirds, meadowlarks, cowbirds, grackles, orioles, finches, weavers and whydahsOther orders: Loons, grebes, flamingos, penguins, tropicbirds, storks, New world vultures, sunbittern, trogons and hoopoes
Syrnix
Blue Heron
Parrots

Syrinx: The Language of Birds

The melodious call of many birds comes from a mysterious organ buried deep within their chests: a one-of-a-kind voice box called a syrinx. Recently, scientists have concluded that this voice box evolved only once and that it represents a rare example of a true evolutionary novelty. “It’s something that comes out of nothing,” says Denis Duboule, a geneticist at the University of Geneva in Switzerland. “There is nothing that looks like a syrinx in any related animal groups in vertebrates. It’s truly bizarre.” Reptiles, amphibians, and mammals all have a larynx, which is a voice box at the top of the throat that protects the airways. Folds of tissue there—the vocal cords—can also vibrate to enable humans to talk, pigs to grunt, and lions to roar. Birds have larynxes, too. But the organ they use to sing their tunes is lower down—where the windpipe splits to go into the two lungs. The syrinx, named in 1872 after a Greek nymph who was transformed into panpipes, has a similar structure: Both are tubes supported by cartilage with folds of tissue. The oldest known syrinx belongs to a bird fossil some 67 million years old; that’s about the same time all modern bird groups became established.