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ody and require a large breastbone (sternum) with a keel for muscle attachment. Modern birds do not have bony tails; instead, the tail vertebrae are fused into a short pygostyle. • Miniaturized organs. Bird organs, in many cases, work very efficiently for their size. Their small lungs allow very efficient oxygen uptake relative to their size, which is essential for flight. Reproductive organs remain atrophied except during the reproductive season. Birds excrete nitrogenous wastes in the form of dry uric acid rather than urea dissolved in water; therefore they need to carry very little water, which is heavy. They excrete white uric acid and dark intestinal contents through a single opening, the cloaca. Bird brains are relatively smaller than the brains of most mammals, since brains (and thickened skulls to protect them) are heavy. • High metabolic rate. Birds have high body temperatures (several degrees higher than those of mammals), which encourage the rapid metabolism necessary for supplying energy to flight. The small size of their cells and the small amount of DNA in each also allows rapid cell growth. This means that birds have to eat a lot, in some cases half of their body weight each day, or more! To “eat like a bird,” a human would have to eat at least 50 pounds of food daily. The evolutionary origin of birds from among reptiles is evident from modern characteristics and from fossil evidence. Modern characteristics. Birds and reptiles share many skeletal and muscular features. Some reptile skull features are present in embryonic but not adult birds. Birds, like reptiles and amphibians, have nucleated red blood cells. Also, feathers are just scales that develop greater complexity. Birds have scales on their feet. Birds, like reptiles, excrete uric acid and have nasal salt glands; both of these adaptations allow them to excrete wastes and maintain salt balance without excessive secretion of water. Bird claws resemble reptile claws; one bird, the hoatzin, retains claws on the wings in the juveniles. Birds, like reptiles, have a cloaca, a common opening for the expulsion of intestinal and kidney wastes. In many birds, as in many reptiles, the cloaca also releases sperm, and mating occurs when males and females press their cloacae together. In some reptiles, and some birds (ratites such as ostriches, cassowaries, and kiwis; and the geese, ducks, and swans), males have penes; bird penes resemble reptile, not mammal, penes. Fossils. Protoavis, from the Triassic period, is the earliest fossil that may have been a bird, but its identity as a bird is uncertain. The oldest undisputed bird fossil is arcHaeopteryx, which lived 150 million years ago during the Jurassic period, at the same time as the dinosaurs. The skeleton of Archaeopteryx was mostly reptilian, but this species had feathers. Archaeopteryx was intermediate between earlier dinosaurs and modern birds. Fossils of birds and other feathered dinosaurs reveal an entire series of characteristics intermediate between Mesozoic dinosaurs and modern birds (see figure on page 62). Sinosau- ropteryx had down feathers that would not have been suitable for flight. Caudipteryx had flight feathers on its forelimbs and tail, but these feathers were symmetrical. Confuciusornis had down feathers on its trunk and asymmetrical flight feathers on its wings. The skeleton of Confuciusornis was mostly reptilian but had reduced tail vertebrae and a toothless beak instead of a toothed jaw. These birds were apparently part of one of the lineages of coelurosaur dinosaurs. The feathered dinosaur Archaeoraptor lianingensis, the discovery of which was announced in 1999, turned out to be a hoax. It was not an evolutionary hoax, since there was no need for one. Several other feathered dinosaurs, including Sinornithosaurus and Beipiaosaurus, had already been legitimately described from the same fossil bed in China (see figures on page 63). The hoax was probably intended for monetary gain, since fossils can bring a lot of money to a Chinese peasant. During the Mesozoic era, feathered coelurosaurian dinosaurs with a whole range of intermediate characteristics ran around all over the place. And it was not just the coelurosaurs. In 2004 scientists announced the discovery of a 130-million-year-old tyrannosaur fossil, named Dilong paradoxus, that had primitive featherlike structures. Scientists are uncertain which of these feathered dinosaurs may have been the ancestor of modern birds, precisely because fossils of so many animals intermediate between reptiles and birds have been found. Numerous birds during the Cretaceous period also had characteristics intermediate between those of reptiles and of modern birds. At least 12 genera are known. Most had toothed jaws rather than toothless beaks, and a sternum not enlarged to the size of that of modern birds. Sinornis had teeth and an enlarged sternum, but the sternum was not keeled as in modern birds. Hesperornis in North America had very small wings, large feet, and was probably a flightless aquatic diving bird. Other Cretaceous birds resembled modern birds in their small size and ability to perch. Birds diversified into numerous lineages, most of which became extinct. Before the end of the Cretaceous period, three modern lineages of birds may have evolved and survived the Cretaceous extinction. These are the lineages that today include waterfowl (represented by the Cretaceous Presbyornis), loons (represented by Neogaornis), and gulls (represented by Graculavus). The albatross lineage may also have been differentiated by the Cretaceous. Although fossil evidence is lacking, cladistic analysis suggests that the earliest divergence in the history of modern birds was between the paleognaths (large flightless birds such as ostriches) and all other birds, the neognaths. Certainly after the Cretaceous Extinction, the evolutionary radiation of birds was spectacular. Modern bird groups include: • waterfowl (ducks, geese, swans) • swifts and hummingbirds • wading birds • herons, storks, and New World vultures birds, evolution of
irds, evolution of • doves and pigeons • raptors (eagles, hawks, and Old World vultures) • chickens • pelicans • woodpeckers • penguins • owls • ratites (large flightless birds) • passerines (perching birds) Birds have sex chromosomes (see Mendelian genetics). Male birds have two Z chromosomes, while female birds have a Z and a W chromosome. In paleognaths, Z and W chromosomes are about the same size, while in neognaths the W chromosome is smaller. Birds represent very interesting examples of convergence. Vultures, for example, are a polyphyletic category. New World vultures have a separate evolutionary origin (from among the herons and storks) from Old World vultures The skeleton of the Jurassic bird Archaeopteryx is intermediate between the dinosaur Dromaeosaurus and the modern pigeon (Columba). During the evolution of birds, the tail shortened, the wishbone got smaller and the breastbone got larger, and teeth were lost. (Redrawn from Benton)
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ENCYCLOPEDIA OF Evolution
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Encyclopedia of Evolution Copyright
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Contents Foreword ix Acknowledgment
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Foreword The theory and facts of ev
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IntroduCtIon What you do not know a
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other issues coming along with it.
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adaptation Adaptation is the fit of
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from the allometric patterns of gro
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considered as an example. (The taxo
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English) were a resounding success,
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Some Centers of the Evolution of Ag
Page 30 and 31: helps the DNA insert into the host
Page 32 and 33: Even within a single patient, HIV e
Page 34 and 35: then into the insect body; carbon d
Page 36 and 37: chromosomes (they are diploid) whil
Page 38 and 39: genetic basis. About 35,000 years a
Page 40 and 41: emained dormant and sprouted after
Page 42 and 43: Further Reading Wise, Steven M. Rat
Page 44 and 45: Because the DNA of many archaebacte
Page 46 and 47: Koi and goldfish have been bred tha
Page 48 and 49: Barringer Crater, Arizona, was form
Page 50 and 51: y a silent wall of darkness advanci
Page 52 and 53: Skeleton of “Lucy,” the Austral
Page 54: Further Reading Alemseged, Zerxenay
Page 57 and 58: acteria, evolution of Examples of t
Page 59 and 60: 0 Bates, Henry Walter advantage. Th
Page 61 and 62: ehavior, evolution of In another sp
Page 63 and 64: ig bang make nests with horizontal
Page 65 and 66: iodiversity How Much Do Genes Contr
Page 67 and 68: iodiversity Biodiversity (as indica
Page 69 and 70: 0 biogeography Another problem with
Page 71 and 72: iogeography Biogeography of Selecte
Page 73 and 74: iogeography their species through d
Page 75 and 76: iology design) or adaptation to the
Page 77 and 78: iology D. Response to environment.
Page 79: 0 birds, evolution of • The foot.
Page 83 and 84: Burgess shale early career. By heat
Page 85 and 86: Burgess shale jointed legs, Anomalo
Page 87 and 88: Cambrian period occurred when anima
Page 89 and 90: 0 Cenozoic era opens the way to an
Page 91 and 92: Chicxulub Pritchard, J., and Dolph
Page 93 and 94: cladistics The above examples used
Page 95 and 96: coevolution descent, and that scien
Page 97 and 98: coevolution Coevolution of Organism
Page 99 and 100: 0 coevolution What Are the “Ghost
Page 101 and 102: coevolution What Are the “Ghosts
Page 103 and 104: commensalism Wilson, Michael. Micro
Page 105 and 106: continental drift was an animal tha
Page 107 and 108: continental drift During geological
Page 109 and 110: 0 convergence bee-pollinated flower
Page 111 and 112: convergence Both birds and bats hav
Page 113 and 114: creationism explained these observa
Page 115 and 116: creationism used to justify militar
Page 117 and 118: creationism • In the early 21st c
Page 119 and 120: 00 Cretaceous period however, other
Page 121 and 122: 0 Cro-Magnon evolution had occurred
Page 123 and 124: 0 Cro-Magnon areas, perforated shel
Page 125 and 126: 0 Cuvier, Georges Cuvier held stron
Page 127 and 128: 0 Darwin Awards Darwin Awards “Th
Page 129 and 130: 0 Darwin, Charles forever. It would
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Darwin, Charles and animals did hav
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Darwin’s finches has its own uniq
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Dawkins, Richard ate the pulp. More
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developmental evolution Part II. In
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0 Devonian period gene from an inve
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dinosaurs what DeVries thought were
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diseases, evolution of • Thyreoph
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disjunct species have happened? Som
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DNA (evidence for evolution) genes,
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0 DNA (evidence for evolution) seco
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DNA (raw material of evolution) DNA
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DNA (raw material of evolution) The
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Dobzhansky, Theodosius Mice have tw
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duplication, gene prominent brow ri
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0 ecology Second, organisms can con
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Eldredge, Niles they possess no str
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eugenics grieving, or experiencing
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eugenics because government officia
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eukaryotes, evolution of of the sor
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0 Eve, mitochondrial within cells,
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evolutionary ethics the ability to
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evolutionary ethics Can an Evolutio
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evolutionary medicine Can an Evolut
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evolutionary medicine variable in t
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0 extinction past (a genetic bottle
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fishes, evolution of his obvious vi
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Flores Island people Christopher St
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fossils and fossilization The grain
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founder effect Further Reading Fort
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0 Gaia hypothesis nitrogen oxide (N
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Galton, Francis constituted a premi
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gene pool Cocos Island is too small
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Gould, Stephen Jay animals, and the
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Gray, Asa he had long accepted Lyel
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0 group selection used the carbon t
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gymnosperms, evolution of began per
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Haeckel, Ernst (1834-1919) German E
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The initial divergence between homi
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Although Homo ergaster, the presume
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tions were spreading through Africa
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Selected Examples of Homo heidelber
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sunlight of tropical regions, and t
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win, Hooker could not pay his own w
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gene transfer from a bacterium, per
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to evolutionary science. He also ap
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Examples of Intergeneric Crosses Re
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ice ages The term ice ages usually
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America had not been connected sinc
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migrated into Europe and displaced
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ence their intelligence. There is a
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This does not mean that all of the
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e exactly the right ones. Bovine in
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Van Till, Howard J. “E. coli at t
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food particles with whiplike struct
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would readily interbreed and produc
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ased, to eat small plankton near th
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isotopes When evaporation from the
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Java man See Homo erectus. Johanson
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0 Kenyanthropus chemist Henri Becqu
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language, evolution of is not consi
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language, evolution of Italian, Por
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Lascaux caves Some of the original
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Leakey, Richard Richard Leakey, in
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0 life history, evolution of it inv
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life history, evolution of is: sele
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life history, evolution of Why Do H
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life history, evolution of Why Do H
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Linnaean system The tree of life us
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0 living fossils admired. The genus
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Lysenkoism about evolution. When Da
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Malthus, Thomas intelligent design)
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mammals, evolution of the reptilian
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markers another precocious and crea
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0 Mars, life on • The spacecraft
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Maynard Smith, John producing a 200
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meiosis Zoology. He became director
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Mendel, Gregor of the fertilized eg
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Mendelian genetics an American gene
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0 Mendelian genetics the environmen
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microevolution Stanley Miller did o
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missing links Batesian mimicry. Nam
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mitochondrial DNA Hominin skulls ha
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molecular clock these scientists di
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0 mutualism function of the protein
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natural selection Fact 1. Populatio
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natural selection Three types of na
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natural theology different kinds of
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Neandertals different species of hu
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0 Neolithic Neandertals lived short
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new synthesis In contrast to progen
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noncoding DNA Some regulatory molec
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origin of life they refer to life t
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origin of life Are Humans Alone in
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00 origin of life It is often said
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0 Origin of Species (book) ribose);
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0 Orrorin ———. On the Origin
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0 Paley, William in the Chordata) e
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0 peppered moths There remained som
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0 Permian extinction produced in la
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Permian period upon the exploitatio
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Piltdown man found in slightly diff
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plate tectonics The Earth’s surfa
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population Percent of Mammal Genera
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0 population genetics Vandermeer, J
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population genetics If allele A is
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Precambrian time at least some gene
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progress, concept of arboreal prima
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promoter Each chromosome contains t
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0 punctuated equilibria and persist
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punctuated equilibria Gradualism wa
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Quaternary period epoch of the Quat
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ecapitulation would cause some of t
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eligion, evolution of pathogens nev
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0 reproductive systems Catkins of m
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eproductive systems Scobell has inv
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eproductive systems fact, there is
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eptiles, evolution of Blanckenhorn,
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esistance, evolution of ineffective
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0 respiration, evolution of There i
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Sagan, Carl (1934-1996) American As
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tain features are universally recog
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The testing of hypotheses accumulat
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the results are sufficiently intere
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een wrong: His hypothesis of the co
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Comparison of Inherit the Wind with
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and others form more complex struct
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endonuclease gene is then used as a
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e able to do the same thing. Second
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mosomes come in groups of five rath
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eliminated—that is, if sexual rec
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one, free of parasites, is likely t
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nesses of resource acquisition and
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Zahavi, Amotz. The Handicap Princip
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and it is not happening extensively
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this, too, is a genetically based u
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monkeyflowers of the genus Mimulus)
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Further Reading Abrahamson, Warren
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comes from the unfertilized egg, ra
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of the bacteriophages. Therefore, h
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technology Technological and Cultur
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thermodynamics • Plants. The flow
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thermodynamics return to their orig
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00 Triassic period more resulting l
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unconformity An unconformity is a g
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sissippi River is getting shorter e
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ago. This was the birth of the Sun.
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0 vestigial characteristics algae.
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Wallace, Alfred Russel (1823-1913)
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genetic inferiority of the lower cl
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that point onward he questioned the
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Carl R. Woese pioneered the use of
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Darwin’s “One LOng argument”:
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the young seedlings must compete wi
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Traits can reappear after even hund
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ated: It has been an advantage in o
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chapter 10. On the imperfection of
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out in competition with the species
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languages. Linguists classify all R
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My theory has been much maligned. T
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Index Note: Boldface page numbers i
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asexual propagation 370-371 Ashfall
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Bryan, William Jennings creationism
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ird evolution 62-63 cladistics 72-7
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divergence molecular clock 278-279
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extinction 159-160. See also mass e
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Gondwana (Gondwanaland) 68, 84, 86,
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Huxley, Julian S. 200 eugenics 146
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Mendelian genetics and 268 Spencer,
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Origin of Species (Darwin) 433-434
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ocean currents 179, 207 Oceanian re
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polar cells 368 Polkinghorne, John
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Sanger, Frederick 55 Sanger, Margar
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spores 264, 370 spotted hyena (Croc
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useless characteristics 409 Ussher,
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