Examine individual changes

'[[File:Archaeopteryx bavarica Detail.jpg|right|thumb|220px|''[[Archaeopteryx]]'' at [[Paläontologisches Museum München]]]] The '''evolution of birds''' is thought to have begun in the [[Jurassic]] Period, with the earliest [[bird]]s derived from a clade of [[theropod]]a [[dinosaur]]s named [[Paraves]]. Birds are categorized as a [[Class (biology)|biological class]], '''Aves'''. The earliest known is ''[[Archaeopteryx|Archaeopteryx lithographica]]'', from the [[Late Jurassic]] period, though ''Archaeopteryx'' is not commonly considered to have been a true bird. Modern phylogenies place birds in the dinosaur [[clade]] [[Theropoda]]. According to the current consensus, Aves and a sister group, the [[Order (biology)|order]] [[Crocodilia]], together are the sole living members of an unranked "[[reptile]]" clade, the [[Archosaur]]ia. [[Phylogenetics|Phylogenetically]], Aves is usually defined as all descendants of the most recent common ancestor of a specific modern bird species (such as the [[house sparrow]], ''Passer domesticus''), and either ''Archaeopteryx'',<ref>{{cite book |author=Padian K & Chiappe LM |editor=Currie PJ & Padian K |title=Encyclopedia of Dinosaurs|origyear= |year=1997|publisher=Academic Press|location=San Diego|isbn= |id= |pages=41–96|chapter=Bird Origins}}</ref> or some prehistoric species closer to [[Neornithes]] (to avoid the problems caused by the unclear relationships of ''Archaeopteryx'' to other theropods).<ref>{{cite book |last=Gauthier |first=J|editor=Padian K |title=The Origin of Birds and the Evolution of Flight. Mem. California Acad. Sci 8|year=1986|isbn= |oclc= |doi= |id= |pages=1–55|chapter=Saurischian Monophyly and the origin of birds}}</ref> If the latter classification is used then the larger group is termed Avialae. Currently, the relationship between dinosaurs, ''Archaeopteryx'', and modern birds is still under debate. <!-- see Sereno 2005, Gauthier & de Queiroz 2001 for details --> On 31 July 2014, scientists reported details of the evolution of birds from [[Theropoda|theropod dinosaurs]].<ref name="AP-20140731">{{cite news |last=Borenstein |first=Seth |title=Study traces dinosaur evolution into early birds |url=http://apnews.excite.com/article/20140731/us-sci-shrinking-dinosaurs-a5c053f221.html |date=31 July 2014 |work=[[AP News]] |accessdate=3 August 2014 }}</ref><ref name="SCI-20140731">{{cite journal |authors=Lee, MichaelS.Y.; Cau, Andrea; Naish, Darren; Dyke, Gareth J. |title=Sustained miniaturization and anatomical innovation in the dinosaurian ancestors of birds |url=http://www.sciencemag.org/content/345/6196/562 |date=1 August 2014 |journal=[[Science (journal)|Science]] |volume=345 |number=6196 |pages=562 - 566 |doi=10.1126/science.1252243 |accessdate=2 August 2014 }}</ref> ==Origins== cool --~~~~--~~~~--~~~~[http://wertyujk13567 wertyujk13567] man its cool {{main|Origin of birds}} {{See also|Avicephala}} [[File:Velociraptor 28-12-2007 15-06-24.jpg|thumb|right|The mounted skeleton of a ''[[Velociraptor]]'', showing the very bird-like quality of the smaller [[theropod]] dinosaurs]] There is [[Origin of birds|significant evidence]] that birds emerged within [[Theropoda|theropod]] [[Dinosauria|dinosaurs]], specifically, that birds are members of [[Maniraptora]], a group of theropods which includes [[dromaeosaur]]s and [[Oviraptoridae|oviraptorids]], among others.<ref>{{cite journal | last1 = Hou | first1 = L | last2 = Martin | first2 = M | last3 = Zhou | first3 = Z | last4 = Feduccia | first4 = A | year = 1996 | title = Early Adaptive Radiation of Birds: Evidence from Fossils from Northeastern China | url = http://www.sciencemag.org/cgi/content/abstract/274/5290/1164 | journal = Science | volume = 274 | issue = 5290| pages = 1164–1167 | doi=10.1126/science.274.5290.1164 | pmid=8895459}}</ref> As more non-avian theropods that are closely related to birds are discovered, the formerly clear distinction between non-birds and birds becomes less so. This was noted already in the 19th century, with [[Thomas Huxley]] writing: <blockquote>We have had to stretch the definition of the class of birds so as to include birds with teeth and birds with paw-like fore limbs and long tails. There is no evidence that ''Compsognathus'' possessed feathers; but, if it did, it would be hard indeed to say whether it should be called a reptilian bird or an avian reptile.''<ref name=Huxley>Huxley, T.H. (1876): Lectures on Evolution. ''New York Tribune''. Extra. no 36. In Collected Essays IV: pp 46-138 [http://aleph0.clarku.edu/huxley/CE4/LecEvol.html original text w/ figures]</ref></blockquote> Discoveries in northeast [[People's Republic of China|China]] ([[Liaoning]] Province) demonstrate that many small theropod dinosaurs [[Feathered dinosaurs|did indeed have feathers]], among them the [[compsognathid]] ''[[Sinosauropteryx]]'' and the [[Microraptoria|microraptorian]] [[Dromaeosauridae|dromaeosaurid]] ''[[Sinornithosaurus]]''. This has contributed to this ambiguity of where to draw the line between birds and reptiles.<ref>Norell, M & Ellison M (2005) ''Unearthing the Dragon, The Great Feathered Dinosaur Discovery'' Pi Press, New York, ISBN 0-13-186266-9</ref> ''[[Cryptovolans]]'', a dromaeosaurid found in 2002 (which may be a junior synonym of ''[[Microraptor]]'') was capable of powered flight, possessed a sternal [[keel (bird)|keel]] and had ribs with [[uncinate processes of ribs|uncinate processes]]. ''[[Cryptovolans]]'' seems to make a better "bird" than ''[[Archaeopteryx]]'' which lacks some of these modern bird features. Because of this, some paleontologists have suggested that [[dromaeosaur]]s are actually basal birds whose larger members are secondarily flightless, i.e. that dromaeosaurs evolved from birds and not the other way around. Evidence for this theory is currently inconclusive, but digs continue to unearth fossils (especially in China) of feathered dromaeosaurs. At any rate, it is fairly certain that flight utilizing feathered wings existed in the mid-Jurassic theropods. The [[Cretaceous]] [[Unenlagiinae|unenlagiine]] ''[[Rahonavis]]'' also possesses features suggesting it was at least partially capable of powered flight. Although [[ornithischia]]n (bird-hipped) dinosaurs share the same [[hip]] structure as birds, birds actually originated from the [[saurischia]]n (lizard-hipped) dinosaurs if the dinosaurian origin theory is correct. They thus arrived at their hip structure condition [[Analogy (biology)|independently]]. In fact, a bird-like hip structure also developed a third time among a peculiar group of theropods, the [[Therizinosauridae]]. An alternate theory to the dinosaurian origin of birds, espoused by a few scientists, notably [[Larry Martin]] and [[Alan Feduccia]], states that birds (including [[maniraptora]]n "dinosaurs") evolved from early archosaurs like ''[[Longisquama]]''.<ref>{{cite journal | last1 = Feduccia | first1 = A | last2 = Lingham-Soliar | first2 = T | last3 = Hinchliffe | first3 = JR | year = 2005 | title = Do feathered dinosaurs exist? Testing the hypothesis on neontological and paleontological evidence | url = | journal = Journal of Morphology | volume = 266 | issue = 2| pages = 125–166 | doi = 10.1002/jmor.10382 | pmid = 16217748 }}</ref> This theory is contested by most other paleontologists and experts in feather development and evolution.<ref>{{cite journal | last1 = Prum | first1 = R | year = 2003 | title = Are Current Critiques Of The Theropod Origin Of Birds Science? Rebuttal To Feduccia 2002 | url = | journal = Auk | volume = 120 | issue = 2| pages = 550–561 | doi=10.1642/0004-8038(2003)120[0550:ACCOTT]2.0.CO;2}}</ref> ==Mesozoic birds== [[File:Iberomesornis-model.jpg|thumb|right|Reconstruction of ''[[Iberomesornis romerali]]'', a toothed [[Enantiornithes|enantiornithe]]]] The basal bird ''[[Archaeopteryx]]'', from the [[Jurassic]], is well known as one of the first "[[Transitional fossil|missing links]]" to be found in support of [[evolution]] in the late 19th century. Though it is not considered a direct ancestor of modern birds, it gives a fair representation of how flight evolved and how the very first bird might have looked. It may be predated by ''[[Protoavis|Protoavis texensis]]'', though the fragmentary nature of this fossil leaves it open to considerable doubt whether this was a bird ancestor. The skeleton of all early bird candidates is basically that of a small theropod dinosaur with long, clawed hands, though the exquisite preservation of the [[Solnhofen Plattenkalk]] shows ''Archaeopteryx'' was covered in feathers and had wings.<ref name=Huxley/> While ''Archaeopteryx'' and its relatives may not have been very good fliers, they would at least have been competent gliders, setting the stage for the evolution of life on the wing. The evolutionary trend among birds has been the reduction of anatomical elements to save weight. The first element to disappear was the bony tail, being reduced to a [[pygostyle]] and the tail function taken over by feathers. ''[[Confuciusornis]]'' is an example of their trend. While keeping the clawed fingers, perhaps for climbing, it had a pygostyle tail, though longer than in modern birds. A large group of birds, the [[Enantiornithes]], evolved into [[ecological niche]]s similar to those of modern birds and flourished throughout the Mesozoic. Though their wings resembled those of many modern bird groups, they retained the clawed wings and a snout with teeth rather than a beak in most forms. The loss of a long tail was followed by a rapid evolution of their legs which evolved to become highly versatile and adaptable tools that opened up new ecological niches.<ref>[http://www.sciencedaily.com/releases/2013/08/130813201426.htm Shortening tails gave early birds a leg up]</ref> The [[Cretaceous]] saw the rise of more modern birds with a more rigid ribcage with a [[keel (bird anatomy)|carina]] and shoulders able to allow for a powerful upstroke, essential to sustained powered flight. Another improvement was the appearance of an [[alula]], used to achieve better control of landing or flight at low speeds. They also had a more derived pygostyle, with a [[ploughshare]]-shaped end. An early example is ''[[Yanornis]]''. Many were coastal birds, strikingly resembling modern [[shorebird]]s, like ''[[Ichthyornis]]'', or ducks, like'' [[Gansus]]''. Some evolved as swimming hunters, like the [[Hesperornithiformes]] – a group of flightless divers resembling [[grebe]]s and [[loon]]s. While modern in most respects, most of these birds retained typical reptilian-like teeth and sharp claws on the manus. The modern toothless birds evolved from the toothed forefathers in the Cretaceous.<ref>{{cite book|last=Hope |first=Sylvia |authormask= |authorlink= |firstn= |authorn-link= |editor=Chiappe, Luis M. & Witmer, Lawrence M. |editorn-last= |editorn-first= |editor-link= |editorn-link= |others= |title= Mesozoic Birds: Above the Heads of Dinosaurs |trans_title= |url= |format= |accessdate= |edition= |series= |volume= |origyear= |year=2002 |publisher= |location= |language= |isbn=0-520-20094-2 |oclc= |doi= |bibcode= |id= |page= |pages=339–388 |nopp= |chapter=The Mesozoic Radiation of Neornithes |trans_chapter= |chapterurl= |quote= |ref= |laysummary= |laydate= |separator= |postscript= |lastauthoramp=|last2= }}</ref> While the earlier primitive birds, particularly the Enantiornithes, continued to thrive and diversify alongside the [[pterosaur]]s, all but a few groups of the toothless [[Neornithes]] were cut short at the [[Chicxulub crater|Chicxulub impact]]. The surviving lineages of birds were the comparatively primitive [[Paleognathae]] ([[ostrich]] and its allies), the aquatic [[Anseriformes|duck lineage]], the terrestrial [[Galliformes|fowl]], and the highly volant [[Neoaves]]. ==Adaptive radiation of modern birds== [[File:Giant Haasts eagle attacking New Zealand moa.jpg|thumb|right|[[Harpagornis|Haast's eagle]] and New Zealand [[moa]], the eagle is a [[Neognathae|Neognath]], the moas are [[Paleognathae|Paleognaths]].]] Modern birds are classified in [[Neornithes]], which are now known to have evolved into some basic lineages by the end of the Cretaceous (see ''[[Vegavis]]''<!-- see also Hitorical Biology 18:205-->). The Neornithes are split into the [[paleognath]]s and [[neognath]]s. The paleognaths include the [[tinamou]]s (found only in Central and South America) and the [[ratite]]s, which nowadays are found almost exclusively on the Southern Hemisphere. The ratites are large flightless birds, and include [[ostrich]]es, [[Rhea (bird)|rhea]]s, [[Cassowary|cassowaries]], [[kiwi]]s and [[emu]]s. A few scientists propose that the ratites represent an artificial grouping of birds which have independently lost the ability to fly in a number of unrelated lineages.<ref>{{cite journal | last1 = Phillips | first1 = M. J. | year = 2010 | title = Tinamous and Moa Flock Together: Mitochondrial Genome Sequence Analysis Reveals Independent Losses of Flight among Ratites | url = | journal = Systematic Biology | volume = 59 | issue = 1| pages = 90–107 | doi = 10.1093/sysbio/syp079 | last2 = Gibb | first2 = G. C. | last3 = Crimp | first3 = E. A. | last4 = Penny | first4 = D. |pmid=20525622| displayauthors = 1 }}</ref> In any case, the available data regarding their evolution is still very confusing, partly because there are no uncontroversial fossils from the Mesozoic. The basal divergence from the remaining Neognathes was that of the [[Galloanserae]], the [[superorder]] containing the [[Anseriformes]] ([[duck]]s, [[goose|geese]] and [[swan]]s), and the [[Galliformes]] ([[chicken]]s, [[Turkey (bird)|turkey]]s, [[pheasant]]s, and their allies). The presence of basal anseriform fossils in the Mesozoic and likely some galliform fossils implies the presence of paleognaths at the same time, in spite of the absence of fossil evidence. The dates for the splits are a matter of considerable debate amongst scientists. It is agreed that the Neornithes evolved in the Cretaceous and that the split between the Galloanserae and the other neognaths - the [[Neoaves]] - occurred before the [[Cretaceous–Paleogene extinction event]], but there are different opinions about whether the radiation of the remaining neognaths occurred before or after the extinction of the other dinosaurs.<ref name = "Ericson">{{cite journal | last1 = Ericson | first1 = PGP | last2 = Anderson | first2 = CL | last3 = Britton | first3 = T | last4 = Elzanowski | first4 = A | last5 = Johansson | first5 = US | last6 = Kallersjo | first6 = M | last7 = Ohlson | first7 = JI | last8 = Parsons | first8 = TJ | last9 = Zuccon | first9 = D et al. | year = 2006 | title = Diversification of Neoaves: integration of molecular sequence data and fossils | url = | journal = Biology Letters | volume = 2 | issue = 4| pages = 543–547 | doi = 10.1098/rsbl.2006.0523 | pmid = 17148284 | pmc = 1834003 | author10 = and others | displayauthors = 9 }}</ref> This disagreement is in part caused by a divergence in the evidence, with molecular dating suggesting a Cretaceous radiation, a small and equivocal neoavian [[fossil]] record from Cretaceous, and most living families turning up during the [[Paleogene]]. Attempts made to reconcile the molecular and fossil evidence have proved controversial.<ref name = "Ericson"/><ref>{{cite journal | last1 = Brown | first1 = JW | last2 = Payne | first2 = RB | last3 = Mindell | first3 = DP ''et al.'' | year = 2007 | title = Nuclear DNA does not reconcile 'rocks' and 'clocks' in Neoaves: a comment on Ericson et al. | url = | journal = Biology Letters | volume = 3 | issue = 3| pages = 257–259 | doi = 10.1098/rsbl.2006.0611 | pmid = 17389215 | pmc = 2464679 | author4 = and others | displayauthors = 3 }}</ref> On the other hand, two factors must be considered: First, [[molecular clock]]s cannot be considered reliable in the absence of robust fossil calibration, whereas the fossil record is naturally incomplete. Second, in reconstructed phylogenetic trees, the time and pattern of lineage separation corresponds to the evolution of the ''characters'' (such as DNA sequences, morphological traits etc.) studied, ''not'' to the actual evolutionary pattern of the lineages; these ideally should not differ by much, but may well do so in practice. Considering this, it is easy to see that fossil data, compared to molecular data, tends to be more accurate in general, but also to underestimate divergence times: morphological traits, being the product of entire [[developmental genetics]] networks, usually only start to [[divergent evolution|diverge]] some time ''after'' a lineage split would become apparent in DNA sequence comparison - especially if the sequences used contain many [[silent mutation]]s. ==Classification of modern species== [[File:Bird Diversity 2011.png|thumb|right|The diversity of modern birds]] {{See also|Sibley-Ahlquist taxonomy|dinosaur classification}} The [[phylogenetic]] [[scientific classification|classification]] of birds is a contentious issue. [[Charles Sibley|Sibley]] & Ahlquist's ''Phylogeny and Classification of Birds'' (1990) is a landmark work on the classification of birds (although frequently debated and constantly revised). A preponderance of evidence suggests that most modern bird orders constitute good [[clades]]. However, scientists are not in agreement as to the precise relationships between the main [[clade]]s. Evidence from modern bird anatomy, fossils and DNA have all been brought to bear on the problem but no strong consensus has emerged. As of the mid-2000s, new fossil and molecular data provide an increasingly clear picture of the evolution of modern bird orders, and their relationships. For example, the [[Charadriiformes]] seem to constitute an ancient and distinct lineage, while the [[Mirandornithes]] and [[Cypselomorphae]] are supported by a wealth of anatomical and molecular evidence. The understanding of the interrelationships of lower level taxa also continues to increase, particularly in the massively diverse [[perching bird]] group Passeriformes. Bird classification and phylogenetic analysis is still under debate and requires more research. A 2008 study published in [[Science (journal)|''Science'']] examined DNA sequences from 169 species of birds that represented all of the major extant groups. The findings may necessitate a wholesale restructuring of the avian phylogenetic tree. The findings also supported unestablished relationships between orders and confirmed disputes over particular groupings.<ref>{{cite journal | last1 = Hackett | first1 = S. J. | last2 = Kimball | first2 = R. T. | last3 = Reddy | first3 = S. | last4 = Bowie | first4 = R. C. K. | last5 = Braun | first5 = E. L. | last6 = Braun | first6 = M. J. | last7 = Chojnowski | first7 = J. L. | last8 = Cox | first8 = W. A. et al. | year = 2008 | title = A Phylogenomic Study of Birds Reveals Their Evolutionary History | url = | journal = Science | volume = 320 | issue = 5884| pages = 1763–1768 | doi = 10.1126/science.1157704 | pmid = 18583609 | last9 = Han | first9 = K.-L. | displayauthors = 8 }}</ref> ==Current evolutionary trends in birds== {{See also|Bird conservation}} Evolution generally occurs at a scale far too slow to be witnessed by humans. However, bird species are currently going [[extinct]] at a far greater rate than any possible speciation or other generation of new species. The disappearance of a population, subspecies, or species represents the permanent loss of a range of genes. Another concern with evolutionary implications is a suspected increase in [[Hybrid (biology)|hybridization]]. This may arise from human alteration of habitats enabling related [[allopatric]] species to overlap. [[Forest fragmentation]] can create extensive open areas, connecting previously isolated patches of open habitat. Populations that were isolated for sufficient time to diverge significantly, but not sufficient to be incapable of producing fertile offspring may now be interbreeding so broadly that the integrity of the original species may be compromised. For example, the many hybrid [[hummingbird]]s found in northwest South America may represent a threat to the conservation of the distinct species involved.<ref name="Fjeldså and Krabbe, 1990">{{cite book |last=Fjeldså |first=Jon |author2=Niels Krabbe. |year=1990 |title= Birds of the High Andes: A Manual to the Birds of the Temperate Zone of the Andes and Patagonia, South America |publisher=Apollo Books|isbn=87-88757-16-1}}</ref> Several species of birds have been bred in captivity to create variations on wild species. In some birds this is limited to color variations, while others are bred for larger egg or meat production, for flightlessness or other characteristics. ==Evolutionary theories== *[[Lack's principle]] *[[Survival of the fittest]] ==Further reading== *{{cite journal|journal=Science|date=12 December 2014 |volume=346|number=6215 |doi=10.1126/science.1253293 |title=An integrative approach to understanding bird origins |author=Xing Xu, Zhonghe Zhou, Robert Dudley, Susan Mackem, Cheng-Ming Chuong, Gregory M. Erickson, David J. Varricchio}} ==References== {{Reflist}} {{Birds}} {{Evolution}} {{Fins, limbs and wings}} {{Portal bar|Evolutionary biology}} [[Category:Evolution of birds| ]]'