Phylogenetic analysis supports the assertion that the ratites are polyphyletic and do not represent a valid grouping of birds. The basal divergence from the remaining Neognathes was that of the Galloanserae , the superorder containing the Anseriformes ducks , geese and swans , and the Galliformes chickens , turkeys , pheasants , 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.
Attempts made to reconcile the molecular and fossil evidence have proved controversial.
Evolution of birds - Wikipedia
On the other hand, two factors must be considered: First, molecular clocks 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. 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: Virtually the same conclusions were already reached before, in a book on avian evolution .
The phylogenetic classification of birds is a contentious issue. 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 clades. 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 mids, 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 study published in Science examined DNA sequences from species of birds that represented all of the major extant groups. The findings may necessitate a wholesale restructuring of the avian phylogenetic tree.
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The findings also supported unestablished relationships between orders and confirmed disputes over particular groupings. 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 hybridization. This may arise from human alteration of habitats enabling related allopatric species to overlap.
The Cretaceous forecast: Tsunamis, a deadly heat pulse, and massive cooling.
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 hummingbirds found in northwest South America may represent a threat to the conservation of the distinct species involved. 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. From Wikipedia, the free encyclopedia. Derivation of birds from a dinosaur precursor, and the adaptive radiation of bird species. Human timeline and Nature timeline. Feathered dinosaur , Paraves , and Avemetatarsalia.
Sibley-Ahlquist taxonomy and dinosaur classification.
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Aurornis Lack's principle Origin of avian flight Origin of birds Survival of the fittest Genomic evolution of birds. The New York Times. Retrieved 28 March The Origin of Birds and the Evolution of Flight. Evidence from Fossils from Northeastern China". In Collected Essays IV: Testing the hypothesis on neontological and paleontological evidence".
Rebuttal To Feduccia ". In Chiappe, Luis M. Above the Heads of Dinosaurs. Proceedings of the National Academy of Sciences. Explicit use of et al. Birds of the High Andes: Origin of birds Origin of flight Evolution of birds Darwin's finches Seabirds. Archaeopteryx Omnivoropterygiformes Confuciusornithiformes Enantiornithes Chaoyangiiformes Patagopterygiformes Ambiortiformes Songlingornithiformes Gansuiformes Ichthyornithiformes Hesperornithes Lithornithiformes Dinornithiformes Aepyornithiformes Gastornithiformes. Struthioniformes ostriches Rheiformes rheas Tinamiformes tinamous Apterygiformes kiwis Casuariiformes emus and cassowaries.
Acryllium Agelastes Guttera Numida. Meleagridinae Perdicinae Phasianinae pheasants and relatives Tetraoninae. Columbiformes doves and pigeons Mesitornithiformes mesites Pteroclidiformes sandgrouses. Phoenicopteriformes flamingos Podicipediformes grebes. Cuculiformes cuckoos Musophagiformes turacos Otidiformes bustards. Caprimulgiformes nightjars and relatives Steatornithiformes Podargiformes Apodiformes swifts and hummingbirds.
Charadriiformes gulls and relatives Gruiformes cranes and relatives. Phaethontiformes tropicbirds Eurypygiformes kagu and sunbittern. Gaviiformes loons or divers Sphenisciformes penguins Procellariiformes albatrosses and petrels Ciconiiformes storks Suliformes cormorants and relatives Pelecaniformes pelicans and relatives. Cariamiformes seriemas and relatives Falconiformes falcons and relatives Psittaciformes parrots Passeriformes perching birds. Cathartiformes New World vultures and condors Accipitriformes eagles and hawks Strigiformes owls Coliiformes mousebirds Trogoniformes trogons and quetzals Leptosomatiformes cuckoo roller Bucerotiformes hornbills and hoopoes Coraciiformes kingfishers and rollers Piciformes woodpeckers and relatives.
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Evolutionary history of life Index of evolutionary biology articles Introduction Outline of evolution Timeline of evolution. Canalisation Evolutionary developmental biology Inversion Modularity Phenotypic plasticity. Cell DNA Flagella Eukaryotes symbiogenesis chromosome endomembrane system mitochondria nucleus plastids In animals eye hair auditory ossicle nervous system brain. The extensively-studied leaf beds in North America show us that at the K-Pg boundary, many of these species suddenly go extinct, and that the plants in leaf beds above the boundary are not as diverse and only a few species dominate.
The Fort Union zero megaflora is thought to represent a mire, or localised swamp. Did mires act as a refuge during the impact and its aftermath, allowing the species from that environment to prosper in the Palaeogene? This would fit with the pattern seen in the amphibian and freshwater reptile species which survived too.
The impact layer itself, about a centimetre of clay, is arguably the most precise and global time marker in the fossil record. This is interpreted as opportunistic, survivor fern species re-colonising a post-apocalyptic landscape. This is something that can be observed following volcanic episodes today. Interestingly, at Palaeogene localities in higher latitudes in Canada, opportunistic angiosperm species can be recognised instead.
A fern spike has also been well-documented as far away as New Zealand, suggesting a scale of devastation well beyond the regional. The plant fossil record is consistent with the impact hypothesis, and that the impact itself killed forests at least regionally, followed by a global nuclear winter which led to widespread extinctions cascading through the terrestrial food chain. While some impact scenarios include global wildfires, there is no evidence of widespread fossil charcoal at the impact layer, which would be expected if that were the case.
The Cretaceous forecast: Tsunamis, a deadly heat pulse, and massive cooling.
In the aftermath, there was a rapid exploitation of the post-impact environment by survival specialists, followed by a more gradual re-colonisation dominated by a few plant species fortunate enough to have been cushioned from the worst effects. No blog post on the K-Pg extinction could be complete without some dinosaur-related discussion, and it is undoubtedly the case that the extinction of the dominant herbivore species on land must have had profound effects on ecosystems. Plant and animals do not evolve in isolation, and this huge shift in herbivory would have resulted in changes to the relative evolutionary successes of the different plant survivors, as the Earth become ever more like the one we recognise today.