Editing Bird (section)

===Diversification of modern birds===
{{See also|Sibley–Ahlquist taxonomy of birds|dinosaur classification}}
{{Cladogram|caption=Major groups of modern birds based on [[Sibley-Ahlquist taxonomy]]
|clades={{clade | style=font-size:85%;line-height:100%;width:325px;
|label1='''Aves'''
|1={{clade
 |label1=[[Palaeognathae]]
 |1=([[ratites]] and [[tinamous]])
 |label2= [[Neognathae]]
 |2={{clade
    |2=(all other birds including [[passerine|perching]] birds)
    |label2=[[Neoaves]]
    |label1=[[Galloanserae]]
    |1=([[landfowl]] and [[waterfowl]])
    }}
   }}
}}
}}

Most studies agree on a [[Cretaceous]] age for the most recent common ancestor of modern birds but estimates range from the Early Cretaceous<ref name="Yonezawa2017">{{cite journal |author=Yonezawa, T. |display-authors=et al |date=2017 |title=Phylogenomics and Morphology of Extinct Paleognaths Reveal the Origin and Evolution of the Ratites |journal=Current Biology |volume=27 |number=1 |pages=68–77 |doi=10.1016/j.cub.2016.10.029|pmid=27989673 |doi-access=free |bibcode=2017CBio...27...68Y }}</ref><ref name=divergence>{{cite journal |last1=Lee |first1=M. S. Y. |last2=Cau |first2=A. |last3=Naish |first3=D. |last4=Dyke |first4=G. J. |title=Morphological Clocks in Paleontology, and a Mid-Cretaceous Origin of Crown Aves |journal=Systematic Biology |date=May 2014 |volume=63 |issue=3 |pages=442–449 |doi=10.1093/sysbio/syt110 |pmid=24449041 |doi-access=free }}</ref> to the latest Cretaceous.<ref name=Prum2015>{{cite journal | last1 = Prum | first1 = R. O. | display-authors = et al | year = 2015 | title = A comprehensive phylogeny of birds (Aves) using targeted next-generation DNA sequencing | journal = Nature | volume = 526 | issue = 7574 | pages = 569–573 | bibcode = 2015Natur.526..569P | doi = 10.1038/nature15697 | pmid = 26444237 }}</ref><ref name="kuhl2020">{{cite journal |first1=H. |last1=Kuhl |first2=C. |last2=Frankl-Vilches |first3=A. |last3=Bakker |first4=G. |last4=Mayr |first5=G. |last5=Nikolaus |first6=S. T. |last6=Boerno |first7=S. |last7=Klages |first8=B. |last8=Timmermann |first9=M. |last9=Gahr |date=2020 |volume=38 |number=1 |pages=108–127 |title=An unbiased molecular approach using 3'UTRs resolves the avian family-level tree of life |journal=Molecular Biology and Evolution |doi=10.1093/molbev/msaa191 |pmid=32781465 |pmc=7783168 |hdl=21.11116/0000-0007-B72A-C |hdl-access=free }}</ref> Similarly, there is no agreement on whether most of the early diversification of modern birds occurred in the Cretaceous and associated with breakup of the supercontinent [[Gondwana]] or occurred later and potentially as a consequence of the [[Cretaceous–Paleogene extinction event|Cretaceous–Palaeogene extinction event]].<ref name="Ericson">{{Cite journal |last1=Ericson |first1=Per G.P. |year=2006 |title=Diversification of Neoaves: integration of molecular sequence data and fossils |journal=[[Biology Letters]] |volume=2 |issue=4 |pages=543–547 |doi=10.1098/rsbl.2006.0523 |pmid=17148284 |url=http://www.senckenberg.de/files/content/forschung/abteilung/terrzool/ornithologie/neoaves.pdf |last2=Anderson |first2=C. L. |last3=Britton |first3=T. |last4=Elzanowski |first4=A. |last5=Johansson |first5=U. S. |last6=Källersjö |first6=M. |last7=Ohlson |first7=J. I. |last8=Parsons |first8=T. J. |last9=Zuccon |first9=D. |pmc=1834003 |first10=G. |last10=Mayr |display-authors=1 |access-date=4 July 2008 |archive-url=https://web.archive.org/web/20090325235703/http://www.senckenberg.de/files/content/forschung/abteilung/terrzool/ornithologie/neoaves.pdf |archive-date=25 March 2009 }}</ref> This disagreement is in part caused by a divergence in the evidence; most molecular dating studies suggests a Cretaceous [[evolutionary radiation]], while fossil evidence points to a Cenozoic radiation (the so-called 'rocks' versus 'clocks' controversy).

The discovery in 2005 of ''[[Vegavis]]'' from the [[Maastrichtian]], the last stage of the [[Late Cretaceous]], proved that the diversification of modern birds started before the [[Cenozoic]] era.<ref>{{cite journal |last1=Clarke |first1=Julia A. |last2=Tambussi |first2=Claudia P. |last3=Noriega |first3=Jorge I. |last4=Erickson |first4=Gregory M. |last5=Ketcham |first5=Richard A. |title=Definitive fossil evidence for the extant avian radiation in the Cretaceous |journal=Nature |date=January 2005 |volume=433 |issue=7023 |pages=305–308 |doi=10.1038/nature03150 |pmid=15662422 |bibcode=2005Natur.433..305C |hdl=11336/80763 |hdl-access=free }}</ref> The affinities of an earlier fossil, the possible [[Galliformes|galliform]] ''[[Austinornis]] lentus'', dated to about 85&nbsp;million years ago,<ref>{{cite journal | last1 = Clarke | first1 = J. A. | year = 2004 | title = Morphology, phylogenetic taxonomy, and systematics of ''Ichthyornis'' and ''Apatornis'' (Avialae: Ornithurae) | journal = Bulletin of the American Museum of Natural History | volume = 286 | pages = 1–179 | doi = 10.1206/0003-0090(2004)286<0001:mptaso>2.0.co;2 | hdl = 2246/454 }}</ref> are still too controversial to provide a fossil evidence of modern bird diversification. In 2020, ''[[Asteriornis]]'' from the Maastrichtian was described, it appears to be a close relative of [[Galloanserae]], the earliest diverging lineage within Neognathae.<ref name="Field2020"/>

Attempts to reconcile molecular and fossil evidence using genomic-scale DNA data and comprehensive fossil information have not resolved the controversy.<ref name=Prum2015/><ref name=Jarvis2014/> However, a 2015 estimate that used a new method for calibrating [[molecular clocks]] confirmed that while modern birds originated early in the Late Cretaceous, likely in Western [[Gondwana]], a pulse of diversification in all major groups occurred around the Cretaceous–Palaeogene extinction event.<ref name=Claramunt2015>{{cite journal |last1=Claramunt |first1=S. |last2=Cracraft |first2=J.|author-link2=Joel Cracraft |title=A new time tree reveals Earth history's imprint on the evolution of modern birds |journal=Sci Adv |date=2015 |volume=1 |issue=11 |doi=10.1126/sciadv.1501005 |pmc=4730849 |pmid=26824065 |page=e1501005|bibcode=2015SciA....1E1005C }}</ref> Modern birds would have expanded from West Gondwana through two routes. One route was an Antarctic interchange in the Paleogene. The other route was probably via Paleocene land bridges between South America and North America, which allowed for the rapid expansion and diversification of Neornithes into the [[Holarctic]] and [[Paleotropics]].<ref name=Claramunt2015/> On the other hand, the occurrence of ''Asteriornis'' in the Northern Hemisphere suggest that Neornithes dispersed out of East Gondwana before the Paleocene.<ref name="Field2020"/>