Editing Giraffe (section)

===Evolution===
The giraffe is one of only two living genera of the family Giraffidae in the order [[Artiodactyla]], the other being the [[okapi]].<ref name="Mitchell20003"/> They are [[ruminant]]s of the clade [[Pecora]], along with [[Antilocapridae]] ([[pronghorn]]s), [[Cervidae]] (deer), [[Bovidae]] (cattle, antelope, goats and sheep) and [[Moschidae]] (musk deer). A 2019 [[genome]] study (cladogram below) finds that Giraffidae are a [[sister taxon]] to Antilocapridae, with an estimated [[Split (phylogenetics)|split]] of over 20 million years ago.<ref name=RumiantPhylo2020>{{Cite journal |last1=Chen |first1=L. |last2=Qiu |first2=Q. |last3=Jiang |first3=Y. |last4=Wang |first4=K. |title=Large-scale ruminant genome sequencing provides insights into their evolution and distinct traits |doi=10.1126/science.aav6202 |journal=Science |volume=364 |issue=6446 |page=eaav6202 |year=2019 |pmid=31221828 |bibcode=2019Sci...364.6202C |doi-access=free}}</ref>
{{Clade | style=font-size: 100%; line-height:100%
 |label1=[[Ruminantia]]
 |1={{clade
  |label1=[[Tragulina]]
  |1=[[Tragulidae]] [[File:Tragulus napu - 1818-1842 - Print - Iconographia Zoologica - Special Collections University of Amsterdam - (white background).jpg|50 px]]
  |label2=[[Pecora]]
  |2={{clade
   |1={{clade
    |1=[[Antilocapridae]] [[File:Antilocapra white background.jpg|50 px]]
    |2=[[Giraffidae]] [[File:Giraffa camelopardalis Brockhaus white background.jpg|50 px]] }}
   |2={{clade
    |1=[[Cervidae]] [[File:The deer of all lands (1898) Hangul white background.png|50 px]]
    |2={{clade
     |1=[[Bovidae]] [[File:Birds and nature (1901) (14562088237) white background.jpg|50px]]
     |2=[[Moschidae]] [[File:Moschus chrysogaster white background.jpg|50 px]] }} }} }} }} }}

The family Giraffidae was once much more extensive, with over 10 fossil [[Genus|genera]] described.<ref name=Mitchell20003>{{cite journal |author1=Mitchell, G. |author2=Skinner, J. D. |year=2003 |title=On the origin, evolution, and phylogeny of giraffes ''Giraffa camelopardalis'' |journal=[[Transactions of the Royal Society of South Africa]] |volume=58 |issue=1|pages=51–73 |doi=10.1080/00359190309519935 |bibcode=2003TRSSA..58...51M |s2cid=6522531}}</ref> The elongation of the neck appears to have started early in the giraffe [[Lineage (evolution)|lineage]]. Comparisons between giraffes and their ancient relatives suggest vertebrae close to the skull lengthened earlier, followed by lengthening of vertebrae further down.<ref name="Danowitz2015">{{cite journal|author1=Danowitz, M. |author2=Vasilyev, A. |author3=Kortlandt, V. |author4=Solounias, V. |year=2015|title=Fossil evidence and stages of elongation of the ''Giraffa camelopardalis'' neck |journal=[[Royal Society Open Science]]|volume=2|issue=10 |page=150393 |doi=10.1098/rsos.150393 |pmid=26587249 |pmc=4632521 |bibcode=2015RSOS....250393D}}</ref> One early giraffid ancestor was ''[[Canthumeryx]]'', which has been dated variously to have lived {{mya|25|20}}, 17–15&nbsp;mya or 18–14.3&nbsp;mya and whose deposits have been found in Libya. This animal resembled an [[antelope]] and had a medium-sized, lightly built body. ''[[Giraffokeryx]]'' appeared 15–12&nbsp;mya on the [[Indian subcontinent]] and resembled an okapi or a small giraffe, and had a longer neck and similar [[ossicone]]s.<ref name=Mitchell20003/> ''Giraffokeryx'' may have shared a clade with more massively built giraffids like ''[[Sivatherium]]'' and ''[[Bramatherium]]''.<ref name=Danowitz2015/>
[[File:Giraffidcomparison.jpg|thumb|upright|The extinct giraffid ''[[Samotherium]]'' (middle) in comparison with the [[okapi]] (below) and giraffe. The anatomy of ''Samotherium'' appears to have shown a transition to a giraffe-like neck.<ref name=Danowitz/>]]
Giraffids like ''[[Palaeotragus]]'', ''[[Shansitherium]]'' and ''[[Samotherium]]'' appeared 14&nbsp;mya and lived throughout Africa and Eurasia. These animals had broader skulls with reduced frontal cavities.<ref name=Mitchell20003/><ref name=Danowitz2015/> ''Paleotragus'' resembled the okapi and may have been its ancestor.<ref name=Mitchell20003/> Others find that the okapi lineage diverged earlier, before ''Giraffokeryx''.<ref name=Danowitz2015/> ''Samotherium'' was a particularly important [[transitional fossil]] in the giraffe lineage, as the length and structure of its [[cervical vertebrae]] were between those of a modern giraffe and an okapi, and its neck posture was likely similar to the former's.<ref name=Danowitz>{{cite journal|author1=Danowitz, M. |author2=Domalski, R. |author3=Solounias, N. |year=2015 |title=The cervical anatomy of ''Samotherium'', an intermediate-necked giraffid |journal=Royal Society Open Science |volume=2|issue=11 |page=150521|doi=10.1098/rsos.150521|pmid=26716010 |pmc=4680625 |bibcode=2015RSOS....250521D}}</ref> ''[[Bohlinia]]'', which first appeared in southeastern Europe and lived 9–7 mya, was likely a direct ancestor of the giraffe. ''Bohlinia'' closely resembled modern giraffes, having a long neck and legs and similar ossicones and dentition.<ref name=Mitchell20003/>

''Bohlinia'' colonised China and northern India and produced the ''Giraffa'', which, around {{mya|7}}, reached Africa. [[Climate change]]s led to the extinction of the Asian giraffes, while the African giraffes survived and radiated into new species. Living giraffes appear to have arisen around {{mya|1}} in eastern Africa during the [[Pleistocene]].<ref name=Mitchell20003/> Some biologists suggest the modern giraffes descended from ''[[Giraffa jumae|G. jumae]]'';<ref name=sim1996/> others find ''[[Giraffa gracilis|G. gracilis]]'' a more likely candidate. ''G. jumae'' was larger and more robust, while ''G. gracilis'' was smaller and more slender.<ref name=Mitchell20003/>

The changes from extensive forests to more open [[habitat]]s, which began 8&nbsp;mya, are believed to be the main driver for the evolution of giraffes.<ref name=Mitchell20003/> During this time, tropical plants disappeared and were replaced by arid [[C4 plant]]s, and a dry [[savannah]] emerged across eastern and northern Africa and western India.<ref>{{Cite journal|last=Janis|first=C. M. |date=1993 |title=Tertiary Mammal Evolution in the Context of Changing Climates, Vegetation, and Tectonic Events |journal=[[Annual Review of Ecology and Systematics]] |volume=24|pages=467–500|doi=10.1146/annurev.ecolsys.24.1.467|jstor=2097187}}</ref><ref>{{Cite journal |last1=Ramstein |first1=G. |last2=Fluteau|first2=F. |last3=Besse|first3=J. |last4=Joussaume|first4=S. |date=1997 |title=Effect of orogeny, plate motion and land–sea distribution on Eurasian climate change over the past 30 million years|journal=[[Nature (journal)|Nature]] |volume=386 |issue=6627 |pages=788–795 |doi=10.1038/386788a0 |bibcode=1997Natur.386..788R |s2cid=4335003}}</ref> Some researchers have hypothesised that this new habitat, coupled with a different diet, including acacia species, may have exposed giraffe ancestors to toxins that caused higher mutation rates and a higher rate of evolution.<ref name=bada/> The coat patterns of modern giraffes may also have coincided with these habitat changes. Asian giraffes are hypothesised to have had more okapi-like colourations.<ref name=Mitchell20003/>

The giraffe genome is around 2.9 billion [[base pair]]s in length, compared to the 3.3 billion base pairs of the okapi. Of the proteins in giraffe and okapi genes, 19.4% are identical. The [[Divergent evolution|divergence]] of giraffe and okapi lineages dates to around 11.5 mya. A small group of [[regulatory gene]]s in the giraffe appears responsible for the animal's height and associated circulatory adaptations.<ref name=Holmes/><ref name=Genome>{{cite journal|author1=Agaba, M. |author2=Ishengoma, E. |author3=Miller, W. C. |author4=McGrath, B. C. |author5=Hudson, C. N. |author6=Bedoya, R. O. C. |author7=Ratan, A. |author8=Burhans, R. |author9=Chikhi, R. |author10=Medvedev, P. |author11=Praul C. A. |author12=Wu-Cavener, L. |author13=Wood, B. |author14=Robertson, H. |author15=Penfold, L. |author16=Cavener, D. R. |year=2016|title=Giraffe genome sequence reveals clues to its unique morphology and physiology |journal=[[Nature Communications]]|volume=7 |page=11519 |doi=10.1038/ncomms11519 |pmid=27187213 |pmc=4873664 |bibcode=2016NatCo...711519A}}</ref>