Editing Forelimb (section)

=== Digit specialization ===
{{See also|Comparative foot morphology}}
Digits may be specialized for different forms of locomotion. A classic example is the horse's development of a single toe (monodactyly).<ref name=":0" /> Other hooves, like those of [[Even-toed ungulate|even-toed]] and [[odd-toed ungulate]]s, and even the hoof-like foot of extinct [[Hadrosauridae|hadrosaurs]],<ref>{{Cite journal|last=Zheng|first=R. ; Farke|date=2011|title=A Photographic Atlas of the Pes from a Hadrosaurine Hadrosaurid Dinosaur|url=https://www.smithsonianmag.com/science-nature/a-detailed-guide-to-a-hadrosaurs-foot-1530987/|journal=PalArch's Journal of Vertebrate Palaeontology|volume=8|issue=7|pages=1–12|issn=1567-2158}}</ref> may be regarded as similar specializations.

To bear their immense weight, [[Sauropoda|sauropods]], the most derived being [[Titanosauria|titanosaurs]], developed a tubular [[Manus (anatomy)|manus]] (front foot) and gradually lost their digits, standing on their metacarpals.<ref>{{Cite journal|last=Apesteguía|first=Sebastián|date=2005-01-01|title=Evolution of the titanosaur metacarpus|url=https://www.researchgate.net/publication/287912481|journal=Thunder-Lizards: The Sauropodomorph Dinosaurs|pages=321–345}}</ref> The stegosaurian forelimb has evidence for a sauropod−like metacarpal configuration<ref>{{Cite journal|last=Senter|first=Phil|date=2010|title=Evidence for a Sauropod-Like Metacarpal Configuration in Stegosaurian Dinosaurs|journal=Acta Palaeontologica Polonica|volume=55|issue=3|pages=427–432|doi=10.4202/app.2009.1105|issn=0567-7920|doi-access=free}}</ref> This was a different evolutionary strategy than megafaunal mammals such as modern elephants.

[[Therapsid]]s started evolving diverse and specialized forelimbs 270&nbsp;million years ago, during the Permian.<ref>{{Cite web|url=https://www.sciencedaily.com/releases/2019/03/190318151719.htm|title=Mammals' unique arms started evolving before the dinosaurs existed|website=ScienceDaily|language=en|access-date=2019-12-10}}</ref>

==== Opposable thumbs ====
Modern humans are unique in the musculature of the forearm and hand, though opposable thumbs or structures like them have arisen in a few animals.

In dinosaurs, a primitive autonomization of the first [[carpometacarpal joint]] (CMC) may have occurred. In primates, a real differentiation appeared perhaps 70 mya, while the shape of the human thumb CMC finally appears about 5 mya.

* [[Primate]]s fall into one of four groups:<ref>{{Cite book|title=Primate anatomy : an introduction|last=Ankel-Simons, Friderun.|date=2007|publisher=Elsevier Academic Press|isbn=978-0-08-046911-9|edition=3rd|location=Amsterdam|oclc=437597677}}</ref>
** Nonopposable thumbs: [[tarsier]]s and [[marmoset]]s
** Pseudo-opposable thumbs: all [[strepsirrhine]]s and [[Cebidae]]
** Opposable thumbs: [[Old World monkey]]s and all [[Hominidae|great apes]]
** Opposable with comparatively long thumbs: [[gibbon]]s (or lesser apes)

Pandas have evolved pseudo-opposable thumbs by extension of the [[sesamoid bone]], which is not a true digit.<ref>{{Cite journal|last1=Salesa|first1=Manuel J.|last2=Antón|first2=Mauricio|last3=Peigné|first3=Stéphane|last4=Morales|first4=Jorge|date=2006-01-10|title=Evidence of a false thumb in a fossil carnivore clarifies the evolution of pandas|journal=Proceedings of the National Academy of Sciences|language=en|volume=103|issue=2|pages=379–382|doi=10.1073/pnas.0504899102|issn=0027-8424|pmid=16387860|pmc=1326154|bibcode=2006PNAS..103..379S|doi-access=free}}</ref>