Editing Animal weapon (section)

== Evolution ==
[[File:Triceratops Hendrickx2.jpg|thumb|upright=1|The horns that give [[Triceratops]] its name were used as weapons.]]

Animal weaponry is capable of drastic and rapid diversification in form, with closely related species, even within the same clade, having distinctly different weaponry.<ref name="Emlen2008"></ref> One hypothesized mechanism for this is the gradual change in weaponry function from purely physical agonistic behavior, to a stronger emphasis on display, resulting in potentially more elaborate weapons. For instance, many dinosaurs may have had structures that were once weapons but were later used as ornaments to attract mates.<ref name="Emlen2008"></ref> Another possible mechanism is the presence of male-male combat, with diverging lineages of animals expanding into different habitats and then fighting under different conditions. Changes in the physical contest between species in different environments may potentially drive the evolution in modified weaponry. Sites that have localized, defendable resources, like a single food or water source, or a breeding burrow, often are where species with weapons are found.<ref name="Emlen2008"></ref>

Sexual selection has been a main focus on weaponry and antagonist interactions between animals, with males that present the largest weapons having the highest probability of winning.<ref name="Emberts2018">{{Cite journal |last1=Emberts |first1=Zachary |last2=St. Mary |first2=Colette M. |last3=Herrington |first3=Tyler J. |last4=Miller |first4=Christine W. |date=2018-05-03 |title=Males missing their sexually selected weapon have decreased fighting ability and mating success in a competitive environment |url=https://doi.org/10.1007/s00265-018-2494-6 |journal=Behavioral Ecology and Sociobiology |language=en |volume=72 |issue=5 |pages=81 |doi=10.1007/s00265-018-2494-6 |s2cid=253820366 |issn=1432-0762|url-access=subscription }}</ref> Sexual selection has been credited by previous researchers as the main influence of nature's extravagant weaponry for the purpose of attractive females.<ref name="Emlen2008"></ref> During agonistic interactions, there is the potential risk of weaponry lost resulting in a possible decrease in an individual's fighting ability and overall fitness.<ref name="Emberts2018" />

[[File:WLA hmns Trilobite Ceratarges sp.jpg|thumb|upright=1.25|A [[trilobite]] of the genus ''[[Ceratarges]]'', showing large spines probably used as weapons.]]

Most animal weapons probably emerged independently. The weapons of ungulates, for instance, are believed to have evolved independently during the [[Age of Mammals]], and are not from an earlier, basal clade of mammals. One group that had weapons early in the history of multicellular life were the [[trilobites]], one of the earliest arthropods, and a dominant life form in the [[Paleozoic]].<ref name="Aria2022">{{Cite journal |last1=Aria |first1=Cédric |title=The origin and early evolution of arthropods |url=https://onlinelibrary.wiley.com/doi/full/10.1111/brv.12864 |journal=Biological Reviews |date=2022-04-26 |language=en |volume=97 |issue=5 |pages=1786–1809 |doi=10.1111/brv.12864}}</ref><ref name="Emlen2008"></ref>  Many species had horns or spikes which are theorized to have been used in intraspecific combat.<ref name="Emlen2008"></ref> Many dinosaurs also had weapons such as spines, spikes, and plates, although the exact use of these is not known for all species—some may have been used for mating displays more than as weapons.<ref name="Emlen2008"></ref>

An exception to the general independence of weapon evolution is found in [[stag beetles]], whose common ancestor is believed to have had mandibles, much like modern stag beetles. However, that species likely had little or no sexual dimorphism in the mandible phenotype, unlike modern stag beetles, in which males usually have markedly larger mandibles than females.<ref name="Hosoya2005">{{Cite journal |last1=Hosoya |first1=Tadatsugu |last2=Araya |first2=Kunio |title=Phylogeny of Japanese stag beetles (Coleoptera: Lucanidae) inferred from 16S mtrRNA gene sequences, with reference to the evolution of sexual dimorphism of mandibles |url=https://bioone.org/journals/zoological-science/volume-22/issue-12/zsj.22.1305/Phylogeny-of-Japanese-Stag-Beetles-Coleoptera--Lucanidae-Inferred-from/10.2108/zsj.22.1305.full |journal=Zoological Science |date=2005 |language=en |volume=22 |issue=12 |pages=1305–1318 |doi=10.2108/zsj.22.1305|pmid=16462103 }}</ref><ref name="Emlen2008"></ref> [[Dung beetles]], on the other hand, have evolved and lost their weapons many, many times over their history,<ref name="Emlen2008"></ref> with the single genus ''[[Onthophagus]]'', whose ancestor likely had horns, undergoing at least ten evolutionary events where horns were gained or lost.<ref name="Emlen2005">{{Cite journal |last1=Emlen |first1=Douglas J. |last2=Marangelo |first2=Jennifer |last3=Ball |first3=Bernard |last4=Cunningham |first4=Clifford W. |title=Diversity in the Weapons of Sexual Selection: Horn Evolution in the beetle genus Onthophagus (Coleoptera: Scarabaeidae) |url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.0014-3820.2005.tb01044.x |journal=Evolution |date=2005 |language=en |volume=59 |issue=5 |pages=1060–1084 |doi=10.1111/j.0014-3820.2005.tb01044.x|pmid=16136805 }}</ref>