Editing Beaver (section)

== Taxonomy ==
[[Carl Linnaeus]] coined the genus name ''Castor'' as well as the [[specific epithet|specific (species) epithet]] ''fiber'' for the Eurasian species.<ref name="ITISfiber">{{cite web|title=Castor fiber|url=https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=573165#null|url-status=live|archive-url=https://web.archive.org/web/20201103070634/https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=573165#null|archive-date=November 3, 2020|access-date=September 21, 2020|website=ITIS}}</ref> German zoologist [[Heinrich Kuhl]] coined ''C. canadensis'' in 1820.<ref name="ITIScandensis">{{cite web|title=Castor canadensis|url=https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=180212#null|url-status=live|archive-url=https://web.archive.org/web/20201103070405/https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=180212#null|archive-date=November 3, 2020|access-date=September 21, 2020|website=ITIS}}</ref> Many scientists considered both names synonymous for one same species{{sfn|Poliquin|2015|pp=79–80}}<ref name="MacDonald"/> until the 1970s, when [[Chromosome#Number in various organisms|chromosomal]] evidence became available confirming both as separate where the Eurasian has 48 chromosomes, while the North American has 40. The difference in chromosome numbers prevents them from interbreeding.<ref>{{cite journal|last1=Lahti|first1=S.|last2=Helminen|first2=M.|year=1974|title=The beaver ''Castor fiber'' (L.) and ''Castor canadensis'' (Kuhl) in Finland|journal=Acta Theriologica|volume=19|issue=4|pages=177–189|doi=10.4098/AT.ARCH.74-13|doi-access=free}}</ref> Twenty-five subspecies have been classified for ''C. canadensis'', and nine have been classified for ''C. fiber''.<ref name="ITISfiber"/><ref name="ITIScandensis"/>

There are two [[Extant taxa|extant]] species: the [[North American beaver]] (''Castor canadensis'') and the [[Eurasian beaver]] (''C. fiber''). The Eurasian beaver is slightly longer and has a more lengthened skull, triangular [[nasal cavity|nasal cavities]] (as opposed to the square ones of the North American species), a lighter fur color, and a narrower tail.{{sfn|Runtz|2015|pp=22–25}}

===Evolution===
{{multiple image
| align     =right
| direction =horizatonal
| width     =220
| image1    =Castor canadensis1.jpg
| caption1  =North American beaver (''Castor canadensis'')
| alt1      =North American Beaver on a river bank
| image2    =Castor fiber eating in Eskilstuna, Sweden.jpg
| caption2  =Eurasian beaver (''Castor fiber'')
| alt2      =A Eurasian Beaver gnawing on a branch
}}
{{cladogram|caption=Phylogeny of extant and extinct relatives of modern beavers based on genetics and morphology.<ref name="Fabre">{{Cite journal|last1=Fabre |first1=Pierre-Henri |last2=Hautier |first2=Lionel |last3=Dimitrov |first3=Dimitar |last4=Douzery |first4=Emmanuel J. P.  |year=2012 |title= A glimpse on the pattern of rodent diversification: a phylogenetic approach |journal=[[BMC Evolutionary Biology]] |volume=12 |number=88 |page=88 |doi=10.1186/1471-2148-12-88 |pmid=22697210 |pmc=3532383 |doi-access=free |bibcode=2012BMCEE..12...88F }}</ref><ref name=Rybczynski/>
|cladogram={{clade|style=width:500px;
      |label1=[[Castorimorpha]]
      |1={{clade
        |label1=[[Castoroidea]]
        |1={{clade
           |label1=[[Castoridae]]<!--[[File:Die Gartenlaube (1858) b 068 white background.jpg|50px]]-->
           |1={{clade
              |1=''Agnotocastor coloradensis''
              |2={{clade
                 |1={{clade
                    |1=''Agnotocastor praetereadens''
                    |2={{clade
                       |1=''[[Anchitheriomys]]'' sp. [[File:Anchitheriomys.JPG|50px]]
                       |2={{clade
                          |1=[[Castorinae]] (modern beavers) [[File:Die Gartenlaube (1858) b 068 white background.jpg|50px]]
                          |2=[[Castoroidinae]] [[File:Giant-beaver-fieldmuseum.jpg|50px]]
                          }}
                       }}
                    }}
                 |2={{clade
                    |1=''[[Agnotocastor]]'' sp.
                    |2={{clade
                       |1=''[[Migmacastor procumbodens]]''
                       |2=Palaeocastorinae [[File:Palaeocastor fossor.jpg|50px]]
                       }}
                    }}
                 }}
              }}
           }}
        |label2=[[Geomyoidea]]
        |2={{clade
          |1=[[Heteromyidae]] (kangaroo rats and allies) [[File:Image taken from page 108 of 'Report of an expedition down the Zuni and Colorado Rivers by Captain L. Sitgreaves (white background).jpg|50px]]
          |2=[[Geomyidae]] (gophers) [[File:Western pocket gopher.jpg|50px]]
           }}
     }}
}}
}}
Beavers belong to the rodent suborder [[Castorimorpha]], along with [[Heteromyidae]] ([[kangaroo rats]] and [[kangaroo mice]]), and the [[gophers]]. Modern beavers are the only extant members of the family [[Castoridae]]. They originated in North America in the late [[Eocene]] and colonized Eurasia via the [[Bering Land Bridge]] in the early [[Oligocene]], coinciding with the ''[[Grande Coupure]]'', a time of significant changes in animal species around 33{{spaces}}million years ago ([[myr]]).<ref name="Doronina 2017">{{cite journal |last1=Doronina |first1=Liliya |last2=Matzke |first2=Andreas |last3=Churakov |first3=Gennady |last4=Stoll |first4=Monika |last5=Huge |first5=Andreas |last6=Schmitz |first6=Jürgen |title=The beaver's phylogenetic lineage ''illumina''ted by retroposon reads |journal=[[Scientific Reports]] |year=2017 |volume=7 |issue=1 |page=43562 |doi=10.1038/srep43562|pmid=28256552 |pmc=5335264 |bibcode=2017NatSR...743562D |doi-access=free}}</ref><ref name=Korth2002/>

The more [[Basal (phylogenetics)|basal]] castorids had several unique features: more complex [[Occlusion (dentistry)|occlusion]] between cheek teeth, parallel rows of upper teeth, premolars that were only slightly smaller than molars, the presence of a third set of premolars (P3), a [[Foramen|hole]] in the [[stapes]] of the inner ear, a smooth [[palatine bone]] (with the palatine opening closer to the rear end of the bone), and a longer [[Rostrum (anatomy)#Vertebrates|snout]]. More [[Synapomorphy and apomorphy|derived]] castorids have less complex occlusion, upper tooth rows that create a V-shape towards the back, larger second premolars compared to molars, absence of a third premolar set and stapes hole, a more grooved palatine (with the opening shifted towards the front), and reduced [[incisive foramen]]. Members of the subfamily ''Palaeocastorinae'' appeared in late-Oligocene North America. This group consisted primarily of smaller animals with relatively large front legs, a flattened skull, and a reduced tail—all features of a [[fossorial]] (burrowing) lifestyle.<ref name=Korth2002>{{cite journal |last=Korth |first=W. W. |year=2002 |title=Comments on the systematics and classification of the beavers (Rodentia, Castoridae) |journal=[[Journal of Mammalian Evolution]] |volume=8 |issue=4 |pages=279–296 |doi=10.1023/A:1014468732231 |s2cid=27935955}}</ref>

In the early [[Miocene]] (about 24 mya), castorids [[Evolution|evolved]] a [[semiaquatic]] lifestyle. Members of the subfamily [[Castoroidinae]] are considered to be a [[sister group]] to modern beavers, and included giants like ''[[Castoroides]]'' of North America and ''[[Trogontherium]]'' of Eurasia.<ref name=Rybczynski>{{cite journal |last=Rybczynski |first=N. |year=2007|title=Castorid phylogenetics: Implications for the evolution of swimming and tree-exploitation in beavers|journal=[[Journal of Mammalian Evolution]] |volume=14 |pages=1–35 |doi=10.1007/s10914-006-9017-3 |s2cid=33659669}}</ref><ref name=Korth2002/> ''Castoroides'' is estimated to have had a length of {{convert|1.9|–|2.2|m|ft|1|abbr=on}} and a weight of {{convert|90|–|125|kg|lb|0|abbr=on}}.<ref name="R&S">{{cite journal |last1=Swinehart |first1=A. L. |last2=Richards |first2=R. L. |title=Paleoecology of Northeast Indiana Wetland Harboring Remains of the Pleistocene Giant Beaver (Castoroides Ohioensis) |journal=[[Proceedings of the Indiana Academy of Science]] |date=2001 |volume=110 |page=151 |url=https://journals.iupui.edu/index.php/ias/article/download/7219/7239 |access-date=November 21, 2014 |archive-date=March 4, 2016 |archive-url=https://web.archive.org/web/20160304084347/https://journals.iupui.edu/index.php/ias/article/download/7219/7239 |url-status=live }}</ref> Fossils of one genus in Castoroidinae, ''[[Dipoides]]'', have been found near piles of chewed wood,<ref name=Rybczynski/> though ''Dipoides'' appears to have been an inferior woodcutter compared to ''Castor''. Researchers suggest that modern beavers and Castoroidinae shared a bark-eating [[Lowest common ancestor|common ancestor]]. Dam and lodge-building likely developed from bark-eating, and allowed beavers to survive in the harsh winters of the [[subarctic]]. There is no conclusive evidence for this behavior occurring in non-''Castor'' species.<ref name=Plint2020>{{Cite journal|last1=Plint|first1=Tessa|last2=Longstaffe|first2=Fred J.|last3=Ballantyne|first3=Ashley|last4=Telka|first4=Alice|last5=Rybczynski|first5=Natalia|year=2020|title=Evolution of woodcutting behaviour in Early Pliocene beaver driven by consumption of woody plants|journal=[[Scientific Reports]]|volume=10|number=13111|page=13111|doi=10.1038/s41598-020-70164-1|pmid=32753594|pmc=7403313|bibcode=2020NatSR..1013111P|issn=2045-2322|doi-access=free}}</ref>

The genus ''Castor'' likely originated in [[Eurasia]].<ref name="speciation"/> The earliest fossil remains appear to be ''C. neglectus'', found in Germany and dated 12–10 mya.<ref>{{cite journal|last1=Samuels|first1=J. X.|last2=Zancanella|first2=J.|year=2011|title=An early Hemphillian occurrence of ''Castor'' (Castoridae) from the Rattlesnake Formation of Oregon|journal=Journal of Paleontology|volume=85|issue=5|pages=930–935|doi=10.1666/11-016.1|s2cid=128866799}}</ref> [[Mitochondrial DNA]] studies place the common ancestor of the two living species at around 8 mya. The ancestors of the North American beaver would have crossed the Bering Land Bridge around 7.5 mya.<ref name="speciation">{{cite journal |last1=Horn |first1=S. |last2=Durke |first2=W. |last3=Wolf |first3=R. |last4=Ermala |first4=A. |last5=Stubbe |first5=M. |last6=Hofreiter |first6=M. |title=Mitochondrial Genomes Reveal Slow Rates of Molecular Evolution and the Timing of Speciation in Beavers (''Castor''), One of the Largest Rodent Species|journal=[[PLOS ONE]]|year=2011 |volume=6 |issue=1 |page=e14622|doi=10.1371/journal.pone.0014622|pmid=21307956 |pmc=3030560 |bibcode=2011PLoSO...614622H |doi-access=free }}</ref> ''Castor'' may have competed with members of Castoroidinae, which led to [[niche differentiation]].<ref>{{cite journal|last1=Samuels|first1=J. X.|last2=Van Valkenburgh|first2=B.|year=2008|title=Skeletal indicators of locomotor adaptations in living and extinct rodents|journal=[[Journal of Morphology]]|volume=269|issue=11 |pages=1387–1411|doi=10.1002/jmor.10662| pmid=18777567|s2cid=36818290}}</ref> The fossil species ''C. praefiber'' was likely an ancestor of the Eurasian beaver.<ref>{{cite journal|last1=Barisone|first1=G.|last2=Argenti|first2=P.|last3=Kotsakis|first3=T.|year=2006|title=Plio-Pleistocene evolution of the genus ''Castor'' (Rodentia, Mammalia) in Europe: ''C. fiber plicidens'' of Pietrafitta (Perugia, Central Italy)|journal=[[Geobios]]|volume=39|issue=6|pages=757–770|doi=10.1016/j.geobios.2005.10.004|bibcode=2006Geobi..39..757B }}</ref> ''[[Castor californicus|C. californicus]]'' from the [[Early Pleistocene]] of North America was similar to but larger than the extant North American beaver.<ref name=K&A>{{cite book | author=Kurtén, B. | author-link=Björn Kurtén | author2=Anderson, E.   | title=Pleistocene Mammals of North America | location=New York | publisher=[[Columbia University Press]] | year=1980 | pages=236–237 | isbn=978-0231037334|oclc=5830693}}</ref>'