# Calcar

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{{Short description|Spur of cartilage in bats}}
thumb|A picture illustrating the location of the calcar on a bat.

The '''calcar''', also known as the [calcaneum](/source/calcaneum),<ref name="multiple">{{cite web|url=http://www.earthlife.net/mammals/bat-anatomy.html|title=The Anatomy of Bats|website=www.earthlife.net|date=2 April 2020 }}</ref> is the name given to a [spur](/source/spur) of [cartilage](/source/cartilage) arising from inner side of ankle and running along part of outer [interfemoral membrane](/source/interfemoral_membrane) in [bat](/source/bat)s,<ref name="multiple"/><ref>The Handbook of British Mammals ({{ASIN|B000WPL1CO}})</ref> as well as to a similar spur on the legs of some [arthropods](/source/arthropods).<ref>{{cite book|url=https://books.google.com/books?id=GZogAAAAQBAJ&pg=PA34| page=34|title=Dictionary of Insect Morphology|first1= Henrik|last1= Steinmann| first2= Lajos| last2= Zombori|publisher=Walter de Gruyter|year=2012|isbn=9783110816471}}</ref>

The calcar serves to help spread the interfemoral membrane,<ref>{{cite web|url=http://www.si.edu/Encyclopedia_SI/nmnh/batfacts.htm|title=Encyclopedia Smithsonian: Bat Facts<!-- Bot generated title -->|website=si.edu}}</ref> which is part of the wing membrane between the tail and the hind legs. 

'''Calcar''' ('''femorale''') also refers to the dense, vertically oriented bone present in the [posteromedial](/source/Anatomical_terms_of_location) region of the [femoral shaft](/source/body_of_femur) [inferior](/source/Anatomical_terms_of_location) to the [lesser trochanter](/source/Body_of_femur).

==Usage history==
It is unclear who first coined the word "calcar" to apply to bat anatomy; records of its usage date to [Joel Asaph Allen](/source/Joel_Asaph_Allen) in 1893. The word calcar is derived from [Latin](/source/Latin) "[calx](/source/wiktionary%3Acalx)," meaning "heel". Other terms or phrases that refer to the same feature include "supplementary calcaneal bones", "styliform bones", ''"les éperons"'' (French), ''"Fußwurzelstachels"'' (German), "spurs", and "stylets".<ref name="Schutt 1998"/>

==Prevalence==
Not all bats have a calcar, as not all bats have a well-developed [uropatagium](/source/interfemoral_membrane). Of the bats that have a developed uropatagium, most, but not all, have a calcar.

The [Kitti's hog-nosed bat](/source/Kitti's_hog-nosed_bat) is the only species of bat that has an extensive uropatagium while lacking a calcar.<ref name="Schutt 1998">{{cite journal|last1=Schutt| first1= W. A.| last2= Simmons| first2=N. B.| date=1998| title= Morphology and homology of the chiropteran calcar, with comments on the phylogenetic relationships of Archaeopteropus| journal= Journal of Mammalian Evolution| volume= 5| issue=1| pages= 1–32| doi=10.1023/A:1020566902992 | s2cid= 20426664}}</ref>

==Structure==
[[File:Indiana Bat Foot.jpg|thumb|Keeled calcar of the [Indiana bat](/source/Indiana_bat)]]
The calcar varies widely among bats. It can be as small as {{convert|1|mm|in|abbr=on}}, or longer than {{convert|30|mm|in|abbr=on}}. In some species of bat, the calcar is very long and bladelike. Examples of this include species in the genera ''[Noctilio](/source/Noctilio)'' and ''[Diclidurus](/source/Diclidurus)''.

In other species, the calcar is very small or absent, such as the [Kitti's hog-nosed bat](/source/Kitti's_hog-nosed_bat) or species in the genera ''[Rhinopoma](/source/Rhinopoma)'', ''[Diaemus](/source/Diaemus)'', ''[Mystacina](/source/Mystacina)'', ''[Syconycteris](/source/Syconycteris)'', ''[Harpyionycteris](/source/Harpyionycteris)'', and ''[Notopterus](/source/Notopterus)''.

In the [hairy-legged vampire bat](/source/hairy-legged_vampire_bat), the calcar has a unique, finger-like form that extends approximately {{convert|3|mm|in|abbr=on}} beyond the edge of the uropatagium.<ref name="Schutt 1998"/>
Some [insectivorous](/source/insectivore) species of bats have an elaborate, pronounced calcar.
This form of calcar is referred to as a "keeled calcar", and it is hypothesized that it may be useful in converting the uropatagium into a basket for catching insects.<ref name="Adams 2000">{{cite book|last1=Adams| first1= R. A.| last2=Thibault| first2= K. M.| date= 2000| chapter= Ontogeny and evolution of the hindlimb and calcar: assessing phylogenetic trends| title= Ontogeny, functional ecology, and evolution of bats|url=https://archive.org/details/ontogenyfunction00adam|url-access=limited| publisher=Cambridge University Press| pages= [https://archive.org/details/ontogenyfunction00adam/page/n324 316]–332|isbn=978-0521626323}}</ref>

For species in some genera (for example, ''[Vampyrum](/source/Vampyrum)'' and ''[Phyllostomus](/source/Phyllostomus)''), the calcar is entirely made of cartilage. In other genera (e.g. ''[Saccopteryx](/source/Saccopteryx)'', ''[Pteronotus](/source/Pteronotus)'', ''[Molossus](/source/Molossus_(bat))''), the calcar is calcified. Intermediate between these two forms is when one end of the calcar is calcified, while the other is cartilaginous (e.g. ''[Noctilio](/source/Noctilio)'' and ''[Trachops](/source/Trachops)''). All [megabat](/source/megabat)s, however, lack any calcification in their calcar. 

In [microbat](/source/microbat)s, movement of the calcar is controlled by several muscles, including the [gastrocnemius muscle](/source/gastrocnemius_muscle), m. calcaneocutaneous, and m. depressor ossis styliformis.
M. depressor ossis styliformis [abducts](/source/Anatomical_terms_of_motion) the calcar towards the foot, which spreads the uropatagium.
M. calcaneocutaneous works in opposition to m. depressor ossis styliformis, helping to stabilize the calcar.
The gastrocnemius muscle aids in [flexion of the foot](/source/Anatomical_terms_of_motion), working in conjunction with m. depressor ossis styliformis to spread the uropatagium.<ref name="Schutt 1998"/>

Unlike microbats, [megabat](/source/megabat)s lack the m. calcaneocutaneous muscle for calcar control; megabats do share the other two muscles for calcar control, however.<ref name="Adams 2000"/>

==Function==
The calcar can assist the uropatagium in forming a basket or pouch to help catch and hold insects captured in flight.<ref name="multiple"/> 
The calcar helps spread the uropatagium during flight, managing its [camber](/source/Camber_(aerodynamics)).
For species of bats that forage via [trawling](/source/bat_flight), such as the [greater bulldog bat](/source/greater_bulldog_bat) and the [fish-eating myotis](/source/myotis_vivesi), the calcar is used to prevent the uropatagium from dragging along the surface of the water.
In the hairy-legged vampire bat, the calcar is not used for flight, but rather as a sixth digit to aid in tree-climbing.<ref name="Schutt 1998"/>

==Evolutionary history==
The oldest known ancestor to present day bats, ''[Icaronycteris index](/source/Icaronycteris)'', apparently did not have a calcar or spur as evidenced by fossil remains.<ref name="multiple3">Ontogeny, Functional Ecology, and Evolution of Bats ({{ISBN|978-0-52-162632-3}})</ref> 
The oldest known bat with a calcar is ''[Onychonycteris](/source/Onychonycteris)'', which lived in the early [Eocene](/source/Eocene).
''Onychonycteris'' had a long calcar, indicative of a broad tail membrane.
In describing ''Onychonycteris'' in 2008, Simmons hypothesized that its calcar was more relevant to the mechanism of flight than capturing prey.<ref name="Simmons 2008">{{cite journal|last1=Simmons| first1= N. B.| last2= Seymour| first2= K. L.| last3= Habersetzer| first3= J.| last4= Gunnell| first4= G. F.| date= 2008| title= Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation| journal= Nature| volume= 451| issue=7180| pages= 818–821| doi=10.1038/nature06549| pmid= 18270539| hdl= 2027.42/62816| s2cid= 4356708| url= https://deepblue.lib.umich.edu/bitstream/2027.42/62816/1/nature06549.pdf| hdl-access= free}}</ref>

Some authors have treated the calcar as a [synapomorphy](/source/synapomorphy), or a unique trait shared by all bats, derived from a common ancestor.<ref name="Adams 2000"/>
However, major differences in calcar structure between the two major clades of bat (formerly [Megachiroptera](/source/Megachiroptera) and [Microchiroptera](/source/Microchiroptera), now [Yinpterochiroptera](/source/Yinpterochiroptera) and [Yangochiroptera](/source/Yangochiroptera)) have led other authors to challenge this designation.<ref name="Adams 2000"/><ref name="Schutt 1998"/>
In a paper published in 1998, Schutt and Simmons advocated for different names for this structure for the two suborders, with the Yangochiroptera (microbats) retaining "calcar" and the Yinpterochiroptera (megabats) using "uropatagial spur."
The calcar-like structure is not a synapomorphy, they argued, but rather a similar structure that evolved independently in each suborder.<ref name="Schutt 1998"/>
In 2000, Adams and Thibault published a book on bat [ontogeny](/source/ontogeny) that supported this assertion, stating that various evidence "[supports] the hypothesis of independent origins for the microchiropteran calcar and the megachiropteran ‘uropatagial spur.’ Hence, the calcar, as currently understood, does not meet the assumptions of [biological homology](/source/Homology_(biology))."
Instead, the calcar of the microbats and the uropatagial spur of the megabats are an example of [convergent evolution](/source/convergent_evolution).<ref name="Adams 2000"/>

==References==
{{reflist}}

Category:Mammal anatomy

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Adapted from the Wikipedia article [Calcar](https://en.wikipedia.org/wiki/Calcar) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Calcar?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.