Editing Ungulate (section)

===Anatomy===
Ungulates have developed specialized adaptations, especially in the areas of cranial appendages, dentition, and leg morphology including the modification of the [[talus bone|astragalus]] (one of the ankle bones at the end of the lower leg) with a short, robust head.

====Hooves====
{{See also|Hoof}}
[[Image:Capreolus capreolus cloven hoof.jpg|right|thumbnail|Cloven hooves of [[roe deer]] (''Capreolus capreolus''), with dewclaws]] 
The hoof is the tip of the [[toe]] of an ungulate [[mammal]], strengthened by a thick horny ([[keratin]]) covering. The hoof consists of a hard or rubbery sole, and a hard wall formed by a thick [[Nail (anatomy)|nail]] rolled around the tip of the toe. Both the sole and the edge of the hoof wall normally bear the weight of the animal. Hooves grow continuously, and are constantly worn down by use. In most modern ungulates, the [[Radius (bone)|radius]] and [[ulna]] are fused along the length of the forelimb; early ungulates, such as the [[Arctocyonidae|arctocyonids]], did not share this unique skeletal structure.<ref>Janis, Christine M.; Scott, Kathleen M. and Jacobs, Louis L. (1998) ''Evolution of Tertiary Mammals of North America'', Volume 1. Cambridge: Cambridge University Press. pp. 322-23. {{ISBN|9780521355193}}</ref> The fusion of the radius and ulna prevents an ungulate from rotating its forelimb. Since this skeletal structure has no specific function in ungulates, it is considered a homologous characteristic that ungulates share with other mammals. This trait would have been passed down from a common ancestor. While the two orders of ungulates colloquial names were based on the number of toes of their members ("odd-toed" for the perissodactyls and "even-toed" for the terrestrial artiodactyls), it is not an accurate reason they were grouped. Tapirs have four toes in the front, yet they were members of the "odd-toed" order; peccaries and modern cetaceans were members of the "even-toed" order, yet peccaries have three toes in the front and whales were an extreme example as they have flippers instead of hooves. Scientists had classified them according to the distribution of their weight to their toes.

Perissodactyls have a mesaxonic foot, meaning that the weight is distributed on the third toe on all legs thanks to the plane symmetry of their feet. There has been a reduction of toes from the common ancestor, with the classic example being horses with their single hooves. In consequence, there was an alternative name for the perissodactyls the nearly obsolete Mesaxonia. Perissodactyls were not the only lineage of mammals to have evolved this trait; the [[Meridiungulata|meridiungulates]] have evolved mesaxonic feet numerous times.

Terrestrial artiodactyls have a paraxonic foot, meaning that the weight is distributed on the third and the fourth toe on all legs. The majority of these mammals have cloven hooves, with two smaller ones known as the [[dewclaws]] that were located further up on the leg. The earliest cetaceans (the [[archaeocetes]]), also had this characteristic in the addition of also having both an [[Astragalus (bone)|astragalus]] and [[cuboid bone]] in the ankle, which were further diagnostic traits of artiodactyls.<ref>{{Cite journal 
| doi = 10.1126/science.1063902 
|date=Sep 2001 
|author1=Gingerich, P.D. |author2=ul Haq, M. |author3=Zalmout, I.S. |author4=Khan, I.H. |author5=Malkani, M.S. | title = Origin of whales from early artiodactyls: hands and feet of Eocene Protocetidae from Pakistan 
| volume = 293 
| issue = 5538 
| pages = 2239–42 
| pmid = 11567134 
| journal = Science
| bibcode=2001Sci...293.2239G
|s2cid=21441797 
| doi-access=free 
}}</ref>

[[File:White-sided dolphin.jpg|thumb|right|[[Pacific white-sided dolphin]] skeleton (missing [[pelvic bones]]), on exhibit at [[The Museum of Osteology]], [[Oklahoma City, Oklahoma]]]]
In modern cetaceans, the front limbs had become [[pectoral fins]] and the hind parts were internal and reduced. Occasionally, the genes that code for longer extremities cause a modern cetacean to develop miniature legs (known as [[atavism]]). The main method of moving is an up-and-down motion with the tail fin, called the [[:wiktionary:fluke|fluke]], which is used for [[Animal locomotion|propulsion]], while the pectoral fins together with the entire tail section provide directional control. All modern cetaceans still retain their digits despite the external appearance suggesting otherwise.

====Teeth====
Most ungulates have developed reduced [[canine teeth]] and specialized [[molar (tooth)|molars]], including bunodont (low, rounded cusps) and [[hypsodont]] (high crowned) teeth. The development of hypsodonty has been of particular interest as this adaptation was strongly associated with the spread of grasslands during the [[Miocene]] about 25&nbsp;million years ago. As forest biomes declined, grasslands spread, opening new [[Ecological niche|niches]] for mammals. Many ungulates switched from browsing diets to grazing diets, and possibly driven by abrasive silica in grass, hypsodonty became common. However, recent evidence ties the evolution of hypsodonty to open, gritty habitats and not the grass itself. This is termed the [[Grit, not grass hypothesis]].<ref>{{cite journal | last1 = Jardine | first1 = Phillip E. | last2 = Janis | first2 = Christine M. | last3 = Sahney | first3 = Sarda | last4 = Benton | first4 = Michael J. | year = 2012 | title = Grit not grass: Concordant patterns of early origin of hypsodonty in Great Plains ungulates and Glires | doi = 10.1016/j.palaeo.2012.09.001 | journal = Palaeogeography, Palaeoclimatology, Palaeoecology | volume = 365–366 | pages = 1–10 | bibcode = 2012PPP...365....1J }}</ref>

Some ungulates completely lack upper incisors and instead have a [[dental pad]] to assist in browsing.<ref name="2001Rouge">{{cite web | title = Dental Anatomy of Ruminants | last = Rouge | first = Melissa | year = 2001 | publisher = Colorado State University | url = http://www.vivo.colostate.edu/hbooks/pathphys/digestion/pregastric/cowpage.html | access-date = 5 May 2010 | archive-date = 28 September 2011 | archive-url = https://web.archive.org/web/20110928131653/http://www.vivo.colostate.edu/hbooks/pathphys/digestion/pregastric/cowpage.html | url-status = dead }}</ref><ref name="WonderQuest">{{cite web | publisher = WonderQuest | title = Toothless cud chewers, To see ourselves as others see us... | url = http://www.wonderquest.com/cows-teeth-mirrors.htm | access-date = 5 May 2010}}</ref> It can be found in camels, ruminants, and some toothed whales; modern baleen whales were remarkable in that they have [[baleen]] instead to filter out the krill from the water. On the other spectrum teeth have been evolved as weapons or sexual display seen in pigs and peccaries, some species of deer, musk deer, hippopotamuses, beaked whales and the Narwhal, with its long canine tooth.<ref name="Nweeia et al.">{{cite journal|last1=Nweeia|first1=Martin T.|title=Vestigial tooth anatomy and tusk nomenclature for ''Monodon monoceros''|journal=The Anatomical Record|year=2012|doi=10.1002/ar.22449|pmid=22467529|volume=295|issue=6|pages=1006–16|first2=Frederick C.|last2=Nweeia|first3=Peter V.|last3=Hauschka|first4=Ethan|last4=Tyler|first5=James G.|last5=Mead|first6=Charles W.|last6=Potter|first7=David P.|last7=Angnatsiak|first8=Pierre R.|last8=Richard|first9=Jack R.|last9=Orr|first10=Sandie R.|last10=Black|s2cid=22907605|display-authors=etal|doi-access=free}}</ref>

====Cranial appendages====
{{See also|Horn (anatomy)|Ossicone|Antler}}
[[File:Red deer stag velvet.jpg|thumb|upright|[[velvet antler|Velvet]] covers a growing antler and provides it with blood, supplying oxygen and nutrients.]]

Ungulates have evolved a variety of cranial appendages that can be found in [[Pecora|cervoids]] (with the exception of musk deer). In oxen and antelope, the size and shape of the [[horn (anatomy)|horns]] varies greatly but the basic structure is always a pair of simple bony protrusions without branches, often having a spiral, twisted, or fluted form, each covered in a permanent sheath of [[keratin]]. The unique horn structure is the only unambiguous morphological feature of bovids that distinguishes them from other [[pecorans]].<ref>{{cite journal |last1=Bibi |first1=F. |last2=Bukhsianidze |first2=M. |last3=Gentry |first3=A. |last4=Geraads |first4=D. |last5=Kostopoulos |first5=D. |last6=Vrba |first6=E. |year=2009 |title=The fossil record and evolution of Bovidae: State of the field |url=http://palaeo-electronica.org/2009_3/169/index.html |journal=Palaeontologia Electronica |volume=12 |issue=3 |pages=10A}}</ref><ref>{{cite journal|last=Gatesy|first=J.|author2=Yelon, D., DeSalle, R., Vrba, E. |year=1992|title=Phylogeny of the Bovidae (Artiodactyla, Mammalia), Based on Mitochondrial Ribosomal DNA Sequences|journal=Mol. Biol. Evol.|volume=9|issue=3|pages=433–446|pmid=1584013|doi=10.1093/oxfordjournals.molbev.a040734|doi-access=free}}</ref> Male horn development has been linked to sexual selection,<ref name=BroJ>{{cite journal|doi=10.1111/j.1558-5646.2007.00111.x|last=Bro-Jørgensen|first=J.|year=2007|title=The intensity of sexual selection predicts weapon size in male bovids|journal=Evolution|volume=61|issue=6|pages=1316–1326|pmid=17542842|s2cid=24278541|doi-access=free}}</ref><ref>{{cite journal|last=Ezenwa|first=V.|author2=Jolles, A. |year=2008|title=Horns honestly advertise parasite infection in male and female African buffalo|journal=Animal Behaviour|doi=10.1016/j.anbehav.2007.12.013|volume=75|pages=2013–2021|issue=6|s2cid=49240459}}</ref> while the presence of horns in females is likely due to natural selection.<ref name=BroJ/><ref name=Stankowich>{{cite journal|last=Stankowich|first=T.|author2=Caro, T. |author2-link=Tim Caro |year=2009|title=Evolution of weaponry in female bovids|journal=[[Proceedings of the Royal Society B]]|pmid=19759035|doi=10.1098/rspb.2009.1256|volume=276|issue=1677|pages=4329–34|pmc=2817105}}</ref> The horns of females are usually smaller than those of males and are sometimes of a different shape. The horns of female bovids are thought to have evolved for defense against [[predator]]s or to express territoriality, as nonterritorial females, which are able to use [[crypsis]] for predator defense, often lack horns.<ref name=Stankowich/>

Rhinoceros horns, unlike those of other horned mammals, consist only of keratin. These horns rest on the nasal ridge of the animal's skull.

[[Antler]]s are unique to cervids and found mostly on males: the only cervid females with antlers are [[reindeer|caribou and reindeer]], whose antlers are normally smaller than males'. Nevertheless, fertile [[wiktionary:doe#English|does]] of other species of deer have the capacity to produce antlers on occasion, usually due to increased testosterone levels.<ref>[http://www.das.psu.edu/research-extension/deer/photos/antlered-doe Antlered Doe] {{webarchive|url=https://web.archive.org/web/20120229040529/http://www.das.psu.edu/research-extension/deer/photos/antlered-doe |date=2012-02-29 }}</ref> Each antler grows from an attachment point on the skull called a pedicle. While an antler is growing it is covered with highly [[Blood vessel|vascular]] [[skin]] called velvet, which supplies oxygen and nutrients to the growing bone.<ref name=Hall>{{Cite book | last = Hall | first = Brian K. | year = 2005 | title = Bones and Cartilage: Developmental and Evolutionary Skeletal Biology | publisher = Academic Press | chapter = Antlers | pages = 103–114 | isbn = 978-0-12-319060-4 | chapter-url = https://books.google.com/books?id=y-RWPGDONlIC&pg=PA103 | access-date = 2010-11-08 }}</ref>  Antlers are considered one of the most exaggerated cases of male secondary sexual traits in the animal kingdom,<ref name="Malo">{{cite journal | last1 = Malo | first1 = A. F. | last2 = Roldan | first2 = E. R. S. | last3 = Garde | first3 = J. | last4 = Soler | first4 = A. J. | last5 = Gomendio | first5 = M. | year = 2005 | title = Antlers honestly advertise sperm production and quality | journal = Proceedings of the Royal Society B | volume = 272 | issue = 1559| pages = 149–157 | doi=10.1098/rspb.2004.2933 | pmid=15695205 | pmc=1634960}}</ref> and grow faster than any other mammal bone.<ref name=W&H>{{Cite book | last1 = Whitaker | first1 = John O. | last2 = Hamilton | first2 = William J. Jr. | year = 1998 | title = Mammals of the Eastern United States | publisher = Cornell University Press | page = 517 | isbn = 978-0-8014-3475-4 | url = https://books.google.com/books?id=5fVymWAez-YC&pg=PA517 | access-date = 2010-11-08 }}</ref>  Growth occurs at the tip, initially as [[cartilage]] that is then mineralized to become bone. Once the antler has achieved its full size, the velvet is lost and the antler's bone dies. This dead bone structure is the mature antler. In most cases, the bone at the base is destroyed by [[osteoclast]]s and the antlers eventually fall off.<ref name=Hall/> As a result of their fast growth rate antlers place a substantial nutritional demand on deer; they thus can constitute an honest signal of metabolic efficiency and food gathering capability.<ref name="Ditchkoff">{{cite journal | last1 = Ditchkoff | first1 = S. S. | last2 = Lochmiller | first2 = R. L. | last3 = Masters | first3 = R. E. | last4 = Hoofer | first4 = S. R. | last5 = Den Bussche | first5 = R. A. Van | year = 2001 | title = Major-histocompatibility-complex-associated variation in secondary sexual traits of white-tailed deer (Odocoileus virginianus): evidence for good-genes advertisement | journal = Evolution | volume = 55 | issue = 3| pages = 616–625 | doi=10.1111/j.0014-3820.2001.tb00794.x | pmid=11327168| s2cid = 10418779 | doi-access = free }}</ref>

[[Ossicone]]s are horn-like (or antler-like) protuberances found on the heads of giraffes and male [[okapi]]s. They are similar to the horns of [[antelope]]s and [[cattle]] save that they are derived from ossified [[cartilage]],<ref>"The Nashville Zoo at Grassmere - Animals :: Masai Giraffe". The Nashville Zoo at Grassmere, n.d. Web. 15 Feb. 2010. {{cite web|title=The Nashville Zoo at Grassmere - Animals :: Masai Giraffe|url=http://www.nashvillezoo.org/animals_detail.asp?animalID=12|url-status=dead|archive-url=https://web.archive.org/web/20101220142807/http://nashvillezoo.org/animals_detail.asp?animalID=12|archive-date=2010-12-20|access-date=2013-02-10}}</ref> and that the ossicones remain covered in [[skin]] and [[fur]] rather than horn.

[[Pronghorn]] cranial appendages are unique. Each "horn" of the pronghorn is composed of a slender, laterally flattened blade of bone that grows from the frontal bones of the skull, forming a permanent core. As in the Giraffidae, skin covers the bony cores, but in the pronghorn it develops into a keratinous sheath that is shed and regrown on an annual basis. Unlike the horns of the family Bovidae, the horn sheaths of the pronghorn are branched, each sheath possessing a forward-pointing tine (hence the name pronghorn). The horns of males are well developed.