Editing Saber-toothed predator (section)

==Morphology==
{{more citations needed section|date=April 2015}}
The different groups of saber-toothed predators evolved their saber-toothed characteristics entirely independently. They are most known for having [[maxillary canine]]s which extended down from the mouth when the mouth was closed. Saber-toothed cats were generally more robust than today's cats and were quite bear-like in build. They are believed to have been excellent hunters, taking animals such as [[ground sloth|sloths]], [[mammoth]]s, and other large prey. Evidence from the numbers found at the [[La Brea Tar Pits]] suggests that ''[[Smilodon]]'', like modern [[lion]]s, was a social [[carnivore]].<ref>{{Cite journal |last1=Carbone |first1=C. |last2=Maddox |first2=T. |last3=Funston |first3=P. J. |last4=Mills |first4=M. G. |last5=Grether |first5=G. F. |last6=Van Valkenburgh |first6=B. |year=2009 |title=Parallels between playbacks and Pleistocene tar seeps suggest sociality in an extinct sabretooth cat, Smilodon |journal=Biol. Lett. |volume=5 |issue=1 |pages=81–85 |doi=10.1098/rsbl.2008.0526 |pmid=18957359 |pmc=2657756}}</ref>

The first saber-tooths to appear were non-mammalian [[synapsids]], such as the [[Gorgonopsia|gorgonopsids]]; they were one of the first groups of animals within Synapsida to experience the specialization of saber teeth, and many had long canines. Some had two pairs of upper canines with two jutting down from each side, but most had one pair of upper extreme canines. Because of their primitiveness, they are extremely easy to tell from machairodonts. Several defining characteristics are a lack of [[coronoid process of the mandible|a coronoid process]], many sharp "premolars" more akin to pegs than scissors, and very long skulls. Despite their large canines, however, most gorgonopsians probably lacked the other specializations found in true saber-toothed predator ecomorphs.<ref name=Kammerer2016>{{Cite journal| pmid=26823998| doi = 10.7717/peerj.1608| issn = 2167-8359| volume = 4|  last = Kammerer| first = Christian F.| title = Systematics of the Rubidgeinae (Therapsida: Gorgonopsia)| journal = PeerJ| date = 2016-01-26| pages = e1608| pmc = 4730894| s2cid = 35831378| doi-access = free}}</ref> Two gorgonopsians, ''[[Smilesaurus]]'' and ''[[Inostrancevia]]'', had exceptionally large canines and may have been closer functional analogues to later sabertooths.

The second appearance is in [[Deltatheroida]], a lineage of [[Cretaceous]] [[metatheria]]ns. At least one genus, ''[[Lotheridium]]'', possessed long canines, and given both the predatory habits of the clade as well as the generally incomplete material, this may have been a more widespread adaptation.<ref>{{cite journal | last1 = Bi | first1 = S. | last2 = Jin | first2 = X. | last3 = Li | first3 = S. | last4 = Du | first4 = T. | year = 2015 | title = A new Cretaceous metatherian mammal from Henan, China | journal = PeerJ | volume = 3 | page = e896 | doi=10.7717/peerj.896 | pmid=25893149 | pmc=4400878 | doi-access = free }}</ref>
 
The third appearance of long canines is ''[[Thylacosmilus]]'', which is the most distinctive of the saber-tooth mammals and is also easy to tell apart. It differs from machairodonts in possessing a very prominent flange and a tooth that is triangular in cross section. The root of the canines is more prominent than in machairodonts and a true [[sagittal crest]] is absent.

The fourth instance of saber-teeth is from the clade [[Oxyaenidae]]. The small and slender ''Machaeroides'' bore canines that were thinner than in the average machairodont. Its muzzle was longer and narrower.

The fifth saber-tooth appearance is the ancient [[Feliformia|feliform]] (carnivoran) family [[Nimravidae]]. Both groups have short skulls with tall sagittal crests, and their general skull shape is very similar. Some have distinctive flanges, and some have none at all, so this confuses the matter further. Machairodonts were almost always bigger, though, and their canines were longer and more stout for the most part, but exceptions do appear.

The sixth appearance is the barbourofelids. These feliform carnivorans are very closely related to actual cats. The best-known barbourofelid is the eponymous ''[[Barbourofelis]]'', which differs from most machairodonts by having a much heavier and more stout [[mandible]], smaller [[orbit]]s, massive and almost knobby flanges, and canines that are farther back. The average machairodont had well-developed incisors, but barbourofelids' were more extreme.

The seventh and last saber-toothed group to evolve were the machairodonts themselves.
<gallery>
Image:Lycaenops_FMNH.jpg|'''1st saber-tooth instance''': [[Gorgonopsidae]] ([[Theriodontia]], [[Therapsida]], [[Synapsida]]) – ''[[Lycaenops]] angusticeps'' skull
Image:Thylacosmilus Atrox.jpg|'''3rd saber-tooth instance''': [[Thylacosmilidae]] ([[Sparassodonta]]) – ''[[Thylacosmilus]] atrox'' skull
Image:Machaeroides eothen.JPG|'''4th saber-tooth instance''': [[Oxyaenidae]] ([[Creodonta]]) – ''[[Machaeroides]]'' skull
Image:Hoplophoneus primaevus 01.jpg|'''5th saber-tooth instance''': [[Nimravidae]] ([[Feliformia]], [[Carnivora]]) – ''[[Hoplophoneus]] primaevus'' skull and upper cervical vertebrae
Image:Barbourofelis loveorum.jpg|'''6th saber-tooth instance''': [[Barbourofelidae]] (Feliformia, Carnivora) – ''Barbourofelis'' skeleton
Image:Smilodon head.jpg|'''7th saber-tooth instance''': [[Machairodontinae]] ([[Felidae]], Feliformia, Carnivora) – ''Smilodon'' skull and upper cervical vertebrae
</gallery>