Editing Reptile (section)

===Phylogenetics and modern definition===
By the early 21st century, vertebrate paleontologists were beginning to adopt [[phylogenetic]] taxonomy, in which all groups are defined in such a way as to be [[clade|monophyletic]]; that is, groups which include all descendants of a particular ancestor. The reptiles as historically defined are [[paraphyly|paraphyletic]], since they exclude both birds and mammals. These respectively evolved from dinosaurs and from early therapsids, both of which were traditionally called "reptiles".<ref name=Brysse2008>{{cite journal |last=Brysse |first=K. |year=2008 |title=From weird wonders to stem lineages: The second reclassification of the Burgess Shale fauna |journal=Studies in History and Philosophy of Science Part C: Biological and Biomedical Sciences |volume=39 |issue=3 |pages=298–313 |doi=10.1016/j.shpsc.2008.06.004 |pmid=18761282 }}</ref> Birds are more closely related to [[crocodilian]]s than the latter are to the rest of extant reptiles. [[Colin Tudge]] wrote:

<blockquote>Mammals are a [[clade]], and therefore the [[Phylogenetic nomenclature|cladists]] are happy to acknowledge the traditional taxon [[Mammal]]ia; and birds, too, are a clade, universally ascribed to the formal taxon [[bird|Aves]]. Mammalia and Aves are, in fact, subclades within the grand clade of the Amniota. But the traditional class Reptilia is not a clade. It is just a section of the clade [[Amniota]]: The section that is left after the Mammalia and Aves have been hived off. It cannot be defined by [[synapomorphy|synapomorphies]], as is the proper way. Instead, it is defined by a combination of the features it has and the features it lacks: reptiles are the amniotes that lack fur or feathers. At best, the cladists suggest, we could say that the traditional Reptilia are 'non-avian, non-mammalian amniotes'.<ref name=tudge>{{RefTudgeVariety}}</ref></blockquote>

Despite the early proposals for replacing the paraphyletic Reptilia with a monophyletic [[Sauropsida]], which includes birds, that term was never adopted widely or, when it was, was not applied consistently.<ref name=modestoanderson2004>{{cite journal | last1=Modesto | first1=S.P. | last2=Anderson | first2=J.S. | year=2004 | title=The phylogenetic definition of Reptilia | journal=Systematic Biology | pmid=15545258 | volume=53 | issue=5 | pages=815–821 | doi=10.1080/10635150490503026 |doi-access=free}}</ref>

[[File:Bearded Dragon Skeleton.jpg|thumb|Bearded dragon ([[pogona]]) skeleton on display at the [[Museum of Osteology]]]]
When Sauropsida was used, it often had the same content or even the same definition as Reptilia. In 1988, [[Jacques Gauthier]] proposed a [[cladistics|cladistic]] definition of Reptilia as a monophyletic node-based [[crown group]] containing turtles, lizards and snakes, crocodilians, and birds, their common ancestor and all its descendants. While Gauthier's definition was close to the modern consensus, nonetheless, it became considered inadequate because the actual relationship of turtles to other reptiles was not yet well understood at this time.<ref name=modestoanderson2004/> Major revisions since have included the reassignment of synapsids as non-reptiles, and classification of turtles as diapsids.<ref name=modestoanderson2004/> Gauthier 1994 and Laurin and Reisz 1995's definition of Sauropsida defined the scope of the group as distinct and broader than that of Reptilia, encompassing [[Mesosauridae]] as well as Reptilia ''sensu stricto''.<ref name="Gauthier-1994-Prothero-Schoch" /><ref name="Laurin 95" />

A variety of other definitions were proposed by other scientists in the years following Gauthier's paper. The first such new definition, which attempted to adhere to the standards of the [[PhyloCode]], was published by Modesto and Anderson in 2004.<ref name=modestoanderson2004/> Modesto and Anderson reviewed the many previous definitions and proposed a modified definition, which they intended to retain most traditional content of the group while keeping it stable and monophyletic. They defined Reptilia as all amniotes closer to ''[[Lacerta agilis]]'' and ''[[Crocodylus niloticus]]'' than to ''[[Homo sapiens]]''. This stem-based definition is equivalent to the more common definition of Sauropsida, which Modesto and Anderson synonymized with Reptilia, since the latter is better known and more frequently used. Unlike most previous definitions of Reptilia, however, Modesto and Anderson's definition includes birds, as they are within the clade that includes both lizards and crocodiles.<ref name=modestoanderson2004/>