Lepidosauria E. Haeckel 1866 [K. de Queiroz and J. A. Gauthier], converted clade name Registration Number: 61 least 35 apomorphies relative to other extant amniotes (only some of which are diagnostic De!nition: !e smallest crown clade contain- relative to di#erent stem lepidosaurs). !ese ing Lacerta agilis Linnaeus 1758 (Squamata) and apomorphies derive from disparate anatomical Sphenodon (originally Hatteria) punctatus (Gray systems, are apparently unrelated functionally 1842) (Rhynchocephalia). !is is a minimum- and developmentally, and have persisted for crown-clade de"nition. Abbreviated de"nition: hundreds of millions of years among lepido- min crown ∇ (Lacerta agilis Linnaeus 1758 & saurs with remarkably divergent ecologies. !ey Sphenodon punctatus (Gray 1842)). include the following apomorphies (those lack- ing citations are from Gauthier et al., 1988a): Etymology: Derived from the Greek lepidos, (1) transversely oriented external opening of scale, plus sauros, lizard, reptile. cloaca and loss of amniote penis (hemipenes of squamatans are neomorphic); (2) kidney in tail Reference Phylogeny: Gauthier et al. base and adrenal gland suspended in gonadal (1988a: Fig. 13), where Lacerta agilis is part of mesentery (Gabe, 1970); (3) lingual prey pre- Squamata and Sphenodon punctatus is part of hension; (4) sagittal crest of scales projecting Rhynchocephalia. See also Gauthier (1984: Figs. from neck, body and tail; (5) scales composed 32–33), Evans (1984: Fig. 2, 1988: Figs. 6.1– of superimposed, rather than juxtaposed, amni- 6.2), Rest et al. (2003: Fig. 3), Hill (2005: Fig. 3), ote alpha keratin and reptilian phi keratin layers Evans and Jones (2010: Fig. 2.1), Crawford et al. (Maderson, 1985); (6) skin shed regularly in its (2012: Fig. 2), Jones et al. (2013: Figs. 3–4), and entirety; (7) prefrontal braces skull roof on pal- Simões et al. (2018: Fig. 2). ate (Gauthier, 1994); (8) lacrimal bone largely con"ned to orbital rim; (9) maxilla broadly Composition: Lepidosauria is composed of contributes to ventral orbital margin (Gauthier, two primary crown clades: the New Zealand 1994); (10) marginal teeth attached super"cially endemic Sphenodon with one currently recog- to lingual surface of jaw (rather than in shal- nized extant species (Hay et al., 2010) and the low sockets; further modi"ed to more apical globally distributed Squamata with approxi- attachment in some taxa); (11) teeth lost from mately 10,078 currently recognized extant transverse process of pterygoid and from sphe- species (Uetz, 2016). See Squamata and Pan- noid bones (Gauthier et al., 1988b); (12) zygos- Squamata (this volume) for references regarding phene-zygantrum accessory intervertebral joints extinct species in those clades. Reviews of dis- formed from dorsal extensions of zygapophysial parate and diverse fossil rhynchocephalians can surfaces (see Petermann and Gauthier, 2018); be found in Jones et al. (2013), Apesteguía et al. (13) autotomic and regenerable tail (autotomy, (2014), and Bever and Norell (2017). but not regeneration, has also been reported in some captorhinids; LeBlanc et al., 2018); (14) all Diagnostic Apomorphies: According to non-ossifying cartilaginous parts of skeleton cal- Gauthier et al. (1988a), Lepidosauria has at cify during postnatal ontogeny; (15) neomorphic Lepidosauria ossi"cation centers in limb bone epiphyses that described as an agamid “lizard” (Gray, 1831, fuse to diaphyses near maximum adult size; 1842), S. punctatus was later separated from aga- (16) medial centrale larger than lateral central mids as Hatteriidae (Cope, 1864), and later still in wrist (Gauthier et al., 1988b); (17) radiale from “lizards” (and snakes) as Rhynchocephalia contacts 1st distal carpal or 1st metacarpal in within Squamata (Günther, 1867). Cope (1875) hand (Gauthier et al., 2012); (18) 4th metacar- furthered the separation, "rst, by not recog- pal shorter than 3rd (symmetrical metacarpals); nizing Squamata, second, by including the (19) fenestrate pelvic girdle; (20) posterodorsally extinct protorosaurs (i.e., Protorosaurus speneri) sloping ilium; (21) embryonic fusion between and rhynchosaurs (i.e., Rhynchosaurus articeps) anlage of lateral centrale and astragalus in tar- along with extant Sphenodon punctatus in his sus; (22) astragalus and calcaneum fused in Rhynchocephalia, and third, by interposing tur- adult (and lack a perforating foramen between tles (Testudines) between Rhynchocephalia and them as neurovascular system passes between “lizards” (and snakes) in his taxonomy. Cope tibia and "bula proximal to tarsus; Rieppel and (1889) later continued this trend by separating Reisz, 1999); (23) absence of separate 1st distal Rhynchocephalia and Squamata as taxa of equal tarsal in foot; (24) hooked 5th metatarsal—and rank (although the taxa were adjacent in his absence of discrete 5th distal tarsal presumably list). Distancing them further still, Cope (1900) incorporated into it—modi"ed to act as both a placed Rhynchocephalia and Squamata in sepa- ‘heel’ and a grasping ‘thumb’ enabling the 5th rate higher taxa, Archosauria and Streptostylica, toe to rotate 90° with respect to rest of the foot respectively, although his phylogenetic diagram according to Robinson (1975). (p. 160) had them closely related. In general, many late nineteenth and early to mid twen- Synonyms: All synonyms are approximate (not tieth century authors treated Sphenodon and phylogenetically de"ned). !e names that fol- Squamata (not always using that name) as rel- low were used after Sphenodon punctatus was atively distantly related among reptiles (e.g., "rst recognized (Gray, 1831, 1842) for taxa that Cope, 1875; Haeckel, 1895; Williston, 1917, explicitly included Sphenodon (sometimes as 1925), or at least considered Sphenodon closer Hatteria or Rhynchocephalus) and squamatans: to rhynchosaurs (and sometimes also to choris- Squamata of Gray (1845), partial (amphisbae- toderans) than to Squamata (e.g., Gadow, 1898, nians excluded); Saura of Gray (1845), partial 1901; Jaekel, 1911; Nopcsa, 1923; Romer, 1933, (amphisbaenians and snakes excluded); Lacertia 1945, 1956, 1966; Underwood, 1957; Kuhn, of Owen (1845), partial (snakes excluded); 1966). Dissolution of Cope’s idea that rhyn- Squamata of Cope (1864) and Günther (1867); chosaurs and “protorosaurs” are closely related Lacertilia of Cope (1864) and Huxley (1886), to Sphenodon began with Hughes’ (1968) study partial (snakes excluded); Saurii of Gegenbaur of the rhynchocephalian tarsus and culminated (1874, 1878), partial (snakes excluded). In in Carroll’s (1975) argument that characters most of these cases (except for Günther, 1867), traditionally used to unite Sphenodon punc- Sphenodon punctatus was considered nested tatus (and its legitimate fossil relatives) with within the taxon corresponding to Squamata. rhynchosaurs and “protorosaurs” are erroneous. Subsequent authors working in an explicitly Comments: Changing ideas about the rela- phylogenetic framework (Benton, 1982; Evans, tionship between Sphenodon punctatus and 1984; Gauthier, 1984; Carroll, 1985) presented Squamata have come nearly full circle. Originally evidence that rhynchosaurs and “protorosaurs” 1080 Lepidosauria (including Protorosaurus speneri and Prolacerta were considered most closely related among broomi) are related to archosaurs while Sphenodon extant taxa. !erefore, when rhynchosaurs punctatus is closer to squamatans. Gauthier were allied to Archosauria and evidence was et al. (1988a) provided extensive morphologi- presented for an exclusive relationship between cal evidence for a close relationship between Rhynchocephalia and Squamata, the name Sphenodon punctatus and Squamata based on a Lepidosauria was applied to the group includ- computer-assisted analysis of 171 characters in ing the latter two taxa (e.g., Benton, 1982, 1983, 13 taxa, and this result has been corroborated by 1985; Gardiner, 1982; Evans, 1984; Gauthier, subsequent studies based on morphology (e.g., 1984; Gauthier et al., 1988a; Pritchard and Evans, 1988; Hill, 2005; Evans and Jones, 2010; Nesbitt, 2017). Gauthier et al., 2012), molecules (e.g., Rest et al., Selection of the name Lepidosauria for the 2003; Crawford et al., 2012; Pyron et al., 2013), Sphenodon + Squamata clade is relatively straight- and combined morphological and molecular forward. Other names that have been applied data (e.g., Jones et al., 2013; Reeder et al., 2015; to a taxon composed of Sphenodon and squa- Simões et al., 2018). matans (see Synonyms) either have been little !e name Lepidosauria was proposed by used (Saura, Lacertia, Saurii) or have been more Haeckel (1866) for what is now known as commonly associated with a less inclusive clade Squamata—that is, “lizards” (a paraphyletic (Squamata) or a paraphyletic group originating group) and snakes. Although Sphenodon punc- in the same ancestor (Lacertilia as well as the tatus was not explicitly included, members of seldom-used names Saura, Lacertia, and Saurii). this taxon were originally thought to be “liz- !e name Lepidosauria was "rst de"ned ards” (e.g., Gray, 1831, 1842). After Günther’s phylogenetically by Gauthier et al. (1988a: (1867) study demonstrating major anatomical 34) as “the most recent common ancestor of di#erences between Sphenodon (as Hatteria) Sphenodon and squamates and all of its descen- and “lizards”, and the subsequent increas- dants.” We have updated that de"nition by ing taxonomic separation of these groups (see using species as speci"ers. In the context of phy- previous paragraph), the name Lepidosauria logenies in which