Squamata: Scleroglossa

Introduction

"Scleroglossa" means "hard tongue," which surely has some significance, although its a bit hard to see. Many of the members of this group have split tongues. However, the reference is probably to the notched, inelastic distal part of the tongue in anguimorphs. Since skinks, gekkos and amphisbaenids don't share this characteristic, the name is somewhat inappropriate. Since few of us think in Classical Greek, little harm is done.

The Sceroglossa includes three kinds of relatively common lizards (skinks, gekkos and varanoids), as well as the legless lizards (amphisbaenids), the mosasaurs and all of the snakes. The latter two groups will be treated in a later section. The relationships of all of these groups are not very well understood, but it is relatively clear that all are related to each other more closely than any of them are to the iguanas and their kin. For example, Michael MSY) Lee, a well-known paleontologist, has written several papers placing the pythonomorphs (snakes and mosasaurs) among the varanoids. In this he is strongly opposed by Olivier Rieppel and co-workers. Rieppel and Lee have been head-to-head on a number of other issues, including the phylogeny of pareiasaurs, the ancestry of turtles, and the marine (Lee) or terrestrial Rieppel) origin of snakes. Their various, often heated, disputes are chronicled in a number of places on this site. We have cautiously chosen a sort of middle ground in this particular dispute, based on the work of Michael Caldwell.

Taxa on This Page

1. Autarchoglossa 
2. Bainguidae X
3. Evansauria
4. Dibamidae 
5. Gekkota 
6. Scleroglossa

Descriptions

Scleroglossa 

Comments: A well defined clade with at least 27 synapomorphies; the most important adaptations being prey capture through jaw prehension (holding in the mouth), the tongue then becomes a well-developed chemosensory system. The name (scleros, tough, hard; glossa, tongue) refers to the flattening and keratinization of at the rear of the tongue. Estes et al 1988's division of Squamata into Iguania and their new clade Scleroglossa revolutionised squamatian phylogenetics and systematics and established the morphological paradigm still used today. However molecular phylogeny consistently fails to recover these two clades (Hedges & Vidal 2009). For now we have retained the morphological arrangement.

Dibamidae: blind lizards

Comments: Small to moderate-sized, burrowers, reduced limbs. Highly specialised, so beyond a scleroglossan placement morphology does not provide much information as regards relationships, in molecular phylogeny they tend to come out at the base of the squamate tree, and so are tentatively placed here. 2 genera with 11 species are known. No fossil record. MAK101106

Gekkota: 

Characters: Usually small (<15 cm); upper temporal arch, postorbital arch, lachrymal, squamosal, and postorbital all absent; jugal bone small or absent; frontals fused and surround the forebrain; pleurodont in marginal teeth; palatal teeth absent; eyelids present; tongue uncleft or slightly cleft; usually four or more transverse rows of belly scales per body segment; amphicoelous vertebrae; facial artery ant. to stapes; unique karyotype; eyes adapted to low light. Typically moving hunters.

Links:Global Gecko Association lots of good stuff); Herpbreeder.dk references); Gekkota also a good, basic site); Gekkota Mikko's Phylogeny); Animal Diversity Web: Gekkota: Classification -- not much here yet except photos); Gekkonidae; Herpetology- Lizards. ATW040205.

Evansauria  

Definition:All taxa sharing a more recent common ancestor with Lacerta viridis and Varanus varius than with Gekko gecko or Iguana iguana.

Comments: Named in honor of Professor Susan E. Evans, who has made many important contributions to our understanding of lepidosauromorph and squamatan evolution, this clade was recovered by Conrad, 2008 and is defined by a number of synapomorphies. It constitutes the stem-based taxon for the node-based Autarchoglossa. MAK101107

Skulls of the small anguimorph-like basal autarchoglossan Bainguis parvus, from the Late Cretaceous (Late Santonian/Early Campanian) Djadochta Formation of Mongolia. Some of the armoured scales are visible preserved at the back of skull. Graphic © from Borsuk-Białynicka 1984 p.20

Bainguidae: Bainguis, Eoxanta, Myrmecodaptria  

Comments: Originally erected as a monospecific family for Bainguis parvus, considered to have both scincomorph and anguimorph (Borsuk-Białynicka 1984), and later synonymized with Anguidae. The cladistic analysis by Conrad, 2008 groups with B. parvus with the non-anguimorph fossil taxa Myrmecodaptria and Eoxanta, and placed the Bainguidae basal to the Autarchoglossa. It is possible that this is a grade of primitive stem-Autarchoglossans rather than a clade . Results grouping bainguids with lacertoids may be the result of convergences between this clade and primitive Scincomorpha or Lacertiformes. MAK101107

Autarchoglossa (= Unidentata)

Characters: Loss of jugal-squamosal contact on supratemporal arch, M. rectas abdominis lateralis present (Estes et al 1988), single egg tooth (for hatching) (Vidal & Hedges 2005)

Comments: This taxon was originally defined by Camp 1923 and is retained in cladistic systems although diagnosed by only a few characters Estes et al 1988 pp.206-7). As defined here it is used to refer to all "higher" squamates, including Scincomorpha, Anguimorpha, Amphisbaenia, and Serpentes (snakes). Inasmuch as most molecular studies give the Gekkota and Dibamidae a basal position, they have an equivalent clade (although in the molecular phylogeny this also includes the Iguania), called Unidentata because of the presence of a single egg tooth (Vidal & Hedges 2005). Because some most molecular phylogenies recover a paraphyletic Scincomorpha (in which are nested further groups like Amphisbaenia, Iguania, Anguimorpha, and Serpentes (Hedges & Vidal 2009)) this makes Autarchoglossa synonymous the latter, cladistically speaking (assuming the phylogeny is correct). In contrast to Gekkota, who as mostly ambush foragers rely morey on olfactory and visual prey discrimination, and retain a relatively low metabolic rate, the Unidentata/Autarchoglossa are more active foragers, with a higher metabolic rate, and rely primarily on vomeronasal and visual prey discrimination (Vidal & Hedges 2005). MAK101105