Tikiguania and the antiquity of squamate reptiles (lizards and snakes)

Abstract

Tikiguania estesi is widely accepted to be the earliest member of Squamata, the reptile group that includes lizards and snakes. It is based on a lower jaw from the Late Triassic of India, described as a primitive lizard related to agamids and chamaeleons. However, Tikiguania is almost indistinguishable from living agamids; a combined phylogenetic analysis of morphological and molecular data places it with draconines, a prominent component of the modern Asian herpetofauna. It is unlikely that living agamids have retained the Tikiguania morphotype unchanged for over 216 Myr; it is much more conceivable that Tikiguania is a Quaternary or Late Tertiary agamid that was preserved in sediments derived from the Triassic beds that have a broad superficial exposure. This removes the only fossil evidence for lizards in the Triassic. Studies that have employed Tikiguana for evolutionary, biogeographical and molecular dating inferences need to be reassessed.

Figure 1.

Dentary of Tikiguania (a) labial and (b) lingual view, with the dentary of the living draconine agamid Calotes versicolor (ETVP 2900) in (c, d) for comparison. Numbers (#) refer to characters discussed in the main text and in table 1. (e–h) Dentaries of a representative selection of living acrodontan lizards, (e) Agama agama (SAMA R60184), (f) Bronchocoela marmorata (SAMA R03608), (g) Hypsilurus godefroyii (SAMA R05253 B) and (h) Uromastyx aegyptia (SAMA R48106). (a, b) Modified from [8]. Scale bars = 2 mm.

Figure 2.

(a) Phylogeny of lepidosauromorph reptiles, based on morphological and molecular data (analysis 1; strict consensus of 20 MPTs), showing that Tikiguania groups with acrodontan lizards, not rhynchocephalians. (b) Phylogeny of acrodontan lizards, based on morphological and molecular data (analysis 2; consensus of 8 MPTs) demonstrating that Tikiguania is nested within crown agamids. Majority-rule consensus; clades found in strict consensus indicated with branch supports >0. Clades without numbers (e.g. within ‘draconines’) are not present on strict consensus (i.e. have Bremer support of 0).