A Fossil Snake with Limbs

Abstract

A 95-million-year-old fossil snake from the Middle East documents the most extreme hindlimb development of any known member of that group, as it preserves the tibia, fibula, tarsals, metatarsals, and phalanges. It is more complete than Pachyrhachis, a second fossil snake with hindlimbs that was recently portrayed to be basal to all other snakes. Phylogenetic analysis of the relationships of the new taxon, as well as reanalysis of Pachyrhachis, shows both to be related to macrostomatans, a group that includes relatively advanced snakes such as pythons, boas, and colubroids to the exclusion of more primitive snakes such as blindsnakes and pipesnakes.

The skull of the round Island boa, Casarea dussumieri Schlegel, based on high‐resolution X‐ray computed tomography

“…The Round Island boas Casarea dussumieri and Bolyeria multicarinata are of relatively small size compared to most other booids, yet they are nested deeply inside the latter (Underwood, 1976;Tchernov et al, 2000;Lee and Scanlon, 2002;Apesteguia and Zaher, 2006;Scanlon, 2006). Thus, some degree of paedomorphosis may be expected, as was indeed noted by Anthony and Guibé (1952).…”

“…2;Tchernov et al, 2000;Apesteguia and Zaher, 2006). These phylogenetic hypotheses stand in stark contrast to the recent findings based on molecular data, which place bolyeriids as sister-taxon to a clade that includes the uropeltines (traditionally considered non-macrostomatan), Acrochordus and colubroids, whereas the tropidophiids were found to be the sister-taxon of the non-macrostomatan genus Anilius (Vidal and Hedges, 2004; see also Vidal and David, 2004).…”

“…The ventral contact between the posteroventral nasal process and the medial frontal pillar is thus present in all the genera referred to Tropidophiidae by Underwood (1976), who recorded its variable presence among other booids also. This character (Underwood, 1976, character 40) was not included as such in more recent analyses of snake interrelationships (Tchernov et al, 2000;Apesteguia and Zaher, 2002;Lee and Scanlon, 2002;Scanlon, 2006), but its significance for the analysis of snake phylogeny will be tested in a forthcoming contribution.…”

“…Some cladistic analyses (Lee and Scanlon, 2002;Scanlon, 2006) do, indeed, place bolyeriids as sister-group to a clade that comprises Acrochordus plus colubroids, whereas competing analyses (Tchernov et al, 2000;Apesteguia and Zaher, 2006) place bolyeriids as sister-group to a clade that comprises tropidophiids, Acrochordus and colubroids. With HRXCT data available for three of the crucial taxa involved (Casarea dussumieri, Trachyboa boulengeri, Tropidophis haitianus) it becomes clear, however, that evidence based on skull characters is rather weak for either hypothesis.…”

Molecular phylogeny of advanced snakes (Serpentes, Caenophidia) with an emphasis on South American Xenodontines: a revised classification and descriptions of new taxa

“…Our results corroborate Lawson et al (2005) in positioning Acrochordus as the sister group to all other caenophidians. A sister-group relationship between Acrochordus and other caenophidians is a wellsupported hypothesis in all recent morphological phylogenetic analyses (Tchernov et al, 2000;Lee & Scanlon, 2002;Apesteguía & Zaher, 2006), as well as other molecular studies and combined molecular/ morphological analyses (Gravlund, 2001;Lee et al, 2004; and references therein). In contrast, Kelly et al (2003) and Kraus & Brown (1998) found Acrochor-dus to cluster with Xenodermus-Achalinus (Xenodermatinae); in addition, Kraus & Brown (1998) found their Acrochordus-xenodermatine clade to cluster well within other caenophidians.…”