Abstract
AbstractGymnophiona, popularly known as caecilians, the most poorly known major taxon of extant amphibians, are elongate and limbless tetrapods, with compact ossified skulls and reduced eyes, mainly adapted to fossorial life as adults. Caecilians are poorly represented in the fossil record, but despite the scarcity of fossil specimens described (only four named taxa, in addition to indeterminate fragmentary material), their fossils play a key role in our knowledge of the origin and evolution of Lissamphibia, as well as contribute directly to a better understanding of the phylogeny, taxonomy and biogeography of extant gymnophionan taxa. These records are scattered throughout geological time (from the Jurassic to the sub-Recent) and space (North and South America and Africa). Here, we revisit the caecilian fossil record, providing a brief description of all known extinct taxa described so far, along with general remarks about their impact on systematics, time range, and geographical distribution of the clade, as well as prospects for future research. Possible calibration constraints based on the caecilian fossil record are provided.
Highlights
The crown-clade Lissamphibia comprises the extant taxa Anura, Urodela, and Gymnophiona
Only one gymnophionan caecilian was known in the fossil record (Estes, 1981), and to date only four extinct taxa originally assigned to this group were have been erected named and described in details (Estes & Wake, 1972; Jenkins & Walsh, 1993; Evans & Sigogneau-Russel, 2001; Pardo et al, 2017)
Recent large-scale molecular analyses strongly corroborate the monophyly of extant Lissamphibia with respect to Amniota, and most find caecilians placed as the sister-group of Batrachia, which consists of includes Anura and Urodela (Irisarri et al, 2017; Vijayakumaret al., 2019Frost et al, 2006; Pyron & Wiens, 2011)
Summary
The crown-clade Lissamphibia (see Laurin et al, 2020, for a review; but see Dubois, 2004, for an opposing view on the use of this nomen) comprises the extant taxa Anura, Urodela, and Gymnophiona. Recent large-scale molecular analyses strongly corroborate the monophyly of extant Lissamphibia with respect to Amniota, and most find caecilians placed as the sister-group of Batrachia, which consists of includes Anura and Urodela (Irisarri et al, 2017; Vijayakumaret al., 2019Frost et al, 2006; Pyron & Wiens, 2011) These results stand in a total evidence analysis (Pyron, 2011) based on a molecular data set designed to be combined with a mainly fossil-oriented data matrix (Vallin & Laurin, 2004). Jenkinsi (along with many other temnospondyls) is a gymnophionomorph, the origin of Lissamphibia and Gymnophionomorpha occurred during the Late Carboniferous (Pardo et al, 2017) These results age estimates are congruent with some previous time divergence time estimates based on molecular data (e.g. Roelants et al, 2007; Zhang & Wake, 2009; San Mauro, 2010), it isthey are incompatible with others (e.g. Marjanović & Laurin, 2007). This low quality in thelimited fossil record hinders limits its use for molecular clock calibrations, and limits hinders interpretations of paleobiogeographical patterns
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