| Chinlestegophis | |
|---|---|
| Scientific classification | |
| Kingdom: | |
| Phylum: | |
| Order: | |
| Suborder: | |
| Superfamily: | |
| Genus: | †Chinlestegophis Pardoet al., 2017 |
| Binomial name | |
| †Chinlestegophis jenkinsi Pardoet al., 2017 | |
Chinlestegophis is a diminutiveLate Triassicstereospondyl that has been interpreted as a putative stemcaecilian, a living group of legless burrowing amphibians.[1] IfChinlestegophis is indeed both an advanced stereospondyl and a relative of caecilians, this means that stereospondyls (in the form of caecilians) survived to the present day; historically the group was thought to have gone extinct by the early Cretaceous.[2]Chinlestegophis jenkinsi, the type and only species, is known from two partial skulls discovered in theChinle Formation inColorado.
Chinlestegophis was described in 2017 by Jason Pardo, Adam Huttenlocker, and Bryan Small based on two specimens collected in the late 1990s by Small.[1] The genus name is derived from the name of the formation (Chinle), the Greek rootstego- ('roof' or 'cover'), and the Greek root -ophis ('serpent'). The species name honorsFarish Jenkins, the longtime curator of theMuseum of Comparative Zoology atHarvard University who describedEocaecilia, the oldest known caecilian. The taxon is readily diagnosed by numerous features given its distinctive small size and consequent diverging morphology from many contemporaneous stereospondyls; Pardo et al. noted numerous features shared betweenChinlestegophis and brachyopoids (e.g., lacrimal-maxilla fusion),Rileymillerus (e.g., lateral exposure of the palate), and caecilians (e.g., double tooth row on the lower jaw).
The phylogenetic positions of many small-bodied temnospondyls have often been controversial, including that of the closely relatedRileymillerus cosgriffi from the Late Triassic of Texas.[3] The analysis by Pardo et al. (2017) used a modified matrix from Schoch (2013), which looked at the relationships of all temnospondyls.[4] In addition to recoveringChinlestegophis as the sister taxon toRileymillerus, the authors also recovered these taxa as the closest relatives ofbrachyopoids, another clade of stereospondyl that were the last non-lissamphibian temnospondyls to survive in the Mesozoic. In turn, the analysis recoveredChinlestegophis as the closest relative toEocaecilia, the oldest known caecilian. As such, these results form the basis for a fourth major hypothesis regarding lissamphibian origins, namely that all lissamphibians are derived from temnospondyls, but thatbatrachians (frogs and salamanders) are descended from dissorophoids, whereas caecilians came fromChinlestegophis-like taxa nested among the stereospondyls.
Other workers have disputed the interpretation ofChinlestegophis as a stem caecilian on various grounds. For example, Marjanović & Laurin (2019) note that the original study reported only a Bayesian consensus and a majority-rule consensus tree of the main data matrix, and while both support the claimedcaecilian affinities ofChinlestegophis jenkinsi, the strictparsimonyconsensus tree does not, given that it is compatible withlissamphibian monophyly (indeed, this topology is found in some of the most parsimonious trees); those workers generally favor and recover support for a monophyletic origin of lissamphibians fromlepospondyls.[5] Criticism of the use of the majority-rule consensus has also been published by Serra Silva & Wilkinson (2021).[6] The use of a modified version of the Pardo et al. matrix by Daza et al. (2020) and Schoch et al. (2020) recovered a single origin of all lissamphibians from dissorophoids, consistent with the historic "temnospondyl hypothesis";[7][8] further analysis in the description of the unequivocal Late Triassic gymnophionomorphFuncusvermis gilmorei also recovered the traditional "temnospondyl hypothesis."[9] The characters that have been used to supportgymnophionan affinities ofChinlestegophis have also been criticized.[10][11] No other studies to date have independently supported the hypothesis of relationships proposed by Pardo et al.
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
