Nectridea

Nectridea is an extinct order of lepospondyl tetrapods from the Carboniferous and Permian periods, including amphibious animals such as Diplocaulus. In appearance, they would have superficially resembled modern newts or aquatic salamanders, although they are not close relatives of modern amphibians (Lissamphibia). They were characterized by long, flattened tails to aid in swimming, as well as numerous features of the vertebrae.

Nectridea is an extinct order of lepospondyl tetrapods from the Carboniferous and Permian periods, including amphibious animals such as Diplocaulus. In appearance, they would have superficially resembled modern newts or aquatic salamanders, although they are not close relatives of modern amphibians (Lissamphibia). They were characterized by long, flattened tails to aid in swimming, as well as numerous features of the vertebrae.

Classification

There has been some controversy over the precise classification of Nectridea over the past century, and even whether it constitutes a valid monophyletic clade. A few older studies consider nectrideans to be very basal tetrapods, related to Ichthyostega or colosteids. However, most studies generally place nectrideans inside the subclass Lepospondyli. Aistopoda, a group of legless lepospondyls, have often been allied with particular families of nectrideans, but not the order as a whole. For example, Anderson (2001) positioned diplocaulids as close relatives of Aistopods with urocordylids and scincosaurids as progressively more primitive members of the group. On the other hand, Ruta et al. (2003) claimed that urocordylids were closer to aistopods. As aistopods do not possess most nectridean features, they have traditionally been excluded from the group. However, this would make Nectridea an invalid paraphyletic group as the aistopods, may have been descended from nectrideans, are not considered nectrideans themselves. At least some nectrideans may be stem-tetrapods, less closely related to modern terrestrial vertebrates than all terrestrial vertebrates are to each other. The following is a cladogram from Ruta et al. (2003): In their 2026 description of the Scottish nectridean Albadris, Herring and colleagues used the phylogenetic dataset of Milner & Ruta (2009) under maximum parsimony to recover the following tree, with aistopods as the outgroup to a clade formed by Urocordylidae as the sister group to Scincosaurus (Scincosauridae) + Diplocaulidae. These results are displayed in the cladogram below:

References

Ahlberg, P. E. & Milner, A. R. 1994: The origin and early diversification of tetrapods. Nature: vol. 368, 7 April, pp. 507–514 Anderson, J. S. 1998: Phylogenetic analysis of the Lepospondyli (Tetrapoda). Journal of Vertebrate Paleontology. Vol. 18, #3, Suppl. to #3, pp. 24A Carroll, R. L., 1988: Vertebrate paleontology and evolution. W. H. Freeman and company, New York, 1988, 698. Carroll, R. L., 1988: Appendix. 594-648. in Carroll, R. L., 1988: Vertebrate paleontology and evolution. W. H. Freeman and company, New York, 1988, 698. Carroll, R. L. 1996: Revealing the patterns of macroevolution. Nature: vol. 381, 2 May, pp. 19–20 Clack, J. A., 1998: A new Early Carboniferous tetrapod with a mélange of crown-group characters. Nature: vol. 394, 2 July, pp. 66–69 Shubin, N., 1998 [preview]: Evolutionary cut and paste. Nature: vol. 394, 2 July, pp. 12–13 Vallin, G. & Laurin, M., 2004: Cranial morphology and affinities of Microbrachis, and a reappraisal of the phylogeny and lifestyle of the first amphibians. Journal of Vertebrate Paleontology: Vol. 24, #1, pp. 56–72

External links

Nectridae Phylogeny.

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