The origin(s) of extant amphibians: a review with emphasis on the “lepospondyl hypothesis”

Abstract

The origins of the extant amphibians (frogs, salamanders, caecilians) remain controversial after over a century of debate. Three groups of hypotheses persist in the current literature: the "temnospondyl hypothesis" (TH) which roots Lissamphibia Haeckel, 1866 (the smallest clade composed of the extant amphibians) within the Paleozoic temnospondyls, the "lepospondyl hypothesis" (LH) which postulates a monophyletic Lissamphibia nested within the Paleozoic lepospondyls, and the "polyphyly hypothesis" (PH), according to which the frogs and the salamanders are temnospondyls while the caecilians are lepospondyls. The discovery of the Middle Jurassic to Pliocene albanerpetontids, which are very similar to the extant amphibians, has complicated rather than resolved this situation. We present a review of recent publications and theses in this field, several of which show more support for the LH than for the TH and considerably more than for the PH. In addition, we show that there is no particular attraction between long-bodied lissamphibians (caecilians) and long-bodied lepospondyls (such as the lysorophians): when they are removed from two published matrices, reanalyses nonetheless find the LH. In one case the LH is found even when all salamanders are removed as well. We furthermore propose that the complex of characters called the salamander mode of autopodium development is (in its less extreme forms) plesiomorphic for limbed vertebrates, so the apparent presence of this mode of development in temnospondyls cannot support the TH or the PH. Still, a consensus will not be reached soon, despite the increasing

Preliminary Analysis of Osteocyte Lacunar Density in Long Bones of Tetrapods: All Measures Are Bigger in Sauropod Dinosaurs

“…Branch lengths were calculated from estimated divergence times of the different nodes taken from the literature, because characters and clustering methods used to construct trees might have been different and thus might have affected branch lengths. Phylogenetic trees were constructed from Vidal and Hedges [68], Mulcahy et al [69] and Amer and Kumazawa [70] for squamates; Hackett et al [71] for birds; Marjanovic and Laurin [72] and Clack [73] for non-amniote tetrapods; Bennett [74] and Nesbitt [75] for non-dinosaurian archosaurs; Pisani et al [76] and Brusatte et al [77] for tyrannosaurid dinosaurs; Yates [78]–[79]; Sereno [80]; Allain and Aquesbi [81]; Remes et al [82] for Sauropodomorpha and Beck et al [83] and Perelman et al [84] for mammals using Mesquite v. 2.75 [80]. Additional information on node divergence times was taken from Benton et al [85] and Müller and Reisz [86].…”

New specimen of <i>Cacops woehri</i> indicates differences in the ontogenetic trajectories among cacopine dissorophids

“…Dissorophoidea is a large clade that was very successful during the Paleozoic and continues to be so today, as most authors consider some or all three groups of modern amphibians to be part of Dissorophoidea (Anderson, 2008;Anderson et al, 2008b;Milner, 1988Milner, , 1993Schoch and Milner, 2004;Sigurdsen and Green, 2011), but see, for example, Marjanović and Laurin (2013) for a different view. Recent phylogenetic analyses have recovered two distinct subclades within fossil dissorophoids, one comprising the Olsoniformes (dissorophids and trematopids) and one comprising the Xerodromes (amphibamids and branchiosaurids) (Anderson et al, 2008b;Fröbisch and Schoch, 2009;Schoch, 2012;Schoch and Milner, 2014).…”

Tail regeneration in the Paleozoic tetrapod Microbrachis pelikani and comparison with extant salamanders and squamates

“…). Whereas the analyses of Laurin & Reisz (), Vallin & Laurin (), Marjanović & Laurin () and Marjanović & Laurin () found lepospondyls (and thus microsaurs) to be stem‐amphibians, the present authors agree with Ruta, Coates & Quicke (), Ruta & Coates (), Sigurdsen & Green (), and Schoch () who regard lepospondyls as stem‐amniotes and lissamphibians as derived from temnospondyls, another large group of early non‐amniotic tetrapods.…”