None were large (the biggest genus, the diplocaulid Diplocaulus, reached a meter in length, but most were much smaller), and they are assumed to have lived in specialized ecological niches not taken by the more numerous temnospondyl amphibians that coexisted with them in the Paleozoic.

[10] All lepospondyls are characterised by having simple, spool-shaped vertebrae that did not ossify from cartilage, but rather grew as bony cylinders around the notochord.

This view is no longer held and all modern amphibians (frogs, salamanders, and caecilians) are now grouped within the clade Lissamphibia.

[11][12][13] However, the dissolution of "labyrinthodonts" into separate groups such as temnospondyls and anthracosaurs has cast doubt on these traditional amphibian subclasses.

[15] Many phylogenetic analyses since Carroll (1995) agreed with his interpretation, including Laurin & Reisz (1997),[16] Anderson (2001),[17] and Ruta et al.

[19] The name Holospondyli has been proposed for a clade including aïstopods, and nectrideans, and possibly adelospondyls, although not all recent phylogenetic analyses support the grouping.

The following cladogram, simplified, is after an analysis of tetrapods and stem-tetrapods presented by Ruta et al. in 2003:[9] Batropetes fritschi Tuditanus punctulatus Pantylus cordatus Stegotretus agyrus Asaphestera intermedia Saxonerpeton geinitzi Hapsidopareion lepton Micraroter erythrogeios Pelodosotis elongatum Rhynchonkos stovalli Cardiocephalus sternbergi Euryodus primus Microbrachis pelikani Hyloplesion longicostatum Odonterpeton triangulare Brachydectes spp.

Acherontiscus caledoniae Adelospondylus watsoni Adelogyrinus simorhynchus Dolichopareias disjectus Scincosaurus crassus Keraterpeton galvani Batrachiderpeton reticulatum Diceratosaurus brevirostris Diplocaulus magnicornis Diploceraspis burkei Ptyonius marshii Sauropleura spp.

Strong support for this relationship comes from a suite of anatomical features shared between lissamphibians and a group of Paleozoic temnospondyls called dissorophoids.

[4] Below is a cladogram from Ruta et al. (2003) that supports the "temnospondyl hypothesis", showing the position of Lepospondyli within crown group Tetrapoda:[9] Lissamphibia + Temnospondyli Caerorhachis bairdi Eoherpeton watsoni Proterogyrinus scheelei Archeria crassidisca Pholiderpeton scutigerum Anthracosaurus russelli Pholiderpeton attheyi (now Eogyrinus) Bruktererpeton fiebigi Gephyrostegus bohemicus Solenodonsaurus janenschi Kotlassia prima Discosauriscus austriacus Seymouria spp.