[7] While both anthracosaurs and/or embolomeres are suggested to be reptiliomorphs closer to amniotes, some recent studies either retain them as amphibians or argue that their relationships are still ambiguous and are more likely to be stem-tetrapods.

[6] In addition, several "anthracosaur" genera of uncertain taxonomic placement would also probably qualify as reptiliomorphs, including Solenodonsaurus, Eldeceeon, Silvanerpeton, and Casineria.

[13] Alfred Sherwood Romer rejected Säve-Söderbergh's theory of a biphyletic amphibia and used the name Anthracosauria to describe the "labyrinthodont" lineage from which amniotes evolved.

In 1970, the German paleontologist Alec Panchen took up Säve-Söderbergh's name for this group as having priority,[14] but Romer's terminology is still in use, e.g. by Carroll (1988 and 2002) and by Hildebrand & Goslow (2001).

[19] Michael Benton (2000, 2004) made it the sister-clade to Lepospondyli, containing "anthracosaurs" (in the strict sense, i.e. Embolomeri), seymouriamorphs, diadectomorphs and amniotes.

Lepospondyls are one of the groups of tetrapods suggested to be ancestors of living amphibians; as such, their potential close relationship to amniotes has important implications for the content of Reptiliomorpha.

University of Bristol paleontologist Professor Michael J. Benton gives the following characteristics for the Reptiliomorpha (in which he includes embolomeres, seymouriamorphs and diadectomorphs):[7] The groups traditionally assigned to Reptiliomorpha, i.e. embolomeres, seymouriamorphs and diadectomorphs, differed from their contemporaries, the non-reptiliomorph temnospondyls, in having a deeper and taller skull, but retained the primitive kinesis (loose attachment) between the skull roof and the cheek (with exception of some specialized taxa, such as Seymouria, in which the cheek was solidly attached to the skull roof[25]).

[28] Unlike most labyrinthodonts, the body was moderately deep rather than flat, and the limbs were well-developed and ossified, indicating a predominantly terrestrial lifestyle except in secondarily aquatic groups.

[32][33] In chroniosuchians and some seymouriamorphs, like Discosauriscus, dermal scales are found in post-metamorphic specimens, indicating they may have had a "knobbly", if not scaly, appearance.

[34] With reptiliomorph anthracosaurs having evolved small near-circular keratinous scales, their amniote descendants further covered almost their entire body with them, and also formed claws of keratin, with both scales and claws making cutaneous respiration and water absorption impossible, making them breathe through their mouths and nostrils, and drink water through mouth.

Some of these tetrapods (e.g. Archeria, Eogyrinus) were elongate, eel-like aquatic forms with diminutive limbs, while others (e.g. Seymouria, Solenodonsaurus, Diadectes, Limnoscelis) were so reptile-like that until quite recently they actually had been considered to be true reptiles, and it is likely that to a modern observer they would have appeared as large to medium-sized, heavy-set lizards.

A possible reason may have been competition for breeding ponds, to exploit drier environments with less access to open water, or to avoid predation on tadpoles by fish, a problem still plaguing modern amphibians.

A striking parallel can be seen in the frog family Leptodactylidae, which has a very diverse reproductive system, including foam nests, non-feeding terrestrial tadpoles and direct development.

Meanwhile, the single most successful daughter-clade of the reptiliomorphs, the amniotes, continued to flourish and evolve into a staggering diversity of tetrapods including mammals, reptiles, and birds.