Lepospondyl

Lepospondyli is a diverse taxon of reptiliomorph tetrapods. With the exception of one late-surviving lepospondyl from the Late Permian of Morocco (Diplocaulus minumus), lepospondyls lived from the Early Carboniferous (Mississippian) to the Early Permian and were geographically restricted to what is now Europe and North America. Five major groups of lepospondyls are known: Adelospondyli; Aïstopoda; Lysorophia; Microsauria; and Nectridea.
 Lepospondyls have a diverse range of body forms and include species
with newt-like, eel- or snake-like, and lizard-like forms. Various
species were aquatic, semiaquatic, or terrestrial. 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. Lepospondyli was named in 1888 by Karl Alfred von Zittel, who coined the name to include some tetrapods from the Paleozoic, that shared some specific characteristics in the notochord and teeth. Lepospondyls have sometimes been considered to be either related or ancestral to modern amphibians or to Amniota (the clade containing reptiles and mammals).

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. In addition,
the upper portion of the vertebra, the neural arch, is usually fused to
the centrum (the main body of the vertebra).

The position of the Lepospondyli within the Tetrapoda is uncertain
because the earliest lepospondyls were already highly specialized when
they first appeared in the fossil record. Some lepospondyls were once
thought to be related or perhaps ancestral to modern salamanders (Urodela), but not the other modern amphibians. This view is no longer held and all modern amphibians (frogs, salamanders, and caecilians) are now grouped within the clade Lissamphibia. For a long time, the Lepospondyli were considered one of the three subclasses of Amphibia, along with the Lissamphibia and the Labyrinthodontia. However, the dissolution of "labyrinthodonts" into separate groups such as temnospondyls and anthracosaurs has cast doubt on these traditional amphibian subclasses.
 Much like "Labyrinthodontia", some studies proposed that Lepospondyli is an artificial (polyphyletic) grouping with some members closely related to extinct stem tetrapod
 groups and others more closely related to modern amphibians or
reptiles. Early phylogenetic analyses conducted in the 1980s and 1990s
often maintained the idea that lepospondyls were paraphyletic, with
nectrideans close to colosteids and microsaurs close to temnospondyls,
which were considered to be ancestral to modern amphibians.
However, a 1995 paper by Robert Carroll
 argued that lepospondyls were actually a monophyletic group closer to
reptiles. Carroll considered them closer to reptiles than the seymouriamorphs, but not as close as the diadectomorphs.
 Many phylogenetic analyses since Carroll (1995) agreed with his
interpretation, including Laurin & Reisz (1997), Anderson (2001),
 and Ruta et al. (2003). A few have still considered lepospondyls
ancestral to amphibians, but came to this conclusion without changing
the position of lepospondyls compared to seymouriamorphs and
diadectomorphs.
Lepospondyl and tetrapod classification is still controversial, and even recent studies have had doubts …