Temporal range: Early Carboniferous - Late Permian
|Lepospondyli diversity. (Rhynchonkos (A), Phlegethontia (B), Lysorophus (C) & Diplocaulus (D))|
Lepospondyli is a group of small but diverse tetrapods that lived from the Early Carboniferous (Mississippian) to the Early Permian. With the exception of one specimen (Diplocaulus minumus) from Morocco, the fossils of this group are restricted to Europe and North America. Six different groups are known: Acherontiscidae; Adelospondyli; Aïstopoda; Lysorophia; Microsauria; and Nectridea. Lepospondyls have a diverse range of body forms and includes 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. 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.
All lepospondyls are characterised by having simple, spool-shaped vertebrae, which were not preformed as 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 centra (the main body of the vertebra).
No clear common ancestors are known, since each of the known clades were already highly specialised when they first appeared in the fossil record. It is not known whether the lepospondyls are an artificial (polyphyletic) group which independently evolved similar characteristics of the vertebrae, or whether they descended from a single common ancestor.
At one time, some lepospondyls were thought to be related or perhaps ancestral to modern Urodela, but not the other modern amphibians, although this view is no longer held (see Batrachomorpha). For a long time, they were considered one of the three subclasses of amphibians. More recently, the lepospondyls are though to be possibly be related or ancestral to modern amphibians, as well as to amniotes (reptiles etc.), that they are an artificial grouping with some members related to both extinct and living amphibians (Batrachomorpha), but not amniotes, or alternatively are a monophyletic group closely related to the ancestry of amniotes, but not to recent amphibians.
Apart from the Nectridea, lepospondyls are limited in distribution to Europe and North America.
- Subclass LEPOSPONDYLI
- Order Adelospondyli
- Family Acherontiscidae
- Order Aïstopoda
- Order Nectridea
- Superorder Microsauria
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