Lepospondyli
Lepospondyli
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Lepospondyli
Lepospondyli
Lepospondyli
Gaucho Palazzo Pants ~ Lepospondyli are a group of small but diverse Carboniferous to early Permian tetrapods. Six different groups are known, the Acherontiscidae, Adelospondyli, Aïstopoda, Lysorophia, Microsauria and Nectridea, and between them they include newt-like, eel- or snake-like, and lizard-like forms, along with species that do not fit any current category. Various species were aquatic, semi-aquatic, or terrestrial. None were large (the biggest genus, the keraterpetontid Diplocaulus, reached a meter in length, but most were much smaller), and it can be assumed that they lived in specialised ecological niches not taken by their more numerous Temnospondyl contemporaries.
Gaucho Palazzo Pants ~ All lepospondyls are characterised by having simple, spool-shaped vertebra, 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) (Colbert 1969).No clear common ancestors are known, since each of the known clades are already highly specialised when they first appear in the fossil record. It is not known whether the lepospondyls are an artificial (polyphyletic) group which independently evolved similar characteristics of the vertebra, or whether they descended from a single common ancestor.
At one time it was thought that some lepospondyls are 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 (Romer 1966, Colbert 1969, Carroll 1988). More recently, it has been suggested that the lepospondyls may be related or ancestral to modern amphibians as well as to amniotes (reptiles etc) (Laurin 1996), that they are an artificial grouping with some members related to both extinct and living amphibians (Batrachomorpha) but not amniotes (Benton 2000), or alternatively are a monophyletic group closely related to the ancestry of amniotes but not to recent amphibians (Benton 2004).Apart from the Nectridea, lepospondyls are limited in distribution to Europe and North America (Carroll 1988).
July 20, 2011
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Lepospondyli
Aistopoda, Lepospondyli
Lepospondyli
Aistopoda
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Lepospondyli
Lepospondyli
Aistopoda
Magnetic Spice Rack ~ Aïstopoda (Greek for “[having] not-visible feet”) is an order of highly specialised snake-like amphibians known from the Carboniferous and Early Permian of Europe and North America, ranging from tiny forms only 5 centimetres (2.0 in), to nearly 1 metre (3.3 ft) in length. The first appear in the fossil record in the Mississippian period and continue through to the Early Permian.
Magnetic Spice Rack ~ The skull is small but very specialised, with large orbits, and large fenestrae. The bones at the back of the skull were reduced or absent. The primitive form Ophiderpeton has a pattern of dermal bones in the skull similar in respects to the temnospondyls. But in the advanced genus Phlegethontia the skull is very light and open, reduced to a series of struts supporting the braincase against the lower jaw, just as in snakes, and it is possible that the Aïstopods filled the same ecological niches in the Paleozoic that snakes do today. They had an extremely elongated body, with up to 230 vertebrae. The vertebrae were holospondylous, having only a single ossification per segment. They lacked intercentra, even in the tail, and had are no free haemal arches. The neural arch was low and fused to the centrum. All of these features are very similar to those of the Nectridea, both representing the typical lepospndylous condition.The ribs were slender, either single or double-headed, with the head shaped like a K. There is no trace of limbs or even limb girdles in any known fossil, and the tail was short and primitive.
Evolutionary relationships with other early tetrapods remain controversial, as even the earliest aïstopod, the Viséan species Lethiscus stocki, was already highly specialised. Aïstopods have been variously grouped with other lepospondyls, or placed at or prior to the batrachomorph-reptiliomorph divide. The group was quite diverse during the Late Carboniferous, with a few forms continuing through to the Permian.
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
Aistopoda
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Dendrerpeton 