Aïstopoda
Encyclopedia
Aïstopoda is an order of highly specialised snake-like amphibian
s known from the Carboniferous
and Early Permian of Europe and North America, ranging from tiny forms only 5 centimetres (2 in), to nearly 1 metres (3.3 ft) in length. The first appear in the fossil record in the Mississippian period and continue through to the Early Permian.
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 niche
s 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 arch
es. 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 tetrapod
s 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
.
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s known from the Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
and Early Permian of Europe and North America, ranging from tiny forms only 5 centimetres (2 in), to nearly 1 metres (3.3 ft) in length. The first appear in the fossil record in the Mississippian period and continue through to the Early Permian.
The skull
Skull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
is small but very specialised, with large orbits
Orbit (anatomy)
In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents...
, and large fenestrae. The bones at the back of the skull were reduced or absent. The primitive form Ophiderpeton
Ophiderpeton
Ophiderpeton is an extinct genus of lepospondyl amphibian from the Carboniferous period. Remains of this genus are widespread and were found in Ohio, USA and the Czech Republic ....
has a pattern of dermal bones in the skull similar in respects to the temnospondyls. But in the advanced genus Phlegethontia
Phlegethontia
Phlegethontia is an extinct genus of lepospondyl amphibian from the Carboniferous and Permian periods of Europe and North America.Phlegethontia was an aïstopod, a group of legless, burrowing, snake-like amphibians...
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 niche
Ecological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...
s 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 arch
Haemal arch
A haemal arch is a bony arch on the underside of a tail vertebra of a vertebrate.The hole so formed is the haemal canal.It sometimes has a haemal spine on.The blood vessels to and from the tail run through the arch....
es. The neural arch was low and fused to the centrum
Centrum
Centrum means center in Latin.Centrum may refer to:* The central portion of a vertebra*Centrum , a Washington state performing arts organization* Centrum , metro station in Warsaw, Poland...
. All of these features are very similar to those of the Nectridea
Nectridea
Nectridea is an extinct order of lepospondyl amphibians from the Carboniferous and Permian periods, which included animals such as Diplocaulus. In appearance, they would have resembled modern newts or aquatic salamanders. They had long flattened tails to aid in swimming, and well-developed hind...
, 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 tetrapod
Tetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...
s remain controversial, as even the earliest aïstopod, the Viséan
Viséan
The Visean, Viséan or Visian is an age in the ICS geologic timescale or a stage in the stratigraphic column. It is the second stage of the Mississippian, the lower subsystem of the Carboniferous. The Visean lasted from 345.3 ± 2.1 to 328.3 ± 1.6 Ma...
species Lethiscus stocki
Lethiscus
Lethiscus is the earliest known representative of the Aïstopoda, a group of very specialised snake-like amphibians known from the Carboniferous and Permian....
, was already highly specialised. Aïstopods have been variously grouped with other lepospondyls
Lepospondyli
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...
, or placed at or prior to the batrachomorph
Batrachomorpha
Batrachomorpha is a name traditionally given to recent and extinct amphibians that are not related to reptiles. It most often includes the extinct groups Temnospondyli and Lepospondyli.-Origin of the term:...
-reptiliomorph
Reptiliomorpha
Reptiliomorpha refers to an order or subclass of reptile-like amphibians, which gave rise to the amniotes in the Carboniferous. Under phylogenetic nomenclature, the Reptiliomorpha includes their amniote descendants though, even in phylogenetic nomenclature, the name is mostly used when referring to...
divide. The group was quite diverse during the Late Carboniferous
Pennsylvanian
The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain...
, with a few forms continuing through to the Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
.