Lethiscus
Encyclopedia
Lethiscus is the earliest known representative of the Aïstopoda
, a group of very specialised snake-like amphibian
s known from the Carboniferous
and Permian
.
Lethiscus is known from only a single specimen from the Holkerian Stage (Middle Viséan
) of the Early Carboniferous
(Middle Mississippian) of Scotland
, and is one of the oldest known post Devonian tetrapods. Despite its very early date, it was already a highly advanced animal.
The skull is specialised and light, very like that of Ophiderpeton
, with the orbits
, far forward, and the cheek region unossified (lacking bone). There are approximately 30 closely spaced teeth on the maxilla
and dentary, and a sutural pattern of the skull closely resembles that of the Late Carboniferous
aïstopod Oestocephalus
.
There is no trace of limbs. However, unlike later members of the aïstopod lineage, the vertebrae still possess intercentra, and the pleurocentra are large.
Lethiscus is the only representative of the family Lethiscidae. Owing to its early date, it has since its discovery been considered ancestral to later aïstopods, and more recent cladistic research (Anderson et al. 2003) confirms its position as the most basal (primitive) aistopod.
Aïstopoda
Aïstopoda 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 , to nearly in length...
, a group of very specialised snake-like amphibian
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 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...
.
Lethiscus is known from only a single specimen from the Holkerian Stage (Middle 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...
) of the Early 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"...
(Middle Mississippian) of Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
, and is one of the oldest known post Devonian tetrapods. Despite its very early date, it was already a highly advanced animal.
The skull is specialised and light, very like that of 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 ....
, with the 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...
, far forward, and the cheek region unossified (lacking bone). There are approximately 30 closely spaced teeth on the maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
and dentary, and a sutural pattern of the skull closely resembles that of 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...
aïstopod Oestocephalus
Oestocephalus
Oestocephalus is an extinct genus of aïstopod lepospondyl that lived during the Carboniferous period. Fossils have been found from the Czech Republic as well as Ohio and Illinois in the United States. It is the type genus of the family Oestocephalidae, although it was previously assigned to the...
.
There is no trace of limbs. However, unlike later members of the aïstopod lineage, the vertebrae still possess intercentra, and the pleurocentra are large.
Lethiscus is the only representative of the family Lethiscidae. Owing to its early date, it has since its discovery been considered ancestral to later aïstopods, and more recent cladistic research (Anderson et al. 2003) confirms its position as the most basal (primitive) aistopod.