Westlothiana
Encyclopedia
Westlothiana lizziae was a reptile
-like amphibian
or possibly early reptile
that bore a superficial resemblance to modern-day lizard
s. It lived during the Carboniferous
period, about 350 million years ago. The type specimen was discovered in East Kirkton Quarry
, Bathgate
, Scotland
, in 1984, and was named after the West Lothian
district where it was found. Westlothiana' s anatomy contained a mixtures of both labyrinthodont and reptilian features, and was originally regarded as the first reptile. Most scientists place them among the Reptilomorpha, as a sister group to the first amniotes.
, another transitional fossil
found in Scotland
, it is one of the smallest reptil-like amphibians known, being a mere 20 cm in adult length. The small size has made it a key fossil in the search for the earliest amniote
, as amniote eggs are thought to have evolved in very small animals. Advanced features that ties it in with the reptilian rather than amphibian group is unfused ankle bones, lack of labyrinthodont infolding of the dentin
, a lack of an otic notch
and a generally small skull.
Ruta & al. (2003) interpreted the long body and small legs as a possible adaption to burrowing, similar to that seen in modern skink
s.
(i.e. a primitive reptile
) to an amphibian Lepospondyl
only distantly related to the Reptiliomorpha
. The actual phyllogenetic position of Westlothiania is uncertain, reflecting both the fragmentary nature of the find and the uncertainty of labyrinthodont phylogeny in general.
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
-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...
or possibly early reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
that bore a superficial resemblance to modern-day lizard
Lizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...
s. It lived during 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"...
period, about 350 million years ago. The type specimen was discovered in East Kirkton Quarry
East Kirkton Quarry
East Kirkton Quarry is a former limestone quarry, now better known as a fossil site known for terrestrial fossils from the fossil-poor "Romer's gap, a 15 million year period at the beginning of the Carboniferous...
, Bathgate
Bathgate
Bathgate is a town in West Lothian, Scotland, on the M8 motorway west of Livingston. Nearby towns are Blackburn, Armadale, Whitburn, Livingston, and Linlithgow. Edinburgh Airport is away...
, 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...
, in 1984, and was named after the West Lothian
West Lothian
West Lothian is one of the 32 unitary council areas in Scotland, and a Lieutenancy area. It borders the City of Edinburgh, Falkirk, North Lanarkshire, the Scottish Borders and South Lanarkshire....
district where it was found. Westlothiana
Westlothiania in life
This species probably lived near a freshwater lake, probably hunting for other small creatures that lived in the same habitat. It was a slender animal, with rather small legs and a long tail. Together with CasineriaCasineria
Casineria was a tetrapod which lived 340 million years ago in the Mississippian epoch. Casineria was a small animal with a total length estimated to have been 15 centimeters. It lived in what was then a fairly dry environment in Scotland. It is noted for its mix of primitive and advanced ...
, another transitional fossil
Transitional fossil
A transitional fossil is any fossilized remains of a lifeform that exhibits characteristics of two distinct taxonomic groups. A transitional fossil is the fossil of an organism near the branching point where major individual lineages diverge...
found in 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...
, it is one of the smallest reptil-like amphibians known, being a mere 20 cm in adult length. The small size has made it a key fossil in the search for the earliest amniote
Amniote
The amniotes are a group of tetrapods that have a terrestrially adapted egg. They include synapsids and sauropsids , as well as their fossil ancestors. Amniote embryos, whether laid as eggs or carried by the female, are protected and aided by several extensive membranes...
, as amniote eggs are thought to have evolved in very small animals. Advanced features that ties it in with the reptilian rather than amphibian group is unfused ankle bones, lack of labyrinthodont infolding of the dentin
Dentin
Dentine is a calcified tissue of the body, and along with enamel, cementum, and pulp is one of the four major components of teeth. Usually, it is covered by enamel on the crown and cementum on the root and surrounds the entire pulp...
, a lack of an otic notch
Otic notch
Otic notches are invagination in the posterior margin of the skull roof, one behind each orbit. Such notches are found in labyrinthodonts and some of their immediate ancestors, but not their reptilian descendants...
and a generally small skull.
Ruta & al. (2003) interpreted the long body and small legs as a possible adaption to burrowing, similar to that seen in modern skink
Skink
Skinks are lizards belonging to the family Scincidae. Together with several other lizard families, including Lacertidae , they comprise the superfamily or infraorder Scincomorpha...
s.
Phylogeny
The phylogenetic placement of Westlothiana has varied from basal amnioteAmniote
The amniotes are a group of tetrapods that have a terrestrially adapted egg. They include synapsids and sauropsids , as well as their fossil ancestors. Amniote embryos, whether laid as eggs or carried by the female, are protected and aided by several extensive membranes...
(i.e. a primitive reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
) to an amphibian Lepospondyl
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...
only distantly related to the Reptiliomorpha
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...
. The actual phyllogenetic position of Westlothiania is uncertain, reflecting both the fragmentary nature of the find and the uncertainty of labyrinthodont phylogeny in general.