| Westlothiana Temporal range: Early Carboniferous |
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|---|---|
| Westlothiana lizziae | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Amphibia/Reptilia |
| Order: | Cotylosauria? |
| Genus: | Westlothiana |
| Species: | W. lizziae |
| Binomial name | |
| Westlothiana lizziae Smithson and Rolfe, 1990 |
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Westlothiana lizziae was a reptile-like amphibian or possibly early reptile that bore a superficial resemblance to modern-day lizards. 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.[1] Most scientists place them among the Reptilomorpha, as a sister group to the first amniotes.[2][3]
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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 Casineria, 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.[4][5] 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.[6]
Ruta & al. (2003) interpreted the long body and small legs as a possible adaption to burrowing, similar to that seen in modern skinks.[2]
The phylogenetic placement of Westlothiana has varied from basal amniote (i.e. a primitive reptile) to an amphibian Lepospondyl only distantly related to the Reptiliomorpha.[1][3] The actual phyllogenetic position of Westlothiania is uncertain, reflecting both the fragmentary nature of the find and the uncertainty of labyrinthodont phylogeny in general.[5]