Name: Petrolacosaurus.
Phonetic: Pet-roe-lak-oh-sore-us.
Named By: H. H. Lane - 1945.
Classification: Chordata, Reptilia, Diapsida, Araeoscelida, Petrolacosauridae.
Species: P. kansensis (type).
Type: Insectivore.
Size: 40 centimetres long.
Known locations: USA, Kansas.
Time period: Gzhelian of the Carboniferous.
Fossil representation: Well enough preserved to reveal the full morphology.

       Petrolacosaurus is the first diapsid known in the fossil record. The teeth are small and sharp suggesting insectivorous feeding, like the vast majority of the other small reptiles of the time. Also like many of the early diapsids, it was superficially similar to today’s small lizards.
       Petrolacosaurus is very similar to another reptile called Araeoscelis that lived in the early Permian, although the latter has more robust dentition.

Further reading
- New Mid-Pennsylvanian Reptiles from Kansas. - Transactions of the Kansas Academy of Science 47(3):381-390. - H. H. Lane - 1945.
- Petrolacosaurus kansensis, a Pennsylvanian reptile from Kansas. - University of Kansas Paleontological Contributions, Paper, 10(1), 1-41. - F. Peabody - 1952.
- Petrolacosaurus, the Oldest Known Diapsid Reptile. - Science, 196(4294), 1091-1093. - R. Reisz - 1977.


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