| Petrolacosaurus Temporal range: Late Pennsylvanian, Gzhelian
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|---|---|
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| Petrolacosaurus kansensis | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | †Araeoscelidia |
| Family: | †Petrolacosauridae Peabody, 1952 |
| Genus: | †Petrolacosaurus Lane, 1945 |
| Species | |
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| Synonyms | |
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Podargosaurus hibbardi Lane, 1945 | |
Petrolacosaurus ("rock lake lizard") is an extinct genus of diapsid reptile from the late Carboniferous period. It was a small, 40-centimetre (16 in) long reptile, and one of the earliest known reptile with two temporal fenestrae (holes at the rear part of the skull). This means that it was at the base of Diapsida, the largest and most successful radiation of reptiles that would eventually include all modern reptile groups, as well as dinosaurs (which survive to the modern day as birds) and other famous extinct reptiles such as plesiosaurs, ichthyosaurs, and pterosaurs. However, Petrolacosaurus itself was part of Araeoscelida, a short-lived early branch of the diapsid family tree which went extinct in the mid-Permian.