Petrolacosaurus was a small, 40-centimetre (16 in) long, reptile, and the earliest diapsid known. It lived during the late Carboniferous period, the Joggins strata where it was found are dated to 302 million years old. The prehistoric reptile's diet may have consisted mainly of small insects. Petrolacosaurus had distinctive canine-like secondary-sized teeth, a trait found primarily in therapsids, and later in mammals. Its fossils were found in Kansas, USA.

 While Petrolacosaurus was indeed a relatively early amniote and was typically lizard-like, as were all the first amniotes, it was nevertheless too derived to be portrayed as the ancestor of all modern forms. In fact, it was already a diapsid, with two openings known as "temporal fenestrae" on each side of its skull to add attachment points for jaw muscles. Hence, it cannot have been the ancestor of any synapsids, which have only one such opening and diverged from the common amniote tree before the diapsids did.

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Tags: Вымершие рептилии, Карбон

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