Spinoaequalis is an extinct genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of diapsid

Diapsid

Diapsids are a group of reptiles that developed two holes in each side of their skulls, about 300 million years ago during the late Carboniferous period. Living diapsids are extremely diverse, and include all crocodiles, lizards, snakes, and tuatara...

 reptile.

The 30 cm (1 ft) long creature, known from fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s found in Kansas

Kansas

Kansas is a US state located in the Midwestern United States. It is named after the Kansas River which flows through it, which in turn was named after the Kansa Native American tribe, which inhabited the area. The tribe's name is often said to mean "people of the wind" or "people of the south...

, USA, was one of the first diapsids, along with Petrolacosaurus

Petrolacosaurus

Petrolacosaurus was a small, 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....

. It was also the first reptile to return to the water, evolving shortly after Hylonomus

Hylonomus

Hylonomus was a very early reptile. It lived 312 million years ago during the Late Carboniferous period.It is the earliest unquestionable reptile ....

, the oldest confirmed reptile. Spinoaequalis was not fully aquatic, frequently returning to dry land. It probably swam using its laterally flattened, fanned tail. Its name means "symmetrical spine" referring to its deep, laterally compressed tail. Spinoaequalis has been found along with beautifully preserved marine fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

, suggesting it occasionally left fresh water streams for the sea.

Spinoaequalis was described and named by Michael deBraga and Robert Reisz in 1995.