Nikkasaurus 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 therapsid.

They were small animal

Animal

Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...

s, with skull

Skull

The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...

s about 5 cm long. Their eye

Eye

Eyes are organs that detect light and convert it into electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement...

s had large orbits

Orbit (anatomy)

In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents...

 and sclerotic rings. The head was tilted back, as with all therapsids.

The skull looks superficially similar to those of the Pelycosaurs, in particular Varanopidae

Varanopidae

Varanopidae was a family of synapsid "pelycosaurs" that resembled monitor lizards and might have had the same lifestyle, hence their name. No known varanopids developed a sail like Dimetrodon. Their size varied from lizard-sized to dog-sized creatures. Varanopids already showed some advanced...

.

Nikkasaurus was probably mainly insectivorous, and possibly nocturnal.

The only known species is N. tatarinovi, described by MF Ivahnenko in 2000, from the Middle Permian Mezen River Basin

Mezen River

The Mezen is a river in Udorsky District of the Komi Republic and in Leshukonsky and Mezensky Districts of Arkhangelsk Oblast in Russia. Its mouth is located in the Mezen Bay of the White Sea. Mezen is one of the biggest rivers of European Russia. It is long, and the area of its basin...

. The family Nikkasauridae also includes the Reiszia

Reiszia

Reiszia is an extinct genus of non-mammalian synapsid.-References:*...

genus with two species (R. gubini and R. tippula) described by Ivahnenko in 2000 from the same sediment

Sediment

Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

.

Nikkasaurus is possibly a relic of a more ancient stage of therapsid development.