Skull

Nochnitsa is small for a gorgonopsian, with a skull only 82 millimetres (3.2 in) long. It had a relatively long snout with five incisors, a canine, and six postcanine teeth on each side. The postcanine teeth are autapomorphic for the genus in being arranged in three pairs of closely placed teeth separated by longer diastemata. In each pair, the posterior tooth is larger. The mandible is relatively slender and lacks a strong "chin", unlike other gorgonopsians.^[1]

Postcranial skeleton

Right side of the block containing the holotype specimen, showing in more detail the rare postcranial elements known of the animal

Although incompletely known, the holotype specimen of Nochnitsa contains part of the postcranial elements with the skull, including the cervical vertebrae, some dorsal vertebrae, and associated ribs. The right forelimb is also preserved and partially articulated.^[1]

In the cervical vertebrae, the axial spine is broadly rounded and similar in morphology to that of other gorgonopsians. The dorsal vertebrae are preserved as central and transverse process fragments interspersed by the ribs. The ribs are also simple and elongated. The scapula is elongated, narrow and weakly curved, comparable to that of other gorgonopsians of similar size like Cyonosaurus, but different from the anteroposteriorly broadened scapular spines of Inostrancevia.^[1]

The humerus is relatively slender, having a short, poorly developed delto-pectoral ridge, where the muscles attach to the upper arm. The radius and ulna, have a distinct distal curvature, and the distal tip of the radius forms a discrete differentiated rim of the shaft. No olecranon process is visible on the ulna, but it is possible that this is the result of a lesion.^{[lower-alpha 1]} The preserved proximal carpal elements consist of the radial, the ulnar and two smaller, irregular elements that would probably represent the centralia. The ulnar is the longest carpus on the proximodistal side and is widened at its proximal and distal ends. The radial is a shorter and more rounded element. The possible centralia, although poorly preserved, appear to be weakly curved. The concave surface of the centralia would presumably have been articulated with the radial, based on the conditions of other gorgonopsians.^{[lower-alpha 2]} Several small irregular bones between the proximal carpals and the metacarpals probably represent distal carpals, but these elements are too poorly preserved to be further identified. Based on their great length relative to the other manual elements, the two best preserved elements probably represent the third and fourth metacarpals, which are the longest of all other gorgonopsians for which the manus are known. A shorter but still elongated element may represent the fifth metacarpal. A semi-articulated set of poorly preserved bones appear to represent fingers, one potentially ending in the ungual. Based on the size of the phalanx-like elements, these probably correspond to the third and fourth fingers, disarticulated from the third and fourth metacarpals. These elements are too poor for a definitive count of the phalanges, and there is no clear evidence of the reduced disc-shaped phalanges commonly present in gorgonopsians.^[1]

Paleoenvironment

Life restoration of N. geminidens

Nochnitsa is known from the Kotelnich locality, which consists of a series of Permian red bed exposures along the banks of the Vyatka River in Russia. It is specifically from the Vanyushonki Member, which is the oldest rock unit in the Kotelnich succession, consisting of pale or brown mudstones (clay and silts, with some fine-grained sand) as well as gray mudstone, and dark red mudstone at the base of this exposure. These mudstones were possibly deposited from suspension in standing water bodies on floodplains or shallow ephemeral lakes, that remained flooded for short periods of time, but the exact environment has not yet been determined, due to the lack of a primary structure of the sediments. The presence of rootlets, roots and tree stumps would show that the landscape represented by the member of Vanyushonki would be relatively humid and well vegetated. Although the age of the Kotelnitch faunal complex is uncertain, it may date to the same age as those found in South Africa, which date from either the Late Middle Permian or the Early Late Permian.^[1][6]

The Vanyushonki Member contains abundant fossils of tetrapods contemporary to Nochnitsa, most including numerous fossils often consisting of articulated and complete skeletons. Apart from its close relative Viatkogorgon, other therapsids from the locality include the anomodont Suminia and the therocephalians Chlynovia, Gorynychus, Karenites, Perplexisaurus, Scalopodon, Scalopodontes, and Viatkosuchus. The pareiasaur Deltavjatia is particularly abundant there, and the parareptile Emeroleter is present.^[1][2][7] Fossil ostracods have also been found.^[6]

Ecological niche

As the fossil record shows, the fauna of Kotelnitch was mainly dominated by the large therocephalians, and more specifically by Gorynychus and Viatkosuchus. These two taxa being much larger than Nochnitsa and Viatkogorgon, this indicates that the gorgonopsians occupied smaller predatory roles than the large therocephalians. This is further confirmed by the fact that several gorgonopsians having appeared after the extinction of the end of the Guadalupian reach considerably larger sizes than the two previously mentioned genera.^[2][4] This type of ecological niche is also similar to that seen in the Pristerognathus Assemblage Zone in the Karoo Basin, South Africa, prior to the main round of gorgonopsian diversification there.^[2] However, he noted that some Guadalupian gorgonopsians, notably Phorcys, are already larger in size, indicating that not all genera shared similar roles.^[5]