The most popular group of Permian reptiles is plant eating lizards pareiasaurs—“big cheek lizards”. They lived in permian deltas and near the rivers sides during all Upper Permian. In spite of plenty of fossil materials from numerous localities pareiasaurs are very bad studied and up to now many details of their anatomy, the way of their eating and reproduction are not clear. There is a point of view that sea and land tartlets and tortoises came from pareiasaurs. Pareiasaurs were very specialized animals, which took strictly fixed ecological niche. By global draining of climate at the end of Permian period, this group of reptiles died out.
Figuratively speaking, pareiasaurs were “hippopotamuses” in their way of life: the most part of life they spent in water and only sometimes they went out on dry land, were they felt uncomfortable. Some of late species of pareiasaurs were 2,5-3 meters lengthwise, and judging by finds of isolated bones, they could reach bigger sizes.
More ancient and primitive pareiasaurs were found on Kotelnich locality. They were not big sizes up to 2 m.in length, had less developed dermal ossicles than their later species, and in opposite to them they had more gracil body structure. That partly points that animals could easily move on the land. To some scientists’ mind, North Dvina’s scutosaurs couldn’t do it.
Typical feature of pareiasaurs is numerous dermal ossicles, part of them grew fast to skull of animal and to vertebrae, the other part were in thick skin. Just this circumstance gave scientists the idea that pareiasaurs were ancestors of tortoises: in the way of dermal ossicles union in united osseous shell (testa?) and following complex of irreversible transformation the pareiasaurs gave the beginning to tortoises.
Pareiasaurs were gregarious animals, they could got over long distances looking for food. They ate some species of plants, probably water-plants, which lizards filtered with peculiarly teeth system. Besides petalous like with big cutting edge teeth pareiasaurs had numerous palatine teeth, served for keeping of plants and directing them to digestive canal. Besides lung breathing probably pareiasaurs had skin breathing. Animals had throat bag, like modern frogs have, by the use of which they pushed through air into lungs. Good developing of voice sinuses in their skulls shows that lizards could associate with each other through strong voice sounds. It was especially actually in breeding period. More developed dermal ossicles (horns) on some skulls and their undevelopment on others, and also some other indications in postcranial skeleton structure show probably on differences between sexes (sexual dichotomy). But for full confidence we need long details research of these original animals rests.
Most of the fossilised animals found at the Kotelnich fossil locality died as a result of being bogged in soft sediment after heavy rain fall, when the water level was higher and boggy substratum became silty swamp. Animals being good at swimming and walking got in natural traps when there was not enough water to swim through but the ground became series of mud traps. As a rule on Kotelnich locality there are absolutely complete skeletons of pareiasaurs, often they have living posture—the back up. It points that animals trapped in mud and their remains were fast hidden by brought sediment. By such burial these is an opportunity for preservation not only the smallest limbs and tail, but also the dermal ossicles.
The most diagnostic feature of the animals is its unusual skull, from where the group derives its name “Kotylosaurus”. If we look at the pareiasaur’s skull from above, we see, that its form resembles the letter V. It was the reason to call Kotelnich pareiasaurs Deltavjatia vjatkensis, in name of Greek letter “Delta”. Why “Kotilosaurus?” – The thing is that the skull of pareiasaurs belongs to anapside type of structure, because it hasn’t temporal holes, like the most part of other reptiles and mammals, and its form is like overturned kettle or pot.
Besides eye sockets and nose foramen on the upper side of skull there is a pineal foramen or “the third eye”. It’s a many function additional organ of sense, which all permian reptiles had. During next evolutional transformations the pineal foramen lost its purpose, and is seen only by mammals in embryogenesis.
In spite of big eye sockets the animal had small eyeballs, because the cornea reinforced additional formation—the ring of sklerotic, consisting from partly cornificationly tendons. Skulls of pareiasaurs with saved ring of sklerotic are very rare.
The surface of skull is uneven. It is covered with horns and ossicles of different sizes. The biggest of them usually are on the scaly bones (“cheeks”), parietal and nosal bones. Sometimes there are big horns on frontale bones, and almost always they are on base of lower jaw (on articulare). On the biggest dermal ossicles horn caps were made fast. They could reach more sizes. Not rare finds of fossilized hornlike formations show on this fact.
In deepenings between dermal ossicles there were, probably, skin glands, which exuded specific muscus for wetting of skin’s surface. May be, there were poisonous warts surveying to frighten off predators.
The structure of pareiasaur’s skull foundation says that there was no divisions between mouth and nose cavities. It made the animals to bolt their food without chewing. Because when the food was in mouth cavity, there was impossible to breathe.
The first finds were of skulls of the little and probably insectivorous reptiles which were referred to the group Nycteroleteridae by M.F.Ivakhnenko, a collaborator of P.I.N. of R.A.S. The collections were made at Kotelnich locality at the beginning of the 1990s by the expedition group of “Stone Flower”, a Moscow company. The name Nycteroleter (from gr.- lat. “a night pilferer”) was given to the find from Arkhangelsk region by I.A.Efremov in 1937. He based this name upon the large size of animal’s eye-sockets and suggested that Nycteroleter were active in nocturnal eating of insects. Finds of representatives of this group of Permian reptiles are not rare in faunal complexes of East European localities, but only at Kotelnich in 1998 have two complete skeletons of Nycteroleter been found. They are presently being prepared in the laboratory of the Kotelnich Palaeontological Museum and at the University of Toronto (Ontario, Canada). The earlier finds were fragmentary and in general they were only represented by skull fragments and complete skulls. These finds of the last few years let us revise our ideas about Nycteroleter.
The structure of Nycteroleter’s skull unites this group of Permian reptiles with pareiasaurs. There is a tendency for size increase. The skull has a high arch, decorated by dermal ossicles and sculpturing, there is a tendency towards acquisition of serrated crowns on the maxillary teeth, similarly to the palatal teeth of Pareiasaurs, which have high combs upon the crown.
The form of Nycteroleter found at Kotelnich was attributed by M.F. Ivakhnenko to a new genus and was called Emeroleter levis. The typical example presents an incomplete skull (there are few finds of isolated upper jaw bones), a fragment of a skull, and now the two complete skeletons, found by the collaborators of Kotelnich Palaeontological Museum in 1998. Both skeletons were found in a crooked position. One of them belonged to a small animal, probably a juvenile Emeroleter. The second specimen belonged to a bigger individual. The skeletons were found in one place separated by a distance of about 10 cm. They were in a similar pose, typical for small animals, which are often found in a crooked position with a skull directed towards the tail and hind limbs. Hence, it’s possible to suppose that both of the individuals perished together in a [dream] or anabiosis. Most likely that these animals lived in burrows.
Nycteroleter is widely represented in Upper Permian faunas throughout East Europe and South Africa. They have been known for a long time; however, the fragmentariness of finds makes it difficult to study this interesting group of Permian reptiles.