Fig. 1. Sundyrsky gorynych (Gorynychus sundyrensis) caught the amphibian of the dvinosaurus (Dvinosaurus) . Drawing by Andrey Atuchin

The Sundyr locality, located on the shore of the Cheboksary reservoir on the border of Chuvashia and Mari El, has a unique “transitional” character: it contains the remains of animals buried during the global faunal restructuring that took place in the middle of the Permian period. Russian paleontologists, having studied the finds made at this location over the past couple of years, described two new carnivorous animals from the group of terocephals. These species are more advanced in an evolutionary sense than all those who have been found in Sundyr before.

In the Permian period, various animals were already roaming overland on land. Many of the Perm tetrapods (four-legged animals) have already been told by the “Elements” more than once (see, for example, the news of Gorynych and the night-night – new Permian predators from the banks of the Vyatka , “Elements”, 08/20/2018; Permian period park: found in Sardinia three types of synapsids , “Elements”, 11/14/2018 and pictures of the day Bilateral chalcosaurus , Erasaurus and Suminia and Sabretooth beast -dog ). Paleontologists distinguish three main faunistic tetrapod groups, which successively replaced each other during the Permian period, and name them according to the group that dominated the corresponding time interval.

In the first third of the Permian period, the pelicosaurus fauna flourished on land. Pelicosaurus were the most ancient and primitive synapsids , among them there were both herbivorous and predatory forms. Of these, the “sailing lizards” are the most famous: pelicosaurs and edaphosaurus (they are called “sailing” for their characteristic appearance: on their back they had a rather large crest of skin stretched over huge spinous processes of the vertebrae, Fig. 2).

Fig. 2. Large representatives of the Permian fauna. On the left  is the Edaphosaurus edanosaurus boanerges , on the right  is the Estemmenosuchus uralensis . These animals could reach 4 meters in length. Drawings from ru.wikipedia.org

In the second third of the Permian period, the pelicosaurus fauna was replaced by the dinocephalic fauna. The most noticeable and widespread tetrapods were descendants of pelicosaurs – dinofephals (among which there were also herbivorous and predatory animals). Dinocephals were distinguished by large sizes, greater adaptability to terrestrial life, and as a whole had a more complex organization. Their distinctive feature was the thick bones of the skull, according to which the animals got their name – “scary-headed”. Bright representatives were herbivorous dinotsefalov ulemosaurus and estemmenosuchidae , predatory – titanofon (Titanophoneus) .

The third and last fauna of the Permian period is the periodontium. The dominant position in it was occupied by the bestial-toothed reptiles of theiodont . According to the paleontologist M.F. Ivakhnenko , they came from the ancient synapsids and were a kind of alternative line in relation to dinocephals.

Almost all the locations of Permian fossils are confined to only one of these groups. But there are rare, even unique locations of a peculiar “transitional type” in which the remains of animals from different groups are found. One of them is located on the banks of the Cheboksary reservoir, on the border of Chuvashia and the Mari El Republic, near the village of Bolshoi Sundyr .

Here, on the high bank of the reservoir, red-colored rocks of 260 million years old are exposed (Fig. 3). The fauna found in them represents a transitional stage between the dinocephalic and theriodontic groups: dinocephalic and theriodonts were found here, the remains of amphibians also belong to more ancient and later taxa (V.K. Golubev et al., 2015. About age Sundyr faunistic complex of Perm tetrapods of the East European platform ).

Fig. 3. Excavations at the Sundyr site and a view of the Cheboksary reservoir. Photo by Olesya Strelnikova, 2018

Excavations at the Sundyr site began in 2010 and are still ongoing. During this time, employees of the Paleontological Institute of the Russian Academy of Sciences collected about seven hundred diagnosed tetrapod remnants there . Most of them belonged to amphibians, mainly to dvinosaurs (Dvinosaurus) , which account for 35% of all bones found.

Fig. 4. The bone remains from Sundyr are mostly small and look unrepresentative like this piece of bone. Photo by Julia Suchkova

16% of the remains found belong to predatory lizards: these are mainly teeth and cranial bones. Previously, these predators were defined as dinofephals close to giant titanophones (Fig. 5). Then, the bones of more advanced predatory gorgonopies, characteristic of the theriodont group, were found at the site. There was an assumption that both carnivorous dinocephals and carnivorous gorgonopies lived here at the same time, which corresponded to the transitional nature of the location.

Fig. 5. On the left  – a predatory titanophone attacks the herbivorous tapinocephalus, illustrated by S. Krasovsky from an article by A. Nelikhov Blue Bones ( National Geographic Russia , No. 12 for 2012). On the right  is the cub of another predator of those times – gorgonopia, illustration by A. Atuchin from the book Ancient Monsters of Russia

However, new finds from the past two years and re-examination of old finds have changed the picture. At first it became clear that there were no predatory dinocephals in the whereabouts. The remains, which were previously defined as titanophones, belonged to other, more advanced forms – terocephals . A further audit of the remains showed that there were no gorgonopies in Sundyr either. All diagnosed predator bones belonged to terocephals. But the herbivorous lizards and a number of amphibians actually belonged to the dinocephalic fauna, so that the “transitional” character of Sundyr did not go away.

Such taxonomic studies are unlikely to be entertaining to an outsider, although in reality we are talking about very serious reevaluations. Imagine that one archaeologist finds a bone and claims that it belongs to a modern person, another believes that it is an Australopithecus bone, and then it turns out that it is from a kangaroo.

According to new studies by Russian paleontologists, all the discovered remains of carnivorous dinosaurs from Sundyr belong to two previously unknown, very large terocephals. The predator, whose remains were found more frequently, was described as a new genus and species of the yognathus crudelis (Julognathus crudelis) , which can be translated as the “ruthless Volga jaw” (Yul – the ancient Mari name of the Volga). To date, 81 teeth and a fragment of skulls of ylognatus have been found (Fig. 6).

Fig. 6. Reconstruction of the skulls of Julognathus crudelis ( above ) and Gorynychus sundyrensis . Images from discussed articles in the  Paleontological Journal

The animal was one of the largest predators of the Permian period. Judging by some fragments, the skull of the ylognatus reached a length of 43 centimeters, that is, it was two times longer than that of a wolf. The animal itself was apparently the size of a bear.

The second lizard belongs to the recently described genus Dragon ( Gorynychus ), but differ in the dental system and has been allocated to a new species – Dragon sundyrsky (Gorynychus sundyrensis) . His remains were less common: 33 bones were found that reliably belonged to him. It was similar in size to the ylognatus, but had a more massive and shortened skull (Fig. 6, bottom).

One cranial fragment of the mountain revealed a curious feature associated with the change of fangs. All animal hunters – both carnivorous and herbivorous – had regular tooth changes throughout their lives: old ones fell out, new ones grew. The shift models were different. The fang and the related African lycosuchids, the new fangs completely grew in advance, even before the old ones fell out, and for some time four upper fangs sat in the mouth at once. Then the old pair of fangs fell out, and next to the remaining, new interchangeable fangs began to grow. Among the jaw bones of lycosuchids, almost 40% of the findings are with double fangs. Now such a model of tooth changes has been found in European terocephals.

Gorynich’s teeth presented another discovery. They show a strong intravital attrition (on the teeth of the ylognatus it is not). The animals obviously used their teeth to work with very hard material (most likely they gnawed bones). Such eating behavior was unusual: the dental apparatus of most Perm predators was cutting, and not tearing. The predator plunged large fangs into the body of the victim and, as it were, cut a piece of meat, but he could not tear off a small piece, as dogs, for example, are doing now. Therefore, large predators hunted for prey comparable to their size. M.F. Ivakhnenko joked that the Permian beastmaker could eat a hippo, but could not cope with a hare.

In Permian sediments, bones with traces of bites are extremely rare. There are such bones in the Sundyr location, and this is the only one of more than two hundred locations in Eastern Europe where the bones were found. The find confirms the opinion that it was the terocephalus who developed the tearing type of dental apparatus, which gave them the opportunity, among other things, to gnaw bones and provided a serious evolutionary advantage.

Sources:
1) Yu. A. Suchkova, V.K. Golubev. New primitive terocephalus (Therocephalia, Theromorpha) from the Middle Perm of Eastern Europe  // Paleontological journal . 2019. №3. DOI: 10.1134 / S0031031X19030176. 
2) Yu.A. Suchkova, V.K. Golubev. New Permian terocephalus (Therocephalia, Theromorpha) from the Sundyr complex of Eastern Europe  // Paleontological journal . 2019. №4. DOI: 10.1134 / S0031031X19040123.

Anton Nelikhov