Inostrancevia BW.jpg

''Inostrancevia'' is an extinct genus of carnivorous therapsids, containing the largest members of gorgonopsians, predators characterized by long, saber-tooth-like canines. The various species inhabited European Russia during the Upper Tatarian (Vyatskian), a Russian regional stage equivalent to the Wuchiapingian and Changhsingian stage of the Late Permian period, dating from approximately 259 to 252.3 million years ago. The genus name was described posthumously, after the Bolshevik Revolution, by the Russian paleontologist Vladimir P. Amalitsky in 1922, in honor of geologist Aleksandr Inostrantsev.

The first fossils attributed to ''I. alexandri'' are found in Arkhangelsk Oblast, near the Northern Dvina at the end of the 19th century, making it the first gorgonopsian known from Russia, the only place outside Africa where they are officially recognized. Some fossils of the species in question are among the most complete remains of gorgonopsians ever identified to date, the majority of other members of the group are known only from skulls, which are often deformed or damaged. Other fossils, including fragmentary, belonging to other species are discovered throughout the western regions of Russia, including ''I. uralensis'' in the Orenburg Oblast.

With skeletons presenting an animal more than , including for the skulls, ''I. alexandri'' is among the largest known representatives of the gorgonopsians, having a size similar of its African counterpart ''Rubidgea''. However, another species, ''I. latifrons'', known from incomplete remains, is the largest gorgonopsian ever discovered, possessing a skull of and an estimated total size of in length and in body mass.

The animal is easily identified by the arrangement of large canines, similar to those of some later predators, the longest of which reach in length and may have served to shear the skin of prey. This feature makes it one of the most specialized predatory tetrapods in Paleozoic history.

''Inostrancevia'' is regularly confused by the general public with the South African ''Gorgonops'', due to their similar appearance and various media such as Walking with Monsters and Primeval tending to refer them by the name of the group they belong to rather than their genus names.

Discovery

''Inostrancevia'' is the first gorgonopsian discovered in Russian territory, the only known region outside of Africa where the group is officially recognized. The first fossils were found in the Sokolki Assemblage Zone of the Kutuluk and Salarevo Formations in the Oblast of Arkhangelsk as part of the Northern Dvina River excavations led by Amalitsky during the end of the 19th century. Two nearly complete skeletons were found alongside several other skeletal remains, one of which was mounted and exhibited in Saint Petersburg in 1900 with the other following a few years later. Proper descriptions of the findings were published posthumously in 1922, shortly before the Stalinist period in the USSR.

The genus name was named by the Russian paleontologist Vladimir P. Amalitsky in honour of the Russian geologist Aleksandr Inostrantsev. In the original description, the taxon was spelled ''Inostranzevia''.Amalitskii, V.P., 1922. Diagnoses of the new forms of vertebrates and plants from the Upper Permian on North Dvina. Известия Российской академии наук. Серия математическая, 16(0), pp.329-340.
/ref> However, following the large and influential 1928 monograph on the North Dvina gorgonopsians, Pavel Aleksandrovich Pravoslavlev altered the spelling to ''Inostrancevia'' and the new name stuck, and thus according to ICZN regulations, it must be maintained.

Description

The proportions of ''Inostrancevia'' detail a large bodied, yet agile predator. The humerus and especially the femur are relatively elongate, suggesting this animal was proportionally longer-limbed and perhaps more cursorial in nature than other gorgonopsids. The front limbs are much more heavily built, with ''Inostrancevia'' possessing a robust and wide humerus. The scapula of ''Inostrancevia'' is unlike any other gorgonopsid in that it is massively expanded, yet relatively thin and plate like.
The skull of ''Inostrancevia'' is equally well built. Analyses show that ''Inostrancevia''‘s jaws were capable of opening at a large gape angle, as opposed to a comparatively smaller gape in contemporary gorgonopsids such as '' Sauroctonus''.
Like several other gorgonopsians, ''Inostrancevia'' was characterized by strongly developed canine teeth, with those of the upper jaw up to long, the root corresponding to half its length. The dentition of ''Inostrancevia'' can be compared to those of saber-toothed cats, such as ''Smilodon'' or other mammals with this similar morphology.

''Inostrancevia alexandri''

The holotype fossil of ''I. alexandri'', PIN 2005/1578, was discovered by the little Dvina river of the Arkhangelsk province in Russia and consists of a near complete skeleton and a skull with a length of around . Subsequent fossil discoveries of other equally complete specimens such as PIN 1758 provide a detailed picture of the anatomy of ''Inostrancevia''. Other referred specimens include other skull material from the same locality. These two fossil skeletons attributed to the species both indicate a size of around in length. The skull of ''I. latifrons'' is wide towards the back, with a tall, long snout containing reduced palatal teeth. Posterior to the canine of the dentary, there are no teeth unlike in other notable gorgonopsid species.

''Inostrancevia latifrons''

''Inostrancevia latifrons'' is perhaps the largest of the genus, with skull lengths of over in length indicating a size approaching long and a mass of , making the genus ''Inostrancevia'' the largest known gorgonopsian, along with the similarly sized South African genus ''Rubidgea''. ''I. latifrons'' holotype is known from a complete skull, PIN 2005/1857 from the same province as ''I. alexandri'', and referred material includes another skull from the same locality along with an incomplete skeleton from Zavrazhye, a village located in the northeast of Vladimir Oblast. ''I. latifrons'' is distinguishable from ''I. alexandri'' not only in size, but also a comparatively lower and wider snout, a wider parietal region, fewer teeth and finally less developed palatal tuberosities.

''Inostrancevia uralensis''

''Inostrancevia uralensis'' is known from only scant remains of part of the braincase. Unlike the other two species, ''I. uralensis'' was discovered by the Ural river of the Orenburg province. The species is smaller than ''I. latifrons'', and is diagnosed by fenestra ovale in shape of a slot elongated transversally.

Classification

Shortly after its description in 1927, the genus ''Inostrancevia'' is classified in the eponymous family erected under the name of Inostranceviidae alongside the related genus '' Pravoslavlevia''. In 1989, Sigogneau-Russell published a monograph which divided the gorgonopsids into three subfamilies: Gorgonopsinae, Rubidgeinae and Inostranceviinae. With the exception of the basal genera ''Viatkogorgon'' and ''Nochnitsa'', studies published by paleontologists Christian Kammerer, Vladimir Masyutin and Eva Bendel in 2018 prove that advanced gorgonopsians are divided into two major clades, one consisting of African representatives and the other Russian (including ''Inostrancevia'', but also many related contemporaries such as '' Suchogorgon'' and '' Sauroctonus''). Previous analyzes did not find gorgonopsians to be grouped geographically, with some studies placing Russian genera such as ''Inostrancevia'' in African families, no one suspecting that different groups of gorgonopsians would be endemic to different regions.

Placement of ''Inostrancevia'' within the taxon Gorgonopsia according to Bendel ''et al.'' (2018):

Paleobiology

Hunting strategy

Perhaps the most famous feature of the gorgonopsian group is the presence of large, sabre like canines on both the top and bottom jaw. How they used these deadly weapons is debated; the bite force of sabre-tooth predators like ''Inostrancevia'', using three-dimensional analyses, was determined by Lautenschlager et al. to uncover answers.Lautenschlager, S., Figueirido, B., Cashmore, D.D., Bendel, E.M. and Stubbs, T.L., 2020. Morphological convergence obscures functional diversity in sabre-toothed carnivores. Proceedings of the Royal Society B, 287(1935), p.20201818. Their findings detail that, despite the morphological convergence amongst sabre-toothed predators, there existed a diversity in possible killing techniques. The similarly sized gorgonopsid ''Rubidgea'' was capable of a bite force of 715 newtons. Although lacking the necessary jaw strength of being capable of crushing bone, the analysis detailed that large bodied gorgonopsids possessed a stronger bite than other sabre-toothed carnivores. The study also indicated that the jaw of ''Inostrancevia'' was capable of a massive gape, perhaps enabling the gorgonopsid to deliver a lethal bite similar to the hypothesised killing technique of ''Smilodon'', another sabre-toothed predator.Brown, J.G., 2014. Jaw function in Smilodon fatalis: a reevaluation of the canine shear-bite and a proposal for a new forelimb-powered class 1 lever model. PLoS One, 9(10), p.e107456.

Paleoecology

During the Late Permian when ''Inostrancevia'' lived, the Southern Urals (close in proximity to the Sokolki assemblage) were located around latitude 28–34°N and defined as a “ cold desert” dominated by fluvial deposits. The Salarevo formation in particular (a horizon where ''Inostrancevia'' hails from) was deposited in a seasonal, semi-arid to arid area with multiple shallow water lakes which was periodically flooded.Yakimenko, E.Y., Targul’yan, V.O., Chumakov, N.M., Arefev, M.P. and Inozemtsev, S.A., 2000. Paleosols in upper permian sedimentary rocks, Sukhona river (Severnaya Dvina basin). Lithology and Mineral Resources, 35(4), pp.331-344. The Paleoflora of much of European Russia at the time was dominated by a genus of Peltaspermaceaen, ''Tatarina'', and other related genera, followed by ginkophytes and conifers. On the other hand, ferns were relatively rare and sphenophytes were only locally present. Bernardi, M., Petti, F.M., Kustatscher, E., Franz, M., Hartkopf-Fröder, C., Labandeira, C.C., Wappler, T., van Konijnenburg-van Cittert, J.H., Peecook, B.R. and Angielczyk, K.D., 2017. Late Permian (Lopingian) terrestrial ecosystems: a global comparison with new data from the low-latitude Bletterbach Biota. Earth-Science Reviews, 175, pp.18-43.''Inostrancevia'' was the top predator of its environment, existing alongside a number of notable species including the pareiasaur ''Scutosaurus'' and the dicynodont '' Vivaxosaurus'' which were likely prey items. Other, smaller predators existed alongside ''Inostrancevia'' such as the smaller related gorgonopsid '' Pravoslavlevia'' and the therocephalian '' Annatherapsidus''.Golubev, V.K., 2000. The faunal assemblages of Permian terrestrial vertebrates from Eastern Europe. PALEONTOLOGICAL JOURNAL C/C OF PALEONTOLOGICHESKII ZHURNAL, 34(SUPP/2), pp.S211-S224.

References

External links

Taxonomical Information
*
Photo-reconstruction
by paleoartist Roman Uchytel

{{Taxonbar, from=Q132835

Gorgonopsia
Prehistoric therapsid genera
Lopingian synapsids of Europe
Wuchiapingian genera
Permian Russia
Fossils of Russia
Fossil taxa described in 1922
Taxa named by Vladimir Prokhorovich Amalitskii