Inostrancevia

*Inostrancevia alexandri*

***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 northern Russia during the Upper Tatarian (Vyatskian), a Russian regional stage equivalent to the Wuchiapingian stage of the Late Permian period, dating from approximately 259 to 252.3 million years ago.

The first fossils attributed to *I. Alexandri* are found in the Arkhangelsk & Vologda Oblasts, near the Northern Dvina. Some fossils of the species in question are among the largest and most complete remains of gorgonopsians ever identified to date, with skeletons showing an animal 3m (9.8 ft.) long, including 50 cm (20 in) for the skulls. Although known from incomplete remains, the largest species, *I. Latifrons, known from the Siberian Traps of North Asia, earning it the nickname the “Siberian Sabertooth”,* is the largest Gorgonopsid species ever discovered, possessing a complete skull of 60 cm (24 in) for an estimated total size of 3.5m (11 ft.) long. Other more fragmentary fossils belonging to other species are also found.

The animal is easily identified by the arrangement of large canines, similar to those of some later predators, the longest of which reach 15 cm (5.9 in) 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* are regularly confused by the general public with the South African *Gorgonops*, due to their similar appearance and various media tending to refer them by the name of the group they belong to rather than their genus names.

## Discovery

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 *Inostrancevia* was named by the Russian paleontologist Vladimir P. Amalitsky in honour of the Russian geologist Aleksandr Inostrantsev. In the original description, *Inostrancevia* was spelled "Inostranzevia". However, following the large and influential 1928 monograph on the North Dvina gorgonopsians (where Pavel Aleksandrovich Pravoslavlev altered the Spelling to "*Inostrancevia*") the new name stuck, and thus according to ICZN regulations 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 15 cm (5.9 in) 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 & consists of a near complete skeleton and a skull with a length of around 51 cm (20 in). 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 3m (9.8 ft.) 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 60 cm (24 in) in length indicating a size approaching 3.5m (11.5 ft) long and a mass of 300 kg (661.3 lbs), 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 Siberian Traps of North Asia, & referred material includes another skull from the same locality along with an incomplete skeleton from Central Siberia. *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

Below is a cladogram from the phylogenetic analysis of Gebauer (2007):

## Paleobiology

### Hunting strategy

One of the most recognizable characteristics of *Inostrancevia*, and other gorgonopsians as well, is the presence of long, saber-like canines on the upper and lower jaws. How these animals would have used this dentition is debated, the bite force of saber-toothed predators like *Inostrancevia*, using three-dimensional analysis, was determined by Stephan Lautenschlager and colleagues in 2020 to uncover answers. Their findings detail that despite morphological convergence among saber-toothed predators, there is a diversity in possible killing techniques. The similarly sized gorgonopsian *Rubidgea* is capable of producing a bite force of 715 newtons. Although lacking the necessary jaw strength of being capable of crushing bone, the analysis details that the most massive gorgonopsians possess a more powerful bite than other saber-toothed predators. The study also indicated that the jaw of *Inostrancevia* was capable of a massive gape, perhaps enabling this latter to deliver a lethal bite similar to the hypothesised killing technique of *Smilodon*, another sabre-toothed predator.

## JPInstitute.com Description

This was a carnivorous Mammal-Like Reptile about the size of a large tiger - almost 10 feet (3 cm) long. Its skull was 18 inches (45 cm) long and filled with the advanced dentary (teeth) of the later Mammal-Like Reptiles. At this stage of the evolution of this family of animals, the limbs were more tucked under the body than they are in modern mammals. This is in contrast to more primitive reptiles that had limbs that projected outward as opposed to the more downward direction of this creature. Inostrancevia lived in the late Permian period of the Paleozoic era about 250 million years ago. It was named after A. Inostrantzev, a famous Russian geologist. Inostrancevia fossils were found in Northern Russia. It is a Therapsid and a member of the Gorgonopidae family.

## Appearance in other media

### *Jurassic Park*

* *Inostrancevia* appears in *Jurassic World: Alive* as a common.

## References

1. ↑ 1.0 1.1 Template:Cite journal
2. ↑ Template:Cite journal