Inostrancevia

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Inostrancevia
Temporal range:
Ma[1][2]
Mounted skeleton of I. alexandri (PIN 1758), exposed at the Museo delle Scienze, Trento, Italy
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Clade: Therapsida
Clade: †Gorgonopsia
Family: †Gorgonopsidae
Subfamily: †Inostranceviinae
Genus: †Inostrancevia
Amalitsky, 1905
Type species
†Inostrancevia alexandri
Other species
Synonyms
List of synonyms
  • Synonyms of genus
      • Amalitzkia Pravoslavlev, 1927
    Synonyms of I. alexandri
      • I. proclivis Pravoslavlev, 1927
    Synonyms of I. latifrons
      • Amalitzkia vladimiri Pravoslavlev, 1927
      • Amalitzkia annae Pravoslavlev, 1927
      • I. vladimiri Vyushkov, 1953

Inostrancevia is an

Late Permian in what is now European Russia and Southern Africa. The first-known fossils of this gorgonopsian were discovered in the Northern Dvina, where two almost complete skeletons were exhumed. Subsequently, several other fossil materials were discovered in various oblasts, and these finds will lead to a confusion about the exact number of valid species in the country, before only three of them were officially recognized: I. alexandri, I. latifrons and I. uralensis. More recent research carried out in South Africa has discovered fairly well-preserved remains of the genus, being attributed to the species I. africana. An isolated left premaxilla suggests that Inostrancevia also lived in Tanzania during the earliest Lopingian age. The whole genus is named in honor of Alexander Inostrantsev, professor of Vladimir P. Amalitsky, the paleontologist who described the taxon
.

Inostrancevia is the biggest-known gorgonopsian, the largest fossil specimens indicating an estimated size between 3 m (9.8 ft) and 3.5 m (11 ft) long. The animal is characterized by its robust skeleton, broad skull and a very advanced dentition, possessing large canines, the longest of which can reach 15 cm (5.9 in) and probably used to shear the skin off its prey. Like most other gorgonopsians, Inostrancevia had a particularly large jaw opening angle, which would have allowed to deliver fatal bites.

First regularly classified as close to African taxa such as

phylogenetic analyses published since 2018 consider it to belong to a group of derived Russian gorgonopsians, now being classified alongside the genera Suchogorgon, Sauroctonus and Pravoslavlevia. According to the Russian and South African fossil records, the faunas where Inostrancevia is recorded were fluvial ecosystems containing many tetrapods
, where it turns out to have been the main predator.

Research history

Recognized species

During the 1890s, Russian paleontologist

Upper Permian in Northern Dvina, Arkhangelsk Oblast, northern European Russia. The locality, known as PIN 2005, consists of a creek with sandstone and lens-shaped exposures in a bank escarpment, containing many particularly well-preserved fossil skeletons.[3] This type of fauna from this period, previously known only from South Africa and India, is considered as one of the greatest paleontological discoveries of the late 19th and early 20th centuries.[4] After the preliminary reconnaissance of the place, Amalitsky conducts systematic research with his companion Anna P. Amalitsky [ru].[3] The first excavations began in 1899,[5] and several of her findings where sent to Warsaw, Poland, in order to be prepared there.[6] The exhumations of the fossils then lasted until 1914, when the research stopped due to the start of the World War I.[7] The fossils discovered within the site will subsequently be moved to the Museum of Geology and Mineralogy of the Russian Academy of Sciences. All the fossils listed were not prepared, and more than 100 tons of concretions were promised for new discoveries by the museum in question.[3]

lectotype
skeleton of I. alexandri

The multiple administrative activities and difficult conditions during Amalitsky's last years have severely hampered his fossil research, leading to his unexpected death in 1917. However, among all the fossils identified before his death are two remarkably complete skeletons of large

clergyman Henry Neville Hutchinson added the specific name alexandri to the genus.[13] Hutchinson's proposal for a new name was probably not intentional for the same reason as Lankester.[12] This time, Amalitsky is credited only for providing the images of the fossil animal and not for the specific epithet.[13] Thus, the authorship of the word alexandri has as formal author Hutchinson.[12] The first formal descriptions of this gorgonopsian were only published posthumously in 1922, but the name of the genus and species were nevertheless kept.[3] Although the etymology of the genus and type species is not provided in the earliest-known descriptions of the taxon, the full name of the animal is named in honor of the renowned geologist Alexander Inostrantsev,[9] who was one of Amalitsky's teachers.[14] Amalitsky's article generally describes all the fossil discoveries made in the Northern Dvina, and not Inostrancevia itself, the article mentioning that further research on this gorgonopsian is subject to research.[3]

It was in 1927 that one of Amalitsky's colleagues,

ICZN.[16] Although Pravoslavlev's work was of major importance, more recent work requires that a re-examination of the skeletal anatomy of the genus is necessary in order to broaden the understanding of the animal's biology.[17]

External picture
image icon Photograph and sketch of the holotype specimen of I. uralensis

In 1974,

Ural River, where the holotype specimen of the taxon was found.[9][18][16] However, due to its poor fossil preservation of this species, Tatarinov argues that it is possible that I. uralensis could belong to a new genus of large gorgonopsians without having a certain confirmation.[19]

The fourth known species, I. africana, was discovered from two specimens found between 2010 and 2011, respectively, by Nthaopa Ntheri and John Nyaphuli at Nooitgedacht Farm in the

stratigraphic significance of the finds and is only a brief introduction to the anatomy of the new fossil material, the latter being subjects for a study to be published later.[2]

Formerly assigned species and synonyms

Due to the poor quality of preservation of some Inostrancevia fossils, several specimens were therefore incorrectly found to belong to separate taxa. Only four species are recognized today, with three (I. alexandri, I. latifrons and I. uralensis) from Russia and one (I. africana) from South Africa.[2]

In his 1927 monograph, Pravoslavlev names two additional species of the genus Inostrancevia: I. parva and I. proclivis.[15] In 1940, the paleontologist Ivan Yefremov expressed doubts about this classification, and considered that the holotype specimen of I. parva should be viewed as a juvenile of the genus and not as a distinct species.[16][21] It was in 1953 that Boris Pavlovich Vyuschkov completely revised the species named for Inostrancevia. For I. parva, he moves it to a new genus, which he names Pravoslavlevia, in honor of the original author who named the species.[22] Although being a distinct and valid genus, Pravoslavlevia turns out to be a closely related taxon.[8][16][23][24] Also in his article, he considers that I. proclivis is a junior synonym of I. alexandri, but remains open to the question of the existence of this species, arguing his opinion with the insufficient preservation of type specimens.[22] This taxon will be definitively judged as being conspecific to I. alexandri in the revision of the genus carried out by Tatarinov in 1974.[25]

Also in is work, Pravoslavlev names another genus of gorgonopsians, Amalitzkia, with the two species it includes: A. vladimiri and A. annae, both named in reference to the pair of paleontologists who carried out the work on the first specimens known of I. alexandri.[15] In 1953, Vjuschkov discovered that the genus Amalitzkia is a junior synonym of Inostrancevia, renaming A. vladimiri to I. vladimiri,[22] before the latter was itself recognized as a junior synonym of I. latifrons by later publications.[26][8] For some unclear reason, Vjuschkov refers A. annae as a nomen nudum,[22] when his description is quite viable.[15] Just like A. vladimiri, A. annae will be synonymized with I. latifrons by Tatarinov in 1974.[26]

In 2003,

Phthinosuchidae rather than the sole Russian representative of the Rubidgeinae.[17] In 2016, Kammerer formally rejected Ivakhnenko's classifications, because the holotype braincase of Leogorgon likely came from a dicynodont, while the attributed canine tooth is indistinguishable from that of Inostrancevia. Since then, Leogorgon has been recognized as a nomen dubium of which part of the fossils possibly come from Inostrancevia.[28]

Other species belonging to distinct lineages were sometimes inadvertently classified in the genus Inostrancevia. For example, in 1940, Efremov classifies a gorgonopsian of then-problematic status as I. progressus.

therocephalian in 1997, and later designated as the holotype of the genus Megawhaitsia in 2008.[31]

Description

Scale chart, showing I. latifrons size compared to a human

Inostrancevia is a gorgonopsian with a fairly robust morphology, the

mammaliaform therapsids such as gorgonopsians were covered in hair or not.[33]

The specimens PIN 2005/1578 and PIN 1758, belonging to I. alexandri, are among the largest and most complete gorgonopsian fossils identified to date. Both specimens are around 3 m (9.8 ft) long,[32] with the skulls alone measuring over 50 cm (20 in).[3] However, I. latifrons, although known from more fragmentary fossils, is estimated to have a more imposing size, the skull being 60 cm (24 in) long, indicating that it would have measured 3.5 m (11 ft) and weighed 300 kg (660 lb).[34] The size of I. uralensis is unknown due to very incomplete fossils, but it appears to be smaller than I. latifrons.[8]

Skull

Close-up of a skull referred to I. alexandri

The overall shape of the skull of Inostrancevia is similar to those of other gorgonopsians,

pineal foramen is located near the posterior edge of the parietals and rests on a strong projection in the middle of an elongated hollow like impression.[3] The sagittal suture is reinforced with complex curvatures. The ventral surface of the palatine bones is completely smooth, lacking traces of palatine teeth or tubercles. Just like Viatkogorgon, the top margin of the quadrate is thickened.[17] The three recognized Russian species have notable characteristics between them: I. alexandri is distinguished by its relatively narrow occiput, a broad and rounded oval temporal fenestra and the transverse flangues of the pterygoid with teeth; I. latifrons is distinguished by a comparatively lower and broader snout, larger parietal region, fewer teeth and a less developed palatal tuberosities; and I. uralensis is characterized by a transversely elongated oval slot-like temporal fenestra.[8]

Canine tooth of I. alexandri (on the top) and Leogorgon klimovensis (on the bottom)

The jaws of Inostrancevia are powerfully developed, equipped with teeth able to hold and tear the

tooth replacement would have taken place by the young teeth, growing at the root of the old ones and gradually supplanting them.[3] The capsule of the canines is very large, containing up to three capsules of replacement canines at different stages of development.[17]

Postcranial skeleton

The skeleton of Inostrancevia is of very robust constitution, mainly at the level of the

paleobiological function.[36]

Taxonomy

Classification

In the original description published in 1922, Inostrancevia was initially classified as a gorgonopsian close to the African genus

sister taxon to the Rubidgeinae, a lineage consisting of robust African gorgonopsians.[40] In 2016 Christian F. Kammerer regarded Gebauer's analysis as "unsatisfactory", citing that many of the characters used by her analysis were based upon skull proportions that are variable within taxa, both individually and ontogenetically (i.e. traits that change through growth).[28]

In 2018, in their description of Nochnitsa, Kammerer and Vladimir Masyutin propose that all Russian and African taxa should be separately grouped into two distinct clades. For Russian genera (except basal taxa), this relationship is supported by notable cranial traits, such as the close contact between pterygoid and vomer. The discovery of other Russian gorgonopsians and the relationship between them and Inostrancevia has never before been recognized for the simple reason that some authors undoubtedly compared them to African genera.[16] The classification proposed by Kammerer and Masyutin will serve as the basis for all other subsequent phylogenetic studies of gorgonopsians.[23][24] As with previous classifications, Pravoslavlevia is still considered as the sister taxon of Inostrancevia.[16][23][24]

Restoration of I. africana

The following cladogram shows the position of Inostrancevia within the Gorgonopsia after Kammerer and Rubidge (2022):[24]

Gorgonopsia

Evolution

Gorgonopsians form a major group of carnivorous therapsids whose oldest-known representatives come from South Africa and appear in the fossil record from the

rubidgeines who occupy this role,[28] while in Russia, only Inostrancevia acquires as such,[16][23][45] the rare gorgonopsians known and contemporary with the latter being smaller.[46][47]

Paleobiology

Hunting strategy

Restoration of I. alexandri attacking Scutosaurus

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:[48] their findings detailed that, despite morphological convergence among saber-toothed predators, there is a range of methods of possible killing techniques. The similarly-sized Rubidgea is capable of producing a bite force of 715 newtons; although lacking the necessary jaw strength to crush bone, the analysis found that even the most massive gorgonopsians possessed a more powerful bite than other saber-toothed predators.[49] The study also indicated that the jaw of Inostrancevia was capable of a massive gape, perhaps enabling it to deliver a lethal bite, and in a fashion similar to the hypothesised killing technique of Smilodon (or 'saber-toothed cat').[48]

Palaeoecology

European Russia

Restoration of I. latifrons chasing Scutosaurus

During the

sphenophytes were only locally present.[50] There are also hygrophyte and halophyte plants in coastal areas as well as conifers that are more resistant to drought and higher altitudes.[52]

The fossil sites from which Inostrancevia was recorded contain abundant fossils of terrestrial and shallow freshwater organisms, including

top predator in its environment and could have preyed on the majority of the previously mentioned tetrapods.[11][45][46] Other smaller predators have existed alongside Inostrancevia, such as the smaller related gorgonopsian Pravoslavlevia and the therocephalian Annatherapsidus.[46][47]

South Africa

According to the fossil record, the Upper Daptocephalus Assemblage Zone, from which I. africana is known, would have been a well-drained floodplain. The area preceding just before the Permian–Triassic extinction, this would explain why there is no more diversification of animals than in the older strata of the Balfour Formation.[2][54]

As in the other formations of the

Karoo Basin, dicynodonts are the most common animals in the Upper Daptocephalus Assemblage Zone. Among the most abundant dicynodonts are Daptocephalus (hence the name of the site), Diictodon and Lystrosaurus. Few genera of therocephalians are known within the site, only Moschorhinus and Theriognathus having been listed. The presence of the cynodont Procynosuchus is also reported.[55] The gorgonopsians Arctognathus and Cyonosaurus should be present based on their wide temporal distribution within the Karoo Basin, but formal fossils have not yet been discovered. As in the Russian fossil record, I. africana would have been the main predator in the area, most likely preying on contemporary dicynodonts.[2]

Extinction

Gorgonopsians, including Inostrancevia, disappeared in the Late

sauropsids, mostly archosaurs, and among the few therapsids surviving the event, mammals.[56] However, some Russian gorgonopsians have already disappeared a little time before the event, having consequently abandoned some of their niches to large therocephalians.[31] Kammerer and his colleagues claimed that as the extinction of the rubidgeines in their respective territory of Africa, Inostrancevia migrated from Russia to take the role of apex predator within this place for a limited time. The presence of dicynodonts like Lystrosaurus would have been an opportunity for being a prey, as the latter thrived throughout the Permian–Triassic boundary.[2] However, an isolated left premaxilla of Inostrancevia from the Usili Formation in Tanzania during the earliest Lopingian age suggested otherwise, since the discovery of this specimen indicated that Inostrancevia already lived in Africa alongside other large rubidgeines such as Dinogorgon and Rubidgea before the latest Permian.[57]

See also

Notes

  1. taxa are already mentioned in the article describing I. alexandri,[3] but were not officially named and described in detail until 1927.[15]
  2. ^ Previously identified as molars by Amalitsky,[3] this type of teeth was later redescribed as postcanine teeth, having a lack of functional range.[23]

References

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  3. ^ a b c d e f g h i j k l m n o Amalitzky, V. (1922). "Diagnoses of the new forms of vertebrates and plants from the Upper Permian on North Dvina". Bulletin de l'Académie des Sciences de Russie. 16 (6): 329–340.
  4. ^ Benton et al. 2000, p. 4.
  5. ^ Gebauer 2007, p. 9.
  6. ^ Lankester 1905, p. 214-215.
  7. ^ Benton et al. 2000, p. 5.
  8. ^ a b c d e f g h i Benton et al. 2000, pp. 93–94.
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  10. ^ Gebauer 2007, p. 229.
  11. ^ a b Lankester 1905, p. 221.
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  19. ^ Tatarinov 1974, p. 99.
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  22. ^ a b c d Vyushkov, Boris P. (1953). "On gorgonopsians from the Severodvinian Fauna". Doklady Akademii Nauk SSSR (in Russian). 91: 397–400.
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Bibliography

External links
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