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''Scutosaurus'' ("shield lizard") is an extinct genus of
pareiasaur Pareiasaurs (meaning "cheek lizards") are an extinct clade of large, herbivorous parareptiles. Members of the group were armoured with scutes which covered large areas of the body. They first appeared in southern Pangea during the Middle Permian, ...
parareptiles Parareptilia ("at the side of reptiles") is a subclass or clade of basal sauropsids ( reptiles), typically considered the sister taxon to Eureptilia (the group that likely contains all living reptiles and birds). Parareptiles first arose near t ...
. Its genus name refers to large plates of armor scattered across its body. It was a large anapsid reptile that, unlike most reptiles, held its legs underneath its body to support its great weight. Fossils have been found in the Sokolki Assemblage Zone of the Malokinelskaya Formation in European Russia, close to the Ural Mountains, dating to the late Permian ( Lopingian) between 264 and 252 million years ago.


Research history

The first fossils were uncovered by Russian paleontologist
Vladimir Prokhorovich Amalitskii Vladimir Prokhorovich Amalitskii (russian: Владимир Прохорович Амалицкий; 1860–1917) (alternative spelling: Amalitzky) was a Russian paleontologist and professor at Warsaw University who was involved in the discovery a ...
while documenting plant and animal species in the
Upper Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...
sediments in the Northern Dvina River, Arkhangelsk District, Northern European Russia. Amalitskii had discovered the site in 1899, and he and his wife Anne Amalitskii continued to oversee excavation until 1914, recovering numerous nearly complete and articulated (in their natural position) skeletons belonging to a menagerie of different animals. Official diagnoses of these specimens was delayed due to World War I. The first published name of what is now called ''Scutosaurus karpinskii'' was in 1917 by British zoologist
David Meredith Seares Watson Prof David Meredith Seares Watson FRS FGS HFRSE LLD (18 June 1886 – 23 July 1973) was the Jodrell Professor of Zoology and Comparative Anatomy at University College, London from 1921 to 1951. Biography Early life Watson was born in the Highe ...
, who captioned a reconstruction of its scapulocoracoid based on the poorly preserved specimen PIN 2005/1535 "''Pariasaurus Karpinskyi'', Amalitz" (giving credit to Amalitskii for the name). Amalitskii died later that year, and the actual diagnosis of the animal was posthumously published in 1922, with the name "''Pareiosaurus''" ''karpinskii'', and the holotype specimen designated as the nearly complete skeleton PIN 2005/1532. Three partial skulls were also found, but Amalitskii decided to split these off into new species as "''P. elegans''", "''P. tuberculatus''", and "''P. horridus''". "''Pariasaurus''" and "''Pareiosaurus''" were both misspellings of the South African '' Pareiasaurus''. In 1930, Soviet vertebrate paleontologist Aleksandra Paulinovna Anna Hartmann-Weinberg said that the
pareiasaur Pareiasaurs (meaning "cheek lizards") are an extinct clade of large, herbivorous parareptiles. Members of the group were armoured with scutes which covered large areas of the body. They first appeared in southern Pangea during the Middle Permian, ...
material from North Dvina represents only 1 species, and that this species was distinct enough from other ''Pareiasaurus'' to justify placing it in a new genus. Though Amalitskii had used a unique genus name "''Pareiosaurus''", this was an accident, and she declared "''Pareiosaurus''" to be a
junior synonym The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently. * In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linna ...
of ''Pareiasaurus'', and erected the genus ''Scutosaurus''. She used the spelling "''karpinskyi''" for the species name, but switched to ''karpinskii'' in 1937. At the same time, she also split off another unique genus "''Proelginia permiana''" based on the partial skull PIN 156/2. In 1968, Russian paleontologist N. N. Kalandadze and colleagues considered "''Proelginia''" to be
synonymous A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...
with ''Scutosaurus''. Because the remains are not well preserved, the validity of "''Proelginia''" is unclear. In 1987, Russian paleontologist Mikhail Feodosʹevich Ivakhnenko erected a new species "''S. itilensis''" based on skull fragments PIN 3919, and resurrected "''S. tuberculatus''", but Australian biologist Michael S. Y. Lee considered both of these actions unjustified in 2000. In 2001, Lee petitioned the
International Commission on Zoological Nomenclature The International Commission on Zoological Nomenclature (ICZN) is an organization dedicated to "achieving stability and sense in the scientific naming of animals". Founded in 1895, it currently comprises 26 commissioners from 20 countries. Orga ...
to formally override the spelling ''karpinskyi'' (because Watson clearly did not intend his work to be a formal description of the species, and ''karpinskii'' was much more popularly used) and list the author citation as Amalitskii, 1922. ''Scutosaurus'' is a common fossil at the North Dvina site, and is known from 6 at least fairly complete skeletons, as well as numerous various isolated body and skull remains, and scutes ( osteoderms). It is the most completely known pareiasaur. All ''Scutosaurus'' specimens date to the Upper Tatarian (Vyatskian) Russian faunal stage, which may roughly correspond with the Lopingian epoch of the
Upper Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...
(259–252 million years ago). In 1996, Russian paleontologist Valeriy K. Golubev described the faunal zones of the site, and listed the ''Scutosaurus'' zone as extending from roughly the middle Wuchiapingian to the middle
Changhsingian In the geologic time scale, the Changhsingian or Changxingian is the latest age or uppermost stage of the Permian. It is also the upper or latest of two subdivisions of the Lopingian Epoch or Series. The Changhsingian lasted from to 251.902 mill ...
, which followed the "''Proelginia''" stage beginning in the early Wuchiapingian.


Anatomy

Pareiasaurs were among the largest reptiles during the Permian. ''Scutosaurus'' is a rather large pareiasaur, measuring about in length. The entire body would have been covered in rough osteoderms, which feature a central boss with a spine. These osteoderms appear to have been largely separate from each other, but may have been closely sutured together over the shoulder and pelvis as in '' Elginia''. The limbs bore small conical studs. Pareiasaurs feature a short stout body, and a short tail. ''Scutosaurus'' has 19 presacral vertebrae. Pareiasaurs, as well as many other common herbivorous Permian tetrapods, had a large body, barrel-shaped ribcage, and engorged limbs and pectoral and
pelvic The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...
girdles. The pareiasaur
shoulder blade The scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on either ...
is large, plate-like, slightly expanded towards the arm, and vertically oriented. The acromion (which connects to the large clavicle) is short and blunt, like those of early turtles, and is placed at the bottom of the shoulder blade. In articulated specimens (where the positions of the jointed bones has been preserved), there is a small gap between the clavicle and the shoulder blade. Early pareiasaurs have a cleithrum which runs along the shoulder blade, but later ones including ''Scutosaurus'' lost this. The digits on the hands and feet are short. The
dorsal vertebra In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebrae and they are intermediate in size between the cervical ...
e are short, tall, and robust, and supported large and strongly curved ribs. The broad torso may have conferred an expansive
digestive system The human digestive system consists of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver, and gallbladder). Digestion involves the breakdown of food into smaller and smaller compone ...
. The cheeks strongly flare out and terminate with long pointed bosses. The bosses of the skull are generally much more prominent than those of other pareiasaurs. The maxilla features a horn just behind the nostrils. The two holes on the back of the palate (the interpterygoid vacuities) are large. All pareiasaurs have broad snouts containing a row of closely packed, tall, blade-like, and
heterodont In anatomy, a heterodont (from Greek, meaning 'different teeth') is an animal which possesses more than a single tooth morphology. In vertebrates, heterodont pertains to animals where teeth are differentiated into different forms. For example, ...
teeth with varying numbers of cusps depending on the tooth and species. ''Scutosaurus'' has 18 teeth in the upper jaw (which feature anywhere from 9–11 cusps), and 16 in the lower (13–17 cusps). The tips of the upper teeth jut outward somewhat. The tongue side of the lower teeth bear a triangular ridge, and some random teeth in either jaw can have a cusped cingulum. Unlike other pareiasaurs, ''Scutosaurus'' has a small tubercle (a bony projection) on the base of the skull between the basal tubera.


Palaeobiology

''Scutosaurus'' was a massively built reptile, with bony armor, and a number of spikes decorating its skull. Despite its relatively small size, ''Scutosaurus'' was heavy, and its short legs meant that it could not move at speed for long periods of time, which made it vulnerable to attack by large predators. To defend itself ''Scutosaurus'' had a thick skeleton covered with powerful muscles, especially in the neck region. Underneath the skin were rows of hard, bony plates (scutes) that acted like a form of brigandine armor. As a plant-eater living in a semi-arid climate, including deserts, ''Scutosaurus'' would have wandered widely for a long time in order to find fresh foliage to eat. It may have stuck closely to the riverbanks and
floodplains A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...
where plant life would have been more abundant, straying further afield only during times of drought. Its teeth were flattened and could grind away at the leaves and young branches before digesting them at length in its large gut. ''Scutosaurus'' swallowed gastroliths to digest plants. Given that it needed to eat constantly, ''Scutosaurus'' probably lived alone, or in very small herds, so as to avoid denuding large areas of their edible plants. Pareiasaurs had long been thought to be terrestrial, but it is difficult to assess their range of locomotion given the lack of modern anatomical analogues. In 1987, Ivakhnenko hypothesised that they were aquatic or amphibious due to the deep and low-lying pectoral girdle, short but engorged limbs, and thick cartilage on the limb joints, which are reminiscent of the aquatic dugong. Subsequent studies—including stable isotope analyses and footprint analyses—on various African and Eurasian remains have all reported results consistent with terrestrial behavior. Caseids have a broadly similar build to pareiasaurs, and possibly exhibited the same locomotory habits. Both have thin, porous long bones which is consistent with modern diving creatures, but the overall heavy torso would impede such a behavior. Nonetheless, similarly graviportal creatures have much thicker long bones. In 2016, zoologist Markus Lambertz and colleagues, based on the thin bones and short neck unsuited for reaching low-lying plants, suggested that caseids were predominantly aquatic and only came ashore during brief intervals. Overall, anatomical evidence seems to be at direct odds with isotopic evidence; it is possible that bone anatomy was more related to the animal's weight than its lifestyle. Like other pareiasaurs, ''Scutosaurus'' have been shown to have had a fast initial growth rate, with cyclical growth intervals. Following this possibly relatively short juvenile period, an individual would have reached 75% of its full size, and continued growing at a slower rate for several years more. This switch from fast to slow growth potentially signaled the onset of sexual maturity. In 2021 a study using volumetric estimates found that ''Scutosaurus'' likely weighed around 1,160 kg, similar to living black rhinoceros or cows.


Paleoecology

''Scutosaurus'' comes from the Salarevskaya Formation, which has a uniformly red coloration and comprises paleosol horizons, which deposit in cyclically shallow-water and dry area. The paleosol horizons are highly variable in shape and size throughout the formation, which may mean they came from different sources (polygenic). Paleosols gradually disappear in the upper part of the formation where the thickness of beds becomes much more discontinuous as well as irregular (from some millimeters to several meters), and the appearance of blue spots which may represent the accumulation of reduced
iron oxide Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. All are black magnetic solids. Often they are non-stoichiometric. Oxyhydroxides are a related class of compounds, perhaps the best known of whic ...
s. These beds are capped off by a carbonate shell, varying from a small knot to up to a meter (3.3 ft) thick. The paleosols and shells feature holes left behind by plant roots, but these are absent in the clay-
siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...
breccias and sand
lenses A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...
. The formation has typically been explained as the result of several catastrophic floods washing over arid to semi-arid plains during wet seasons, featuring several temporarily filled channels and permanently
dry lake A dry lake bed, also known as a playa, is a basin or depression that formerly contained a standing surface water body, which disappears when evaporation processes exceeds recharge. If the floor of a dry lake is covered by deposits of alkaline c ...
s. ''Scutosaurus'' was a member of the pareiasaurian– gorgonopsian fauna dating to the Upper Tatarian, dominated by pareiasaurs,
anomodont Anomodontia is an extinct group of non-mammalian therapsids from the Permian and Triassic periods. By far the most speciose group are the dicynodonts, a clade of beaked, tusked herbivores.Chinsamy-Turan, A. (2011) ''Forerunners of Mammals: Ra ...
s, gorgonopsians, therocephalians, and
cynodont The cynodonts () (clade Cynodontia) are a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 mya), and extensively diversified after the Permian–Triassic extinction event. Cynodonts had a wide variety ...
s. Unlike earlier beds, dinocephalians are completely absent. ''Scutosaurus'' is identified in the Sokolki fauna, which features predominantly the former 3 groups. The only herbivore other than ''Scutosaurus'' is ''
Vivaxosaurus ''Vivaxosaurus'' is a genus of dicynodont from Late Permian (Changhsingian) of Russia. It has been found at Sokolki on the Northern Dvina River near Kotlas in Arkhangelsk Oblast, Russia. It lived during the latest Permian, and was a contempora ...
''. Carnivores are instead much more common, the largest identified being ''
Inostrancevia ''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 ...
'' (''I. latifrons'' and ''I. alexandri''); the other gorgonopsians are ''
Pravoslavlevia ''Pravoslavlevia'' is an extinct genus of gorgonopsian therapsids that lived in the late Permian and is part of the Sokolki subcomplex of Russia. It had a skull long. The total length of the animal was about . Only one species (''P. parva'') is ...
'' and '' Sauroctonus progressus''. Other carnivores include the therocephalian '' Annatherapsidus petri'' and the cynodont ''
Dvinia ''Dvinia'' is an extinct genus of cynodonts found in the Salarevo Formation of Sokolki on the Northern Dvina River near Kotlas in Arkhangelsk Oblast, Russia. It is the only known member of the family Dviniidae. Its fossil remains date from t ...
''; chroniosuchid and
seymouriamorph Seymouriamorpha were a small but widespread group of limbed vertebrates (tetrapods). They have long been considered reptiliomorphs, and most paleontologists may still accept this point of view, but some analyses suggest that seymouriamorphs are s ...
amphibians have also been identified, including '' Karpinskiosaurus'', ''
Kotlassia ''Kotlassia'' is an extinct genus of seymouriamorph. Fossils of it are found in Russia, in the village of Novinki, close to the city of Kotlas. The name of the genus is derived from the city. The layers in which the fossils were found date from ...
'', and ''
Dvinosaurus ''Dvinosaurus'' is an extinct genus of amphibious temnospondyls localized to regions of western and central Russia during the middle and late Permian, approximately 265-254 million years ago. Its discovery was first noted in 1921 by Russian pal ...
''. As for plants, the area has yielded various
moss Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta (, ) '' sensu stricto''. Bryophyta (''sensu lato'', Schimp. 1879) may also refer to the parent group bryophytes, which comprise liverworts, mosses, and hor ...
es,
lepidophyte Paleobotany, which is also spelled as palaeobotany, is the branch of botany dealing with the recovery and identification of plant remains from geological contexts, and their use for the biological reconstruction of past environments (paleoge ...
s, ferns, and
peltaspermaceae Peltaspermaceae is a natural family of seed ferns (Pteridospermatophyta) widespread in both northern and southern hemispheres coal measures of Permian and Triassic age. Peltasperms persisted in a relictual distribution in Patagonia during the Ea ...
ns.


References


External links


Pareiasaurinae
at Palaeos {{Taxonbar, from=Q131745 Pareiasaurs Lopingian genera Permian reptiles of Asia Permian Russia Fossils of Russia Fossil taxa described in 1930 Prehistoric reptile genera