Ennatosaurus
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''Ennatosaurus'' is an
extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of caseid
synapsid Synapsida is a diverse group of tetrapod vertebrates that includes all mammals and their extinct relatives. It is one of the two major clades of the group Amniota, the other being the more diverse group Sauropsida (which includes all extant rept ...
that lived during the Middle
Permian The Permian ( ) is a geologic period and System (stratigraphy), 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 251.902 Mya. It is the s ...
(late
Roadian In the geologic timescale, the Roadian is an age or stage of the Permian. It is the earliest or lower of three subdivisions of the Guadalupian Epoch or Series. The Roadian lasted between and million years ago (Ma). It was preceded by the Kun ...
- early
Wordian In the geologic timescale, the Wordian is an age or stage of the Permian. It is the middle of three subdivisions of the Guadalupian Epoch or Series. The Wordian lasted between and million years ago (Ma). It was preceded by the Roadian and fo ...
) in northern
European Russia European Russia is the western and most populated part of the Russia, Russian Federation. It is geographically situated in Europe, as opposed to the country's sparsely populated and vastly larger eastern part, Siberia, which is situated in Asia ...
. The genus is only represented by its
type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
, ''Ennatosaurus tecton'', which was named in 1956 by Ivan Antonovich Efremov. The
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
is known from at least six
skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...
s associated with their
lower jaw In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...
s (two of them preserved with the hyoid apparatus), as well as from the postcranial bones of several juvenile individuals. ''Ennatosaurus'' has the typical caseid skull with a short snout tilted forward and very large external nares. However, it differs from other derived caseids by its postcranial
skeleton A skeleton is the structural frame that supports the body of most animals. There are several types of skeletons, including the exoskeleton, which is a rigid outer shell that holds up an organism's shape; the endoskeleton, a rigid internal fra ...
with smaller proportions compared to the size of the skull. As with other advanced caseids, the
teeth A tooth (: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...
of ''Ennatosaurus'' were well suited for slicing and cutting vegetation. The presence of a highly developed hyoid apparatus indicates the presence of a massive and mobile
tongue The tongue is a Muscle, muscular organ (anatomy), organ in the mouth of a typical tetrapod. It manipulates food for chewing and swallowing as part of the digestive system, digestive process, and is the primary organ of taste. The tongue's upper s ...
, which had to work in collaboration with the
palatal The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly sepa ...
teeth during
swallowing Swallowing, also called deglutition or inglutition in scientific and medical contexts, is a physical process of an animal's digestive tract (e.g. that of a human body) that allows for an ingested substance (typically food) to pass from the mou ...
. With a late Roadian - early Wordian age, ''Ennatosaurus'' is one of the last known caseids (with '' Lalieudorhynchus'' from southern
France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
).


Etymology

''Ennatosaurus tecton'' means "ninth carpenter lizard". The strangeness of the name of this synapsid is related to its very unusual origin since the genus and species names correspond to the translation into
Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...
of the meaning of the Russian names of the discoverers of the first fossils of this animal. The genus name is dedicated to Tatyana A. Devyataya (the feminine form of Devyatyi whose name means ‘ninth’ = "ennatos" in Greek) and of "saurus" meaning lizard. The species honors Mikhail Alekseevich Plotnikov (after the Russian plotnik, meaning "carpenter" = "tecton" in Greek).


Description

''Ennatosaurus'' is known by several adult skulls (PIN 1580/14, 17 (
holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...
), 122, 4543/1), as well as by a juvenile skull (PIN 1580/24) associated with many postcranial elements from several individuals. All these elements allowed the reconstruction of a composite skeleton. Unlike all other derived caseids that have a tiny skull relative to the body size, ''Ennatosaurus'' is peculiar by the small size of its postcranial skeleton compared to that of its skull. However, almost all of the postcranial material in ''Ennatosaurus'' belongs to juvenile individuals, and the unusual proportions of this composite skeleton could be explained by the mounting of an
adult An adult is an animal that has reached full growth. The biological definition of the word means an animal reaching sexual maturity and thus capable of reproduction. In the human context, the term ''adult'' has meanings associated with social an ...
skull on a juvenile skeleton. However, the existence of some bones of subadult and adult individuals suggests that ''Ennatosaurus'' did indeed have a proportionally smaller body than that of other derived caseids. The largest adult skull of ''Ennatosaurus'' (the holotype PIN 1580/17) is approximately 17 cm long, a size similar to the skull of '' Cotylorhynchus romeri'', while the few adult bones of ''Ennatosaurus'' are half the size of the corresponding adult elements in ''C. romeri''. As in other caseids, ''Ennatosaurus'' has a very short skull with a snout sharply sloping forward and very large external nares. ''Ennatosaurus'' is distinguished, however, by its proportionally longer facial region than in ''
Casea ''Casea'' is a genus of Herbivore, herbivorous Caseidae, caseid synapsids that lived during the late Lower Permian (Kungurian) in what is now Texas, United States. The genus is only represented by its type species, ''Casea broilii'', named by Sam ...
'' and '' Euromycter''. The dorsal ramus of each
premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...
contributes to a narrow intranarial bar, narrower than that of ''Euromycter'', but of width similar to that of ''Cotylorhynchus romeri''. The skull roof is distinguished by the very large contribution of the frontal to the dorsal margin of the
orbit In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an ...
. It occupies about 50% of the length of the latter while in ''Euromycter'' and ''C. romeri'' the frontal represents less than 10% of the margin of the orbit. The jugal is very characteristic in having a thick and very elongated anterior ramus creating an area of extended contact with the lacrimal. In other caseids, the anterior ramus is very thin and ends in narrow vertical contact with the lacrimal. ''Ennatosaurus'' also differs from all other caseid in its temporal fenestrae significantly larger than the nostrils and orbits, its
palate The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly sep ...
with a narrower
parasphenoid The parasphenoid is a bone which can be found in the cranium of many vertebrates. It is an unpaired dermal bone which lies at the midline of the roof of the mouth. In many reptiles (including birds), it fuses to the endochondral (cartilage-derived ...
, and its upper dentition more reduced in number. In ''Ennatosaurus'', each premaxilla and
maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...
only have two and eight teeth respectively against 4 and 11 teeth respectively in ''Euromycter'' and 3 and 15 or 16 teeth in ''C. romeri''. The premaxillary teeth are conical in shape, the following teeth are spatulate with five to seven cuspules arranged longitudinally. The postcranial skeleton also shows many original characters. The
vertebra Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spina ...
l centra of all regions of the body are characterized by the presence of two well-developed ventrolateral pits, deep and elongated anteroposteriorly. The neural spines of the vertebrae show a diamond-shaped section along its entire length, a condition similar to that observed in '' Ruthenosaurus''. The vertebrae of the "lumbar region" are characterized by the absence of fused or co-ossified ribs (a characteristic to be taken with caution given the juvenile condition of the specimens). The
humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...
has a robust ectepicondyle and a not completely closed ectepicondylar foramen. A deep and well marked fossa is present immediately behind the acetabular buttress of the ilium. The
femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...
is very characteristic, its
proximal Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
articular surface is much wider dorsoventrally than anteroposteriorly and an elevated and robust bony crest extends from the narrowest part of the shaft to the top of the posterior
condyle A condyle (;Entry "condyle"
in
with which it merges to form a single support structure. The intertrochanteric fossa is much more developed mediolaterally than anteroposteriorly in relation with the conformation of the proximal articular surface. The
tibia The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...
is distinguished by its flattened shaft with a subelliptic and non-circular cross section, as is the case in most caseids which have not undergone diagenetic deformation. The manus is not fully known and the preserved elements indicate a phalangeal formula 2-2-3-?-2. It was probably similar to that of the
foot The foot (: feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is an organ at the terminal part of the leg made up o ...
, more complete, whose formula is 2-2-3-3-2. The
toe Toes are the digits of the foot of a tetrapod. Animal species such as cats that walk on their toes are described as being ''digitigrade''. Humans, and other animals that walk on the soles of their feet, are described as being ''plantigrade''; ...
s are short and terminated by small
ungual An ungual (from Latin ''unguis'', i.e. ''nail'') is a highly modified distal toe bone which ends in a hoof, claw, or nail. Elephants and ungulates have ungual phalanges, as did the sauropod Sauropoda (), whose members are known as sauropods (; ...
s similar to blunt
claw A claw is a curved, pointed appendage found at the end of a toe or finger in most amniotes (mammals, reptiles, birds). Some invertebrates such as beetles and spiders have somewhat similar fine, hooked structures at the end of the leg or Arthro ...
s.


Geographic and stratigraphic range

All the fossils of ''Ennatosaurus tecton'' are from
Arkhangelsk Arkhangelsk (, ) is a types of inhabited localities in Russia, city and the administrative center of Arkhangelsk Oblast, Russia. It lies on both banks of the Northern Dvina near its mouth into the White Sea. The city spreads for over along the ...
Oblast An oblast ( or ) is a type of administrative division in Bulgaria and several post-Soviet states, including Belarus, Russia and Ukraine. Historically, it was used in the Russian Empire and the Soviet Union. The term ''oblast'' is often translated i ...
in northern
European Russia European Russia is the western and most populated part of the Russia, Russian Federation. It is geographically situated in Europe, as opposed to the country's sparsely populated and vastly larger eastern part, Siberia, which is situated in Asia ...
. The holotype and the majority of the referred specimens were discovered in 1955 in the Nijneoustinskaia Formation (Karpogorskaia Member), on the banks of the Pinega River, and come from the locality of Moroznitsa near the town of Karpoga in the Pinezhsky District. A nearly complete skull with lower jaw, a fragment of the cheek region of a second skull, and an incomplete dentary were also discovered in the Krasnoshelskaia Formation, near the village of Nisogora (
Leshukonsky District Leshukonsky District () is an administrative district ( raion), one of the twenty-one in Arkhangelsk Oblast, Russia.Law #65-5-OZ Municipally, it is incorporated as Leshukonsky Municipal District.Law #258-vneoch.-OZ It is located in the northeast ...
), on the banks of the
Mezen River The Mezen (; Komi: ''n'') is a river in Udorsky District of the Komi Republic and in Leshukonsky and Mezensky Districts of Arkhangelsk Oblast in Russia. Its mouth is located in the Mezen Bay of the White Sea. Mezen is one of the biggest rivers ...
, more than 100 km east of the first site. ''Ennatosaurus'' has long been known as one of the last caseids with a middle Permian age. But a more precise age was difficult to assess because ''Ennatosaurus'' is the only known vertebrate at the Moroznitsa locality. A
Capitanian In the geologic timescale, the Capitanian is an age or stage of the Permian. It is also the uppermost or latest of three subdivisions of the Guadalupian Epoch or Series. The Capitanian lasted between and million years ago. It was preceded by t ...
age was sometimes mentioned. However, the Nisogora locality, which has yielded ''Ennatosaurus'' remains, contains a more diverse fauna containing the
parareptiles Parareptilia ("near-reptiles") is an extinct group of basal sauropsids ("reptiles"), traditionally considered the sister taxon to Eureptilia (the group that likely contains all living reptiles and birds). Parareptiles first arose near the end ...
'' Nyctiphruretus acudens'', ''
Macroleter poezicus ''Macroleter'' is an extinct genus of nycteroleterid parareptile which existed in Oklahoma and Russia during the upper Permian period. It was a quite generalized primitive reptile, in many ways resembling their amphibian ancestors. It was first ...
'' and '' Lanthaniscus efremovi'', the
Varanopidae Varanopidae is an extinct family (biology), family of amniotes known from the Late Carboniferous to Middle Permian that resembled monitor lizards (with the name of the group deriving from the monitor lizard genus ''Varanus'') and may have filled ...
'' Mesenosaurus romeri'', and the juvenile therapsid of uncertain affinity '' Niaftasuchus zekkeli''. All these species (except ''Ennatosaurus'') are also known in at least eight other localities of the Arkhangelsk Oblast which have yielded additionally the parareptiles '' Lanthanolania ivachnenkoi'', '' Bashkyroleter mesensis'' and '' Nycteroleter ineptus'', the Varanopidae '' Pyozia mesensis'', and several basal therapsids : the Nikkasauridae '' Nikkasaurus tatarinovi'', '' Reiszia gubini'' and ''R. tippula'', the
biarmosuchia Biarmosuchia is an extinct clade of non-mammalian synapsids from the Permian. Biarmosuchians are the most basal group of the therapsids. They were moderately-sized, lightly built carnivores, intermediate in form between basal sphenacodont " pel ...
n '' Alrausuchus tagax'', and a yet undescribed basal anteosaurid
dinocephalia Dinocephalians (terrible heads) are a clade of large-bodied early therapsids that flourished in the Early and Middle Permian between 279.5 and 260 million years ago (Ma), but became extinct during the Capitanian mass extinction event. ...
n. This fauna constitutes the Mezen assemblage which is more or less contemporary with the Ochyor (or Ocher) assemblage. Magnetostratigraphic data suggests that these two faunal assemblages are late Roadian to early Wordian in age. Compared to the Ochyor assemblage largely dominated by therapids (''
Estemmenosuchus ''Estemmenosuchus'' (meaning "crowned crocodile" in Greek language, Greek) is an extinct genus of large, early omnivore, omnivorous therapsid. It is believed and interpreted to have lived during the middle part of the Middle Permian around 267 m ...
'', the anteosaur '' Archaeosyodon'', '' Biarmosuchus'', and the anomodont '' Otsheria''), the Mezen assemblage, characterized by the presence of
pelycosaur Pelycosaur ( ) is an older term for basal or primitive Late Paleozoic synapsids, excluding the therapsids and their descendants. Previously, the term mammal-like reptile was used, and Pelycosauria was considered an order, but this is now thoug ...
s, the great diversity of small terrestrial parareptiles, and more primitive therapsids, seems more archaic. These two faunal assemblages were geographically separated from each other by a marine area. It is possible that the Mezen assemblage is a relict fauna which lived in the regions of marshy plains west of the Kazanian Sea, while the Ochyor fauna lived east of this sea, along the Paleo-
Urals The Ural Mountains ( ),; , ; , or simply the Urals, are a mountain range in Eurasia that runs north–south mostly through Russia, from the coast of the Arctic Ocean to the river Ural (river), Ural and northwestern Kazakhstan.
mountains. In 2016, Mujal and colleagues attributed to cf. ''Ennatosaurus tecton'', an incomplete posterior dorsal vertebra (including the dorsal half of the centrum and the base of the neural arch) found in deposits possibly dating from the Middle Permian of La Vansa i Fórnols in northern
Spain Spain, or the Kingdom of Spain, is a country in Southern Europe, Southern and Western Europe with territories in North Africa. Featuring the Punta de Tarifa, southernmost point of continental Europe, it is the largest country in Southern Eur ...
(
Province of Lleida The Province of Lleida (; ; ) is one of the four provinces of Catalonia. It lies in northeastern Spain, in the western part of the autonomous community of Catalonia, and is bordered by the provinces of Girona, Barcelona, Tarragona, Zarag ...
). This tentative determination was based on the presence of a small pit on the lateral surface of the centrum. However, Romano and colleagues have shown that the very small size and location of the pit of the Spanish vertebra does not correspond to the large elongated pits clearly visible in lateral and ventral views on all vertebrae of ''Ennatosaurus tecton'' (as Olson had already figured in 1968). The small pit of the Spanish vertebra probably represents a perforation for the
blood vessel Blood vessels are the tubular structures of a circulatory system that transport blood throughout many Animal, animals’ bodies. Blood vessels transport blood cells, nutrients, and oxygen to most of the Tissue (biology), tissues of a Body (bi ...
s, and its owner currently remains unidentified.


Phylogeny

In the first
phylogenetic analysis In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...
of Caseidae published in 2008, ''Ennatosaurus'' was identified as the sister group of a clade containing ''Cotylorhynchus romeri'' and '' Angelosaurus dolani''. The Wordian age of ''Ennatosaurus'' compared to the two American species dated to the Lower Permian indicates that the Russian species is the product of a ghost lineage of several million years. Below the first phylogenetic analysis of Caseidae published by Maddin et al. in 2008. In 2015, Romano and Nicosia published the first cladistic study including almost all the Caseidae (with the exception of '' Alierasaurus ronchii'' of
Sardinia Sardinia ( ; ; ) is the Mediterranean islands#By area, second-largest island in the Mediterranean Sea, after Sicily, and one of the Regions of Italy, twenty regions of Italy. It is located west of the Italian Peninsula, north of Tunisia an ...
, considered too fragmentary). In their most
parsimonious In philosophy, Occam's razor (also spelled Ockham's razor or Ocham's razor; ) is the problem-solving principle that recommends searching for explanations constructed with the smallest possible set of elements. It is also known as the principle o ...
analysis, '' Ennatosaurus '' is more closely related to the genus '' Angelosaurus ''. However, the close relationship between '' Angelosaurus dolani '' and '' Ennatosaurus tecton '' may be distorted by the extreme incompleteness of the material of the North American species. Below the most pasimonious phylogenetic analysis published by Romano & Nicosia in 2015. Two other cladogams published in 2020 by Berman and colleagues recover ''Ennatosaurus'' as the sister xaxon of a clade containing the taxa ''Angelosaurus romeri'', ''Alierasaurus ronchii'', and the three species of ''Cotylorhynchus''. Below are the two Caseidae cladograms published by Berman and colleagues in 2020. In the cladogram published by Werneburg and colleagues in 2022, ''Ennatosaurus'' occupies a similar position between ''Euromycter'' and all more derived caseids. Below is the cladogram published by Werneburg and colleagues in 2022.


References


See also

*
List of pelycosaurs This list of pelycosaurs is an attempt to create a comprehensive listing of all Genus, genera that have ever been included in the synapsida excluding therapsida and purely vernacular terms. The list includes all commonly accepted genera, but also g ...
{{Taxonbar, from=Q60383 Caseidae Prehistoric synapsid genera Guadalupian synapsids Extinct animals of Russia Taxa named by Ivan Yefremov Fossil taxa described in 1956 Wordian genus first appearances Wordian genus extinctions