Ozimek Volans
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''Ozimek'' (named after the town of the same name) is a genus of sharovipterygid
archosauromorph Archosauromorpha (Greek for "ruling lizard forms") is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs (such as crocodilians and dinosaurs, including birds) than to lepidosaurs (such as tuataras, lizards, a ...
reptile, known from
Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...
deposits in
Poland Poland, officially the Republic of Poland, is a country in Central Europe. It extends from the Baltic Sea in the north to the Sudetes and Carpathian Mountains in the south, bordered by Lithuania and Russia to the northeast, Belarus and Ukrai ...
and closely related to the
Kyrgyzstan Kyrgyzstan, officially the Kyrgyz Republic, is a landlocked country in Central Asia lying in the Tian Shan and Pamir Mountains, Pamir mountain ranges. Bishkek is the Capital city, capital and List of cities in Kyrgyzstan, largest city. Kyrgyz ...
i ''
Sharovipteryx ''Sharovipteryx'' ("Sharov's wing", known until 1981 as ''Podopteryx'', "foot wing") is a genus of early gliding reptiles containing the single species ''Sharovipteryx mirabilis''. It is known from a single fossil and is the only glider with a me ...
''. It contains one species, ''O. volans'', named in 2016 by
Jerzy Dzik Jerzy Dzik (born 25 February 1950) is a Polish paleontologist. He has described many species, genera, and families of conodonts, including the Order (biology), order Ozarkodinida (in 1976). In 2003, he described the Dinosauriformes, dinosaurifor ...
and Tomasz Sulej. Like ''Sharovipteryx'', ''Ozimek'' had long, slender limbs with the hindlimbs longer than the forelimbs; the hindlimbs likely supported gliding membranes as fossilized in ''Sharovipteryx''. Another unusual characteristic was the shoulder girdle, where the massive
coracoid A coracoid is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is present as part of the scapula, but this is n ...
s formed a shield-like structure covering the bottom of the shoulder region that would have limited mobility. In other respects, such as its long neck, it was a typical member of the non-natural grouping
Protorosauria Protorosauria is an extinct, likely paraphyletic group of basal archosauromorph reptiles from the latest Middle Permian ( Capitanian stage) to the end of the Late Triassic ( Rhaetian stage) of Asia, Europe and North America. It was named by t ...
.
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 ...
has indicated that it, possibly along with ''Sharovipteryx'', may have been an unusual member of the protorosaur group
Tanystropheidae Tanystropheidae is an extinct family (biology), family of archosauromorph reptiles that lived throughout the Triassic Period, often considered to be "protorosaurs". They are characterized by their long, stiff necks formed from elongated cervical ...
, although further study of its anatomy is needed to resolve its precise relationships. Five articulated skeletons and 30 fragmentary specimens constitute the known fossil material of ''Ozimek'', which comes from the
Krasiejów Krasiejów is a village in the administrative district of Gmina Ozimek, within Opole County, Opole Voivodeship, in south-western Poland. It lies approximately east of Ozimek and east of the regional capital Opole. Paleontological localities ...
clay pit A clay pit is a quarry or Mining, mine for the extraction of clay, which is generally used for manufacturing pottery, bricks or Portland cement. Quarries where clay is mined to make bricks are sometimes called brick pits. A brickyard or brickwor ...
near
Opole Opole (; ; ; ) is a city located in southern Poland on the Oder River and the historical capital of Upper Silesia. With a population of approximately 127,387 as of the 2021 census, it is the capital of Opole Voivodeship (province) and the seat of ...
. Its remains were found uniformly distributed within a rock layer containing fossils of terrestrial animals. During the Late Triassic, the Krasiejów region would have been a lake surrounded by
conifer Conifers () are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a sin ...
ous forests, where ''Ozimek'' would have glided between trees feeding on insects such as cupedid beetles. A
delta wing A delta wing is a wing shaped in the form of a triangle. It is named for its similarity in shape to the Greek uppercase letter delta (letter), delta (Δ). Although long studied, the delta wing did not find significant practical applications unti ...
hindlimb membrane configuration and possible forelimb membranes like those inferred for ''Sharovipteryx'', along with hollow bones, would have allowed ''Ozimek'' to glide in a controlled fashion. However, individuals of ''Ozimek'' still fell into the lake on occasion, where they were possibly subjected to scavenging by amphibians such as ''
Cyclotosaurus ''Cyclotosaurus'' is an extinct genus of temnospondyl within the family (biology), family Mastodonsauridae. It was of great size for an amphibian, had an elongated skull up to . Etymology The name means "round eared lizard" in Ancient Greek, de ...
'' and reptiles such as ''
Parasuchus ''Parasuchus'' is an extinct genus of basal phytosaur known from the Late Triassic (late Carnian to early Norian stage) of Andhra Pradesh and Madhya Pradesh, India. At its most restricted definition, ''Parasuchus'' contains a single species, '' ...
'' before burial.


Discovery and naming

Starting in 1974, the
Krasiejów Krasiejów is a village in the administrative district of Gmina Ozimek, within Opole County, Opole Voivodeship, in south-western Poland. It lies approximately east of Ozimek and east of the regional capital Opole. Paleontological localities ...
clay pit A clay pit is a quarry or Mining, mine for the extraction of clay, which is generally used for manufacturing pottery, bricks or Portland cement. Quarries where clay is mined to make bricks are sometimes called brick pits. A brickyard or brickwor ...
near
Opole Opole (; ; ; ) is a city located in southern Poland on the Oder River and the historical capital of Upper Silesia. With a population of approximately 127,387 as of the 2021 census, it is the capital of Opole Voivodeship (province) and the seat of ...
, Poland was excavated by the cement plant Strzelce Opolskie, with the excavated clay being mixed with water for cement production. In the 1980s, amateur fossil collectors discovered bone fragments in the outcrops exposed by these excavations and brought them to the attention of
Magdalena Borsuk-Białynicka Maria Magdalena Borsuk-Białynicka (born January 29, 1940) is a Polish paleontologist and phylogeneticist born in 1940 in Warsaw, Poland. She received both her Master of Science A Master of Science (; abbreviated MS, M.S., MSc, M.Sc., SM, S ...
at the Institute of Paleobiology of the
Polish Academy of Sciences The Polish Academy of Sciences (, PAN) is a Polish state-sponsored institution of higher learning. Headquartered in Warsaw, it is responsible for spearheading the development of science across the country by a society of distinguished scholars a ...
(ZPAL). The locality was not found until 1993, when
Jerzy Dzik Jerzy Dzik (born 25 February 1950) is a Polish paleontologist. He has described many species, genera, and families of conodonts, including the Order (biology), order Ozarkodinida (in 1976). In 2003, he described the Dinosauriformes, dinosaurifor ...
discovered a skull of ''
Paleorhinus ''Paleorhinus'' (Greek: ''"Old Nose"'') is an extinct genus of widespread basal phytosaur known from the Late Triassic (late Carnian stage). The genus was named in 1904 based on the type species ''Paleorhinus bransoni'', which is known from Wyo ...
''. More extensive excavations took place from 2000 to 2002, which were sponsored by the Górażdże cement plant that owned the pit by this point. The clay made the fossils easy to extract, but they were also fragile and needed to be protected by a plaster jacket (for large fossils) or
cyanoacrylate Cyanoacrylates are a family of strong fast-acting adhesives with industrial, medical, and household uses. They are derived from ethyl cyanoacrylate and related esters. The cyanoacrylate group in the monomer rapidly polymerizes in the presence ...
glue (for small fossils). Two bone-bearing rock layers exist at Krasiejów: one mainly preserving lake-dwelling animals, and the other mainly preserving terrestrial animals. Based on comparisons of its fauna with sites in Germany (including the presence of ''Paleorhinus''), these layers likely date to the Late
Carnian The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227.3 ...
age Age or AGE may refer to: Time and its effects * Age, the amount of time someone has been alive or something has existed ** East Asian age reckoning, an Asian system of marking age starting at 1 * Ageing or aging, the process of becoming older ...
of the
Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...
, approximately 230 million years ago, as part of the
Grabowa Formation Grabowa may refer to the following places: *Grabowa (river) (), a river in Pomerania, northern Poland *Grabowa, Opoczno County in Łódź Voivodeship (central Poland) *Grabowa, Wieluń County in Łódź Voivodeship (central Poland) *Grabowa, Święt ...
. Most of the terrestrial fossils were found towards the north of the clay pit, which was likely the shore of a lake during the Late Carnian. These consist of a number of large
tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...
skeletons, as well as uniformly distributed fossils from smaller reptiles. At some point before 2007, a single, extremely elongated vertebra was discovered among these small reptile fossils; it was compared to the neck vertebrae of ''
Tanystropheus ''Tanystropheus'' (~ 'long' + 'hinged') is an extinct genus of archosauromorph reptile which lived during the Triassic period, Triassic Period in Europe, Asia, and North America. It is recognisable by its extremely elongated neck, longer than t ...
'', or the tail vertebrae of
pterosaur Pterosaurs are an extinct clade of flying reptiles in the order Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 million to 66 million years ago). Pterosaurs are the earli ...
s. Many additional specimens of this animal were recognized afterwards, with it being the most common among these small reptile fossils. An almost complete, articulated skeleton missing the head was designated as the
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 ...
of a new genus and species, and catalogued as ZPAL AbIII/2512. Other articulated skeletons included ZPAL AbIII/2012, which preserves a crushed head, a nearly complete neck, and partial limbs; ZPAL AbIII/2511, which is the most complete specimen (lacking only the head) but is disarticulated; ZPAL AbIII/3191, which is almost complete with some disarticulated skull bones; and UOPB (
University of Opole The University of Opole () is a public university in the city of Opole. It was founded in 1994 from a merger of two parallel educational institutions. The university has 17,500 students completing 32 academic majors and 53 specializations. The ...
) 1148, which preserves parts of the neck and limbs. Another 30 fragmentary specimens in the ZPAL collection include neck and
back vertebrae 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 of intermediate size between the cervical and lumbar ve ...
, neck ribs,
gastralia Gastralia (: gastralium) are dermal bones found in the ventral body wall of modern crocodilians and tuatara, and many prehistoric tetrapods. They are found between the sternum and pelvis, and do not articulate with the vertebrae. In these reptil ...
("belly ribs"),
humeri 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 and ulna, and consists of three sections. The humeral upper extremity consists of ...
,
femora The femur (; : femurs or femora ), or thigh bone is the only bone in the thigh — the region of the lower limb between the hip and the knee. In many four-legged animals the femur is the upper bone of the hindleg. The top of the femur fits in ...
,
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 ...
e,
fibula The fibula (: fibulae or fibulas) or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. ...
e, and tarsi (ankle bones). In 2016, Dzik and Tomasz Sulej named this new genus and species ''Ozimek volans''. The genus name, ''Ozimek'', is derived from
Ozimek Ozimek (; ) is a town in Opole County, Opole Voivodeship, Poland, with 8,657 inhabitants (2019). History Ozimek dates back to an early modern period, early modern settlement. It was named both ''Ozimek'' and ''Małapanew'', with both names bei ...
, the nearby town of the same name. The species name ''volans'' (Latin "flying") refers to its possible gliding lifestyle (see §Paleobiology).


Description

''Ozimek'' was a rather small reptile, with an estimated total length of about .


Skull and vertebrae

The skull of ''Ozimek'' is only known from fragmentary fossils; from the identifiable fragments, the skull appears to have been
diapsid Diapsids ("two arches") are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The earliest traditionally identified diapsids, the araeosc ...
, broad, and compact, unlike the elongated skulls of ''
Protorosaurus ''Protorosaurus'' (from , 'earlier' and , 'lizard') is an extinct genus of reptile. Members of the genus lived during the late Permian period in what is now Germany and Great Britain. Once believed to have been an ancestor to lizards, ''Protoro ...
'' and other small
archosauromorphs Archosauromorpha (Greek language, Greek for "ruling lizard forms") is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs (such as crocodilians and dinosaurs, including birds) than to Lepidosauria, lepidosaurs ( ...
. In particular, like ''
Langobardisaurus ''Langobardisaurus'' (, meaning Reptile of Langobardi, in reference to the Long Bearded People, an ancient Central-European civilisation of North Germanic origin) is an extinct genus of Tanystropheidae, tanystropheid Archosauromorpha, archosaurom ...
'', the
squamosal bone The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral ...
of the skull roof was large. By contrast, the likewise poorly-preserved skull of ''Sharovipteryx'' was interpreted as having been narrow and deep by David Unwin and colleagues in 2000, although Dzik and Sulej suggested that its skull was actually similar to ''Ozimek''. The preserved portions of the jaws show numerous small, sharp teeth. Based on the shape and arrangement of teeth in the
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 ...
, ''Ozimek'' may not have had an
antorbital fenestra An antorbital fenestra (plural: fenestrae) is an opening in the skull that is in front of the eye sockets. This skull character is largely associated with Archosauriformes, archosauriforms, first appearing during the Triassic Period. Among Extant ...
(opening in front of the eye socket). In the eye socket, the
sclerotic ring The scleral ring or sclerotic ring is a hardened ring of plates, often derived from bone, that is found in the eyes of many animals in several groups of vertebrates. Some species of mammals, amphibians, and crocodilians lack scleral rings. The rin ...
may have been fossilized. On the side of the skull, the
jugal bone The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic bone, zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by spe ...
would have formed a complete arch. Like ''Langobardisaurus'' and ''
Tanytrachelos ''Tanytrachelos'' is an extinct genus of tanystropheid archosauromorph reptile from the Late Triassic of the eastern United States. It contains a single species, ''Tanytrachelos ahynis'', which is known from several hundred fossil specimens pres ...
'' but unlike ''Tanystropheus'', ''Ozimek'' had vertebrae that were procoelous (i.e., with articulating surfaces that were concave in front and convex behind). Like the latter two, the
neural spines 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 spinal ...
were low. It appears that ''Ozimek'' had 9 neck vertebrae, 16 back vertebrae, 3 hip vertebrae (in contrast to the 4 to 6 estimated for ''Sharovipteryx''), and at least 7 tail vertebrae. The neck vertebrae were very elongated and thinly-walled, with the fourth, fifth, and sixth being the longest; the initially-discovered elongated vertebra was one of them. The neck ribs were also long, with some of them extending for the length of three vertebrae. Elongated neck vertebrae and ribs were a common characteristic among protorosaurs. Like other
tanystropheids Tanystropheidae is an extinct family of archosauromorph reptiles that lived throughout the Triassic Period, often considered to be " protorosaurs". They are characterized by their long, stiff necks formed from elongated cervical vertebrae with v ...
, the neural spine of the
axis An axis (: axes) may refer to: Mathematics *A specific line (often a directed line) that plays an important role in some contexts. In particular: ** Coordinate axis of a coordinate system *** ''x''-axis, ''y''-axis, ''z''-axis, common names ...
(second neck vertebra) sloped upwards at the front. For the back vertebrae, the wide neural spines with straight, thickened top margins were similar to ''
Macrocnemus ''Macrocnemus'' is an extinct genus of archosauromorph reptile known from the Middle Triassic (Late Anisian to Ladinian) of Europe and China. ''Macrocnemus'' is a member of the Tanystropheidae family and includes three species''. Macrocnemus bas ...
''. The gastralia suggest that the underside of the animal was gently convex. In the tail, the
transverse processes 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 ...
of the first few vertebrae were very long like ''Tanytrachelos'', which would have given the base of the tail a rhomboidal shape.


Limb girdles and limbs

An anatomical characteristic that distinguished ''Ozimek'' from other protorosaurs was the
coracoid A coracoid is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is present as part of the scapula, but this is n ...
s in its shoulder girdle, which were large and plate-like, and formed a convex shield covering the bottom of the shoulder region. This structure probably originated by the coracoids fusing with the
sterna ''Sterna'' is a genus of terns in the bird family Laridae. The genus used to encompass most "white" terns indiscriminately, but mtDNA sequence comparisons have determined that this arrangement was paraphyletic. It is now restricted to the typi ...
; ''Tanytrachelos'' in particular had large, quadrangular sterna, but they were unfused to the coracoids. Overall, the fused
scapulocoracoid The scapulocoracoid is the unit of the pectoral girdle that contains the coracoid and scapula. The coracoid itself is a beak-shaped bone that is commonly found in most vertebrates with a few exceptions. The scapula is commonly known as the ''shoulde ...
complex was the largest bone among fossils attributable to ''Ozimek''. Each coracoid bore two openings in front of each other. The front opening may have been homologous with the coracoid
foramina In anatomy and osteology, a foramen (; : foramina, or foramens ; ) is an opening or enclosed gap within the dense connective tissue (bones and deep fasciae) of extant and extinct amniote animals, typically to allow passage of nerves, arter ...
found in other animals, but the origin of the rear opening is unclear. Another distinguishing characteristic is that its
scapula The scapula (: 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 side ...
e were low (like ''
Tangasaurus ''Tangasaurus'' is an extinct genus of aquatic animal, aquatic basal (phylogenetics), basal tangasaurid neodiapsid known from the Late Permian geological timescale, period (late Changhsingian stage) of Tanga Region, Tanga, northeastern Tanzania. ...
'') but crescent-shaped (like ''Tanystropheus'' and ''Tanytrachelos''). The
glenoid fossa The glenoid fossa of the scapula or the glenoid cavity is a bone part of the shoulder. The word ''glenoid'' is pronounced or (both are common) and is from , "socket", reflecting the shoulder joint's ball-and-socket form. It is a shallow, pyrifo ...
where the humerus articulated with the scapulocoracoid seemed to have been limited to the coracoids. The pelvic girdle of ''Ozimek'' was more typical of protorosaurs, being similar to ''Prolacerta'', ''
Malerisaurus ''Malerisaurus'' is an extinct genus of archosauromorph known from Telangana of India and Texas of the USA. Description ''Malerisaurus'' was a medium-sized archosauromorph which averaged 1.2 meters in length. ''Malerisaurus'' is known from the h ...
'', and ''
Pamelaria ''Pamelaria'' is an extinct genus of allokotosaurian archosauromorph reptile known from a single species, ''Pamelaria dolichotrachela'', from the Middle Triassic of India. ''Pamelaria'' has sprawling legs, a long neck, and a pointed skull with no ...
''. As in ''Sharovipteryx'', the portion of the ilium in front of the
acetabulum The acetabulum (; : acetabula), also called the cotyloid cavity, is a wikt:concave, concave surface of the pelvis. The femur head, head of the femur meets with the pelvis at the acetabulum, forming the Hip#Articulation, hip joint. Structure The ...
(hip socket) was well-developed. The limbs of ''Ozimek'' were exceptionally elongated compared to all other members of the
Protorosauria Protorosauria is an extinct, likely paraphyletic group of basal archosauromorph reptiles from the latest Middle Permian ( Capitanian stage) to the end of the Late Triassic ( Rhaetian stage) of Asia, Europe and North America. It was named by t ...
, with the hindlimbs being generally longer than the forelimbs and the femur being 18 times as long as its diameter at its top end. Like ''
Sharovipteryx ''Sharovipteryx'' ("Sharov's wing", known until 1981 as ''Podopteryx'', "foot wing") is a genus of early gliding reptiles containing the single species ''Sharovipteryx mirabilis''. It is known from a single fossil and is the only glider with a me ...
'', the tibia of ''Ozimek'' was longer than its trunk; however, ''Ozimek'' had proportionally shorter legs relative to its trunk (1.2 times as long, compared to 2.1 times in ''Sharovipteryx'') but thinner femora (14.5 times as long as the top end diameter in ''Sharovipteryx''). The specimens ZPAL AbIII/2511 and ZPAL AbIII/2512 have similarly-sized torsos but differ notably in limb proportions; the latter, probably a juvenile specimen, had smaller forelimbs in relation to its hindlimbs along with disproportionately thin humeri but thicker femora. Its feet were also large, with ZPAL AbIII/2511 suggesting that they were twice the size of the hands. Like ''
Azendohsaurus ''Azendohsaurus'' is an extinct genus of Herbivore, herbivorous archosauromorph reptile from roughly the late Middle Triassic, Middle to early Late Triassic, Late Triassic Period of Morocco and Madagascar. The type species, ''Azendohsaurus laarou ...
'' and also other protorosaurs such as '' Prolacerta'', however, the fifth
metatarsal The metatarsal bones or metatarsus (: metatarsi) are a group of five long bones in the midfoot, located between the tarsal bones (which form the heel and the ankle) and the phalanges ( toes). Lacking individual names, the metatarsal bones are ...
in the heel was robust, curved, and hooked, an adaptation related to the stiffening of the foot for more efficient standing and locomotion in
diapsid Diapsids ("two arches") are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The earliest traditionally identified diapsids, the araeosc ...
s. Like ''Sharovipteryx'', there was a pulley-like projection at the bottom of the femur.


Classification

Protorosauria is a diverse group of
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 ...
and Triassic archosauromorph reptiles generally characterized by long necks, especially so in specialized members of the group such as tanystropheids and dinocephalosaurids. Along with its long neck, other features that allowed Dzik and Sulej to refer ''Ozimek'' to the Protorosauria included the curvature of its scapulae and the procoelous vertebrae. However, the poor preservation of its skull inhibited them from comparing it to many other protorosaurs. Dzik and Sulej also recognized the many shared features between ''Ozimek'' and ''Sharovipteryx'': the elongated
hyoid bone The hyoid-bone (lingual-bone or tongue-bone) () is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid-cartilage. At rest, it lies between the base of the mandible and the third cervical verte ...
s, the expansion of the ilium in front of the acetabulum, the femoral projection, and the elongated tibia. These were previously listed as distinguishing characteristics of ''Sharovipteryx'' by Unwin; Dzik and Sulej therefore assigned ''Ozimek'' to the
Sharovipterygidae Sharovipterygidae is a family of strange gliding archosauromorphs from the mid-Triassic of Eurasia, notable for their short forelimbs and long, wing A wing is a type of fin that produces both Lift (force), lift and drag while moving through ...
, which otherwise contained only ''Sharovipteryx''. The relationship between Sharovipterygidae and Protorosauria is related to uncertainty over the definition of Protorosauria. In 1945,
Charles Camp Charles Lewis Camp (March 12, 1893 – August 14, 1975) was an American palaeontologist and zoologist, working from the University of California, Berkeley. He took part in excavations at the 'Placerias Quarry', in 1930 and the forty ''Shonisaurus' ...
recognized a close relationship between ''Protorosaurus'' and ''Prolacerta''; he defined the Protorosauria as being divided into the Prolacertiformes (including ''Prolacerta''), Trachelosauria (i.e., Tanystropheidae),
Thalattosauria Thalattosauria ( Greek for "sea lizards") is an extinct order of marine reptiles that lived during the Triassic Period. Thalattosaurs were diverse in size and shape, and are divided into two superfamilies: Askeptosauroidea and Thalattosauroide ...
, and Acrosauria (i.e.,
Pleurosauridae Pleurosauridae, from Ancient Greek πλευρά (''pleurá''), meaning "rib" or "side", and σαῦρος (''saûros''), meaning "lizard", is an extinct family of sphenodontian reptiles, known from the Jurassic of Europe. Members of the family h ...
). By the 1980s, it was recognized that Protorosauria and Prolacertiformes were functionally equivalent groups, with the former taking priority but the latter being preferred due to uncertainty over the position of ''Protorosaurus''. An emerging consensus in the 1980s and 1990s held that ''Sharovipteryx'' belonged to the Prolacertiformes, albeit based on characteristics that were either not determinable or widely present among diapsids. In 2000, Unwin and colleagues provided a list of characteristics to better support a prolacertiform attribution: long neck vertebrae and ribs, low neural spines on neck vertebrae, straight femora, tibiae longer than femora, long second
phalanges The phalanges (: phalanx ) are digit (anatomy), digital bones in the hands and foot, feet of most vertebrates. In primates, the Thumb, thumbs and Hallux, big toes have two phalanges while the other Digit (anatomy), digits have three phalanges. ...
in the fifth digits of the feet, seven or less neck vertebrae, and fourth metatarsals less than three times the length of the fifth. However, in subsequent years, first ''Prolacerta'' and then ''Protorosaurus'' were increasingly recognized as no longer belonging to the same group as other traditional members by
phylogenetic analyses In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as Computational phylogenetics, phylogenetic inference. It infers the relationship among organ ...
, thus making both Prolacertiformes and Protorosauria non-
monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...
(i.e., composed of groups that were not
sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...
s). The poor preservation of ''Sharovipteryx'' itself prevented its inclusion in these analyses. In 2019, a phylogenetic analysis by Adam Pritchard and colleagues incorporated ''Ozimek''. They found it as a member of the Tanystropheidae, as the sister group to a
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
formed by ''Langobardisaurus'' and ''Tanytrachelos''. Pritchard and colleagues suggested that this did not preclude the inclusion of ''Ozimek'' in Sharovipterygidae, and that both ''Ozimek'' and ''Sharovipteryx'' may represent tanystropheids despite representing an
ecomorph Ecomorphology or ecological morphology is the study of the relationship between the ecological role of an individual and its morphological adaptations. The term "morphological" here is in the anatomical context. Both the morphology and ecology ex ...
distinct from traditional members of the group. In 2021, Steven Spiekman and colleagues performed several analyses based on a new dataset. Two variants of the analysis that excluded unstable
taxa In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...
found ''Ozimek'' to be within the Tanystropheidae, as the sister group to a clade formed by '' Sclerostropheus'' and '' Raibliania''. Their
phylogenetic tree A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA. In ...
for one of these analyses is shown below; this tree had to be three steps longer, and thus less
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 ...
, if they forced ''Ozimek'' to not be included in Tanystropheidae. However, in two other variants of the analysis that included the unstable ''
Czatkowiella ''Czatkowiella'' is an extinct genus of long-necked archosauromorph known from Early Triassic (Olenekian age) rocks of Czatkowice 1, Poland. It was first named by Magdalena Borsuk−Białynicka and Susan E. Evans in 2009 and the type species is ' ...
'', it formed a group with ''Ozimek'' that lay outside of the Tanystropheidae. The analysis indicated that the two shared one anatomical characteristic: the back vertebrae were between 2.16 and 2.20 times as long as they were tall. ''Czatkowiella'' is a problematic species, because it is unclear that the attributed fossil remains actually belong to a single species. Spiekman and colleagues concluded that the position of ''Ozimek'', and by extension ''Sharovipteryx'', remained uncertain and that additional study of its anatomy would be required to elucidate its relationships.


Paleobiology


Gliding

''Ozimek'' likely had membranes that reached from the tips of its elongated hindlimbs to the base of its tail, as is preserved in the holotype of the similarly-proportioned ''Sharovipteryx''. This membrane may either have been stiff (as is the case in many reptiles) or flexible. In 1987, Carl Gans and colleagues put forth three hypotheses for the function of the membranes: (1) that they were used for
camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...
; (2) that they were used as display features for
sexual selection Sexual selection is a mechanism of evolution in which members of one sex mate choice, choose mates of the other sex to mating, mate with (intersexual selection), and compete with members of the same sex for access to members of the opposite sex ...
; or (3) they were used for gliding, a hypothesis supported by the likely density of the pelvic musculature in ''Sharovipteryx'' and also ''Ozimek''. They found that it was plausible for ''Sharovipteryx'' to have used the membranes for gliding. The length of the hindlimbs was also inferred to have aided jumping in ''Sharovipteryx'', as is the case in modern lizards such as ''
Otocryptis ''Otocryptis'' is a genus of Agamidae, agamid lizards from the Indian subcontinent. It is the sister group for the clade formed by ''Sitana'' and ''Sarada (lizard), Sarada''. The divergence is estimated to have occurred about 12 million years ago ...
'' and ''
Amphibolurus ''Amphibolurus'' is a genus of lizards in the family Agamidae. The genus is endemic to Australia. Description Characteristics of the genus ''Amphibolurus'' include: * Moderate size nout–vent length * Long limbs and long tail * One to five cr ...
''. Altogether, they suggested that ''Sharovipteryx'' likely jumped from elevated places, extended its membranes to glide, and then eventually
stalled ''Stalled'' is a 2013 British zombie comedy film directed by Christian James. It stars Dan Palmer, who also wrote the screenplay, as a man confined to a bathroom stall after zombies attack. Produced by Richard Kerrigan and Daniel Pickering, the ...
until it landed against a tree. While Gans and colleagues suggested that the hindlimbs of ''Sharovipteryx'' extended forwards, leading to an unstable mode of gliding, aerodynamic modelling by
Gareth Dyke Gareth John Dyke is a paleontologist whose work is concerned with the evolutionary history of birds and their dinosaurian relatives. His specific research interests include the phylogenetics of birds, the functional morphology of aves and non-av ...
and colleagues in 2006 suggested instead that the hindlimbs were extended outwards and backwards to support a
delta wing A delta wing is a wing shaped in the form of a triangle. It is named for its similarity in shape to the Greek uppercase letter delta (letter), delta (Δ). Although long studied, the delta wing did not find significant practical applications unti ...
that could be controlled by the angle of the knee. Other anatomical characteristics may have supported gliding in sharovipterygids. The holotype of ''Sharovipteryx'' does not preserve forelimbs. Both Gans and colleagues and Dyke and colleagues hypothesized that the forelimbs may have supported an additional pair of membranes, which would have served as a canard wing to improve control and balance the
pitching moment In aerodynamics, the pitching moment on an airfoil is the Moment (physics), moment (or torque) produced by the aerodynamic force with respect to the aerodynamic center on the airfoil . The pitching moment on the wing of an airplane is part of ...
of the hindlimb wings. Dzik and Sulej noted that the structure of the scapulocoracoid in ''Ozimek'' would prevent flapping flight, and that they were at best used for gliding. They also noted that the vertebral bodies and
long bone The long bones are those that are longer than they are wide. They are one of five types of bones: long, short, flat, irregular and sesamoid. Long bones, especially the femur and tibia, are subjected to most of the load during daily activities ...
s of ''Ozimek'' were hollow, but did not have external openings for
air sac Air sacs are spaces within an organism where there is the constant presence of air. Among modern animals, birds possess the most air sacs (9–11), with their extinct dinosaurian relatives showing a great increase in the pneumatization (presence ...
s that would allow air to fill them; these spaces may have been filled with fat instead, but either way they would have lightened the skeletal structure of ''Ozimek''.


Histology

''Ozimek volans'' was the subject of a 2024
histological Histology, also known as microscopic anatomy or microanatomy, is the branch of biology that studies the microscopic anatomy of biological tissue (biology), tissues. Histology is the microscopic counterpart to gross anatomy, which looks at large ...
analysis, focusing on the internal structure of two limb bones of the referred specimen UOPB 1148: a humerus in length, and a femur long. The femur is the largest known for the species, though the humerus is 46% of the maximum size. The
endosteum The endosteum (: endostea) is a thin vascular membrane of connective tissue that lines the inner surface of the bony tissue that forms the medullary cavity of long bones. This endosteal surface is usually resorbed during long periods of malnutr ...
and
periosteum The periosteum is a membrane that covers the outer surface of all bones, except at the articular surfaces (i.e. the parts within a joint space) of long bones. (At the joints of long bones the bone's outer surface is lined with "articular cartila ...
are well-delineated in the
cortex Cortex or cortical may refer to: Biology * Cortex (anatomy), the outermost layer of an organ ** Cerebral cortex, the outer layer of the vertebrate cerebrum, part of which is the ''forebrain'' *** Motor cortex, the regions of the cerebral cortex i ...
, and minor patches of coarse compact cancellous bone (dense spongy-textured bone) can be found along the inner edge of the periosteum. The
medullary cavity The medullary cavity (''medulla'', innermost part) is the central cavity of bone shafts where red bone marrow and/or yellow bone marrow (adipose tissue) is stored; hence, the medullary cavity is also known as the marrow cavity. Located in the ma ...
is large and vascular canals are simple, rare, and entirely longitudinal (lengthwise in orientation) wherever they occur. The bones are notable for their abundance of strongly-defined lamellae (thin regular layers) ringing along the circumference of the cortex. These lamellae are formed from longitudinal fibers, and are only clearly visible in a transverse cross-section. In most tetrapods, lamellae are concentrated in
osteons In osteology, the osteon or haversian system (; named for Clopton Havers) is the fundamental functional unit of much compact bone. Osteons are roughly cylindrical structures that are typically between 0.25 mm and 0.35 mm in diameter. Their ...
rather than the bone as a whole, so the long bones of ''Ozimek'' superficially resemble gigantic osteons. This condition helped to strengthen the bone. Longitudinal fibers in a cylindrical bone add rigidity and resistance to bending in multiple directions, a useful adaptation against the various aerodynamic forces experienced while gliding. Unlike birds or pterosaurs, ''Ozimek'' lacks pneumaticity (weight-saving air sacs in bone) in the balance of strength against weight. Extensive lamellar bone serves the same purpose by maximizing strength without adding weight. Bats use a similar strategy in their wing bones, though past a certain size threshold lamellar bone may lose effectiveness relative to pneumaticity. The femur appears to be from a juvenile: the periosteum is still developing rapidly (according to the higher density of vascular canals), secondary
remodeling Renovation (also called remodeling) is the process of improving broken, damaged, or outdated structures. Renovations are typically done on either commercial or residential buildings. Additionally, renovation can refer to making something new, o ...
is minimal, and the endosteum has barely begun development. Three
lines of arrested growth Growth arrest lines, also known as Harris lines, are lines of increased bone density that represent the position of the growth plate at the time of insult to the organism and formed on long bones due to growth arrest. They are only visible by ra ...
are preserved in the femur, indicating the animal was probably at least three years old and likely older. The humerus, on the other hand, has presumably reached its maximum size, and a thickened outer layer on the periosteum shows that its growth has ceased. The femur is already twice as long as the humerus, an extreme and unexpected difference in proportion (in comparison, the mature holotype has a femur which is only 70% longer than its humerus). The simplest explanation for this discrepancy is that the referred femur and humerus do not belong to the same animal as each other. Possible additional factors include
sexual dimorphism Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...
, multiple species, or developmental plasticity (strongly different growth strategies and maximum sizes between individuals of the same species). On the basis of the results for UOPB 1148, it is also conceivable that the holotype represents multiple individuals rather than a single skeleton.


Paleoecology

The
mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...
and
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. Although its permeabil ...
deposits of the Krasiejów clay pit indicate that it was deposited in a
lacustrine A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from t ...
(lake-based) environment; mudstone and siltstone made up about 45% of the rock, with another 40% being
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...
and the rest being
calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
. Meandering rivers likely flowed into the lake from the south and southeast, carrying calcite from eroded
Muschelkalk The Muschelkalk (German for "shell-bearing limestone"; ) is a sequence of sedimentary rock, sedimentary rock strata (a lithostratigraphy, lithostratigraphic unit) in the geology of central and western Europe. It has a Middle Triassic (240 to 230 m ...
(chalk) deposits to the south. This made the water alkaline, which combined with the anoxic conditions at the bottom of the lake (as indicated by dark-coloured rocks) would have preserved the bones while preventing organic matter from being preserved. The conditions of the ''Ozimek'' fossils suggests that they fell into the lake while gliding, and then possibly underwent scavenging by lake-dwelling tetrapods before they were finally buried in the mud.
Conifer Conifers () are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a sin ...
seeds and cone scales show that Krasiejów was surrounded by a forest; Dzik and Sulej inferred that the long neck and gliding membrane of ''Ozimek'' was an adaptation to hunting insects in the forest. Indeed,
elytra An elytron (; ; : elytra, ) is a modified, hardened forewing of beetles (Coleoptera), though a few of the true bugs (Hemiptera) such as the family Schizopteridae are extremely similar; in true bugs, the forewings are called hemelytra (sometime ...
(forewings) of cupedids (reticulated beetles) have been found. Two types of conifers were present. One, with cone scales similar to '' Pseudohirmerella platysperma'', was more common and likely had long, pointed leaves. Another, with cone scales similar to '' "Pachylepis" quinquies'', was associated with tape-like leaves. The fern '' Sphenopteris schoenleiniana'' was also present, as was the bennettitalean ''
Pterophyllum ''Pterophyllum'' is a small genus of freshwater fish from the family Cichlidae known to most aquarists as angelfish. All ''Pterophyllum'' species originate in the Amazon Basin, Orinoco Basin and various rivers in the Guiana Shield in tropical ...
''. These plants indicate that the climate was relatively dry. Calcified remains indicate that the water supported
charophyte Charophyta () is a paraphyletic group of freshwater green algae, called charophytes (), sometimes treated as a division, yet also as a superdivision. The terrestrial plants, the Embryophyta emerged deep within Charophyta, possibly from terres ...
algae. On land, large tetrapods included the
aetosaur Aetosaurs () are heavily armored reptiles belonging to the extinct order (biology), order Aetosauria (; from Ancient Greek, Greek, (aetos, "eagle") and (, "lizard")). They were medium- to large-sized Omnivore, omnivorous or Herbivore, herbivor ...
''
Stagonolepis robertsoni ''Stagonolepis'' is an extinct genus of stagonolepidid aetosaur known from the Late Triassic (Carnian stage) Hassberge Formation The Hassberge Formation is a Formation (geology), geologic formation in Bavaria, Germany. It preserves fossils dat ...
'' (or ''S. olenkae''), the
rauisuchid Rauisuchidae is a group of large (up to ) predatory Triassic archosaurs. Some disagreement exists over which genera should be included in the Rauisuchidae and which should be in the related Prestosuchidae and Poposauridae, and indeed whether thes ...
'' Polonosuchus silesiacus'', and the
silesaurid Silesauridae is an extinct family of Triassic dinosauriforms. It is most commonly considered to be a clade of non-dinosaur dinosauriforms, and the sister group of dinosaurs. Some studies have instead suggested that most or all silesaurids compr ...
''
Silesaurus opolensis ''Silesaurus'' is a genus of silesaurid dinosauriform from the Late Triassic, of what is now Poland. Discovery and naming The Krasiejów claypit near Opole, Poland, was first discovered as a fossil locality in the 1980s after quarrying for a ...
''; other than ''Ozimek'', small tetrapods included a sphenodontid. In the water, the
unionid The Unionidae are a Family (biology), family of freshwater mussels, the largest in the order Unionida, the bivalve molluscs sometimes known as river mussels, or simply as unionids. The range of distribution for this family is world-wide. It is a ...
(river mussel) '' Silesunio parvus'' was the most common fossil, and was accompanied by other invertebrates such as the
conchostraca Clam shrimp are a group of bivalved branchiopod crustaceans that resemble the unrelated bivalved molluscs. They are extant and also known from the fossil record, from at least the Devonian period and perhaps before. They were originally classifi ...
n (clam shrimp) '' Laxitextella laxitexta'', the
ostracod Ostracods, or ostracodes, are a Class (biology), class of the crustacean, Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 33,000 species (only 13,000 of which are extant taxon, extant) have been identified,Brandão, S.N.; Antoni ...
s (seed shrimp) ''
Darwinula ''Darwinula'' is a genus of ostracods belonging to the family Darwinulidae. Species: * ''Darwinula aurea'' * ''Darwinula stevensoni ''Darwinula'' is a genus of ostracods belonging to the family Darwinulidae. Species: * ''Darwinula aurea ' ...
'' and '' Suchonella'', a crab-like cyclid, and a
gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...
. Poorly-preserved fish fossils indicate the presence of the
ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of sk ...
'' "Dictyopyge" socialis'' and the
lungfish Lungfish are freshwater vertebrates belonging to the class Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, inc ...
'' Ptychoceratodus roemeri''. These would have been the primary food source of the large
temnospondyl Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') or temnospondyls is a diverse ancient order (biology), order of small to giant tetrapods—often considered Labyrinth ...
'' Metoposaurus krasiejowensis'', the most common aquatic tetrapod, while the larger, semi-aquatic temnospondyl '' Cyclotosaurus intermedius'' may have been a crocodile-like predator of land animals. The second-most common aquatic tetrapod was the
phytosaur Phytosaurs (Φυτόσαυροι in Greek, meaning 'plant lizard') are an extinct group of large, mostly semiaquatic Late Triassic archosauriform or basal archosaurian reptiles. Phytosaurs belong to the order Phytosauria and are sometimes ref ...
''Parasuchus'' cf. ''arenacus''. Prolonged droughts may have resulted in mass deaths of ''Metoposaurus'' and ''Parasuchus'' in the disappearing lake.


References

{{Portalbar, Paleontology, Poland Archosauromorpha Carnian life Late Triassic reptiles of Europe Fossils of Poland Gliding animals Fossil taxa described in 2016