''Sisteronia'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

platypterygiine Platypterygiinae is an extinct subfamily of ophthalmosaurid thunnosaur ichthyosaurs from the early Late Jurassic to the early Late Cretaceous (Kimmeridgian - Cenomanian) of Asia, Australia, Europe, North America and South America. Currentl ...

ophthalmosaurid Ophthalmosauridae is an extinct family of thunnosaur ichthyosaurs from the Middle Jurassic to the early Late Cretaceous (Bajocian - Cenomanian) worldwide. Almost all ichthyosaurs from the Middle Jurassic onwards belong to the family, until the ex ...

ichthyosaur Ichthyosaurs (Ancient Greek for "fish lizard" – and ) are large extinct marine reptiles. Ichthyosaurs belong to the order known as Ichthyosauria or Ichthyopterygia ('fish flippers' – a designation introduced by Sir Richard Owen in 1842, altho ...

known from the 'middle' Cretaceous of southeastern

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

and southeastern

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...

. It contains a single species, ''Sisteronia seeleyi''.

Discovery

''Sisteronia'' was named by Valentin Fischer, Nathalie Bardet, Myette Guiomar and Pascal Godefroit in

2014 File:2014 Events Collage.png, From top left, clockwise: Stocking up supplies and personal protective equipment (PPE) for the Western African Ebola virus epidemic; Citizens examining the ruins after the Chibok schoolgirls kidnapping; Bundles of wat ...

and the

type species In 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 species that contains the biological type specimen ...

is ''Sisteronia seeleyi''. The generic name honors

Sisteron Sisteron (; , oc, label=Mistralian norm, Sisteroun; from oc, label=Old Occitan, Sestaron) is a commune in the Alpes-de-Haute-Provence department, Provence-Alpes-Côte d'Azur, southeastern France. Sisteron is situated on the banks of the rive ...

, a commune in the

Alpes-de-Haute-Provence Alpes-de-Haute-Provence or sometimes abbreviated as AHP (; oc, Aups d'Auta Provença; ) is a department in the Provence-Alpes-Côte d'Azur region of France, bordering Alpes-Maritimes and Italy to the east, Var to the south, Vaucluse to the west ...

, southeastern France, where relatively complete specimens referable to ''Sisteronia'' were collected, including a partial articulated

skeleton A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...

and at least three additional articulated specimens held in a private collection. The

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

, ''seeleyi'', honors the renowned British

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

Harry Govier Seeley who cataloged thousands fragmentary

specimens from the Cambridge Greensand Member of the Lower Chalk Formation. Now housed in the collections of

Sedgwick Museum of Earth Sciences The Sedgwick Museum of Earth Sciences, is the geology museum of the University of Cambridge , mottoeng = Literal: From here, light and sacred draughts. Non literal: From this place, we gain enlightenment and precious knowledg ...

(CAMSM), the

Royal Belgian Institute of Natural Sciences The Museum of Natural Sciences of Belgium (french: Muséum des sciences naturelles de Belgique, nl, Museum voor Natuurwetenschappen van België) is a museum dedicated to natural history, located in Brussels, Belgium. The museum is a part of t ...

(IRSNB), Hunterian Museum and Art Gallery (GLAHM), Leicester Museum & Art Gallery (LEICT) and Natural History Museum (NHMUK), most of these specimens have never been reassessed thoroughly since Seeley's publication in 1869, and include the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

of ''Sisteronia''. Fischer ''et al.'' (2014) designated CAMSM B58257_67 as the holotype of ''Sisteronia''. It is one of the most complete specimens from the Cambridge Greensand member, representing an incomplete, articulated

, including a partial basicranium (the inferior portion of the

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

), a

scapula 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 eithe ...

, a

humerus The humerus (; ) 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 a roun ...

, and five

centra Centra is a convenience shop chain that operates throughout Ireland. The chain operates as a symbol group owned by Musgrave Group, the food wholesaler, meaning the stores are all owned by individual franchisees. The chain has three different f ...

Description

''Sisteronia'' possesses three autapomorphies, unique traits, that differentiate it from all other currently known

ophthalmosaurids. In ''Sisteronia'', the

basioccipital The basilar part of the occipital bone (also basioccipital) extends forward and upward from the foramen magnum, and presents in front an area more or less quadrilateral in outline. In the young skull this area is rough and uneven, and is joined t ...

possesses a raised process on the floor of

foramen In anatomy and osteology, a foramen (;Entry "foramen"
in

magnum. As observed only in a

juvenile Juvenile may refer to: *Juvenile status, or minor (law), prior to adulthood *Juvenile (organism) *Juvenile (rapper) (born 1975), American rapper * ''Juvenile'' (2000 film), Japanese film * ''Juvenile'' (2017 film) *Juvenile (greyhounds), a greyho ...

specimen of ''"

Platypterygius ''Platypterygius'' is a historically paraphyletic genus of platypterygiine ichthyosaur from the Cretaceous period. It was historically used as a wastebasket taxon, and most species within ''Platypterygius'' likely are undiagnostic at the genus or ...

" australis'', the opisthotic lacks nearly completely a paroccipital process. Mature individuals of ''"P." australis'' lack this condition, unlike mature specimens of ''Sisteronia''. The teeth of ''Sisteronia'' are rectangular in cross-section with small crown and root, the labiolingual length being usually equal to one half of the anteroposterior length. As suggested by its delicate, slender and unworn teeth, ''Sisteronia'' preyed on soft and small prey such as small fishes and neocoleoid

cephalopod A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...

s. ''Sisteronia'' can be also distinguished from other platypterygiines by a combination of characters. Unlike ''

Aegirosaurus ''Aegirosaurus'' is an extinct genus of platypterygiine ophthalmosaurid ichthyosaurs known from the late Jurassic and early Cretaceous of Europe. It was originally named as a species of ''Ichthyosaurus''. Discovery and species Originally describe ...

'' and ''

Sveltonectes insolitus ''Sveltonectes'' (meaning "agile swimmer" in Greek) is an extinct genus of platypterygiine ophthalmosaurid ichthyosaurs known from Ul’yanovsk region, western Russia. Etymology ''Sveltonectes'' was named by Valentin Fischer, Edwige Masure, Ma ...

'', the anterior process of its

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates 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 t ...

is elongated anteriorly, reaching the level of the

nasal bone The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face and by their junction, form the bridge of the upper one third of the nose. Eac ...

. As in ''S. insolitus'', ''Sisteronia'' has prominent opisthotic facets on the basioccipital, and an expanded sacculus impression on the opisthotic, as seen in ''

Acamptonectes ''Acamptonectes'' is a genus of ophthalmosaurid ichthyosaurs, a type of dolphin-like marine reptiles, that lived during the Early Cretaceous around 130 million years ago. The first specimen, a partial adult skeleton, was discovered in Spee ...

'' and mature individuals of ''"P." australis''. ''Sisteronia'' possesses a U-shaped supraoccipital, like ''"P." australis'', ''"P." hercynicus'' and ''"Ophthalmosaurus" natans'', and an anteroposteriorly shortened

quadrate Quadrate may refer to: * Quadrate bone * Quadrate (heraldry) * Quadrate lobe of liver * Quadrate tubercle The quadrate tubercle is a small tubercle found upon the upper part of the femur. It serves as a point of insertion of the quadratus femori ...

condyle as also present in ''

Ophthalmosaurus icenicus ''Ophthalmosaurus'' (meaning "eye lizard" in Greek) is an ichthyosaur of the Jurassic period (165–150 million years ago). Possible remains from the Cretaceous, around 145 million years ago, are also known. It was a relatively medium-sized icht ...

'' and ''S. insolitus''. Finally, the

of ''Sisteronia'' has a facet for a posterior accessory element, as seen in ''"Ophthalmosaurus" monocharactus'', ''"P." hercynicus'', ''"P." americanus'' and ''"P." sp.'' from

Texas Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...

and the

Northwest Territories The Northwest Territories (abbreviated ''NT'' or ''NWT''; french: Territoires du Nord-Ouest, formerly ''North-Western Territory'' and ''North-West Territories'' and namely shortened as ''Northwest Territory'') is a federal territory of Canada. ...

. Fischer ''et al.'' (2013) assigned ''Sisteronia'' to Platypterygiinae as it possesses several

synapomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...

of this

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

and lacks the

ophthalmosaurine Ophthalmosaurinae is an extinct subfamily of ophthalmosaurid thunnosaur ichthyosaurs from the Middle Jurassic to the late Early Cretaceous (Bajocian - Albian) of Europe, North America and South America. Currently, the oldest and the basalmost kno ...

ophthalmosaurids. A yet unpublished phylogenetic analysis reportedly supports this assignment.

Phylogeny

A large

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

analysis performed by Fischer (2013) in his unpublished thesis found ''Sisteronia'' to be a member of Platypterygiinae. Even though variants of this analysis have been formally published, the scorings of ''Sisteronia'' are based mainly on undescribed referred material currently held in a private collection, and therefore the publication of this cladogram is pending. The following cladogram shows a possible phylogenetic position of ''Sisteronia'' in Platypterygiinae according to the analysis performed by Zverkov and Jacobs (2020).

References

{{Taxonbar, from=Q15636066 Early Cretaceous ichthyosaurs Albian life Early Cretaceous reptiles of Europe Cretaceous England Fossils of England Cretaceous France Fossils of France Fossil taxa described in 2014 Ichthyosauromorph genera

Discovery

Description

Phylogeny

See also

References