''Sisteronia'' 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 ...

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. Currently, the ...

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 e ...

ichthyosaur Ichthyosauria is an order of large extinct marine reptiles sometimes referred to as "ichthyosaurs", although the term is also used for wider clades in which the order resides. Ichthyosaurians thrived during much of the Mesozoic era; based on fo ...

known from the 'middle' Cretaceous of southeastern

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

and southeastern

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 ...

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

Discovery

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

2014 The year 2014 was marked by the surge of the Western African Ebola epidemic, West African Ebola epidemic, which began in 2013, becoming the List of Ebola outbreaks, most widespread outbreak of the Ebola, Ebola virus in human history, resul ...

and the

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 ...

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

Sisteron Sisteron (; , ; from ) 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 river Durance just after the confluence of the rivers Buëch and Sasse. ...

, a commune in the

Alpes-de-Haute-Provence Alpes-de-Haute-Provence (sometimes abbreviated as AHP; ; ; ), formerly until 1970 known as Basses-Alpes (, ), is a department in the Provence-Alpes-Côte d'Azur region of France, bordering Alpes-Maritimes and Italy to the east, Var to the sou ...

, 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 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 ...

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 as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...

Harry Govier Seeley Harry Govier Seeley (18 February 1839 – 8 January 1909) was a British paleontologist. Early life Seeley was born in London on 18 February 1839, the second son of Richard Hovill Seeley, a goldsmith, and his second wife Mary Govier. When his fa ...

who cataloged thousands fragmentary

specimens from the Cambridge Greensand Member of the

Lower Chalk Formation The Chalk Group (often just called the Chalk) is the lithostratigraphic unit (a certain number of rock strata) which contains the Upper Cretaceous limestone succession in southern and eastern England. The same or similar rock sequences occur acr ...

. 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. It is part of the Department of Earth Sciences and is located on the university's Downing Site in Downing Street, central Cambridge, England. The Sedg ...

(CAMSM), the

Royal Belgian Institute of Natural Sciences The Museum of Natural Sciences (, ; , ) is a Brussels museum dedicated to natural history. It is a part of the Royal Belgian Institute of Natural Sciences (; ), itself part of the institutions of the Belgian Federal Science Policy Office (BELSP ...

(IRSNB),

Hunterian Museum and Art Gallery The Hunterian is a complex of museums located in and operated by the University of Glasgow in Glasgow, Scotland. It is the oldest museum in Scotland. It covers the Hunterian Museum, the Hunterian Art Gallery, the Mackintosh House, the Zoology M ...

(GLAHM),

Leicester Museum & Art Gallery The Leicester Museum & Art Gallery (until 2020, New Walk Museum and Art Gallery) is a museum on New Walk in Leicester, England, not far from the city centre. It opened in 1849 as one of the first public museums in the United Kingdom. Leicest ...

(LEICT) and

Natural History Museum A natural history museum or museum of natural history is a scientific institution with natural history scientific collection, collections that include current and historical records of animals, plants, Fungus, fungi, ecosystems, geology, paleo ...

(NHMUK), most of these specimens have never been reassessed thoroughly since Seeley's publication in 1869, and include 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 ''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, 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 ...

), a

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 ...

, a

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 ...

, 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 individual shops are all owned by individual franchisees. The chain has three ...

Description

''Sisteronia'' possesses three

autapomorphies In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to ...

, 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 ...

possesses a raised process on the floor of

foramen 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, artery, ...

magnum. As observed only in a juvenile 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 Euclidean plane geometry, a rectangle is a rectilinear convex polygon or a quadrilateral with four right angles. It can also be defined as: an equiangular quadrilateral, since equiangular means that all of its angles are equal (360°/4 = 90 ...

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 Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...

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 des ...

'' and '' Sveltonectes insolitus'', the anterior process of its

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 ...

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 Speeton, ...

'' 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

condyle A condyle (;Entry "condyle"
in

as also present in ''

Ophthalmosaurus icenicus ''Ophthalmosaurus'' (Greek ὀφθάλμος ''ophthalmos'' 'eye' and σαῦρος ''sauros'' 'lizard') is a genus of ichthyosaur known from the Middle-Late Jurassic. Possible remains from the earliest Cretaceous, around 145 million years ago, a ...

'' 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 ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...

and the

Northwest Territories The Northwest Territories is a federal Provinces and territories of Canada, territory of Canada. At a land area of approximately and a 2021 census population of 41,070, it is the second-largest and the most populous of Provinces and territorie ...

. 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 ...

of this

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 ...

and lacks the

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

Phylogeny

A large

phylogenetic 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 dat ...

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 A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

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