Sisteronia Temporal range: Albian ~ | |
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Basicranium of the holotype | |
Scientific classification | |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Reptilia |
Order: | † Ichthyosauria |
Family: | † Ophthalmosauridae |
Subfamily: | † Platypterygiinae |
Genus: | † Sisteronia Fischer et al., 2014 |
Type species | |
†Sisteronia seeleyi Fischer et al., 2014 |
Sisteronia is an extinct genus of platypterygiine ophthalmosaurid ichthyosaur known from the 'middle' Cretaceous of southeastern England and southeastern France. It contains a single species, Sisteronia seeleyi. [1]
Sisteronia was named by Valentin Fischer, Nathalie Bardet, Myette Guiomar and Pascal Godefroit in 2014 and the type species is Sisteronia seeleyi. [1] The generic name honors Sisteron, a commune in the Alpes-de-Haute-Provence, southeastern France, where relatively complete specimens referable to Sisteronia were collected, including a partial articulated skeleton and at least three additional articulated specimens held in a private collection. The specific name, seeleyi, honors the renowned British paleontologist Harry Govier Seeley who cataloged thousands fragmentary ichthyosaur specimens from the Cambridge Greensand Member of the Lower Chalk Formation. Now housed in the collections of Sedgwick Museum of Earth Sciences (CAMSM), the Royal Belgian Institute of Natural Sciences (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 of Sisteronia. [2] [1]
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 skeleton, including a partial basicranium (the inferior portion of the skull), a scapula, a humerus, and five centra. [1]
Sisteronia possesses three autapomorphies, unique traits, that differentiate it from all other currently known platypterygiine ophthalmosaurids. In Sisteronia, the basioccipital possesses a raised process on the floor of foramen magnum. As observed only in a juvenile specimen of "Platypterygius" 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 cephalopods. [1]
Sisteronia can be also distinguished from other platypterygiines by a combination of characters. Unlike Aegirosaurus and Sveltonectes insolitus , the anterior process of its maxilla is elongated anteriorly, reaching the level of the nasal bone. As in S. insolitus, Sisteronia has prominent opisthotic facets on the basioccipital, and an expanded sacculus impression on the opisthotic, as seen in Acamptonectes 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 as also present in Ophthalmosaurus icenicus and S. insolitus. Finally, the humerus of Sisteronia has a facet for a posterior accessory element, as seen in "Ophthalmosaurus" monocharactus, "P." hercynicus, "P." americanus and "P." sp. from Texas and the Northwest Territories. Fischer et al. (2013) assigned Sisteronia to Platypterygiinae as it possesses several synapomorphies of this clade and lacks the synapomorphies of ophthalmosaurine ophthalmosaurids. A yet unpublished phylogenetic analysis reportedly supports this assignment. [1]
A large phylogenetic analysis performed by Fischer (2013) in his unpublished thesis found Sisteronia to be a member of Platypterygiinae. [2] 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. [1]
The following cladogram shows a possible phylogenetic position of Sisteronia in Platypterygiinae according to the analysis performed by Zverkov and Jacobs (2020). [3]
Ophthalmosauria |
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Ophthalmosaurus is an ichthyosaur of the Jurassic period. Possible remains from the Cretaceous, around 145 million years ago, are also known. It was a relatively medium-sized ichthyosaur, measuring 4 m (13 ft) long and weighing 930–950 kg (2,050–2,090 lb). Named for its extremely large eyes, it had a jaw containing many small but robust teeth. Major fossil finds of this genus have been recorded in Europe with a second species possibly being found in North America.
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 species level, or represent distinct genera, even being argued as invalid. While fossils referred to Platypterygius have been found throughout different continents, the holotype specimen was found in Germany.
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.
Caypullisaurus is an extinct genus of platypterygiine ophthalmosaurid ichthyosaur from the Late Jurassic to the Early Cretaceous of Argentina. Its holotype was collected from the Vaca Muerta Formation of Cerro Lotena, Neuquen, dating to the early Tithonian stage of the Late Jurassic, about 150 million years ago. Caypullisaurus was first named by Marta Fernández in 1997 and the type species is Caypullisaurus bonapartei. It was a large ichthyosaur, measuring about 7 m (23 ft) long.
Ophthalmosauridae is an extinct family of thunnosaur ichthyosaurs from the Middle Jurassic to the early Late Cretaceous worldwide. Almost all ichthyosaurs from the Middle Jurassic onwards belong to the family, until the extinction of ichthyosaurs in the early Late Cretaceous. Opthalmosaurids appeared worldwide during early Bajocian, subsequent to the disappearance of most other ichthyosaur lineages after the end of the Toarcian. Currently, the oldest known ophthalmosaurids is Mollesaurus from the early Bajocian of Argentina, as well as indeterminate remains of the same age from Luxembourg and Canada. Named by George H. Baur, in 1887, the family contains the basal taxa like Ophthalmosaurus. Appleby (1956) named the taxon Ophthalmosauria which was followed by some authors, but these two names are often treated as synonyms; Ophthalmosauridae has the priority over Ophthalmosauria. However, some researchers argue that Ophthalmosauridae should be restricted to the group typically referred to as Ophthalmosaurinae, with classic Platypterygiinae instead being referred to as Undorosauridae or Brachypterygiidae and Ophthalmosauria being used to unite these two groups.
Brachypterygius is an extinct genus of platypterygiine ophthalmosaurid ichthyosaur known from the Late Jurassic of England. The type species was originally described and named as Ichthyosaurus extremus by Boulenger in 1904. Brachypterygius was named by Huene in 1922 for the width and shortness of the forepaddle, and the type species is therefore Brachypterygius extremus. The holotype of B. extremus was originally thought to be from the Lias Group of Bath, United Kingdom, but other specimens suggest it more likely came from the Kimmeridgian Kimmeridge Clay of Kimmeridge Bay, Dorset, UK.
Undorosaurus is an extinct genus of ophthalmosaurid ichthyosaur known from western Russia, Svalbard, and Poland.
Mollesaurus is an extinct genus of large ophthalmosaurine ophthalmosaurid ichthyosaur known from northwestern Patagonia of Argentina.
Chacaicosaurus is a genus of neoichthyosaurian ichthyosaur known from the Middle Jurassic of Argentina. The single known specimen of this genus was excavated from the Los Molles Formation in Neuquén Province, and is housed at the Museo Olsacher under the specimen number MOZ 5803. This specimen consists of a skull, forelimb, some vertebrae, and some additional postcranial elements. The genus was named by Marta Fernández in 1994, and contains a single species, Chacaicosaurus cayi, making it the first named distinctive ichthyosaur from the Bajocian stage. It is a medium-sized ichthyosaur with a very long snout, which bears a ridge running along each side. The forelimbs of Chacaicosaurus are small and contain four main digits.
Grendelius is a genus of platypterygiine ophthalmosaurid ichthyosaur from the Late Jurassic (Kimmeridgian-Tithonian) of the UK and European Russia. It was a medium-sized ichthyosaur, measuring 4 m (13 ft) long and weighing 300 kg (660 lb).
Maiaspondylus is an extinct genus of platypterygiine ophthalmosaurid ichthyosaurs known from Northwest Territories of Canada, the Cambridge Greensand of England and the Voronezh Region of Russia.
Simbirskiasaurus is an extinct genus of ichthyosaur from the Early Cretaceous of Ulyanovsk Oblast, Russia. Its type specimen is YKM 65119, a fragmentary skull and vertebral column.
Arthropterygius is a widespread genus of ophthalmosaurid ichthyosaur which existed in Canada, Norway, Russia, and Argentina from the late Jurassic period and possibly to the earliest Cretaceous.
Athabascasaurus is an extinct genus of platypterygiine ophthalmosaurid ichthyosaur known from Alberta, Canada.
Sveltonectes is an extinct genus of platypterygiine ophthalmosaurid ichthyosaurs known from Ul’yanovsk region, western Russia.
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, England, in 1958, but was not formally described until 2012 by Valentin Fischer and colleagues. They also recognised a partial subadult skeleton belonging to the genus from Cremlingen, Germany, and specimens from other localities in England. The genus contains the single species Acamptonectes densus; the generic name means "rigid swimmer" and the specific name means "compact" or "tightly packed".
Platypterygiinae is an extinct subfamily of ophthalmosaurid thunnosaur ichthyosaurs from the early Late Jurassic to the early Late Cretaceous of Asia, Australia, Europe, North America and South America. Currently, the oldest known platypterygiine is Brachypterygius. Platypterygiines were characterized by square tooth roots in cross-section, an extremely reduced extracondylar area of the basioccipital, prominent dorsal and ventral trochanters on humerus and ischiopubis lacking an obturator foramen.
Leninia is an extinct genus of basal ophthalmosaurine ichthyosaur known from the late Early Cretaceous of western Russia. Leninia was first named by Valentin Fischer, Maxim S. Arkhangelsky, Gleb N. Uspensky, Ilya M. Stenshin and Pascal Godefroit in 2013 and the type species is Leninia stellans. It was named for Vladimir Lenin, one of the leaders of the Communist Revolution in Russia, as the museum it is currently housed in is also named for him.
Pervushovisaurus is a genus of platypterygiine ichthyosaur from the Late Cretaceous (Cenomanian) of the Saratov region in western Russia, the La Penthiève Beds of France and the Cambridge area of the UK.
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