Thalattosuchia is a clade of mostly marine crocodylomorphs from the Early Jurassic to the Early Cretaceous that had a cosmopolitan distribution. They are colloquially referred to as marine crocodiles or sea crocodiles, though they are not members of Crocodilia and records from Thailand and China suggest that some members lived in freshwater. The clade contains two major subgroupings, the Teleosauroidea and Metriorhynchoidea. Teleosauroids are not greatly specialised for oceanic life, with back osteoderms similar to other crocodyliformes. Within Metriorhynchoidea, the Metriorhynchidae displayed extreme adaptions for life in the open ocean, including the transformation of limbs into flippers, the development of a tail fluke, and smooth, scaleless skin, and probably gave live birth, seemingly uniquely among archosaurs.
Teleosauridae is a family of extinct typically marine crocodylomorphs similar to the modern gharial that lived during the Jurassic period. Teleosaurids were thalattosuchians closely related to the fully aquatic metriorhynchoids, but were less adapted to an open-ocean, pelagic lifestyle. The family was originally coined to include all the semi-aquatic thalattosuchians and was equivalent to the modern superfamily Teleosauroidea. However, as teleosauroid relationships and diversity was better studied in the 21st century, the division of teleosauroids into two distinct evolutionary lineages led to the establishment of Teleosauridae as a more restrictive family within the group, together with its sister family Machimosauridae.
Pelagosaurus is an extinct genus of thalattosuchian crocodyliform that lived during the Toarcian stage of the Lower Jurassic, around 183 Ma to 176 Ma, in shallow epicontinental seas that covered much of what is now Western Europe. The systematic taxonomy of Pelagosaurus has been fiercely disputed over the years, and was assigned to Thalattosuchia after its systematics within Teleosauridae were disputed. Pelagosaurus measured 2–3 m (6.6–9.8 ft) long.
Steneosaurus is a dubious genus of teleosaurid crocodyliform from the Middle or Late Jurassic of France. The genus has been used as a wastebasket taxon for thalattosuchian fossils for over two centuries, and almost all known historical species of teleosauroid have been included within it at one point. The genus has remained a wastebasket, with numerous species still included under the label ‘Steneosaurus’, many of which are unrelated to each other.
Aeolodon is an extinct genus of teleosaurid crocodyliform reptile from the Late Jurassic (Tithonian) of Germany and France that was initially named as a species of Crocodylus in 1814. Although previously synonymized with Steneosaurus, recent cladistic analysis considers it distantly related to the Steneosaurus type species and the type species is A. priscus, named in 1830 and described in 2020.
Mycterosuchus is an extinct genus of teleosaurid crocodyliform from the Middle Jurassic (Callovian) of England. Although previously synonymized with Steneosaurus, recent cladistic analysis considers it distantly related to the Steneosaurus type species.
Sericodon is an extinct genus of teleosaurid crocodyliform from the Late Jurassic (Tithonian) of Germany and Switzerland. The genus contains a single species, S. jugleri. Sericodon was placed in 'Clade T' (Aeolodontinae) and was found to be the sister taxon to Bathysuchus, another teleosaurid.
The Calcaire de Caen or Calcaires de Caen Formation; French for Caen Limestone, is a geological formation in France. It dates back to the mid-Bathonian of the Jurassic. It was often quarried for building work and is referred to as Caen Stone.
Metriorhynchoidea is an extinct superfamily of thalattosuchian crocodyliforms from the Early Jurassic to the Early Cretaceous of Europe, North America and South America. Metriorhynchids are fully aquatic crocodyliforms. Named by Fitzinger, in 1843, it contains the basal taxa like Teleidosaurus, Zoneait and Eoneustes and the family Metriorhynchidae. An unnamed taxon is known from Chile.
Bathysuchus is an extinct genus of teleosaurid thalattosuchian from Late Jurassic (Kimmeridgian) deep water marine deposits in England and France. Bathysuchus displays features that suggest it was more pelagic than other teleosaurids, including smoother skull bones and reduced armour plating, similar to the fully marine metriorhynchids. This was possibly an adaptation to rising sea levels during the Kimmeridgian, as its earlier relatives such as Teleosaurus were suited for shallow coasts and lagoon environments.
Lemmysuchus is a genus of machimosaurid thalattosuchian from the Middle Jurassic Callovian of England and France. Like many other teleosauroids from Europe, it has had a convoluted taxonomic history.
Teleosauroidea is an extinct superfamily of thalattosuchian crocodyliforms living from the Early Jurassic to the Early Cretaceous. It is phylogenetically defined by Mark T. Young and colleagues in 2024 in the PhyloCode as "the largest clade within Thalatttosuchia containing Teleosaurus cadomensis, but not Metriorhynchus brevirostris". This group contains two main families, the more piscivorous and gracile Teleosauridae and the more macropredatory and robust Machimosauridae.
Plagiophthalmosuchus is a genus of teleosauroid, known form the Early Jurassic Whitby Mudstone Formation of Whitby, Yorkshire, UK, and Dudelange, Luxembourg. The type species, P. gracilirostris, was originally named as a species of Teleosaurus in 1836, but then it was moved to Steneosaurus in 1961, but it was again moved to its own genus in 2020.
Neosteneosaurus is a genus of machimosaurid, known from the Middle Jurassic Oxford Clay of the UK, and Marnes de Dives, France. The type species, N. edwardsi, was originally named as a species of Steneosaurus in 1868, but was moved to its own genus in 2020. Steneosaurus durobrivensis and Steneosaurus hulkei are considered junior synonyms.
Machimosauridae is an extinct family of teleosauroid thalattosuchian crocodyliforms. The family was first identified in 2016, when fossils of teleosauroid thalattosuchians, including an indeterminate close relative of Lemmysuchus and Machimosaurus, were described from the Middle Jurassic (Bathonian) of Morocco. The family was largely expanded in 2020 when the systematics of Teleosauroidea were re-reviewed. Members of this family generally were larger than the teleosaurids.
Andrianavoay is an extinct genus of teleosauroid from the Bathonian, probably from the Isalo III Formation of Madagascar.
Charitomenosuchus is an extinct genus of machimosaurid teleosauroid from the Callovian Oxford Clay Formation of England.
Clovesuurdameredeor is an extinct genus of machimosaurid teleosauroid from the Bathonian Cornbrash Formation of England.
Proexochokefalos is an extinct genus of machimosaurid teleosauroid from the Jurassic of France
Seldsienean in an extinct genus of machimosaurid thalattosuchian from the Middle Jurassic of England and France. It is known from the Calcaire de Caen and the Cornbrash Formation.
