Steneosaurus


Steneosaurus is a dubious genus of teleosaurid crocodyliform from the Middle or Late Jurassic of France and possibly also India. 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.

Discovery and assigned species

The type species, S. rostromajor, was only formally recognised as such in 2020, and this revision determined the type specimen of Steneosaurus was undiagnostic, and so declared the genus Steneosaurus a nomen dubium. The history of this specimen has been detailed in 2017. It was discovered in three pieces by abbot Charles Bacheley in the Vaches Noires near Villers-sur-Mer. Bacheley offered these pieces to Alexandre Besson who had built up an important cabinet of fossils and minerals in Paris. Besson gave one of the pieces to Barthélémy Faujas de Saint-Fond, professor of geology in the Muséum national d'Histoire naturelle, Paris. Georges Cuvier first illustrated in 1808 the two anterior pieces of the specimen kept in the Besson collection and then figured the third piece in 1824 in association with the anterior pieces and other cranial remains belonging to Metriorhynchidae.
The skulls of two marine crocodiles were found in the Chari Formation, India and have been putatively identified as Steneosaurus by Phansalkar et al..
The remaining species referred to Steneosaurus thus require new generic names, and some species have already been assigned to new genera prior to Steneosaurus being declared a nomen dubium.
Species in this genus are traditionally classed into two skull groups: longirostrine and mesorostrine.
;Longirostrine
  • S.' atelestatus - Oxfordian Marnes de Villers of France
  • S.' blumembachi - Oxfordian Marnes de Villers of France
  • S.' oplites - Toarcian La Caine-Curcy of France
  • S.' rudis - France

    Reassigned species

  • Steneosaurus' baroni = Andrianavoay
  • Steneosaurus' bollensis = Macrospondylus
  • S.' bouchardi - = Proexochokefalos
  • Steneosaurus' boutilieri = Yvridiosuchus
  • Steneosaurus' brevior = Mystriosaurus
  • Steneosaurus' deslongchampsianus
  • Steneosaurus' edwardsi = Neosteneosaurus
  • Steneosaurus' gracilirostris = Plagiophthalmosuchus
  • Steneosaurus' heberti = Proexochokefalos
  • Steneosaurus' larteti = Deslongchampsina
  • Steneosaurus' leedsi = Charitomenosuchus
  • Steneosaurus' megarhinus = Bathysuchus
  • Steneosaurus' megistorhynchus = Seldsienean
  • Steneosaurus' obtusidens = ''Lemmysuchus''

    Classification

A 2005 phylogenetic analysis into the evolutionary relationships of Thalattosuchia did not support the monophyly of Steneosaurus, as the genera Machimosaurus and Teleosaurus both fell within Steneosaurus. Reinforcing the paraphyly of Steneosaurus, the Callovian species "Steneosaurus" obtusidens has been recovered as the sister species of Machimosaurus in recent cladistic analyses of Thalattosuchia and renamed Lemmysuchus, while 'Steneosaurus' bollensis was recovered in a basal position to other members of Steneosaurus sensu lato.