Steneosaurus obtusidens

"Steneosaurus" obtusidens is a species of teleosaurid thalattosuchian from the Middle Jurassic Callovian of England and France. Like many other teleosaurids from Europe, it has had a convoluted taxonomic history.

"Steneosaurus" obtusidens was first described from the Callovian-aged Oxford Clay Formation of Cambridgeshire, southeastern England on the basis of a partial skeleton (NHMUK R.3168). Characters cited as diagnostic for "S." obtusidens included: short rostrum (preorbital length 52 percent of total skull length); teeth blunt and rounded at the tips; armor adorned with elongate pit ornamentation.

The validity of "Steneosaurus" obtusidens was disputed in a 1987 paper reviewing the type specimens of nominal teleosaurid species from the Oxford Clay. Characters used by Charles William Andrews to distinguish "S." obtusidens from other species were dismissed as variable within specimens of Steneosaurus edwardsi, and "S." obtusidens was sunk as a junior synonym of Steneosaurus durobrivensis (=S. edwardsi). Some authors considered this taxon a probable junior synonym of Machimosaurus hughii based on a subsequently discovered specimen found in Callovian-age exposures in Calvados, Lower Normandy, France, though they stressed that a taxonomic review of blunt-snouted teleosaurids was needed. This synonymy was accepted in a 2009 paper regarding thalattosuchian morphometrics without comment.

In 2013, a new specimen of Machimosaurus was described from Late Jurassic (Kimmeridgian deposits in southern Germany (later named Machimosaurus buffetauti), and it became clear that variation within blunt-toothed teleosaurids was taxonomically significant enough for "Steneosaurus" obtusidens to be recognized as generically distinct from Machimosaurus. Other cladistic and comparative studies agreed with this assessment, recovering "S." obtusidens in a clade with Machimosaurus and Steneosaurus edwardsi. As it stands, "Steneosaurus" obtusidens is clearly related to Machimosaurus, but is generically distinct and in need of a new generic name.