Thalattosaurus alexandrae (Merriam 1904, 1905) Late Triassic ~210 mya, ~2 m in length, was a thalattosauriform related derived from a sister to Endennasaurus. Clarazia was a sister taxon and both represent the last taxa in this lineage

Distinct from Clarazia, the skull of Thalattosaurus had a longer, down-curled rostrum and a reduced postorbital region. The naris was raised closer to the top of the skull. The maxilla was longer. The upper temporal fenestrae were mere slits. The squamosal was a vestige. The jugal and postorbital were reduced. The prefrontal produced a lateral 'brow.' The lateral temporal fenestra is narrower than the orbit. The mandible was straight.

The post-crania has not been well documented, but the humerus and femur both appear shorter and more robust.

A complete tree of the Reptilia is here.

Thalattosaurs (Thalattosauria) to scale.

Wachtlerosaurus ladinicus (Perner 2018; Middle Triassic) was originally considered an archosaur, but a reconstruction nests it wit Thalattosaurus in the LRT. Perner 2018 identifies two long, parallel dorsal ribs surrounding a jumble of ?vertebrae as parts of an oversized pelvis. Perner employs the humerus in place of a scapula. Probably this scattered bone specimen is incomplete, not nearly complete, as described.

Merriam JC 1904. A new marine reptile from the Triassic of California. University of California Publications, Bulletin of the Department of Geology, 3, 419–421.

Merriam JC 1905. The Thalattosauria, a group of marine reptiles from the Triassic of California. Memoirs of the California Academy of Sciences, 5, 52 pp.

Nicholls EL 1999. A reexamination of Thalattosaurus and Nectosaurus and the relationships of the Thalattosauria (Reptilia, Diapsida). Paleobios 19:1–29.

Perner T 2018. A new interesting archosaur from the Ladinian (Middle Triassic) of the Dolomites (Northern Italy) Preliminary report. Pp 1–8 in Some new and exciting Triassic Archosauria from the Dolomites (Northern Italy). Perner T and Wachtler M eds. Dolomythos-Museum, Oregon Institute of Geological Research.

wiki/Thalattosaurus