Lariosaurus balsami (Curioni 1847) Middle Triassic ~ 240 mya, ~80+ cm long, , was derived from a sister to Pachypleurosaurus and was basal to the Eusauropterygia, the clade of the giant plesiosaurs.
Distinct from Pachypleurosaurus, the skull of Lariosaurus was extremely low and long. The nares were dorsally oriented. The postorbital portion of the skull was lengthened and the upper temporal fenestra were enlarged. The teeth were much larger and spread laterally like a rake.
The cervical count was increased to 20, increasing the presacral count to 48. The cervical ribs were reduced to absent. The dorsal ribs enclosed a broad, shallow torso.
The limbs were early in the process of transforming into paddles.
The family tree of the Enaliosauria is here. The complete reptile family tree is here.