For a nothosaur,
Lariosaurus was primitive, possessing a short neck and small flippers in comparison to its relatives. This would have made it a relatively poor swimmer, and it is presumed to have spent much time on dry land, or hunting in shallows. It had a large postorbital region of the
skull with the
temporal fossae noticeably larger than the orbits. The
premaxillary and anterior dentary
teeth are strongly elongated, like fangs, and could have acted as a 'fish trap'. The
parietal and
squamosal bones are elongated into a small occipital crest for the attachment of jaw muscles. The
vertebrae are
pachyostotic and have a low neural spine. Ribs are present from the neck all the way down to the
sacrum, which has a cluster of four or five pairs. There are caudal ribs, but they are very small and not present beyond the 15th caudal vertebra. The gastral ribs are made up of multiple elements and form a sturdy kind of armour. The
humerus has a weakly developed deltapectoral crest, and increases gradually in width towards the distal end. There is a distinct space between the
radius and the more slender
ulna. The fingers have more bones than the toes and clearly show how
Lariosaurus was unique among nothosaurs because its front legs were adapted into paddles, while the back legs remained five-toed. The femur is more lightly built than the humerus but longer. There is less difference between tibia and fibula than between radius and ulna. Further, based on skeletal findings of immature lariosaurs inside the adults,
Lariosaurus is believed by many to be
viviparous, or able to bear live young. Another
Lariosaurus skeleton was found with two juvenile
placodonts of the genus
Cyamodus in its stomach, giving an indication of its diet. In 2014 a skull was found in the Winterswijk Muschekalk quarry, of what appeared to be a new species, that was named
Lariosaurus vosseveldensis. In 2015 it was added to the collection of Museum TwentseWelle in Enschede. It was registered TW.480000504. Also found was an isolated, fused parietal, that was registered TW.4800000505. ==In popular culture==