Pliosauridae is a family of plesiosaurian marine reptiles from the Earliest Jurassic to the early Late Cretaceous (Hettangian to Turonian stages) of Australia, Europe, North America and South America. Past the Turonian, they may have been replaced by the mosasaurs. It was formally named by Harry G. Seeley in 1874.
|Cast of Attenborosaurus conybeari, Natural History Museum|
|Liopleurodon ferox mounted skeleton, Museum of Paleontology, Tübingen|
Pliosauridae is a stem-based taxon defined in 2010 (and in earlier studies in a similar manner) as "all taxa more closely related to Pliosaurus brachydeirus than to Leptocleidus superstes, Polycotylus latipinnis or Meyerasaurus victor". The family Brachauchenidae has been proposed to include pliosauroids which have very short necks and may include Brachauchenius and Kronosaurus. However, modern cladistic analyses found that this group is actually a subfamily of pliosaurids, and possibly even the "crown group" of Pliosauridae.