Rhomaleosauridae is a family of from the Early Jurassic to the latest Middle Jurassic (Hettangian to Callovian stages) of Europe, North America, South America and possibly Asia. Most rhomaleosaurids are known from England, many specifically from lower Blue Lias deposits that date back to the earliest Jurassic, just at the boundary with the Triassic. In fact, to date only two undisputed rhomaleosaurids were named from outside Europe - the closely related Borealonectes russelli and Maresaurus coccai from Canada and Argentina, respectively. These two species are also the only Middle Jurassic representatives of the family.[ Rhomaleosauridae was formally named by Oskar Kuhn in 1961, originally proposed to include Rhomaleosaurus cramptoni and its relatives, which have short necks and large heads relatively to like Elasmosaurus and Plesiosaurus, but longer necks and smaller heads relatively to advanced like Pliosaurus and Kronosaurus.]
Phylogeny
Rhomaleosauridae is a stem-based taxon defined in 2010 (and in earlier studies in a similar manner) as "all taxa more closely related to Meyerasaurus victor than to Leptocleidus superstes, Pliosaurus brachydeirus or Polycotylus latipinnis".[ while other analyses recover Rhomaleosauridae as , to the exclusion of Plesiosauroidea, either as the sister taxon of Pliosauridae or, rarely, as a paraphyletic array of taxa leading to it.][ The following two are simplified after two recent analyses, showing only the relationships within Rhomaleosauridae, and some other relevant basal taxa whose position within the family is highly uncertain.
]
Following Benson et al. (2012):
Following Benson & Druckenmiller (2014), with Macroplata and Eurycleidus excluded, and Borealonectes added:
