Rhomaleosauridae is a family of

plesiosaur The Plesiosauria (; Greek: πλησίος, ''plesios'', meaning "near to" and ''sauros'', meaning "lizard") or plesiosaurs are an order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia. Plesiosaurs first appeared ...

s from the Earliest Jurassic to the latest

Middle Jurassic The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare, but geological formations co ...

(

Hettangian The Hettangian is the earliest age and lowest stage of the Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (My ...

to Callovian stages) of Europe,

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

, 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 ''Borealonectes'' is a genus of rhomaleosaurid pliosauroid, a type of plesiosaur. Its fossils were found in the Callovian-age (Middle Jurassic, about 165-161 million years ago) Hiccles Cove Formation of Melville Island, Canada, one of ...

'' and '' Maresaurus coccai'' from Canada and Argentina, respectively. These two species are also the only

representatives of the family. Rhomaleosauridae was formally named by

Kuhn Kuhn is a surname of German origin. It may refer to the following: * Abraham Kuhn (banker) (1819–1892), German-American founder of Kuhn, Loeb & Co. * Abraham Kuhn (otolarynologist) (1838–1900), Alsatian otolaryngologist * Adam Kuhn (1741–181 ...

in 1961, originally proposed to include '' Rhomaleosaurus cramptoni'' and its relatives, which have short necks and large heads relatively to plesiosauroids like '' Elasmosaurus'' and '' Plesiosaurus'', but longer necks and smaller heads relatively to advanced pliosaurids 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 ''Leptocleidus'' is an extinct genus of plesiosaur, belonging to the family Leptocleididae.Smith AS, Dyke GJ. 2008. The skull of the giant predatory pliosaur ''Rhomaleosaurus cramptoni'': implications for plesiosaur phylogenetics. ''Naturwissensc ...

'', '' Pliosaurus brachydeirus'' or ''

Polycotylus latipinnis ''Polycotylus'' is a genus of plesiosaur within the family Polycotylidae. The type species is ''P. latippinis'' and was named by American paleontologist Edward Drinker Cope in 1869. Eleven other species have been identified. The name means 'muc ...

''". Modern cladistic analyses are divided in the position of Rhomaleosauridae; some recover it at the base of Plesiosauria in a position

basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...

to Neoplesiosauria that contains both the pliosauroids and the plesiosauroids, while other analyses recover Rhomaleosauridae as pliosauroids, to the exclusion of Plesiosauroidea, either as the sister taxon of Pliosauridae or, rarely, as a

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

array of taxa leading to it. Additionally, many putative rhomaleosaurids from the early deposits of Blue Lias, vary greatly in their position across various phylogenetic analyses. Some of these are recovered as

rhomaleosaurids in certain analyses, or alternatively outside Rhomaleosauridae in more basal positions within Plesiosauria. The following two cladograms are simplified after two recent analyses, showing only the relationships within Rhomaleosauridae, and some other relevant

taxa whose position within the family is highly uncertain. Following Benson ''et al.'' (2012): Macrocephalus

Following Benson & Druckenmiller (2014), with ''Macroplata'' and ''Eurycleidus'' excluded, and ''Borealonectes'' added:

References

{{Taxonbar, from=Q144081 Hettangian first appearances Prehistoric reptile families