''Martinectes'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus of

polycotylid Polycotylidae is a family of plesiosaurs from the Cretaceous, a sister group to Leptocleididae. They are known as false pliosaurs. Polycotylids first appeared during the Albian stage of the Early Cretaceous, before becoming abundant and widesprea ...

plesiosaur from the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

Sharon Springs Formation of the United States. The genus contains a single species ''M. bonneri'', known from multiple skeletons and skulls. ''Martinectes'' was historically considered to represent a species of the genus '' Trinacromerum'' and later '' Dolichorhynchops'' before it was moved to its own genus. It was a large polycotylid measuring around long.

History

Two very large specimens of a polycotylid plesiosaur (KUVP 40001 and 40002) were collected from the Pierre Shale of Wyoming and later reported on by Adams in her 1997 Masters thesis, and in the same year, she officially described the specimens as a new species of ''Trinacromerum'' (''T. bonneri''). The specific name honoured University of Kansas preparator Orville Bonner. Unknown to her at the time, Carpenter (1996) had revised the Polycotylidae and separated ''Dolichorhynchops'' from ''Trinacromerum'', raising the question as to whether or not the specimens represented a separate species or just larger individuals of ''D. osborni''. A study in 2008 found that ''T. bonneri'' is a valid species of ''Dolichorhynchops'', ''D. bonneri''. Carpenter (1996) estimated that KUVP 40001, with a skull measuring long, had a total body length of more than approximately . Everhart (2017) suggested that KUVP 40001 would have measured up to in length. A 2023 study assigns ''D. bonneri'' to a new genus, ''Martinectes''; the name means "

Martin Martin may refer to: Places Antarctica * Martin Peninsula, Marie Byrd Land * Port Martin, Adelie Land * Point Martin, South Orkney Islands Europe * Martin, Croatia, a village * Martin, Slovakia, a city * Martín del Río, Aragón, Spain * M ...

's swimmer".

Classification

Clark, O'Keefe & Slack (2023) recovered ''Martinectes'' as a

member of the plesiosaur clade Leptocleidia, as the

sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

to an unnamed polycotyline from the

Niobrara Formation The Niobrara Formation , also called the Niobrara Chalk, is a geologic formation in North America that was deposited between 87 and 82 million years ago during the Coniacian, Santonian, and Campanian stages of the Late Cretaceous. It is com ...

. This clade, in turn, is sister to ''

Unktaheela ''Unktaheela'' is an extinct genus of polycotylid plesiosaur from the Late Cretaceous Sharon Springs Formation of the United States. The genus contains a single species, ''U. '', known from two partial skeletons. ''Unktaheela'' represents the ...

''. These species, together with '' Dolichorhynchops'' spp. (''D. osborni'' and ''D. herschelensis''), form the clade Dolichorhynchia within the Polycotylinae. The results of their

phylogenetic analyses In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as Computational phylogenetics, phylogenetic inference. It infers the relationship among organ ...

are shown in the

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

below:

References

{{Taxonbar, from=Q123991308 Polycotylidae Late Cretaceous plesiosaurs of North America Sauropterygian genera Fossil taxa described in 2023