Martinectes

Martinectes is an extinct genus of polycotylid plesiosaur from the Late Cretaceous 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 6 - 7 m 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 1977 Masters thesis, and in the same year, she officially described the specimens as a new species of Trinacromerum (T. bonneri). 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 98 cm long, had a total body length of more than approximately 5.1 m. Everhart (2017) suggested that KUVP 40001 would have measured up to 6 - 7 m in length. A 2023 study assigns D. bonneri to a new genus, Martinectes; the name means "Martin's swimmer".

Classification
Clark, O'Keefe & Slack (2023) recovered Martinectes as a polycotylid member of the plesiosaur clade Leptocleidia, as the sister taxon to an unnamed polycotyline from the Niobrara Formation. This clade, in turn, is sister to Unktaheela. These species, together with Dolichorhynchops spp. (D. osborni and D. herschelensis), form the clade Dolichorhynchia within the Polycotylinae. The results of their phylogenetic analyses are shown in the cladogram below: