[2][3][4][6] Christian Erich Hermann von Meyer in 1837 named isolated conical, blunt teeth with numerous longitudinal lines from Switzerland, Madrimosaurus hugii.

However, in 1838, realising he had misspelled the name, he emended Madrimosaurus to Machimosaurus, from the Greek machimoi, ancient Egyptian troops deployed during the Ptolemaic Dynasty plus the -saurus suffix, literally meaning "pugnacious lizard".

They hypothesized that Machimosaurus may have been analogous to the Pliocene–Holocene genus Crocodylus in having one large-bodied taxon suited to traversing marine barriers and additional, geographically limited taxa across its range.

The fossilized anterior portion of the lower jaw from the Late Jurassic (Oxfordian or Kimmeridgian) of Ethiopia referred to the pliosaur Simolestes nowackianus, is in fact a large species of Machimosaurus.

[17] Bite marks on an early Kimmeridgian sauropod (Amanzia) femur from Switzerland match teeth known from Machimosaurus hugii, also found in the same deposits.

[8][21] Based on the vertebrae (zygapophysial) articulations, Machimosaurus is considered to have lived in open-seas, swimming by lateral undulations of the tail with the limbs used for steering and balancing.