| Named By: | Adam S. Smith, Ricardo Araujo & Octavio Mateus in 2011 |
| Time Period: | Early Jurassic, Toarcian |
| Location: | Portugal - Sao Giao Formation |
| Size: | Uncertain due to lack of fossil material |
| Diet: | Piscivore |
| Fossil(s): | Partial skull with articulated mandible (lower jaw) |
| Classification: | | Chordata | Reptilia | Sauropterygia | Plesiosauria | Plesiosauridae | |
Lusonectes (meaning "Portuguese swimmer") is an extinct genus of plesiosaurid from Lower Jurassic (Toarcian stage) deposits of Alhadas, Portugal. It is known from the holotype MG33, a partial skull and articulated mandible. It was found by Henri Emile Sauvage, a French paleontologist, in the 19th century from the Sao Giao Formation, near Murtede, Portugal. It was first named by Adam S. Smith, Ricardo Araujo and Octavio Mateus in 2012 and the type species is Lusonectes sauvagei. The generic name is derived from the prefix Luso meaning "Portuguese" and nectes ("swimmer" in Greek). The specific name honors Henri Emile Sauvage. It is based on a single autapomorphy, a broad triangular parasphenoid cultriform process that is as long as the posterior interpterygoid vacuities, and also on a unique character combination. Cladistic analysis of Jurassic plesiosauroids found Lusonectes to be "microcleidid elasmosaurs", equivalent to the clade Plesiosauridae after Ketchum and Benson, 2010. Lusonectes is the only diagnostic plesiosaur from Portugal to date.