Gideonmantellia is an extinct genus of basal ornithopod dinosaur known from the Early Cretaceous (Barremian stage) Camarillas Formation of Galve, Province of Teruel, Spain.

[1] In 1982, amateur palaeontologist José María Herrero Marzo together with his son Jesús uncovered in a loam pit near Galve, the Poyales Barranco Canales site, the remains of a small euornithopod.

The specific name honours the late palaeontologist Olga María Amo Sanjuán, who studied the Cretaceous Galve fauna.

More recently, a 2017 study by Madzia et al. describing the genus Burianosaurus found Gideonmantellia to be the most basal ornithopod.

The cladogram is reproduced below:[7] Hypsilophodon Marginocephalia Gideonmantellia Elasmaria Burianosaurus Muttaburrasaurus Rhabdodontidae Tenontosaurus Dryosauridae Camptosaurus Iguanodon Ouranosaurus