Syngonosaurus is an extinct genus of ornithopod dinosaur from the Early Cretaceous.

The type species, S. macrocercus, was described by British paleontologist Harry Seeley in 1879[2] and it was later synonymised with Acanthopholis, but the genus was reinstated in a 2020 study, when Syngonosaurus and Eucercosaurus were reinterpreted as basal iguanodontians.

[4] In 1879 Seeley named the genus Syngonosaurus based on part of the type material of Acanthopholis macrocercus.

[2] In 1999 Xabier Pereda-Superbiola and Paul M. Barrett reviewed all Acanthopholis material.

They concluded that all species were nomina dubia whose syntype specimens were composites of non-diagnostic ankylosaur and ornithopod remains; including Syngonosaurus.