Syngonosaurus is an extinct genus of ornithopod dinosaur from the Early Cretaceous. It was an iguanodontian discovered in the Cambridge Greensand of England[1] and was first described in 1879. 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.[3]
In 1869 Harry Govier Seeley named several new species of Acanthopholis based on remains from the Cambridge Greensand, including A. macrocercus, based on specimens CAMSM B55570-55609.[4]
In 1879 Seeley named the genus Syngonosaurus based on part of the type material of Acanthopholis macrocercus.
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.[5]
Syngonosaurus was synonymised with Acanthopholis in 1999, but the genus was reinstated in a 2020 study, when Syngonosaurus and Eucercosaurus were reinterpreted as basal iguanodontians.
Syngonosaurus was seen as an ankylosaur in both a 2001 publication and a 2004 publication.[6] In 2020, Syngonosaurus was classified into Iguanodontia.