I. hollingtoniensis ( also spelled I. hollingtonensis ) , described by Lydekker in 1889 have variously been considered a synonym of Hypselospinus fittoni or a distinct species assigned to the genus Huxleysaurus . A specimen from the Valanginian Wadhurst Clay Formation , variously assigned to I. hollingtoniensis and I. mantelli over the years , have an unusual combination of hadrosaurid @-@ like lower jaw and very robust forelimb ; Norman ( 2010 ) assigned this specimen to the species Hypselospinus fittoni , while Paul ( 2012 ) made it the holotype of a separate species Darwinsaurus evolutionis .