Osmakasaurus (meaning "canyon lizard", ósmaka meaning "canyon" in the Lakota language) is a genus of herbivorous iguanodontian dinosaur.

It is a basal iguanodontian which lived during the Early Cretaceous period (Valanginian age) in what is now Buffalo Gap of South Dakota, United States.

This genus was named by Andrew T. McDonald in 2011 and the type species is O.

[1] The holotype, USNM 4753, was discovered by Nelson Horatio Darton in 1896 within a layer of the Lakota Formation.

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