Hadrosaurus foulkii was the first dinosaur known outside Europe from partially complete skeletal elements. It is the holotype of the family Hadrosauridae and the subfamily Hadrosaurinae. The history of its discovery and taxonomy is reviewed, and the holotype of H. foulkii is redescribed. The holotype of H. foulkii lacks distinguishing characters; therefore, this taxon is a nomen dubium. It is not synonymous with species of Gryposaurus and/or Kritosaurus. We also reevaluate the taxonomy and osteology of H. tripos, H. minor, H. cavatus, H. breviceps, H. paucidens, and Ornithotarsus immanis. In agreement with previous studies, these taxa are considered nomina dubia due to the absence of distinguishing characters and are therefore referrable only to Hadrosauridae indeterminate; H. paucidens is referrable to Lambeosaurinae indeterminate. Finally, our phylogenetic analysis indicates that the holotype of H. foulkii belongs to a member of Euhadrosauria and, tentatively, of Hadrosaurinae.

Key words: Hadrosauridae, Cretaceous, East Coast, North America, phylogeny.

Albert Prieto-Márquez amarquez@bio.fsu.edu, Department of Biological Science, Florida State University, Tallahassee, Florida, 32306-1100, U.S.A.; David B. Weishampel dweisham@mail.jhmi.edu, Center for Functional Anatomy and Evolution, Johns Hopkins University, School of Medicine, Baltimore, Maryland 21205, U.S.A.; John R. Horner jhorner@montana.edu, Museum of the Rockies, Montana State University, Bozeman, Montana 59717, U.S.A.