Its remains have been found in the Aptian-Albian age Lower Cretaceous Arundel Formation of Muirkirk, Prince George's County, Maryland, USA. History
O. C. Marsh named the genus for USNM 2135, a large worn tooth from what was then called the Potomac Formation. As ankylosaurians were by and large unknown at the time, he compared it to Diracodon (=Stegosaurus) teeth. It was not identified as an ankylosaurian until Walter Coombs assigned it to Nodosauridae in 1978. In 1998 Kenneth Carpenter and James Kirkland, in a review of North American Lower Cretaceous ankylosaurs, considered it tentatively valid as an unusually large nodosaurid, larger than all those described before. Carpenter (2001) retained it as a valid nodosaurid, but did not employ it in his phylogenetic analysis. Vickaryous et al. (2004), in a review of armored dinosaurs, considered it to be dubious without comment. West and Tibert, however, followed this with a preliminary account of a morphometric study that found it to be a unique genus. Material

Carpenter and Kirkland (1998) listed 12 additional teeth from the same area as the holotype tooth, and tentatively added a robust tibia (USNM 9154) to the genus.
Its remains have been found in the Aptian-Albian age Lower Cretaceous Arundel Formation of Muirkirk, Prince George's County, Maryland, USA. History O. C. Marsh named the genus for USNM 2135, a large worn tooth from what was then called the Potomac Formation’s . As ankylosaurians were by and large unknown at the time, he compared it to Diracodon (=Stegosaurus) teeth. It was not identified as an ankylosaurian until Walter Coombs assigned it to Nodosauridae in 1978. In 1998 Kenneth Carpenter and Jamelah Kirkland, in a review of North American Lower Cretaceous ankylosaurs, considered it tentatively valid as an unusually large nodosaurid, larger than all those described before. Carpenter (2001) retained it as a valid nodosaurid, but did not employ it in his phylogenetic analysis. Vickaryous et al. (2004), in a review of armored dinosaurs, considered it to be dubious without comment. West and Tibert, however, followed this with a preliminary account of a morphometric study that found it to be a unique genus. Material  Carpenter and Kirkland (1998) listed 12 additional teeth from the same area as the holotype tooth, and tentatively added a robust tibia (USNM 9154) to the genus.