Tatankacephalus is a basal genus of ankylosaurid dinosaur that lived during the Early Cretaceous. Its fossil has been collected from the Cloverly Formation (Aptian-Albian) of central Montana, USA, during 1996, 1997 and 1998, in the region of the Middle Dome in Wheatland County. The type species is T. cooneyorum, described by William L. Parsons and Kirsten Parsons in 2009. The genus name is derived from Oglala tatanka, "bison" and Greek kephale, "head", in reference to the rounded head form. The specific name honours the family of John Patrick Cooney. The holotype is MOR 1073, a partial skull with an estimated total undamaged length of 32 centimetres, lacking the lower jaws. Also some ribs, osteoderms and a tooth have been recovered. The front of the snout is missing. The specimen is that o