Abstract A complete and well-preserved right ankylosaurian humerus from the Upper
Cretaceous (Santonian) Csehbánya Formation of Iharkút, western Hungary is described
here. Based on its osteological features and 21.5 cm adult length, the new specimen
is markedly different from the slender humerus of Hungarosaurus, the previously known
ankylosaur from the locality, and more similar to that of Struthiosaurus. Thus, the
new Hungarian specimen is tentatively assigned here to cf. Struthiosaurus thereby
dating back the first occurrence of this genus to the Santonian. The new fossil demonstrates
the sympatric co-existence of two different nodosaurid ankylosaurs (a smaller, robust
form with 2–2.5 m total body length and a larger, cursorial form with 4–4.5 m body
length) in the Iharkút fauna. This also suggests that the pattern of the European
ankylosaur diversity was more complex than previously thought.
