How these prehistoric animals compare
Ankylosaurus and Stegosaurus were both armored plant-eating dinosaurs, but they belong to different branches of Thyreophora and lived in different geological periods.
Two different armor designs
Stegosaurus carried a double row of upright plates along its back and spikes on its tail. Ankylosaurus was covered by bony plates embedded in the skin and ended in a heavy tail club. The shared label of armored dinosaur hides very different body plans.
Tens of millions of years apart
Stegosaurus belongs to the Late Jurassic of western North America. Ankylosaurus comes from the very end of the Cretaceous, also in North America. They were never contemporaries, and the Jurassic and Cretaceous settings were different.
Why the evidence is uneven
Stegosaurus is known from several fairly complete skeletons. Ankylosaurus is known from fewer specimens, so some details of its armor and club are reconstructed from relatives. Purpose of the plates and clubs, such as display or defense, remains an interpretation.
Sources and specimen context: Ankylosaurus references · Stegosaurus references · Geological timeline
