R is for Regnosaurus
Regnosaurus northamptoni was a stegosaur from the Early Cretacous of England, about 125 million years ago. It may have reached around 4m in length (13ft). Known only from a jaw fragment, it was classfied as various different types of herbivorous dinosaur until finally being confirmed as being a stegosaur in the 1990s. It was probably similar in appearance to the closely-related Chinese Huayangosaurus.
Stegosaurs are a fantastically odd group of dinosaurs. Tiny heads and short front legs, arching backs, long hind legs, a double row of bony plates along the back and spiked tail tips (which bear the wonderful informal anatomical term of “thagomizer”). Stegosaurus itself is obviously the most famous and recognizable — but other stegosaurs possessed plates and spikes along their backs in a variety of shapes and sizes, and many also had large spikes on the shoulders for additional defense.
The exact function of the plates has been debated for many years, with some theories being stranger than others. Although often explained as temperature-regulating structures, the fact that some stegosaurs such as Kentrosaurus had more lower-surface-area spikes than plates suggests that this wasn’t a vital function for them. It’s more likely that the plates served to make the stegosaurs look larger and more intimidating to enemies, and may have been used in sexual display.