Tuesday, June 5, 2012

The Smallest (Mesozoic) Theropods

The online community of paleontology fans seems to have an unnatural preoccupation with size. Visit any dino-related message board, and you will find near-daily debates over which carnivorous theropod was bigger (or more specifically, longer). Carcharodontosaurus? Giganotosaurus? Tyrannosaurus? Hint: if the length estimates are within a meter of each other, the weight estimates vary widely, and the beasts in question are known only from one or two fragmentary skeletons, the correct answer is "eh, they're all about the same size, give or take." Also, Therizinosaurus and Deinocheirus, being wimpy herbivores, definitely do not count.
Size comparison of select small non-pygostylian theropods.
From left: Palaeopteryx thompsoni, "Ornithomimus" minutus,
Parvicursor remotus, Epidexipteryx hui.
By Matt Martyniuk, licensed.
Less often, you may come across a discussion about which dinosaur was the smallest. These usually are not the heated debates you find with the mega-carnivores, but rather casual examination of minutiae and bringing up oft-forgotten species. Yes, everybody knows Compsognathus. But did you know the "chicken-sized" type specimen is a subadult or juvenile, and the referred French specimen is much larger? And anyway, Parvicursor was daintier by far. At 34cm (13in) long, Anchiornis was hailed as the smallest dinosaur when it was initially described, but subsequent specimens were larger (up to half a meter in length; still smaller than Compsognathus and slightly shorter than the ~40cm Parvicursor). Epidexipteryx, at a stubby, tail-free 25cm (10in) in length, was the shortest of them all, but its lack of a long tail means that it was a bit larger than the competition in mass. And anyway, isn't Epidexipteryx a bird?