The strange history of the grand-daddy dinosaur

This image explains how Megalosaurus, a large carnivorous dinosaur that probably looked similar to a T. Rex, almost ended up with the deeply embarrassing taxonomic name of Scrotum humanum.
Joe Hanson at It's Okay To Be Smart has more on the name that would have gotten Megalosaurus beaten up in dinosaur junior high for sure. But there's also some really interesting history surrounding how this particular dinosaur's presumed body shape changed between its discovery in the 18th century and today.
Found at the very early end of the age of dino digging — so early that its fossils were first mistaken for the remains of Roman war elephants — the earliest reconstructions of Megalosaurus are an object lesson in how modern expectations can skew how we see ancient bones. Like Iguanodon, it was originally conceived as a squat, four-footed, lumbering creature — like a cross between a monitor lizard and medieval illustrations of dragons. The depiction worked because the proto-paleontologists of the time didn't have any complete skeleton, had few other dinosaurs to compare Megalosaurus to, and what bones they did have could be configured in any number of ways ... depending on the viewers preconceived biases about what a giant, lizard-esque monster "should" look like. This is one of those Wikipedia entries that's definitely worth reading.