The early history of dinosaur discoveries has always fascinated me. I love comparing modern knowledge to what we knew earlier, to see how ideas develop and change over time with new discoveries, and also because it's fun to think about what we might think we know right now that could turn out in the future to be completely wrong. The story of Megalosaurus bucklandii exemplifies this process. Found in Oxfordshire, England, from the middle Jurassic, in 1676 it became the first dinosaur ever discovered, and was known only from a segment of the thigh bone. Thought to be from a Roman war elephant, or possibly a Biblical giant, an illustration of the bone appeared in Robert Plot's Natural History of Oxfordshire. A hundred years later, the Linnean system of scientific nomenclature was in use, and the illustration reappeared in another book, which was attempting to apply the binomial system to rocks - and thus the fossil took on its first official name, Scrotum humanum.
Luckily, Megalosaurus escaped being called that permanently when more bones were discovered in 1827 and the skeleton was officially published in the paleontological literature as the giant iguana-like lizard Megalosaurus bucklandii. Although it is the first dinosaur ever discovered, it remains one of the least well-known, with only portions of the skull, pelvis, one leg, and a few vertebrae and other miscellaneous bones known. Still, that's enough to be able to classify it as a large Tyrannosaur-like theropod - but there's still a lot about its skeleton that we don't actually know for sure.