01 of 11 Scrotum the Dinosaur, RIP The 19th century was the golden age of dinosaur discovery--but it was also the golden age of over-enthusiastic paleontologists bestowing less-than-successful names on their freshly unearthed fossils. Here are 10 dinosaurs of dubious provenance that you won't see mentioned in many books published after the turn of the 20th century.

02 of 11 Ceratops Triceratops, one species of which was briefly known as Ceratops (Wikimedia Commons). Think about it: we have Diceratops, Triceratops, Tetraceratops (not actually a dinosaur, but an archosaur), and Pentaceratops, so why not plain old Ceratops? Well, that's the name the famous paleontologist Othniel C. Marsh assigned to a pair of fossilized horns discovered in Montana in 1888. Unknown to him, though, that name had already been assigned to a genus of bird, and in any event the remains were too inconclusive to be convincingly attributed to any one dinosaur. The seven named Ceratops species were soon distributed to (among other genera) Triceratops and Monoclonius.

03 of 11 Colossosaurus Pelorosaurus, which was once almost named Colossosaurus (Nobu Tamura). The paleontologists of the early 19th century were flummoxed by the enormous remains of fossilized sauropods--generating sufficient paper to fill a Brachiosaurus backbone. Colossosaurus was the name proposed by Gideon Mantell for a new sauropod that had been (incorrectly, in his eyes) assigned to Cetiosaurus by Richard Owen. Unfortunately, Mantell decided to go with Pelorosaurus ("monstrous lizard") instead, when he found out that the English translation of "colosso" was technically "statue" and not "colossal." In any event, Pelorosaurus is now a nomen dubium, persisting in the paleontology archives but not receiving much respect.

04 of 11 Cryptodraco Ankylosaurus, to which Cryptodraco may have been related (Wikimedia Commons). Remember the movie Crouching Tiger, Hidden Dragon? Well, the latter part of that title is the English translation of Cryptodraco, a 19th-century dinosaur that generated a large amount of controversy based on very few fossil remains. This dinosaur, represented by a single femur, was initially named Cryptosaurus by the paleontologist Harry Seeley, who classified it as a relative of Iguanodon. A few years later, another scientist saw the genus name Cystosaurus in a French encyclopedia, misconstrued it as Cryptosaurus, and renamed Seeley's dinosaur Cryptodraco to avoid any confusion. The effort was unavailing; today Cryptosaurus and Cryptodraco are both considered nomen dubia.

05 of 11 Dinosaurus Brithopus, the therapsid once known as Dinosaurus (Dmitry Bogdanov). Surely, you must think, the regal name Dinosaurus was bestowed on the biggest and most terrifying prehistoric reptile of the early 19th century. Well, think again: the first use of Dinosaurus was actually as a "junior synonym" of an existing genus of small, inoffensive therapsid, Brithopus. About a decade later, in 1856, another paleontologist availed himself of Dinosaurus for a newly discovered genus of prosauropod, D. gresslyi; when he found out this name was "preoccupied" by the therapsid, he settled for Gresslyosaurus ingens. Once again, it was all to no avail: later scientists determined that G. ingens was actually a species of Plateosaurus.

06 of 11 Gigantosaurus A fanciful depiction of Gigantosaurus from a 1914 issue of Scientific American (Wikimedia Commons). Not to be confused with Giganotosaurus, the "giant southern lizard," Gigantosaurus was the name Harry Seeley assigned to a newly discovered sauropod genus in 1869. (Not only that, Seeley's species name, G. megalonyx, referenced the "great clawed" prehistoric ground sloth named by Thomas Jefferson over 50 years earlier.) As you probably guessed, Seeley's choice didn't stick, and was eventually "synonymized" with two other genera that didn't survive the 19th century, Ornithopsis and Pelorosaurus. Decades later, in 1908, the German paleontologist Eberhard Fraas tried to resurrect Gigantosaurus for another genus of sauropod, with comparably useless results.

07 of 11 Laelaps Leaping Laelaps (Charles R. Knight). "Leaping Laelaps!" No, that's not a catch phrase from a 19th-century comic strip, but a famous 1896 watercolor painting by Charles R. Knight, depicting this fearsome dinosaur tussling with another member of the pack. The name Laelaps ("hurricane") honors a canine from Greek mythology that always bagged its quarry, and was bestowed on this newly discovered tyrannosaur in 1866 by the American paleontologist Edward Drinker Cope. Unfortunately, Cope failed to notice that Laelaps had already been assigned to a genus of mite, with the result that this name has vanished from the annals of history, replaced by the less evocative Dryptosaurus.

08 of 11 Mohammadisaurus Mohammadisaurus, the dinosaur now known as Tornieria (Heinrich Harder). As you've probably surmised by now, sauropods have caused more confusion vis-a-vis their nomenclature than any other type of dinosaur. Remember Gigantosaurus, described above? Well, once Eberhard Fraas failed to make that moniker stick for a pair of recently discovered sauropods, the door was open for other paleontologists to fill the gap, with the result that one of these northern African dinosaurs was briefly known as Mohammadisaurus (Mohammad being a common name among the area's Muslim residents, and only indirectly referring to the Muslim prophet). Eventually, both of these names were cast aside for the more prosaic Tornieria, after the German herpetologist (snake expert) Gustav Tornier.

09 of 11 Scrotum Guess what this dinosaur's femur looks like? (Wikimedia Commons). Okay, you can stop laughing now. One of the first dinosaur fossils ever to be described in the modern era was part of a femur bearing a marked resemblance to a pair of human testicles, discovered in a limestone quarry in England in 1676. In 1763, an illustration of this find appeared in a book, accompanied by the species name Scrotum humanum. (At the time, the fossil was believed to belong to a giant prehistoric human, but it's unlikely that the author of the caption actually believed he was looking at a pair of petrified testicles!) It was only in 1824 that this bone was reassigned by Richard Owen to the first identified genus of dinosaur, Megalosaurus.

10 of 11 Trachodon The teeth of Trachodon probably belonged to Lambeosaurus (Wikimedia Commons). The American paleontologist Joseph Leidy had a mixed record when it came to naming new dinosaur genera (though, to be fair, his failure rate wasn't much higher than that of famous contemporaries like Othniel C. Marsh and Edward D. Cope). Leidy came up with the name Trachodon ("rough tooth") to describe some fossilized molars that, later, turned out to belong to a mix of hadrosaur and ceratopsian dinosaurs. Trachodon had a long life in the literature of the 19th century--both Marsh and Lawrence Lambe added separate species--but in the end, the center could not hold and this dubious genus vanished into history. (Leidy had more success with Troodon, "wounding tooth," which has persisted to this day.)