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The head and neck of "Gordo" the Barosaurus on display at the Royal Ontario Museum. From Wikipedia.

Stretching 90 feet long in life, Barosaurus was one of the largest of all dinosaurs. Despite its size, however, this sauropod was able to hide in the collections of the Royal Ontario Museum for over four decades.

Barosaurus were rare dinosaurs. One of the few skeletons ever found was uncovered by paleontologist Earl Douglass during his excavations of Utah’s Dinosaur National Monument in the early 20th century. As with many specimens from this site, the bones were sent to Pittsburgh’s Carnegie Museum of Natural History, but in 1962 they were traded to the ROM in Toronto, Canada.

The skeleton was thought at the time to be a Dipolodocus—which it does resemble, albeit with a proportionally longer neck and shorter tail. The ROM intended to include it in a revamped dinosaur exhibit set to debut in 1970, but the skeleton was left in storage due to a lack of floorspace. The sauropod expert Jack McIntosh later recognized the bones as belonging to Barosaurus, but after this point the skeleton simply sat in museum storage, effectively forgotten.

The bones were finally dusted off in 2007. With the ROM planning to open a new dinosaur hall, the museum assigned paleontologist David Evans, their new Associate Curator of Vertebrate Palaeontology, to find a sauropod skeleton for the exhibit. Evans investigated numerous options, from using a cast to finding a new specimen, and while searching for dinosaurs in Wyoming he came across McIntosh’s reference to a Barosaurus at the ROM. Evans immediately flew back to Toronto, and after a bit of searching he discovered the dinosaur’s lost skeleton. While not entirely complete, the dinosaur was represented by both femurs, both upper-arm bones, four neck vertebrae, the complete set of back vertebrae, fourteen tail vertebrae and other assorted parts.

Finding the skeleton was only the first challenge. The second was putting it all together in time for the opening of the new dinosaur hall. Evans had only eight weeks to do so, and this included creating casts of all the missing parts. The team of paleontologists and reconstruction experts was able to pull it off, though, and today the Barosaurus—nicknamed “Gordo”—looms over the ROM’s dinosaur hall. It was recently featured on the miniseries Museum Secrets, and the show’s web site includes several video clips about the behind-the-scenes work put into Gordo’s assembly.