How we Almost Lost T. rex

Tyrannosaurus rex is without doubt the world’s most famous dinosaur. It’s the one dinosaur everybody knows, the only species known by its full name and quite possibly the biggest carnivore to ever walk the Earth. To many it represents the ultimate predator. It’s no wonder T. rex is almost guaranteed to appear in any form of dinosaur media. Whether it be books, games and of course films and documentaries like Jurassic Park and Walking with Dinosaurs. It’s crazy to think then that we came very close to losing this icon of the prehistoric world. At least its name…

Figure 1: The “Dynamosaurus imperiosus” mandible at the NHM. Photographed by the author in a Mickey Mouse shirt, 2022.

I came across the source of this problem when I visited the London Natural History Museum (NHM) in 2022. Within its spectacular dinosaur hall is the mandible of a Tyrannosaurus rex discovered all the way back in 1900. Upon reading the little description plaque underneath it I noticed something – it included the name “Dynamosaurus.” Being a dinosaur superfan I instantly knew what I was looking at and I was utterly gobsmacked. I then proceeded to tell my mum what was at least the 50th dinosaur story she had heard in the last hour!

It was discovered by Barnum Brown, hailed as the greatest fossil hunter of his day, while he was hunting for skulls of T. rex’s famous rival Triceratops in Wyoming. In addition to the jaw, it also included some vertebrae, pelvic and limb bones and some scutes (bony plates in the skin like on crocodiles).

Two years later, Brown found another skeleton, this time in Montana, and was astonished by his find. After three years of excavation, he sent both skeletons to palaeontologist (and massive racist) Henry Fairfield Osborn at the American Museum of Natural History. Due to the scutes in the Wyoming skeleton, Osborn thought the two specimens belonged to different species. He named the Montana specimen Tyrannosaurus rex – “Tyrant Lizard King” – and the Wyoming specimen Dynamosaurus imperiosus – “Power Dynamic Lizard” – and published the names and descriptions in the same paper in 1905.

A few months later, Osborn realised his mistake and that the two species were one in the same. The rules of animal nomenclature state that if two names are synonyms, whichever name was published first has priority and becomes that official name. As both Tyrannosaurus and Dynamosaurus were named in the same paper, whichever appeared first would be the proper name. Luckily for us, Tyrannosaurus rex appeared one page before Dynamosaurus imperiosus, so T. rex became the proper name and the rest is history, or rather PRE-history! Had it not been for that page, we wouldn’t have T. rex.

The “Dynamosaurus” specimen was moved to the NHM in 1960 and the mandible now sits in a cabinet in the dinosaur hall for all to see. The scutes likely came from an ankylosaur, heavily armoured plant-eating dinosaurs whose namesake lived alongside T. rex and in this case, may have been the predator’s last meal. The Montana specimen is the holotype of T. rex (the specimen that defines the species) and now stands proudly at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, with the rest of the skeleton reconstructed with other T. rex bones and plaster casts.

The legacy of “Dynamosaurus” lives on however. It was honoured in 2018 when palaeontologists named a new tyrannosaurid species Dynamoterror dynastes.

Class: Reptilia Laurenti, 1768

Clade: Dinosauria Owen, 1842

Clade: Theropoda Marsh, 1881

Family: Tyrannosauridae Osborn, 1905

Genus: Tyrannosaurus Osborn, 1905

Species: T. rex Osborn, 1905

Figure 2. The Montana specimen and holotype of Tyrannosaurus rex at the Carnegie Museum of Natural History. Courtesy of ScottRobertAnselmo.

Jack Lawes is currently a student on the MA Museum Studies program at the University of Leicester.