The Crisis of the Disappearance of the Name "Tyrannosaurus"

International Code of Zoological Nomenclature and Priority

Did you know that the famous genus name "Tyrannosaurus" was once at risk of disappearing?

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The rules for determining the scientific names of animals are established by the International Code of Zoological Nomenclature. The naming of animals is based on the principle of priority. In other words, "the first to publish a paper and name it wins."

It is a famous story that the dinosaur called [Brontosaurus (named in 1879)] was found to be the same genus as the previously named [Apatosaurus (named in 1877)], making "Apatosaurus" the valid name and invalidating the scientific name "Brontosaurus". (A new theory regarding the genus names of Brontosaurus and Apatosaurus was proposed in 2015, but it seems the debate will continue. There are opposing opinions to the 2015 paper that argued they should be considered separate genera.)

The Naming of Tyrannosaurus and the First Crisis

Tyrannosaurus, meaning "tyrant lizard," was named in a 1905 paper described by paleontologist Henry Fairfield Osborn. It investigated fossils discovered in Montana, USA, in 1902.

Tyrannosaurus faced its first "crisis of name disappearance" at the time of its naming. In the same 1905 paper, Osborn had also given the name "Dynamosaurus imperiosus" to another fossil specimen.
The following year, Osborn himself realized that "these two fossils belong to the same dinosaur" and decided to unify the scientific names.

At this time, because the description of "Tyrannosaurus" appeared a few pages earlier in the paper (page priority), Tyrannosaurus remained as the valid name, and the name Dynamosaurus disappeared. If the order of description had been reversed, we might be calling this most famous dinosaur "Dynamosaurus" today.

The First Fossil Discovery: "Manospondylus"

Time passed, and in June 2000, the greatest crisis that would shake the name of Tyrannosaurus arrived.

Let's turn back the clock. In 1892, 13 years before Tyrannosaurus was named, prominent paleontologist Edward Drinker Cope had named a dinosaur fossil excavated in South Dakota "Manospondylus gigas".
However, the fossil Cope discovered at the time consisted of "only two incomplete vertebrae (backbones)". Because there were so few fossils, it was not accurately known for many years what kind of dinosaur this was.

The Rediscovery in 2000 and the Second Crisis of Name Disappearance

In 2000, Peter Larson and his team from the Black Hills Institute of Geological Research in South Dakota (a team world-famous for excavating the Tyrannosaurus "Sue") re-identified the exact location (type locality) where Cope had excavated over 100 years earlier and conducted additional excavations.

As a result, an astonishing fact was revealed. From that location, many remaining bones, including parts clearly identifiable as Tyrannosaurus, were discovered. They were bones from the same individual as the "Manospondylus" excavated in 1892. This showed that Manospondylus and Tyrannosaurus belong to the same genus.

Now, according to the principle of priority regarding scientific names, the priority of the name belongs to "Manospondylus" described in 1892. A huge controversy arose in the paleontology community, with concerns that "the genus name of Tyrannosaurus will become invalid, and Manospondylus will become the valid name."
If that were to happen, all published dinosaur encyclopedias would have to be replaced. After all, there is no dinosaur encyclopedia that doesn't feature the popular Tyrannosaurus. Also, it was inevitable that this would cause great confusion in natural history museums, educational settings, and places dealing with paleontology worldwide.

The "Exceptional Measure" That Saved Tyrannosaurus

What saved the name "Tyrannosaurus" was an exceptional measure based on the strict rules set by the International Code of Zoological Nomenclature.

If the priority of scientific names is strictly applied, a widely accepted scientific name could be replaced by a completely unknown name. Since this would result in a massive loss of convenience in scientific communication, an exceptional measure called "Reversal of Precedence" (invocation of sweeping powers) is allowed only when certain conditions are met.

Coincidentally, just half a year before the uproar, the "International Code of Zoological Nomenclature, 4th Edition (Article 23.9)," which came into effect in January 2000, clearly stated the specific conditions for applying this exceptional measure as follows:

• Nomen oblitum (Forgotten name): The older name (Manospondylus) has not been used as a valid scientific name since 1899.
• Nomen protectum (Protected name): The newer name (Tyrannosaurus) has been established and used as a valid scientific name in "at least 25 publications, published by at least 10 authors" over the immediately preceding 50 years.

Tyrannosaurus met these strict conditions. As a result of this rule being applied, the older "Manospondylus" was rejected as a nomen oblitum, and "Tyrannosaurus" was officially protected as a nomen protectum.

It almost feels as if the provision of this exceptional measure itself was set up with perfect timing to protect the scientific name of the world's most famous dinosaur. Thus, the name "Tyrannosaurus" will continue to remain in our encyclopedias from now on.