International Code of Zoological Nomenclature and the Principle of Priority
Did you know that the famous genus name "Tyrannosaurus" was once in danger of disappearing?
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The standard for determining the scientific names of animals is set by the International Code of Zoological Nomenclature. The naming of animals is based on the principle of priority. In other words, "first come, first served" in publishing a paper and naming a species.
It is a well-known 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." (Although a new theory was proposed in 2015 regarding the genus names of Brontosaurus and Apatosaurus, the debate seems likely to continue. There is opposition to the 2015 paper that argued they should be separate genera.)
The Naming of Tyrannosaurus
This is the fossil featured when Osborn named it.
Tyrannosaurus was named in a 1905 paper by Osborn. It was based on a study of a fossil discovered in Montana, USA, in 1902. "Tyrant Lizard" - Tyrannosaurus is one of the most famous dinosaurs.
The Crisis of the Name's Disappearance
The crisis for the name "Tyrannosaurus" arrived in June 2000.
In that year, a Tyrannosaurus fossil was excavated in South Dakota, USA, but surprisingly, it was discovered to be the same individual as one excavated and described in a paper in 1892 as Manospondylus. This showed that Tyrannosaurus and Manospondylus were the same genus.
Since Tyrannosaurus was named in a paper in 1905, the priority for the name belongs to Manospondylus, described in 1892. A debate arose over a name change, suggesting that "the genus name Tyrannosaurus would become invalid, and Manospondylus would become the valid name."
If that had happened, all published dinosaur encyclopedias would have needed to be replaced. After all, there's no dinosaur encyclopedia without Tyrannosaurus...
What Saved the Name "Tyrannosaurus"
What saved the name "Tyrannosaurus" was the intervention of the International Commission on Zoological Nomenclature.
Strict application of the principle (priority of scientific names) can sometimes lead to a well-accepted scientific name being replaced by an unknown one. To avoid such inconvenience, an exception (overruling priority) is allowed only when recognized by the International Commission on Zoological Nomenclature.
The Commission used its authority to conserve the genus name "Tyrannosaurus" under a provision for exceptions established in the "International Code of Zoological Nomenclature, Fourth Edition," published just six months earlier in January 2000. (The timing makes it seem as if this exception was created specifically to preserve the name Tyrannosaurus.)
Thanks to the application of this exception, the name "Tyrannosaurus" continues to be used.