Nomen oblitum


In zoological nomenclature, a nomen oblitum is a disused scientific name which has been declared to be obsolete in favor of another "protected" name.
In its present meaning, the nomen oblitum came into being with the fourth edition of the International Code of Zoological Nomenclature. After 1 January 2000, a scientific name may be formally declared to be a nomen oblitum when it satisfies the following conditions:
  1. No uses as a valid name in a scientific publication are known after 1899.
  2. It is either a senior synonym or a senior homonym.
  3. The preferred junior synonym or homonym is shown to be in wide use, defined as appearing in 25 or more publications in the past 50 years and by at least 10 distinct individual authors.
Once a name has formally been declared to be a nomen oblitum, the now obsolete name is to be "forgotten". By the same act, the other available name must be declared to be protected under the title nomen protectum. Thereafter it takes precedence. This procedure as a whole is termed a reversal of precedence.
An example is the case of the scientific name for the leopard shark. Despite the name Mustelus felis being the senior synonym, an error in recording the dates of publication resulted in the widespread use of Triakis semifasciata as the leopard shark's scientific name. After this long-standing error was discovered, T. semifasciata was made the valid name and Mustelus felis was declared invalid.

Use in taxonomy

The designation nomen oblitum has been used relatively frequently to keep the priority of old, sometimes disused names, and, controversially, often without establishing that a name actually meets the criteria for the designation. Some taxonomists have regarded the failure to properly establish the nomen oblitum designation as a way to avoid doing taxonomic research or to retain a preferred name regardless of priority. When discussing the taxonomy of North American birds, Rea stated that "...Swainson's name must stand unless it can be demonstrated conclusively to be a nomen oblitum."
Banks and Browning responded directly to Rea's strict application of ICZN rules for determining nomina oblita, stating: "We believe that the fundamental obligation of taxonomists is to promote stability, and that the principle of priority is but one way in which this can be effected. We see no stability in resurrecting a name of uncertain basis that has been used in several different ways to replace a name that has been used uniformly for most of a century."