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Dinosaur names, error, and biodiversity

Error in naming dinosaurs

At times, all sorts of non-dinosaurian material has been ascribed to Dinosauria-remains later assigned to other fossil reptile groups, such as crocodilians, basal archosaurs, synapsids, or marine reptiles. Some forms even turned out to be mammals or inorganic remains. Further, some taxa that were originally assigned to other groups were later identified as dinosaurian and added to the list long after they had been named.

Of the 1401 dinosaurian species named to the end of 2004, 726 (51.8%) are regarded as invalid (the figures for genera are 1036 named, of which 388 [37.4%] are invalid). So the error rate for species is considerably higher than for genera. This is partly because most dinosaurian genera contain only one species, and where multiple species have been established within a genus, systematists have debated these endlessly. The minor anatomical differences used to establish species of dinosaurs are easier to reject than the more substantial characters used to diagnose genera.

This species-level error rate of 51.7% is frightening. This means that more than half the species of dinosaurs (and Mesozoic birds) ever named were in error.. How could so-called dinosaur experts be so wrong? Is this error rate excessively high, or is it more or less the norm? This is an issue that has concerned researchers in the fields of biodiversity and conservation.

Errors in naming species have generally been ascribed to synonymy, the invention of a new name for a species that has already been named. Are all the 726 erroneous dinosaurian species synonyms? It is meaningful to look at patterns of invalidity among species, rather than genera, of dinosaurs, because the determinations were made at species level. In the present species list of dinosaurs, 230 of the 1401 names (16.4%) are currently regarded as synonyms, 340 (24.3%) are designated nomen dubium, 47 (3.4%) are designated nomen nudum, and 58 (4.1%) are not dinosaurs. So, of invalid dinosaurian species, twice as many have been invalidated for reasons other than synonymy (16.4% of the total are synonyms; 31.8% are invalid for other reasons).

A note on terminology. Synonyms are species, or higher taxa, that have been given a name in error by an investigator who is unaware that the species had already been named. There are other reasons for rejecting a species name as incorrect or invalid. It may be:
  • a nomen vanum (improperly established name for something that is already named);
  • a nomen nudum (no type material identified);
  • a nomen oblitum (name never used after its establishment);
  • a nomen dubium (based on undiagnostic and incomplete material);
  • preoccupied (given a name that has already been given to some other organism);
  • misassigned (correctly named, but belonging to another group).

The unexpected finding, that synonyms are outnumbered substantially by other taxonomic errors, may apply only to fossils, where the temptation to name new taxa on the basis of inadequate type material (e.g., an isolated tooth or single bone) is higher than for most living taxa. Among extant taxa, high invalidity for reasons other than synonymy would presumably be found only in groups where it is hard to collect and preserve complete specimens, or where there has been a major shift in practice (e.g., earlier workers named taxa on the basis of external ornament, whereas modern workers exclusively use internal organ characters).

Read more about the study

Dicynodon Illustration courtesy of John Sibbick.
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