Same or Different? When Should You Invent a new Genus? or Just Add a Species? Or Revise the Whole Clade?

Now that new pterosaurs are being added to the large pterosaur tree on a fairly constant basis, it’s time to figure out what to name them.

In the old days everything was named “Pterodactylus,” no matter what it was. Sharp-eyed observers soon figured out that there were differences that set certain specimens apart and these were then renamed. Others have not yet been widely recognized as distinct, but they need to be (Fig. 1).

The Pterodactylus lineage and mislabeled specimens formerly attributed to this "wastebasket" genus

Figure 1. Click to enlarge. The Pterodactylus lineage and mislabeled specimens formerly attributed to this “wastebasket” genus

Nowadays, new pterosaurs distinct from all others are being given new generic names, and that’s a good thing. However some of the new specimens nest within long lists of other genera. Others are given new species names within certain genera without nesting near those genera. The problem is a result of the incompleteness of all previously published pterosaur trees. They simply do not include enough taxa. They have a priori deleted all tiny specimens and all congeneric variations that, in the large pterosaur tree, provide clues to the evolution of more derived variations, some of which are distinct genera, as in the Campylognathoides/Rhamphorhynchus transition.

Some examples
MPUM6009 was considered a Eudimorphodon and a Carniadactylus despite nesting far from both genera. MCSNB 8950 was considered a Eudimorphodon, but nested with anurognathids.

Nesodactylus nested within the genus Campylognathoides. Bellubrunnus and Qinglongopterus nested within the genus Rhamphorhynchus.

Fenghuangopterus, Sericipterus and Cacibupteryx nested within the genus Dorygnathus.

Eosipterus and Cuspicephalus nest within the genus Germanodactylus.

Kellner (2010) renamed one Pteranodon, Dawndraco, but it remains surrounded by other Pteranodon specimens.

The question is, do we revise all the old genera and give them new names now that we know how distant some were from each other? Or do we retain those genera and take away the new generic names of the new specimens between them to reflect their traditional generic nesting?

Now all this doesn’t take into account marginal generic names, like Ningchengopterus at the base of the Pterodactylus clade or Muzquizopteryx at the base of the Nyctosaurus clade. These names are likely to be valid because they are distinct genera, but so are many of the species within Pterodactylus and Nyctosaurus. If they were modern birds, not prehistoric pterosaurs, their differences would be recognized.

Part of the historical problem, of course, goes back to Chris Bennett and others who considered smaller species to be immature forms of larger species without adequately describing them or placing them in analysis. It turns out that the vast majority of those where simply smaller forms that were evolving to become the larger forms – or vice versa.

It’s a problem. It needs to be recognized and dealt with. But it will only be recognized if pterosaur specimens are not a priori deleted from analysis for whatever reason.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Kellner AWA 2010. Comments on the Pteranodontidae (Pterosauria, Pterodactyloidea) with the description of two new species. Anais da Academia Brasileira de Ciências 82(4): 1063-1084.

5 thoughts on “Same or Different? When Should You Invent a new Genus? or Just Add a Species? Or Revise the Whole Clade?

  1. I’m curious- how many pterosaur species do you think are represented by multiple specimens? The impression I get from your posts is that almost everything is a different species, whereas I would be wary of individual variation and taphonomy, in addition to ontogeny.

  2. The pterosaurs in the taxon list all appear to be sufficiently different from one another to represent distinct species. Several species of Pterodactylus and Rhamphorhynchus probably are represented by several specimens. It’s difficult to say without reconstructing them and running analyses. The ontogeny thing would show up only in the scale bars, as all known babies look virtually identical to all known grownups. More specimens will show the subtleties of ontogeny. Too few now to demonstrate any patterns other than isometry.

    • Don’t you find that suspicious, considering how it works with other kinds of fossils? Twenty kinds of Pteranodon, but just one kind of Tyrannosaurus. I think it might be instructive to check the amount of apparent variation in specimens of Messel birds and such.

      • Just one kind of Tyrannosaurus? I understand there are several specimens. I’m curious, have the specimens and outgroups ever been phylogenetically analyzed as individuals? That’s what I did with Pteranodon and Rhamphorhynchus, just to see what would happen, an experiment. Sometimes the differences were small in Pteranodon, but did they represent speciation or variation? At some point the two blend together and reversals at that level more readily occur. I try to let the data speak for itself. Lumpers and splitters can argue it out later.

  3. I can only relay the results. In Pteranodon the smaller forms with smaller crests nest closer to the outgroups, like Nyctosaurus and that one specimen of Germanodactylus. The larger and larger crested forms are derived, just like evolution actually works! And they split up into distinct clades, just like evolution works. And one clade actually produced smaller Pteranodon with smaller crests, just like elsewhere in the pterosaur tree. I trust the computer and the PAUP software here. Who would have guessed this? And there’s no financial gain either, so its pure science.

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