Number Of Plesiosaurs Remaining To Be Discovered

[DD1991]

I'm doing a survey of all valid plesiosaur genera described to date and so far, about 100 valid plesiosaur genera have been described so far. Has there been any published study regarding the estimated generic diversity of plesiosaurs?

[FossilDAWG]

I don't know of any such published study, but perhaps you could try to estimate the number yourself, as you have been collecting the literature. Graph the number of new taxa described/decade, and see if you can fit a curve that comes to some sort of an asymptote. This is termed "rarefaction analysis". You should only count "valid" taxa, so exclude genera that have later been deemed to be synonyms or nomen dubia, and probably also names that are restricted to a single type specimen because that specimen lacks diagnostic characters. Names based on a single good diagnostic holotype are fine to include, obviously.

There are lots of biases that apply to such an analysis, of course. Rate of description of new taxa might reflect the number of people working in the field, as well as issues of specimen quality already mentioned. The concept of "genus" (which is an artificial construct) changes over time. Perhaps "species" would be a better metric to use, as new genera are sometimes described based not on new discoveries but on long known genera being split up.

I'd guess that the curve you get will show an increasing slope, in which case no asymptote can be calculated. It's only when the curve is starting to flatten out that the method yields a meaningful estimate.

Don

[Regg Cato]

I'm not aware of one either, but as Don mentioned, estimating species diversity is probably a more useful project than basing a study on an artificial and somewhat subjective rank. What would be the objective in this project? What do you mean by "survey"? Are you looking for misidentified species? Biodiversity? Paleobiogeography?

[DD1991]

I'm not aware of one either, but as Don mentioned, estimating species diversity is probably a more useful project than basing a study on an artificial and somewhat subjective rank. What would be the objective in this project? What do you mean by "survey"? Are you looking for misidentified species? Biodiversity? Paleobiogeography?

I was simply performing a preliminary biodiversity study for plesiosaurs along the lines of the paper by Wang and Dodson (2006) concerning the number of non-avian dinosaur genera that existed in the Mesozoic. There is a graph by Adam Smith illustrating the number of valid plesiosaur species (http://www.plesiosauria.com/news/index.php/new-plesiosaurs-lots-of-new-plesiosaurs) and there are about 160 valid plesiosaur species described so far (ncluding the four species of pliosaurs and the recently described leptocleidid Gronausaurus described this year). After seeing how Anningasaura and Megacephalosaurus were initially thought to be specimens of "Plesiosaurus" macrocephalus and Brachauchenius respectively, later to be recognized as distinct from the latter two, it's been routine for the plesiosaur workers to describe new species and revise old species based on examination of the types specimens of old species.

[FossilDAWG]

That's exactly the graph I was suggesting. Based on that graph, I'd say there is no way to estimate how many plesiosaur taxa remain to be discovered, as the curve shows no sign of beginning to level out. Lots of discoveries still be be made, it would seem.

Don

[painshill]

Hi Darren

This paper may be interesting if you haven’t seen it. Doesn’t answer your question but nevertheless has some great information:

http://www.plosone.org/article/fetchObject.action?uri=info%3Adoi%2F10.1371%2Fjournal.pone.0031838&representation=PDF