Re: [dinosaur] Psittacosaurus amitabha, new species from Cretaceous Ondai Sayr Locality, Mongolia

["David Marjanovic" <david.marjanovic@gmx.at>]

Gesendet:ÂFreitag, 26. Juli 2019 um 22:42 Uhr
Von:Â"Paul P" <turtlecroc@yahoo.com>

> Genus vs. species is sometimes arbitrary, but not always. Clustering 
> algorithms can help to determine which it should (probably) be. 
> Morphometrics, cladistics, etc.

Technically, it's always arbitrary, because the International Code of 
Zoological Nomenclature doesn't recognize any definition at all for "genus" or 
for that matter "species". While there is now a widespread consensus in 
vertebrate paleontology that genera should be monophyletic, even that is not in 
the Code. Additional criteria have been proposed on rare occasions, but never 
implemented across the board.

*Psittacosaurus* as currently understood is monophyletic; but any decision 
whether to call that clade *Psittacosaurus* or Psittacosauridae or anything 
else like that is arbitrary.