[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: Ceratops (was RE: Pterosaur diversity (was: Re: Waimanu))

Tim Williams wrote-

So the size of the horn cores is useless for diagnosing Chasmosaurinae/Ceratopsinae. Thus _Ceratops_ cannot be demonstrated to be a "ceratopsine", and it cannot be demonstrated not to be a centrosaurine, or a non-ceratopsid ceratopsoid for that matter. <snip>
Sereno does not use _Ceratops_ as a specifier, but _Ceratops_ is the eponymous genus for Ceratopsoidea, Ceratopsidae, and Ceratopsinae. It might be best to abandon these names, and replace Ceratopsidae with Centrosauridae. Sereno suggested replacing Chasmosaurinae with Ceratopsinae back in 1998, but the idea didn't exactly take off (as Sereno [2005] admits), so Ceratopsinae can just be brushed under the carpet, IMHO.

Well, not so fast. Horn core size isn't necessarily the only character which can be evaluated for Ceratops. Perhaps other skull roof or occipital characters can distinguish ceratopsids from more basal taxa, or centrosaurines from chasmosaurines. In fact, Ryan's thesis finds that his unpublished taxon is extremely similar with Ceratops and from equivalent beds. I wouldn't be surprised if they were synonymous, though Ceratops' holotype is not as obviously diagnostic.

Salgado (2003) also cites PhyloCode Recommendation 11.8B to support upholding the use of the name Titanosauridae, because _Titanosaurus indicus_ (usually regarded as a nomen dubium) is clearly a member of the clade Titanosauridae, which is diagnosed by procoelous middle caudals. However, there is no guarantee that this character might not turn up in a more basal titanosaurian taxon (or even a non-titanosaurian sauropod - some of which show procoelous proximal caudals).

True, but again we have other characters to consider (e.g. neural arch placement). I don't think anyone doubts Titanosaurus is a titanosaurid (in the sense of being more closely related to Saltasaurus than Andesaurus; not a phylogenetic definition, but you get the clade I mean). I'd agree with Salgado. There's nothing in the ICZN saying family names shouldn't be based on nomina dubia.

My point (sorry I didn't get there sooner) is that it is bad policy to name family-level clades after nomina dubia (or even fragmentary taxa). _Ceratops_/Ceratopsinae/Ceratopsidae is a good test case.

To play devil's advocate, both Ceratops and Titanosaurus were very distinctive when they were first found. It's only with hindsight that we know strongly procoelous caudals and large brow horns have wide distributions.

Mickey Mortimer