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

Re: [dinosaur] Ceratopsid (Centrosaurinae: Nasutoceratopsini) from Oldman Formation of Alberta (free pdf)

I was going to comment on this myself, but of course in the well-worn opposite direction.  I think the current state of ceratopsid nomenclature is unrealistically oversplit, where a few differences or million years are considered enough to doubt conspecificity (ditto for Tschopp's Morrison diplodocids).  Compare this to theropods, where there are tons of differences between e.g. Tyrannosaurus rex specimens, which are known from the lower and upper parts of the Hell Creek Formation, as well as the Scollard, Denver, Lance, Frenchman, etc. Formations all over the continent.  I would call Ryan et al.'s Nasutoceratopsini Avaceratops.

Notably, Ryan et al. are confusingly contradictory in their discussion of Avaceratops.  They first state the holotype specimen "ANSP 15800 has three unambiguous autapomorphies: Ch 36 (jugal infratemporal process, 1>0; absent), Ch 49 (parietal, sharp median crest, 1>0; absent), and Ch 53 (marginal dermal ossifications on parietal and squamosal, 1>0; absent)", but then they say "it is currently difficult to diagnose Avaceratops because it appears to lack autapomorphies or any unique combination of characters."  Their conclusion is "As a result, Avaceratops is represented only by the type specimen

(ANSP 15800). This immature individual exhibits no undisputed apomorphies, rendering a diagnosis of the taxon problematic. Nevertheless, the specimen cannot be attributed to any other known centrosaurine, and so the genus cannot be synonymized or declared a nomen dubium."

Which is it?  If it has no autapomorphies or character combinations considered taxonomically valid, then it _could_ be synonymized with Nasutoceratops or alternatively declared a nomen dubium if it also couldn't be distinguished from other diagnostic nasutoceratopsin genera (e.g. maybe the Malta taxon once it's named).  But if it can't be attributed to any other known taxon, then that must be based evidence which would thus form the diagnosis.

Finally, why do you continue the myth that ICZN-covered taxa like Ceratopsidae are affected by the eponymous genus' diagnosability?  Haven't I put enough stakes into Wilson and Upchurch's baseless assertion this is the case?

Mickey Mortimer

From: dinosaur-l-request@usc.edu <dinosaur-l-request@usc.edu> on behalf of Tim Williams <tijawi@gmail.com>
Sent: Tuesday, December 13, 2016 9:40 PM
To: dinosaur-l@usc.edu
Subject: Re: [dinosaur] Ceratopsid (Centrosaurinae: Nasutoceratopsini) from Oldman Formation of Alberta (free pdf)
In light of the problems surrounding the genus _Ceratops_ (see below;
but short version - it's toast), this might be a good opportunity to
abandon the 'family' Ceratopsidae.  Instead, raise Centrosaurinae and
Chasmosaurinae to 'family' level (Centrosauridae, Chasmosauridae), so
the new 'tribes' Centrosaurini and Nasutoceraratopsini (coined by Ryan
et al. [2016]) would each become 'subfamilies': Centrosaurinae and
Nasutoceratopsinae.  Similarly, Triceratopsini would be bumped up to
Triceratopsinae within Chasmosauridae. I'm not a huge fan of these
Linnaean constructs (and the obtruse ICZN rules that govern them), but
since we seem to be stuck with them, it's clear that _Ceratops_ should
not be giving its name to any coordinated family-level taxon.

_Ceratops_ (type species _C. montanus_) is known only a pair of
postorbital horn cores and a partial occiput.  The horn cores are
quite long and dorsolaterally projecting.  _Kosmoceratops_ and
_Albertaceratops_ specimens also have long and dorsolaterally
projecting postorbital horncores (Mallon et al., 2016).
_Albertaceratops_ is a centrosaurine, whereas _Kosmoceratops_ is a
chasmosaurine; so the horns of _Ceratops_ can't even be used to sort
it into either Centrosaurinae or Chasmosaurinae.  So _Ceratops_ is
useless as a specifier.

_Ceratops_ is clearly a nomen dubium.  The only way to salvage the
name _Ceratops_ is designate a neotype that is diagnostic.  This is
highly unlikely ever to happen.  The best chance was the Judith River
Formation chasmosaurine specimen CMN 57081.  From Mallon et al.
(2016): "It is possible - even likely, given their close stratigraphic
and geological association - that ‘_Ceratops_’ and CMN 57081 are the
same species, but without conclusive evidence for such, it is
preferable to erect a new species for CMN 57081."  So CMN 57081 became
_Spiclypeus_, rather than being referred to _Ceratops_, or nominating
it as the neotype of _Ceratops_.  This was undoubtedly the best
decision.  The nasutoceratopsin skull MOR 692 (tentatively regarded as
an adult _Avaceratops_ by Penkalski and Dodson [1999], but removed
from _Avaceratops_ by Ryan et al. [2016]) comes from the Coal Ridge
Member of the Judith River Formation, like _Spiclyepus_; but MOR 692
is an even weaker choice than CMN 57081 to become a _Ceratops_

The only reason to nominate a neotype for _Ceratops_ at all would be
for book-keeping/nomenclatural reasons: _Ceratops_ is the name-giver
for Ceratopsidae and coordinated taxa like 'superfamily'
Ceratopsoidea.  (Ceratopsia, Ceratopsomorpha etc are fine, because
they are exempt from ICZN rules.)  But promoting Centrosaurinae and
Chasmosaurinae to families - or simply changing the name of
Ceratopsidae to Centrosauridae - means that _Ceratops_ can be
forgotten forever.

On Wed, Dec 14, 2016 at 4:56 AM, Ben Creisler <bcreisler@gmail.com> wrote:
> The official news release with illustrations:
> Researchers name two new horned dinosaur tribes
> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.cmnh.org_announcements_ceratopsian-2Dtribes&d=DgIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=IRbuPQptQNlXoZq8JovgUI5ojPaPTN8TdtaKzKaQBeA&s=dkv3SQEX9GiwGDvDZ2Y5V6unoWajl4NvLyWRRmuybuQ&e=
> https://urldefense.proofpoint.com/v2/url?u=http-3A__phys.org_news_2016-2D12-2Dscientists-2Dredefine-2Dhorned-2Ddinosaur-2Drelationships.html&d=DgIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=IRbuPQptQNlXoZq8JovgUI5ojPaPTN8TdtaKzKaQBeA&s=v-9lru50LBa481z6Bnw8L-ce1VZgUU53Wu6t5Z9Bg9U&e=