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[darren.naish@port.ac.uk: Diplodocimorpha vs Diplodocoidea]
Forwarded with permission from Darren Naish.
Very enlightening.
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From: "Darren Naish" <darren.naish@port.ac.uk>
Organization: University of Portsmouth
To: mike@indexdata.com
Date: Thu, 13 May 2004 09:04:57 +0100
Subject: Diplodocimorpha vs Diplodocoidea
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Hi Mike
Saw your discussion on DML of Diplodocoidea vs
Diplodocimorpha. You may or may not find the following
useful, please post it on DML....
- ---------------
In coining Diplodocimorpha, Calvo & Salgado (1995)
wrote (both p. 14 and p. 30) that it was erected to include
_Rebbachisaurus tessonei_ (= _Rayososaurus tessonei_),
Diplodocidae (used by them for both diplodocids s. s. and
dicraeosaurids), and all the descendants of their common
ancestor. Recent work indicates that _Rayososaurus_ is part
of a monophyletic Rebbachisauridae, so Diplodocimorpha
as employed by Calvo & Salgado (1995) =
(Rebbachisauridae + (Diplodocidae + Dicraeosauridae)). If
you adhere to PhyloCode rules then Calvo & SalgadoÂs
(1995) Âincluded taxa section of their paper could be
regarded as a formal phylogenetic definition of
Diplodocimorpha.
UpchurchÂs (1995) usage of Diplodocoidea for the
ostensible diplodocid-dicraeosaurid-nemegtosaurid clade is
therefore less inclusive (because he didnÂt include
rebbachisaurids) and Diplodocimorpha and Diplodocoidea
are arguably not synonymous. While Upchurch 1995 was
published before Calvo & Salgado 1995 (the former is dated
as having been accepted in February 1995 and the latter
appears in an issue dated December 1995), it is less clear
from Upchurch (1995) whether his discussion of
Diplodocoidea includes what could unambiguously be
regarded as a phylogenetic definition. [Note that
Diplodocoidea is Marsh, 1884 because MarshÂs coining of
Diplodocidae in that year automatically made him author of
Diplodocinae and Diplodocoidea were they to be erected in
the future, even though Upchurch (1995) was first to use
this name in the published literature. To acknowledge this
you could write it ÂDiplodocoidea (Marsh, 1884) sensu
Upchurch, 1995Â, as Carvalho et al. 2003 did.]
However, Wilson & Sereno (1998) regarded
Diplodocimorpha as synonymous with Diplodocoidea and
on the subject of the two names write ÂWe use the available
name Diplodocoidea for this clade (Upchurch, 1995), which
has been used elsewhere in this manner (Wilson and Smith,
1996), and which includes two subgroups normally
accorded familial rank (Dicraeosauridae and Diplodocidae;
both were placed as subfamilies within Diplodocidae by
Calvo and Salgado [1995]). (p. 6). This isnÂt a satisfactory
argument: itÂs sort of saying Âthese two names refer to the
same group because, well, we say soÂ, BUT if the
phylogenetic definition proposed by Sereno (1998) is
employed, then Diplodocoidea is a stem-based taxon that
incorporates all taxa closer to _Diplodocus_ than to
_Saltasaurus_: consequently Diplodocimorpha really would
be redundant. As discussed above though, Calvo & Salgado
(1995) provided what appears to be a satisfactory
phylogenetic definition of Diplodocimorpha. Obviously
though, not everyone regards the first use of a phylogenetic
definition as important and if this is the case then
Diplodocoidea Marsh, 1884 clearly has precedence. At
some stage the community really is going to have to decide
whether to adopt PT rules or not until then messes like
this will remain unresolved.
Most recent works on sauropod phylogeny appear to follow
the line of reasoning employed by Wilson & Sereno.
Upchurch (1998, 1999) doesnÂt use Diplodocimorpha in
connection with diplodocoids and Wilson (2002, Fig. 13)
labels the rebbachisaurid + dicraeosaurid + diplodocid clade
Diplodocoidea. Leo Salgado of course has continued to use
Diplodocimorpha (Salgado 1999) as have some other, but
not all, South American palaeontologists.
So, bottom line: as originally conceived phylogenetically
(by Calvo & Salgado 1995 and by Upchurch 1995), no,
Diplodocimorpha and Diplodocoidea were not synonyms. If
SerenoÂs phylogenetic definition for a stem-based
Diplodocoidea is followed then, yes, they are. On that note I
am increasingly finding in my own research (which, believe
it or not, still goes on from time to time) that SerenoÂs
definitions are not helpful and create more problems than
they solve: I therefore advocate that at least some of them
not be followed. One final comment phylogenetic
nomenclature is meant to be (in part) about promoting
stability in taxonomy, and given that more sauropod
workers are using Diplodocoidea than Diplodocimorpha,
one could make a good argument that Diplodocoidea
becomes the favoured term.
Refs --
Calvo, J. O. & Salgado, L. 1995. _Rebbachisaurus tessonei_
sp. nov. a new Sauropoda from the Albian-Cenomanian of
Argentina; new evidence on the origin of the Diplodocidae.
_Gaia_ 11, 13-33.
Carvalho, I. de Sousa, dos Santos Avilla, L. & Salgado, L.
2003. _Amazonsaurus maranhensis_ gen. et sp. nov.
(Sauropoda, Diplodocoidea) from the Lower Cretaceous
(Aptian-Albian) of Brazil. _Cretaceous Research_ 24, 697-
713.
Salgado, L. 1999. The macroevolution of the
Diplodocimorpha (Dinosauria; Sauropoda): a
developmental model. _Ameghiniana_ 36, 203-216.
Upchurch, P. 1995. The evolutionary history of sauropod
dinosaurs. _Philosophical Transactions of the Royal
Society, London_ 349 365-390.
- - . 1998. The phylogenetic relationships of sauropod
dinosaurs. _Zoological Journal of the Linnean Society_
124, 43-103.
- - . 1999. The phylogenetic relationships of the
Nemegtosauridae (Saurischia, Sauropoda). _Journal of
Vertebrate Paleontology_ 19, 106-125.
Wilson, J. A. 2002. Sauropod dinosaur phylogeny: critique
and cladistic analysis. _Zoological Journal of the Linnean
Society_ 136, 217-276.
- - . & Sereno, P. C. 1998. Early evolution and higher-level
phylogeny of sauropod dinosaurs. _Society of Vertebrate
Paleontology Memoir_ 5, 68 pp.
- --
Darren Naish
School of Earth & Environmental Sciences
University of Portsmouth UK, PO1 3QL
http://web.port.ac.uk/departments/sees/staff/NaishD.htm
email: darren.naish@port.ac.uk
tel: 023 92846045
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