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Re: Nopcsaspondylus has no hypophene, please



On 22 November 2011 19:38, Sebastian Apesteguia
<sebapesteguia@yahoo.com.ar> wrote:
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Rescued from truncation, as this is a particularly important subject.

-- Mike.




Hi,
in the last two years I've seen some papers with mistakes concerning
the distinction between two specimens which I described in "The
sauropod diversity of the La Amarga Formation (Barremian),
Neuquén (Argentina)" (Gondwana Research, 2007).

Specimens are:
-MACN PV N35, a dorsal vertebra, which I described and figured, but not named.

-Nopcsaspondylus alarconensis, another dorsal vertebra (which I didn't
figured, only referred to the original paper by Nopcsa in 1902)


Concerning MACN PV N35, I said:
"MACN PV N35 is considered here a basal diplodocoid......"

".....it is possible that MACN PV N35 could belong to a form related
to Zapalasaurus or that taxon itself. However, I prefer to maintain
the distinction of MACN PV N35 from Zapalasaurus considering that..."
"MACNPVN35 shares with rebbachisaurids........It must be noted,
however, that the presence of a well-developed hyposphene shows a very
basal position in the
clade, like that of Histriasaurus boscariolli (Dalla Vecchia, 1998).
Additionally, MACN PV N35 lacks all the following rebbachisaurid
diagnostic dorsal neural arch features, the La Amarga taxon having a
plesiomorphical condition for all of them: absence of
hyposphene–hypantrum articular complex in dorsal vertebrae; posterior
dorsal neural spine reaching four times the
length of the centrum; and petal-shaped posterior dorsal and anterior
caudal neural spines. All these features point to the need for
creating a more inclusive category to include rebbachisaurids
and the basal most forms related to them, as a lineage related to
rebbachisaurids, but lacking several of their diagnostic nodebased
features".
and, finally:

"However, although the material from Barda Alarcón and MACN PV N35
indicate low spined rebbachisaurids (it should say rebbachisauroids),
the latter specimen also retains a well-developed hyposphene".


Concerning Nopcsaspondylus (a regular, Cenomanian rebbachisaurid), I
offered the following diagnosis:
"diplodocoid sauropod characterized by mid to posterior dorsal
vertebrae with very reduced centra, forked medial
centropostzygapophyseal lamina, lateral lamina of the neural spine
formed by the spinodiapophyseal lamina plus a lateral
spinopostzygapophyseal (different from that forming the postspinal
lamina)."

Well, in the paper of Demandasaurus, Torcida et al. say:
"There are only two other rebbachisaurids in which the
hyposphene-hypanthrum articulation is developed: Histriasaurus and
Nopcsaspondylus (Apesteguía 2007)."


Additionally, Whitlock say:
"Apesteguía (2007) assigned MACN PV N35 to Nopcsaspondylus
(??????????), which is contradicted by the presence of a hyposphene in
MACN PV N35 and its absence in Nopcsaspondylus (Nopcsa, 1902)....For
this reason, MACN PV N35 cannot be assigned to Nopcsaspondylus."

Please, MACN PV N35 is an Early Cretaceous (Barremian) basal
diplodocoid, perhaps a rebbachisauroid (in my concept, including
Histriasaurus).
Nopcsaspondylus is a Late Cretaceous (Cenomanian) regular
rebbachisaurid, which I named in the paper only in order to
differentiate from other specimens, thats why is not described, but
added in an Appendix of Systematic definitions.

I never mixed them or referred one to each other.
Just that,
Best regards,
Sebastian




Dr. Sebastián Apesteguía

Fundación de Historia Natural 'Félix de Azara' -
CEBBAD (CONICET) - Universidad Maimónides. Virasoro 732,
Buenos Aires, ARGENTINA
Tel-fax: 5411-49051100 ext. 1228,
sebapesteguia@gmail.com, www.fundacionazara.org.ar