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

Correction/update #3 - Mesozoic dinosaur species



http://dml.cmnh.org/2007Jun/msg00363.html

Publication appears to be imminent for these two...

Amargatitanis macni Apesteguía, 2007
   (type of Amargatitanis Apesteguía, 2007)
Nopcsaspondylus alarconensis Apesteguía, 2007
  (type of Nopcsaspondylus Apesteguía, 2007)

Amargatitanis macni - titanosaur (lithostrotian?)
Nopcsaspondylus alarconensis - diplodocoid (rebbachisaurid)


As Ignacio Ruiz mentioned, the holotype dorsal for _Nopcsaspondylus_ was described by Nopcsa (1902), but is now lost. Does that mean that this sauropod has only a figure as its holotype? I know this is not unique, given that the holotypes of other dinosaur genera are now lost (e.g., _Spinosaurus aegyptiacus_, _Amphicoelias fragillimus_). But in the case of _Nopcsaspondylus_, the holotype specimen was named *after* it was lost. Are there other cases of this among non-avian dinosaurs?


I don't know how Mike Taylor feels about this, but Apesteguía (2007) also erects a new clade Rebbachisauroidea, and defines it as such:

"Definition (node-based): The most inclusive clade containing WN-V6 (_Histriasaurus boscarollii_, see Appendix A), _Rebbachisaurus garasbae_ Lavocat, 1954, and _Limaysaurus tessonei_ (Calvo and Salgado, 1995), and MACN PV N35."

There are a couple of problems with this definition, both real and potential. Firstly, under current phylogenies, Rebbachisauroidea matches Rebbachisauridae in content, given that the latter is a stem-based clade defined as "_Rebbachisaurus_, but not _Diplodocus_" (Salgado et al., 2004; Taylor and Naish, 2005).

Secondly, Rebbachisauroidea is inside Diplodocoidea, since Diplodocoidea is defined as "_Diplodocus_, but not _Saltasaurus_". Apesteguía seems OK with this, but it strikes me as well.... weird. It also defies the ICZN Code (Articles 29, 34, etc). Like it or not, Rebbachisauroidea and Diplodocoidea are both coordinated family-level taxa ("superfamilies") and so subject to the ICZN.

Thirdly, should monophyly of the Rebbachisauroidea break down, such if one of the four taxa/specimens in Apesteguía's definition be shown to be outside (basal to) a _Rebbachisaurus_ +_Diplodocus_ clade, then Rebbachisauroidea would include dicraeosaurids and diplodocids, as well as rebbachisaurids. This wouldn't be the end of the world, but it does go against the grain of the original intention of the definition. This situation could be avoided by including _Diplodocus_ and _Dicraeosaurus_ as negative qualifiers, for example.

Cheers

Tim

P.S. I'll also use this opportunity to add another species to the list. It's almost certainly a nomen dubium, but its nevertheless valid in the nomenclatural sense.

Tyrannosaurus zhuchengensis Hu, Cheng, Pang, and Fang, 2001

Tyrannosaurus zhuchengensis - tyrannosauroid (tyrannosaurid)

References

Apesteguía, S. (2007) The sauropod diversity of the La Amarga Formation (Barremian), Neuquén (Argentina). Gondwana Research, doi:10.1016/j.gr.2007.04.007

Hu, C. C., Cheng, Z., Pang, Q., and Fang, X., (2001) _Shantungosaurus giganteus_. Geological Publishing House, 139pp.

_________________________________________________________________
http://imagine-windowslive.com/hotmail/?locale=en-us&ocid=TXT_TAGHM_migration_HM_mini_2G_0507