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Re: when is a Lazarus Taxon not a Lazarus Taxon?



Mike Taylor wrote:

The age of _Wuerhosaurus_ seems to be given, rather schizophenically, as "Valanginian or Albian" in Galton and Upchurch 2004. I leave it to lovers of Chinese stratigraphy to sort that one out :-)

I've seen Valaningian-Albian (i.e., Valanginian TO Albian), which makes more sense. :-)


I've not seen the material so I'm hesitant to be too emphatic about this; but since the sole _Sonorasaurus_ specimen ADSM-500 was originally thought to be a hadrosaur (Thayer and Ratkevich 1995) and then a Therizinosaur (Ratkevich's talk at DinoFest 1997), and since the "nearly complete skull" turned out to be distorted dorsal, you will forgive me if I am not quick to believe that the material can be definitively identified as _Brachiosaurus_ :-)

The version I heard... The folks who first worked on _Sonorasaurus_ were not dinosaur experts, and their opinion of this beastie certainly transmogrified over time. By the time the description was published, it was clear that _Sonorasaurus_ was a sauropod. However, it was Brian Curtice who remarked upon how similar _Sonorasaurus_ was to _Brachiosaurus_, and I'd take his opinion to the bank. Although Curtice did not actually advocate synonymizing _Sonorasaurus_ with _Brachiosaurus_.


It doesn't seem unreasonable that it should be brachiosaurid, but since the EK was crawling with putative brachiosaurids, or at least basal titanosauriforms, that's not surprising.

I'd say "stomping" rather than "crawling". :-) However, given the incompleteness and the state of preservation of the _Sonorasaurus_ material, it may just be the case that the *known* material appears brachiosaurid. There's no doubt that it's a basal titanosauriform, but the taxon is poorly represented. Galton and Upchurch (2004) actually treat _Sonorasaurus_ as a nomen dubium, which seems harsh IMHO.



Roberto Takata wrote:

What about Lazarussuchus?

The choristodere _Lazarussuchus_ (Oligocene) was named with this in mind. Further, if _Lazarussuchus_ is a basal choristodere (as some phylogenetic analyses have found), it implies a very long ghost lineage indeed.


Cheers

Tim

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