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

[Tim Williams <twilliams_alpha@hotmail.com>]

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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