RE: Fw: Spinosaurus again

[Tim Williams <twilliams_alpha@hotmail.com>]

Jean-Michel Benoit wrote:

> This is the point I don't get, Spinosaurus being a quite new type of 
> dinosaur at this time and even now, you cant't expect it to "fall" into 
> pre-calibrated "families",

You raise an excellent point, Jean-Michel.  Some dinosaur species that are 
based on incomplete and disarticulated material have been regarded as 
chimeras (=composite taxa) largely because they didn't fit easily into any 
established phylogenetic "families".  Again, you can't fault the researchers 
because often they had good reason to suspect that the material derived from 
more than one taxon.

For example, _Tsintaosaurus_ has been called a composite of lambeosaurine 
and hadrosaurine material (I don't know if this view is still current); and 
it's been proposed that _Antarctosaurus_ is a composite of diplodocoid and 
titanosaur material (the discovery of _Bonitasaura_ seems to have quashed 
that idea).  The oddball theropod _Avimimus_ was once regarded as a chimera 
made of up several unrelated species, with oviraptorid, bird, and even baby 
hadrosaur material suggested as going into the mix.  Now it's pretty clear 
that _Avimimus_ is just a peculiar theropod.

But some "species" are genuine chimeras, and come about because the bones 
and/or teeth of different species become fossilized together (or at least in 
close proximity), and are assumed to belong to the same species.  Many 
"teratosaurid" species were based on a combination of basal sauropodomorph 
bones jumbled together with the teeth of carnivorous archosaurs, thus 
spawning an alleged family of primitive theropods, the Teratosauridae.  In 
other examples, _Alectrosaurus_ was originally given the arms of a 
therizinosaur, and _Sanpasaurus_ was named from a mixture of sauropod and 
ornithopod bones.  There is a lot of speculation that _Protoavis_ is a 
chimera based on material from several species.  _Alwalkeria_ may be a 
chimera composed of dinosaur and crocodylomorph bones.  There are plenty of 
other examples of possible dinosaur chimeras.

Then there's the case of "Archaeoraptor", which was deliberately cobbled 
together from partial avian and dromaeosaur skeletons.

> MVHO; look at feathered non-avian theropods, who could have guessed they 
> ever existed
> before the Liaoning finds [ok, cladistics could have predicted it :-] .

As David mentioned, the idea of feathered non-avian theropods came long 
before they were actually discovered.

Cheers

Tim