Re: Ah ha! That's where therizinosaurs came from

[Tim Williams <tijawi@gmail.com>]

OK, when a mommy therizinosaur and a daddy therizinosaur love each
other very much...


(Sorry, low-hanging fruit... had to go there.)


<GSP1954@aol.com> wrote:

> I was in the Hopkins library gathering material to restore the skeleton of
> Johelornis now that there are enough skulls and skeletons lying around


Oh no...


> when
> I did the proverbial dope slap as I realized the probable ancestoral source
> for therizinosaurs.


Oh yes...    :-(


> I have long been pointing out that all flightless "theropods" with
> extensive flight adaptations are likely to be secondarily flightless because 
> no one
> has come up with really satisfactory arguments for why and how those flight
> characters evolved outside the context of flight,


I have some ideas.  And it doesn't involve flying dromaeosaurs.  And
it's consistent with current cladograms.


> At the same time I was pointing out, and Osmolska too, that oviraptorosaurs
> were probably more avian than archaeopterygids and secondarily flightless.


The same was once said about _Mononykus_ - which was initially
interpreted as a "bird" - closer to modern birds than _Archaeopteyx_.
_Mononykus_ has a whole armada of derived bird-like characters not
seen in _Archaeopteryx_: reduced postorbital bar, streptostylic
quadrate, keeled sternum, fused carpometacarpus, splint-like fibula.
For _Mononykus_, these "avian" characters were subsequently shown to
have arisen by convergence.  In this case, the discovery of *more*
fossils (= more basal alvarezsaurs) showed us that _Mononykus_ was
*not* secondarily flightless ("neoflightless"), and *not* a bird.


> In the Field Guide I noted that the ancestoral group or type is likely to be
> your herbivorous omnivoropterygids.


I don't think we need to invoke an omnivoropterygid-oviraptorosaur
link in order to explain shared herbivorous adaptations.
Herbivory/omnivory appears to be prevalent among maniraptorans, and is
probably primitive for this clade.  I've thought for a long time now
that the role of predation in the evolution of avian flight has been
overstated.  So I was happy to see Avialae joining the ranks of
maniraptoran clades that were (at least primitively) non-predatory.


> What has become most vexing is those pesky therizinosaurs. Some have those
> very long tails. So what basal flying theropods were herbivores with long
> tails? Well duh, jeholornithids. Not that jeholornirds specifically are
> prototherizinosaurs, they lack sufficient teeth for one thing. Now, other
> therizinosaurs have shorter tails. It is unlikely for that to be adaptative 
> among
> evolving land herbivores that should retain long tails to counter balance the
> exapnding belly.


I disagree.  A lot of sauropods have short tails - like camarasaurids
and brachiosaurids.  Besides, why would the expanding belly of
therizinosaurs need a counterbalance?  Therizinosaurs probably didn't
move very far, or very fast.  The tail was useless for defense -
that's what those lethal hand-claws were for.  So from the perspective
of a heavy-bodied therizinosaur, what's the point of keeping a long
tail?


> Now it all makes sense, phylonirvana has been achieved and what was
> perplexing now is a lot more logical. Blessed thanks be to the deities that
> probably do not exist.


I agree that said blessed deities probably don't exist.  But I very
much doubt that flying proto-therizinosaurs existed either.


At the moment the lack of any proto-therizinosaurs (_Eshanosaurus_
doesn't count) or proto-oviraptorosaurs is creating a vacuum.  This
vacuum is being filled by highly speculative ideas about volant,
tree-dwelling ancestors.  But if and when we do find
proto-therizinosaurs or proto-oviraptorosaurs I predict they'll be
thoroughly non-volant.  Boring, I know.  But although this is not the
most exciting scenario, it is the most parsimonious - and it doesn't
require rampant character reversals.






Cheers

Tim