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Re: Deinonychus claw, er, no, still Catch-22, really...



Don Ohmes <d_ohmes@yahoo.com> wrote:

> The trouble w/ *that* hypothesis is that vertical-climbing, refuge, roosting
> and even perch-hunting are very limited forms of arboreal locomotion, and do
> *not* require "arboreal adaptations", which occur in animals that *live* in
> trees.


Yes I agree.  Mostly.  I tend to think that roosting requires arboreal
adaptations, because it requires remaining still (or fairly still) in
a tree for a prolonged period of time.  But otherwise, yes I agree.
Nevertheless...


What I was talking about was hypothesis testing.  If you were to say
"Hey theropods didn't need arboreal adaptations in order to get up
trees, and stay there - they could simply use the abilities they
already have", it becomes very difficult to test this scientifically.


>> Even if (and it is still an*if*) certain characters in
>> the hands and feet improved trunk-climbing or branch-holding ability,
>> these characters must be set against the rest of the skeleton, which
>> remained resolutely terrestrial.
>
> Why? The same can be said of birds.


Birds can fly up from the ground into a tree.  Flight removed the need
to climb.  Aside from the juveniles of a few species (such as the
hoatzin), no bird is an arboreal quadruped.  And even juvenile
hoatzins have excellent branch-grasping feet.


>> Theropods lacked the flexible
>> vertebral columns and range of motion at the joints which, by and
>> large, are present in mammals.
>
>
> And theropods need these traits to climb vertically or roost? Why?


I was using these traits to demonstrate that theropods are/were not
like mammals - or lepidosaurs or turtles, for that matter.  Simply
because goats and certain turtles can (and do) climb trees does not
mean that it was as easy for theropods.  The "even goats can climb
trees, why not dinosaurs?" analogy is unhelpful for so many reasons.


Yeah, it is possible that small theropods did climb trees.  I tend to
believe they did.  But this is my intuition at work here, not hard
science.  I'd like to have a more rigorously grounding to my *belief*
that theropods could climb.  Simply saying that there was nothing that
precluded small theropods from climbing trees isn't sufficient
evidence in my book.  I want an explicit hypothesis that can be tested
against what we know about theropod anatomy.


> No one argues (in this thread) that theropods were arboreal - or if they
> did, I missed it...


No, you didn't miss it.  But if we going to put non-avian theropods in
trees (such as to sleep, seek refuge, or perch-hunt), I want to see
*positive evidence* for an ability to climb or roost in trees.  The
evidence should drive our assumptions, not the other way round.






Cheers

Tim