[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: You could lead a sauropod to water ...



Matthew Bonnan wrote:
>just keep in mind that we find camarasaurs and diplodocids together in the
>river channel sands of Dinosaur National Monument.
        Oooh, geology! If I recall correctly, these are *articulated*
skeletons, which, to my limited understanding, suggests even more strongly
that these animals inhabited the same enviornments. Of course, one does
wonder how far a flood could transport a bloated sauropod skeleton.
Fortunately, there is an entire taphonomy literature out there, waiting for
us all to consult it. Let's go! :)

>While I wholeheartedly agree that diplodocids and camarasaurids were probably
>pursuing different feeding strategies (you can even see statistically
>significant differences in their feet -- oh, wow, how incredibly cool), 
        Careful, there is more to morphology than simple function (although,
I suppose one might argue that there is no morphology without function). It
would be meaningful to explore the phylogenetic signal within the foot
structure of these taxa as well. Chalicotheres and therizinosaurs also had
different foot structures, but, according to the two Dales Russell, persued
the same feeding strategy. Marine iguanas and land iguanas share the same
foot structure (I presume), but persue different feeding strategies.
        I am not trying to be trite, these examples make a point: morphology
and phylogeny are intimately intertwined, and our artificial concepts of
taxonomic rank and morphological distance are not necessarily an effective
guide to the degree of difference we should expect. Phylogeny can help us
reconstruct the common starting point, not only morphologically, but also
functionally, and therefore strengthen our hypotheses and point out
inconsistencies in them.

>I have my doubts that camarasaurids were desert animals or were somehow
>conserving water like desert mammals and/or reptiles.
        I believe the original posting on this subject (before the "desert
evolution" hypothesis was presented), asserted little more than that
_Camarasaurus_ possessed the water-conserving adaptations presumed to be
ancestral in reptiles. Beyond that, it was pretty much rampant speculation.
I believe that the Morrisson is believed to represent an arid depositional
environment. Not a desert, certainly, but arid. Drat, geology again! ;)

>Camarasaurids have stiffer hind feet and a taller hand (manus) than 
>diplodocids, and this seems like it might exapt them to feeding on a bit 
>more solid ground.
        Or it might be that diplodocids required the flexible hind feet for
fine-tuning a tripodal feeding posture, whereas the longer manus of
_Camarasaurus_ was related to high-browsing from a quadrupedal stance. How
do the morphologies expressed in these taxa relate to the morphology of,
say, _Brachiosaurus_, or _Shunosaurus_? What is the polarity of these
features (i.e. is the state seen in _Camarasaurus_ truly derived and
therefore requiring special explanation, or is it ancestral)?
        BTW: "exapt" refers to an adaptation initially used for one purpose
with allows the animal to do something else. It might be the correct phrase,
if the original (different) functions of the features are understood, (and
that they are derived relaive to the common ancestral condition of
_Camarasaurus_ and diplodocids).

>However, it would seem that both camarasaurids and diplodocids were living in
>the same areas, just exploiting different regions within those areas so as to
>not directly compete with one another.
        Not necessarily different physical regions, maybe just different
niches of any sort... say, "medium" browser versus high browser.

>Or, you know that sauropods were great at knocking over vending machines to 
>get at cokes.  Need a bottle opener?  Just use your big ol' thumb claw.  Or 
>your hind feet.  Great for parties. =) =P ;)
        Or, as the old saying goes, cans of Dinty Moore Tree Fern Stew...

        :)

        Wagner
--------------------------------------------------------------------------------
     Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock, TX 79409-1053
  "Why do I sense we've picked up another pathetic lifeform?" - Obi-Wan Kenobi