Sauropod Trunks: Nuh-uh!

["Ralph Miller III" <gbabcock@best.com>]

Dwight Stewart <Dwight.Stewart@VLSI.com> writes:
>       I know I've heard this suggestion
SNIP--
 (the trunk explanation for highly placed nares in sauropods)

> before somewhere, but can't recall
> where; but it's an intriguing idea!
>       After the concept of the top located nostrils used as a 'snorkel'
> was pretty much abandoned, I don't recall a viable alternate explanation
> being floated that has been as widely accepted.  Some people 
>       have suggested it was for auditory purposes.  Of course, even IF the
> auditory explanation is true, that doesn't preclude the presence of a
trunk.
> Elicits an interesting mental image.

And it makes for a typically amusing Robert Bakker illustration on page 141
of _The Dinosaur Heresies_.  In his 1986 book, Dr. Bakker claims that the
idea of trunked dinosaurs had been floating around for half a century (in
paleontological journals, no citations given).  While Bakker states that
the trunk remains a possibility, he finds problems with the hypothesis. 
For one thing, sauropods, unlike elephants, do not appear to be descended
from a lineage of animals which feature a complex of lip muscles (whence
the lips are derived).  Nor does Bakker see scars from big trunk muscles
near the edges of sauropod nares.  He seems to favor the nose flute
hypothesis (as depicted on page 145), but admits that there is some mystery
surrounding the faces and noses of "brontosaurs," as he calls them.

Another objection to the sauropod trunk should be the pointlessness of it. 
Elephants have massive, bulky heads mounted atop short necks, so the need
for a long trunk to reach up to high branches or down to low branches is
intuitively obvious, whether the elephant is knocking down a tree to get at
the foliage or leaving the tree standing in place.  Needless to say,
sauropods are built along very different lines, with an awesome reach and
the ability to rear up to feed on high branches.  What is the adaptive
advantage for developing a trunk on such an animal?

Furthermore, the elephant has only grinding molars (and tusks, of course),
so it requires something other than teeth (the trunk) to draw food into the
mouth.  As in many other mammals, with their cropping incisors and their
grasping lips and tongues followed by grinding molars, there is a
decoupling of the feeding and grinding processes.  The same is true of many
ornithischian dinosaurs, with their cropping beaks up front and grinding or
dicing teeth aft.  In sauropods, it is believed that the grinding may have
occurred much further aft within gastrolith-laden crops and gizzards (as
indicated by the _Seismosaurus_ specimen).  The teeth were therefore
employed to merely collect, rather than to grind up the food.  So, unlike
the elephant, the sauropod has teeth up front, which could be peg-like for
raking the twigs and leaves into the mouth (as in _Apatosaurus_), or
spatulate and chisel-like, for cropping the twigs off (as in
_Camarasaurus_).  This would seem to be a sufficient and expedient method
for ingesting the massive quantities of vegetation that these giants must
have required, and the capacious guts could continually digest the food
once it comes down the pike, aided by the usual assortment of acids,
microbes, and what have you.  Again, I fail to see the point of a sauropod
trunk.  Display?

David Norman writes in _The Illustrated Encyclopedia of Dinosaurs_ that the
enormous nostrils of _Brachiosaurus_ may have accommodated a strong sense
of smell, a resonating device, or "a cooling surface for the blood."  Or
some combination of these, I should think.  The snorkel hypothesis is
definitely out.  At least we can agree on something!

-- Ralph Miller III     gbabcock@best.com 

Who nose?