Mysticete evolution (was Re: Speculative dino species)

[christian farrell kammerer <cfkammer@midway.uchicago.edu>]

On Sun, 29 Jul 2001, David Marjanovic wrote: 
> I've read a very simple explanation for this in Carl Zimmer's book At The
> Water's Edge: Macroevolution and the Transformation of Life: Baleen whales
> evolved when the loop of cold currents closed around Antarctica, which
> produced the present enormous amounts of krill. So we should expect
> _something_ (something endothermic, according to HPs Paul & Leahy) to become
> a giant filter feeder at that time (early Oligocene), but not before.

I've read this too, and while it's an interesting idea, I'm quite
skeptical. If this were the case, one would expect the most primitive
mysticetes to be found in the Southern Hemisphere, but with only a few
exceptions (most of which, I might add, are from the Pliocene, thus making
them too late to play a part in this debate) the cetotheres (ostensibly
the most basal balaeniferous [is that a word?] mysticetes) are Northern
Hemisphere creatures, with many representatives in Europe, Asia, and North
America but few if any from the supposed epicenter of mysticete
evolution. Also, the cetotheres, especially the early ones, were small
whales (some less than 20 feet)--hardly "giant" filter feeders. Also, true
giant filter feeders in the form of the whale sharks were around at least
as early as the Eocene--how does the Antarctic solution explain their
evolution? Whale sharks conceivably arose from some form of generalized
orectolobiform in the Cretaceous, yet no reptiles followed suit. Finally,
a brand spankin' new paper on krill evolution (I don't have the ref handy,
but I can find it) claims that, based on molecular data, the swarming
krill family Euphausiidae dates back to the Early Cretaceous. If this is
true (and admittedly, there's a good chance it isn't, and even if so, we
can't know the behavior of ur-krill for sure), then why weren't the
Cretaceous reptiles taking advantage of it? Perhaps they were, albeit not
in a mysticetimorph form? Who knows, maybe the closest reptiles got to
suspesion feeding was in things like Aristonectes. Now if only we could
figure out what Shonisaurus was eating back in the Triassic...

-Christian Kammerer