Freethought & Rationalism Archive

Doubting Didymus · 10-14-2002, 05:52 PM

Its all good, then.

Xeluan · 10-14-2002, 06:52 PM

Regarding the quick discussion between Liquidrage and Doubting Didymus, Dr Thewissen said the following in regards to a question I had:

Quote:

There is really no consistent trend toward size increase in cetaceans.
The largest diversity of modern cetaceans (delphinids) has body sizes very
similar to those of Eocene whales. Very large forms (mysticetes) originated
when bulk filterfeeding originated. The worldwide cooling in the climate
caused ocean currents to change, and concentrated zones of upwelling, where
krill flourished, making filterfeeding possible (work by Ewan Fordyce).
This happened long after the basilosaurids went extinct.

Xeluan

[ October 14, 2002: Message edited by: Xeluan ]</p>

Doubting Didymus · 10-14-2002, 07:11 PM

That quote seems to support Liquidrage's point about food source. However, I do not think that the extra food source would have been enough to fuel the increase.

I would suggest that there is a constant pressure on many species towards greater size, for mating and defensive purposes. This pressure causes an increase in size until it is checked by another pressure, such as an inability to derive enough food to support any greater size. It seems as though the 'invention' of filter feeding allowed whales to break through this barrier, allowing further increase to an even more advantageous size, that other species are not able to reach due to their inability to tap the krill resource.

Xeluan · 10-15-2002, 02:38 AM

Quote:

Originally posted by Doubting Didymus:
<strong>
I would suggest that there is a constant pressure on many species towards greater size, for mating and defensive purposes. This pressure causes an increase in size until it is checked by another pressure, such as an inability to derive enough food to support any greater size. It seems as though the 'invention' of filter feeding allowed whales to break through this barrier, allowing further increase to an even more advantageous size, that other species are not able to reach due to their inability to tap the krill resource.</strong>

This is quite interesting. I got to thinking about how dinosaurs started off small and (while obviously some dinosaurs didn't grow that much) then quickly evolved into quite large animals. It could be that the selection pressures above are involved but WARNING RANK SPECUALTION TO FOLLOW PROBABLY WAY OFF there also existed quite a few niches that allowed certain species to grow. Also, when a new group arises, it may rapidly (given smaller population hence rapid evolution) fill available niches and size may be more readily selected.

Mammals did this also. Remember that only 15,000 years ago there were some quite large mammilian beasties roaming the planet. It is too far out to suggest that the presence of homo sapiens encourages a trend against size in evolution?

Xeluan

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10-14-2002, 05:52 PM	#11
Doubting Didymus Veteran Member Join Date: Jul 2002 Location: East Coast. Australia. Posts: 5,455	Its all good, then.

10-14-2002, 07:11 PM	#13
Doubting Didymus Veteran Member Join Date: Jul 2002 Location: East Coast. Australia. Posts: 5,455	That quote seems to support Liquidrage's point about food source. However, I do not think that the extra food source would have been enough to fuel the increase. I would suggest that there is a constant pressure on many species towards greater size, for mating and defensive purposes. This pressure causes an increase in size until it is checked by another pressure, such as an inability to derive enough food to support any greater size. It seems as though the 'invention' of filter feeding allowed whales to break through this barrier, allowing further increase to an even more advantageous size, that other species are not able to reach due to their inability to tap the krill resource.

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