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Re: Dino size: go on, laugh at me
On Tue, 27 Jan 1998, Gigi Babcock or Ralph Miller III wrote:
> The story goes that the herbivorous dinosaurs -- at least up until the
> Cretaceous burgeoning of the angiosperms -- ate food which was high in
> fiber, but poor in nutrition. The largest of these, the sauropods,
> flourished mostly before the advent of flowering plants (although, as we
> know, a number of Cretaceous sauropod fossils have been found).
The spectacle of monster sauropods masks the possibility that n.a.
dinos got bigger _after_ angiosperm radiation (though the impact of that
radiation is still argued--for example, Wing found an ash fall which
froze a slice of late Cretaceous plant life. It showed fern dominance at
least in this one locality). Recognizing the incompleteness of the
record, small dinos nevertheless disappear and many lineages were at their
peak size right before their extinction. Together, these lines of
evidence suggest a force other than (or at least in addition to) poor
quality food driving size increase.
> I don't know how valid this hypothesis is, considering that today's
> folivores (leaf eaters), hoatzins and koalas for example, do not attain
> gigantic size.
Yes. And there is nothing I know of prohibiting large mammals from
processing large quantities of food, via tooth batteries, and capacious
guts, for example. Such economies of scale are not propriety. Besides,
though it is roundly assumed that bigger things need less food per gram
body weight suggesting a causal relationship between size and efficiency
of intake (and therefore advantage of size), there is significant
within-taxon variation in such allometries. This suggests such apparent
relationships may be side effects of some other force or forces. Even
looking at the familiar graph of metabolic rate/gram vs. body mass, there
seems to be practically no advantage above horse size from this effect.
Indeed, I have presented an entirely valid hypothesis for dino-size -- the
need to protect a fixed-site nest (is this even an original idea with
me?)-- and, though plenty of alternate hypotheses are presented (all with
significant holes as you and I have noted) -- the only criticism I have
had is the dubious claim that dino eggs were so cheap
they could be abandoned and another clutch laid. Not only is this
counter-intuitive (a nest has many other costs besides the egg), it
contradicts the behaviour of extant species. Crocs, even though they
suffer regular predation on their nests, do not double clutch (one
exception is apparently due to two mating seasons not double clutching).
Who was it on this list that said words to the effect of "science without
data is philosophy"? I think this issue shows the inadequacy of such a
position. We have a ton of data on apparent allometric relationships.
But all of it is next to useless because no theory exists to bind it into
a coherent theoretical framework. Here is my hypothesis which is utterly
reasonable but also utterly untestable. And it has almost no quantitative
foundation (except deFraiport's allometric relationship between snake size
and nest defense!), yet it is a more reasonable idea. We are like the 15
century Spanish populace who, upon seeing solid gold evidencefrom the new
world, imagined El Dorado.
Empiricism shouldn't prevent us from making reasonable hypotheses and
taking them seriously.
(Ralph, I realize this goes beyond the scope of your reply, and I
apologize for hijacking your good points).