Re: Armadillos at the K/T!

["David Marjanovic" <david.marjanovic@gmx.at>]

----- Original Message -----
From: "John Bois" <jbois@umd5.umd.edu>
To: "David Marjanovic" <david.marjanovic@gmx.at>
Cc: "The Dinosaur Mailing List" <dinosaur@usc.edu>
Sent: Monday, October 01, 2001 3:21 AM
Subject: Re: Armadillos at the K/T!


> There are reasons for organisms becoming extinct.

Nobody doubts that.

> Apparent rates of extinction have no theoretical grounding: to me
> it is absurd to suggest that extinctions are basically two
> flavors--background or catastrophic.

Regardless of theory, they have AFAIK a practical grounding. All these neat
little graphs, extinction curves, come to mind...

> The evidence for terrestrial
> vertebrates at the K/T in the Western Interior is neither.

You're AFAIK the first to say so for several years. Why?

> However, the idea that all
> organisms are happily oscilating for eternity around a comfy carrying
> capacity is romantic.

Probably it is, but the idea that these oscillations can suddenly crash to 0
for thousands of species all around the globe in most ecosystems is even
less founded IMHO.

> I don't think the hypothesis does a good job of explaining 100% of the
> extinctions.

It isn't a perfect explanation (it doesn't offer testable hypotheses why
every single known K-T species did or didn't die out). It is, however, by
far the best explanation available. It needn't be perfect -- it's just
science. :-)

> when confronted with a problem
> as ecologically complex as this one).

Why do you (pre?)suppose this problem is ecologically complex? It could have
been very simple, couldn't it? Simply hell broke loose :-)

> I would like to decouple other extinctions.

Have you got evidence that we _should_ decouple other extinctions? (Sorry if
I'm annoying you by repeating the same questions all the time. I'm just
trying to believe that you have more evidence than the three big mammals of
LK western NA on which to build a hypothesis.)

> First comes mortality, then extinction.  Right?

Maybe. Maybe not. That's surely common in background extinction (I guess),
but...

> If extant organisms
> suffer much mortality due to a certain factor, that factor should be
> suspect if extinction occurs.

It should not necessarily be the prime suspect, just because extant
organisms have been under this pressure for tens of millions of years and
still not died out. It surely shouldn't be among the prime suspects in a
sudden mass extinction. (Things are different in a gradual mass
extinction -- but the only definitely gradual mass extinction is now, having
probably begun IIRC 500,000 years ago when *Homo erectus* killed off pygmy
*Stegodon* on some Indonesian island, and the cause is clear.)

> > > Species that couldn't cope are gone!
> >
> > So why don't we see progress in evolution?
>
> Greater computational power in most vertebrates relative to Triassic
> species.

Most vertebrates, you say? What about the 23,000 known recent species of
"fish" (or are these just "bony fish"?), the (some thousands... 4000?)
species of amphibians and the 6500 (IIRC) species of "reptiles"? Sure, there
are almost 10,000 species of birds left, but that doesn't topple the
average.

> Ditto speed.

Among fish? Amphibians? Lepidosaurs?

> Reproductive security and specialized nutritional
> structures in mammals vs. "stem reptiles".

Nothing of that sort in most other amniotes. BTW, we don't know when mammals
gave up laying and shelling eggs.

> Ability to engage specialized
> vectors to carry your sperm in flowering plants.

Even among flowering plants large groups (e. g. grasses, lots of trees) have
reversed to engaging wind. I am allergic against several sorts of angiosperm
pollen.

> Independence from water in plants and animals.

To varying degrees in whatever-you-mean-by-plants, not counting several
reversals, and not at all in lots of animals (even there with reversals).

> I mean, I could go on forever.  From which planet
> must a visitor come that doesn't see these as progressions of a
> kind?  The eye.  Birds' wings. etc., etc.

The most complex eyes, with lens, cornea and stuff, have evolved only 3
times: in killer jellyfish (Cubozoa), a clade of cephalopods (any ammonite
or belemnite eyes known?) and vertebrates (all vertebrates, including
conodonts!). Complex eyes have probably evolved once in arthropods. And the
rest of animals? "Pigment-cup ocelli" or just sensitive spots as ever.
Vertebrate eyes have not improved since the Early Cambrian. OK, birds have
increased the resolution. But mammals have lost two of four opsins* (and
only some primates have recently re-evolved a third one) -- this is not a
progression but a regression IMHO. You could go on forever, but in a very
small circle, IMHO. Yes, the range of complexity or whatever covered by
organisms has increased, but there is no progress when you closely look at
it.
        You have limited yourself to vertebrates. So you can unconciously
overlook most life -- most of which is microscopic, and on the whole devoid
of progress. And there are parasites, many of which are simplified beyond
recognition.
        I heartily recommend Stephen J. Gould's book Full House.

* In case someone needs an explanation: The proteins that enable color
vision. The plesiomorphy is to have one each for red, green, blue and
ultraviolet IIRC; mammals have lost those for red and ultraviolet (probably
due to a nocturnal lifestyle), and some primates, such as humans, have
duplicated and slightly modified the gene for the green one and so are able
to see red again.