[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Pre-K/T mammal wrap-up
If the list will forgive me I will make these final comments on the subject
of mammal fossils.
Off-the-cuff comments in the press can be reckless. This is why I quoted
them. Writers will say things they would never say in a peer reviewed
paper. Right or wrong, Hedges revealed his beliefs, beliefs which mark one
boundary of the discussion. Tom Holtz correctly called me on this: why,
if I knew as much as I say I knew, did I use the "Paleontologists hardly
ever look for mammals in Cretaceous rocks" quote? Because I am skeptical
that Hedges is that ignorant (though I have had a private message claiming
he really is!). There is a part in Woody Allen?s _Annie Hall_ where
Keaton and Allen?s character separately visit a psychiatrist. The
each how often they have sex. Keaton says: "All the time!" Allen, looking
at the same data set, says: "Hardly ever." I am with Allen. I mean with
regard to mammals in K. rocks. As a layman I am always scandalized to hear
how few people are out there at any particular time, actually searching for
_any_ fossils. Also, responses to this topic were fascinating, but I didn?t
get a sense of the relative amount of research going into either dinosaur or
mammal research. Certainly the cooperation between groups is admirable, and
it is an onerous task to choose between funding for one or the other
enterprise. Indeed, members of this list, as intimated by Chris
Brochu, are inured to low funding levels! To me this is somewhat
scandalous. How much research, for example, could be funded from one
Space Shuttle flight? We are all for moving forward in space, but we have
some big questions to answer at home as well: as Jim Kirkland pointed out,
research into any aspect of this time sheds light on all aspects of
evolutionary ecology. Whatever else, Hedges? data raises some big
Then there is Benton?s off-the-cuff comments. He seems rather cavalier in
ignoring Chris Brochu?s position (certainly he has heard of it) that the
data sets are not necessarily contradictory. Surely this venerable
gentleman is aware you can have genetic without morphological change.
Chris claims his comments were ignorant. I claim that he was being ironic
(I admit I could
be wrong--but if I were a betting man...). Here is the off-the-cuff
quote in question: you make the call!
From Anne Gibbons _Science_ Vol. 280 15 May.
"The thought of all these different creatures living under the feet of
dinosaurs is intriguing," says Hedges.
But many paleontologists are deeply skeptical. "It suggests that
the fossil record is horribly incomplete," says Michael Benton." They?re
saying side by side with lower Cretaceous dinosaurs, we should be finding
ducks and hens and squirrels and rabbits." Instead, he thinks that the
molecular clock can?t keep time.
Now, to me this sounds like a piece of rhetoric among the initiated. That
is, that we would recognize it as such. After all, we surely know (don?t
we) that he couldn?t be serious? In the long run, I suppose, both of
these examples illustrate why it is important to keep the language of
science as dry as possible to keep misunderstandings to a minimum.
Indeed, as I have learned (having recently stepped out of the frying pan)
to play with scientific language is to play with fire!
_Perceptions of mammal diversity._
Tom Holtz says:
(That pre-K/T mammals lack diversity) is not a generally held view. Check
out any textbook on vertebrate paleontology (from Romer to Carroll to
Chris Brochu says:
(The view that pre-K/T mammals lacked diversity) is not generally held,
Two things: perceptions are changing to the view expressed above; and
"lacking diversity" needs definition.
Compared with post-dino times, I believe their is a general (if innacurate)
view that mammals were at least morphologically (and probably ecologically)
Here is Benton (I only have 1990 version of his _Vertebrate Palaeontology_:
"The global diversity of mammalian families rose from 15 in the latest
Cretaceous to 32 in the Early Palaeocene."
This indicates at least a relative lack of diversity. _If_ Hedges? data
accurately reflects reality we would have to revise the pre-K/T numbers
upward considerably (whatever they looked like!). And then: "This phase of
placental mammals during the Palaeocene and Early Eocene is usually treated
as one of the best-known examples of adaptive radiation."
Our friend Ann Gibbons opens her piece with a similar idea; "It?s hard to
imagine humbler beginnings than those usually assigned to mammals. The
long-standing view from the fossil record is that our furry ancestors first
appeared 225 million years ago as small, shrew-like creatures living in the
shadow of the dinosaurs. But a new genetic study is challenging that
view, saying mammals were already a diverse lot during the age of
I have seen it argued that it wasn?t really until Archibald?s find in 1996
that researchers could really begin claiming that placental radiations were
underway before the Cretaceous ended.
I imagine that Chris Brochu could agree with the statement: adaptive
radiation is an indicator of increasing diversity; just as he would claim:
increasing diversity doesn?t necessarily cause adaptive radiation. But it
seems to me that there is no right _a priori _ to a null hypothesis in
either position, i.e., whether or not genetic and fossil data sets agree
with each other is a very open question.
Finally, with regard to perceptions, mammal studies is a strange business.
As Cathy Forster says:
"We, like most other field workers, are interested in the entire fauna, not
just the dinosaurs. But unlike dinosaurs, beloved of the popular press, the
other equally interesting animals tend to appear only in the scientific
literature. And it's a shame."
Indeed. It appears as if practically the only ones who are aware of the
"mainstream" are those who are swept up in it. Would that I could take the