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Re: "Dinosaurs don't count"



At 03:56 PM 4/21/99 PDT, Jessica Wagar wrote:
>I recently got the boo "1001 things everyone should know about 
>science" by James trefil from the library..while browsing through it, 

[snip]

>"From the viewpoint of science dinosaurs do not count"...
>"There were never more than a few species of the large dinosaurs 
>around at any one time...they were angolous to modern elephants and 
>rhinos: beautiful and interesting, but carying little information....
>Add to this the fact that dinosaurs, because they were land animals 
>rarely left fossils, and you have a situation where the kind of fossil 
>that is most interesting to the public is probably least interesting 
>to scientists"....

[snip]

>So, I'm asking list members your opinions:
>Why would dinosaurs be or not be scientificly "important" or 
>noteworthy? and do dinosaur fossils have "little scientific value"?, 
>if so, what is their value?

I am going to do something astonishingly weird and defend his position.
(Okay, I will then tear it down, but I'll start by defending it).

Scientifically, things at which dinosaurs suck:
I) Almost anything requiring large sample sizes.  With dinosaurs we're often
happy with a single partial individual.  With population-level studies of
variation or evolution or stratigraphy, though, you want to have lots of
samples (as in "statistically significant sample sizes").  With rare
exceptions, Mesozoic dinosaurs aren't available in those kinds of numbers.
Stephen J. Gould, Niles Eldredge, or Phil Gingerich wouldn't have gotten
very far in quantifying rates and modes of evolution if they had used
dinosaurs: they needed organisms with lots of specimens on each horizon and
on multiple stratigraphic levels in given localities.  Dinos would suck at
this, while pulmonate snails, or trilobites, or Tertiary mammals could serve
a WHOLE lot better.

II) As index fossils.  Related to the above (very poor sample size).  Sure,
when you *DO* find a dinosaur fossil identifiable to a species, you might
make some strong inferences about correlating it with other localities with
the same species.  However, a good index fossil is one that you are
practically guaranteed to find everytime you go to that outcrop.  With rare
cases, dinosaurs aren't like that.

III) In terms of global biomass.  Just as today only a small fraction of the
total biomass of the Serengeti is actually "on the hoof" (i.e., incorporated
in large vertebrates), so too in the past only a small fraction of the total
biomass of the Morrison or the Tendaguru or the Judith River was in the
dinosaurs.  In that sense, dinosaurs were just some really spectacular parts
of the fringes.

IV) Short term or small scale environmental changes.  Since a) we don't know
too much about the environmental tolerances of Mesozoic dinosaurs and b)
even if we did, most species are known only from a partial data point (i.e.,
a single incomplete skeleton), dinosaurs aren't very useful for mapping out
environmental changes "upsection" (through stratigraphic time, particularly
on the outcrop scale: thousands of years rather than tens of millions of
years).  Similarly, dinosaur fossils are exceedingly poor at recording
environmental differences within a single stratigraphic horizon at a single
region.  For these types of problems, microfossils, invertebrates, and
plants are a LOT more useful than dinosaur fossils.

However, variation, rates of evolution, index fossils, biomass, and
environmental changes are NOT the only scientifically interesting things in
paleontology!!  Far from it.  Dinosaurs are spectacularly useful in other
aspects of the field:

I) Evolutionary patterns: Okay, so calculations of rates are difficult when
you are happy to find a single partial skeleton.  However, *pattens* of
evolution (i.e., origins of novel structures, important shifts in life
habit, etc.) can and are revealed by the spotty dinosaur record.  I'll pit
the significance of a single specimen of _Archaeopteryx_, _Caudipteryx_,
_Eoraptor_, or hadrosaur nest against a sauropods-weight of _Phacops_ or
_Cerion_ in this aspect.  Individual specimens of these latter two (the
trilobite and snail that made up lots of Eldredge & Gould's, respectively,
early work) have not greatly altered previous notions of the history of life
nor strongly supported previously hypotheses of paleobiology nor added
greatly to reconstructing phylogeny: the dinosaur fossils I mentioned,
however, did.

II)  Functional morphology: Single specimen fossils can also provide
important new insight towards interpreting functional morphology.  Sure,
more specimens would be useful (especially to determine if the structure
observed isn't pathological!), but think of all the studies that are done in
interpreting fossil structures from dinosaur skeletons.  Even outside the
paleontological community, people love to speculate on the functional
anatomy of dinosaurs (witness many postings to this list, or some of the
more infamous "hey,-ANYBODY-can-do-paleo" studies such as the
multiple-hearted _Barosaurus_ paper some years ago).

III)  Ichnology:  Despite what is implied by James Trefil, dinosaurs are not
simply known from body fossils (hey, they're not all elephant- or
rhino-sized, either, but I'll let that pass...).  There is a huge abundant
record of dinosaur footprints out there, to which many interesting questions
have been asked and answered: questions of speed, of distribution, of
variation (in horizons and over time), etc.

There are other aspects we could come up with as well, but this is a good start.

So, I've worked on both sides of paleo: I've sat for hours picking literally
hundreds of Cenozoic podocopid and polycopid ostacods from samples of
sediment you could fit in a 35 mm film canister, and I've been excited when
a colleague faxes me a photo of a single vertebra from the Turonian of...,
well, you'll hear about that soon enough. (:-).  I can appreciate the
sentiment (?) of Trefil, but I think it is misguided.  There is more to
paleontology than sample sizes.  For some questions, you need a few
godzillion trilobites or snails or brachs or pollen grains or whatever to
answer; for others, a single partial skeleton can be much more informative.

Hope this helps.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:tholtz@geol.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661