Paleontological Society of Austin
Book Review
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Richard Fortey
Richard Fortey has the same enthusiasm for trilobites that the late
Steve Irwin had for crocodiles. As a senior paleontologist at the
Natural History Museum in London and a member of the Royal Society,
his credentials are impeccable to author this book and several others
related to evolutionary science. It is reasonably technical, but not
so much that it bewilders readers who are just interested in the
subject. Trilobites stayed around for more than two hundred and
ninety million years, and must be expected to have evolved and
diversified considerably over this period. The book takes chapter by
chapter the principal parts of trilobites, starting with a chapter
each for shells, legs, and eyes, and then takes up the controversial
subject of the Cambrian Explosion.
There are several little bits of information that I had never
considered before. Most (if not all) arthropods, including trilobites,
shed their exoskeletons the same way that lobsters and crabs still
do. This means that a single trilobite can leave a number of empty
shells during its lifetime. Normally, the shells are shed piecemeal,
so that a complete empty shell is seldom fossilized. This is
responsible for the disarticulated 'trilobite hash' found when a large
number of empty shells accumulate and are fossilized. Some trilobite
fossils may only be empty shells and not the critter itself. Fortey
named one trilobite Cloacaspsis because it had evolved the ability to
live in stagnant, sulfurous water that was almost devoid of oxygen. It
was fossilized in iron pyrite, and even now a sulfurous smell is
detected when the rock strata are split open. He derived the name
Cloacaspsis from the Cloaca, the canal that channeled waste and sewage
from Rome to the Tiber River. This is also the term used by zoologists
describing the terminus of the alimentary canal in the anatomy of
reptiles and birds.
Dr. Fortey’s explanation of trilobite eyes has some points that are
hard to accept. He claims that trilobites’ compound eyes are made of
pure calcite crystals oriented along the c axis. (Calcite crystals
exhibit double refraction, having two indices of refraction according
to the planes of polarization. The c axis is neutral to this effect.)
Exactly how trilobites pulled this crystal -growing feat is a secret
that died with the trilobites. The crystals had to be rounded on the
exposed end, which is not a favored shape of crystal terminations.
He further explains how one species, the Phacops, corrects for
spherical aberration in the calcite lenses by including atoms of
magnesium in the crystal structure. Since magnesium carbonate and
calcium carbonate have different indices of refraction, the spherical
aberration was supposedly corrected. This study was done by Dr.
Riccardo Levi-Setti, a nuclear physicist at the University of
Chicago. While not wishing to cast doubt upon his conclusions, there
are some rather serious flaws in the explanation. Simply combining two
materials having different indices of refraction will not do
much. This might possibly pass for a flawed explanation of correction
for chromatic aberration in lenses but has nothing whatsoever to do
with spherical aberration, which is best corrected by the shape of the
lens. Combining calcium carbonate and magnesium carbonate would have
the optical properties of dolomite.
The chapter covering the Cambrian Explosion, titled Exploding
Trilobites, is excellent but is at odds with some of the other
explanations, notably that of Stephen Jay Gould. Fortey cited several
instances of opposing theories on how so much life suddenly appeared
during the Cambrian Period. One prominent paleontologist launched a
personal verbal attack on Gould resulting in acrimonious statements
reminiscent of James Thurbur’s fictitious rival paleontologists,
Drs. Millmoss and Ponsonby. (During one encounter, Dr. Millmoss was
heard to say, "A Millmoss assumption is more important than a
Ponsonby proof." Dr. Ponsonby retorted, "The old boy [Millmoss] has
never dug up half as many specimens as he has dreamed up.")
Dr. Fortey’s account of the Cambrian Explosion was that it was more of
an explosion of size rather than a sudden proliferation of new
species. His favored theory is that the fauna of the Cambrian Period
had been quietly evolving for a long time, but was small and not prone
to leaving remains that were conducive to preservation as fossils. It
is not necessary to be large to be perfectly good arthropods. The sea
swarms with tiny arthropods today that have left no fossil records of
their ancestry. For example, tiny copepods, which are members of the
plankton, are so numerous that they can turn the seas black, yet their
only fossil is a species preserved in the bodies of fossil fish. (In
jest, I propose that if trilobites were sufficiently smart to grow
calcite eyelenses oriented along the c axis, they might have developed
a kind of Paleozoic steroid to enhance their growth.)
Having read Trilobite! and Stephen Jay Gould’s Wonderful Life, which
preceded the former by eleven years, my conclusion is that both are
excellent books. Trilobite! was written for nonprofessional people who
have a healthy interest in paleontology, while Gould’s book is so
technical in places that I question how many of the people who bought
it and put it on the best seller list actually understood and retained
much of the material. Also, Fortey’s book has taken advantage of
intervening eleven years of intense research to present several views
of the Cambrian Explosion, of which there is no clear consensus.
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