We've all heard the term "living fossil" many times
describing living species that appear little changed from their
distant extinct relatives. Two that should come to mind quickly
are the living nautilus and the coelacanth. This month I review
an older book by Peter Douglas Ward that involves many living
fossils.
Methuselah's Trail, Living Fossils and the Great
Extinctions was published in 1992 by the W. H.
Freeman Company. I recently picked up a remaindered paperback
edition at Half Price books. The cover price is $12.95. You may
recall my review of The Call of Distant
Mammoths by Ward from the February,
1998 bulletin wherein I mentioned liking his writing so well
I intended to obtain his older books. Methuselah's
Trail is one of the books to which I had referred.
The first chapter of Methuselah's Trail
is introductory in content. The concept of living fossils is
explained with the aid of Darwinian evolution, recent
evolutionary concepts, rates of evolution, and geologic time.
Ward manages to reduce some complex technical information into
easily understandable terms. I find this to be a plus for the
reader. The discussions of Darwinian evolution includes the
comments of nineteenth century opponents to the theory. One of
the typical statements referred to the "living fossils"
as proof that evolution was not valid. Opponents argued that
because these creatures had not evolved but remained the same for
vast amounts of time the theory could not be true. The fallacy in
this statement, as brought out by Ward, is that evolutionary
theory neither requires progress to higher forms nor does it
establish a pace for the process. Unfortunately even today many
people continue to equate evolution with progress.
The following seven chapters deal with specific "living
fossils" or groups of them. Subject matter includes the
brachiopods, flat clams (modern scallops fall into this group),
nautilus and the rise of the ammonites, ammonite extinction,
horseshoe crabs, land plants, and lobe finned fishes.
The beauty of each chapter lies not so much with the exotic
nature of the groups under discussion but with Ward's treatment
of them. He begins with information about the origin and
radiation. The ecology of the animals (or plants) is discussed.
Lastly, information about the extinction or decline of the group
is presented. These topics are woven into the adventures of field
discoveries.
I can guarantee that anyone reading Methuselah's Trail
will gain new knowledge. I was most fascinated with the chapters
on nautiloids and ammonites which happen to be Peter Ward's
specialty. Ammonite extinction versus nautiloid survival appears
to be caused by a difference in breeding methods coupled with the
mode of the Cretaceous extinction event (asteroid impact). As
Ward explained, ammonites had a planktonic stage in their
ontogeny (development from egg to adult). The Cretaceous
extinction event wiped out most of the worlds plankton and
destroyed the ammonites ability to reproduce.
The decline of the brachiopods and subsequent rise of clams
involves differences in life style. Although both are filter
feeders, brachiopods are intolerant of varying water salinity,
can not survive if their pedicle attachment becomes detached, and
can not dig out if buried in sediment. Changes brought about at
the Permian extinction event adversely affected the brachiopods
in one or more of these ways leaving the world to the clams.
Brachiopods survive today in very restricted environmental
niches.
I have to repeat some of the comments I made in my review of The Call of Distant Mammoths regarding
Peter Ward's writing. I am once again very impressed with Ward's
ability to paint such vivid word pictures that the reader can
feel he's a part of the story. His style makes the reading
experience so enjoyable that you may not realize you are learning
something. I have found Ward's books to be as difficult to put
down as an exciting novel. Interestingly enough, next month's
review will be of a brand new book by Ward.
