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
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.