3 The Fossil Record
Lucky Accidents of Fossilization
Now let us turn to our richest geological museums, and what a paltry display we
behold! That our collections are imperfect is admitted by everyone. Many fossil spe-
cies are known from single and often broken specimens. Only a small portion of the
earth has been geologically explored, and no part with sufficient care. Shells and
bones decay and disappear when left on the bottom of the sea where sediment is not
accumulating. We err when we assume that sediment is being deposited over the
whole bed of the sea sufficiently quickly to embed fossil remains. The remains which
do become embedded, if in sand or gravel, will, when the beds are upraised generally
be dissolved by rainwater charged with carbonic acid.
—Charles Darwin, On the Origin of SpeciesTo debunk creationist distortions about fossils, we must start with a clear understand-
ing of the fossil record and the process of fossilization. As discussed in the prologue, the fos-
sil record was embarrassingly incomplete when Darwin published On the Origin of Species in
1859, but it soon became one of his strongest lines of evidence. During the twentieth century,
our fossil collections were vastly improved and hundreds of evolutionary sequences and
transitional forms were documented.
This transformation from an embarrassing fossil record in 1860 to an embarrassment
of riches by 1960 represented the hard work of thousands of dedicated paleontologists and
geologists. Yet they battle against enormous odds. Creationists often assert that the fossil
record is nearly complete and should show the innumerable insensibly graded transitions
that Darwin expected in 1859. Yet, even with nearly 200 years of collecting behind us, the fos-
sil record is relatively complete only in certain areas as indicated by the quote from Darwin.
Fossilization is still a highly improbable event, and most creatures that have ever lived do
not become fossils.
How do we know this? A whole subfield of paleontology, known as taphonomy (Greek
for “laws of burial”), is dedicated to understanding how and why organisms become fossils
(see Prothero 2013a: chap. 1). Consider the chain of events that happen to an organism after it
dies (fig. 3.1). First, there are the biological agents (bacteria, fungi, insects, and other decom-
posers, scavengers, etc.) that break down or destroy an organism after death. The soft parts
of animals decay or are eaten quickly, so they almost never fossilize. Only the hard parts, the
shell or skeleton, have a reasonable chance of preservation. After an animal dies, its bones
are typically scavenged and broken, so few or no remnants of the skeleton may actually sur-
vive. Taphonomists have done lots of research in places such as East Africa, where they have
observed and documented the details of how hyenas and other scavengers tear up a carcass
and break up nearly every bone. When the taphonomists mark and photograph these sites
and return a year later to document the changes, even the bones that survive scavenging
may have been broken or scattered by trampling or by other agents of destruction.