Page 72 - Introduction to Paleobiology and The Fossil Record

TAPHONOMY AND THE QUALITY OF THE FOSSIL RECORD 59

dead organism

potential body fossil
immediate burial decay and transport

complete preservation only hard parts
(rare) left
burial

preserved recrystallized material material
unaltered
removed added

e.g. aragonite
calcite
mineral sediment/ molecular
partial complete into mineral replacement
pores infill

natural
mould

natural cast internal cast

Figure 3.1 How a dead bivalve becomes a fossil. The sequence of stages between the death of the
organism and its preservation in various ways.

and others in plants, and chitin, collagen Decay processes exist because dead organ-
and keratin in animals, which may exist in isms are valuable sources of food for other
isolation or in association with mineralized organisms. When large animals feed on dead
tissues. plant or animal tissues, the process is termed
scavenging, and when microbes, such as fungi
or bacteria, transform tissues of the dead
Decay
organism, the process is termed decay. Well-
Decay processes typically operate from the known examples of scavengers are hyenas
moment of death until either the organism and vultures, both of which strip the fl esh
disappears completely, or until it is mineral- from large animal carcasses. After these large

ized, though mineralization does not always scavengers have had their fill, smaller animals,
halt decay. If mineralization occurs early, then such as meat-eating beetles, may continue the
a great deal of detail of both hard and soft process of defleshing. In many cases, all fl esh

parts may be preserved, so-called exceptional is removed in a day or so. Decay is dependent
preservation (see below). If mineralization on three factors.
occurs late, as is usually the case, decay pro- The first factor controlling decay is the

cesses will have removed or replaced all soft supply of oxygen. In aerobic (oxygen-rich)
tissues and may also affect many of the hard situations, microbes break down the organic
tissues. carbon of a dead animal or plant by convert-