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GEOL 104 Dinosaurs: A Natural History

Fall Semester 2017
Bones in the Stones: Fossils and Fossilization


Vertebra of the ornithischian dinosaur Thescelosaurus weathering our of the Hell Creek Formation, near Ekalaka, MT

Key Points:
•Fossils are the physical remains or traces of their behavior preserved in the rock record.
•Trace fossils (such as footprints, burrows, nests, and coprolites [fossilized feces] are the record of behaviors of extinct animals.
•Body fossils (such as teeth, bones, shells, wood, leaves, pollen, etc.) were once part of a living thing.
•Taphonomy is the process by which parts of a living thing are buried and preserved as fossils.
•Different environments of deposition are better at preserving different types and sizes of fossils. •Depending on the taphonomic history, a fossil might be complete, or only fragmentary, or anything in between.
•After burial, different diagenetic processes may alter the composition of the original hard parts of the body.
•Normally the soft tissue (flesh and so forth) decays after death, but in some diagenetic conditions they might be preserved (either unaltered, as carbonized stains, as permineralized material, or as impressions.)

Fossils: The physical traces of past life.

Or, more fully, a fossil is any remain of an ancient organism or its behavior preserved in the rock record.

(Derived from the Latin word "fossilium": that which is dug up. Originally used for anything found in the ground, but by the 19th Century had come to mean traces of past life.)

Fossils are the only direct evidence of past life, although indirect evidence exists in the form of the evolutionary and biogeographic distribution of modern organisms.

Two major types of fossils:

Trace fossils are, essentially, biologically-generated sedimentary structures. They include:

Preservation of trace fossils is just like other sedimentary structures: must have rapid burial, and preserved by lithification of the rock itself.

Body fossils: can be preserved in a variety of ways.

In general, only organisms with hard parts can be preserved: shells, bones & teeth, wood, etc.

For vertebrates (such as dinosaurs), body fossils are primarily bones and teeth

Bone:

But the rest of the vertebrate is soft tissue (and in many organisms there are NO hard parts), and so these are only preserved in rare instances.

Bone (like shell and wood) is not solid material, but porous. Pore space is occupied by organic material in life. Upon death, organic material begins to decay.

In order for bones and teeth to become fossilized (turned into a fossil):

The study of burial and fossilization is called taphonomy. There are various modes of preservation after the bone is buried:

Different organisms have different potential for fossilization:

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Last modified: 22 June 2017

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Tibia of the oviraptorosaur Anzu in the Hell Creek Formation, near Ekalaka, MT.