Fossilization
and Fossils
So what exactly is a fossil?
ANY evidence of
ancient life.
Body fossil
teeth or bones
Trace fossil
cast, track, burrow
Next question…
What is a scientist who studies fossils
called?
paleontologists
Archaeologists study the remains of
ancient humans and their cultures.
Write this down; it is an IMPORTANT distinction!
Fossils
• If the layers of sedimentary rock are the pages that tell the story
of the Earth, fossils are the words.
• Literally, the word fossil means “dug up”.
• Technically speaking fossils are remains of life that are at least
15,000 years old.
• Preservation can include both altered and unaltered hard and
soft parts. Fossils can also be casts and molds.
• Found in shales, sandstones, limestones, amber, ash, nodules,
tar, and ice.
• The study of an organism from death to fossilization is called
taphonomy (can include post-fossilization events as well).
Process of fossilization
Process of fossilization
Fossilization depends on two critical steps:
• rapid burial by sediment
• mineralization
Helpful conditions:
• anoxia (lack of oxygen following burial)
• minimal disturbance subsequently
• mineral-rich water in sediment
Types of Fossilization
Unaltered Remains
Original material, including soft parts preserved
Rapid burial in ice, tar, or mummification
Recrystallization
Original material dissolved
New mineral deposited simultaneously
Permineralization
Minerals infill pores and holes
Molds and casts
Infilling with other material
Often, sedimentary infill
Carbonization
Preservation as thin films of carbon
Outline and sometimes detailed structures preserved
Unaltered Soft Parts (Amber)
Scorpion
Feather
Mosquito
Unaltered Soft Parts (Ice)
“Blue Babe” bison
Siberian Wooly Mammoth
Unaltered Hard Parts: Tar and Anoxic Silt
LaBrea Tar Pit
Avitelmessus, NC
Beetle in tar
Fish from Messel, Germany
Unaltered Hard Parts (skeletal)
Smilodon
Ashfall Park
Columbian Mammoth
Pliocene
Recrystallization: Aragonite to Calcite
Pterorhytis conradi
Chesapecten jeffersonius
Eocene
Cretaceous
Busycon carica
Urosalpinx sp.
Polinices sp
Athleta petrosus
Recrystallization: Change in Crystal Structure
Cyclonema
Euproops
Mississippian Crinoids
Edrioasteroid
Dalmanites
Carbonization
Knightia
Opabinia
Spider
Dragonfly larva
Canadia
Carbonization
Sphenopteris
Permineralization
Petrified Wood Brazil
Jurassic Pinecone
Dinosaur Bone
Shark Teeth
Permineralized Dinosaur Bone:
Cell Structure Preserved
Altered Hard Parts (replacement)
Silicified Mollusks
Pyritization
Silicified Stromatolite
Molds and Casts
shell
cast
external mold
shell dissolves
sediment infilling
interior
shell
shell
Sediment fills void
steinkern
Shell dissolves
Casts and Steinkerns
Trace Fossils
• Reflect the activity, or behavior, of organisms on land and
in marine settings.
• Exogenic – on the surface.
• Endogenic – within the substrate.
• Shape of the trace fossil does not always mirror the
animal.
• Trace fossils are named for their particular shape and form
and not for the animal that made the trace.
Same animal may make several different types of
trace fossils.
Trilobite resting trace
Trilobite trackway
Grazing trace
• Other trace fossils include trackways on land (mostly
dinosaur, reptile, and amphibian) and coprolites (fossilized
feces, “poop”).
Dinosaur Ridge, CO
Glen Rose, TX
Coprolites
Dinosaur
Turtle
Mammal
Crocodile
Factors that Affect Fossilization