Chapter 1 Outline
TYPES OF FOSSILS
- BODY FOSSILS
- USUALLY HARD PARTS (FOR DINOSAURS = SKELETAL MATERIAL LIKE BONES, TEETH,
CLAWS);
- RARELY SOFT TISSUE (USUALLY DUE TO MUMMIFICATION)
- TRACE FOSSILS (ALSO CALLED - ICHNOFOSSILS)
- FOOTPRINTS & TRACKWAYS, NESTS & EGGS, COPROLITES (fossilized
feces) AND GASTROLITHS (stomach stones) for dinosaurs
- Useful for deducing life styles
TAPHONOMY
- STUDY OF THE THINGS THAT HAPPEN TO ORGANISMS AFTER DEATH
- SURPRISING ANYTHING IS EVER PRESERVED
- ORGANIC MATERIALS ARE EASILY DESTROYED & RAPIDLY SCAVENGED
- BEFORE BURIAL
- IF A DINOSAUR IS KILLED
- Disarticulation
- Consumption and decomposition of soft tissue
- Only a few, if any, isolated bones remain
- IF A DINOSAUR DIES FROM OLD AGE, DROWNING OR DISEASE - [Herd animals
sometimes suffer mass deaths (from floods, sand storms, or volcanic ash
falls)]
- Might not suffer much disarticulation
- Soft tissues dry and shrink (if carcass is not in water)
- Many bones, or even whole skeletons, remain
- BURIAL
- MOST COMMON IN AREAS OF DEPOSITION
- Rapid burial increases chances that something will be
preserved
- Sand dunes in deserts, floodplains or channels associated with rivers
- ASSEMBLAGES - COLLECTIONS OF FOSSILS
- IN-PLACE: carcasses haven't moved far (lots of articulated bones)
- REWORKED: disarticulated bones of several species
- buried in one area, exposed by erosion, and redeposited in another
area(often in river channels)
- BONEBEDS: lots of bones of many individuals of only a few species (may
or may not be articulated)
- AFTER BURIAL
- UNALTERED BODY FOSSILS
- Bone &teeth minerals (calcium phosphate) remain unchanged
- dinosaur bones are not usually found in an unaltered state
- ALTERED BODY FOSSILS
- Carbonization: soft tissues preserved as thin carbon
films (not discussed in text, but important for small dinosaurs found
recently in China)
- Permineralization: porous bones filled with secondary minerals
- Recrystallization: dissolution & reprecipitation
of bone or tooth minerals
- Replacement: dissolution of original bone or tooth minerals,
precipitation of new mineral, equal in volume to that dissolved
- CAN PRESERVE FINEST DETAILS
- Molds (dissolution of bone) & Casts (filling
of mold)
- TRACE FOSSILS - SEE ABOVE
COLLECTING FOSSILS
- PROSPECTING
- WHERE TO LOOK -
- Sedimentary rocks of
- igneous rocks started out molten -no organisms, and
- metamorphic rocks are heated and compressed, processes that destroy
bones
- Triassic, Jurassic or Cretaceous age (~230 to
66 million years ago) [together known as the Mesozoic Era (245 to
66 million years)] that were
- dinosaur fossils are sometimes reworked into Cenozoic sedimentary rocks
- deposited in terrestrial environments
- although dinosaur carcasses were sometimes washed into lake and ocean
environments
- chances of finding fossils are increased where more surface
area is exposed
- often badlands & deserts - dry, less vegetation
- COLLECTING
- EXPOSING, CLEANING AND HARDENING
- matrix (rock surrounding fossil) is removed until fossil
sits on pedestal (pillar of matrix under the fossil)
- glue applied that soaks into bone and then hardens
- PADDING AND JACKETING
- padding (to cushion fossil & prevent jacket from sticking)
often consisting of wetted toilet paper is applied
- jacketing (to protect fossil) often consists of strips of burlap
soaked in plaster
- after the jacket has hardened, specimen is turned by separation at
the base of the pedestal
- a plaster cap is applied to open bottom of jacket
- transporting out of field can be easy or difficult
- PREPARING AND CURATING
- PREPARATION = FREEING FROM MATRIX AND PUTTING FRAGMENTED FOSSILS BACK
TOGETHER
- variety of techniques used
- CURATION = DISPLAYING AND ARCHIVING
- fiberglass or resin casts used by most museums now for
display
- actual fossils archived in conditions best suited for protection
and study