Fossil Record & Geologic Time Lab Flashcards
Unaltered remains (Unaltered remains)
When hard parts of a fossil remain unchanged due to their resilience
Desiccation (Unaltered remains)
Freezing/mummification
Embedding (Unaltered remains)
In wax or amber
Recrystallization (Altered Remains)
Old minerals rearrange, usually involving an increase in crystal size. In shells, this destroys the original, internal reflective structures, making them appear dull
Replacement (Altered Remains)
Old minerals are replaced with new ones
Permineralization (Altered Remains)
Pores or empty body chambers of organisms are filled with a mineral
Petrification (Altered Remains)
The tissue of a fossil is replaced by a new mineral, for example, silicified, or petrified (pores within the woody tissue are permineralized)
Carbonization (Altered Remains)
Volatile such as water are removed through heat and compaction, leaving a thin carbon film
Molds (Indirect Preservation)
If the organism is stamped into the sediment and the sediment and the sediment is subsequently lithified, an external mold is produced (Trackways are external molds of feet)
If the interior of an organism such as a shell dissolves away, an internal mold is produced
Cast (indirect Preservation)
If an external mold later becomes filled with sediment/minerals, an exact replica, or cast, of the original fossil is made. Molds are negatives and casts are positives
Burrows and Borings
Many animals excavate burrows in soft sediment. Some bore holes into solid rock, wood, or shells. These structures are often tubular and horizontal (for deposit feeding or dwelling)
Resting traces
When an animal stops moving for a short while (either for rest or protection), they produce a shallow impression or mold on the sediment surface that may record their shape or morphology
Trackways, Trails, and Footprints
Many animals travel across soft sediment surfaces. Evidence of their passage is often preserved as molds on top of beds or as casts on the bottoms of overlying beds. Many trails are formed by organisms that are surface feeding or grazing
Coprolites (Fossil Excrement) and Gastroliths (Gut area of Skeleton)
Coprolite is a term applied to fossil excrement. Gasthroliths are only positively identifiable if they are found in the gut area of a skeleton; they are rounded stomach stones used for grinding down food after it is swallowed