History and the Fossil Record

Question 1

Fossil

Answer 1

Any trace left by an organism that lived in the past

Question 2

Compression Fossil

Answer 2

Preserved in sedimentary rock and have undergone physical compression
- common to find plants preserved this way (similar to a plant press)
> internal structure is usually obliterated as the cells become flattened, and frequently all that us left is a delicate carbonaceous film that conforms to the original outline of the plant part
- uncommon to find animals preserved this way
> physical compression of the rock often leads to distortion of the fossil

Question 3

Cast and Mold

Answer 3

Is a type of fossilization where the physical characteristics of organisms are impressed onto rocks
- especially coarse, porous rocks such as sandstones
- usually, the harder parts of an organism
> shells of mollusks
> skeletal structures of coelenterates
> bones and teeth of vertebrate
> chitinous exoskeleton of arthropods
> trunks of trees
> sphenophyte (horsetail)
(these leave the best impression because they are usually composed of calcium carbonate, calcium phosphate, silica, or chitin, which provide a rigid structure and do not decay as easily)

Question 4

Cast (endocast or internal mold)

Answer 4

Is formed when sediments or minerals fill the internal cavity of an organism, such as the inside of a bivalve or snail or the hollow of a skull

Question 5

External mold

Answer 5

When the original remains of the organism completely dissolve or are otherwise destroyed. The remaining organism-shaped hold in the rock

Question 6

Permineralization

Answer 6

Involves deposits of minerals within the cells of organisms
> most common method of fossilization
> calcite, iron, and silica
> organism must become covered by sediment soon after death, or risk being destroyed by scavengers or decomposition
- Some fossils consist of only skeletal remains or teeth; other fossils contain traces of skin, feathers or even soft tissues
- Petrified wood is the most common, but all organisms such as marine fossils (from bacteria to vertebrates) can become petrified
> petrifaction is the result of a tree or tree-like plants having been replaced by stone via a mineralization process that often includes permineralization

Question 7

Carbon Mineralization

Answer 7

Involves the formation of coal balls. Coal balls are the fossilizations of many different plants and their tissues. They often occur in the presence of seawater or acidic peat. Coal balls are calcareous permineralizations of peat by calcium and magnesium carbonates

Question 8

Pyritized Ammonite

Answer 8

Organisms become pyritized when they are in marine sediments saturated with iron sulfides (pyrite is iron sulfide).

Question 9

Unaltered remains

Answer 9

Fossils of organisms, or parts or organisms, that are preserved with little or no change
- Freezing: ancient organisms are sometimes frozen in ice or permafrost (frozen soil) at high latitudes and/or high altitudes, or amber

Question 10

Desiccation or “Mummification”

Answer 10

• unique and rare
• Mosses prefer acidic soils and are able to absorb tremendous amounts of water
• Often used to pack wounds
• High acidity + antibacterial properties = excellent preservation material

Question 11

Ichnofossils (trace fossils)

Answer 11

Do not record body, but some other aspect
- Footprints = mud or sand
- Coprolites = fossilized feces
- Burrows = usually shows behavior record of animal

Question 12

Index fossils (guide, indicator, or zone fossils)

Answer 12

• fossils that are characteristic to a particular span of geologic time
  > although different sediments may look different depending on the conditions under which they were deposited, they may include the remains of the same species of fossil
• good index fossils are found in many locations, but only one layer (time period)
• therefore, rapidly evolving species are really good index fossils
  > the shorter the species’ time range, the more precisely different sediments can be correlated, so rapidly evolving species’ fossils are particularly valuable
  > the best index fossils are common easy to identify at species level and have a broad distribution
• rock formations separated by great distances but containing the same index fossil species are thereby known to have both formed during the limited time that the species lived

Question 13

Geography bias

Answer 13

Most fossils are generated by being covered with sediments – so mostly lowland organisms and marine

Question 14

Taxonomic bias

Answer 14

Organisms with bones and shells amenable to fossilization – going to be hard to see soft-bodied animals, do not see flower parts in fossil record. This is why best fossil records left by marine inverts are those that are shelled

Question 15

Temporal bias

Answer 15

Earth’s crust is constantly being recycled so older rockers are rarer than new
- This leads to gaps in time because older rocks have been recycled into new rocks

Question 16

Why have the origins of higher taxa not been documented?

Answer 16

• Many kinds of organisms rarely leave remains, because they are completely consumed by other organisms
• Sediments usually form only sporadically at a given location
• Fossil-bearing sediments must solidify into rocks and persist for millions of years
• The rock must be exposed and accessible to paleontologists
• No reason to assume that all evolutionary changes in which we are interested occurred at the few localities of a time interval that actually allowed fossilization

Question 17

How do we know the fossil record is incomplete?

Answer 17

• Many periods are represented by few known sedimentary formations, and strata are often represented by more than 10,000 years
• Many lineages are represented only at very widely separated time intervals
• Many extinct species of large, conspicuous organisms are known from only one or a few specimens
• New fossil taxa are discovered at a steady rate (hundreds of thousands of fossil species have already been described)

Question 18

Two difficulties in the interpretation of fossils:

Answer 18

• age can only imprecisely be estimated by their location in the strata
• many fossils are crushed, fragmented, or distorted

Question 19

Chronospecies

Answer 19

• when morphology changes enough to call it something else

Question 20

Anagenesis

Answer 20

“again/backwards origin” - evolution of a new species that replaces the old species, no branching/splitting

Question 21

Cladogenesis

Answer 21

“branch origin” - evolution by divergence of taxa from an ancestral form

Question 22

Morphospecies

Answer 22

Using morphology to describe a new species

Question 23

Extinction (“real” extinction)

Answer 23

A lineage that fails to leave any descendants

Question 24

Pseudoextinction “taxonomic” extinction

Answer 24

A lineage that changes so much its original name disappears

Question 25

Background Extinction

Answer 25

Natural Extinction without human interference
- “normal extinction rate”