Lecture 3

Question 1

Fossils-What are they, what do they tell us, examples

Answer 1

• remains of former life
• give a view of extinct morphologies, species, ecosystems, and evolutionary transitions between now clearly separate forms
• include bacteria, algae, plants, invertebrates, and vertebrates
• also include tracks, traces, burrows, that give us a view of the activities of extinct life

Question 2

Modes of preservation

Answer 2

• actual remains, such as frozen mammoth, wood, shells, bone
• mineral replacement “petrified”
• impressions
• casts
• special modes like amber
• chemical fossils-event ancient DNA
• trails and other trace fossils
• coprolites
• eggs, nests, fossil fetuses
• environmental traces, including fossil raindrops, ripples, dunes, mud cracks, glacial scrape marks

Question 3

Pre-modern interpretation of fossils

Answer 3

-generally seen as items created in place and mimicking shells, teeth, or bones

Question 4

Leonardo da Vinci and Nicklaus Steno

Answer 4

• realized that fossils were remains of former life
• da Vinci speculated that shells on mountains showed that they were once covered by the sea
• most famous demonstration was of fossil tongue stones to teeth of living sharks

Question 5

John Woodward

Answer 5

-by 1680 fossils are seen as remains from the Deluge (flood of Noah)

Question 6

George Curvier

Answer 6

• introduces reality of extinction, long history of life, repeated catastrophes and re-population by new organisms
• use of biostratigraphy and index fossils
• invented archeology

Question 7

Modes of preservation

Answer 7

• sediments-almost all fossils in sedimentary rocks

- biases: these affect what we see as fossils

Question 8

conglomerate

Answer 8

-rocks cemented

Question 9

sandstone

Answer 9

-sand cemented

Question 10

shale

Answer 10

-mud cemented

Question 11

limestone

Answer 11

-shell bits

Question 12

chert

Answer 12

-silica

Question 13

Environmental Bias

Answer 13

• fossilization requires sedimentation

- best sites: shallow marine basins, reefs, lakes, river flood plains

Question 14

Preservational bias

Answer 14

-hard parts of large creatures best; small creatures with soft bodies least likely to leave fossils

Question 15

Depositional environmental bias

Answer 15

-fossilization unlikely if scavengers are present, soil is acidic, there are high O2 levels which encourage decah, strong water currents or bioturbation moves things around

Question 16

How do fossils come to be?

Answer 16

• have to know how rocks are made
• sediment and these things get stuck under layers and layers of sediment over thousands of years make a fossil
• most of the time what dies rots away so no fossil is made
• so the fossil record is kind of sparse, not a complete record of everything that ever lived

Question 17

Sampling biases and gaps

Answer 17

• over and under representation by environment (shallow water marine–>good, mountains–>poor)
• by taxon: mollusks, brachiopods, corals, echinoderms, all well represented while insects, spiders are poorly represented and flatworms, nematodes, rotifers, and ctenophores are almost not at all represented
• by geological time period
• by continent: Australia is a poor record of invertebrates

Question 18

taphonomy

Answer 18

-do experiments to determine how dead things get preserved

Question 19

Nematodes

Answer 19

• most diverse species

- only have fossils of 5 kinds

Question 20

gaps

Answer 20

• missing rock sequenes common in geological record
• due to non-deposition, non-preservation, destruction by tectonic forces
• destruction by erosion
• the higher you go in the taxonomic category the more representation you get so you can see the big picture

Question 21

Importance of fossil record

Answer 21

-without it we would know that whales are mammals but we wouldn’t know how they got there

Question 22

special and unusual preservation in fossil record

Answer 22

• most valuable kinds of fossils
• unusual deposition, fast, fine sediment, no O2 microbial action to replace and mineralize soft tissue
• entire small soft bodied animals, hair, feathers, dinosaur eggs with embryos, body tissue of frogs and mammals, wings/internal ears of bats

Question 23

Cabrian

Answer 23

-Burgess shale, Chengjiang

Question 24

Pennsylvanian

Answer 24

-Mason Creek

Question 25

Jurassic

Answer 25

-Solnhoffen

Question 26

Eocene

Answer 26

-Messel

Question 27

Mesozoic/Cenozoic

Answer 27

-Ambers

Question 28

What we learn from fossil record

Answer 28

- sampling-how complete is our view of life history in the fossil record? - extinct diversity - times of origination and extinction-confidence intervals and data to use for determining evolutionary rates - observe evolutionary transitions - rates and patterns of evolution in the past - paleobiogeography - paleoclimate - paleoecology

Question 29

Sampling

Answer 29

- if we look at living marine animals, only 20% would leave fossils under normal circumstances - gaps in deposition/erosion - if only a tiny minority of extinct species is known, how good can our record of the major patterns of evolution be? - ex: for animal fossil record should recover nearly all phyla, most classes and proportionally fewer lower taxonomic categories

Question 30

Extinct diversity

Answer 30

- reveals former life on earth. Trilobites, dinosaurs, strange Cambrian animals all known only via the fossil record - patterns change through time

Question 31

Kinds of questions

Answer 31

- was live always as divers as now? - does the record reveal trends or underlying regularities? (past extinctions only known this way) - is there progress? - can we find transitional forms in evolutionary series?

Question 32

Evolutionary transitions

Answer 32

- to observe speciation - to observe macroevolution, transitions between major groups: fish to amphibian, reptile to mammal, reptile to bird, land mammal to whale - to test theories of evolution: gradual vs. punctuational

Question 33

Vertebrates in the fossil record

Answer 33

- origins and new structural features (jaws, lungs, legs) - rise and fall in diversity - transition to land life - meaning of extinctions-competition vs. convergence

Question 34

Species origins

Answer 34

-difficult to pick up in fossil record because of the sampling problem. However some species to species transitions are known from the fossil record

Question 35

Transitional forms between distinct groups

Answer 35

- several | - fish to amphibian, dinosaur to bird, land mammal to whale, lizard to snake, hominid to human