Fossils & Evolution—Chapter 11 Fossils and Evolution 870:125 Review syllabus –Text –Supplemental resources –Objectives –Tests and grading –Trip to Ashfall (NE)

Fossils & Evolution—Chapter 12 Ch. 1—Key concepts to know The fossil record is incomplete. Biological, mechanical and diagenetic agents all destroy potential fossils. Normal fossil preservation is favored by rapid burial of durable hard parts. Exceptional preservation occurs via rapid burial in fine- grained sediments under low oxygen conditions. The fossil record is biased because of differential preservation and uneven sampling. It is biased in favor of: 1) durably skeletonized organisms; 2) marine organisms; 3) geologically recent organisms Because of biases, knowledge of past life is far better at higher taxonomic levels than at lower taxonomic levels

Fossils & Evolution—Chapter 13 Key terms (know definitions) Taphonomy Biocenosis Thanatocenosis Necrolysis Biostratinomy Diagenesis Lagerstätten

Fossils & Evolution—Chapter 14 Why study fossils? Fossil = remains or traces of a once-living organism Paleontology = the study of fossils Importance of paleontology –Biostratigraphy (age dating of rocks) –Evolution –Paleoecology/paleoenvironmental interpretation –Paleogeography/paleobiogeography –Simple fascination

Fossils & Evolution—Chapter 15 Modes of preservation 1.Unaltered remains (frozen mammoths; insects in amber; unaltered shells & bones) 2.Permineralization (infilling of void spaces) 3.Replacement (molecule by molecule substitution) 4.Impressions 5.Carbonization 6.Molds / casts

Fossils & Evolution—Chapter 16 Eocene mammal with partially preserved fur and flesh (Germany) Carbonized Jurassic leaf

Fossils & Evolution—Chapter 17 Taphonomy = science of fossilization Many steps in the process of fossilization, with significant removal of specimens at every step Once fossilized, the odds of being collected are low (uplift and exposure; weathering; discovery; chance, etc.) Life assemblage (biocenosis) Death assemblage (thanatocenosis) Necrolysis (scavenging, decay) Biostratinomy (break-up, scattering and shallow burial of remains) Initial fossil assemblage Diagenesis (deep burial, recrystallization, dissolution, metamorphism, etc.) Final fossil assemblage

Fossils & Evolution—Chapter 18 Life assemblage (biocenosis) Death assemblage (thanatocenosis) Total fossil assemblage Fossils actually discovered Destruction of most soft tissues Destruction of most hard tissues Destruction of most fossils

Fossils & Evolution—Chapter 19 The fossil record is highly biased –Number of fossils is but a fraction of the number of once-living plants and animals Quality of the fossil record

Fossils & Evolution—Chapter 110 Fossilization is a rare event! Some estimates: –> 4,500,000 living species of plants and animals –250,000 described fossil species –Thus, all described fossil species represent < 5% of the total number of living species –Yet, fossil record covers billions of years and today’s biota is but a snapshot –If preservation were truly efficient, then number of fossil species should dwarf number of extant species

Fossils & Evolution—Chapter 111 Standing crop in ¼ m 2 (offshore Japan) ½ m 197 shells (~ 200) Average lifespan = 2 years, thus:……… 1000 empty shells in 10 years 100,000,000 empty shells in 1 m.y. A stack of shells 1000 m high if a layer of 1000 shells is 1 cm thick (actual sedimentary thickness is ~320 m/m.y.)

Fossils & Evolution—Chapter 112 Sources of bias Uneven preservation potential Sampling bias

Fossils & Evolution—Chapter 113 Uneven preservation potential Preservation potential of organisms is goverened by –Resistance to destruction Biological, mechanical, chemical Hard parts vs. soft parts –Habitat (during life)

Fossils & Evolution—Chapter 114 Destruction Biologic destruction includes –Predation –Scavenging –Boring –Bacterial decay Example: Radiograph of heavily bored gastropod

Fossils & Evolution—Chapter 115 Destruction Mechanical destruction includes breakage and abrasion due to particle interactions caused by wind, waves, currents –Some shells and bones are more resistant to abrasion and breakage than others –Different sizes of the same shells vary in their resistance to abrasion and breakage

Fossils & Evolution—Chapter 116 Abrasion experiment gastropod coral alga (multitaxa)

Fossils & Evolution—Chapter 117 Abrasion experiment (marine bivalves) large shells small shells

Fossils & Evolution—Chapter 118 Durability of vertebrate bones Durability is governed by bone density and thickness; also by surface area-to-volume ratio: –Least durable Ribs, vertebrae, breastbone, hip (part), shoulder blade, fingers, toes –Intermediate Thigh, shin, upper and lower arms, ankles and wrists, hip (part) –Most durable Teeth, jaws, skull

Fossils & Evolution—Chapter 119 Destruction Chemical destruction varies with: – the original skeletal mineralogy of a fossil – the chemistry of subsurface fluids – temperature of burial environment

Fossils & Evolution—Chapter 120 Relative chemical stability

Fossils & Evolution—Chapter 121 Destruction Chemical stability vs. temperature and pressure –Silica is more stable in cold water –Carbonate is more stable in warm water and under low pressures Dissolution occurs under high pressure and low temperature conditions

Fossils & Evolution—Chapter 122 Distribution of modern deep sea pelagic sediments

Fossils & Evolution—Chapter 123 Resistance to destruction Hard parts are much more likely to be preserved than soft parts (but soft parts and even pigments can be preserved)

Fossils & Evolution—Chapter 124 Environment and preservability Best preservation generally occurs in calm, aquatic environments Exceptional preservation occurs in fine- grained sediments in the absence of oxygen, (“biologically inert” burial conditions)

Fossils & Evolution—Chapter 125 Environment and preservability Lagerstätten (“Mother lode”) = deposits that contain large numbers of unusually well preserved fossils –Burgess Shale (Cambrian, Canada) –Hunsrück Shale (Devonian, Germany) –Mazon Creek Shale (Pennsylvanian, Illinois) –Solnhofen Limestone (Jurassic, Germany) –Baltic amber (Oligocene, Germany) –La Brea tar deposits (Pleistocene, California)

Fossils & Evolution—Chapter 126 Lagerstätten (Hunsrück Shale, Devonian of Germany)

Fossils & Evolution—Chapter 127 Lagerstätten (Solnhofen Limestone, Germany)

Fossils & Evolution—Chapter 128 Lagerstätten (Burgess Shale, Cambrian of Alberta)

Fossils & Evolution—Chapter 129 Tully monster (Mazon Creek Shale, Pennsylvanian of Illinois) Check out U-Haul website

Fossils & Evolution—Chapter 130 Sampling bias Fossil record is best in most recent geologic systems –Younger rocks are less likely to be covered or obscured by other rocks –Younger rocks are less likely to have been eroded, metamorphosed or subducted

Fossils & Evolution—Chapter 131 Fossil species diversity vs sediment volume/exposure

Fossils & Evolution—Chapter 132 Consequences of preservation and sampling bias Knowledge of past life is far better at higher taxonomic levels than at lower taxonomic levels –In a given sample, you’d only need to look at a small number of specimens to find all of the phyla present, but you’d have to look at a lot of specimens to find all of the species present!

Fossils & Evolution—Chapter 133 Sampling bias: Danish Miocene mollusks Phyla1 Classes3 Orders12 Families44 Genera64 Species86 Individual shells 2,954

Fossils & Evolution—Chapter 134 Sampling bias: Danish Miocene mollusks If sample size were larger, then more species and possibly more genera might have been found, but probably no more classes or phyla If sample size were smaller, then fewer genera and species would have been found, but probably no fewer classes or phyla

Fossils & Evolution—Chapter 135 Rarefaction curve [How many taxa would have been found had the sample been smaller?]

Fossils & Evolution—Chapter 136 Conclusions Every assemblage of fossils represents an extremely biased sample of the organisms once living in an area Lack of fossils in a rock cannot be taken to mean that organisms were not living in the area –“Absence of evidence is not evidence of absence”