L03-Taphonomy

Why is the fossil record incomplete? Tell me ideal find and what we typically find.

Ideal

1. Soft tissue intact

2. complete skeleton

3. articulated parts

4. no distortion

Typically

1. no soft tissue (bc predation)

2. incomplete skeleton

3. disarticulated (separated) parts

4. compacted, recrystalizzed

what determines this: biological and environmental factors filter what is preserved.

SQ: What is taphonomy?

This is the fossilization process

Everything that happens from death of organism to discovery of fossil—> anything that affects fossil record(can you find fossil?)

Typically flow: death and decay—> deposition —> burial—> discovery(due to being preserved)

What does decomposition inhibit the preservation of? What is the worst and best environment for decomposition?

Decomposers inhibit soft tissue preservation—>So decomposers and other predators eat all tissues(muscles,tendon,organs), usually leaving only the bones(but can eat that too).

Worst Env: Decay facilitated by warm, wet, oxygenated environments(b/c decomposers fxn better her and depend on oxygen). Ex: Rainforest

Best env: Cold, dry, no oxygen. Ex: underground.

What is dissolution? What are the two types of it?

Dissolution: break down of hard mineralized tissues via dissolving.

Biological dissolution: Organisms bore into and dissolve the mineralized hard parts of dead organisms to live in and feed on it. Ex: sponges bore into the shell(mineralized hard part) by dissolving it.

Weathering: Chemical(water, gases, acids—>changes molecular/chemical composition) and mechanical (physical—>no change in comp) weathering

What is disarticulation, breakage, and loss? What causes it?

Disarticulation: Separation of body parts (so whole skeleton—>separated into the different parts).

Causes:

Biologic Factors: From predators and scavengers (take bone—>scatters parts).

Environmental Factors: From high-energy environments and environmental events like floods, landslides, coastal areas with strong waves, etc.., taking fossils with it and scatters it or breaks it.

Although disarticulation, breakage, and loss does occur, what is a body part that is most likely to be preserved?

Sturdier, denser parts(thick and whole bone) more likely to be preserved (like teeth of shells)—>fragile parts are lost

TEETH—> Often preserved, most common and often the only fossil preserved from tiny animals like mammals in the time of dinosaurs.

What is compaction and how does it relate to distortion and degradation?

Even if fossils end up somewhere cold and dry, things could still go wrong, like compaction

Compaction: Compression from overburden and tectonic activity movement of tectonic plates, earthquakes, etc.

• squishes fossils flat, so can’t really see mechanics of body parts.—>distortion

• However, can learn about skin color through this and sometimes preserves the muscles.

What is diagenesis and how does it relate to distortion and degradation? What causes this to happen?

Chemical/structural change to the specimen while buried(so the specimen changes in the place to something else)

Cause: Heat and pressure transforms in to oil, coal and natural gas(fossil fuels)

• Soft tissue (organic)—>fossil fuel(inorganic)

Includes the fossilization process and fossil fuel formation—> the sum of all physical, chemical, and biological changes that occur in sediments after their deposition, during and after burial, leading to their transformation into solid sedimentary rock (lithification)—>fossil fuels

SQ: What is recrystallization? How does it form?

Formation of new inorganic crystal overrides(take over) the structure of original biologically formed crystal

• Organic (original) form of mineral is dissolved and reformed back to native inorganic crystal

Transform organic mineral—>inorganic mineral as the organism is dead and can’t control how they use the organic material, so the inorganic form appears instead on the organism(still the SAME mineral, just different form),

Ex: When the clam is alive, water with calcite flow on the clam shell and the clam controls how they use the calcite, but once the clam is dead and water with calcite flows on the clam, it is reformed into the native, inorganic calcite crystal as the clam is dead and can’t control how the calcite is formed.

How does recrystallization relate to distortion and degradation?

Basically, organisms controls the growth of mineral crystals in their hard parts

In the absence of biological control, the crystals in their hard parts will grow inorganically when it is exposed to more of the SAME mineral ions

Ex: Organic calcite: Organisms like the clam genetically control the growth of CaCo3 crystals on their bodies to form their shell, bone, etc…,

Inorganic calcite: In the absence of life, CaCO3, will grow into crystals like this as this is the path of least energy as this is the path of least energy.

So, once a dead clam no longer controls the growth the CaCO3 crystals so the crystal grows inorganically, more brought by water b/c lack of control

Difference between replacement and recrystallization

Think-What is water bringing?

Replacement- Occurs when water contains high concentrations of DIFFERENT dissolved minerals ions as the mineral in the hard parts. Water coming in brings DIFF mineral—>replacement

Recrystallization- Occurs when water contains high concentrations of the SAME dissolved minerals ions as the mineral in the hard parts. Water coming in brings SAME mineral—>recrystallization

What is another example of replacement?

Organic silicate(SiO2 crystal)-sponge spicule (microscopic sponge skeletal components)—>dead, so sponge no—>inorganic chert: in the absence of life, SiO2 will grow into chert (microcrystalline quartz)

How does destruction work?

Volcanism (most fossils, lava destroys)

Subduction: Recycled into Earth, melted in lava—> Earth’s lithosphere including the crust descends into the mantle and is recycled

Plants: Plants evolved to break down rocks, including fossils, to obtain nutrients—> get minerals from rocks, so this will break down fossil as hard parts made of minerals

Paleobiogeographic location of fossils: How do you know where to find the fossils? Is discovery limiting?

Extinct organisms are found in theri biogeographic and temporal range

Discovery: Need to know where and when they lived in the past AND where and when those places are today—?need to loook at env where org lived in the past and translate that onto present day land.

Discovery is also a limit for fossil discovery: need to actually be able to find the fossils—>luck is important and knowledge of wehre org lived.

Screenwashing for tiny teeth—>some fossils are so tiny, the best way is to screenwash through bags of soil

Invisible Discoveries: Fossil poachers? Legitimate private collections?

Fossils in private collections are often inaccessible to researchers and effectively do not exist in science

Fossil Poachers: Unlawful excavation and destruction of fossils form public and private lands—>loses where and when fossils came from, to find age of fossils, look at surrounding rocks

Legitimate private collections: many well-preserved, nearly complete dinosaur fossils have are owned by private collectors

Juveile: imp for growht, rate (immature, fragile bones), so pred eat more.

Why do marine organisms have a better fossil record than terrestrial organism?

Because dead marine organisms go to sea floor, which has low energy, fine sediment, very low energy, and low oxygen, so all of this is perfect.

SQ: How do biologic factors limit what is preserved in the fossil record? What are they?

Biologic conditions that facilitate preservation—>hard tissue (bone, shells) are good

basically, certain body parts leads to better preservation

Intrinsic anatomy:

• Hard body parts (mineralized or not?)

• Multiple body parts

• Molts

Ecology

• High abundance vs. large body size

• Habitat and widespread range

Mineralized hard body part=body fossil—>fossils favor this

SQ: How do environmental and geologic factors limit what is preserved in the fossil record? How does discovery affect the fossil record?

Environmental conditions that facilitate good preservation—> bad conditions, bad preservation, limiting what is in the fossil record, as places with bad conditions and bad preservation won’t have good fossils, so the fossil record is missing parts of the world/environments that don’t preserve fossils well.

Since not preserved well—>can’t get a good overview of what organisms lived there

Affects discovery as geographic and accessibility bias (may look there more), and sampling and commercial/academic bias—> basically fossils are added to the fossil record but there may be a bias to look there due to it being good env.

SQ: What are the environmental and geologic factors that limit what is preserved in the fossil record?

Good env:

Cool and dry

Low energy:

• Calm env. like a swamp or the bottom of the deep ocean

• Reduces environmental disarticulation(bone separation) pre-burial (bc not lots of energy to disrupt)

Anoxic Env:

• Little to no oxygen

• Many decomposers require oxygen

High sedimentation—>Need sediments (dirt) to be able to have burial and low env. So rocks=bad sedimentation

• High sedimentation results in rapid burial (which results in:)

• Creates anoxic environments

• Reduced disarticulation and destruction by predators and scavengers

• Fossilization process occurs after burial

• Sediments=small and fine: 1. low-energy env. 2. preserve fine details in fossil

SQ: How does decay affect the preservation potential of an environment(how well can it turn into a fossil)?

For an organism to become a fossil, its remains must survive long enough to undergo mineralization.

Because micro-organisms and chemical reactions rapidly break down tissues after death, environments that minimize or halt decay have a high preservation potential, while environments that accelerate decay have a low preservation potential.

Warm, wet, oxygenated env=decay FASTER=worst preservation

Cold, dry, no oxygen env=decay SLOWER=better preservation

SQ: How does sedimentation rate affect the preservation potential of an environment(how well can it turn into a fossil)?

High sedimentation(fast burial)—>Need sediments (dirt) to be able to have burial and low env. So rocks=bad sedimentation

• High sedimentation results in rapid burial (which results in:)

• Creates anoxic environments

• Reduced disarticulation and destruction by predators and scavengers

• Fossilization process occurs after burial

• Sediments=small and fine: 1. low-energy env. 2. preserve fine details in fossil

Basically, rapid burial=better preservation bc of the reasons above, slow burial=worse preservation bc doesn’t follow the reasons above.

SQ: How does energy affect the preservation potential of an environment(how well can it turn into a fossil)?

Low energy:

• Calm env. like a swamp or the bottom of the deep ocean

• Reduces environmental disarticulation(bone separation) pre-burial (bc not lots of energy to disrupt)

SQ: How does anatomy affect the preservation potential of an environment(how well can it turn into a fossil)?

1. Presence of hard parts(how much org composed of mineralized tissue)

• Mineralized skeletons are more likely to be preserved as fossils, If don’t got that, less likely to be preserved

2. Single vs. multi-part skeleton(how make up organism too)

• Single/few part skeletons: Single piece is highly informative—>BUT limited to 1 per individual, so rarer

• Multi-part skeletons: Higher chance of being preserved and discovered: Easy to find at least 1 part so higher chance that something will be discovered BUT more likely to be disarticulated (not connected), less information per piece

3. Molted skeletons (best fossil record)

• Each molt is multiple copies per individual: multiple exoskeleton copies per skeleton

• Highly informative because exoskeleton(made of calcite) preserves external anatomy and body plan

• Organisms that molt several mineralized skeletons as they grow are more likely to be represented in the fossil record.

• You know the difference bc the molt has a breakage on the head.

SQ: How does ecology affect the preservation potential of an environment(how well can it turn into a fossil)?

Quality vs. quantity vs. visibility

1. Large body sizes:

• Quality: Easier to discover and preserve

• Quantity: Longer lifespans=fewers individuals

• Visibility: Harder to bury=higher exposure to decay, disarticulation, and weathering

2. Small body sizes

• Quality: Harder to discover, easy to miss due to size

• Quantity: Shorter lifespans= numerous individuals

• Visibility: Easier to bury(bc need less sediment and lighter)= more likely to be fossilized

3. Habitat:

• High energy—>BAD

• High sedimentation rate—>GOOD

• Hot, warm, oxygen, wet—>BAD

SQ: How does biogeography(paleobiogeographic range) affect the preservation potential of an environment(how well can it turn into a fossil)?

Geographically and temporally widespread organisms are more likely to end up in a favorable environment and be discovered

1 spot(limited)= worse preservation: may be in a place that is not good at preserving fossils

Multiple spots (widespread)= better preservation: end up in an environment good at preserving fossils.

SQ: What are Lagerstätten(singular=lagerstätte)?

Sites of superbly preserved fossils(basic the perfect environment for fossil preservation)

Unusual chemical condition

• Typically anoxic (low oxygen) environments with fine sediment (also means low energy b/c takes less energy to make into rock), preserves details better

• Very little to no post mortem disruption (preserved in place)

Rare sites with exceptional soft-tissue preservation like the Burgess Shale, extraordinarily well-preserved fossils, often including soft tissues or a massive accumulation of specimens

SQ: In what ways is the fossil record biased environmentally?

Better environment preserves better, so more fossils there, so those with a worse environment preserves worse, so less fossils there

Fossilization requires specific conditions that are heavily concentrated in certain geographic and geological settings while completely absent in others.

Organisms living in high-sedimentation, low-energy aquatic environments are highly overrepresented, while those from upland or erosional environments are almost entirely lost to time

SQ: In what ways is the fossil record biased biologically?

Organisms with hard body parts and those that are highly abundant are significantly more likely to be preserved than soft-bodied or rare species.

Hard=better