L3: Exceptional preservation

Question 1

What are Lagerstätten?

Answer 1

Sedimentary deposit that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues

Question 2

What two types of fossil Lagerstätten generally occur?

Answer 2

Concentration deposits and conservation deposits

Question 3

Why is exceptional preservation rare?

Answer 3

Because liable tissue decays much more rapidly that recalcitrant structures

Question 4

What is a concentration (Konzentrat-Lagerstätten)deposit?

Answer 4

Remarkable due to the sheer abundance of specimens, would appear in bone beds and mass kills

Question 5

What is a conservation (Konservat-Lagerstätten) deposit?

Answer 5

Exceptional preservation, where preservation is of unusual quality, e.g. articulated skeletons and fossilised soft tissues

Question 6

How do concentration deposits typically form?

Answer 6

Accumulate over a significant period of time

Question 7

How do conservation deposits typically form?

Answer 7

Usually the result of a catastrophic event, such as rapid burial and represent an instant in geological time

Question 8

What are the three basic types of exceptional preservation?

Answer 8

Preservation of organisms that are not usually preserved e.g. slugs and embryos
Preservation of parts of organisms that are not usually preserved e.g. skin
Organs are preserved unusually articulate or in unusual configurations

Question 9

What does the widespread occurrence of ediacaran fossils indicate about the pre/early Cambrian?

Answer 9

Reflects the absence of grazing invertebrates and the resultant prevalence of microbial mats

Question 10

Where are Burgess Shale type Lagerstätten of the Cambrian most common?

Answer 10

In deeper slop/basin settings, where fine grained sediments accumulated. Deep bioturbators had yet to invade deeper water settings

Question 11

What are the major conditions that are important for exceptional preservation?

Answer 11

Absence of scavengers and bioturbators

Unusual chemical environment

Question 12

What may result in the exclusion of scavengers?

Answer 12

Anoxic conditions, rapid burial, elevated salinity

Question 13

Why are anoxic conditions important for exceptional preservation with regards to bacteria?

Answer 13

Oxic bacteria are highly destructive, unlike anoxic bacteria, which produce byproducts, such as H2S, which precipitate out and replace the organic materials

Question 14

What conditions favour exceptional preservation?

Answer 14

Anoxic bottom conditions and large episodic influxes of sediment, an environment that is unfavourable for life

Question 15

What are microbial mats?

Answer 15

Thin laminated ecosystems dominated by bacteria., prokaryotic cyanobacteria form the key component, producing viscous layers

Question 16

What role do microbial mats play in exceptional preservation?

Answer 16

Bacterial activity in the mats induces replacement of soft tissues by calcium phosphate within a few weeks

Question 17

What are the different types of conservation traps?

Answer 17

Amber, Ice, Tar pits, Hot siliceous springs, Tufa, Ash falls

Question 18

What is a death mask?

Answer 18

The rapid growth of microbial mats over a carcass, which prevents against decay and destruction by scavengers

Question 19

What is amber?

Answer 19

A fossilised resin produced by angiosperms and gymnosperms.

Question 20

How does resin preserve specimens?

Answer 20

Insects get trapped and are embalmed in the resin

Question 21

How does ice preserve specimens?

Answer 21

Animals caught in the cold are preserved as the freezing temperature prevents bacteria decay

Question 22

How do tar pits result in exceptional preservation?

Answer 22

Animals get caught and are preserved, no scavenging can occur

Question 23

What are tar pits?

Answer 23

Oil forms from organic material as it heats up and is crushed. It makes its way up to the surface, forming tar pits

Question 24

Ho who ash fall preserve specimens?

Answer 24

Volcanos explode and release a mixture of hot gas and ash, may be as a pyroclastic flow. Everything below this is preserved.

Question 25

What types of tissue may be preserved?

Answer 25

Biomineralised endotherm/exoskeletons - easy to preserve
Robust structural tissue e.g. arthropod cuticle, wood
Decay prone muscle

Question 26

How may decay prone muscle be preserved by minerals?

Answer 26

either by precipitation around the tissues which are later replaced by a cast
or
precipitation within the tissues, infilling and preserving actual cells

Question 27

What is the mineral that most commonly preserves soft tissue?

Answer 27

Apatite

Question 28

How does apatite form?

Answer 28

requires a sufficient conc of phosphate and specific pH and redox conditions. Precipitates rapidly as tiny crystals, so preserves the specimen in the highest fidelity

Question 29

Where might phosphate for preservation be sourced from?

Answer 29

Released from decaying carcasses and accumulated in the surrounding sediment

Question 30

What are the two main tissues that can be recognised through apatite preservation?

Answer 30

Microbial - mineralization of the infesting microbes resulting in preservation
Substrate - Tissues themselves are phosphatized, has a much higher fidelity

Question 31

How do clay minerals preserve specimens?

Answer 31

Can replicate soft tissues in cold and low pH conditions,

Question 32

How does pyrite preserve specimens?

Answer 32

Where iron concentration is high and organic material is confined mainly to isolated carcasses soft tissues are preserved in pyrite. Is a slow process

Question 33

What are the limitations of preservation by phosphate?

Answer 33

Phosphate is in high demand in the modern world, meaning not many conditions today are ideal for replacement

Question 34

Why do Lagerstätten confuse palaeobiologists?

Answer 34

False biodiversity peaks

Preferentially occur in certain periods, such as the Cambrian

Question 35

Why did exceptional preservation occur more frequently in the Cambrian?

Answer 35

No deep sea bioturbators, less oxygen, high levels of phosphate in the sea

Question 36

Give examples of specimens preserved by silica

Answer 36

Flint nodules form around sponges on sea beds in calcite chalky seas, or when wood is preserved as lignin

Question 37

What minerals may cause exceptional preservation?

Answer 37

Apatite, clay, pyrite, silica, calcite

Question 38

What is the tertiary exceptional preservation deposit in Germany called?

Answer 38

Messel, bituminous shales

Question 39

How did the shales in messed form?

Answer 39

Messel was a volcanic lake, occasionally loads of CO2 was released, killing all organisms in and around the lake. Strange bottom conditions meant animals would remain undisturbed

Question 40

What can be seen in the insects preserved in the Messel shales?

Answer 40

colour patterns

Question 41

What is the Devonian exceptional preservation deposit in Germany called?

Answer 41

Hunsrück slate, made form black shales

Question 42

What were past conditions like in Hunsrück?

Answer 42

Hunsrück was a shallow ocean, with anoxic bottom waters, it was a stratified ocean, so there is a low rate of oxygen turnover. Was a high concentration of sulphur

Question 43

How did exceptional preservation occur in the Hunsrück slate?

Answer 43

Fossils are preserved by soft tissue pyritisation

Question 44

What is the most famous case of exceptional preservation in dinosaurs?

Answer 44

Jehol biota in china, from the cretaceous

Question 45

What were conditions in like in the jehol?

Answer 45

A volcanically active area characterised by a series of lakes. Clouds of ash would fall on the lakes in pyroclastic flows. Everything in the lakes was killed instantly and sank to the bottom. Fossils are often found in ash layers

Question 46

What does the jehol biota preserve, along with the physical specimens?

Answer 46

Can get an idea about the behaviour of the animals, as death is instant