Exceptional Preservation Flashcards
What are the two basic types of Fossil-Lagerstatten?
1) Konzentrat-Lagerstatten = concentration desposists aka where fossils occur in unusual concentrations e.g. bone beds, mass kills. Could be from a lake drying up or an avalanche killing a heard of animals
2) Exceptional preservation = conservation desposits where preservation is of unusual quality
Give the different types of exceptional preservation. Give some examples of each
1) Preservation of organisms that are not usually preserved e.g. embryos
2) Preservation of parts of organisms that are not usually preserved e.g. skin, organs
3) Organisms are preserved unusually articulated or in unusual configurations e.g. there is a fossil of an ichthyosaur giving birth
What are the major controls for exceptional preservation to take place?
The exclusion of scavengers and bioturbators - often by the area being anoxic or having elevated salinity or due to rapid burial
Unusual chemical environment which permits exceptional preservation - nodule fromation or microbial mats are usually important for this
What are some conservation traps for exceptional preservation?
Amber
Ice
Tar pits
Hot silicious springs
Tufa
Ash falls
What do microbial mats do?
Stabilise the sediment and set up geochemical gradients that promote early mineralisation
What tissues are more likely and least likely to decay?
Decay prone tissues e.g. muscles, eyes
Robust structural tissue e.g. arthropod cuticle, woody tissue
Bimineralised endo or exoskeletons
When are decay prone tissues preserved?
When they are replicated very rapdily by authigenic (grown in place) minerals
These minerals can either:
1) Precipitate around the tissue and it is replicated by mould/cast
2) Precipitate on and within the tissues (often by infilling or preserving actual cells)
What performs a critical role for exceptional preservation?
Microbes
They mineralise (phosphatise) themselves
Microbial mats can form a death mask
Give some ways exceptional preservation can occur
Apatite - infested with microbes that froze themselves
Clay minerals - often found in cold environments
Iron pyrite
Other metal sulphides
Silica - hot springs, nodule/concretion formation via flint, wood permineralisation
Calcite - coal balls
What is the problem with phosphate during exceptional preservation?
Phosphate has a limit of 2mm and so cannot preserve large organisms - unless in patches
What is a nucleation point?
Where the concretians often accumulate around an organism
How can Fossil-Lagerstatten help us? How can they confuse us?
Help us - it allows us to reconstruct an organism which helps give a more accurate and deeper insight
Confuse us:
-get false biodiversity peaks
-preferentially occur during certain periods of geological time e.g. Cambrian
-certain unusual environments are over-represented
Give some examples of areas with exceptional preservation
Messel pit in Germany - many fossils from the Cenzoic (current) era
The bottom of the lake was anoxic so this allowed for preservation. Get lots of coprolites and some insects even have cuticle colouring preserved
Hunsruck Slate in Germany - fossils from the Devonian period
Bottom of the sea was anoxic so could preserve fossils
The Jehol Biota in China - from the Cretaceous period
Why is the Jehol Biota so special?
Found fossils of dinosaurs with feathers (integument) e.g. found that pterosaurs had feathers
Found some behaviour of animals in the fossils - possible parental care in some species
Changed our view of dinosaurs and changed how people reconstructed them
