L3- Exceptional Preservation

Fossil-Lagerstatten:

A sedimentary layer with unusual occurrences of well-preserved remains

  1. Konzentrat-Lagerstatten

    • fossils occur in unusual concentrations

      • e.g. bone beds, mass kills

  2. Exceptional Preservation (Konservat)

    • fossils occur of unusual quality

      • of an organism that is not usually preserved e.g. soft-bodied organisms, embryos preserved in phosphate:

      • parts of organism that are not usually preserved e.g. tissue, skin

      • of an organism that is preserved in an unusual configuration e.g. whole organism

What permits Exceptional Preservation?

  1. Exclusion of scavengers and bioturbators

    • anoxia, rapid burial, elevated salinity

  2. Unusual chemical environment

    • nodules (water excludes in rock, high pressure, dissolves minerals- made of silica, flint, caco3…), microbial mats (over a body and hold together-death masks, promote early mineralisation)

Conservation Traps:

  1. Amber deposits

    • amber (tree resin) drips down and is very sticky

    • traps insects, hair , feathers

  2. Ice

    • Ice age, permafrost deposits that are melting, have become frozen in slurries of mud and are now unfreezing, can preserve DNA too

  3. Tar Pits

    • oil sucked up to the surface, rain rests on top and is an illusion

    • usually birds, animals trying to eat those stuck get stuck too

  4. Hot Silicious Springs

    • silica deposited by volcanic activity, usually plants, can go from very hot to very cold so traps different aspects of the ecosystem

  5. Tufa

    • calcium carbonate released from limestones, forms stalactites and stalagmites

  6. Ash Falls

    • ash collapsing down the side of an erupting volcano in pyroclastic flows→ a mixture of gas and ash erupt from the volcano at high speeds and forms rocks that perfectly preserve immediately

The Process of Exceptional Preservation-

Tissues within an organism have a spectrum of resistance to decay:

  • Recalcitrant→ highly resistant e.g. teeth and bones

  • Labile→ highly non-resistant e.g. soft tissue

    • Biomineralised endoskeletons and exoskeletons are the best e.g. made of silica, caco3, phosphate

    • Robust structural tissue→ cuticle, woody tissue

    • Decay prone muscle e.g. eyes

      • are only preserved when they are replicated rapidly by authigenic minerals (minerals that grow in their place)

        • precipitate around the tissue→ replicate it by a mould/cast

        • precipitate on/inside the tissue→ infilling and preserving the cells

        • microbes can do this

        • microbrial mats can form a death mask→ stabilises the chemical environment to allow exceptional preservation

Concretions accumulate around an organism and allow exceptional preservation:

  • Phosphate:

    • Apatite→ phosphate mineral forms very small crystallites, animals rot and bacteria release the phosphate inside them

    • Clay minerals→ also form crystallites but unsure of how this works, usually in glacial environments

    • Embryos releasing phosphate→ cambrian era was very rich in phosphate

    • Phosphate has a size limit→ can only preserve up to 1mm in size

  • Iron Pyrite→ nodules

  • Other Metal Sulfides

  • Silica→ hot springs, nodules, wood (lignin)

  • Calcite→ CaCO3 in coal balls and nodules

Fossil-Lagerstatten can be misleading:

  • are bound to be everywhere but just haven’t preserved there

  • Mainly occur in certain time periods e.g. Cambrian Burgess Shell

  • Certain unusual environments are over-represented

Example of Exceptional Preservation-

Messel, Germany→ Cenozoic:

  • Volcano erupted, a deep lake built up, the bottom layers are anoxic

  • Every so often, the area bursts out CO and traps any organisms around it/flying

  • There are both bones and soft bits preserved in the same deposit

Hunsruck Slate, Germany→ Devonian:

  • Is older than Messel

  • Is a shallow sea, the bottom layer is anoxic black mud

  • Can X-ray the fossils to see the internal structures

Case Study→ Exceptional Preservation in Dinosaurs-

Did not get much until the Jehol Biota, China→ Cretaceous:

  • dammed up lakes, has volcanic ash, ash reacts with water to create unusual chemical environments

  • there were lots of tuff beds at this time, are mined today

  • get exceptional preservation and unusual structures: