Fossils and Taphonomy

Dr. Allen

Fossil Record

Evidence of life preserved in geological context

Two types:

• Body Fossils

• Trace Fossils (Ichnofossils)

Information Provided by Fossils

Anatomy

Feeding strategies

Geographical distribution

Ecological relationships

Past climates and environments

Body Fossils

Examples:

• Bones and Teeth

• Shells and Exoskeletons

• Wood

Remains can represent a whole organism or just parts of an organism

Remains may be in one piece or fragmented/scattered

More rarely discovered:

• Skin, Soft tissues, and Organs

• Leaves and Flowers

Types of Preservation:

Typical and Exceptional

Typical Preservation

Unaltered skeleton

Permineralization → pored become filled with silica

Replacement with another material like quartz or pyrite

Molds and Casts → Original material is dissolved and sediment fills the space

Carbonization → preserving as Carbon films

Exceptional Preservation - Fossil Lagerstätten

Konzentrat (concentration) Lagerstätten → anomalously high amounts of fossil material

Konservat (conservation Lagerstätten → unusually well-preserved fossils, including soft parts

• Strgnation deposits (anoxia, low current flow)

• Obrution deposits (very rapid burial)

• Conservation traps (for example: amber)

Trace Fossils (Ichnofossils)

Don’t necessarily know the identity of a trace marker

• Trace Marker → the activity the fossil individual was doing

Taxonomy: Ichnogenera and Ichnospecies

Provides Information about:

• How can organism moved

• Feeding patterns

• Burrowing patterns in sediment

• Community structure

Examples:

• Footprints, trackways, and resting traces

• Burrows and Tunnels

• Feeding traces

• Coprolites → fossilized fecus (poop)

Fodinichnia - Feeding Burrows

Branching burrow traces of a deposite-feeding invertebrate

• Example: Chondrites

  • Environmental settings: fully marine conditions perhaps indicative of low oxygen

• Example: Teichichnus

  • Environmental settings: found in lower marine shorefaces, intertidal settings, lagoons, deep-marine fans and abyssal plains, and brackish water settings like marine estuaries

Feeding Burrow - Chondrites

Feeding Burrow - Teichichnus

Domichnia - Dwelling Burrows

Unbranched burrow traces of a suspension-feeding invertebrate

• Example: Skolithos

  • Environmental settings: found in virtually every type of environment from marine to terrestrial. Present in high-energy marine conditions, especially in nearshore shallow marine facies, deep marine submarine channels and canyons: contintental floodplain and dune settings

Straight or gently curved burrows, horizontal to oblique bedding planes

• Example: Planolites

  • Environmental settings: shallow marine- deep marine deposits to continental. Found in alluvial, lacustrine, and eolian settings

Dwelling Burrow - Skolithos

Dwelling Burrow - Planolites

Rhizoliths

Plants can also produce trace fossils

Plant root structures

Analysis of Track Traces

Different parts of a track can create different traces

Type of substrate, and texture of sediment is important → can reveal details about the track marker’s anatomy and movement

Dinosaur Footprints and Trackways

Give clues about:

• Locomotion styles

• Dinosaur families and communities

• Predation behaviors

  • example: dinosaurs hunting in groups

Repichnia - Locomotive Traces

Example: Chirotherium from the Triassic

• Pentadactyl footprints

• Not obvious who the producer was

Adolf Seilacher

Interest included trace fossils, evolution of invertebrates, and exceptional preservation (Lagerstätten)

Changes in Setting Reflected in Changes in Observed Traces

Seilacher created a naming system based on using ichnotaxa to describe trace fossil types

• Cubichnia → Resting traces

• Domichnia → Dwelling traces

• Fodinichnia → Feeding traces

• Pascichnia → Grazing traces

• Repichnia → Locomotory traces

Lots of other terms have since been created

Frameworks Developed by Seilacher

Constructional morphology and Morphodynamics

Taphonomy

Coined by Ivan Efremov in 1940

The study of the laws governing the transition of organic remains from the biosphere into the lithosphere

Also includes discovery, collection bias, and curation of remains

Natural sampling of biotas

• Microorganims, Plants, Animal

Occurrence in the fossil record also depends on Species diversity, Morphological disparity, and Ease of preservation

Differing preservation potentials

A Collection of Filters

The stufy of the transitions from the biosphere to the lithosphere

Sources of Bias:

• Biochemical

• Anatomical

• Ecological

• Geological

Sequential Staged of Taphonomy

Necrology/ Necrolysis

• Death

Biostratinomy

• Decay

• Disintegration/Destruction

• Disarticulation

• Transportation

• Burial

  • Biological factors:

    • Decay

    • Scavenging

    • Gnawing

    • Boring

    • Bioturbation

  • Physical factors:

    • Differential transportation

    • Size and shape sorting

    • Alignment

    • Mechanical breakage and/or abrasion

    • Sedimentology

    • Chemical dissolution

Diagenesis

• Fossolization

Assemblages

Biocenosis (Life assemblage)

• Organisms have the correct orientation

• Trace of fossils may ne present

• Different organims from the same community are present

• Mature and juvenile individuals may be present

Thanatocenosis (Death assemblage)

• Organims are of similar size and/or shape

• Organisms may be from different ecological communities

Autochthonous (In situ)

Allochthonous (Trasnported)

Single-event (census/catastrophic) assemblages

• Unusual events like sudden anoxia, severe storms, droughts and volcanic eruptions that kill large numbers of individuals at one time

  • Short term “Snapshot”

Attritional (time-averaged) assemblages

• Discard organic products like pollen and leaves and input from normal mortality over time

  • Long tern