Ichnology

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Ichnology

• Ichnology is a subfield of geology that deals
  with traces of organismal activity.
• The area of ichnology concerned with trace
  fossils is paleoichnology.

Plio-pleistocene ancient hominid footprints
preserved in volcanic ash at Laetoli in Tanzania,
Africa.
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So why is it useful?

• Paleontologists use ichnology to decode the
  possible anatomy and behavior of trace-making
  fossils even if no body fossils can be found.

Protichnites, an ichnogenus of arthropod walking
activity found in central Wisconsin in Late
Cambrian sandstone.
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What kind of fossil traces do organisms leave?

• There are several types of organismal traces that
  can be fossilized. Examples include

• Burrows

Climatichnites fossilized burrow from Central
Wisconsin, Late Cambrian.
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Other examples include

• Coprolites, or fossilized dung. Coprolites are
  valuable because they give information on the
  diet and behavior of instinct animals, rather
  than just morphological information.

Coprolite of carnivorous dinosaur, found in
southwestern Saskatchewan, Canada.
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• Another interesting ichnofossil are gastroliths,
  or stomach stones or gizzard stones used by
  animals for grinding food. Modern animals such as
  herbivorous birds, crocodiles, alligators, seals,
  and sea lions use gastroliths. Some
  paleontologists also believe sauropod dinosaurs
  may have used them for chewing and that
  plesiosaurs may have used them for ballast.

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Other ichnofossils include

• Borings and etchings
• Regurgitaliths
• Nests
• Leaf mines
• Bite gnaw structures
• Organismal secretions, such as coccoons, pupal
  casings, spiderwebs, embedment structures, and
  plant galls.

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Classification

• Because trace fossils cannot always be positively
  identified to the species that produced them,
  they are given scientific nomenclature separate
  from morphologically classified species. The
  International Code of Zoological Nomenclature
  defines an ichnospecies as a taxon based on the
  fossilized work of an organism. They are given
  an italicized Latin genus and species name with
  the prefix ichno- added for clarity.

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• Ichnofossils can also be classified by the type
  of behavior the organism engaged in while
  producing the fossilized traces. The Seilacherian
  System is a long-accepted system of classifying
  an ichnofossil based ethological divisions,
  including
• Cubichnia traces of an organism left in soft
  sediment (ex outline of a starfish in sand).
• Domichnia dwelling structures that represent
  the life position of the organism (ex burrows).
• Fodinichnia feeding traces which are formed as
  a result of organisms disturbing the sediment in
  their search for food.
• Pascichnia a different type of feeding trace
  caused by grazers scraping substrate in search of
  food.
• Repichnia locomotory tracks that show evidence
  of organisms moving from one station to another

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Sponge borings and encrusters on a modern bivalve
shell from North Carolina, a modern example of
Domichnia.
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• Below are examples of Repichnia.

Footprint of ichnogenus Grallator, a bipedal
theropod dinosaur that roamed Pangaea in the Late
Triassic and early Jurassic.
The ichnospecies Anomoepus gracillimus, a set of
footprints found in the Late Triassic beds of the
Connecticut River Valley, Massachussets