EES 227: Paleobiology

Spring 2004

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Lecture 17: April 8

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Lecture Notes: Trace Fossils (Ichnofossils)

o Eubrontes giganteus (Hitchcock): Connecticut State Fossil

Trace fossils <-> Body Fossils (body fossils: all or part of body/skeleton preserved).

Trace fossils are also called  ichnofossils, or biogenic sedimentary structures; include all results of activities of living organisms:

  • Tracks, trails, burrows, borings (e.g., in shells)
  • Nests, 'stomach stones', fossil fecal matter (coprolites), eggs, bite marks upon body fossils

Note: there is an ongoing discussion whether the shells of large ammonites (specifically, Placenticeras) show bite marks by mosasaurs or whether these marks are limpet home impressions.

Advantages trace fossils:

  • Behavior of extinct animals
  • Nature of soft-bodied animals and their environment
  • Present where body fossils are not preserved
  • Little affected by diagenesis (part of rock)
  • Not transported

Disadvantages of trace fossils:

  • Usually no bodyfossils with trace fossils; we do not know whose behavior
  • Many similar structures made by different organisms
  • One type of organism makes different structures (e.g., while resting, burrowing, crawling, running)

Example: trilobites ichnofossils

  • Rusophycus: trace of resting trilobite
  • Cruziania: trace of trilobite plowing through sediment
  • Diplichnites: track of trilobite walking on sediment
  • Different behaviors leave behind different looking tracks
  • Different looking tracks receive different names, which look like names of genera of body fossils (but are not)

Ichnofossil taxonomy: names given to specific morphological structures

  • Not organisms; no hierarchical structure of relationships
  • Many 3-dimensional structures, not always easy to understand from outcrop
  • Many marine ichnofossils: thought sea-weeds (names ending in -phycus)
  • Genus and species name; many genus names have endings -ichnus, -ichnites, -craterion.
  • Unknown species often abbreviated as 'isp.', i.e., ichnospecies
  • NO higher hierarchical classification than genus

Preservation of trace fossils

  • Depends upon type of structure:
  • If indentation in surface: semi-relief (foot print)
  • If 3-dimensional within sediment (burrow): full structure preserved
  • Some structures back-filled by organism (spreite)

Example: Diplocraterion yoyo

  • U-shaped burrow
  • Perpendicular surface sediment
  • Animal moved up-down (sedimentation- erosion)

Example: Zoophycos

  • horizontally to obliquely oriented burrow;
  • helical structure as a result of overlapping U-shaped burrows

How to classify ichno-fossils?

  • Ethology (behavior)
  • Overlapping classes of behavior; subdivisions of: feeding, locomotion, dwelling, escape

Classification of ichnofossils by behavior  (Seilacher's wheel)

  • FARMING TRACE Agrichnia: network of burrows, regular, dwelling and feeding
  • FEEDING TRACE Fodinichnia: feeding by deposit feeders
  • PREDATOR TRACE Praedichnia: traces left by hunting predators
  • GRAZING TRACE Pascichnia: grazing, combing surface of sediment
  • CRAWLING TRACE Repichnia: crawling (sediment surface)
  • RESTING TRACE Cubichnia: resting, when animnals stopped, sat in place
  • ESCAPE TRACE Fugichnia: escape structures (from sediment)
  • DWELLING TRACE Domichnia: house

Ichnofossil concepts:  beyond the single trace

  • Ichnofacies: record of original ichnocoenose (which various types of burrows present); classified by water depth and type of substrate (soft mud, hard rock, wood) - main types marine (1-7)
  • Ichnofabric: quantitative estimate of amount of bioturbation in rock (how much % of sediment disturbed by burrowing), from ichnofabric index 1 (undisturbed to ichnofabric index 6 (homogenized by burrowing)

Common Ichnofacies:

  • Ichnofacies 1: Skolithos
    • Many vertical (including U-shaped) burrows
    • Clean, well-sorted sands, close to shore. Very shallow water, marine, high energy (wave, current action)
  • Ichnofacies 2: Cruziania
    • Cruziania Trilobite trace fossils; trough-shaped (Paleozoic only)
    • Thalassinoides isp.: complex web, feeding and house burrows (maybe crabs, shrimps?)
    • Marine; shallow, < ~ 100 m; low energy
  • Ichnofacies 3:Zoophycos
    •  Broad, looping, helical, U-shaped traces; low diversity
    • Typical for lower oxygen conditions; low energy
    • Much organic matter in sediment
    • Outer shelf/slope
  • Ichnofacies 4:Nereites
    • Meandering/polygonal  traces at sediment surface
    • Systematic ëminingí; low-food environment
    • Bathyal to abyssal (>1000m deep); low energy
  • Ichnofacies 5-7: Controlled by substrate
    • Glossifungites: firm, not rock
    • Trypanites: rock boring
    • Teredolites: wood borer (shipworm)
  • Ichnofacies 8; Psilonichnus
    • On land: close to coast, above tide level (maybe crabs?)
    • Vertical, Y-shaped
    • Also in dunes in land (lakes)

Ichnofabric:

  • Quantitative estimate of amount of bioturbation in rock
  • Standard: index 1 through index 6
  • 1: not bioturbated; 6; homogenized
  • Conclusions regarding environmental changes if various ichnofabrics/ ichnofacies alternate
  • Tiered communities expressed in complex patterns of ichnofossils

Dinosaur tracks

There is considerable variability in tracks made by one and the same organism, depending not only on the anatomy of the organism, but also on the type of substrate (soft mud, sand, etc.), and the way in which the animal was moving (kinematics: run, walk, etc.). There is also considerbale variability in the size of animals within one species (all dinosaurs come from eggs, start small).

Information on dinosaurs:

  • How large? How fast? Attitude of legs? Social life (herding)? Predation?
  • oEnvironment: walk? Swim? What food?