After learning about various animal fossils, now it’s time for us to switch topics for a bit—but don’t worry, we’re not straying too far. In this discussion, we’re still dealing with animals, but this time, it’s not about their body parts. So… what part are we talking about then? Curious? Let’s check it out!
A. Definition
Ichnofossils can be defined as sedimentary structures that result from the life activities of animals—or in cooler terms, trace fossils.
B. Types
a. Burrow: A hole or tunnel dug into soft, unconsolidated substrate.
b. Bioerosion trace fossil / Boring: A hole created in hard, consolidated substrate.
c. Track: An animal footprint formed while walking, usually characterized by a discontinuous trail.
d. Trail: A trace left by an animal moving with its belly in contact with the ground, usually characterized by a continuous, connected path.
e. Coprolite: Fossilized droppings or feces from an organism.
f. Egg/Nest: Fossilized eggs or preserved nests.
C. Principles of Ichnology
a. Same species, different structures
b. Same burrow, different substrates
c. Different tracemakers, identical structures
Similar-looking sedimentary structures can be produced by different species.
D. Bioturbation, Ichnofacies, and Ichnofabric
a. Definitions
- Bioturbation: The process by which primary sedimentary structures and properties are modified by the activities of organisms living within the sediment, often resulting in sediment mixing.
- Ichnofacies: An ecological assemblage of trace fossils produced by a particular group of organisms.
- Ichnofabric: The total amount and nature of sediment disruption caused by burrowing organisms, typically given a score from 1 to 5 to represent the degree of bioturbation.
b. Similarity between Ichnofacies and Ichnofabric
c. Difference between Ichnofacies and Ichnofabric
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Ichnofacies: Data collection is done qualitatively.
- Ichnofabrics: Data collection is done quantitatively.
E. Classification of Ichnofossils
Ichnofossils can be classified based on four main aspects:
a. Taxonomic Classification
- Based on the International Code of Zoological Nomenclature.
- When referring to a fossil at the genus level, it is called an ichnogenus, abbreviated as igen. When referring to a fossil at the species level, it is called an ichnospecies, abbreviated as isp.
- The abbreviation isp is written after the species name, and igen is written after the genus name.
For example, Skolithos isp:
Here, Skolithos represents the fossil’s taxonomic genus name, and isp indicates that the species has been identified based on trace fossil characteristics. If the species cannot be clearly identified due to lack of distinctive features, only the genus name is used, followed by the abbreviation igen to indicate it as an ichnogenus.
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| Skolithos isp |
b. Preservation Model
Classified by Seilacher based on the position of the trace fossil relative to the sedimentary layer. There are three types of classification:
- Semirelief: The trace fossil is located on the top surface of the sediment layer.
- Hyporelief: The trace fossil is located on the bottom surface of the sediment layer.
- Full relief: The trace fossil is found within the sediment layer, between semirelief and hyporelief.
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| ©️ researchgate.net |
In the image above, you can see positive (+) and negative (–) signs. The positive (+) sign indicates that the trace fossil is convex (raised), while the negative (–) sign indicates that the trace fossil is concave (depressed) relative to the rock layer.
c. Life Patterns / Ethological Classification
The behavior of an organism can be observed in sedimentary structures and is classified into several types of behavior. Seilacher grouped them as follows:
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Cubichnia: Traces formed by an organism when resting, hiding, or positioning itself to ambush prey. Characteristics include:
- Reflects the size of the organism’s body.
- Resembles the underside of the organism.
- Preserved as semirelief.
- Example: starfish.
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| ©️ es.ucl.ac.uk |
Repichnia: Traces resulting from the movement of an organism, such as crawling, walking, or running. Characteristics include:
- The shape follows the upper or lower part of the organism as it moves.
- Preserved as semirelief.
- The organism moves in a random or unsystematic manner.
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| ©️ es.ucl.ac.uk |
In the image above, there are two examples of Repichnia: Cruziana and Gyrochorte. Cruziana has a concave (–) semirelief shape that reflects the underside of the organism. This contrasts with Gyrochorte, which has a convex (+) semirelief shape reflecting the upper side of the organism.
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Domichnia: Traces representing the dwelling or living place of an organism. Characteristics include:
- Orientation can be horizontal (parallel to sediment layers) or vertical (perpendicular to sediment layers).
- Usually shaped like cylindrical tubes (straight or U-shaped) or more complex branching forms.
- May show evidence of scratches, cemented walls, or striations.
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| ©️ es.ucl.ac.uk |
Examples of Domichnia:
- Skolithos: simple, unpaired tubes.
- Ophiomorpha: tubes with wall linings, typically associated with crustaceans.
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Pascichnia: Traces formed by a combination of feeding and moving behavior. Characteristics include:
- Preserved as semirelief.
- Meandering (winding) shapes arranged systematically and at regular intervals.
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| ©️ es.ucl.ac.uk |
The image above shows an example of Pascichnia, specifically Helminthopsis, which has a meandering shape.
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Fodinichnia: A combination of temporary dwelling and feeding traces. Characteristics include:
- Penetrates sediment layers (full relief formation).
- Shapes are progressive or systematic.
- Marked by sediment infillings.
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| ©️ es.ucl.ac.uk |
Examples of Fodinichnia:
- Chondrites: branching burrows extending downward.
- Zoophycos: complex spiral burrow structures extending downward.
- Diplocraterion: vertical dwelling/feeding burrows, U-shaped.
- Thalassinodes: feeding/dwelling traces showing three-way burrow intersections (one vertical and two horizontal).
d. Past Environment / Depositional Setting
Trace fossils are grouped into 5 ichnofacies. The formation of these ichnofacies is controlled by salinity, bathymetry, substrate surface, and rock type. The five ichnofacies are:
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Scoyenia ichnofacies
Formed in terrestrial or freshwater environments. Examples of genera: Scoyenia, Planolites, and Isopodichnus. -
Skolithos ichnofacies
Formed in intertidal zones with sandy substrates and high water fluctuations. Organisms in this environment build deep burrows to:
- Protect themselves against drying out or unfavorable temperatures.
- Adapt to changes in seawater salinity.
- Protect themselves from sediment surface shifts due to tides or waves.
- The fossils are dominated by U-shaped, vertical, and some horizontal burrows. Examples of genera: Skolithos, Diplocraterion, Thalassinodes, and Ophiomorpha.
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Cruziana ichnofacies
Formed in shallow marine environments with lower tides and deeper water than Skolithos ichnofacies. Generally, the burrows are vertical or horizontal. Examples of genera: Rusophycus, Cruziana, and Rhizocorallium. -
Zoophycos ichnofacies
Formed in bathyal marine zones. Due to the deep water, wave influence is minimal, the water is calm, oxygen levels are relatively low, and the seabed is muddy. Dominated by horizontal burrow forms such as Zoophycos. -
Nereites ichnofacies
Formed in abyssal marine zones with clay substrates. Trace fossil abundance is low, but diversity of trace types is high. Examples of genera: Nereites and Scalarituba. -
Psilonichus ichnofacies
Formed in non-marine and very shallow environments. Burrows are Y or U shaped, with vertical shafts and horizontal tunnels. An example is Track.
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| Ichnofasies (Seilacher 1967) ©️ sepmstrata.org |
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| Ichnofasies (Pemberton, 1985) ©️ sepmstrata.org |
e. Burrow Taxonomy
Here, I’m using burrow taxonomy as an example because in our recent paleontology lab, the main focus was on burrows. The parameters used as the basis for naming burrows are as follows:
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Orientation relative to bedding planes (Orientation)
There are two types of orientation relative to bedding planes:
- Subhorizontal: when the burrow runs parallel to the bedding planes.
- Subvertical: when the burrow runs perpendicular to or cuts across the bedding planes.
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Presence or absence of branching (Branching)
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Branched: The burrow has branches. Branching is further classified into three types:
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Tunnel: horizontal branches
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Shaft: vertical branches
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Boxwork: combination of tunnel and shaft
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- Unbranched: No branches present.
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General morphology (Shape)
The general shapes vary and include:
- U-shaped
- Cylindrical
- Wall-shaped
- J-shaped
- Winding/meandering
- Lobate
- Radial
- Tunnel with shaft
- Club-shaped
- Helicoidal
- Prismatic
- Funnel-shaped
- Plug-shaped
- Bifurcated
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Burrow filling (Filling)
The burrow cavity is filled with other minerals. Filling is classified based on the origin of the minerals:
- Active filling: minerals deposited by the organism itself, characterized by curved and perpendicular septa (walls) within the burrow, showing the organism’s digging effort.
- Passive filling: minerals deposited by non-biological processes such as gravity or water currents.
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Burrow lining (Burrow lining)
The lining of the burrow is produced by the organism, typically from excreted minerals, and is usually smoother than the surrounding sediment minerals. There are two types:
- Burrow lining present
- No burrow lining present
Note: Filling and burrow lining are often difficult to distinguish clearly.
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| Taxonomi burrow |
For instance, if we find a burrow fossil that looks like this:
The identification steps are as follows:
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Check the orientation
In the image, the orientation isn’t directly visible. Let’s hypothesize that the image was taken looking down from above the rock layer. Therefore, we can determine that the trace fossil shape is a positive semirelief with a subhorizontal orientation because it runs parallel to the bedding plane. -
Check the branching
The next identification step follows the burrow taxonomy flowchart, which is to identify whether branching exists or not. In the image, there is no branching (unbranched). -
Check the shape
Next, we identify the shape. The form is cylindrical because it looks like an elongated tube. -
Check the filling
The next step is to identify the type of filling. Since there are no visible septa (partitions) inside the tube, we conclude that the filling is passive filling. -
Check the burrow lining
At the final step, we examine the burrow edges to see if there is any burrow lining. Burrow lining can be recognized by a noticeable difference in color between the burrow edge and the burrow itself. It can also be seen in the grain size uniformity (coarse or fine). The image shows that the color and grain size between the burrow edge and the burrow are not uniform, so we conclude that there is burrow lining.
In summary, the information we have gathered is:
Subhorizontal – unbranched – cylindrical – passive filling – lining
When we compare this information with the burrow taxonomy chart, we identify that the fossil is called Palaeophycus.
That’s all from me. Thanks for reading my blog! I appreciate any feedback or suggestions :)
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