Trace fossil classification
Encyclopedia
Trace fossil
s are classified
in various ways for different purposes. Traces can be classified taxonomically (by morphology), ethologically (by behavior), and toponomically, that is, according to their relationship to the surrounding sedimentary layers. Outside of special cases, phylogenetic classification of trace fossils is unsatisfactory because the makers of most trace fossils are unknown.
The taxonomic classification of trace fossils parallels the taxonomic classification of organism
s under the International Code of Zoological Nomenclature
. In trace fossil
nomenclature a Latin
binominal name is used, just as in animal
and plant
taxonomy
, with a genus
and specific epithet. When talking about trace fossils the genus is called an ichnogenus, and the species is an ichnospecies, the ichno- prefix coming from the Greek
ιχνος (transliterated ikhnos), meaning "trace". The name is similarly italicized, and in full reference the author plus the year of publication should be cited. "Ichnogenus" and "ichnospecies" are commonly abbreviated as "igen." and "isp.", respectively.
Most researchers classify trace fossils only as far as the ichnogenus rank, based upon trace fossils that resemble each other in morphology but have subtle differences. Some authors have constructed detailed hierarchies up to ichnosuperclass, recognizing such fine detail as to identify ichnosuperorder and ichnoinfraclass (e.g. http://www.paleofile.com/Demo/Localities/Africademo/Algeria.htm), but such attempts are controversial.
The most promising cases of phylogenetic classification are those in which similar trace fossils show details complex enough to deduce the makers, such as bryozoan borings
, large trilobite
trace fossils such as Cruziana
, and vertebrate
footprints. However, most trace fossils lack sufficiently complex details to allow such classification.
Adolf Seilacher
was the first to propose a broadly accepted ethological
basis for trace fossil classification. He recognized that most trace fossils are created by animal
s in one of five main behavioural activities, and named them accordingly:
Over the years several other behavioural groups have been proposed, but in general they have been quickly discarded by the ichnological community. Some of the failed proposals are listed below, with a brief description.
Fixichnia is perhaps the group with the most weight as a candidate for the next accepted ethological class, being not fully described by any of the eleven currently accepted categories. There is also potential for the three plant traces (cecidoichnia, corrosichnia and sphenoichnia) to gain recognition in coming years, with little attention having been paid to them since their proposal.
of origin. Martinsson has provided the most widely accepted of such systems, identifying four distinct classes for traces to be separated in this regard:
Other classifications have been proposed, but none stray far from the above.
Trace fossil
Trace fossils, also called ichnofossils , are geological records of biological activity. Trace fossils may be impressions made on the substrate by an organism: for example, burrows, borings , urolites , footprints and feeding marks, and root cavities...
s are classified
Biological classification
Biological classification, or scientific classification in biology, is a method to group and categorize organisms by biological type, such as genus or species. Biological classification is part of scientific taxonomy....
in various ways for different purposes. Traces can be classified taxonomically (by morphology), ethologically (by behavior), and toponomically, that is, according to their relationship to the surrounding sedimentary layers. Outside of special cases, phylogenetic classification of trace fossils is unsatisfactory because the makers of most trace fossils are unknown.
Taxonomic classification
The taxonomic classification of trace fossils parallels the taxonomic classification of organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s under the International Code of Zoological Nomenclature
International Code of Zoological Nomenclature
The International Code of Zoological Nomenclature is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals...
. In trace fossil
Trace fossil
Trace fossils, also called ichnofossils , are geological records of biological activity. Trace fossils may be impressions made on the substrate by an organism: for example, burrows, borings , urolites , footprints and feeding marks, and root cavities...
nomenclature a Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
binominal name is used, just as in animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
and plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
taxonomy
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
, with a genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
and specific epithet. When talking about trace fossils the genus is called an ichnogenus, and the species is an ichnospecies, the ichno- prefix coming from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
ιχνος (transliterated ikhnos), meaning "trace". The name is similarly italicized, and in full reference the author plus the year of publication should be cited. "Ichnogenus" and "ichnospecies" are commonly abbreviated as "igen." and "isp.", respectively.
Most researchers classify trace fossils only as far as the ichnogenus rank, based upon trace fossils that resemble each other in morphology but have subtle differences. Some authors have constructed detailed hierarchies up to ichnosuperclass, recognizing such fine detail as to identify ichnosuperorder and ichnoinfraclass (e.g. http://www.paleofile.com/Demo/Localities/Africademo/Algeria.htm), but such attempts are controversial.
The most promising cases of phylogenetic classification are those in which similar trace fossils show details complex enough to deduce the makers, such as bryozoan borings
Bioerosion
Bioerosion describes the erosion of hard ocean substrates – and less often terrestrial substrates – by living organisms. Marine bioerosion can be caused by mollusks, polychaete worms, phoronids, sponges, crustaceans, echinoids, and fish; it can occur on coastlines, on coral reefs, and...
, large trilobite
Trilobite
Trilobites are a well-known fossil group of extinct marine arthropods that form the class Trilobita. The first appearance of trilobites in the fossil record defines the base of the Atdabanian stage of the Early Cambrian period , and they flourished throughout the lower Paleozoic era before...
trace fossils such as Cruziana
Cruziana
Cruziana is a trace fossil consisting of elongate, bilobed, approximately bilaterally symmetrical burrows, usually preserved along bedding planes, with a sculpture of repeated striations that are mostly oblique to the long dimension...
, and vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
footprints. However, most trace fossils lack sufficiently complex details to allow such classification.
The Seilacherian System
Adolf Seilacher
Adolf "Dolf" Seilacher is a German palaeontologist who has made major contributions to evolutionary and ecological palaeobiology in a career stretching over 60 years. He won the Crafoord Prize in 1992, the Paleontological Society Medal in 1994 and the Palaeontological Association's Lapworth Medal...
was the first to propose a broadly accepted ethological
Animal behaviour
Animal behaviour is the subject of:* The field of Ethology* Animal Behaviour, a scientific journal...
basis for trace fossil classification. He recognized that most trace fossils are created by animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
s in one of five main behavioural activities, and named them accordingly:
- Cubichnia are the traces of organisms left on the surface of a soft sedimentSedimentSediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
. This behaviour may simply be resting as in the case of a starfish, but might also evidence the hiding place of prey, or even the ambush position of a predator.
- Domichnia are dwelling structures that reflect the life positions of organisms, for example the subsurface burrowBurrowA burrow is a hole or tunnel dug into the ground by an animal to create a space suitable for habitation, temporary refuge, or as a byproduct of locomotion. Burrows provide a form of shelter against predation and exposure to the elements, so the burrowing way of life is quite popular among the...
s or boringsBioerosionBioerosion describes the erosion of hard ocean substrates – and less often terrestrial substrates – by living organisms. Marine bioerosion can be caused by mollusks, polychaete worms, phoronids, sponges, crustaceans, echinoids, and fish; it can occur on coastlines, on coral reefs, and...
of suspension feeders, and are perhaps the most common of the established ethological classes.
- FodinichniaFodinichniaFodinichnia are trace fossils formed by deposit feeders as they excavate the sediment in search of food. They tend to have repeated patterns or spreites , the shape reflecting the systematic feeding strategy used by the organism as it scours the sediment...
are feeding traces which are formed as a result of organisms disturbing the sediment in their search for food. They are normally created by deposit feeders as they tunnel through soft sediments, usually producing a 3D structure.
- Pascichnia are a different type of feeding trace for which the trophic guild responsible are grazerGrazingGrazing generally describes a type of feeding, in which a herbivore feeds on plants , and also on other multicellular autotrophs...
s. They create 2D features as they scour the surface of a hard or soft substrateSubstrate (biology)In biology a substrate is the surface a plant or animal lives upon and grows on. A substrate can include biotic or abiotic materials and animals. For example, encrusting algae that lives on a rock can be substrate for another animal that lives on top of the algae. See also substrate .-External...
in order to obtain nutriment.
- Repichnia are locomotory tracks that show evidence of organisms moving from one station to another, usually in a near-straight to slightly curved line. Most of the very few traces to be verifiably assigned to a specific organism are in this category, such as various arthropodArthropodAn arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
and vertebrateVertebrateVertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
trackways.
Other ethological classes
Since the inception of behavioural categorization, several other ethological classes have been suggested and accepted, as follows:- Aedificichnia: evidence of organisms building structures outside of the infaunal realm, such as termiteTermiteTermites are a group of eusocial insects that, until recently, were classified at the taxonomic rank of order Isoptera , but are now accepted as the epifamily Termitoidae, of the cockroach order Blattodea...
mounds or waspWaspThe term wasp is typically defined as any insect of the order Hymenoptera and suborder Apocrita that is neither a bee nor an ant. Almost every pest insect species has at least one wasp species that preys upon it or parasitizes it, making wasps critically important in natural control of their...
nests.
- Agrichnia: so called "gardening traces", which are systematic burrow networks designed to capture migrating meiofauna or perhaps even to culture bacteriaBacteriaBacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
. The organism would have continually inspected this burrow system to prey on any smaller organisms that strayed into it.
- Calichnia: structures that were created by organisms specifically for breeding purposes, e.g. beeBeeBees are flying insects closely related to wasps and ants, and are known for their role in pollination and for producing honey and beeswax. Bees are a monophyletic lineage within the superfamily Apoidea, presently classified by the unranked taxon name Anthophila...
cells.
- Equilibrichnia: burrows within the sediment that show evidence for organisms' responses to variations in sedimentation rate (i.e. the burrow moves upwards to avoid burial, or downwards to avoid exposure). Typically this evidence will be in the form of spreiten, which are small laminations in the sediment that reflect previous positions the organisms were in.
- Fugichnia: "escape traces" that are formed as a result of organisms' attempts to escape burial in sudden high-sedimentation events like turbidity currentTurbidity currentA turbidity current is a current of rapidly moving, sediment-laden water moving down a slope through water, or another fluid. The current moves because it has a higher density and turbidity than the fluid through which it flows...
s. The burrows are often marked with chevron patterns showing the upward direction the organisms were tunnelling.
- Praedichnia: trace fossils that show evidence of predatory behaviour, such as the drill holes (boringsBioerosionBioerosion describes the erosion of hard ocean substrates – and less often terrestrial substrates – by living organisms. Marine bioerosion can be caused by mollusks, polychaete worms, phoronids, sponges, crustaceans, echinoids, and fish; it can occur on coastlines, on coral reefs, and...
) left in shells by carnivorous gastropods, or more dramatically, the bite marks found on some vertebrateVertebrateVertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
boneBoneBones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
s.
Over the years several other behavioural groups have been proposed, but in general they have been quickly discarded by the ichnological community. Some of the failed proposals are listed below, with a brief description.
- Chemichnia: a type of agrichnia applied specifically to those instances of bacteriaBacteriaBacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
l harvesting.
- Cecidoichnia: a plant trace in which a gall is left on the plant as a result of interaction with animals, bacteria, or other plants.
- Corrosichnia: traces that are left by plant rootRootIn vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...
s as a result of their corrosiveCorrosiveA corrosive substance is one that will destroy or irreversibly damage another surface or substance with which it comes into contact. The main hazards to people include damage to the eyes, the skin, and the tissue under the skin; inhalation or ingestion of a corrosive substance can damage the...
action on the sediments.
- Cursichnia: a subgroup of the repichnia, created by a crawling or walking habit.
- Fixichnia: traces left by sessileSessility (zoology)In zoology, sessility is a characteristic of animals which are not able to move about. They are usually permanently attached to a solid substrate of some kind, such as a part of a plant or dead tree trunk, a rock, or the hull of a ship in the case of barnacles. Corals lay down their own...
organisms that anchored themselves to a hard substrate.
- Mordichnia: a praedichnial subgroup that shows evidence of the prey's death as a result of the attack.
- Natichnia: a type of repichnia caused by disturbances to a soft sediment by a swimming organism, e.g. a benthic fishFishFish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
.
- Polychresichnia: traces that show an origin in the combination of two or more established trace-producing behaviours, e.g. domichnia that served as the feeding position of the organisms.
- Sphenoichnia: a plant trace created by the bioturbationBioturbationIn oceanography, limnology, pedology, geology , and archaeology, bioturbation is the displacement and mixing of sediment particles and solutes by fauna or flora . The mediators of bioturbation are typically annelid worms , bivalves In oceanography, limnology, pedology, geology (especially...
al action of roots.
- Taphichnia: fugichnia in which the organism failed to escape and was buried, often resulting in its body fossil being found in association with the trace.
- Volichnia: traces that show the position a flying organism (usually an insect) landed on a soft sediment.
Fixichnia is perhaps the group with the most weight as a candidate for the next accepted ethological class, being not fully described by any of the eleven currently accepted categories. There is also potential for the three plant traces (cecidoichnia, corrosichnia and sphenoichnia) to gain recognition in coming years, with little attention having been paid to them since their proposal.
Toponomic classification
Another way to classify trace fossils is to look at their relation to the sedimentSediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
of origin. Martinsson has provided the most widely accepted of such systems, identifying four distinct classes for traces to be separated in this regard:
- Endichnia are those traces that are found wholly within the casting medium, and therefore can only have been made by an infaunal organism.
- Epichnia are found on the tops of the strata of origin, being those ridges and grooves that were formed by benthic organisms or infaunal burrows that have been exposed by erosionErosionErosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
.
- Exichnia are traces that are made of material that is different from the surrounding medium, having either been actively filled by an organism or eroded out and re-covered by an alien sediment.
- Hypichnia are ridges and grooves found on the soles of the beds of origin at their interfaces with other strataStratumIn geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
, representing the opposite of epichnia.
Other classifications have been proposed, but none stray far from the above.
External links
- http://www.peripatus.gen.nz/paleontology/trafos.html
- http://www.envs.emory.edu/ichnology/
- http://www3.wooster.edu/geology/Bioerosion/Bioerosion.html