Ichnological terminology is essential for studying trace fossils and analyzing trackways, and it allows researchers to interpret complex ancient ecosystems and understand the behavior and environments of past life. This article clarifies key terms, improving communication and understanding in ichnology while aiding the interpretation of ichnological evidence.
Ichnological terminology began to appear in scientific literature to describe traces in the early nineteenth century. However, there is still no complete agreement on its definitions and usage. Despite this, efforts to systematize these terms have gradually progressed over time.
General Ichnological Terminology and Definitions
Ichnology. The name of the term is derived from the Greek words “ichnos” (trace) and “logia” (study). This branch of paleontology examines biogenic sedimentary structures and trace fossils related to the movement and activities of organisms. More broadly, it encompasses the study of bioturbation, which refers to the alteration of sediment by animals. The term “ichnolithology” was in use until 1851. Additionally, biogenic structures play a crucial role in the paleoecological reconstruction of sedimentary environments.
Types of Ichnology
Researchers sometimes divide ichnology into neoichnology and paleoichnology.
Neoichnology. The scientific study of modern traces left by living organisms (contemporary biogenic structures).
Paleoichnology. The study of fossil traces left by extinct organisms (fossil biogenic structures, or ichnofossils). Paleoichnology further subdivides into the study of plant, vertebrate, and invertebrate traces.
Key Ichnological Terminology
To decipher the traces of ancient life, it is necessary to understand the basic concepts of ichnological terminology.
Ichnofossil (or Trace Fossil). Evidence of the life activity of a fossil organism preserved in an inorganic or organic, soft or hard substrate. Ichnofossils include imprints of the body or its parts (mainly appendages) resulting from an organism’s active behavior but do not preserve the actual remains of the organism itself. They encompass movement traces, crawling trails, burrows, borings, coprolites, and similar structures. Ichnofossils provide insight into how organisms moved, fed, built shelters, and rested. Scientists estimate the oldest known ichnofossils to be around 3.5 billion years old.
Ichnite. An ichnite refers to any trace fossil that contains imprints of animals on the surface of sedimentary rock. These can include footprints, tail marks, running and crawling traces, nests, hollows, burrows, and more. Today, the term is rarely used, as it has largely been replaced by more specific terms such as “track” (walking traces) and “trail” (crawling traces), or collectively as “ichnofossils.”
Ichnofauna. A fauna whose composition is determined by the traces of activity left by the species within it. The term “ichnofauna” can refer to fossil trace associations from a specific stratigraphic level or an entire sequence. It encompasses any group of trace fossils created by animals, including ichnoassemblages, ichnocoenoses, and ichnofacies.
For example, the “dinosaur ichnofauna” from the Late Cretaceous (Cenomanian–Turonian) of the Santo Anastácio Formation, Bauru Group, Southeast Brazil, includes traces of four theropod morphotypes, quadrupedal and small bipedal ornithischians, bipedal and graviportal ornithopods, and a small sauropod. In later layers, these taxa are no longer present. Specialized crocodyliforms, such as sphagesaurians, filled the niches left by small herbivorous dinosaurs, while titanosaurs became the dominant medium-to-large herbivores in these ancient ecosystems. (Navarro et al., 2025)
Ichnocoenose (or Ichnocoenosis). An association of fossil traces created by members of the same biological community. It represents the activity of a group of previously coexisting organisms in relation to their environment.
The term ichnocoenose is correctly used to refer to fossil trace associations that can be characterized by morphological criteria (regardless of the depositional environment or biological affinity) and only from the same stratigraphic level. The term paleoichnocoenos (or palichnocenose, palichnocenosis) may also be used. It includes ichnofauna (animal traces) and ichnoflora (plant trace fossils).
For example, Fuersichnus ichnocoenosis (part of Cruziana ichnofacies); Megalosauripus ichnocoenosis (part of Grallator ichnofacies).
Synonym: ichnocommunity.
Ichnofacies. These are recurring ichnocoenoses, groups of trace fossils that indicate specific environments (depth, wave and current energy, marine or non-marine conditions) and time periods. Ichnofacies serve as reliable records of ancient environments.
Ichnological Disturbances and Diversity
Dinoturbation. This refers to the trampling and disturbance of soils and substrates by the movement of dinosaurs. Highly dinoturbated layers are a relatively common feature of non-marine deposits, such as the Saltwick, Cloughton, and Scalby formations in Yorkshire or the Vega Formation in Spain.
Typical sandstone layers have a flat upper surface and highly irregular bases. These layers may preserve signs of disrupted stratification and contain undertracks with or without toe impressions, or nearly homogeneous layers with only rarely recognizable tracks and toe prints. Although they seldom retain detailed foot morphology, they provide important information about dinosaur habitats.
Ichnofabric. Also known as “ichnotexture,” this biogenic texture forms when ichnofossils are so abundant that they almost completely cover the surface of a layer, creating a distinctive pattern and altering its appearance. Alternatively, it can result from the complete reworking of the sediment into a nearly homogeneous mass composed of individual trace elements and the surrounding matrix.
Ichnofabric generally refers to all elements and aspects of the texture and structure of sedimentary rocks created by bioturbation and bioerosion. The concept of ichnofabric focuses on identifying the characteristic ways in which organism activity affected the texture and fabric of the sediment. Ichnotissue indices allow us to assess the degree and intensity of bioturbation.
Ichnodiversity. The taxonomic richness of trace fossils, i.e., the number of ichnotaxa (usually at the ichnogenus level) present in a sample.
Taphonomic Processes
Taphonomy. Taphonomy is the study of the destruction of sedimentary textures and the natural processes governing the burial of organisms. It includes all processes that affect an organism after death, including burial (chemical changes within the organism), transportation, surface weathering, and eventual discovery or collection by a geoscientist.
Ichnotaphonomy. The study of all processes that modify a trace fossil from the moment of its formation until its discovery.
Ichnostratinomy. The study of all processes that influence trace fossils from their formation until their final burial.
A Few Additional Ichnological Terminology Concepts
Ichnolite. A rock containing the imprint of an ancient animal’s trace, such as a footprint or trail. For instance, a sandstone slab bearing dinosaur footprints qualifies as an ichnolite.
Biogenic Sedimentary Structure. Biogenic sedimentary structure. A term referring to both fossil and modern traces formed in unconsolidated sediments. The activities of organisms form these structures and influence the formation of the sedimentary environment.
These terms are in addition to the ichnological terminology discussed earlier.
Trackways
Trackway. A trackway is a series of at least three consecutive footprints on a sediment surface, left by a single moving animal with locomotory appendages. Generally, observers do not consider two consecutive footprints a trackway, but they can still indicate the trackmaker’s direction of movement.
The length of fossilized dinosaur trackways can reach hundreds of meters. Trackway analysis helps in understanding various aspects of animal behavior. For example, a set of pterosaur tracks revealed that they were capable of quadrupedal locomotion on land using their front limbs.
Tetrapod trackways exhibit an alternating arrangement of footprints, whereas arthropod trackways typically show a parallel (side-by-side) arrangement of tracks.
Runway. This term is sometimes used to describe repeatedly overlapping trackways that have turned into surface grooves or trenches, frequently used as movement routes. This phenomenon commonly occurs on snow during winter. The fossil record of such pathways is extremely rare.
Traceway. A more general term used to describe a series of impressions made during locomotion, which do not necessarily represent tracks. In ichnological terminology of tetrapods, the term “traceway” often describes trackways made by swimming trackmakers. It functions as a synonym for trackway in this situation.
A closely related term is trail. The term movement path is even broader and does not necessarily imply the formation of physical traces.
Trail. A trace of movement in general. A trail is a trace left by a moving animal on a sediment surface, typically when locomotion occurs without the use of limbs. This includes marks made by worm-like animals, certain arthropods, and vertebrate body parts such as the belly or tail, but not limbs. Common examples include trails left by gastropods, worms, fish, and snakes. Trails can result from various forms of movement, such as those seen in “snail trails” or “fish trails.”
In invertebrate ichnology, a trail refers to a continuous locomotion trace on the substrate surface, whereas a trackway consists of multiple individual impressions.
A notable example of ancient trails is the Mesoproterozoic (about 1.25 billion years ago) trace fossils (left by early metazoans) from the Van Horn region of Texas.
Trackway Characteristics
Trackway Pattern. The recurring characteristics of a trackway as a whole (excluding features specific to the hand or foot). This includes trackway width, the relative positioning of tracks, their orientation, and associated traces such as drag marks and tail traces.
Compared to ornithopods, theropods like Tyrannosaurus, Baryonyx, and Velociraptor had narrow and elongated tracks. Theropod footprints typically feature long, slender toes and a V-shaped outline, whereas ornithopod footprints have a more rounded shape with wider toes.
Ankylosaurs generally had longer toes than ceratopsians. Additionally, ceratopsians walked with their toes touching the ground and did not leave handprints, whereas ankylosaurs moved with their palms spread out.
Among dinosaurs, sauropods left the largest tracks. Sauropods, among dinosaurs, left the largest tracks, their footprints being large and round with crescent-shaped impressions on their front feet. Sauropod front feet had five toes, usually with claws, while the hind feet typically had three claws.
Trackway Gauge (Gait Width). The width of a trackway, or gait width, refers to the distance of the tracks from the trackway midline relative to the size of the trackmaker. Trackway width is typically expressed as the ratio of trackway width to the length (or width) of the pes (foot) or manus (hand).
Tetrapod trackways can be classified as narrow-gauge if the tracks are “close to or intersect the trackway midline” and wide-gauge if they are “far from the trackway midline.” Narrow-gauge sauropod trackways are much more common than wide-gauge ones. This ichnological terminology is particularly popular when describing sauropod tracks, and more recently for the trackways of other quadrupedal tetrapods as well.
Ontogenetic Series of Tracks (or “growth series”) describes tracks of different sizes that apparently represent different ontogenetic stages of the same trackmaker species.
Tortuosity. The degree of curvature in a movement path. Tortuosity is high if an animal makes many turns and low if it moves in a straight line.
Milling. Non-directional movement of a trackmaker, characterized by a highly tortuous and often self-intersecting movement path. Large mammals that congregate around a water source or herbivores that forage in a specific area demonstrate this behavior. Such activity can result in a localized accumulation of tracks.
Morphotype (Ichnomorph). A group of tracks that share morphological similarity. It is not necessary that the same trackmaker made these tracks.
Track Morphology
Track, Fossil Track, is defined within ichnological terminology as any mark or impression left by an animal’s limb (autopodium) or part of it on a surface. It forms because of the foot interacting with the substrate. A limb print on the sediment surface is the most common type of track for vertebrates. Therefore, only animals with limbs, such as arthropods, amphibians, reptiles, birds, and mammals, can make such tracks.
An animal creates a walking mark when its weight makes the substrate sink, leaving an imprint on the sediment surface. This results in a concave epirelief on the upper surface of the layer. In ichnological terminology, “track” can also refer to convex hyporelief, which is a raised imprint on the underside of the layer above. This raised imprint forms as a natural cast of the original depression.
Footprint. The term “footprint” is preferable in a narrow sense: literally, a “footprint.” For example, “track” should not be used to describe swimming traces (here, “footmark” is more appropriate). Thulborn defines the term “footprint sensu stricto” as an area of substrate directly imprinted by the underside of the trackmaker’s foot, excluding “any surrounding or subsurface features” such as track walls, displacement rims, undertracks, and natural casts. Thus, “footprint” is synonymous with “true track sensu stricto.”
Trilobite-like arthropods left the first such tracks, called Cruziana, about 550 million years ago. The first traces of vertebrates—tetrapods (amphibians)—date back to the Middle Devonian, 391 million years ago.
Fossil tracks are semi-reliefs on the surface of a rock layer. If they are on the upper surface, they usually form a depression, a mark called a “concave epirelief,” and at the base (sole) of the layer, they form a ridge, a cast called a “convex hyporelief” (Seilacher, 1953).
In the first case, these reliefs are more or less deep imprints; in the second—more or less elevated areas. In both cases, the term “relief thickness” is used.
An animal creates a footprint by pressing its limb into a pliable substrate. The resulting imprint typically also contains evidence of the foot’s movement and the physical state of the sediment. To preserve the imprint, later deposits need to cover the surface where the animal walked and fill the imprint.
The surface of the imprint is a deformed sediment surface onto which the foot was imprinted.
True Track (Actual Track). A track imprinted on a real surface (actual tracked surface). In ichnological terminology, “true track” means a clear, well-preserved, visually distinct track, not deformed by overprinting. True tracks sometimes preserve details such as skin impressions. However, the track may lack anatomical details, for example, if it forms on a very soft or coarse substrate.
Synonyms of “true track” in the narrow sense are “true track sensu stricto” and “footprint sensu stricto.”
Ichnosurface. In ichnological terminology, “ichnosurface” refers to the surface of the bed (layer) containing tracks, as it is today. This general term can refer to any surface containing ichnofossils. Closely related terms include track horizon and paleosurface.
Surface Track. A track formed and exposed on the same sediment-air or sediment-water interface on which the animal walked. This includes the upper surface of penetrative tracks and collapsed tracks.
Elite Track (Elite Footprint). The clearest and most distinct tracks on a trampled surface that overlie previously created tracks. Elite tracks often, but not necessarily, have higher anatomical fidelity than the tracks they overlie. Synonyms include “high-fidelity tracks” and “stamps.”
Overstep—a condition in which the pes is positioned in front of the manus. The opposite positioning, with the pes posterior to the manus, defines the term “understep.” In the same set of prints, a footprint can appear in front of the handprint.
Overlap (Overprint). A condition in which the pes is positioned over the manus track. The footprint partially or completely overlaps the handprint immediately after the manus retracts. They also use this term more generally to refer to any overlapping tracks. In ichnological terminology, “amalgam” (synonyms: compound track; composite track) describes the accidental overlap of two or more tracks, usually belonging to different individuals.
Track Measurements
Stride Length. The distance between two successive footfalls of the same foot. This segment is more or less parallel to the midline. Stride length in trackways is very often constant. However, it varies depending on the type of gait and speed of movement.
Pace Length. The distance between two successive footprints of the left and right foot (or left and right hand) projected onto the midline. Its average value corresponds to half the average stride length. The pace line is an imaginary line along which the pace length is measured.
[Oblique] Pace. The distance between the footprints of the right and left hand (manus) or the right and left foot (pes) is measured at an angle to the midline of the trackway. In very narrow tracks, it corresponds to half the stride length.
Pace Angulation (Pace Angle). This is simply the angle formed by three consecutive footprints. It helps us understand how wide or narrow the dinosaur’s walk was. A small pace angle means the dinosaur walked with its feet relatively far apart. A larger angle shows a narrower, more straight-line walk. Its value on the same trackway often remains constant when maintaining the same type of gait, but its magnitude is directly proportional to speed. The faster the dinosaur moved, the larger the pace angle tended to be. A 180-degree pace angle means the dinosaur’s feet landed perfectly in a straight line. Anything less than that shows a bit of a zigzag in their walk. By measuring the pace angle, paleontologists can get clues about a dinosaur’s speed, gait, and overall movement.
Gruipeda gryponyx, plover-like birds (Charadriiformes). Upper Cretaceous–Pliocene, Eocene Green River Formation, USA (Hogue and Hasiotis). Anisodactyl track with an angle of divarication less than 140 degrees. The angle of divarication of digits I–II is smaller than IV–I. The webbing is absent. Digits have pad impressions with two on I and II, three on III, and four on IV. Water-margin environment, ethological class: Repichnia. Junior synonym: Trisauropodiscus.
Divarication of Digits. The angle between two digit axes on the same footprint. Usually, the angles between adjacent digits are measured (partial divarication). Additionally, the angle between digits II and IV (in tridactyl tracks) and the angle between digits I and V (total divarication) are measured. The sum of the interdigital angles from digit II to III and digit III to IV gives the total divarication angle. The angles can be acute, right, or obtuse; they can also have zero or negative values (though rarely).
Track Formation and Types
This chapter includes definitions of ichnological terminology relevant to the study of track formation and exploring the diverse types of trace fossils found in the geological record.
Mold (Mould) and Cast. When a footprint is buried, sedimentary rocks fill the concave impression (or natural mold), forming a natural cast of the footprint. In reality, the impression (mold) is the negative of the animal’s foot (a concave epirelief), while the cast is its positive copy (a convex hyporelief).
Natural Cast. Natural casts form on the underside of the overlying layer when sediment fills the depression with the original footprint, resulting in a three-dimensional shape of the animal’s foot. This shape replicates the original fossil in positive relief. Natural casts, like true tracks, can preserve informative details of the foot (such as skin impressions), though some details are inevitably lost during cast formation.
When erosion removes the less resistant layer containing molds, natural casts become visible on the underside of ledges in cliffs or escarpments. These casts may sometimes fall and accumulate as loose blocks ex situ.
Natural Mold. Natural molds form on the upper surface of a layer. Fossil trackways, a type of trace fossil, are a type of external mold. Some famous dinosaur tracks demonstrate this type of preservation.
Impression. A general term for a depression left by an object on a substrate. An impression is a low relief, almost two-dimensional representation of a print or cast, which may not necessarily preserve the fine details of the organism’s surface.
Imprints are shallow disturbances in sediment left by a resting trackmaker, often capturing surface textures.
Mark. The term “mark” typically refers to small accessory traces, such as claw marks, or those formed by significant horizontal movement, like drag marks, tooth marks, and slide marks. In invertebrate ichnology, “mark” is generally used for non-biogenic structures created by physical processes (e.g., tool marks, scour marks). This is contrasted with “trace,” which denotes structures formed by biological activity. However, in vertebrate ichnology, “mark” can also apply to structures resulting from an organism’s activity, such as tail drag marks, tooth marks, and claw marks.
Trace. The term “trace” can be used interchangeably with “impression” and “mark,” but it is usually limited to structures organisms actively create. The term “trace” finds more use in invertebrate ichnology than in tetrapod ichnology.
Hypichnia and Epichnia
Hypichnia. Refers to fossil traces preserved on the underside of sedimentary layers. These structures form when organisms burrow into sediments, leaving impressions or ridges that later fossilize.
Epichnia. Refers to fossil traces preserved on the upper surface of sedimentary layers. Epichnial structures can include pits or trails created by organisms interacting with the sediment surface, such as foraging or moving across it, which is typically characteristic of environments with minimal bioturbation.
Variations of Tracks in Layers
A – surface prints: in which the rock splits cleanly along the surface on which the animal moved, to reveal the original footprint-bearing substrate and the infill as part and counterpart (A3).
B – underprints: in which the rock splits along a surface intersecting with the print so that part of the original substrate adheres to the infill (B4), or part of the infill adheres to the substrate (B5), or both.
C – transmitted prints: in which the rock splits along a surface that is entirely below the print and print-bearing surface so that both part and counterpart reveal only transmitted features (C3, C4).
©Romano, Whyte.
Subtraces, Transmitted Prints, Ghost Prints. The impact of a vertebrate foot can affect not only the surface sediments it walks on but also the buried layers beneath, creating subtraces that only partially reflect the shape of the original prints. Some parts of such prints remain hidden, and the size and depth of the subtrace relief may differ from the true dimensions of the surface track. Because subtraces form indirectly, they preserve only the basic anatomy of the trackmaker’s foot. In contrast, true tracks can retain fine details, like skin impressions, under favorable conditions.
Undertrack (Underprint). A track formed in a subsurface layer, as opposed to a surface track that is exposed on the tracking surface. Ichnological terminology originally used the term to refer to tracks created by limulids as their limbs penetrated surface layers and left marks at varying depths. In tetrapod ichnology, the term refers to a track formed in a subsurface layer through transmission, without direct contact with the foot. The term “underprint” often serves as a synonym for the term “undertrack” and, in such cases, refers to transmitted undertracks.
Subtrack. In ichnological terminology, subtrack refers to the deformation or disturbance of the substrate beneath a true footprint or track. It occurs when the weight of an organism is transmitted through soft sediment, affecting deeper layers. Sometimes, subtracks can persist even when the original surface track erodes away. This concept is similar to a “penetrative track” and “transmitted undertrack”.
Overtrack (Overprint, Overtrace, Supertrace, and Ghost Track). A track in a sediment layer above the true track. A series of thin sediment layers may completely cover the track-bearing layer (track bed) while still reflecting the contours of the tracks beneath. Overtracks are depressions in the upper layer indicating the presence of a track at a lower level. In layered deposits, multiple overtracks per track may be present. They form in sediments that fill true tracks and are usually very faint and indistinct. “Internal overtrack” refers specifically to the track sensu stricto rather than the entire general track.
Transmitted Undertrack. An undertrack formed by the transmission of force through a sediment volume. Transmitted undertracks form indirectly, without direct contact with the foot, and should be distinguished from penetrative tracks, in which the foot physically penetrates the layers. Synonyms include “compressive undertrack” and “ghost track.”
Non-anatomical Features of Tracks
Penetrative Track (Sealed Track). A track in which the path of the foot seals by substrate flowing around the descending foot or by collapse of the track walls. Layers, or laminae, dragged down by the descending foot are V-shaped in cross-section. Erosion may produce edges of such downfolded laminae around the track. Researchers sometimes refer to such structures as “wrinkle structures.” Penetrative tracks generally do not reflect the anatomy of the trackmaker.
Deep Track. Deep tracks result when a foot deeply penetrates soft sediments. This track can be a “penetrative track,” if sediment seals the foot’s path, or an “open track,” if the track walls remain. Natural casts often preserve these open tracks. Deep tracks typically capture more foot movement but less anatomical detail of the trackmaker compared to shallow tracks.
The differences between terms such as “penetrating footprint” and “deep footprint” do not seem to be very significant, but they matter in ichnological terminology for accurate interpretation.
Shaft. The three-dimensional space enclosed by the walls of a footprint. Essentially, it represents the depth or vertical cavity formed when an animal’s foot presses into a soft surface. When a track is deep, the “shaft” creates a well-defined, noticeable depression between the track walls. Shallow tracks, however, might not produce a visible “shaft.” This term helps to assess how deeply the animal’s foot sank into the substrate.
Track Infills (Infilling, Sediment Filling, Plug). Sometimes, depressions within the sediment layer above tracks can fill with sediment. This can be any sediment present in the natural mold of a surface track.
Like undertracks, “track infills” contain fewer morphological details. However, in some cases, they help paleontologists locate fossil footprints that erosion has not fully exposed, thus assisting them in finding true tracks. These “infills” may protect the mold from erosion, but researchers must remove them for proper track examination. The infill can sometimes be more resistant to erosion than the surrounding sediments, resulting in a positive relief of the track.
Modification and Disturbance of Tracks
Collapsed Track (Collapsed Print). When the walls of a track collapse due to gravity, usually after the foot withdraws, it creates a “collapsed track.”
Leptodactylous and Pachydactylous Tracks. These terms describe very thin and very wide toes, respectively. Researchers now interpret leptodactylous tracks as penetrative tracks. This means that the narrow appearance of the toe impressions is due to sediment flow or collapse, rather than the trackmaker having naturally thin toes.
Exit Trace. A feature of a track that forms when the foot lifts off from the substrate. In tracks of three-toed birds and dinosaurs, the toes usually collapse (are pulled together) to facilitate departure. Because of this, “exit traces” in these groups can be much smaller than the overall track. Exit traces can also appear as large, inverted mounds at the front of the track, as observed in some sauropod trackways.
Displacement Rim (synonyms: raised rim, lip, marginal ridge, extrusion rim, pressure ridge, displacement field, mud rim). A raised bulge around a track, formed by the displacement of sediment as the foot presses down. When an animal steps on soft or plastic sediment, it pushes the sediment outward under pressure. This creates a rim of sediment surrounding the footprint that is always higher than the track surface. Mammalian ichnology prefers the term “marginal ridge.” If sediments are more brittle, “marginal thrusts” may accompany or replace the “marginal upfold.”
Withdrawal Rim. Similar to a displacement rim, it forms as a foot lifts sediment upon withdrawal.
Sediment Mound. A small buildup of sediment on the track surface, created by foot movement. These mounds most often appear behind the toes as they push backward. People also call them “push-back” structures. Swimming tracks commonly exhibit sediment mounds.
Pressure Pad. A semicircular mass of sediment around the track shaft, slightly displaced (rotated) from its original position and sharply defined by microfaults. Pressure pads can form behind the shaft when the foot pushes backward before withdrawing. On inclined surfaces, larger pressure pads are usually oriented downslope.
Overhang and Undercut. In a mold, the track walls may extend into the shaft, forming “overhangs” that obscure part of the track floor when viewed from above. In a cast, this morphology results in “undercuts,” where the track walls appear recessed. Overhangs/undercuts are often found at the distal ends of digit casts, either because the toes were pressed forward into the sediment (then withdrawn backward) or because the sediment collapsed around the descending toe.
In molds, extreme overhangs can create “toe tunnels,” while in casts, extreme undercuts can produce “free” digit impressions that extend below the bedding plane.
Footprints and Substrate
Footprints are imprints of feet on the substrate over which an animal has passed. A substrate that is too hard and dense will not allow footprints to form. The impression of the underside of the foot will be accurate if the top surface of the layer is sufficiently fine and capable of adhesion, not too dry, and not too wet. The shape may clearly show not only the main morphological features such as claws, nails, or hooves, but also less noticeable ones such as scales or even bristles.
If the substrate is too coarse or dry, these details will not be visible. When the substrate is too wet or too soft, the prints can become deformed. If water submerges the substrate, it can severely damage or completely erase the tracks. In any case, tracks left on beaches or in shallow river mouths are likely to be washed away by the next high or low tide, while prints left on sand dunes are usually (though not always) erased by winds and landslides.
There is a scale of ichnological terminology that reflects the consistency of the substrate. They allow for a concise explanation of the substrate consistency that the animal dealt with when leaving a particular track: soupground, softground, stiffground, firmground, hardground, and rockground.
Counter-relief. A track on the upper surface of a sedimentary layer that has a positive relief (i.e., raised relative to the surrounding surface). This can occur due to erosion, where the compacted sediment beneath the track surface is more resistant to erosion than the surrounding less compacted sediment, resulting in a relief inversion as erosion progresses. When a foot lifts from the surface, suction or adhesion can pull sediment upward, which also creates counter-relief.
Main Slab and Counter Slab. Main slab and counter slab. An ex situ slab containing only concave epireliefs is called the main slab, and the corresponding slab containing convex hyporeliefs is called the counter slab.
Substrate Influence on Track Formation
Substrate strength (substrate consistency). The shape and clarity of footprints can vary significantly depending on the firmness of the ground. The ideal conditions for well-preserved tracks occur when the surface is neither too hard nor too soft. If the sediment is too soft and loose, it may partially collapse back into the impression after the foot lifts. This process, known as mud collapse or mud back-flow, can obscure important details, causing distinct toe marks to shrink into narrow slits or disappear entirely. In some cases, the pressure from the foot may create secondary impressions beneath the surface, known as undertracks, which can alter the footprint’s appearance.
The proper application of ichnological terminology, such as the substrate consistency scale, is essential for accurately describing these variations.
