Morphology guide

Ichthyoliths are described by a list of keywords. Each keyword describes a specific characteristic feature, like being curved or having a serrated edge. Omitting a keyword implies that the ichthyolith does not possess the given feature – e.g., if an ichthyolith does not have the "curved" keyword, it is straight.

Some keywords are base keywords that may be used in conjunction with more specific sub-keywords. For example, if an ichthyolith has a veined cavity, it would have both the base keyword "cavity" and the more specific keyword "cavity veined".

Some keywords can be pluralized if they refer to multiple features. For example, an ichthyolith with multiple median keels would have the keyword "keels median". (Any associated base keywords would also be pluralized – i.e. "keels".)

This system does not record complete, technically precise descriptions of all of an ichthyolith's features. Keywords are intended to be general enough to remember and search easily, but specific enough to provide a useful description. A more detailed (but harder-to-use) classification system is given by Doyle; see, e.g., Doyle, P. S., and W. R. Riedel, 1979, Ichthyoliths: present status of taxonomy and stratigraphy of microscopic fish skeletal debris: La Jolla, Calif., University of California, Scripps Institution of Oceanography, SIO Reference Series 79-16, 230 p.

Citation: Ichthyolith morphology classification system by Daniel Gaskell (2014), version 1.

Type
Denticle: The ichthyolith is a shark denticle, as opposed to a fish tooth.
Outline
Triangular: The base of the ichthyolith is the widest part.
Linear: The base, middle, and tip of the ichthyolith are of similar width (tabular, cylindrical, etc.)
Fanned: The tip/end of the ichthyolith is the widest part.
Diamond: The middle of the ichthyolith is the widest part.
Arrangement
Multicuspid: The ichthyolith has multiple cusps (for teeth) or lobes (for denticles).
Pointed: At least one cusp (or lobe) is pointed.
Rounded: At least one cusp (or lobe) is rounded.
Blunt: At least one cusp (or lobe) has an end that is more or less flat.
Curved: The overall shape of the ichthyolith curves in one direction.
Concave: The main body lines of the ichthyolith are distinctly concave (outside of that caused by normal curvature).
Long: The ichthyolith is at least three times longer than it is wide.
Short: The ichthyolith is shorter than it is wide, or its length and width are approximately equal.
No definition available.
Edged: The ichthyolith has a distinct cutting edge along one or more sides; may include keels.
Features
Capped: At least one cusp or lobe of the ichthyolith has a cap of a noticeably different color or texture.
Serrated: The ichthyolith has a jagged, sawtooth edge.
Projection: The ichthyolith has a non-cuspid projection or platform emerging from one side, generally near the base.
Projections: The ichthyolith has more than one non-cuspid projection or platform emerging from the sides, generally near the base.
Protrusion: The ichthyolith has a non-cuspid outgrowth, such as a hook.
Protrusions: The ichthyolith has multiple non-cuspid outgrowths, such as hooks.
Cavity
Cavity: The ichthyolith has a central nerve cavity. This is a base keyword included whenever an ichthyolith has a cavity, even when the cavity is further categorized with an additional keyword.
Cavity Narrow: The ichthyolith's cavity is distinctively narrow (defined as narrower than the "walls" surrounding it at its midpoint; alternately phrased, the cavity takes up less than one-third of the total width of the cross-section at its midpoint).
Cavity Wide: The ichthyolith's cavity is distinctively wide (defined as more than four times as wide as the "walls" surrounding it at its midpoint; alternately phrased, the cavity takes up more than than two-thirds of the total width of the cross-section at its midpoint).
Cavity Partial: The ichthyolith's cavity extends less than halfway down its full length.
Cavity Veined: The ichthyolith's cavity has veins or other projections branching off it.
Cavity Irregular: The ichthyolith's cavity has an irregular structure - for example, multiple anastomosing channels.
Keels
Keel: The ichthyolith has a keel - a narrow, raised line or edge running across or around it. If not specified further, implies that the keel runs around the outer margin of the ichthyolith. This is a base keyword included whenever an ichthyolith has a single keel, even when the keel is further categorized with an additional keyword.
Keels: The ichthyolith has multiple keels - narrow, raised lines or edges running across or around it. If not specified further, implies that the keels run around the outer margin of the ichthyolith. This is a base keyword included whenever an ichthyolith has multiple keels, even when the keels are further categorized with additional keywords.
Keel Median: The ichthyolith has a median keel - a narrow, raised line or edge running down it from tip to base.
Keel Cross: The ichthyolith has a cross keel - a narrow, raised line or edge running across or around it laterally (perpendicular to the axis running tip-to-base).
Keels Median: The ichthyolith has multiple median keels - narrow, raised lines or edges running down it from tip to base.
Keels Cross: The ichthyolith has multiple cross keels - narrow, raised lines or edges running across or around it laterally (perpendicular to the axis running tip-to-base).
Keels Radial: The ichthyolith has radial keels - narrow, raised lines or edges radiating outward from a point. (If the point is on the edge of the ichthyolith, or an imaginary point beyond the edge, the keels are instead considered cross or median based on their average orientation.)
Keels Concentric: The ichthyolith has concentric keels - narrow, raised lines or edges running in circles or polygons of different sizes around the same center point. (The keels need not be complete circles, but if the center is an imaginary point beyond the edge of the ichthyolith, they are instead considered cross or median based on their average orientation.)
Lines
Line: The ichthyolith has a flat or indented line running across or around it. This is a base keyword included whenever an ichthyolith has a single line, even when the line is further categorized with an additional keyword.
Lines: The ichthyolith has multiple flat or indented lines running across or around it. This is a base keyword included whenever an ichthyolith has multiple lines, even when the lines are further categorized with additional keywords.
Line Median: The ichthyolith has a median line - a narrow flat or indented line running down it from tip to base.
Line Cross: The ichthyolith has a cross line - a narrow flat or indented line running across or around it laterally (perpendicular to the axis running tip-to-base).
Lines Median: The ichthyolith has multiple median lines - flat or indented lines running down it from tip to base.
Lines Cross: The ichthyolith has multiple cross lines - flat or indented lines running across or around it laterally (perpendicular to the axis running tip-to-base).
Lines Radial: The ichthyolith has radial lines - flat or indented lines radiating outward from a point. (If the point is on the edge of the ichthyolith, or an imaginary point beyond the edge, the lines are instead considered cross or median based on their average orientation.)
Lines Concentric: The ichthyolith has concentric flat or indented lines running in circles or polygons of different sizes around the same center point. (The lines need not be complete circles, but if the center is an imaginary point beyond the edge of the ichthyolith, they are instead considered cross or median based on their average orientation.)
Optional
Platform: The ichthyolith has a basal stalk or lobe. (Note that platforms may not be preserved as well as the rest of the ichthyolith.)
Platforms: The ichthyolith has multiple basal stalks or lobes. (Note that platforms may not be preserved as well as the rest of the ichthyolith.)
Cutout: The ichthyolith has a gap or rounded hole "cut out" of the base. (This may be a permanent feature, or the result of preferential breakage.)
Cutouts: The ichthyolith has multiple gaps or rounded holes "cut out" of the base. (These may be permanent features, or the result of preferential breakage.)