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from article Acanthodii

Jaws of an Early Devonian ischnacanthid from northern Canada. The upper palatoquadrate and lower meckelian cartilages have tooth-bearing jawbones along their facing edges. (From University of Alberta, Laboratory for Vertebrate Paleontology…

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from article Acanthodii

Examples of acanthodians from the Early Devonian of northern Canada. (a) Primitive climatiiform Lupopsyrus. (b) Diplacanthid Tetanopsyrus. (c) Ischnacanthiform Ischnacanthus. (d) Unnamed mesacanthid acanthodiform. (From the University of Alberta,…

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from article Index fossil

Three cephalopod genera forming an evolutional sequence. Their short ranges (indicated by bars) and distinctive suture lines (the area between two sutures is shown in black) make them ideal index fossils for the early Pennsylvanian Period. (After A.…

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from article Index fossil

Different concepts of range zones based on various combinations of overlap of two or more index species. (From D. R. Prothero and F. Schwab, Sedimentary Geology: An introduction to Sedimentary Rocks, Freeman, 1996)

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from article Index fossil

Potential range versus actual range of an index fossil species. Note that the actual time of occurrence at a given locality is generally some fraction of the actual range of the species because of the limitations of environment, immigration, and…

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from article Index fossil

Graphic correlation method of Alan Shaw. Note that the X and Y axes of the graphs are scaled diagrams of measured sections of the two different outcrops to be correlated. The points plotted on the graphs are the corresponding heights of the first or…

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from article Permian