A track, or footprint, is an impression made by an appendage of an animal while it was alive.
Although most fossil tracks were formed and preserved in originally soft sediment, solid materials compressed or fractured by the weight of a moving animal also constitute tracks. Crushed eggshells in a nest on the ground, twigs broken underfoot in a forest, or trampled bones in a watering hole are all tracks. This is because they leave visible impressions made by appendages of animals. Likewise, claw marks left in solid substrates are tracks, too. When a domestic cat (Felis domestica) scratches furniture to get attention, a modern aardvark (Orycteropus afer) tears apart a termite nest in search of a meal, and a grizzly bear (Ursus arctos) rakes a tree with its claws to mark its territory, these animals are also leaving tracks.
Individual tracks can provide many quantitative measurements, especially if clear impressions of digits are made. Among these measurements (Fig. 14.1) are:
■ Overall length and width of the track
■ Number of digits
■ Digit widths and lengths
■ Angles between digits
■ Depth of penetration of the track or individual claws (if the latter are present)
■ Number of fleshy pads associated with digits
■ Width and height of any visible zone of deformation around the track.
For dinosaurs, the number of digits that could have touched the ground while they walked varied from two, in some dromaeosaurs such as Deinonychus (Chapter 9), to five, present in some sauropodomorphs, stegosaurs, and ceratopsians (Chapters 10, 12 and 13). But the numbers also varied for the manus and pes tracks from
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