Trackways are trace fossils that preserve the footprints and other impressions of an ancient animal's passage, such as drag-marks from tails and bellies.
Most of the tracks that have fossilized were made in large expanses of firm, moist sediment, such as near shorelines and tidal flats.
The best conditions for preservation of trackways are different from those that produce good fossils of animal remains. Animal remains need quick burial of the animal's carcass to fossilize over time; trace fossils need a much slower and gentle process.
The first beneficial condition is a delay before the tracks are covered. If the moist sediment has a chance to dry out and harden somewhat, the impressions are better able to withstand subsequent burial under a new layer of sediment.
The next requirement is a slow, gentle burying by sediments, so that the impressions are not damaged in the process.
Eventually, the trackways are buried under further layers of sediment, and then over millions of years the layers compress into rock. The layers remain distinct despite the compression, and so the layer with the tracks can be exposed millions of years later. It is usually erosion by wind and water that reveals them.
Trackways are just one kind of trace fossil. Trace fossils include anything made by an animal while it was alive, including tooth marks, dens, eggs and coprolites (excrement). No remains of the animal are present.
Trackways are an important source of information on dinosaurian behaviour, anatomy and physical abilities:
- Tracks found in Texas (U.S.A) show brontosaurs walked in single file and cooled themselves in a shallow sea.
- From Connecticut (U.S.A) comes evidence of a carnivorous dinosaur drifting along on the tips of its toes in a shallow lake.
- The tale of a stampede of small, plant-eating dinosaurs upon the arrival of a large predator is told by tracks found in Australia.
- Imprints have shown that ostrich dinosaurs, such as Dromiceiomimus had soft, fleshy heels.
Running speeds are also revealed by trackways; estimates include:
- 12 km/h (7.5 MPH) for a small brontosaur whose tracks were found in Niger
- 20 km/h (12.5 MPH) for a giant brontosaur that once lived in what is now Morocco
- 27 km/h (17 MPH) for a large hadrosaur that once lived in what is now Colorado (U.S.A.).
Cretaceous-age dinosaur tracks have been recovered at many sites in Canada, to name but a few: along the Peace River in near Hudson’s Hope, British Columbia; Tumbler Ridge, also in northern B.C.; near Grand Cache, Alberta; and along the Ross River in central Yukon.