Disadvantages of trace fossils are relatively fewer than their advantages but mainly center on the fact that one trace maker can make many different traces or many different trace makers can make the same trace. Because of these considerations, most trace fossils have limited value for biostratigraphy. Trace fossils are most commonly represented in the geologic record by features formed through animal activity in a substrate of some sort, such as sediment, rock, or wood. These features include burrows , tracks , trails , and borings . Burrows are excavations made into an unconsolidated substrate.
Tracks are imprints on a sediment surface by an animal with legs.
Trails are imprints on a sediment by a legless animal dragging its body across a surface. Borings are excavations made into a consolidated substrate, which could include rock or wood. Another type of trace fossil is biostratification, which can be represented by stromatolites or biogenic graded bedding . Stratification refers to the layering of sediments, hence biostratification is layering caused by organisms. Stromatolites are biogenic sedimentary structures formed by sediment binding and trapping in cyanobacterial or algal colonies.