benthic (paleo)ecology, ichnology, paleobiology
Natural scientists looking at fossils in the XIXth century were getting pretty good in correlating fossils with modern analogues or otherwise interpreting them as remains of strange and previously unknown life forms. Nevertheless, there was a particular group of fossils, known by the informal name of ‘fucoids’, which most naturalists had problems to understand. They were interpreted as fossil algae, plants or worms. By the end of the century some scientists realized that they were not body fossils (i.e. fossilized remains of the skeleton or soft tissue of an organism) but rather indirect records of organism behavior produced by the interaction with the substrate (trace fossils).
Thus, trace fossils are evidences of ancient organism behavior, which are preserved in the fossil record. They include fossilized tracks, burrows, borings, trails, predation marks, excrements, etc. These structures are true ‘fossils of life’ as they are not recording dead plants and animals, but rather their life activities. Ichnology studies trace fossils and also modern analogues. That allows to differentiate between paleoichnology and neoichnology.
PICTURE ABOVE: Different types of trace fossils (or ichnofossils), from left to righ, above to below: a dinosaur track (Upper Cretaceous, Pyrenees), a decapod burrow system (Ophiomorpha, Pleistocene, Brazil), an invertebrate trail (Psammichnites, Cambrian, Sweden), bivalve borings on an ancient rocky shore (Gastrochaenolites, Miocene, SE Spain), decapod faecal pellets (Palaxius, Middle Jurassic, England), scars produced by shell reparing after predator attack (Pliocene, SE Spain).
Trace fossils may be considered as the result of the interaction of three intervening elements: an organism, a substrate and a behavior or function. These three parameters are in a way or another controlled by paleoecological, paleoenvironmental and evolutionary factors.
(… to be continued)