Trace fossils


Unlike marks (abiotic origin), trace fossils always result from a direct interaction between a living animal and the sediment.

Trace fossils can be found in nearly all formations of South West Germany's Triassic. Especially where bad preservation conditions are responsible for a partial or total lack of body fossils they are the only way to get at least a small glimpse of the diversity of the ancient faunas. The mass appearance of a single trace fossil genus in certain layers is very characteristic and indicates good living conditions for a certain group of organisms. The marine sediments only contain trace fossils that are typical for shallow water.

Traces of terrestric and semiaquatic animals (arthropods, amphibians, reptiles) mainly occur in the Upper Bunter where the desert-like conditions where not this strong any more and the mud of large lake basins and flood plains helped to preserve the traces. The five-toed traces of the "handed animal" Chirotherium are typical for this time. No skeletal remains of the reptile that caused these tracks have been found so far - or to be more precise, there were no vertebrate fossils found that can be clearly assigned to the tracks by pure evidence, e. g. when the dead reptile would be found directly at the end of it's own trackway. So the reconstruction of the animal is highly speculative, based on the distance between the tracks and the depth of the imprints, which led to a reconstruction that has a strong resemblance to thecodontians. The famous location Monte San Giorgio (Italy) yielded some entirely preserved thecodontian skeletons that match the assumptions for the Chirotherium anatomy.

The Lower Muschelkalk can also contain traces of terrestric vertebrates in it's marginal tidal flat facies (e. g. in the Netherlands). The most common vertebrate track there is Rhynchosauroides, a five-toed, four-feet trace with large back and small front imprints (that are sometimes not recognizable any more) of different sizes that was caused by lizard-like reptiles. Sometimes one can find so-called "swimming traces" of Rhynchosauroides type. That's the smeared imprint of the back foot that formed when the reptile, swimming in shallow water, pushed itself away from the ground in order to move forward. Burrows of marine organisms are abundant within the sea basin.

While the marine trace fossils Thalassinoides and Rhizocorallium totally dominate the Upper Muschelkalk, the Keuper sediments have on offer a large variety of ichnospecies. This results from the permanent change of sedimentary environments during that time. There are resting and feeding traces (Lockeia, Pelecypodichnus), traces from insects and arthropods left on subaerial sediment surfaces, resting traces from marine brittle stars (Asteriacites) and, quite rarely, tracks from small reptiles (Rhynchosauroides, Chirotherium) and dinosaurs (Atreipus).

Rhizocorallium commune

U-shaped burrow with spreiten between two rock layers. Often has a grain-like texture due to fecal pellets. Crustaceans are believed to be the burrowers.

Upper Muschelkalk, Héming, Lorraine (F)

Planolites isp.

Lower Keuper (Lettenkeuper Hauptsandstein), Ilsfeld

Lockeia isp.

Caused by burrowing shells.

Lower Keuper (Lettenkeuper Hauptsandstein), Ilsfeld

Asteriacites lumbricalis SCHLOTHEIM

Five-armed resting trace of brittle stars. This trace fossil of the Upper Keuper (Rhaetian) can cover entire layer surfaces. This proves for a growing marine influence on the Germanic Basin, finally leading to the heavy transgression that defines the beginning of the Lower Jurassic.

(Section of an approx. 50x50 cm large slab with around 100 Asteriacites individuals)

Upper Keuper (Rhaet Sandstein), Tuebingen

Chirotherium isp.

Bunter, Kielce (PL)

There are also some current marks on the back of the slab that prove for a fluviatile environment.

Rhynchosauroides peabody

Small, five-toed imprints, left by a lizard-like reptile.

Lower Muschelkalk, Winterswejk (NL)

Rhynchosauroides isp.

Small, five-toed imprints, left by a lizard-like reptile.

Middle Keuper (Coburger Bausandstein), Zeil a. Main

Rhynchosauroides isp., swimming trace

Both tracks probably belong to different individuals as they follow different directions.

Middle Keuper (Coburger Bausandstein), Zeil a. Main

Atreipus metzneri

Large three-toed foot imprint of a primitive dinosaur.

Middle Keuper (Coburger Bausandstein), Zeil a. Main

Scale length, if not otherwise stated: 1 cm