What can be concluded from these tidal flat observations concerning the 

 interpretation and exploration of fossil trails and burrows? Too many animals 

 in their activity produce such similar traces that a morphologic distinction be- 

 comes impossible. On the other hand as shown by the amphipod Corophium one 

 animal is able to make such different trails that nobody would interpret them, 

 found in fossil state, in a correct manner and ascribe them to the single pro- 

 ducer. Therefore it is very difficult and mostly impossible to determine the 

 producer of a trace -fossil with certainty. The forms of the trails depend not 

 only on the special activity of the animal but also on the sediment, its charac- 

 ter and state. There may be little chance for these surface trails to be preser- 

 ved for the future and to become fossil, but we know such transient markings 

 as ripplemarks well preserved after many years in eroded tidal flats. 



The study of recent trails of animals in the tidal flats has given some 

 help in erecting a "system" of all trace -fossils as proposed some years ago 

 by the German paleontologist A. Seilacher. Such a classification cannot be 

 founded on morphological features nor can it be based on the zoological system 

 as shown above. It seems only possible to distinguish trails and burrows ac- 

 cording to their ecological value and to elaborate common features of trails 

 produced under the same ecological conditions. Such results of neo-ichnolog- 

 ical studies which are to be extended to other marine and non-marine biotopes 

 will help to evaluate trace -fossils better than it is now possible. They will 

 probably also give some assistance to paleogeographical investigations. Ac- 

 cording to biocoenoses "ichnocoenoses" could already be distinguished in some 

 ancient formations, but such explorations are still "in statu nascendi". It is 

 also to be hoped that new methods and techniques in sedimentology will be de- 

 veloped in order to detect recent trails made within the sediment which are 

 also of greatest interest and importance for the paleontologist. 



DISCUSSION 



Vallentyne: I was wondering about the presence of these tracks in pre -Cam- 



brian sediments. Do they occur there? 



Hantzschel: In pre -Cambrian sediments trace -fossils are only rarely to be 

 found. There is an interesting newer investigation by A. 

 Seilacher (Der Beginn des Kambriums als biologische Wende. 

 Neues Jahrb. Geol. Palaont. Abh. , 103, pp. 155-180, 

 Stuttgart 1956); he collected and compared trails and burrows of 

 the pre -Cambrian and of the Cambrian sediments of the Grand 

 Canyon, Arizona. He showed that only very few and uncharac- 

 teristic forms of ichnofossils are to be found in the Precambrium, 

 while Cambrian sediments (also in Scandinavia and Pakistan) con- 

 tain much more and more differentiated forms of trails and bur- 

 rows. 



Oppenheimer: Do you know if any animal at all secretes any substance which 



allows the sand to become more permanently impressed because 



1Z9 



