KESULTS OF PAL^EONTOLOGICAL EESEARCH 23 



(1) First appearance of life in the lowest (oldest) 

 sedimentary formations. 



The oldest well-preserved fauna (of plants nothing 

 has survived but a few marine algae) is that of the 

 Cambrian system. It occurs in striking abundance 

 and extent. ' The majority of the important groups 

 of invertebrate animals were already clearly differen- 

 tiated/ and the Foraminifera, Sponges, Corals (and 

 Medusae), Brachypods, Snails, Cephalopods, and Arthro- 

 pods were present. These groups were partially again 

 split up into many species and genera : the Trilobites 

 (Crabs) formed fifty genera with 150 species ; the 

 Echinidee occur in three types ; the Cephalopods, the 

 ' highest type of the Mollusc class/ are already repre- 

 sented (Orthoceratidae). The Crabs proper (independ- 

 ently of the Trilobites) form two well-separated groups 

 (Ostracoda and Malacostraca). 1 



On the other hand no remains of Vertebrates have 

 yet been found. 



In the pre-Cambrian formations, which have nearly 

 everywhere experienced great metamorphic changes, 

 fossils are found only now and then. According to 

 the latest investigations undertaken by J. Walther 3 

 on the spot (in California, Scotland, and Norway, the 

 sites of the most important discoveries in pre-Cambrian 

 strata) there have been found, as the most ancient traces 



1 Deperet-Wegner : Die Umbildung der Tierwelt, p. 233. Kayser : 

 Lehrbuch der Geolog. Formationskunde, p. 75. 



2 Ueber AlgcmJcische (=pre-Camb.) Sedimente, Naturw. Rundshau, 1910, 

 p. 158. 



