PALEOBIOOKOGRAPHY OF THE MARINE REALM 177 



Samples and Problems from Marine Paleobiogeographic Record 



In the immense ranges of geologic time it is inevitable not only 

 that a great range of individual paleobiogeographic patterns should 

 occur but also that certain broadly overriding combinations will 

 repeat themselves. The most familiar of these overriding patterns 

 to the marine paleobiogeographer are the Tethyan and Antarctic 

 transport routes and the Panamanian and Gondwana barriers 

 (or filters). 



By way of illustrating both that reasonable biogeographic 

 interpretations can be made over a wide range of past time and 

 that great problems remain unsolved, a few lines will now be 

 devoted to these and other reconstructions from different parts of 

 the geologic record. 



Early Cambrian Biotal Provinces 



Near the dawn of recognized metazoan life, in the opening 

 scenes of the Paleozoic era, an expansive paleobiogeographic realm 

 is represented by the broad-headed olenellid trilobites (Order 

 Redlichiida) of Early Cambrian and earliest Middle Cambrian age, 

 with three provinces defined by distinctive genera or generic 

 groups. Figure 8 illustrates the known global distribution of these 

 provinces, compiled by the Termiers from the labors of generations 

 of Cambrian specialists. Although the distinctive "genera" are 

 now sometimes finely subdivided, and are not strictly contem- 

 poraneous (Opik, 1958), their paleobiogeographic distinction is a 

 fact. In a general way Olenelliis represents a North American 

 province, Redlichia a combined Tethyan and Cathaysian province, 

 and Holmia a North Eurasiatic province. The generic names are 

 simply by-names for the larger faunal (mainly trilobitan) assem- 

 blages they characterize, like Petersen's communities and 

 d'Orbigny's zones. These assemblages are primarily associated 

 with argillaceous detrital deposits near the continental margins of 

 their time; and, as for the olenellids themselves, their broad, flat 

 shapes, their inability to enroll in adult stages, and the tracks 

 they have left in the sediments suggest that they were members of 

 a mud-grubbing benthonic fauna whose early broad differentiation 

 into endemic genera and faunal provinces reflects the gradual 



