92 HISTORY OF THE OCEANS 



archecyatheans as may have existed. On the whole the known 

 fauna gives the impression of an assemblage that could have got 

 on well without skeletons. In the absence of predation it is probable 

 that a heavy skeleton denser than sea water would always be an 

 encumbrance to a marine animal. Cloud's (1948) view that skele- 

 tons are needed for muscle attachment has obvious merit, but the 

 heavy type of skeleton that fossilizes well must go far beyond 

 such needs, as is evident from the existence of an animal such as 

 Marella, with as complex a set of appendages as a trilobite, but 

 with a skeleton only fossilized under the exceptional circumstances 

 of deposition of the Burgess Shale. 



It is therefore difficult to avoid the conclusion that the rise of 

 fossilizable skeletons implies the rise of predation, and that this 

 affected animals of many different sizes at about the same time. 



Since we find no evidence of powerful predators among the 

 known lower Cambrian fossils, we only can assume that the 

 predators did not fossilize. The most reasonable hypothesis as to 

 their nature, implied rather vaguely by Raymond, would be to 

 suppose the presence of protonautiloids perhaps with feeble 

 conchiolin shells but quite powerful schleroprotein or horny jaws, 

 cruising about just over the bottom. Some of the contemporaneous 

 polychaetes would also probably have had well-developed jaws. 

 What we know about the existence of nautiloids and polychaetes 

 in the earlier part of the Phanerozoic record would practically 

 compel us to assume their existence in an unfossilizable form in 

 the lower Cambrian; the only really hypothetical part of the 

 hypothesis is the postulation of jaws. 



Current biological knowledge would therefore appear to be con- 

 sistent with the existence of a relatively modern type of ocean 

 well before the Cambrian, with no inevitable geochemical break 

 at the opening of the fossil record. The events supposed to bear 

 witness to such a break can be much better explained on biological 

 grounds. 



Much further back the facts that I have reviewed earlier would 

 not be inconsistent with the emergence of the earliest complete 

 organisms in quite shallow pools, wet rocks, or damp sediments on 

 the growing continents, under conditions of low and variable 



