48 THE OCEAN RIVER 



extends a flower-like rosette of brilliantly colored arms. These 

 bizarre creatures, the most colorful features of the shallow 

 waters of Paleozoic seas, were so plentiful that the limy joints 

 of their stalks form almost the entire mass of some of the lime- 

 stone rocks laid down in the continental seas over 200 million 

 years ago. Today the stalked sea lilies are rarely found in shal- 

 low water, though there are large groves of them off the north 

 coast of Cuba and they have been dredged from deep waters 

 in many parts of the ocean. 



There would have been no rise and fall of nations on the 

 River's banks and no early explorations to tell of unless, very 

 early in the story of the sediments, a small worm-like creature 

 had not embarked on a path of evolution which was to revolu- 

 tionize the living world by making possible the later appearance 

 of all the higher animals, including man himself. Nobody can 

 be certain how this began. Some have imagined that the verte- 

 brates originated from the horseshoe crabs and the sea scor- 

 pions, the eurypterids. Others believe that the start was made 

 among worms similar to the sea worms or the ribbon worms 

 of the present day, and there is some evidence to support these 

 beliefs. There has even been a curious and fanciful suggestion 

 that insects could readily have evolved into vertebrates if they 

 had turned upside down and their legs had become ribs. Today 

 a much more likely theory is accepted. 



We can at least be fairly certain that the remote vertebrate 

 ancestor began its long path of change and development very 

 early in the history of the sea floor, at a time when most of 

 the present-day invertebrates were only beginning to leave their 

 traces in the sediments. This soft-bodied, wormlike forebear 

 was perhaps related to the bilaterally symmetrical ancestor of 

 the now five-rayed sea cucumbers, sea stars, and sea lilies. 

 When a nonbony stiffening rod began to form along the length 

 of the body and so provided a rigid basis of attachment for 

 muscles, the scaffolding of the vertebrate backbone was laid; 



