Charles Seaborn; Odyssey Productions 



About the size of a golf ball, a Caribbean 

 bryozoan colony, right, attaches itself to 

 the sea floor in waters more than one 

 hundred feet deep. Species closely related 

 to it are abundant in the fossil record and 

 go back at least 100 million years. Below: 

 A living cheilostome bryozoan extends its 

 lophophores, which waft food particles 

 into a few of the colony's many mouths. 



Kjell B. Sandved; Visuals Unlimited 



We identified both fossil and modem spe- 

 cies by tlieir skeletal features, as before, 

 and used these measurements to construct 

 our hypothesis of relationships. 



We then looked at the genetic chem- 

 istry, using Stylopoma from Panama and 

 some from the island of Cura9ao, which 

 are far enough apart (about 600 miles) to 

 contain quite different faunas. According 

 to the genetic tests, only one of the 237 

 colonies we had classified by skeletons 

 was proved to be incorrectly identified. 

 Even more striking, each pair of species 

 we compared showed about the same 

 magnitude of genetic differences, skeletal 

 differences, and the presumed distance of 

 their phylogenetic relationship. 



The excellent agreement among all 

 these different methods and measures of 

 relationship means that skeletal characters 

 hold up as a valid method of defining bry- 

 ozoan species, hi studying those species 

 through millions of years, we can trace the 

 same patterns: relatively abrupt appear- 

 ances, followed by enormous periods of 

 unchanging sameness. Because our results 

 have been consistent across three distantly 

 related genera, our studies support punctu- 

 ated equilibrium as a measurable reality. 

 So far as living and fossil bryozoans can 

 tell us, patterns of punctuation and sta- 

 sis — rather than slow and steady gradual 

 evolution — really do exist in the history of 

 these ancient colonial creatures. 



58 Natural History 6/94 



