94 



the prevalent habitat for the major portion of the shoreline of the Gulf 

 of California. 



The rocky shore assemblage is entirely an epifaunal one, dominated by 

 algae (or diatom film) and suspension feeders, plus a number of inverte- 

 brates which prey upon the others. Since a rock bottom is not conducive 

 to the accumulation of detritus (except under the rocks), deposit feeders 

 are virtually absent. Savilov (1961), in a similar study of feeding types 

 in the Okhotsk Sea, states that sessile suspension feeders dominate the 

 rocky shores. The majority of the gastropods are adapted to living in a 

 rigorous environment, and nearly all of the lamellibranchs possess byssal 

 threads by which they attach themselves firmly to the rocks. Some of the 

 forms are thought to have a rather long planktonic development, per- 

 mitting a wide dispersal over long stretches of coast line while many of 

 the prosobranchs develope from egg capsules, which guarantee that they 

 will be retained on the rocks and not swept into an unfavorable environ- 

 ment (Thorson, oral communication). According to Thorson (personal 

 communication), many of the larvae of intertidal invertebrates also exhibit 

 strong negative and positive phototropisms, which would facilitate settle- 

 ment at the proper time during the tidal cycle, so as not to be swept off 

 their selected place of attachement during early stages of settling. There is 

 little doubt that the feeding habits and types of reproduction of the 

 major components of this epifaunal community are similar on all rocky 

 shores throughout the world. Many of the same characteristic genera 

 {Littorina, Ostrea, Mytilus, Fissurella, Balanus and Bugula) occur nearly 

 everywhere, although tropical shores are often characterized by many 

 more genera and species and fewer individuals of each than temperate or 

 boreal regions. The environmental factors exerting the most influence upon 

 this assemblage are certainly rocky substratum, great turbulence, extreme 

 range of water temperature, high oxygen and normal oceanic salinities. 



Most of the fossil assemblages studied in the Baja California region and 

 in the Gulf of California are of Pliocene to Pleistocene age. All of them are 

 composed of a mixture of intertidal rocky shore and nearshore shelf 

 assemblages. Discussions of these deposits can be found in Hertlein and 

 Emerson (1959), Emerson (1956 and 1960a), and Addicott and Emerson 

 (1959). Only two recent papers describe fossil assemblages from the Gulf 

 of California proper, one by Emerson (1960a) on the Pleistocene inverte- 

 brates of Ceralvo Island, and the other by Hertlein and Emerson (1959) 

 on the Pleistocene fauna of the Tres Marias Islands. An earlier review of 

 the paleontology of the Gulf of California can be found in Durham (1950). 

 Of the 34 species of invertebrate fossils from Ceralvo Island listed by 



