ELASMOBRANCH BRAIN ORGANIZATION 183 



learn to recognize potential predators, do they learn to identify and locate 

 seasonally limited resources, and do they learn migratory routes? 



Many birds and mammals exhibit extensive motor skills in the manipula- 

 tion of food. Prolonged learning periods are frequently involved in mastering 

 such skills as the oystercatchers' manipulation of mollusks and rodent and 

 parrot manipulation of fruits and nuts. Considerable learning may be neces- 

 sary for even recognition of food items. Comparable behaviors are unknown 

 in elasmobranchs, but some aspects of feeding strategies appear to be cor- 

 related with brain size. Most squalomorph sharks, for example, have short 

 jaws and feed on prey smaller than themselves by grasping or shearing the 

 prey into smaller pieces. Many advanced galeomorph sharks possess a highly 

 modified jaw apparatus that allows deep, gouge-like bites that are effective in 

 attacks against prey larger than the predator (Moss 1977). Such an adapta- 

 tion allows a predator to attack new prey species, but it also entails new 

 types of risks to the predator. Large brain size in advanced galeomorph 

 sharks could be correlated with increased sensory and motor abilities needed 

 for successfully attacking large prey. It is also possible that learning plays an 

 important role in modifying attack behavior. 



In addition, the most successful large-brained sharks (carcharhinids) occur 

 widely in reef communities, which are also the habitat of the largest-brained 

 teleosts (Bauchot et al. 1977). The reef habitat is the most complex and 

 stratified in the aquatic environment, and there would be selective advantage 

 in predators' learning the complex spatial organization of the reef habitat, 

 and recognizing and pursuing prey that is well-camouflaged or has complex 

 defense mechanisms. 



Our knowledge of chondrichthian biology is insufficient to allow accurate 

 assessment of the neural capacities of these forms. However, the existing in- 

 formation is sufficient to discredit characterization of chondrichthians as 

 creatures of limited behavioral abilities. The great variation in size and com- 

 plexity of their central nervous systems argues strongly for a wide range of 

 neural capabilities. Future studies may well reveal that advanced sharks and 

 batoids possess, many behaviors thought to be characteristic of only birds 

 and mammals. 



Persistent Central Nervous System Problems 



Experimental data on chondrichthian CNS organization have accumulated 

 rapidly in the last 10 years. However, the information is still rudimentary. 

 No detailed quantitative data exist for chimaerids, thus it is impossible to 

 compare them to elasmobranchs. In addition, analysis of their forebrain 

 organization requires experimental data on olfactory and thalamic projec- 

 tions in chimaerids, as well as histochemical studies. It is possible that 

 chimaerid forebrains retain a large number of ancestral characters common 

 to early chondrichthians, but it is also possible that they possess pallial 

 specializations acquired independently. This problem can be solved only by 

 extensive experimental studies. 



