782 EMERY [chap. 28 



(1950), iiont^ contained stones. Support is also given by the fact that the stones 

 are only slightly polished, far less than typical gastroliths of dinosaurs (VVieland, 

 1907). On the other hand, Fleming (1951, 1953) reported finding basalt pebbles, 

 presumably sea-lion gastroliths, on Snares Island off New Zealand about 250 

 km from the closest shallow water or land source of basalt. 



Data are scanty, but porpoises also are known to carry stomach stones. 

 According to Kenneth S. Norris (Marineland of the Pacific, Palos Verdes, 

 California, in litt.) three or four freshly caught porpoises, Tursiops gilli, were 

 found to contain shells and gravel to about 1 cm in diameter. One stomach was 

 so tightly packed with gravel as to be a possible contributing cause of death. 

 During captivity porpoises are observed frequently to pick up and play with 

 stones in the tank, sometimes swallowing them. Stomach stones have not been 

 reported in whales, not even in the sperm whale, which feeds on benthos by 

 plowing its lower jaw through the bottom at water depths as great as 1135 m, 

 in the process sometimes becoming entangled in telegraph cables (Heezen, 1957). 



An interesting method of transportation is provided by sea-otters, which use 

 stones as tools to break up and detach prey (Kenyon, 1959; Limbaugh. 1961). 

 Sea-otters may thus be the only mammals in the natural state other than man to 

 use tools. The animals commonly float on their backs carrying a stone as large as 

 20 cm in diameter on their stomachs. Mussels and other shells are rapped against 

 the stone until broken open. The otter carries its stone during dives, keeping the 

 same one for periods that are unknown but in at least one instance more than 

 eight hours (R. A. Boolootian, University of California at Los Angeles, in litt.). 

 During its foraging the otter may transport a stone as far as 20 km along the 

 shore. 



Another curious form of transportation is as enteroliths, concretionary bodies 

 which grow in the kidneys, gall bladder, lungs, and other organs. They are 

 best known in land mammals, but also occur in fishes and lobsters (Hutton, 

 1942, 1945). Some enteroliths of land mammals reach diameters of 8 cm and 

 most consist of several phosphate minerals; others are composed of various 

 organic salts. Some are probably passed from the system during life by sea 

 mammals as they are by land mammals. 



The sea mammals which most commonly carry stones are those which 

 inhabit shallow water and spend a large part of their lives ashore or on floe ice. 

 Their distribution, like that of kelp, is antipodal (Scheffer, 1958), and probably 

 most of the depositions of stones by these animals is on or close to shore (Fig. 2). 

 Bones of sea mammals are fairly common in strata as old as Miocene, and at 

 least one instance is known of gastroliths associated with fossil seal and walrus 

 bones — on an island off Massachusetts (Woodworth and Wigglesworth, 1934, 

 pp. 19-20). 



5. Fishes 



Many fishes of coral islands are known to bite off coral tips in search of polyps 

 and worms and to graze upon algae growing upon dead coral and other rocks 

 (Wood-Jones, 1912, pp. 164, 664; Emery, 1956, and included references; Gohar 



