Report of the Committee on Paleoecology, 1936-1937; Presented at the Annual Meeting of the Division of Geology and Geography, National Research Council, May 1, 1937 (1937)

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REPORT OF THE CCMMITTSE ON PALEOECOLCGY ' :. • -. Introduction - , r ' • * n . W. H. .Twenhofei i '••• - All biologists agree that organisms arid the'environments in which they live are so adjusted as to seem to have been especially created each for the other, and before the formulation of the doctrine, of evolu- tion something like this was generally believed. The idea is 'still more or less true but not in the original sense. The doctrine of evolution explains the adjustments as due to gradual selection and elimination and shows.the struggle that organisms must make to keep pace with an ever changing environment, since at about the same time as the presentation of the doctrine it was learned that the "Everlasting hills" and'the "Hills, rock-ribbed and ancient as the sun" are but figments of the imag- ination, that no environment op the,earth's surface remains the same for long, but is constantly in a state of change, and that this has been so since the dawn of recorded geologic history and probably' will continue for aeons into-the far distant future, •, Students of fossil .organisms have been 'mainly interested in mor- phology and classification, and stratigraphers have been mainly inter- ested in the use of organisms for correlation and the building of sequences. Neither branch of geology greatly concerned itself with the conditions under which the fossil organisms had lived and the relations and adapta- tions of the organisms to these conditions. Thus, there are thick tomes with profuse illustrations giving descriptions of fossils and equally- thick tomes describing sequences and presenting correlations. This is not said in depreciation;as these works have been of immense importance., but they state nothing or very little with respect to the conditions under which the organisms lived and the meaning of the sequences of fossils that change in association and in character from bed tovbed. Stratigraphers and paleontologists have more orless generally as- sumed that organisms migrated freely from sea to sea and tha-t within any epicontinental or marginal shelf sea the same organism's^ had -rather general •distribution. It has also been rather generally assumed by some paleon- tologists and stratigraphers that the fossil organisms 'of'afty. given body of water, if not generally distributed during life for some'cause or -other, attained that distribution a,fter death through transportation by waves and currents* Others have tended to assume that fossil organisms are close to, if hot at, the places of life and that there was little transportation after death, Neither of these assumptions can b.e entirely correct. It is doubtless true that from time to time a few organisms may have existed which, Like the ubiquitous dandelion of today, lived nearly everywhere..on.all bottoms of each epicontinental and marginal water, but • • , . , •• f •• <•: :..-!•. •; •

- 2 - It should be remembered that even the dandelion does not live everywhere and that it is not probable that plants and animals with such general adaptations to environments often lived in the past, and that most plants and animals of the past were restricted in distribution just as most plants and animals of the present are. While paleontologists and stratigraphers were thus occupied, eco- logical biologists concerned themselves with qualitative and quantitative adaptations of organisms to their environmental conditions, and produced a wealth of data showing the mutual adjustments of organisms to each "other and how both in kind and quantity each environment contains organisms in adjustment to the places in which they live. The problems of existing environmental impacts are extremely com- plex, and perhaps the feature that is given least concern by ecologists is the possible geologic record that each individual factor and the cont- bined environmental factors leave in the sediments and sedimentary mate- rials upon which the organisms dwell. But this record is all important to paleoecologists, paleontologists, and stratigraphers since upon this record must be based any interpretation of past conditions, as direct observations of rainfall, humidity, temperature of the air, depth and tem- perature of water etc. cannot be made. The records of these various factors are preserved in the textures, structures, and materials of sedi- mentary .rocks and every student of past environments should be primarily a sedimentation!st, or at least versed in the significance of sedimentary processes and informed as to the meaning of sedimentary structures. The significance of ripple mark of the various kinds, the meaning of cross . lamination, mud cracks, etc. should be understood. Unfortunately this is all too frequently not the case. As an example may be cited the otherwise excellent paper by Homer and Groves on the "Environment of the Early Ver- tebrates"1 in which they state that "invertebrates may be numerous during life but their shells are rapidly destroyed by a solution of calcium car- bonate" (p. 807). Unfortunately, solutions of calcium carbonate do not increase solubility for additional calcium carbonate. Again it is stated, "We find puzzling the fact that in the case of the Cleveland shale, for example, remains are found not only of the bones and cartilages of fishes, but also exceedingly delicately preserved muscle fibers and kidney tubules" (p. 808). The "difficulty" seems to be in the absence of the shells of in- vertebrates, but there is no difficulty if the significance of the high organic content of the shales and the presence of pyrite nodules are under- stood. The missing organisms are largely benthonic; those present are planktonic and nektonic. The blackness shows reducing conditions, the pyrite or marcasite the presence of hydrogen sulphide, and both indicate a paucity of oxygen so that benthos could not live on the bottom or in the bottom materials. The plankton and nekton evidently lived in overly- ing waters in the equivalents of the epilimnion and thermocline where oxy- Am. Midland Naturalist, vol. 16 (1935), 805-856.

-3 - •"• gen was plenty. These on death ultimately sank to the bottom where the absence of scavenger organisms made preservation easily possible* In another place it is stated that "Horizontal gradations of sediments and cross-bedding.are generally indicative of deltaic or aeolian conditions" (p, 809), but every student of sediments has known for years that these features are equally, if not better, developed under shallow water marine conditions, and that lateral gradation is found in every deposit made by aqueous or eoli.an transportation and that cross-lamination is developed wherever sediments are transported by traction. Cross-lamination is fully as abundant in shallow water marine deposits as the deposits of any delta. It is also stated that "mud cracks, ripple marks, and rain di-op impressions indicate shallow water exposed at times to the air, but with- out additional criteria may range from tidal flats to lake margins in their origin." (p. 809.) Mud cracks and rain drop impressions develop under the conditions postulated but they probably develop best on the playas of deserts and on the flood plains of rivers, but ripple marks do not indicate exposure to the air at all and they are known to develop on the bottoms of waters hundreds of feet in depth, and it is probable that current ripple mark forms as deep in the ocean as currents exist,, It has been known for many years that these extend to depths of at least 2000 meters. There are other statements in this paper that indicate ignorance of the significance of sedimentary features. Marine biologists and ecologists continue to produce evidence show- ing the importance of the environment. One of the most important contri- butions of recent years has been made by Professor G0 E. MacGinitie in his studies on the distribution of organisms in Elkhorn Slough, a tributary of Monterey Bay, California.l Studies were made of the physical geogra- phy of Elkhorn Slough, the tides therein, bottom materials, plant life, temperatures of the waters, oxygen supply in the waters, salinity, light penetration, pollution from sewage, food supply, etc. These factors form the physical and chemical background of the environmental conditions ex- isting in the Slough to the sum total of all factors of which the animals are adapted. The food chain of the animals dwelling in the Slough was studied and an excellent diagram showing this chain from plants to final decomposition, elimination, or burial is given<• There are also considered the associations, zoning, and density of the bottom and burrowing popu- lation. • .' • ; i. The conditions in the Slough are shown to be rather uniform,, Never- theless, the animals tend to segregate in groups and may be placed in as- sociations in which one animal is predominant,, The activities of this ani- mal regulate to a greater or less extent the activities of the animals associated with it and provide the set of conditions which to some extent determines."what animals may live within the boundaries of the association." The associations are by no means permanent and apparently change within !«, geological Aspects of a California Marine Estuary, Am, Mid. Nat., vol. 16, (1935), 629-765.

-4 - i* " - relatively short periods of time to give place to other associations with another,animal predominant. This is. the condition one finds in the geo- logic column in which beds succeed.each other, with different assemblages of organisms. On the other hand there are associations with no predomi- .nant:animal, for which parallels may also.be found in beds of the geologic column. Among other matters considered are parasitism, commensalism, trophism, .nocturnal activities, migrations from water to land, and geolog- ical indications. Under the last topic it is pointed out that there is considerable movement of bottom materials, and from the age of shells of clams it is shown that in certain places the bottom has remained stable for definite periods of time, OCt :is also shown how erosion of the bottom may lead to removal of fine materials originally deposited around shells, thus leading to concentration to make a layer composed entirely of shells* Attention is called to tracks, trails, fecal pellets and borings,5" , ;. . ; •.. -, •-• . .••-..' '.''•' This article contains a wealth of material of great value to sedi- mentationists, stratigraphers, and paleoecologists and it is particularly important in that it shows the distribution and associations of organisms existing in a body of shallow water not subject to strong waves or tides and, in general, one subjected to rather uniform conditions where varia- tions of distribution are commonly considered not to be present. •'•- . •. j •' i'. r •.•' Another study by a marine biologist is that by W. G. Hewatt . This study was made on the more open waters of Monterey Bay, to which bay Elk- horn Slough noted above is satellitic. The studies were made on the southern margin of Monterey Bay on a transect 108 yards long and 1 yard wide. The animals dwelling on this area were studied in detail. The area studied is rocky and on the whole it is characterized by apparent monotony with respect to most of the physical and chemical factors of the environ- ment. Nevertheless, the studies show that there is a definite zonation in the distribution of the animals dwelling on the area. Among factors governing the zonation it was found that the relative.lengths of the pe- riods of tidal exposure are important; and that the limits of ranges of some of the animals are biological rather than physico-chemical, a fact long ago pointed out by Petersen as being the case in Danish water (See report of this committee for 1935-36.) :. '..:.:-. ... '...-. ••:-.-. 'n.'.'i. •> -. . . '• , ••- Two diagrams of the food cycle or chain are given, one of the ani- mals found on the exposed littoral of Cabrillo Point and the other .on.. protected littoral at the same place ("littoral" is defined as the area between the mean higher high water and the mean lower ;low. water, lines of .spring tides.) The study loses in importance for palepecology and sedi- mentation as there is only the most remote chance that a :coast like the one studied will leave a record in the geologic column, but the study in- dicates that shores upon which sediments are in process of deposition and sediment-covered bottoms in the neritic life zone may also be expected to show zonation, but from other causes among which it. is probable that light, ^-* Ecological. Studies on Selected Marine Intertidal Communities of terey Bay, California, Am. Mid. Nat., vol. 18 (1937), 161-206. .'

-5- pressure, .arid1; circulation have importance. When it is remembered that stratigraphers and sedimentationists as yet have little on which to base a determination of depth of the seas of the past it should be obvi- ous, that the pale oecological characteristics and relations shown by the ^ zoning. of animals should be of great importance once their significance fc< "'has been determined. - :Y- ' "• :' • • ' ' ., ' . .-. 4. ••» . The Danish Biological Station continues to contribute ecological data of great importance as this phase of biology is 'particularly pertin- ent to the objectives of the station in 'its studies of the food for fish. A report published during the past year contains two items bearing on ecology that are of interest. The vegetation in Dyps/f Fjord is arranged in three different communities, designated the 'Chara, RujpjD:i.a, and Zosbera- Fucus. The Chara 'community covers the largest a-rea, the 2ojtera^ucu£ second, and the. RupjJia. third. These. communities are so arranged that the Chara covers something more than the eastern three-fourths, and then in . order westward, the Rupjjja and the Zostera-Fucus. Reasons 'for this dis- tribution are not apparent. i:-. ••• • - '• . '- • - •,. .A second fact of interest, and one that shows the great difficulty ;,',in determining what is .the factor (or the factors) in an environment that 'controls the presence or absence of a species, relates to the little neck .. .Clam JJ^tilus. edulis. The waters and the bpttcasjs of Dyps/f$ Fjord. seem suited to the clam and it should be common 'therei but it has been found only along the western .half of the northern side of the Fjord. The waters over the other parts of tlie Fjord do not seem to be greatly different and there seem.no reasons! .why it should not be gene raliljr, present. The reason for the limited distribution is not known. .-,'",.. . • . i , . . On the other side of the world about the Japanese Islands, S, Nomura and K«. Hatai during the past several years nave given attention to the ecological problems connected with the distribution of organisms in the outlying waters, and they conclude that studies need to be made of the distribution and kinds of organisms in the various aquatic environ- ments and that information is needed as to how far a shell may be moved after death and the places to which it may be carried „ Bearing on the transportation of shells and showing the extent that transported shells may give to an interpretation of such shells from the point of view of ecology, if it is not realized that the shells are trans- ported, is the following: A half pound stone was picked up on the coast of New Zealand on which several individuals of Boltenia Eachjrdermata were 1_• K. Larsen. The distribution of the invertebrates in the Dypsjd Fjord, i.tjheir biology and "their 'importance as Tish'foOdc ..... Rept,' Danish Biol. Sta., vbl. 41 (1936)'. o The geologic significance of the recent Mollusca from the vicinity of Isinomake, Riknjen, Jour0 Geol. Soc. Japan, vol. 43 (1936), 808-813.

growing. The stone had evidently been transported buoyed up by the ascid— ians and to the stalks of these were attached Hydrozoa, Bryozoa, and other marine organisms.^ Other papers by students of marine biology could be cited but the need for such is not apparent. Marine biologists are fully cognizant of the influence of the environment on the distribution of organisms and the modifications that environments produce, and are aware of the fact that this influence applies to both plants and animals from the most complex to the most simple forms. Paleontologists and stratigraphers need to be- come ecologically minded and to fully appreciate that there are no places, unless it is the bottom of the deep sea, that the environment does not differ over very limited areas. The view expressed by one eminent paleon- tologist that the epicontinental seas of the Paleozoic at any particular time were of such uniformity in the physical and chemical factors as to make possible uniform distribution of organisms in kind and perhaps in quantity from shore to shore, should be totally abandoned. The statement, is one that is impossible of occurrence in any shallow body of water.. This report brings the work of the Committee on Paleoecology to an end. Specialists have presented in a previous report consideration of the Paleoecological relations of the Porifera, Arthropoda, Trilobita, Vertebrata, and Paleozoic plants. On following pages there are considered the Brachiopoda, Gastropoda, and Pelecypoda, Cephalopoda, and Protozoa* No consideration has been given to the Echinodermata as no one has been found willing to undertake the task. Little or nothing seems to be known of the environmental conditions controlling distribution of living bryo- zoans, and less seems to be known of the environmental conditions of those of the past. The Coelenterata have been given much consideration in pre- vious publications by Dr. T. Wayland Vaughan and a forthcoming paper by him and Dr. J. A. Wells will explore the field to a greater degree. University of Wisconsin, Madison, Wisconsin. !• C. Chilton, Trans, and Proc., New Zealand Jour., vol. % (1926), . ' 523-524.