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EBPOHS OF /jnfl! COMMI'Jl'EE ON PAUSOKCOLOG-J ORGANISMS AND 'EffllR ENVIRONMENT By W. H. Twenhofel (University of Wisconsin) Every organism lives where it does because the combined impact of all the environmental conditions permits it to live there. 'JIhe relations thus existing between an organism and its environment constitute that division of biological scionco tormod oculogy. It can not be doubted that environmen- tal or ecologic relations have influenced organisms since their first appear- ance. Past environmental relations are termed paleoecology. Existing eco- logic relations have received considerable study, but tho field is still es- sentially unexplored. Hot a great deal is known of the ecologic relations of past organisms. The matter of ecology is extremely complex and the factors that com- pose the physical and chemical environment are very numerous. Each grade of the temperature range has its influence on the distribution of organisms; likewise light, cloudiness, humidity, moisture, elevation, composition of the medium, character of the substratum, and other factors are equally im- portant. On plants the acidity and alkalinity of the soil have great influ- ence. Certain plants require soils with a low Pfc before they will live; others must have soil of high alkalinity. As plants constitute the fundamen- tal food of animals, the soil characters thus ultimately influence the dis- tribution of animals. In waters temperature, depth, clearness, agitation, character of the bottom and the quality and quantity of the dissolved mater- ials havo largo influence. In addition there are biologic factors which are almost as numerous as there are kinds of organisms. VJith this great number of variables, it follows, of course, that there are hosts of combinations - to each of these within the limits of life some organisms aro adapted. \Vhen tho combinations change, either because of the appearance of a new factor, or the dropping out of one, the consequences aro immediate reactions in the organic associations to meot the new conditions. Ihe ultimate result may be a complete change in the constitution of an organic group. '.Che statement given in the first sentence of this paper should have tho validity of an axiom. Nevertheless, until recently, little attention lras been given to paleoocologic relations by American paleontologists and stratigraphers. Correlations have not boon made between certain formational units because of the eTosonce of conmon species, or because of only a few. 'JSiis inability to correlate did not necessarily prove unlike time relations, as was generally assumed, but just as likely unlike environments. In some instances the percentage basis has been used in the attempt to correlate in bland disregard of tho fact that, if this basis wore usod in correlation of deposits of the present sea-bottom, it could readily be proven that the sediments and associated organisms on two different areas of the sea-bottom, which are known to be of tho same ago, are not of the same ago; a reasoning as fallaceous as that of the algebraic problem by which it can be shown

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- 2 - that 2 is equal to zero. Many occurrences are known vjhere closely adjacent areas of the sea-bottom have almost totally different poptzlations and in some instances these areas are remarkably close together on the present bottom, Viflren two deposits of the geologic column have been found to hold pretty much tho samo organisms it has boon assumed that the two deposits have synchronous time relations.. It is equally, if not more, valid to as- s\ime that the two deposits were laid down in similar environments and may actually be somewhat different in age. Animals of tie sea, like plants on the land, organize themselves into communities of which the individuals are adapted to each other so that each constitutes a definite cog in the economy of the association. The principle of animal communities v/as strongly emphasized in 1914 by Petorsen on tho basis of work-done by him and his associates in Danish waters, the principle applying specifically to the waters about Zealand and in tho Kattegat and Skagerrak. Petersen (1) distinguished at loast eight well-defined animal communities of which each was differentiated from the others by "character- istic animals" belonging to the molluslcs and the echinoderms. Among the physical factors found important by Potersen were the char- acter of the bottom, clearness of the. waters, temperature, salinity, and depth. Some of these factors are not independent^ as for instance, temper- ature to some extent is dependent upon depth. Soma organisms and some an- imal communities seem to be essentially independent of the physical factors of the environment and yet these were not found to have general distribution. The answer was found in the biological factor whereby certain animal commun- ities can not exist in the face of competition of other animal communities and in the illustration given by Petersen it is stated that the Macoma an- imal community is essentially independent of many physical conditions, but, nevertheless, it does not have general distribution over the bottom. Its boundary limits are determined by the competition of the Venus community against the pressure of which the Maooma community must retreat. Vflien the distribution of the animal communities in Danish waters was placed upon a map it was found that these communities form belts more or less parallel to the shore as descent is made from shallow to deep water, thus showing that distance from the shore and depth are two of the fundamental factors con- trolling distribution and that these in turn determine or modify the inten- sities of such other factors as temperature, turbidity, and character of the bottom. It is doubtful if all of the environmental factors that bear on any marine animal community are at all well understood or even known, ifflie fac- •tors are obviously many in addition to the more apparent ones of depth, salinity, temperature, turbidity, and character of the bottom. It seems probable that no one is fully informed relatively to all the environmental factors that impinge upon any marine animal organism. Hre oysters and edi- ble clams may form possible exceptions. IBro same statement may be made rel- atively to the undcmesticatod animals and plants of the land. Slight physical changes are often adequate to totally eliminate growth of plants at a place. Each plant serves as the protector and food supply of PI' 1-62.

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— 3 — othor organisms of which each in turn serves other organisms in a similar ca- pacity. If any plant of a land community is eliminated a long chain of con- sequences is initiated which may ultimately lead to complete transformation of the animal community supported by a plant community into another of quite different personnel. The chain of consequences leads from one organism to another and ultimately to the submicroscopic organisms so that the impact of an initial single elimination may ultimately affect the elimination of every organism in the community. \Vhile this uiay be an exaggerated statement, it is felt that in some way the welfare of every organism in any community is to some degree tied up with that of all other members of the community. Thus, the modification of an animal community may ultimately be caused by some non-appar- ont factor that vitally affected an insignificant member of an adjacent plant community. Eliminate the gooseberry and currant from a region, the \vhite pine blister is at the same time eliminated, and the white pine thrives and it may thus set up a white pine forest with submergence of other forest trees and develop a fauna dependent upon the white pine and its associates.. Many plants can not grow in soils unless these contain certain fungi with which the plants have symbiotic relationships. It seems probable that a somewhat similnr setup exists for every an- imal community, tha« the presence of each member in some way affects every othor member and that the various members of the community exist in the re- lationship they do because a condition of eqrulibrium has been reached with respect to tho biological relationships, the physical characters existing in the n.edium in which they live, and the character of the substratunj'.' This con- dition of equilibrium is one that may easily be disturbed and when such takos place an entirely new setup may be produced. The more important generalizations that may be drawn from the work of Petersen and his associates were assembled by Miss Elles (l) which in summary \vith some modifications are as follows: 1. Certaii: characteristic animal communities exist undor certain phys- ical conditions with the community coextensive with the same physical condi- tions unless restricted by biological factors. 2. Ch^igos in physical conditions aro accompanied by changes in the character and composition of the animal community. 3. The important physical changes correlated with changes in the animal communities are those of temperature, salinity, clearness of water, and depth. Depth seems to bo important chiofly in that it servos as a fr.ctor in control of temperature, light, character of the bottom, and quietness of water. There are few of the physical factors that are not more or less related to changes in othor factors. 4. Certain organisms may be found in more than one community. 5. The characteristic animals .of communities living in waters of (1) Elles, G. L., Evolutionary palaeontology in relation to the Lower Paleo- zoic rocks, Kept. Brit. Ansoc. Adv. Science (1924), pp. 83-107.

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- 4 - different depths are so greatly different that few or none of these animals are conmon to two communities. Peterson distinguished five animal communities in the North Kattegat . in depths ranging from 7 to 50 meters which with depth, character of the bottom and temperature of the water are as follows: Echinocardium community, 7 meters, fine sand. . Bchinocardium-Turritella. 12-19 meters, dark sand with fine detritus. BrissQpsis-Turritella-Echinooardium. 24.5 meters, fine sand, 14°C. Brissopsis-rjarri.tella. 35 meters, gray clay, 13.4°C. Brissopsis-Nucula. 50-52 meters, light clay, 8-6°C. In another section were found these communities: Macoma. 8 meters, pure sand, 18.5°C. Calcarea. 18 meters, light clay and sand, 10.1°C. Modiola-Kchinodem. 18 meters, coarse gravel with sand, clay and pebbles, 10.S°C. The geographical distribution of the various animal communities on the nearly level bottom is: Macoma, on all southern coasts of Denmark and in Baltic. Abrju especially in the belt sea and in tho fiords. Venus. open sandy coasts of the Kattegat and the North Sea. Echinocardium-Filiformis. at intermediate depths in the Kattegat. Brissopsis-Ch.ia.ioi* deepest parts of the Kattegat. Brissopsis-aarsii. deeper parts of the Skagerrak. Amphilepis-pecten, deepest water of the Skagerrak. Haploops, locally in southeastern Kattegat. It is stated that transition stages between the successive communities are doubtless found, but that they seem to be narrow. After organisms are dead, the shells and tests are inorganic sediments and are thus. subject to the fates to which. inorganic sediments uay be sub- jected. If the shells and tests contain gases of any kind or are buoyed up

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— 5 — by other means they may be floated and ultimately sink to the bottom and be- come entombed in sediments of environments to which they are in no way related. Such not infrequently. must have happened to the shells of the ancient ceph- alopoda and protozoans. ffhe very small and very fragile tests with large surface to volume as exemplified by tho ancient graptolites and modern radio- . laria must frequartly have been entombed in places where their owners could not have lived. If the builders of the skeletal structures lived in waters agitated by waves and currents there is strong likelihood that these skeletal structures would be carried to other bottoms less agitated by waves and cur- ronts. 'Bus to some extent might integrate the faunal complex, but it would also carry the shells to environments when the shell builders did not live. '.Chat conditions like those of the present sea-bottom existed over every sea-bottom of the past can hardly be doubted. '.Chat parts of tho an- cient soa-bottoms of unlike physical and chemical characters held-animal com- munities totally different must also have been the case. There should also be ready acceptance that sea-bottoms alike as to depth, temperature, and oth- er physical and. chemical factors, may have had different animal communities because of variations of the biological factors.- Little seems to be loaown of the biologi-cal factors of the existing .marine environments and essential- • ly nothing of those of ancient environments. It is a field that invites re- search. 'Biere needs to be assembled an overwhelmingly convincing array of facts proving that organisms of the past were controlled by the physical and chemical ecological factors and relationships just as it is known that most modern organisms are. 'JMs should be so completely done that strati- graphic problems can not be seen except through the inlet of ecology. As essentially nothing is known of the biological factors in the ancient environ- ments, it follows, of course, that there is little information to assemble and only the future may show what may be done in this field. (Chore also needs to be assembled information showing the extent to which the waves and currents distribute dead shells so that this factor in the distribution of fossil shells may be placed on some basis other than that of surmise. . In a recent study of the Lower Devonian Keefton Beds of New Zealand Allan' (1) has attempted to apply the teachings of Peterson to tho solution of some of the problems of Lower Devonian stratigraphy. Ho has adopted tho principle of animal communities with "characteristic members" as having ap- plication to the marine faunas of tho past as well as to those of the present and he has decided that the "characteristic animals" of the animal communi- ties of the present are represented in the past by the characteristic animals of a fauna. He states "All attempts in the past to delineate Lpwer Devonian provinces have failed to take into consideration the fundamental factor of the physical environment, and its resultant impress upon tho sediments, and upon the contained faunas." He suggests "that facies has been the dominant element in the distribution of the marine faunas of this period. Ihe evi- dence points to a cosmopolitan fauna, which, as today, would vary with such factors as temperature, light, salinity, food conditions and so on".and tint it is "possible to state that the Heefton fauna is most closely related to that of the same age In V/estern Europe not because of geographical .station, (1) Allan, H. S., The fauna of tho Roefton Beds, Geol..Surv. New Zealand, Pal. Bull., no. 14 (1935), pp. 1-72. . . ,

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- 6 - but becauso in both areas the same physical conditions were identical, and that those parts of the cosmopolitan fauna inhabiting those areas being sub- jected to, or stimulated by, a similar set of environmental controls, are therefore closely related in their characteristic fossils." He further states that "the Reefton fauna differs in its charactoristic members from those of the BoJcseveld beds in South Africa not because one area is isolated from the other, but because the environment was dissimilar in the two areas." The above quotations give ?. clear statement of the application of the rela- tionship of paleoecology to the problems of stratigraphy, a relationship to which most stratigraphers have given general acquiescence and almost as fully have generally ignored. In other connections the writer has called attention to the neod for consideration of the environment in connection with sedimentation and stratigraphy and has given illustrations supporting the relationship (1). 'fhere is no need to repeat these illustrations beyond stating that on Anticosti Island, where the entire section can be seen on opposite sides of the island - on tlie north side from 10 to 35 miles nearer the coasts of the Silurian and the Ordovician seas than on the south, the case is clear and the close connection of the organisms contained in the sediments with the environmental conditions as portrayed in the character of the sediments is excellently shown. Limestones on the south side carry one fauna or animal comnunity and equivalent sandstones on the north side have a different fauna or animal community. Something of lilce relations may bo soen in tho Gotland section of the Baltic Sea where there is a close re- lationship between faunas and the sediments in which they are contained. With respect to fauna and lithology, which is pretty much tho same thing as fauna and physical environment, Allan states as c. gonoral conclu- sion that "Apart from certain cosmopolitan groups, the characteristic fossils of tliis age (Lower Erasian, Lower Devonian) differ according to the facies of tue strata containing them. Pour main Lower Emsian communities are recog- nised - viz., the fauna of the Orislranian of Maryland in calcareous strata; the flaspensis-fauna of the Moose Biver sandstone of Maine in arenaceous strata; the antarctious-fauna of South American in argillaceous strata; and the hercyniae-fauna of western Europe in psanmo-pelitic strata. "The chief condition governing the distribution of these Lower Emsian faunas appears to have been the degree of clearness of the water. It is, however, impossible to assess the value of such factors as salinity, temper- ature, and competition." "Where the physical conditions are identical, even in widely separ- ated areas, the characteristic fossils of the same age are identical or closely related." "Certain Lov;er Devonian types appear to have had a wide range of physical stability, and occur in strata of various facies." "These types ....are of groat importance in that they allow correlation from facies to facies." Some of the problems of the New York Devonian stratigraphy have been "'I Twenhofel, W. H., Environment in sedimentation and stratigraphy, Bull. Gaol. Soc. Am., vol. 42 (1931), pp. 407-424.

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- 7 - attacked in recent years on the basis of differing environmental conditions with somewhat surprising results. It has been shov/n tliat some of the Devon- ian units previously considered sequential to other units are lateral there- to. Chadv/icJc (1) states "As, on any sea-coast sector, unlike societies co- exist at different dopths, 30 each faunal assemblage of this uppor Devonian terrene embraces several contemporaneous congeries , straying at times (lat- erally) into each others door-yards, .and all holding the same definite time value."• Cooper (2) has shown that the Devonian Hamilton of western New York changes lithology when traced eastward from blade shales in the west to ul- timately pass into red beds, largely sandstones, formerly assigned to the Catsid.ll. 'J5ie change in lithology is accompanied by a very great increase in thickness. YJith the changes in lithology, that is, expressions of the changes in the environment, there are corresponding faunal changes, Chad- wicl: (5), in addition, states that the Cheinung instead of being above the Portage is really a part of it and that in proceeding northwestward from southeastern New York one passes from the continental sand facies of "Pocono" lithology into the red muds and sands of the Catslrill. [Chase lose the red color in the presence of much organic matter and become the Chemung with a marine fauna of brachiopods. Passing into the region farther northwestward v/here the conditions of deposition were those of deeper water the Chomuug changes into the fine muds of the Naples with a molluscan fauna of fossil shells. Farther northwestward this passes into the black shales of the Geneseo. Caster (4) (after Clarke) has shown that the Maples shale fauna of the Genesoe Valley is the equivalent of the lighter colored shale fauna of the Itliaca region (Ithaca shale) and that into this there is inserted in the Chenango Valley the tongue of sandstone containing .the Oneonta fauaa. • . It is suspected that when the application of paleoecology to the other parts of the New York section and also other Appalachian region sections has been fully made that many of the various troughs and barriers so much in vogue in the later decades of the nineteenth century and the first two dec- ades of this century will vanish into the discard and in their place will come explanations based on pr-leoecology. It is also thought that there will be some modifications of the sections of the Cincinnati Arch and the Nash- ville Dome when application of paleoecolocy has been made to interpretation of those strata and it is suggested that it may ultimately be shown that some units now placed in sequence to others wi 11 be found to bo lateral there- to. Other places where paleoecolooy should be given serious consideration (1) Chadvick, G. H,, Faunal difforentiation in tho Uppor Devonian, Full. Geoi. Soc. Am., vol. 46 (1935), p. 507. (2) Cooper, G. A., Stratigraphy of the Hamilton Group of Hew York, Am, Jour. Sci., vol. 19 (1950) pp. 116-134, 214-236; Stratigraphy of the Hamilton Group of eastern New York. Ibid., vol. 26 (1933), pp. 557-551. (3) Chadwick, G. H., Chemung is Portage, Bull. Geol. Soc. Am., vol. 46 (1935), pp. 345-554. U) Caster, K. E., Guide Book, no. 4, XVIth Intern. Geol. Cong. -(1932), p. 46.'

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- 8 - is about the Wisconsin Arch, the Ozarlc Dome, the Central Mineral Region of Texas, the Arbuckle Region, and in any other region where it seems obvious that different conditions of environment were probable. The work of Philip King and the petroleum geologists (1) in unravel- ing the geology of the Permian strata of southv;est Texas has shown that salt, gypsum, dolomite, shale and sandstone are lateral to each other and were all deposited in the Permian sea at the same time, each representing a different environment of deposition. "The faunal assemblage varies from one rock type to another." "Each faunal aggregate appears to have been adapted to a limited environment, the influence of which is also expressed by the nature of the rock laid down at the time" (P. B. King). There are deposits of lagoons, the confining barriers, the open sea and the coastal plain, the range being from continental deposits to deposits more or less typically marine. There is much to be learned and hardly a beginning has been made. The ancient methods and doctrines of stratigraphy are so deeply ingrained that one almost instinctively tends to correlation by comparison of fossils with little or no attempt to see what the fossils really mean and what may have been- the relations on the ancient sea-bottom. Deposits have boen iden- tified as estuarine, la-joonal, or of some other environment with littlo ap- preciation if such were the case that there must have been marginal de- posits of another environment. Lately, Poerste (2) lias statod that in the Paleozoic strata "as far as present observations pormit it appears that wherever cephalopods are abundant the mobile gastropods also are relative- ly comnon, while the sedentary brachiopods, corals, and bryozoans are less common than elsewhere. On the contrary, where the bracliiopods, corals, and bryozoans are common, cephalopods usually are rare." "Possibly segregation is due occasionally to violent storms result- ing in strong ocean currents which sweep along the mobile forms into areas whore sedentary life is less abundant, overwhelming these mobile forms with muddy and arenaceous deposits. This might account for local segrega- tions of cephalopods and gastropods, but would not account for their rel- ative absence over large aroas." It is suggested by the writer that there may have been some competitive biological relationship whereby the presence of the mobile foras is connected with the absence of the sedentary forms. At Graf, Iowa, in a rather well-known section of the Maquoketa, there are s. half dozen feet of impure limestono in the middle of the section that are literally jammed with Orthoceras socialis. but this is the only place in the upper Mississippi Valley known to the writer where this species is abundant. It is rare elsewhere. Almost no other organisms are present. (1) King, P. B., and King, R. E., The Ponnsylvanian and Permian stratigraphy of the Glass Mountains, Univ. Texas Bull., 2801 (1918), p. 139; Lloyd, E.H., Capitan limestone and associated formations, Bull. Am. Assoc. Petroleum Geol., vol. 13 (1929), pp. 645-65?; King, P.B., Permian stratigraphy Of of trans-Pocos, Texas, Bull.Geol.Soc.Am.,vol. 45 (1934), pp. 720-723. (2) Foerste, A. P., Silurian cephalopods of the Port Daniel Area on Gaspe' Pen- iusula, in eastern Canada, Bull. Denison Univ., vol. 31 (1936), p. 26.

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- 9 - is the meaning? The abundance or rarity caii only be ascribed to the paleoecologic relations of the time. foregoing is intended to be a brief introduction to this report of the Committee on Paleoecology» It is hoped that each great group of or- ganisms may be considered in detail. In the articles that follov; there are considered the paleoecology of the vertebrates by E, C. Case of the University of Michigan; the arthropods by P. E. Raymond of Harvard University, with an appendix on the habits of the trilobites by \7. E. Schevill; the sponges by M, Y/. de Laubenfels of Pasadena Junior College of Pasadena, California; and the paleoecology of the Paleozoic plants by C. A. Arnold of the University of Michigan. It is hoped that the palooecology of the other great groups may bo considered in a later report. .