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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.•; FALEOECOLOGY OF THE PAIEOZOIC GEPHAJJOPODA;- A. K. Miner and W. M. Furnish The host of tetrabranchiate cephalopods that inhabited the Paleo- zoic seas are today represented by only three closely related species, all of which belong in one genus. Nautilus. The habitat of these three - '.'.'• species is very restricted, their habits are not well known, and they represent an archaic type. Therefore, it is not possible to draw general inferences in regard to the paleoecology of the ancient cephalopods from a comparison with their modern relatives. Forms with heavy unornamented coiled shells, like Nautilus. have-••-'•' existed since Early Paleozoic times, and the lithology and faunal charac- teristics of the rocks in which their remains occur as fossils indicate that they lived in a variety of habitats. However, the shells of dead cephalopods, after the fleshy bodies had decayed and dropped out of them, must have drifted widely much as do those of modern Nautilus. That is, all three of the existing nautiloid species live only in the shallow waters about the shores and coral reefs of the South Pacific from the Malay re- gion to the Philippine and Fiji islands; their empty shells, however, drift to such remote places as Japan, Africa, and ttew South Wales. Ob- viously the character of the sediments in which drifting shells finally come to rest can yield no information in regard to the ecology (or paleo- ecology) of the species represented. The local abundance of "Orthoceras" sociale Hall.in the Maquoketa formation at Graf, Iowa, to which Twenhofel (1936) has recently called attention may well be due to a concentration of drifting shells by eddies or currents. The shells of-the goniatites were even lighter in weight than were those of the nautiloids, and pre- sumably therefore they must have drifted very readily—their relatively fragile construction, however, may have kept them from drifting as far as those of the nautiloids. It would seem then that we can not draw re- liable inferences from the associations of isolated fossil cephalopods, and that in only those cases where we find an abundance of adolescent and mature specimens in close association are the lithologic, faunal, and other characteristics of the inclosing rocks likely to give us trustworthy data in regard to the paleoecology of the species represented. There is so much uncertainty as to the affinities of the structures which are believed to be goniatite anaptychi by some paleontologists and crustaceans by others that it is hardly possible at present to discuss them intelligently. However, it should perhaps be noted that Matern (1931) believes that the anaptychi were lost with the bodies soon after the death of the animals that bore them, whereas the empty shells drifted into other regions before settling and therefore are found in different lithologic facies.

-55 - - ,"" • • It is generally recognized that the chances of preservation of a marine shell are indeed small, and our present knowledge is not sufficient to give us a satisfactory understanding of the relationships of fossils and lithology. Since the shells of modern Nautilus, and presumably those of fossil nautiloids and ammonoids, .are composed almost entirely of ara-.'1 gonite their chances of preservation were even less than averagec It is ••' conceivably possible therefore that conditions in the normal habitat of many of ttye ancient, cephalopoda were suc,h as to be almost prohibitive to preservation and that only when shells were washed into an abnormal habi- tat were they preserved... '' '."''•" • ••.•>• i •;..• ::"-j- Insofar as is 'now known, cephalopods, both fossil and recent, are exclusively marine, and the nature_of the rocks in which the fossil forms occur as well as the faunal associations indicate that the vast majority of them lived in shallow water. From a study of the color markings pre~ served on certain fossil nautiloids Foerste (1930) has found additional evidence to support the conclusion that they lived in shallow water. He states that evidently there "is an intimate connection between the pres- ence of color markings on shells and their access to light during the life of the animal. Forbes (1844, 1854) has called attention to the fact that in shallow waters shells present more varied colors and more distinct color designs. At greater depths the colors tend to become uniform over ' the entire surface of the shell, so that color patterns disappear. More- over, at these depths the variety of colors is restricted more and-more to various shades of dull red or of. reddish .brown, Newton (1907) stated that in the Mediterranean only 1 out of 18 shells showed colors below the 100-fathom line; between. 35 and 55 fathoms, 1 out of 3$ and at depths of, only.2 fathoms or less, more than half, From the vividness of the color patterns of the..Carboniferous limestone specimens studied by him, Newton concluded that the Carboniferous limestone was deposited in water less than 50 fathoms -deep. The relatively numerous species of gastropods- with color .^patterns found by JB Brookes Knight in a single horizon of-the Pennsylvanian- division of the Carboniferous, ,in'the vicinity of St. Louis, Missouri,, suggests deposition in an equally shallow sea,. By a similar line of reasoning, it seems probable that the portion of the Alpena lime- stone which retained color markings in a 'species of cephalopod and- also in a species of brachiopod .•. was deposited in relatively shallow waters." Modern nautiloids are confined to the tropics and the 'fact that many of the Paleozoic forms possessed rather brilliant color markings suggests that they also.lived in warm waters. .. Many, of .the Early Paleozoic nautiloids were --large and their shells were heavy. The majority of these forms were straight and circular or broadly elliptical in cross section, "but some of them were subeircular, subtriangular, or even lenticular in cross section. The latter types were., of course adapted for life on the bottom, anci "it has been suggested that the lenticular types, for example, Gon.ioceras and Lambeoceras, were

- 56- mud grovellers. Although the shells that were circular or nearly so in cross section were undoubtedly rolled over by storm waves,, many of them ,--. like the endoceratoids possessed large heavy (secondarily weighted) siphuneles which were ventral in position and therefore served to right and stabilize them* The available information in regard to color markings, hyponbmic sinuses, etc. seems to indicate that the straight cephalopods lived in a horizontal position, and the'view expressed by Jaekel and Clarke that some of them lived vertically attached to the bottom never had many adher- ents and now seems to be entirely rejected (See Teichert, 1933, pp. 196- 197). Most of the large straight heavy-shelled fOi"ms were almost cer- tainly benthonic, and we agree with Ruedemann (1921) that in all proba- bility "the conchs, buoyed up by gas in the air chambers /camerae/, were lightly dragged over the soft mud by the sluggish animals." Judging these forms by their modern relatives we conclude that they could move forward by crawling on their tentacles or backward by jetting water cut of their mantle cavity through a hyponome. Since no trace of a hyponomic sinus is present on the shells of most of the early forms like the endo- ceratoids, it seems probable that at first progression was accomplished chiefly by crawling and that only later in the history of the race was the jet-propulsion method of locomotion perfected. The Silurian strata of the Upper Mississippi Valley contains nu- merous nautiloids, and in many cases they are particularly abundant along the flanks of bioherms. Most of the seventy-five species of cephalopods recently described by Foerste from the Port Byron formation came from the flanks of a single large bioherm. Presumably we should picture these animals as rather inactive or sluggish creatures which spent most of their lives in the shallow waters on the flanks of the bioherms where we find their remains today• However, the large cephalopod fauna described from the near shore facies of the Upper Ordovician of the Northwest probably did not live precisely where we find its remains today. That is, most of the cephalopods described from the Wind River Mountains and the Black Hills, for example, came from what appear to be littoral deposits, and the shells are almost invariably somewhat worn and broken. Presumably the creatures that secreted these shells lived in the shallow waters beyond the littoral zone, and when they died their shells were distri- buted by waves and currents. The large straight forms^ belonging in the general Endoceras and Cyclendoceras, are far more abundant in these littoral deposits then elsewhere in the same formation, indicating again that they flourished rather close to the shore. In his recent study of the actinoceratoids, Teichert (1933, 1935) concluded that some of the known genera must have been almost entirely benthonic as they had large heavy siphuneles, strongly developed inter- cameral deposits, and a distinctly flattened ventral side; some "may have been capable of swimming, but perhaps mainly inclined to a benthonic life;"

and the curved forms, "all of them conspicuously lacking a distinct flat- ness of the ventral side, may -have been mainly swimming;" He continues with the conclusion that the "benthonic forms, however, vteire the more or less persistent ones. The last representation of the 'Actinoceroids is the genus Rayonnoceras in the Mississippian of Oklahoma and the lower Carboniferous of England. It is by far the largest Actinoceroid we know of and at the same time its endosiphuncular and intercameral deposits show such a hypertrophical development, that a benthonic life of that ani- mal can be assumed with certainty*" When color markings are preserved on the breviconic Paleozoic nautiloidss they are as a general rule equally well developed on all sides of the conch, indicating that the shell .was carried more or less vertically rather than horizontally. Therefore forms of this type probably rested on the bottom of the sea like certain gastropods with the aperture of the shell down; of, if the weight of the animal was more than counter- balanced by the buoyancy of the gas in the phragmacone, when the creatures came to rest they may have been suspended in the water head downwards like modern SpirulaV Rapidly expanding conchs form large apertures which facilitate crawling, whereas constricted apertures interfere with the protrusion of the body from the conch and therefore tend to retard crawl- ing. Since many of the breviconic nautiloids possessed rapidly expanding conchs which only at maturity developed constricted apertures, it seems likely that during adolescence these creatures were primarily crawlers, but that as maturity was approached and the number of camerae increased the shell tended to be used more and more as a float and the tentacles were protruded almost exclusively for the purpose of obtaining food and not for locomotion. Hexameroceras and Phragmoceras can be considered as typical examples of this type of development. However, other breviconic forms, like Westonoceras, which had relatively long fusiform conchs were, as Teichert (1935),has recently pointed out, more active swimmers and presumably they were normally oriented with the long axis of the conch more or less'horizontal. In the breviconic nautiloids with greatly re- stricted apertures, typified by Hexameroceras, there is a well developed hyponomic'sinus, and therefore one might conclude that these forms were .not. entirely floaters. However, it is possible that they had lost their ability to swim effectively and that they had retained their hyponome merely as part of their respiratory apparatus. Modern Nautilus and pre- sumably most fossil nautiloids can move vertically by protruding or re- tracting their fleshy bodies and thereby varying the amount of water dis- placed. However, forms with greatly restricted apertures, like the gen- era cited aboVe, apparently had no such provision, and,presumably they were, relatively inactive and were feeble swimmers, '.'" The habits of coiled nautiloids, whether or not they were involute, must have been cdmparable to those of modern Nautilus. Although compara- tively little is known- about the details of ;the life habits of Nautilus,

- 58 - *« : * . • almost certainly representatives of that genus are not particularly good-swimmers.. The weight and general configuration of their shells would be prohibitive' to rapid locomotion. They are belieV-ed to, spend a considerable portion of their time hovering over beds of cj-ustaceans upon which they .feed,. .. r . • :' .''"-'^ •'••••,... • During adolescence the mixochoanitic cephalopods. developed long - slender conchs, which would seem to indicate that.they were crawlers. These conchs were curved longitudinally and therefore it would have been almost impossible for the animals which bore themto have swum backwards ' by .Jet propulsion and controlled the direction of their progression.' '."•"i However, when the animals reached maturity they are believed to have broken off the early stages of the phragmacone and thus removed much of the impediment.to rapid and straight progression. Such truncation how- ever necessitated the development of a few large camerae or gas chambers , .next to the living chamber to serve as buoys, and this will perhaps ac- count for the globular form assumed by the early mixochoanites. Per- fection was not attained however by these early forms for they apparently had two serious handicaps: first, when the animal came to rest its conch must naturally have assumed a vertical position with the aperture down (cf. modern Spirula); and,' second, its globular form must have retarded its passage through the water. The.first of these handicaps was sur- mounted by the development of long, deep dorsal saddles in the, adoral * septa (the ones that were retained after truncation), so that the phrag- macone (buoy) was extended all along the dorsal part of the conch and the weight of the animal1s body was distributed all along the. ventral. The second handicap was overcome by what .superficially appears to be a reversal in evolution in that the conch tended to become long and narrow . .again^ but this time it assumed- a spindle-like or-fusiform shape, which is particularly advantageous for subaqueous progression... > ' "•,.''' The shells of the Paleozoic ammonoids Were relatively light in construction, which seems to be an adaptation for swimming. The septa of these forms were crenulate, ivhich strengthened the shells greatly without the addition of much weight. Strength achieved in this way would allow the creatures to Withstand the varying pressures encountered with changes of depth—it would not,- however, protect them against concussions, and therefore it seems probable that these animals lived in the zones that were relatively free from wave-action. As Schindewolf (1930) has pointed out, there seems to be no good reason to believe that E. Perna was correct when.in 1915 he assumed "fttr evolute Goniatiten eine nekto- planktonische Lebenweise, filr involute eine benthonische." , . '•*'- It should perhaps be noted that almost no Paleozoic cephalopods lost their bilateral symmetry, as did certain of the Mesozoic forms, and therefore presumably none of them became immobile. Uncoiling forms like Lituites probably represent a reversion from swimming to crawling habits. -'• •••,., .... -,' :

- 59 - , .... .;:.W -•...•;;:.-.,:,• ,. < ' •:'• ^'J <•' .'•;. In many cases-we call derive considerable information in regard ,.•• to the paleoecology of 'any "group of organisms f rpm a study of the asso— ; elated faunas* In the ISarly Paleozoic deposits cephaloppds are commonly- found associated with heavy-shelled behthonic animals, indicating that .., the entire:'fauna lived in relatively.'shallow water. F.oerste. (1936) ...:- has*recently stated that where EaViy Paleozoic cephalopods are abundant so are the mobile gastropods but not the sedentaryvbrachiopods, corals, and bryozo'ahsi, However, it has been our observation that in the Upper Or- v : • doviciah:of• n6rthwestern United States the remains of nautiloids, mo-- bile'gastropods, and corals are all very common and all occur together* ,; This association is particularly noticeable in the.near-shore deposits .. like the Lander sandstone member of the Bighorn formation^ and it may. well be that the abundant fauna of this tljin sandstone represents a. . - , heterogeneous mixture of forms which lived near the shore and those. ,}„;. which lived farther out but whose remains washed into the near-shore zones. However, in the Middle Silurian rocks of the .Upper Iflississippi , Valley both cephalopods and corals are common, and as stated above the cephalopoda are most abundant on the flanks.of certain of the biohe-rms where the remains of many types of sedentary animals are to be found , . in quantity. Ruedemann (1934) has noted that nautiloids occur in Silurian graptolite shales in both this country and"England. Also, in certain of the Devonian rocks of Iowa, for example, in the Cedar Valley formation, cephalopods;, brachiopods, corals, etc. occur in close association. Rela- tively recently Troedssdn (1926) has stated that in "several horizons of the' Baltic Orthbceras limestone the bedding plane.s,,are crowded with straight cephalopods thrown toge'ther parallel to each other.. Some- , times they, are even Weathered before embedding. In one,Endoceras from KinnekuHe, now kept in the collections of Stockholms '^idgskola, the . camerae are filled with mud arid the dorsal side weathered. dow$ to a plane surface^ this is overgrown by sessile animals,., among others two .£,,. basal parts of a crinoid, (similar to A.spidocrinus), indicating that the-:.-,., mud filling was consolidated before the last embedding. of the fossil. ... Briefly speaking, a great many observations show that''th'e. Orthocera.s. , . limestone is not only a shallow water deposit' but also that the deposit- ing of the rock ceased at times on account of upheaval'.'„.'.,„' In the v^ f~' ••/ . . • '.•--. Gonioceras Bay limestone ^.of northern Greenland/ most cephalopods are weathered on their dorsal side before embeddingj as is seen, in jtSSHL'-JII" thoceras and Gonioceras hpltedahlj.. The same weathering has' also been , found in the Cape GalhouiT^nbrthern Greenland/ specimens, , for instance, ......"., in Gon'ioceras angulatum. ;In most instances\this weathering cannot be. ,^ definitely stated because the fossils are almost free from rock." .... In America Devoniati goniatites are much less commpn.than .in EurbpeV. and we are not'^riy too familar with the details of many of t;he E)irppean ; ','. occurrences. However, it can be stated that in thei;.thick Deypniaii liine- ..." stones of central United States goniatites are almost.entirely absent, '. . whereas in certain of the shaley rocks of the Appalachian Geosyncline,

- 60 - from New York south to Virginia, they are relatively common. For the most part the prolific ammorioid faunas of the uppermost Devonian of Europe do hot occur in North America. Their absence here may be due . in part to the fact that over much of our. continent the uppermost Devonian is represented by a black shale facies. The Kinderhook gonia- tite faunas of North America, like those of the lower Upper Devonian (zone of Mahticoceras). are, however, surprisingly like those of Europe. ••'-•• " - '. . '.'.";:. ' . •. • • In the Northern Mid-Continent Region the Late Paleozoic gonia- tites occur in association with shallow water deposits which seem to have been formed fairly close to the shore. In some cases these gonia- tites occur in limestone but it is generally argillaceous or arenaceous, and apparently it represents a shallow-water deposit which was fprmed sufficiently Close to the shore that it received a considerable amount of land-derived or terrigenous material. In many places in United States and Mexico, at least, where goniatites are found in carbonaceous marine shales they occur in calcareous concretions, in which they are particularly well preserved. It has been suggested that many shells were deposited along with these concretionary shales, but that only those inside the concretions were preserved. In the Cherokee shales of Henry County, Missouri, John Britts Owen has found that cephalopods (both nautiloids and ammonoids) are abundant in the calcareous concretions which locally occur at several horizons, and that only rarely are good specimens to be found outside the concretions. It seems reasonably certain that the presence of the animals was directly or indirectly re- sponsible for the formation of the concretions. The occurrence of some shells outside the concretions and some concretions in which there are no shells might be taken to indicate that it was the fleshy bodies of the creatures that caused the concretions to form. That is, fossils found outside the concretions would then be regarded as shells which were empty when they were buried, and concretions which ^contain no shells would be explained by assuming that they formed around fleshy bodies which contained no hard-parts. In the Coffeyville formation of Oklahoma the camerae of the cephalopods, which occur in calcareous concretions, are in many cases filled with black viscous petroleum, and amraonoids which contain petroleum have been found in the Union Valley sandstone of Oklahoma. In many places the faunas of Late Paleozoic carbonaceous shales are composed almost entirely of goniatites. It seems probable that in these areas the bottom of the sea in which the containing beds accumu- lated was inhospitable and that therefore only nektonic and pelagic or- ganisms are represented. Of course it is possible that the cephalopods • did not live in these areas but that their empty shells floated into them after the death of the animals which bore them. However, in many of these cases we find numerous adolescent as well as mature shells which would indicate that the forms were indigenous to the areas in which we now find their remains. In the Caney and Wewoka formations of Okla-

. A ~ 61 - homa and in the Sabden shales of.northern England many adolescent and mature goniatites occur in close association and along with them we get an abundant molluscan fauna. In general it can be said that goniatites occur in association with molluscan faunas and Professor Gr Delepine has informed us that the same is true for European occurrences and that there pelecypods are particularly, abundant in gonjatite-bearing beds. Only rarely do goniatites and fusulinids occur in direct association though oolite commonly they are to be:found in the same formation. However, we have studied one small block of limestone from the Permian of Sicily that contains both cephalopods and. fusulinids and Dr. G, A. Doutkevitch has observed the same, association in rare instances in the Permain of the Urals and Central Asia. It seems apparent that in general fusulinids and ammonoids represent distinct facies and that the few exceptions are prob- ably due to specimens being washed into an environment in which normally they did not live. Nautiloids also are rare in Late Paleozoic goniatite faunas and are generally limited to a few ubiquitous types like Metac^oce^ras and Coloceras. The fact that ammonoid and nautiloid faunas generally do not occur together may be explained by assuming that the two types require different ecological conditions or by assuming that the ammonoids are more active than the :nautiloids and either-.ate them or ate the food on which they otherwise would have subsisted. : This lack of general association of the two groups is well emphasized in the Xate Paleozoic of the Mid-Continent Region for in Texas ammonoids are abundant whereas in Nebraska and Wyoming they are almost entirely lacking though nautiloids are fairly common. The fact that nautiloids and not ammonoids were able to thrive in the northern portion of the Mid-Continent Late Paleozoic seas may have been due to a subnormal salinity of those seas* This conclusion would be entirely in harmony with the general belief that nautiloids were always less special- ized and therefore better able to adapt themselves to changing conditions than ammonoids.

-62 - REFERENCES Foerste, Aug. F, 1930. The color patterns of fossil cephalopods and brachiopods, •with notes on gastropods and pelecypods: Univ. Michigan Mas, Pal. Contr., vol. 3, no, 6, pp. 109-150, p1s. 1-5 1936* Silurian Cephalopods of the Port Daniel area on Gaspe Peninsula, in eastern Canada: Denison Univ. Bull., Jour. Sci. Lab., vol. 31, pp. 21-92, p1s. 4-26. Forbes, E. 1844- Report on the Mollusca and Radiata of the Aegean Sea, and on their distribution considered as bearing on geology: Rept, 13th Meeting British Asscc. Adv. Sci,, pp» 120-194' 1854. Note on an indication of depth of primeval seas, afforded by the remains of colour in fossil Testacea: Proc, Roy. Soc. London, vol. 7, pp. 21-23. Kerr, J. Graham* 1931• Notes upon the Dana specimens of Spirula and upon certain problems of cephalopod morphology: The Danish "Dana"- Expeditions 1920-22 in the North Atlantic and the Gulf . of Panama, Oceanographical Reports, No. 8, pp. 1-36, p1s. 1-20. Matern, Hans. 1931. Oberdevonische Anaptychen in situ und fiber die Erhaltung von Chitin-Substanzen: Senckenbergiana, Bd. 13, PP- 160- 167. Newton, R. B. 1907. Relics of coloration in fossil shells: Proc. Malac. Soc. London, vol,. 7, pp. 280-292, p1. 24, Ruedemann, Rudolf. 1921. Observations on the mode of life of primitive cephalopods: Bull. Geol. Soc. Am., vol. 32, pp. 315-320. 1934. Paleozoic plankton of North America: Geol. Soc. Am., Mem. 2, pp, 1-141, p1s. 1-26.

-63 - Schindewolf, 0* H. 1930. Diskussion /of Hermann Schmidt's paper entitled Uber die Bewegungsweise der Schalencephalopoden^ t Pal, Zeitschrc, Bd. 12, p. 208. Schmidt, Hermann. 1930. Wber die Bewegungsweise der Schalencephalopoden: Pal. Zeitschr,, Bd. 12, pp. 194-207. Teichert, Curt. 1933• Der Bau der actinoceroiden Cephalopoden: Palaeontographica, Bd, 78, Abt. A, pp. 111-230, p1s, 8-15. 1935• Structure and phylogeny of actinoceroid cephalopods: Am. Jour. Sci., 5th ser0, vol. 29, pp. 1-23» Troedsson, G. T. 1926. On the Middle and Upper Ordovician faunas of northern Greenland, I, Cephalopods: Mus, Min0 et Geol. Univ0 Copenhague, Comm, pal,, No. 25 /reprinted from Meddelelser om Gr^nland, vol. 71/ , PP. 1-157, p1s. 1-65. Twenhofel, W. H. 1931* Environment in sedimentation and stratigraphy: Bull. Geol. Soc. Am., vol. 42, pp. 407-424. 1936. Organisms and their environment: Nat. Research Council, Division Geol, and Geogi., Rep. Comm. on Paleoecology, 1935-1936, pp. 1-9. State University of Iowa, Iowa City, Iowa,

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