# The Habitat of the Eurypterida/Chapter II

CHAPTER II
A Résumé of the Opinions on the Habitat of the Eurypterida
From 1818 when the first Eurypterus was discovered in America by Dr. S. L. Mitchell until 1900, the order of the Eurypterida was held to be made up of marine organisms. This belief in the marine habitat of the oldest Arthropoda known suddenly became the centre of contention at the beginning of the present century in spite of its long period of security. As soon as geologists considered the possibility of origins other than marine for conglomerates, shales and even limestones, there arose discussion as to the nature of the beds in which eurypterids had been found and opinions were perceived to be divergent. It is of interest, then, to take up a systematic review of the literature for the last hundred years and to note what has been the general opinion of geologists and palaeontologists about the ​bionomy of the eurypterids, and to note also the change from an unquestioning assumption that the habitat was marine, to doubt and finally to opposition to the old idea.
Mitchell considered the form which he found in Westmoreland, New York, to be the impression of a catfish and so placed it under the genus Silurus, noting that the nearest living relative was the electrical silure of the Nile (180). He had no idea of the great age of the fossil, but supposed it to have been the remains of a fish which had lived in the Mohawk which was then generally believed to have been dammed so that the river waters and their fauna spread over a wide area. It is curious to see that the first man to find a eurypterid should, without any clear idea of its age or its true nature, have supposed that it lived in a river. This was mere speculation on his part and of no real significance. In 1825, however, Dekay, recognizing its true relation to the arthropods, established a new genus, Eurypterus, for it. He considered it most nearly related to the genera Apus, Binoculus and Lepidurus among modern forms, and placed it with the crustaceans of the order Branchiopoda. He mentions no other fofssil associates, nor does he make any statement concerning the habitat, but he evidently considered it marine, for had he not, it is only natural to suppose that he would have made some statement to that effect, since it would have been a new and, indeed, a startling idea to advance. In 1841 Conrad, writing of the Eurypterus from the Bertie says (44, 38): "It has been suggested that this genus was of fresh water origin, but the presence of fucoids in the same stratum where the Eurypterus occurs, and the absence of the slightest evidence of a fresh water deposit in any part of the Silurian system, leave no room to doubt that this singular crustacean inhabited the sea." Conrad did not state who the bold spirit was that made such an original suggestion and his reasons for rejecting this explanation are unconvincing, because so-called fucoids are not necessarily marine, and non-marine deposits are now extensively known from the Siluric. Furthermore, even if the "fucoids" prove to be graptolites, as now claimed by Ruedemann, a non-marine habitat for the Eurypterus is not precluded. All the early writers seem to have agreed to consign the eurypterids to the class of the Crustacea, and to maintain for them a marine habitat. It has taken many years of patient labor for the students of the anatomy of these organisms and of the taxonomic relations of the Eurypterida to the Crustacea, to Limulus and to the scorpions, to convince the geological world that the Eurypterida are ​not Crustacea, but belong to the class Arachnida. The work has only just begun of convincing that same geological world that the habitat never was marine, but always fluviatile.
For nearly fifty years after Conrad made his statement authors described new species, erected new genera and worked out the affinities of the eurypterids to Limulus, but they gave not a thought to the habitat. It was not until 1889 that a direct reference was again made to the habitat. In Nicholson and Lydekker's Manual of Paleontology (196) we find the statement that "the nature of the deposits in which the remains of the Eurypterids are found, and of the fossils associated with them, would prove that these animals were essentially marine, their habits, probably being very similar to those of the existing King-crabs. It is, however, possible that certain of the Eurypterids were inhabitants of brackish or even of purely fresh waters" (196, 544).
In 1893, Malcolm Laurie, studying the eurypterid remains in the "Upper Silurian" of Scotland, i.e. the Siluric as generally used in America, found in those rocks of the Pentland Hills only one other fossil, Dictyocaris ramsayi, a crustacean (?) (144). The large eyes in most of the eurypterids which he found caused him to think that they must in some way be due to the conditions under which the creatures lived, and from a comparison with recent forms he was led to believe that the eurypterids lived in deep water, whether marine or not he does not say, but the former seems to be implied.
Amadeus W. Grabau writing in 1898 of the eurypterids said: "these crustacea were undoubtedly marine" (81, 362) thus accepting the usual classification and also the current opinion as to the habitat. On the other hand, Frech (70) at about the same time, said that the most evident proof of the retreat of the sea in the formation of the Old Red sandstone in England was the appearance in the Devonic of the eurypterids from the Baltic. This marks the beginning of the change in ideas and embodies the first statement contrary to the prevailing opinion that the habitat of the eurypterids was marine.
The period during which it was either tacitly assumed or definitely stated that these extinct merostomes had lived in the sea was thus brought to a close. There had been a few hints of a possible non-marine existence, but on the whole geologists and palaeontologists had for eighty years been agreed upon the marine habitat.
With the beginning of the new century we find a radical and sudden change of opinion. Chamberlin in his paper on "The Habitat ​of the Early Vertebrates" gives a philosophical discussion of the question which is extremely interesting and suggestive, though not backed up by much data. He calls attention to the fact that eurypterids and fishes are found associated in the Ludlow (Upper Siluric) of England, in the Island of Oesel in the Russian Baltic, in Podolia, Russia, in Galicia, and in the Waterlime group of North America. "The physical conditions in all these cases seem to have been peculiar," he continues, "and in the case of the Waterlime group they were singularly so, for they permitted a host of these large Eurypterids and other Crustaceans to flourish in seeming luxuriance, while only a meagre and pauperate marine fauna found an occasional entrance into the series. The conditions seem to have been congenial to the fish and Eurypterids, but not to a typical marine fauna" (32, 401, 402). The association of eurypterids and fishes in the Old Red sandstone where marine life was only occasional and meagre does not, as Chamberlin points out, imply prevalent marine conditions, for the Old Red and its homologues are the deposits of fresh water, and yet both the fishes and eurypterids found congenial conditions of life there. Chamberlin, recalling that fishes and eurypterids are found both earlier and later than the Devonic in marine deposits, puts the following question: "Were the fishes and eurypterids primarily marine and later became adapted to fresh water, or were they primarily fresh water forms which were occasionally carried out to sea and which later became adapted to salt water?" He reminds us that we are always in the habit of considering all life at first marine, then terrestrial, but, though this is true in general, the idea should not be held to with too great tenacity in every case. That the eurypterids may well furnish an example of an exceptional case is shown by various lines of evidence which Chamberlin cites. First, of the dozen genera of eurypterids known in 1900 only two or three of the least well known are without associations with formations regarded as fresh water; secondly, he says: "The relics found in marine sediments may be attributed to transportation from the land just as is one in the case of terrestrial plants and land insects not infrequently found in marine beds; but transportation in the opposite direction cannot be assigned" (32). One may, however, take exception to this last statement, for many marine forms migrate up rivers in the spawning season, as for instance, the crabs which go up the Hudson as far as Albany; and there are many marine molluscs which become adapted to conditions in rivers and may even in time migrate ​to the land. Chamberlin says further that the eurypterids are found in abundance in fresh-water deposits with only a few trails of annelids suggesting marine conditions; they are assumed, therefore, to have been marine first and then fresh water, but in this case also why may we not consider that these forms were carried out to sea, rather than that they lived in marine water?
In direct opposition to this line of argument, Zittel in his Grundzüge der Palæontologie (327, 527) offers the following: "The Eurypterida are found associated with Graptolites, Cephalopods, and Trilobites in the Ordovician of Bohemia and North America; with marine Crustacea (Phyllocarids and Ostracods) in the Silurian; with Ostracoderms and Arthrodires in the Devonian; and with land plants, scorpions, insects, fishes, and fresh-water amphibians in the productive Coal Measures. It is apparent, therefore, that from being originally marine forms, they became gradually adapted to brackish, and possibly even to fresh water conditions."
Clifton J. Sarle in 1898 discovered a new eurypterid fauna at the base of the Salina, Middle Siluric, of western New York (240). This formation had hitherto been considered particularly barren of fossils, but Sarle found in two layers of the Pittsford black shales such an abundance of eurypterids that some layers were "literally packed" with their remains. The two shale beds are intercalated between dolomite layers which, Sarle remarks, represented more open water and were apparently unfavorable to the eurypterids. The occupation of the black shales by these animals "was apparently of comparatively short duration, merely an incursion, as it were, since the black shale all told does not exceed 2 feet in thickness. The fact that the eurypterids are often dismembered and their parts distributed over considerable areas, and that a dozen or more are frequently found side by side . . . . suggests that they may have been drifted up by a current. On the other hand, the fine preservation of much of the material, extending even to the delicate appendages, shows that the currents were very weak, thus practically leaving the animals in the position of death or molting" (240, 1086).
A. W. Grabau in his Physical and Faunal Evolution of North America during Ordovicic, Siluric, and Early Devonic Time (1909) makes the facts of distribution an argument in favor of a fluviatile habitat, thus calling attention to one of the most important aspects ​of the problem. "The Eurypterid fauna also occurs in the mud layers in the Shawangunk conglomerate, which hardly admits of any other interpretation than deposition by torrential rivers. This would make the Eurypterid fauna a fresh-water fauna, an interpretation which best corresponds with the distribution of these fossils geologically as well as geographically. The Salina series is best understood as a desert deposit. The absence of organic remains (with the exceptions noted), known to be abundant in all modern salt deposits of sea-margin origin; the thickness of the salt beds; their limitation to circumscribed basins, the red color of the lower shales, their mudcracks, all point to a continental origin" (84, 245). Clarke in reference to this fauna says: "Our present knowledge of the habits of the merostome crustaceans derived both from the living and fossil forms, indicates the shallow water or barachois origin of all sediments in which these remains abound" (36, 302). He does not, however, accept Grabau's interpretation of a torrential origin for the Shawangunk deposits, but thinks rather that they were formed in an Appalachian Gulf cut off from the ocean on the east by the Shawangunk Mountains, the material being swept down from the land and forming a delta deposit, the terrestrial waters preventing a highly saline condition in the gulf. The eurypterids, according to this view, were marine, forms caught in a gulf of not too great salinity.
In the second volume of Chamberlin and Salisbury's Geology published in 1907, the eurypterid problem is again taken up as follows: "These giants among their kind seem clearly to have been aquatic forms, but whether they were primarily marine or fresh-water habitants is not so obvious. They are wholly extinct, and their habitat can only be inferred from their associations. Some crustacean fragments that seem to belong to the same sub-class as the eurypterids (Merostomata) have been found by Walcott in Pre-Cambrian beds, but their associates are too few to throw much light on this question, though they favor a marine habitat." (Walcott considers that they favor non-marine conditions.) "A very few eurypterids appear in the Ordovician, where they are associated with marine invertebrates. In the Waterlime beds they are associated with ceratiocarids and ostracods which are usually marine, and very rarely, with certain brachiopods which are marine. In the transition beds of England, Sweden, and Russia, the eurypterids are associated more freely with marine forms, but they are also associated with the seeds of land plants and with fish which in the succeeding stage, seem to have ​occupied land waters chiefly. In the Devonian and Carboniferous periods, in which the eurypterids reached their climax and passed into their decline, and where they seem to have been in their more natural relations, they are associated with land plants, scorpions, insects, fishes, and fresh-water amphibians, which seem to imply a fresh-water habitat. In the light of these facts, the more common inference has been that they were originally marine forms, and became adapted later to brackish and fresh-water conditions. The alternative inference is that they were originally denizens of the land waters, and that their remains were occasionally and sometimes quite freely carried out to sea by stream waters, and were thus fossilized with marine forms. Their occasional presence in the earlier periods is thus explained, while their seemingly sudden appearance in abundance and in gigantic forms in the closing Silurian, and their prominence in the land-water deposits of the Devonian and Carboniferous finds ready explanation in the fact that these are the first well-preserved fossil-bearing deposits of land waters. In these deposits the eurypterids often appear without any marine associates, while occasionally there are some marine or at least brackish water forms associated with them, implying either that they lived in brackish or salt water at times, or that their remains were carried out into such waters by the land streams or estuarine currents" (33, 412).
It is to be noted that European authors have said very little about the habitat of the eurypterids, though there are a few brief references. Geikie is the one exception, for he has a good deal to say about the merostomes and the faunas which occur with them. I shall at this point merely quote a few of these passages, written in the discussion of the Upper Siluric occurrences and of those in the Old Red sandstone. "Vegetable remains, some of which seem to be fucoids, but most of which are probably terrestrial and lycopodiaceous, abound in the Downton sandstone and passage-beds into the Old Red Sandstone. The eurypterid genera continue to occur, together with phyllocarids (Ceratiocaris) and vast numbers of the ostracod Beyrichia (B. Kloedeni). Prevalent shells are Lingula cornea and Platyschisma helicites. The Ludlow fishes are also met with" (74, 961). In the discussion of the deposition of the Old Red Sandstone in basins Geikie says: "An interesting confirmation of the view that these basins were isolated is supplied by the occurrence of what is believed to be the oldest lacustrine or fluviatile mollusk yet known, Amnigenia (Anodonta, Archanodon) jukesii. This shell has been ​found in the Upper Old Red Sandstone of Ireland and England associated with land-plants (Archaeopteris, Sphenopteris, Bothrodendron, Ulodendron, Stigmaria, Calamites), fishes (Coccosteus) and arthropods (Eurypterus)" (74, 1003, 1004).
Steinmann in his Einführung in die Palæontologie merely states that: "These remarkable Crustacea reaching a length of 2 meters appear in the Cambrian and Silurian in association with marine animals, in the Devonian they live with the armor-plated fishes in the Old Red, in the Carboniferous and Permic they are found in fresh-water" (266, 373) Haug speaks of the salt and gypsum deposits of New York as lagoon formations, and includes here also the eurypterid beds at the end of the Siluric, thus reaching the same conclusion that many American authors have come to (112, 626)
Walther in the chapter entitled Das Aufblühen der Tierstämme in Silur in the Geschichte der Erde und des Lebens has accepted the statement of several American geologists that the eurypterids were marine organisms saying that they lived in sea-water of normal salinity "as the section in North America proves with certainty" (294, 251). The reference cited for this proof is Sarle's paper on the fauna from the Salina of Western New York. The significance of this occurrence will be discussed below, but we may say at this point that this instance seems hardly to furnish proof positive of a marine habitat. He also calls attention to the restriction of the eurypterids to the black shales, and of the absence of marine forms in association with the merostomes. He notes that in synchronous formations the eurypterids are found only in isolated localities. "Thus is the upper Silurian of Pennsylvania devoid of Eurypterus for a thickness of 500 meters" (294, 251). Walther's explanation of the isolated occurrences seems hardly to accord with the facts. He assumes that the regions devoid of eurypterid remains were great salty lakes cut off from the sea in which the eurypterids are supposed to have lived.
Ernst Stromer in the Lehrbuch der Palaeozoologie has added ​nothing new to the opinions already expressed by so many authors. "It is an oft observed phenomenon that groups originally nourishing in the sea are confined during their decline in fresh-water. Here this applies only to the Gigantostraca [Merostomata], while the Xiphosura which appear formerly to have lived mainly in inland seas, are, today, however, marine only" (269, 308).
During the year 1911 several papers on the Eurypterida appeared in America. Clarke still held to his former opinion that "the few eurypterids we know were doubtless marine, and the creatures gradually acquired the brackish-water habit at their climax, which seems to have eventually changed to a fresh-water life" (37, 280). Stuart Weller in his discussion of the nature of seas in which dolomites are formed, brings out several good points. "In such magnesian beds as are present in the Cayugan period of the Silurian [i.e., Middle and Upper Siluric] we find a most peculiar fauna, constituted almost wholly of the strange Eurypteroid Arthropods whose fossil remains are almost never found in association with typical marine faunas, but which are present in situations, such, for instance as the plant-bearing beds of the Pennsylvanian, which indicate that they musthave lived in non-marine waters. The stratigraphic association of these Cayugan, Eurypterus-bearing beds with beds of salt and gypsum at once suggests that the waters of the period were highly saline and perhaps shallow; but, so far as I am aware, there is no inherent characteristic of the fossil Eurypterus which can in any way suggest that it may not have been a truly marine organism, and our conclusion that it was not such an organism is drawn from the physical surroundings of the fossil itself, rather than that the physical conditions are what we believe them to be on account of some peculiarity of the fossil" (296, 228). This point is well made, and is worth while remembering, namely, that there is nothing in the physical characters of the eurypterids to indicate that they lived in non-marine any more than in marine waters, but from their surroundings the former habitat is suggested. Moreover, the interpretation of the physical conditions of that time has not been based upon speculations about the characters of the eurypterids; it was definite knowledge about the physical conditions that makes it possible to say what must have been the character of the habitat of the eurypterids.
At the Kingston Meeting of Eastern Geologists in the spring of 1910 there was a warm discussion about the eurypterid habitat, Ruedemann, Schuchert, Hartnagel and others arguing in favor of the ​marine, Grabau in favor of the non-marine. The Waterlime formation was particularly under discussion, but though many arguments were brought up on both sides, neither was able to convince the other.
In the June number of the Bulletin of the Geological Society of America (1911) Clarke writing, on the "Relation of the Palaeozoic Arthropods to the Strand-Line," speaks of the size of the eyes of eurypterids and crustaceans as indications of the depth of water in which the forms lived. It was formerly supposed that crustaceans with large eyes had acquired them by adaptation to great depth of water. Clarke cites the case of a trilobite with enormous compound eyes living among many Cambric forms wholly devoid of lenses, and other examples of a contradictory character, so that the size of the eye cannot be taken as proof of either deep or shallow water, but rather implies that the complex, highly-specialized eyes of certain forms enables these individuals better to adapt themselves to either deep or shallow water conditions. Clarke reiterates the opinion that "the few early eurypterids we know were doubtless marine, and the creatures gradually acquired the brackish-water habit of their climax, which seems to have eventually changed to a fresh-water life" (37, 280).
In 1912 the most recent contribution to the study of North American eurypterids was made in Clarke and Ruedemann's Monograph on the Eurypterida of New York (39). While the work has to do mainly with the description of species and the study of larval stages and of the anatomy, leading to fuller knowledge of the ontogeny and phylogeny of the eurypterids as well as their taxonomic relations, still the authors have given some attention to the question of the bionomy (39, 96–113), coming to the following conclusions:
"Summarizing these data we conclude that the eurypterids lived in the sea from Cambric to Siluric time. They had then become less sensitive to changes, positive and negative, in the salinity of the water. In fact they seem to have thrived best under conditions of life that excluded most other marine groups of animals, that is, in the marginal, more or less inclosed marine lagoons, accompanied by estuaries receiving delta-forming terrestrial drainage, with prevailing arid or sub-arid climate, the waters being in some places more than normally briny, in others having less than normal salinity. In other words they were euryhaline or able to live in both salt and brackish water.
​"Their adaptation to such conditions is paralleled today by such crustaceans as Apus and Artemia which not only thrive under rapid diminution of normal salinity but, by means of strongly protected eggs, even survive salt pan conditions which end in complete desiccation, as shown by their well known occurrence in desert lakes. The usual associates of the Siluric eurypterids are peculiar crustaceans whose nature emphasizes the reference above made. They are phyllocarids and ostracods and members of the strange family Hemiaspidae (Neolimulus, Bunodes, Hemiaspis, Pseudoniscus). This congeries of peculiar crustaceans seems to constitute a fauna especially adapted to, and therefore highly characteristic of, lagoon and estuary conditions.
"Thus while the earlier eurypterids were marine and their climacteric fauna euryhaline; their later habit throughout the Devonic and Carbonic led them finally into the fresh water.
"The succession of habitats is hence, according to our evidence, the reverse of that suggested by Chamberlin's hypothesis noted at the beginning of this discussion" (39, 112, 113).
In 1913 appeared the first extensive discussion of the habitat of the eurypterids in a paper entitled "Early Palaeozoic Delta Deposits of North America" by Professor Grabau, in which he brings forward arguments for the fluviatile habitat of these merostomes in the Ordovicic and Siluric of North America, and he includes a summary of the distribution and occurrence of the eurypterids by myself, reviewing the evidence and coming to the conclusion that the eurypterids were river-living at least during the two periods mentioned. The significance of the occurrences in the Pittsford, Shawangunk, and Bertie are discussed especially.
At the end of the same year Grabau's Principles of Stratigraphy was published. In Chapter XXVIII on the "Bionomic Characteristics of Plants and Animals" and elsewhere in the book the eurypterids are spoken of as fluviatile organisms as indicated by their distribution, faunal associates and mode of occurrence. A single statement taken from this book will show the position which Grabau holds. ". . . . The early remains of fish as of eurypterids are not found in normal marine deposits, but in those which are at least open to the suspicion that they are formed by rivers or at least at the mouths of rivers, while the best preserved remains, and the most abundantly represented in the Palaeozoic, are found in river ​floodplain deposits and in deltas" (87, 989). For further references on this subject in the Principles see pp. 377, 425, 945, 950, 1029, 1030.
This gives us, then, the last word on the subject up to the present time. Looking over the opinions which have been recorded in the preceding pages, one is struck with the diversity of conclusions arrived at by our greatest American geologists and by not a few of those of Europe. From 1818, when the first Eurypterus was found, though it was not described as such till 1825, down to the end of the century, it was practically a universal opinion that the eurypterids had been denizens of the sea. The species were described along with marine forms and were considered to have been marine also. The study of the taxonomic position of the Eurypterida, showing always more and more clearly their close relationship to the modern Kingcrab, Limulus, gave an added reason for assuming a marine habitat for the fossil forms. With the beginning of the present century came the awakening of geologists and paleontologists to the fact that perhaps these extinct Merostomata had not always lived in the sea, that they may even never have known marine conditions. The current opinion now is that the eurypterids lived in the sea from Pre-Cambric time through the Ordovicic. During the Siluric they gradually became adapted to brackish and fresh-water conditions, living in estuaries and lagoons in the Devonic and becoming entirely fresh-water habitants in the Mississippic, Carbonic and Permic. Grabau is the only staunch advocate of the non-marine habitat even from the earliest times, though Chamberlin, to be sure, has argued such a possibility, but his discussion is purely philosophical, and while interesting and full of suggestive ideas, it is, nevertheless, unsupported by the evidence necessary for definite proof of his theory.
In attacking this problem the most important thing to determine is whether the Eurypterida began their existence in the sea or in the land waters, and under what conditions they lived in pre-Devonic time, for after that, it is now generally conceded, they lived in terrestrial waters.
* ↑ No eurypterids have been found in the Ordovicic of Bohemia. This statement was not corrected in the 1910 edition of the Grundzüge der Palæontologie, p. 568, but has been corrected in the 1913 edition of the Text-Book of Palæontology, p. 779.
* ↑ "Diese merkwürdigen, bis 2m. langen Krebse erscheinen in Kambrium und Silur in Begleitung von Meerestieren, im Devon leben sie mit Panzerfischen in Oldred, im Karbon und Perm finden sie sich in Süszwasserablagerungen."
* ↑ "Les formations lagunaires jouent un rôle peu important et l'on ne peut guère citer comment elles que des grès et des argiles rouges, qui, dans l'état de New-York et sur les bords de la Léna, renferment du gypse et du sel gemme, puis les couches à Gigantostraces et à Poissons, par lesquelles se termine souent le Silurien."
* ↑ "Hier folgt auf den fossilreichen Riffkalk ein dunkler Kalkmergel, der kein einziges der vorher hier so üppig gedeihenden Meerestiere enthält. Nur ein paar Schalen von Orthoceras wurden durch Stürme in die Bucht hineingetrieben, und einige genügsame Zweischaler lebten darin. Dann folgt ein schwarzer Mergel, reich an Eurypterus, und sobald dieses Gestein verschwindet, fehlen auch die Schildtiere und treten erst wieder auf sobald der schwarze Mergel nochmals erscheint." (294, 251.)
* ↑ Grosse Muschelkrebse (Leperditia) mögen hier einen salzigen Binnensee ohne Verbindung mit dem Meere belebt haben, so dasz die Schildtiere nicht hineinzudringen vermochten (294, 251).