Eurypterida

“ The eurypyterids occur in thin seams not associated with the fast diminishing marine fauna, but with crustacea such as Beyrichia, with the thin-shelled Platyschisma helicites and occasional Lingulas, and especially with fishes. The eurypterids are scarce in the Aymestry and Upper Ludlow groups, but become abundant in certain layers in the Temeside group where they are found in cross-bedded sandstones, in bone-beds, and characteristically, in olive-colored shales. ”

“ The Bertie contains the largest eurypterid fauna of any one formation in the world, there being recorded fourteen species (39, 89) referred to four genera: Eurypterus (5 sp.) , Pterygotus (5 sp.) , Eusarcus (1 sp.) , and Dolichopterus (3 sp.) . The specimens are for the most part astonishingly well preserved, but other organisms are extremely rare. In the Museum above referred to are a few specimens of marine organisms obtained from the formation which furnished the eurypterids. ”

“ It is a fauna in which the genera Eurypterus and Pterygotus prevail in number of species (Eurypterus with five, Pterygotus with three) and in the size of the creatures, which are there obviously near the climax of their development. It is also the horizon where individual development is greatest. [5]
One or two stragglers, notably Eurypterus remipes, return in the Rondout waterlime in greatly diminished number, and a new peculiar type of Eurypterus (E. microphthalmus) appears in waterlime intercalations of the Manlius limestone above. ”

“ Omitting for the present the peculiar case of the Eurypterus horizons in the Frankfort shale and the Shawangunk grit and returning to the more typical Eurypterus facies represented by the waterlimes and shales of the Salina formation of western New York, we encounter the venerable and still current view that these beds were formed under conditions of much abnormal salinity. ”

“ The alternation of limestone conglomerates and shales in the lower Potosi series indicates near-shore conditions of sedimentation, and the occurrence of the single specimen of a eurypterid, far from pointing to a marine habitat for this one individual, militates very strongly against such a mode of life. In all cases the occurrence of a single individual is one of the strong arguments against the assumption that the individual belongs to the fauna of the bed in which it is found. ”

“ James Hall described for the Second Geological Survey of Pennsylvania an interesting fauna of eurypterids found in the Productive Coal Measures. The first announcement of a eurypterid of Carbonic age from the American continent had been made in 1868 by Meek and Worthen who described Eurypterus mazonensis from the Coal Measures of Illinois, erecting for it the subgenus Anthraconectes, and in 1877 C. E. Hall described two species (E. pennsylvanicus and E. mansfieldi) from the Coal Measures of Pennsylvania. ”

“ The single eurypterid fragment found in this belt, it will be recalled, was discovered in the track-crowded shales and greywackes at Slitrig Water. These being interpreted as basal beds of an advancing sea, it is most natural to expect that the sea, rolling landwards and up the rivers, slowly but unceasingly converting the dry land into seafloor, should catch river-dwellers who were not able to or did not migrate upstream fast enough, and even if there were none such, at least dead remains would inevitably be passed over by the sea in its continued advance. ”

“ There are thus ten species of eurypterids from the Devonic of Great Britain, all occurring in the Old Red Sandstone facies of deposits associated with fishes, land plants, fluviatile molluscs, myriopods and crustacea, such as the fresh or brackish-water phyllopod, Estheria, the ostracod Beyrichia and certain phyllocarids. With the exception of Pterygotus anglicus none of the eurypterids is either abundant or well preserved, most of the species being represented by a single portion of the exoskeleton or by a number of fragments. ”

“ 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. ”

“ The fullest development of the eurypterid fauna is seen in the rocks underlying Rootziküll on the west coast of the island of Oesel in the parish of Kielkond. Here the beds of the lower part of zone K are a fine-grained "plattenkalk" or dolomitic calcilutyte, in which the chitinous exoskeletons of Eurypterus fischeri Eichwald, E. laticeps Schmidt and Pterygotus osiliensis Schmidt have been so excellently preserved. Associated with the eurypterids in the same bed have been found the tail of Ceratiocaris notlingi Schmidt, [11] the shields of two cephalaspid fishes Thyestes verrucosus Eichw. ”

“ If the eurypterids lived in the marine waters, why are their remains not found with those of the other marine organisms? Band D contains many genera, species, and individuals of brachiopods, pelecypods, gastropods, cephalopods, crustacea, crinoids, trilobites, corals, the first three groups being especially well represented, the last three by only two or three species. But not a trace of a eurypterid is found in this fauna which, according to the criteria given on p. 76 is a typical marine fauna. ”

“ In the black shales the eurypterid remains are rarer, but their surface sculpture is excellently retained, and here their organic associates are Climacograptus typicalis and Triarthrus becki. As a result of imperfect retention of these eurypterids in the rocks where they most abound and their sparseness in the shales which have best preserved them, we are still left in ignorance of the full composition of the assemblage, but it is safe to say genera, species and individuals were abundant at this early period and the evolution of distinctive characters . ”

“ Of the general preservation and faunal associates of these eurypterids Barrande remarks:
"Our basin, so privileged in respect to the frequency and the state of preservation of the trilobites and the other crustacea, appears, on the contrary, very poor in the fossils representing the two types of eurypterids, which are recognized in our formations. (Pterygotus and Eurypterus) .
". . . . Far from finding individuals complete and well preserved, it will prove difficult to add any new facts of importance to those already published on the organization of the species of this type. ”

“ Clarke and Ruedemann have described the species and also the beds from which they come. The eurypterids are very abundant in the sandstones though poorly preserved, but in the intercalated black shales, while less numerous they show better preservation. They are associated with graptolites and plant remains. Six species have been described by Clarke and Ruedemann. Eurypterus chadwicki, Eusarcus linguatus, Dolichopterus breviceps, Stylonurus modestus, Pterygotus ? (Eusarcus) nasutus, P. normanskillensis. Entire individuals are absent, the fauna being made up chiefly of carapaces. ”

“ In summing up the evidence regarding the life mode of the eurypterids, and in view of the variety of forms with incipient adaptations, it would be a legitimate inference that the whole group was not so highly specialized as the recent merostomes and was still able to use different methods of locomotion though no one of them with great proficiency. Some were best adapted to swimming, others to crawling and many to finding their food by grubbing in the mud. [6]
Some light seems also to be shed on their probable mode of life by a consideration of the separate faunules to which they pertain. ”

“ A transverse row of small semicircular scales delimits the exposed portion of the tergites and postabdominal segments from the frontal overlapped portion. The ventral side [pl. 8, fig. 3] is ornamented with closely arranged semicircular to semilunar scales, largest and most prominent in the middle anterior region of the operculum, otherwise rather faint.
Ontogeny. Eurypterus remipes has not yet afforded any growth stages as young as those of species from Otisville. The smallest specimens are already of neanic age. ”

“ In addition there is a certain group of occurrences which appear to be able to throw little light upon the determination of the habitat, and they have not been discussed so far, for, if from the best material which we have at hand it can be proved that the eurypterids lived in the rivers from the very beginning of their history, then we need be no more distressed at finding a fragment among marine remains than we are when we find a single leaf or piece of wood associated with brachiopods and molluscs. ”

“ The first prolific eurypterid fauna in North America, the first to offer sufficient material and a large enough representation in genera and species to make it possible to state what are the general affinities of the fauna as a whole, is the newly discovered one in the Normanskill shales at Catskill, New York, which has so far been found to contain six species, included in five genera, but undoubtedly many more will be discovered as the material is worked over. ”

“ The fact that they occur in a given band which, when traced even a short distance laterally, shows no lithological change, but only an absence of eurypterids, indicates that migrations along shore were non-existent; while the fact that new species and even new genera appear at horizons far separated from underlying and overlying eurypterid horizons seems to deprive "marine" eurypterids of ancestors or descendants, while to account for a marine Stylonurus ornatus in the Wenlock of Lanarkshire and in the uppermost Ludlow of the Pentland Hills, is not within the inventive powers of the author. ”

“ Eurypterus pygmæus Salt. and Stylonurus megalops Salt. are common as fragments in the higher olive shales of the Temeside group. Pterygotus banksii Salt. together with numerous indeterminable species of Eurypterus are found in the Ludlow Bone-Bed; this species is also common in the Platyschisma bed and the upper olive shales of the Temeside group; in the same shale P. ludensis Salt. is abundant. In all cases where species are reported to be common it is to be remembered that no entire specimens are found but only fragments and disjecta membra. ”

“ Many important points in the ontogeny and phylogeny of the eurypterids are here set forth for the first time, and all of the North American species are described in great detail and figured in a volume of plates that surpass all former illustrations.
I wish to express my thanks to Dr. R. Ruedemann, who allowed me to study the large collection of New York eurypterids at the State Museum in Albany; to Dr. C. D. Walcott, who showed me the large Beltina fauna and the beautiful specimens of Limulava from the Middle Cambric Stephen shale of Canada in the Smithsonian Institution at Washington, D. C ”

“ This striking similarity of the two faunas (one of Chazy, the other of Trenton age) amounting almost to identity, seems to indicate a very slow progressive development of the eurypterid faunas, probably owing to their early adaptation to particular marine conditions. Similar stability of the eurypterids is also suggested by the identity or extremely close relationship of the species in the Shawangunk grit at Otisville and the possibly older beds at the Delaware Water Gap and Swatara Gap [see p. 417] in Pennsylvania ”

“ Soon thereafter followed the discovery of the Eurypterus-bearing black shales at Pittsford, Monroe co., which were brought to light by the work of enlargement of the Erie canal in 1895, the species of which were described in our reports by Mr Clifton J. Sarle from material now in possession of the State Museum. To this notable addition to our knowledge has been added in years still more recent the new fauna in the dark shales of the Shawangunk grit at Otisville, Orange co., an assemblage of eurypterids remarkable for its profusion of immature growth stages ”

“ If we are to consider that a single fragment of a eurypterid when found in marine strata proves that the eurypterid lived in the sea, then, provided no other proof existed to the contrary, insects, land shells, leaves, logs, spiders, scorpions and other land forms which are often floated or blown out to sea and which are found today thousands of miles from land, and have often been met with in the rocks associated with marine forms would also be considered as inhabitants of the sea. ”

“ The impossibility of considering either fish or eurypterids as washed in from the sea is indicated by the absence of these forms in the open marine waters to the south. While I have made no attempt to prove the fluviatile habitat of the fishes, yet the bone-beds seem capable of explanation on no other hypothesis. Sometimes the beds are only inch thick, containing no complete remains but only a great mass of broken bones, spines, and scales. ”

“ The cause of the withdrawal from the sea of these well armed and often gigantic eurypterids into the brackish and fresh water is a problem of much interest. Perhaps the development of the more agile and more advanced fishes put these slow and archaic merostomes on the defensive and finally forced them altogether out of the sea. Their association with clumsy and heavily armed, equally archaic Old Red fishes which clearly suffered a like fate from their own more advanced relatives, would seem to be very suggestive in this connection. ”