Eurypterus

“ The group represented by Eurypterus and Dolichopterus is characterized by the prevailing broad carapace with dorsal eyes, broad to slender body, relatively strong swimming legs and a spiniform telson. The stout walking legs in all members of this group leave no doubt that they were able crawlers on the bottom, but there is considerable evidence to show that they burrowed in the mud and were also well able to swim; some species more given to one, some to the other habit. ”

“ Imperfect remains are all that have been found of the five species of Eurypterus: scoticus, punctatus, minor, cyclopthalmus and conicus.
In the Girvan area near Straiton where continuous marine, though near-shore deposition was going on through Tarannon on into Wenlock time, the strata are found to be highly fossiliferous at certain horizons and graptolite bands are well made out. Collections made in a quarry near Blair Farmhouse not far from the village of Straiton have yielded a number of fossils, among which is a Eurypterus sp. ”

“ The species which seem to us of especial interest in the explanation of the strange structure of the swimming leg are Eurypterus (Onychopterus) kokomoensis and Dolichopterus macrochirus. The former [pl. 26, fig. 2] shows the most primitive shape of the swimming leg known to us. This primitive character manifests itself most distinctly in the following features. Beginning at the distal end, the ninth segment is a well developed terminal claw, such as is found on the other legs, indicating that the minute ninth segment of Eurypterus is a reduced terminal claw. ”

“ In Eurypterus the structure of the legs has been most minutely described by Schmidt and Holm in E. fischeri, and our large collection of E. remipes and lacustris corroborates their excellent work. The first three pairs are thick and heavy and increase in length regularly backward. The first leg consists of seven, the second and third of eight segments each, the terminal claw included. They are convex on the upper and flat on the underside and so articulated that they can be bent only downward. ”

“ This form, represented by a single species, resembles nothing more than our eurypterid larvae from Otisville and it is very possible that these and some other primitive-looking small species of Eurypterus are cases analogous to those occurring among the recent crustaceans where development has been arrested by parasites which prevent molting and result in dwarfed adults retaining larval characters. ”

“ 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. ”

“ But the question remains open whether E. remipes, the genotype by right of priority, is a faithful expression of the structure displayed by the genus Eurypterus. To determine this point we may briefly survey the phylogenetic relations of the species of Eurypterus.
The American species of Eurypterus readily fall into three subdivisions, viz, (a) those that group themselves around E. remipes; (b) those that vary in different directions from this group but are approximately contemporary; and (c) the later Carbonic species. Group (a) is represented by E. remipes, E. lacustris and its var. ”

“ Though at first glance it is apparently of minor importance, it gives species of Eusarcus a very different aspect from those of Eurypterus and indicates a difference of habit in the two genera. In Eurypterus the walking legs are invariably bent backward in the fossil state, while in Eusarcus they are as invariably bent forward. [18] In the living animals their direction was downward in Eurypterus as well as in Eusarcus but while in the former the posterior spines are the longer, in Eusarcus the anterior ones were either longer or at least of equal length with the posterior. ”

“ The seventh and eighth segments are broad and relatively short, their longitudinal and transverse diameters being about equal. Their outer edges are obscurely serrate. The lobe of the seventh segment which is narrowly triangular in Eurypterus, is here produced into a leaflike process, which in length equals the segment. The eighth segment, which is the palette in Eurypterus and Pterygotus, is in this genus of similar form as the preceding segment. The ninth segment, the small "claw" in other eurypterids, has here assumed the bladelike shape of the eighth segments in Eurypterus and Pterygotus. ”

“ The cephalothorax is comparatively shorter and wider than in Eurypterus, the eyes are further forward, nearer together, and more oblique, and besides the telson but 11 abdominal somites can be determined on the dorsal side, instead of 12, as in Eurypterus. These differences are considered as indicative of a new genus and it is proposed to recognize this type under the name Strabops nov. gen., with Strabops thacheri n. sp. as the type species. ”

“ The Carbonic species of Eurypterus develop spines wherever possible; the surface scales are produced into pointed wedges or spines; the ends of the epimera grow out to a great length; spines develop on the appendages not only in rows along the various segments but also on the lines of junction between segments: showing that the final expression of morphological characters in the eurypterids was the development of spines which was followed by extinction. ”

“ The Eurypterus beds have a fairly wide extent in western Oesel, but the fullest development of the fauna is seen only near Rootziküll, on the west coast of the island, in the parish of Kielkond. Here the beds are a dolomite in which the chitinous exoskeletons of Pterygotus and Eurypterus have been excellently preserved, and even the tail sting of a Ceratiocaris and the shields of two cephalaspid fishes, Thyestes verrucosus Eichw. ”

“ 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. ”

“ As illustrations of the scattered occurrence of single specimens of eurypterids may be mentioned: Strabops thacheri in the Upper Cambric, Echinognathus clevelandi from the Utica, Eurypterus prominens from the Clinton, Eurypterus boylei from the Guelph, Eurypterus microphthalmus from the Manlius, and Eurypterus douvillei from the Rothliegende.
(2) As an instance of the same species occurring in places many miles apart, Eurypterus remipes may be cited. This species has been found in Waterville, Oneida County, N. Y. in great numbers; at Jerusalem or Wheelock's Hill, Herkimer County ”

“ The most famous locality of our Eurypterus beds is Rootzikull, near Kielkond. Here, besides the crustaceans, we have also found fish remains—two cephalaspidean genera, Thyestes, Eich., and Tremataspis, described some years ago by Eichwald, Pander and myself. ”

“ The greater size of the carapace in such trilobites as Harpes is considered as a larval character retained to maturity, but this is no evidence of the primitive character of the genus. Likewise eurypterids with large carapaces, as certain species of Eurypterus, are not at all to be considered as primitive. The philosophy and phylogeny of the arthropods agree in postulating a gradual growth and consolidation of a greater number of segments into the cephalothorax. ”

“ While the characteristics of this stage will be the basis of our reconstruction of the prototype, others may be safely inferred from a comparison of Strabops with the general characters of the Siluric eurypterids and from theories of the development of the arthropods in general.
In Strabops the carapace [pl. 1] is short, and a little less wide than the greatest width of the body. It is so in most of the later eurypterids, notably in Eurypterus, Hughmilleria and Pterygotus. ”

“ It consists of one species of Eurypterus, one of Eusarcus, one of Dolichopterus, six of Stylonurus, one of Hughmilleria and one of Pterygotus. It has furnished a contribution to the organization of the eurypterids in a specimen of Stylonurus, retaining all four posterior legs of one side, in the light of which previous restorations of that genus are greatly modified. The most novel feature of the Shawangunk grit fauna, is the presence of larval stages of Eurypterus, Hughmilleria, Stylonurus and Pterygotus from the nepionic, almost microscopic, stage onward. ”

“ The carapace is typically subrectangular in Eurypterus, Dolichopterus, Slimonia and Stylonurus, semiovoid to semicircular in Strabops and Hughmilleria, and subtriangular in Eusarcus. [2] The broadly semielliptic or semicircular form is manifestly original and primitive, as indicated both by the larval stages of the eurypterids and the carapace of the Cambric Strabops, while the subrectangular and subtriangular forms are the extremes of different lines of development. ”

“ Precise information is given regarding localities, species are fully described and compared with related forms and excellent illustrations are given, so that with these papers and one by Nieszkowski in 1859 on "Der Eurypterus remipes aus den obersilurischen Schichten der Insel Oesel" (197) one may gain an accurate knowledge of the fauna and the sediments. Notes by Nieszkowski in connection with his work on the trilobites have proved helpful, and for further details the reader is referred to the titles under his name in the bibliography as well as to numerous papers by Schmidt. ”

“ This specimen also demonstrates that the scalloping of the edge of the carapace is due to the presence of scales.
The National Museum contains a fragment [pl. 23, fig. 2] of a very large carapace of this species from the waterlime at Buffalo which indicates that the species must have attained much larger proportions than any other known Eurypterus. This carapace was approximately 250 mm wide in front of the eyes, to which a basal width of about 300 mm and a length of the carapace of about 160 mm would correspond. The whole body must have measured fully one meter. ”

“ This convexity both of the dorsal and ventral sides producing the subcircular section of both preabdomen and postabdomen, is shown by several specimens which are but slightly compressed. A species quite similar to our type in both form of body and size is E. pygmaeus Salter from the Downtonian (uppermost Ludlow) of Great Britain. Its carapace, however, seems to have been a little longer
and the eyes a little more forward in position. From the other species of Eurypterus these two forms differ in their long, gradually tapering, terete body and the small size of the swimming legs. ”

“ Similarly the serrations of the edges of the rudder plate of the swimming legs, of the epimera of the abdominal segments and of the telson are independent of scales. But it appears that the spinules on the dorsal crust originate from scales, we surmise from a lengthening of the point of the angle of the V. In Eurypterus remipes, lacustris and pittsfordensis, as well as fischeri, but a single transverse row of such spines is developed on each segment. ”

“ The difference in the walking legs finds its strongest expression in the fourth pair. In Eurypterus the fourth is not only longer and thinner than the others, but also lacks the spines, while in Eusarcus, it is the shortest leg of the last three pairs, though equally strong and, like the others, provided with spines on all segments. ”

“ 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. ”

“ Its relatively great width will be disregarded here as not characteristic of the prototype. It suggests that Strabops is already nearer to the Eurypterus than to the Pterygotus stock.
The Siluric and later genera of the eurypterids distinctly fall into two groups or stocks, namely, that of Pterygotus and that of Eurypterus. The former group (Hughmilleria, Slimonia, Pterygotus, Erettopterus) is principally distinguished by the marginal, faceted eyes; the latter, containing the genera Eurypterus, Dolichopterus, Echinognathus (?) ”

“ In the Eurypterus these large eyes are large single eyes, not separate ocelli, as in the scorpion.
All, then, that is required is that in the first formed fishes, which still possessed the dorso-ventral muscles of their Eurypterid ancestors, the lateral eyes should be the important organs of sight, large and near the mid-dorsal line. Such, indeed, is found to be the case. In amongst the masses of Eurypterids found in the upper Silurian deposits at Oesel, as described by Rohon, numbers of the most ancient forms of fish are found belonging to the genera Thyestes and Tremataspis. ”