Bull. geo!. Instn Univ. Upsala: N. S. 4, 6: 81-114, 1974 GROWTH AND VARIATION IN EURYPTERUS REMIPES DEKAY By H. E. Andrews, ]. C. Brower, S. ]. Gould, and R. A. Reyment Andrews, H. E., Brower, ]. C., Gould, S. ]., Reyment, R. A.: Growth and Variation in EurypteruJ remipes DeKay, Bull. geo!. Instn Univ. Upsala, Vol. N. S 4, pp. 81-114. Th e statistic al analysis of two subspecies of Eurypterus remipes shows that both of them display very high integratio:� among all measures considered. The prosomal set of variables are highly integrated with the body set. There is little allometry in bivariate growth sequences. As best known at the present time, trilobites show an analogous leve! of integration; there is therefore reason to suspect that the gr owth relationships here recorded are wide-spread among some arthropods. Ontogenetic growth is analysed for E. remipes remipes, after the establishment of growth stages by a stepwise multivariate technique. Canonical correlation is used to examine the pattern of integration between head and body. This is, again, exceptionally high. Other methods of multi­ variate statistics are applied the analysis of the underlying relationships between variables. The palaeoec ology of the Fiddlersto Gr een Member (Bertie Formation, Upper Silurian) is discussed. H. E. Andrews, Department of Geology, \'(/ellesley Colle�;e, \'(/ellesley, Mass., U.S.A., S. ]. Gould, Museum of Comparative Zoology, Harvard University, Cambridge, Mass., U.S.A., ]. C. Brower, Department of Geology, Syracuse University, U.S.A., R. A. Reyment, Paleontologiska Institutionen, Uppsala Unit;ersitet. Su,eden. INTRODUCTION remipes and the E. tetragonophthalmus of Fischer Ever smce Mitchill (1818) recorded the first de Waldheim (synonym E. fischeri) , the other eurypterid from the Upper Silurian of Oneida taxon examined in this paper, became E. remipes County, New York, this group of fossils has fasci­ tetragonophthalmus. nated palaeonrologists. The original Eurypterus Kjellesvig-Waering (1958, p. 1136) , in dis­ remipes DeKay came from the Fiddlers' Green cussing the high degree of likeness between the Member of the Bertie Formation: this stratigra­ two subspecies (for a long time, the European phical leve! is still an abundant source of excell­ one was referred the American remipes), wrote to e:uly preserved specimens. The original specimen that "differences between them are minor and was imerpreted as a catfish of the genus Silurus probably of a geographic or tempora! character" (the appendages of the prosoma were identified and on p. 1137, "E. remipes tetragonophthalmus as the barbels of the fish). Since E. remipes, the is doser to E. remipes remipes than to any other type species of the genus, was first described by American subspecies". He noted that the prosomas DeKay (1825, p. 375, pl. 29), it has been the of the two have the same length-to-width propor­ object of numerous studies. Note-:vorthy are those tions, but the lateral eyes of tetragonopbthalmus of Hall (1859), Holm (1899), and Clarke and appear be larger, the prosomal ornament is to Ruedemann (1912). Kjellesvig-Waering (1958) different, the relative proportions of the sixth grouped several taxa, previously considered as and sevemh segments of the paddle are reversed species, around E. remipes as subspecies. Conse­ and the pre-telson of remipes lacks the epimeral quently, according ro this revision, the E. remipes spines possessed by the other subspecies. More of DeKay, Hall and Clarke became E. remipes recently, StØrmer (1973) has come to the con- 82 H. E. Andrews, ]. C. Brower, S. ]. Gould, and R. A. Reyment dusion that differences in the paddles of the indeed: the extreme intensity of integration among European and American forms are great enough nearly all measures is also the primary condusion warrant generic separation and has therefore of Andrews' and Gould's work. Moreover, the few to made tetragonophthalmus the type of his new multivariate studies of trilobites that we know genus, Baltoeurypterus. Kjellesvig-Waering has (Eldredge, 1972, in particular, and references informed us that he is in agreement with StØnner. therein) have independently discovered the exi­ We have Iooked into the grounds for this genus stence of very high correlations and little allometry and Gould and Reyment think that such slight in omogenetic series. W e feel that we may there­ differences can hardly be of more than minor fore be stating a quite general principle of growth taxonomic importance. There is a distinct danger in certain arthropods. Ostracods display a much that we have here a case of the "key character lower leve! of integration (Reyment, 1960, 1963, concept". That is, a certain character is defined as 1966). being of "generic" value (rather than "specific" Gould and Andrews studied a collection of or "varietal") and then one is forced honour eurypterids from the upper Silurian of the Baltic to every variation in this character with a high-leve! island Saaremaa, Estonian S.S.R. The collection taxonomic designation. The variational patterns was made in 1930 by W. Patten (who used them of the European and American eurypterids are to help argue his case for an arthropod origin of very dose indeed. Future study may bring light the vertebrates). Several hundred excellent speci­ to more substantial differences, bur until then, we have mens, ranging fro:n l to 30 cm in length, are chosen a conservative approach by retaining both in the Museum of Comparative Zoology, Harvard taxa as subspecies of Eurypterus remipes. University. The analysis was made on 44 specimens evenly spanning the entire range of size; all had As far as we know, this is the first detailed complete prosomas as well as the first segment of statistical study of a eurypterid appear. Indeed, to the mesosoma and seem to be preserved without Kjellesvig-Waering (1958) observed that the distortion. variability of the eurypterids had yet to be studied. The material studied by Brower and Reyment Qualitative observations occur scattered through­ comes from collections at Colgate University, out the literature, the most comprehensive being Hamilton, N.Y. and Syracuse University, Syracuse, those of Clarke and Ruedemann (1912); most of N.Y. the growth changes they noted in their qualitative appraisal of E. remipes remipes show up dearly in our statistical study. ACKNOWLEDGMENTS The purposes of this work are to study the ontogeny and variation of two dosely related Brower and Reyment are indebted to Colgate eurypterids, to contrast and compare the results University for giving them access a magnificient to obtained, and to attempt a palaeoecological analy­ collection of E. remipes remipes and, in particular, sis for E. remipes remipes. Professor Robert M. Linsley of the Geology to Befare making any general statements about the Department for giving us a set of prosomal nature of functional integration in eurypterids, we measurements on the Colgate specimens. A great must know whether the patterns discovered in one deal of the basic work on the material of E. remi­ species can be detected in related taxa. Thus, pes remipes was carried out as a dass project Brower and Reyment were pleased to learn that by the following students at Syracuse University: Andrews and Gould had done an independent Maurice Cucci, John Douglas, Duane Eppler, Susan mu!tivariate analysis of a European eurypterid. Siwek, John Kennedy, and Ghan Shyam Srivastava. Because the two groups worked in complete in­ Acknowledgment is made in the text for the resu!ts dependence and used different measures and obtained by them. methods, a set of similar results would seem all Measurements on the Syracuse University E. re­ the more compelling. The similarity is striking mipes remipes prosomas and Limulus polyphemus Growtb and Variation in Eurypterus remipes DeKay 83 were made by Edna S. Kaneshiro (1962, un­ ANALYSIS OF EURYPTERUS REMIPES published Master's thesis) who also did much pre­ TETRAGONOPHTHALMUS liminary processing of these data. By The Syracuse University specimens were collec­ Harold E. Andrews and Stephen Jay Gould ted by Adawia Alousi, Nora Kula, Sachiko Naka­ gawa, E. S. Kaneshiro, Ralph Watson, J. L. Craft Twenty seven measurements were made on each and the writers. specimen. We attempted to establish a well-spaced We thank Robert M. Linsley, Erik N. Kjelles­ grid of general lengths, widths and diagonals; vig-Waering (Amoco International Oil Co., Chi­ allometric changes produced by gradients of diffe­ cago, Illinois, USA), C. D. Waterston (Royal rential growth (Huxley, 1932; Gould, 1966) should Scottish Museum, Edinburgh) and D. F. Merriam have a multivariate expression in the clustering (Syracuse University) for reviewing the manu­ of dimensions expressing a gradient. W e also script and making helpful suggestions for im­ constructed a set of measures for anatomical fea­ provement. tures of particular interest (the eyes and the first The identifications of most of the species occur­ mesosomal segment). ring with Eurypterus remipes remipes were kindly We analyzed our 44 X 27 matrix with COVAP made by Professor John W. Wells of Cornell for R and Q mode principal components factor University (lthaca, New York), Dr. Erik Kjel­ analysis with options for varimax and oblique lesvig-Waering, and Professor Robert M. Linsley. rotations. As these techniques assume a linear The text figures were drawn by Mrs. Dagmar relationship between pairs of variables, we trans­ Engstrom and the manuscript typed by Mrs. Eva formed all measures tO their logarithms before Eklind, both of the Palaeontological Department, the analysis. About the only allometric relation­ Uppsala University. The Syracuse University and ship consistently found in arthropods is the nega­ Uppsala University Computer Centers provided tive differential growth of the eyes. Bivariate computer time; James Wilson of the Syracuse plots show that the Saaremaa eurypterids are no Computer Center aided in APL programming. exception to this general trend. Reyment's contribution to the study was made The variables are listed in the explanation to while he was a Visiting Professor at Syracuse Fig.