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A Comparison of Fourteen Elphidiid (Foraminiferida) Taxa

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A Comparison of Fourteen Elphidiid (Foraminiferida) Taxa JOURNAL OF PALEONTOLOGY, V. 59, NO. 5, P. 1075-1090, 8 FIGS., SEPTEMBER 1985 A COMPARISON OF FOURTEEN ELPHIDIID (FORAMINIFERIDA) TAXA MARTIN A. BUZAS,' STEPHEN J. CULVERS AND LAWRENCE B. ISHAM' 'Department of Paleobiology, Smithsonian Institution, Washington, D.C. 20560 ^Department of Geophysical Sciences, Old Dominion University, Norfolk, Virginia 23508 ABSTRACT—Eleven morphological variables were measured or scored on 12 groups belonging to Elphidium and two belonging to Haynesina. The 14 groups were compared along canonical axes. The mean canonical variates for the groups E. cf. mexicanum and E. mexicanum are so close we consider them conspecific. E. discoidale, E. gunteri, E. advenum, and E. mexicanum are clearly discriminated from the other groups. E. margaritaceum, E. excavatum, and H. orbiculare are fairly well discriminated from the others. The remaining six groups form two overlapping sets. One set contains E. bartletti, E. frigidum, and E. subarcticum, while the other contains E. williamsoni, E. excavatum (deep), and H. germanica. Two more analyses were made on these overlapping sets and the resuhs indicate each of the groups can be discriminated. We conclude each group is a separate species, with the exception of E. excavatum (deep) which we regard as conspecific with E. excavatum. The specimens from 1,530 m depth simply do not exhibit as much variation as the specimens from shallower water used in the group E. excavatum. This suggests that not only species, but also some morphological groups can be used as ecological indicators. INTRODUCTION figure by about one half This was not a sim- ple task, however, and some specific desig- THE FORAMINIFERAL genus Elphidium de Montfort is a diverse and abundant taxon in nations were more certain than others. modem and Cenozoic shelf sediments. Al- The first purpose of this paper is to statis- though many constituent species have been tically evaluate several troublesome elphidiid studied in great detail over the past 50 or so morphological groups to determine their re- years, disagreement still exists over the spe- lationship to one another, and, at the same cific names given to various morphological time, provide further information on a rea- groups (see Cushman, 1930, 1939; Loeblich sonable scheme for designating species. We and Tappan, 1953; Buzas 1965a, 1965b, chose 14 morphological groups that are com- 1966;Feyling-Hanssen, 1972;Haynes, 1973; monly recorded on the North American At- Hansen and Lykke-Anderson, 1976; Banner lantic continental margin. These groups and and Culver, 1978; Poag, 1978; Wilkinson, the names we gave them are listed in Table 1979; Miller et al., 1982; Rodrigues and 1. Twelve of these elphidiids we placed in the Hooper, 1982). Geographic isolation of var- genus Elphidium, and two in the genus ious researchers and problems of commu- Haynesina (elphidiids lacking sutural bridges nication are obvious reasons for identifica- and pores and often assigned to the genus tion problems, but we consider the main Protelphidium, see Banner and Culver, 1978). factor involved is the very great inherent The second purpose of this paper is to re- morphological variation within the elphid- illustrate several holotypes and additional carefully chosen specimens. We do this be- iids. In a study dealing with all published rec- cause many of the original illustrations do ords of modem benthic foraminifera on the not allow a researcher to see the characters Atlantic continental margin of North Amer- clearly. ica, Culver and Buzas (1980) found that ap- proximately 40 names have been used to sub- MATERIALS AND METHODS divide the genus Elphidium. Examination of We examined the primary types of El- type and figured specimens in the U.S. Na- phidium advenum (Cushman), E. bartletti tional Museum of Natural History, the Brit- Cushman, E. frigidum Cushman, E. mar- ish Museum (Natural History), and various garitaceum Cushman, E. mexicanum Kom- smaller collections enabled us to reduce this feld, E. subarcticum Cushman, E. william- Copyrighl © 1985, The Society oFEconomic 1075 0022-3360/85/0059-1075503.00 Paleontologists and Mineralogists and The Paleontological Society 1078 M. A. BUZAS, S. J. CULVER AND L. B. ISHAM TABLE 4—Group means for variables. (See Tables 1 and 2 for key.) Variables Species A B C D E F G H I J K 1 0.4 0.3 0.2 10.9 3.0 3.0 3.7 0.6 0.0 0.0 2.2 2 0.7 0.6 0.3 9.2 1.0 2.0 3.6 0.0 0.3 0.0 1.1 3 0.6 0.5 0.3 15.5 2.0 1.0 3.6 1.0 0.0 0.0 3.0 4 0.5 0.4 0.2 10.6 1.2 1.9 1.9 2.7 0.0 0.0 2.1 5 0.6 0.6 0.2 7.7 1.0 2.0 4.2 0.0 0.2 0.4 1.8 6 0.3 0.3 0.2 10.9 1.1 1.0 2.7 3.8 0.0 0.0 2.2 7 0.4 0.4 0.2 10.8 2.2 2.0 3.7 0.0 0.0 0.0 1.8 8 0.4 0.3 0.2 9.9 1.0 3.0 2.5 1.0 0.0 0.0 2.0 9 0.3 0.3 0.2 9.9 1.0 3.0 1.8 4.2 0.0 0.0 1.8 10 0.6 0.5 0.2 7.9 1.0 2.0 3.9 0.0 1.0 0.0 1.8 11 0.4 0.4 0.2 10.2 1.0 2.0 4.0 0.5 0.0 0.0 2.0 12 0.3 0.3 0.1 7.5 1.0 2.0 0.0 0.0 0.1 0.0 2.0 13 0.5 0.5 0.3 9.3 1.0 2.0 0.0 0.0 0.1 0.0 2.0 14 0.4 0.3 0.2 8.7 1.0 2.0 2.3 0.6 0.0 0.0 2.0 give us some idea of strong similarities among E. excavatum (deep) (14), Haynesina ger- groups. Figures 1 and 3 indicate a strong sim- manica (12). ilarity between E. bartletti (2), E. frigidum Because of the large amount of overlap of (5), and E. subarcticum (10). Figures 1 and these last two subsets, we decided to run a 3 also indicate a close similarity between E. canonical variate analysis on each of the sub- mexicanum (8), and E. cf. mexicanum (9). sets. Figures 2 and 3 indicate once again a close The canonical variate analysis for Elphid- relationship between E. frigidum (5) and E. ium bartletti, E. frigidum, and E. subarcti- subarcticum (10). In addition E. williamsoni cum has N = 90 individuals, h = 3 groups, {\\), E. excavatum (deep) (14), and Haynes- and p = 8 variables. Angularity of margin, ina germanica (12) show a close relationship. porosity, and umbilical boss development An option of the SPSS package is a listing were deleted as variables because for these of the predicted group membership of every three groups they are constants. Because p > observation. In this case each specimen of h there are only h — 1 or two possible ca- every morphological group is assigned to the nonical variates. Table 8 lists the eigenvalues group with the highest probability of mem- and the percent of the variability they ac- bership. In the present analysis, 93% of the count for. Both eigenvalues are statistically 420 specimens were correctly classified. The significant. The mean canonical variates are great variability ofE. excavatum is shown by listed in Table 9 and are plotted in Figure 4. its assignment to six different groups. Only The first canonical variate, accounting for 63% were correctly classified. 78% of the variability, clearly separates the In summary, the analysis allows the place- three groups. The standardized canonical dis- ment of the 14 groups into three sets: those criminant function coefficients shown in Ta- groups which are clearly discriminated from ble 10 indicate that length (thickness) of the the rest, those groups which are fairly well test is the most discriminating variable fol- discriminated from the rest, those groups lowed by the spiral diameter at 90 degrees to which show a good deal of overlap with other gsd. groups. The first set contains E. discoidale (3), E. gunteri (6), E. advenum (1), E. mex- icanum (8), and E. cf mexicanum (9). The TABLE 5—The first three eigenvalues with the percentage second category consists of E. margarita- of variability accounted for: analysis of the 14 groups. ceum (7), E. excavatum (4), and Haynesina Percent of Cumulative orbiculare (13). The third set consists of two Eigenvalue variability percent subsets each containing three groups. These 28.11 46.88 46.88 are Elphidium bartletti (2), E. frigidum (5), 13.22 22.05 68.93 E. subarcticum (10), and E. williamsoni (11), 7.97 13.30 82.22 CENOZOIC ELPHIDIID FORAMINIFERA 1079 TABLE 6—Mean canonical variates for the first three canonical variates: analysis of the 14 groups. Species Mean Mean Mean No. Name CVl CV2 CV3 1 Elphidium advenum 9.11 7.51 2.23 2 E. bartletti -1.40 -2.88 2.64 3 E. discoidale -9.45 5.72 -0.15 4 E. excavatum -1.42 -0.55 -2.46 5 E. frigidum -0.94 -2.30 3.99 6 E. gunteri -7.98 1.92 -4.95 7 E. margaritaceum 0.40 4.99 2.00 8 E. mexicanum 8.00 -1.32 -1.28 9 E. cf mexicanum 8.37 -1.37 -5.19 10 E.
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