Cretaceous Research (1980) 1, 193-206

Multivariate Analysis of Environmentally Controlled Variation in Lugena: Late Maastrichtian, Sweden

J. 0. R. Hermelin

and B. A. Malmgren Department of Geology, Stockholm University, Box 6801, S-113 86 Stockholm, Sweden

Received 18 October 1979 and in revised fornz 24 January 1980

J. 0. R. Hermelin and B. A. Malmgren. Multivariate Analysis of Environmentally Controlled Variation in Lagena: Late Maastrichtian, Sweden. Cretaceous Research (1980) 1, 193-206. Costate forms of Lagena (benthonic foraminifer) have been studied in an uppermost Maastrichtian bore-hole core sequence (28 levels) from southern Sweden. Analysis of a large sample shows that consistent assignment to previously described “species” of costate Lagena is not possible. This observation is supported by multivariate analysis of five morphologic variables which indicates that there are no distinct clusters of specimens along principal component axes associated with general size, number of costae, and relationships between roundness of test/length and number of costae. Specimens with a basal ring differ from specimens with an apical spine and those with no basal structure with regard to average number of costae. They also differ from specimens with no basal structure with regard to relationships between roundness of test/length and number of costae. These characters grade into each other thus preventing them from being used as taxonomic criteria.

Mean ratios of benthonic foraminifers to total benthonic and planktonic foraminifers determined individually for each level are inversely related to mean relative frequencies of costate Lagena and directly related to mean general sizes of costate Lagena. The benthonic/ planktonic ratio has been suggested by other workers to represent a paleobathymetric index across a continental slope and shelf when open marine conditions prevailed. If this were so in the Danish basin at the end of the Cretaceous, costate Lagena would have been relatively less frequent and larger at shallower depths.

As a result of the study, the analyzed specimens are considered as representing a single morphospecies of the costate species Lagena sulcatu. Between-level variation is regarded as ecophenotypic, and within-level variation as natural biologic variation of no taxonomic significance. A total of about 1000 species of-Lagena has been described in the literature which is probably many orders of magnitude too great for a genus with such a simple morphology as Lagena. A revision of the taxonomy of Lagena is, therefore, probably neces- sary on a wide scale.

Department of Geology, Stockholm University, Box 6801, S-l 13 86, Stockholm, Sweden.

KEY WORDS : Benthonic Foraminifera; Biometric analysis ; Cretaceous; Lugena ; Maastrich- tian; Paleoecology; Sweden; Taxonomy.

1. Introduction

The flask-shaped calcareous tests of Lagena are among the most well-known representatives of benthonic Foraminifera. Lagena evolved in the Jurassic and has adapted to a wide variety of environments ranging from the shelf through the deep- sea, and from the tropics through the polar areas.

Four basic morphotypes may be distinguished in Lagena: a spinose form, a costate form with ribs arranged longitudinally in various fashions along the test, a form with a reticulate, usually hexagonal, surface pattern, and an unornamented form. The shape of the test may vary from almost globular to oblong, and this, together with the form of the costae, and other ornamentational and apertural characteristics, form the basis for taxonomic subdivisions of Lagena.

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194 J. 0. R. Hermelin and B. A. Malmgren

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Figure 1. Location of the limestone quarry at Limhamn, southern SW&den.

We have studied a large sample of costate Lagena from a bore-hole core sequence from the Upper Maastrichtian deposits of southern Sweden (Figure 1). We concentrated the study on costate forms because they were the most abundant Lagena in our material. We also found spinose and smooth forms, and forms with a reticulate pattern, but some of these specimens may be referable to other genera such as Amphioryna, Dentalina, Glandulina, Globulina, Nodosaria, Oolina, and Polymorphina.

Since we noticed at an early stage of the study that consistent allocation of our specimens to previously described “species” was not possible, we have applied multivariate morphometric methods for studying the phenotypic variation within the genus. The purpose was to determine whether natural groupings exist, and, if so, whether the morphologic diagnostics of the groups agree with those of previous “species”.

We also present an attempt at paleo-environmental interpretations of morphologic variation and variation in relative frequencies of Lagena.

2. Material and methods

Samples for this study were collected from core D104 drilled in the vicinity of the large limestone quarry at Limhamn, southern Sweden (Figure 1). In this core, which is 188 m long, the Maastrichtian/Danian boundary is located at 67.50 (Malmgren, 1974). Here, the lithology changes from Upper Cretaceous white chalk to Danian bryozoan limestones. A typical boreal Upper Cretaceous planktonic

Multivariate Analysis of Maastrichtian Lagena 195

foraminiferal fauna dominated by Heterohelix striata (Ehrenberg) and Globigerinel- Zoides multispina (Lalicker) is replaced by typical lowermost Tertiary Subbotina pseudobulloides (Plummer) and Globoconusa daubjergensis (Bronniman). The Creta- ceous section lies within the Upper Maastrichtian Bolivinoides petevssoni zone (benthonic foraminifer) of Brotzen (1945) (Malmgren, unpublished).

Twenty eight samples (2 cm slices) were collected at varying intervals throughout the uppermost 32 m of the Upper Maastrichtian section of the core (Table 1). Since the sequence cannot be chronostratigraphically correlated with any other dated sequence because of diachronous biostratigraphic boundaries (Figure 5) (Malmgren, unpublished), the only way of obtaining a rough estimate of the time span of the sequence is to calculate it from the average sedimentation rate of 15 cm per 1000 years given by Hakansson et aE. (1974) for the Maastrichtian white chalk in the central part of the Danish basin. If the sedimentation rate were similar in the Limhamn area and if a compaction of the deposits of 10% be accepted (Hakansson et al., 1974), the sequence would span about 200 000-250 000 years of latest Maastrichtian sedimentation.

Each sample was disaggregated using the Glauber’s salt (sodium sulphate) method (Kirchner, 195S), and washed through 125 pm, 500 pm and 1000 pm screens. Lagena were picked from random splits of the 125 pm-500 pm fraction, The larger fractions were routinely scanned, but did not contain any Lagena.

The number of specimens of Lagena picked from any one sample (Table 1) depends upon the absolute frequencies of benthonic foraminifers, and the propor- tions of Lagena in relation to total benthonic foraminifers. The proportions of Lagena vary between 0.3% and 3.7% (Figure 5). A total of 312 specimens of costate Lagena were picked.

The following dimensions were measured with a Leitz binocular microscope at a magnification of x 160 (Figure 2):

L: Maximum length of the test [Figures 2(A) (B)] L,. : Length of the costae [Figures 2(C) (D) (E)] W X4X : Maximum width of the test measured from the center of the aperture

to the distal part of the costae [Figure 2(F)] W MIN : Minimum width of the test measured from the center of the aperture

to the trough between two costae [Figure 2(F)].

In addition, the number of costae (N,) was counted in each specimen, and the occurrence of an apical spine [Figure 2(H)] or a basal ring [Figure 2(G)] was re- corded.

Table 1. Sampling levels in the Upper Maastrichtian section of core Limhamn D104, and numbers of specimens of Lagena included in the morphometric analyses

.- Depth in Number of Depth in Number of core (m) specimens core (m) specimens

99.75 98.00 97.00 96.00 95.00 94.10 93.00 92.00 91.00 89.75 89.00 87.25 86.00 i 85.00 6

14 29 16 17 24

5

83.90 82.85 81 .oo 80.30 79.30 78.90 77.00 74.50 73.60 72.70 70.85 70.00 69.10 68.00

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196 J. 0. R. Hermelin and B. A. Malmgren

Figure 2. Orientation of the measurements made on Lugena: L, maximum length (A, B); Le, length of the costae (C, D, E); WMAX, maximum width (F); and WMIN, minimum width (F). G shows a specimen with a basal ring, and H shows a specimen with an apical spine.

Table 2. Basic statistical parameters for the length of the test (L), the length of the costae (Lc), the maximum and minimum widths of the test (Wn~x and WMIN), and the number of costae (NC) based on 312 specimens of costate Lagena. X is the mean value expressed in microns for L, L,, WMAX, and

WMIN, s the standard deviation, and V the coefficient of variation

x Confidence s V Observed interval range

L 288.4 282.6-294.2 52.7 18.3 175-500 L, 234.4 229.1-239.7 47.4 20.2 120-460 WMAx 91.4 89.5- 93.3 16.7 18.3 70-175 WMIN 80.8 79.0- 82.6 16.3 20.2 60-160 NC 11.4 10.9- 11.9 4.6 40.5 6-32

Multivariate Analysis of Maastrichtian Lagena 197

Basic statistical parameters for L, L,, WItas, W1\rIN, and N, based on all speci- mens are shown in Table 2. Tests for normality of the distributions show that both the skewness and kurtosis measures based on logarithms of the raw data deviate only slightly from expected values of zero in most instances (Table 3), and thus the distributions approximate log-normality. ,4 log-normal distribution is frequent in dimensional data of foraminifers (Malmgren, 1979). In the multivariate analysis of structure, the specimens have, as a consequence, been analyzed as representing a single sample.

Computer program BMDOlM (Dixon, 1973) was used for the principal com- ponent analysis.

Table 3. Skewness (b,) and kurtosis (6,) coefficients for the distribution of length of the test (L), length of the costae (Lc), maximum and minimum widths of the test (WMAX and WMIN), and number of costae (NC) based on logarithmically transformed raw data. Expected values of both coefficients

are zero in a log-normal distribution

b, b,

0.16 0.35 0.09 0.38

WMAX 0.81 0.32 WMIN 0.84 0.29 NC 0.51 -0.27

3. Results

3.1. Taxonomic study

We have recognized the following “species” or morphotypes of Upper Cretaceous Lagena: L. acuticosta (Reuss), L. amphora (Reuss), L. grahami (Sliter), L. semi- interrupta (Berry), L. semilineata (Wright), L. stratifera (Tappan), L. substriata (Williamson), and L. sulcata (Walker & Jacob). However, individual specimens could often be assigned to two or more “species” because of morphological gradations. To determine whether distinct morphotypes occur in this material, we applied principal component analysis for determining the relationships among

variables L, L,, WIRrAix, W3tIN, and N,, and for determining the structure of the specimen points along the principal component axes. Three principal components account for 9.5% of the variance in these variables, and thus efficiently summarize the phenotypic variation (Table 4). The first principal component is associated with

L, L,, W~r_~x, and W,n, (Table 4), and is (Jolicoeur & Mosimann, 1960 ; Gould, 1967) interpreted as showing size variations. The similarity in loadings indicates isometric relationships among these variables. This shows that the shape of Lagena is essentially the same in specimens of different sizes. The second principal com- ponent, dominated by N,, shows that the number of costae is not size dependent,

Table 4. Principal component analysis based on length of the test (L), length of the costae (L,.), maximum (WMAX) and minimum width (WMIN), and number of costae (NC). The principal com-

ponents were extracted from the correlation matrix

1 2

Eigenvalue 3.08 1.24 Percentage explained 61.5 24.9 Cumulative percentage 61.5 86.4 Eigenvector L 0.50 -0.27

k,X 8.X

-0.39 0.12

WMlN 0:51 0.30 NC 0.10 0.82

3 4 5

0.45 0.20 0.03 9.1 3.9 0.6

95.5 99.4 100.0

0.18 0.80 0.03 0.60 - 0.54 - 0.08

-0.42 -0.22 0.69 -0.37 -0.10 -0.71

0.55 0.08 0.13

198 J. 0. R. Hermelin and B. A. Malmgren

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and thus that specimens with many costae may occur in small as well as in large specimens.

In the third principal component, variables L,. and N,. are inversely related to the

widths (W,t.ix and WU ). This contrasts relatively rounded morphovariants with few short costae, and relatively elongated morphovariants with many long costae (henceforward called the roundness/costation ratio).

If the sample had contained distinctly different morphospecies, we shouid have expected discontinuous distributions of specimens in the principal component space. However, plots of first and second, and first and third principal component scores (Figures 3 and 4) show homogeneous clusters without any tendency for the isolation of subsamples. Thus, no subdivision of the sample is possible either on the basis of general size (first principal component), number of costae (second princi- pal component), or the roundness;‘costation ratio (third principal component). We observed the form variants shown by the third principal component in our material, but also the occurrence of forms intermediate between the extremes, and this is in agreement with the principal component plots (Figures 3 and 4).

We have also tested possible differences in morphology among specimens with an apical spine, a basal ring, and no basal structure. Specimens with a basal ring dominate in our sample (74.736) followed by approximately equal frequencies of specimens with an apical spine (12.Pb) and specimens lacking a basal structure (12.S0,). The students’ t tests show that the general size (first principal component) does not differ among these variants (Table 5). The specimens possessing a basal ring have fewer costae on the average (second principal component) than the other forms (Table 5). H owever, no tasonomic significance can be attached to this feature because of almost complete overlap in the number of costae (Table 5). Furthermore, there is a tendency for the basal-ring group to have rounder tests’with fewer and shorter costae (third principal component) than the group lacking basal structure (Table 5). The apical-spine group is intermediate with respect to this character, but does not differ significantly from the other groups. Overlap in principal component scores, however, prevents the use of this shape difference as a taxonomic criterion (Table 5).

Table 5. t tests of differences in morphology (first three principal components) among specimens with an apical spine, a basal ring, and no basal structure. Y? is the mean and O.R. the observed range of the principal component scores. Figures in parentheses after the R and O.R. values of the second principal component are original values for the number of costae. Numbers in parentheses after the

t values are degrees of freedom. *** denotes the 0.1 ‘I(, level of significance

First principal component

8 O.R.

Second principal component

9 O.R.

Third principal

x componPnt

O.R.

Apical spine -0.52 - 2.59-6.45 0.45 (13.1) - 3.43-2.37 (7-28) 0.07 - 1.98-1.58 Basal ring 0.06 -2.98-8.20 -0.18 (10.6) -3.33-2.42 (6-27) -0.06 - 2.25-2.37 No basal structure 0.20 - 2.43-4.16 0.61 (14.7) -4.14-3.51 (6-32) 0.31 - 1.40-2.37

t tests: First principal component (general six)

Basal ring No basal structure Apical spine 1.94 (271) 1.73 (77) Basal ring 0.47 (270)

Second principal component (number of costae) Basal ring No basal structure

Apical spine 3.80*** (271) 0.53 (77) Basal ring 4.28*‘” (270)

Third principal component (roundness/costation ratio) Basal ring No basal structure

Apical spine 1.25 (271) 1.32 (77) Hasal ring 3.39*** (270)

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3.2. Paleoecological study

The means of the first three principal component scores for each level are plotted in stratigraphic order in Figure 5. Samples with more than five measurable specimens were included (Table 1). The fluctuations in general size (first principal component) and the width/costation ratio (third principal component) are random as shown by regression analyses of the relationships between core depth and mean principal component scores (Table 6). The regression coefficient for the means of the second principal component deviates from zero which indicates that the mean number of costae increases upwards in the sequence (Table 6).

These sequences were compared to series in time based on relative frequencies of costate Lagena in relation to total benthonic foraminiferal frequencies (hence- forward called percentage Lagena), and relative frequencies of benthonic fora- minifera in relation to total benthonic and planktonic foraminifers (henceforward called the benthonic/planktonic ratio) (Figure 5).

The percentages of Lagena and benthonic/planktonic ratios are inversely related (Table 7) indicating that Lagena is relatively more abundant when benthonic foraminifers are rare compared to planktonic forms. A positive correlation between the means of the first principal component and the benthonic/planktonic ratios (Table 7) indicates that general size of Lagena is larger at levels with high benthonic frequencies.

We believe that these correlations among independent variables must indicate a common response to some environmental factor. Little is known about the detailed environmental preference of Lagena. However, interpretations have been made concerning the benthonic/planktonic ratio. Several authors have shown that in areas where the continental shelf is openly connected to the adjacent ocean, this ratio generally increases with decreasing water depth from the continental slope to the shelf (Phleger, 1951; Phleger, 1954; Grimsdale & van Morkhoven, 1955; Smith, 1955; Either, 1969; Murray, 1976). This is based on the fact that planktonic foraminifers are primarily oceanic and that their presence in shelf sediments is essentially due to transport from their normal habitat (Murray, 1976). However, in enclosed seas like the Persian Gulf, the benthonic/planktonic ratio is not primarily related to water depth, but to the passage of oceanic water to the enclosed sea (Lutze, 1974; Sarnthein, 1975; Murray, 1976). Al so, surface circulation patterns may prevent transport of planktonic foraminifers onto the shelf yielding benthonic/ planktonic ratios of 1OOqb (e.g. Long Island Sound, U.S.A.; Murray, 1969).

Table 6. Regression analyses of the relationships between core depth (independent variable) and the means of the first three principal component scores for each level plotted in stratigraphic order (Figure 5). b is the slope of the regression line, sb the standard error of b, and z a normal deviate. ** marks the 1 “A level of significance. A b value of zero would be expected in a sequence lacking trend

b Sb z

First component Second component Third component

- 0.0012 0.0142 0.09 - 0.0402 0.0125** 3.21** + 0.0051 0.0081 0.63

Table 7. Correlation analyses of time series based on the first three principal components, benthonic/ planktonic ratios, and percentages of Lagena. ** denotes significance at the 100 level

Percentage First Second Third Lagena component componat component

Benthonic/planktonic ratio Percentage Lagena

-0.59X’ + 0.54’” + 0.08 - 0.41 -0.33 + 0.07 + 0.24

Multivariate Analysis of Maastrichtian Lugena 203

Several workers, assuming open marine conditions, have applied benthonic/ planktonic ratios for estimating approximate depths of deposition in sediments from the Cretaceous and the Tertiary (Grimsdale & van Morkhoven, 1955 ; Basov & Belyaayeva, 1964; Clark & Bird, 1966; Either, 1969; Hart & Tarling, 1974). If the assumptions were met in the Limhamn area, the generalizations concerning the relationship between the ratio and absolute water depth made by Murray (1976) would indicate that the sediments of core D104, in which the ratio varies between 23% and 99o/o (Figure 5), were deposited in environments ranging from the upper- most slope through the inner shelf (Malmgren, unpublished). This is in agreement with the results obtained by Hakansson et al. (1974) who, using other methods, showed that the Maastrichtian white chalk of Scandinavia was deposited within the euphotic zone, but generally at greater depths, extending down to about 250 m.

If the benthonic/planktonic ratio does represent a paleobathymetric index in the Limhamn area, the negative correlation with percentage Lagena (Figure 5 ; Table 7) indicates that Lagma was relatively more frequent at greater depths. Phleger (195 1) observed such a tendency in modern shelf sediments from the Gulf of Mexico. Similarly, the mean size would have been smaller at greater depths than at shallower depths as indicated by the positive correlation with the first principal component (Figure 5; Table 7). Several species of benthonic foraminifers are known to live in symbiosis with algae (Boltovskoy, 1963; Riittger, 1972; Hansen, 1975; Buchardt & Hansen, 1977). No such observation has been made in Lagena, but it is reasonable that such a symbiotic relationship, if it existed in Lagena, could enhance growth in shallow-water assemblages, thus explaining the mean size variation.

The number of costae (second principal component), showing a trend in our samples (Figure 5 ; Table 7), may also be controlled by some ecologic parameter in turn varying in a systematic way, but not recorded in the sediments. This is probably a more likely explanation of the trend than assuming true evolutionary changes involving shifts in the genotype because of the relatively short time span of the sequence. The ornamentation (length of costae and keel) in Recent Bolivina argentea Cushman has been shown to be more strongly developed in biotopes with high oxygen contents in the bottom waters (Lutze, 1964). In Miocene and Pliocene Uvigerina, Bolivina, and Cassidulina, the ornamentation is strongly bound to the sediment type (Hendrix, 1958).

4. Discussion

This study has shown that there is no basis for taxonomic subdivision of the upper- most Cretaceous Lagena from Limhamn, although several previously described “species” were recognized in the material. The problem we had in differentiating our specimens is equivalent to that frequently experienced by paleontologists, namely that of classifying forms intermediate between extremes. This situation, an indication of a poorly conceived taxonomical subdivision, is in most cases caused by over-splitting of a group of organisms which could be shown by variational statistical analysis to represent a homogeneous unit of specimens (morphospecies) containing naturally varying morphs. Also, the sample size is frequently not large enough to allow detailed inferences about phenotypic variation and, in such a case, the sample should not be used as a basis for creating new morphospecies. It must always be borne in mind that a morphospecies, and thus not only a biospecies, is represented by a population and not by single specimens. We fully agree with Lutze (1964) who wrote: “. . . no new species should be erected if material is available from one locality only and no attempt has been made to find eventual transitional populations from other biotopes” and “. . . it is the duty of any taxonomist to prove the inde-

204 J. 0. R. Hermelin and B. A. Malmgren

pendence of his new species himself according to the momentary stage of research (variation studies included)“.

The study has also indicated that the morphology of costate Lugena is probably controlled to a high degree by the environment. Therefore, it is likely that several of the previously described “species” of costate Lagena are merely ecophenotypic variants and not genotypically different. Thus we believe that the specimens we have studied represent a single morphospecies of costate Lugena. The interlevel differences in certain morphologic characteristics are due to environmental in- fluences and the variation at different individual levels is due to natural biologic variation. None of these is of any taxonomic significance.

We propose that all the Limhamn specimens be referred to Lugena sulcata (Walker & Jacob). L. sulcata, the type species of Lagena, was originally described from modern English coastal sediments (Walker &Jacob, 1798), but its diagnostics, as given by Walker & Jacob (1798), are very general and agree completely with our Upper Cretaceous morphotypes of Lagena. The species was only described as having a round, striated, and furrowed flask “wormshell”. In later descriptions, the species is also not clearly defined, but from the illustrations and discussions of several authors, it can be inferred that L. sulcata is characterized by a round to ovate test with longitudinal costae running from the posterior end of the test and with the neck ending in a simple aperture. Parker & Jones (186.5) and Brady (1884), although describing several different morphotypes, considered all known living forms of Lagena as varieties of a single species, L. sulcata, because of the extreme variability in shape and ornamentation. This is a strong support for our inferences about what we consider the Upper Cretaceous representatives of L. sulcata.

A total of about one thousand “species” of Lagena has been described from Jurassic through Recent deposits. This seems to us an excessively high number for an organism with such a simple morphology as Lugena. Therefore, the situation found here may occur in other morphotypes of Lagena, and we believe that a revision of the taxonomy of Lagena is necessary. Such a revision could only be carried out through careful multivariate biometric analysis of morphologic variables like the ones we have used here. The analyses would have to be based on long- ranging sequences containing adequate numbers of specimens from widely different environments to clarify phenotypic relationships.

5. Summary

Costate forms of the benthonic foraminiferal genus Lagena have been studied in a 32 m long uppermost Maastrichtian section of core D104 from Limhamn, southern Sweden (Figure 1). The sequence is referable to the uppermost part of the Upper Maastrichtian Bolivinoides peterssoni zone of Brotzen (1945). A total of 312 speci- mens of costate Lugena was analyzed from 28 different stratigraphic levels (Table 1). Five morphologic variables (length of the test, length of the costae, maximum and minimum widths of the test, and number of costae) were measured in each speci- men and the form of the ornamentation at the basal part of the test was recorded (basal ring, apical spine, or no basal structure) (Figure 2).

(1) In addition to costate Lugena, the material contains other calcareous monotha- lamous forms with smooth or hispid surface, and a few specimens with a reticulate pattern some of which may be referable to Lugena.

(2) A few previously described “species” of costate Lagena were recognized, but consistent assignment was not possible because the majority of the specimens are intermediate between two or more “species”.

Multivariate Analysis of Maastrichtian Lagena 205

(3)

(4)

(5)

(6)

Principal component analysis was carried out in an attempt to subdivide the specimens into biometrically defined groups that could form a basis for the definition of different morphospecies. Three principal component axes, accounting for 95% of the variation in the space of the five morphologic variables, are associated with variation in general size (first principal com- ponent), number of costae (second principal component), and roundness of test/length of costae relationships (third principal component) (Table 4). The result thus indicates that the number of costae is independent of the general size. Plots of the component scores for these axes (Figures 3 and 4) show that the specimens do not cluster into distinct groups thus indicating that the specimens form a homogeneous group.

Specimens with a basal ring (74.70,; of all costate Lugena) have fewer costae (second principal component) on average than specimens with an apical spine (12.876) and specimens lacking basal structure (12.57;) (Table 5). The speci- mens with a basal ring also tend to have rounder tests with fewer and shorter costae (third principal component) than the specimens with an apical spine, but there is no difference compared to the specimens without basal structure. None of these differences can be used as a taxonomic criterion, because individual component scores overlap almost completely despite the differences in means.

Plots in stratigraphic order of the score means of the first three principal com- ponents for each level show that the number of costae (second principal component) increases gradually with time (Figure 5). General size (first principal component) of costate Lagena is directly related to the percentage of benthonic foraminifers relative to total benthonic and planktonic fora- minifers (benthonic/planktonic ratio) (Figure 5). The relative frequencies of costate Lagena in relation to total benthonic foraminifers are inversely related to the benthonic/planktonic ratio (Figure 5). The benthonic/plank- tonic ratio has been suggested by several workers to represent a paleobathy- metric index (higher values in near-shore deposits) in areas where a continental shelf was openly connected to the adjacent ocean. If this were so also in the Limhamn area at the end of the Cretaceous, costate Lugena would have been relatively more frequent at depths greater than that of the majority of benthonic foraminifers. Also, the mean size of costate Lugena would have been larger at shallower depths.

Because there are no discontinuities in distributions of the. morphologic characteristics (first three principal components), the specimens are here considered to represent a single morphospecies of costate Lagena, L. sulcata. The morphologic differences among stratigraphic levels are considered to be due to ecophenotypic va’riation, and the morphologic variation within different stratigraphic levels is regarded as natural biologic variation, neither being of any taxonomic significance. An excessively high number of “Lagena” has been described in the literature (about one thousand), but because of the simple morphology of this genus, this is probably much too many. A revision of the taxonomy of Lqgena would therefore seem desirable.

Acknowledgments

We wish to thank James P. Kennett (University of Rhode Island, Kingston, R.I.) for comments on the manuscript. We also thank BGrje Sgwensten and Kristina Edstriim for secretarial assistance, and Solveig Jevall and Inger Arnstriim for the drafting work.

206 J. 0. R. Hermelin and B. A. Malmgren

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