BRIAN T. HUBER TO PALEOBIOLOGY Ontogenetic Morphometries of Some Late Cretaceous Trochospiral Planktonic Foraminifera from the Austral Realm SERIES PUBLICATIONS OF THE SMITHSONIAN INSTITUTION Emphasis upon publication as a means of “diffusing knowledge” was expressed by the first Secretary of the Smithsonian. In his formal plan for the institution, Joseph Henry outlined a program that included the following statement: “It is proposed to publish a series of reports, giving an account of the new discoveries in science, and of the changes made from year to year in all branches of knowledge." This theme of basic research has been adhered to through the years by thousands of titles issued in series publications under the Smithsonian imprint, commencing with Smithsonian Contributions to Knowledge in 1848 and continuing with the following active series: Smithsonian Contributions to Anthropology Smithsonian Contributions to Botany Smithsonian Contributions to the Earth Sciences Smithsonian Contributions to the Marine Sciences Smithsonian Contributions to Paleobiology Smithsonian Contributions to Zoology Smithsonian Folklife Studies Smithsonian Studies in Air and Space Smithsonian Studies in History and Technology In these series, the Institution publishes small papers and full-scale monographs that report the research and collections of its various museums and bureaux or of professional colleagues in the world of science and scholarship. The publications are distributed by mailing lists to libraries, universities, and similar institutions throughout the world. Papers or monographs submitted for series publication are received by the Smithsonian Institution Press, subject to its own review for format and style, only through departments of the various Smithsonian museums or bureaux, where the manuscripts are given substantive review. Press requirements for manuscript and art preparation are outlined on the inside back cover. Robert McC. Adams Secretary Smithsonian Institution SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY • NUMBER 77 Ontogenetic Morphometries of Some Late Cretaceous Trochospiral Planktonic Foraminifera from the Austral Realm Brian T. Huber SMITHSONIAN INSTITUTION PRESS Washington, D.C. 1994 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY ABSTRACT Huber, Brian T. Ontogenetic Morphometries of Some Late Cretaceous Trochospiral Planktonic Foraminifera from the Austral Realm. Smithsonian Contributions to Paleobiology, number 77, 85 pages, 37 figures, 10 plates, 15 tables, 1994.—Biometric analysis of ontogenetic changes in test morphology is employed to determine the taxonomic status of several trochospiral planktonic foraminiferal species from southern high latitude Upper Cretaceous sediments. Ontogenetic morphometric data obtained from specimens of Hedbergella sliteri Huber, Archaeoglobigerina australis Huber (both micromorph and normal-sized populations), and Archaeoglobigerina mateola Huber are compared with topotype populations of Hedbergella holmdelensis Olsson, H. monmouthensis (Olsson), Costellagerina pilula (Belford), and Rugoglobigerina rugosa (Plummer). Southern South Atlantic specimens of Archaeoglobigerina bosquensis Pessagno and Archaeoglobigerina cretacea (d’Orbigny) are also analyzed for comparison. Numerous biometric data, measured from exterior observations of whole tests, contact microradiographs, and Scanning Electron Microscope (SEM) micrograph images of serially dissected foraminifera, are used to characterize developmental changes in morphology of the planktonic foraminiferal species. The most useful variables for discriminating taxonomic differences are discussed for each method. Results indicate that the ontogenetic morphometric approach to study of planktonic foraminifera can be effectively used to resolve problems in taxonomic classification, particularly for species that appear homeomorphic in exterior view. This approach was particularly useful for demonstrating that the ontogenetic morphologies of A. australis, C. pilula, and R. rugosa are very different and, therefore, previous assignment of A. australis morphotypes to various species of Rugoglobigerina and Costellagerina were incorrect. This study also demonstrates that the growth morphology of the new high latitude species H. sliteri significantly differs from H. holmdelensis and H. monmouthensis, thus confirming recognition of H. sliteri as a valid taxon. However, taxonomic uncertainty persists for some high latitude morphotypes that have external characteristics similar to R. rugosa (e.g., faint umbilical apertures, faint costellae that are meridionally aligned, presence of tegilla), but ontogenetic morphologies more similar to A. australis. Morphologic changes during ontogeny, including changes in (1) shell pore characteristics (pore diameter, pore density, and porosity), (2) rates of increase in cross-sectional chamber area, (3) apertural position, (4) chamber surface ornamentation, and (5) umbilical diameter, were used to recognize ontogenetic stages in the foraminiferal shells. These include the prolocular, juvenile, neanic, and adult stages. The growth patterns of H. holmdelensis, H. monmouthensis, H. sliteri, and C. pilula are very uniform and do not show discemable transitions from the juvenile to neanic and adult stages. All four ontogenetic stages were recognized in A. australis, A. bosquensis, A. mateola, A. cretacea, and R. rugosa, although the abruptness of the transitions and the chamber number where these transitions occur are variable within and between species. Recognition of these growth stages enables taxonomic identification of pre-adult morphologies that occur in smaller size fractions. This is particularly useful since these smaller forms have dominated in unstable environments such as the highly seasonal circum-antarctic oceans. Official publication date is handstamped in a limited number of initial copies and is recorded in the Institution’s annual report, Smithsonian Year. Series cover design: The trilobite Phacops rana Green. Library of Congress Cataloging-in-Publication Data Huber, Brian T. Ontogenetic morphometries of some Late Cretaceous trochospiral planktonic foraminifera from the austral realm / Brian T. Huber. p. cm. — (Smithsonian contributions to paleobiology ; no. 77) Includes bibliographical references. 1. Foraminifera, Fossil. 2. Paleontology—Cretaceous. 3. Foraminifera—Morphology. I. Title. II. Series. QE701.S56 no. 77 [QE772] 560 s-dc20 [563M2] 93-27089 ® The paper used in this publication meets the minimum requirements of the American National Standard for Permanence of Paper for Printed Library Materials Z39.48—1984. Contents Page Introduction. 1 Acknowledgments. 4 Materials ...... 4 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY Hedbergella sliteri Huber, 1990 . 25 Observations of the Test Exterior.25 Observations of the Test Interior.25 Initial Whorl.25 Penultimate Whorl.25 Ontogenetic Growth Curves.25 Porosity.25 General Remarks.29 Genus Costellagerina Petters, El-Nakhal, and Cifelli, 1983 . 29 Type Species.29 Description.29 Remarks .29 Costellagerina pilula (Belford, 1960). 29 Observations of the Test Exterior.29 Observations of the Test Interior.29 Initial Whorl.29 Penultimate Whorl.29 Ontogenetic Growth Curves.29 Porosity.29 General Remarks.32 Genus Archaeoglobigerina Pessagno, 1967 . 32 Type Species.32 Description.32 Remarks .32 Archaeoglobigerina australis Huber, 1990 . 34 Observations of the Test Exterior.34 Observations of the Test Interior.34 Initial Whorl.34 Penultimate Whorl.34 Ontogenetic Growth Curves.34 Porosity.34 Phenotypic Variability.34 Premature Termination of Growth.34 Environmental-related Size and Morphology Differences.37 Heterochrony.40 General Remarks.40 Archaeoglobigerina bosquensis Pessagno, 1967 . 41 Observations of the Test Exterior.41 Observations of the Test Interior.41 Initial Whorl.41 Penultimate Whorl.41 Ontogenetic Growth Curves.41 Porosity.41 General Remarks.41 Archaeoglobigerina cretacea (d’Orbigny, 1840). 44 Observations of the Test Exterior.44 Observations of the Test Interior.44 Initial Whorl.44 Penultimate Whorl.44 Ontogenetic Growth Curves.44 Porosity.44 General Remarks.44 Archaeoglobigerina mateola Huber, 1990 . 46 Observations of the Test Exterior.48 NUMBER 77 V Observations of the Test Interior.48 Initial Whorl.48 Penultimate Whorl.48 Ontogenetic Growth Curves.48 Porosity.48 General Remarks.48 Genus Rugoglobigerina Bronnimann, 1952 . 51 type Species.51 Description.51 Remarks .51 Rugoglobigerina rugosa (Plummer, 1927). 51 Observations of the Test Exterior.51 Observations of the Test Interior.51 Initial Whorl.51 Penultimate Whorl.51 Ontogenetic Growth Curves.51 Porosity.51 General Remarks.51 Ontogenetic Comparisons.54 Hedbergella holmdelensis, H. monmouthensis, and H. sliteri .54 Costellagerina pilula .54 Archaeoglobigerina australis .57 Archaeoglobigerina bosquensis .57 Archaeoglobigerina cretacea .57 Archaeoglobigerina mateola .57 Rugoglobigerina rugosa .58 Summary and Conclusions.58 Literature Cited.61 Plates.65 Ontogenetic Morphometries of Some Late Cretaceous Trochospiral Planktonic Foraminifera from the Austral Realm Brian T. Huber Introduction A stable taxonomic framework is of paramount importance in all faunal analyses for biostratigraphic, paleoclimatic, and paleoceanographic reconstructions. Therefore, the first and most important stage in any paleontological study should be to accurately identify fossil species using as many morphologic criteria as preservation will allow. Identification depends, however, on an adequate knowledge of the species in question, including its range of morphologic variability in space and time, which is lacking for most fossil groups. Although limitations of the fossil record prevent complete attainment of this information, the continuing refinement of stratigraphic knowledge on a global scale affords a considerably improved basis for correlation and a more detailed knowledge of species distributions. Nearly all taxonomic schemes used in the classification of foraminifera are based on the external morphology of the adult shell, and have thus overlooked considerable ontogenetic information preserved in the early growth stages. Small sized (<150 pm) planktonic foraminifera are often ignored in biostratigraphic studies because of the difficulty in relating the simpler morphologies of juvenile specimens with the more complex adult morphotypes of the same species. Because early growth stages are often obscured by the addition of chambers and shell thickening during the development of involute taxa, the ontogenetic morphology of whole specimens cannot be characterized using standard methods of light microscope or scanning electron microscope (SEM) observation of the test exterior. Some specialists have used internal and external shape characteristics of thin-sectioned planktonic foraminifera as a Brian T. Huber, Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560. basis for species identification (see Sliter, 1989, and references therein). This approach is particularly useful for biostratigra- phic correlation of indurated carbonate sequences that will not yield isolated specimens using conventional disaggregation methods. Among the criteria used to identify species in thin-section are the ontogenetic changes in chamber size and shape and wall microstructural characteristics as determined from axial views. Taxonomic accuracy is diminished using this approach, however, because of limitations of using a two- dimensional rather than three-dimensional view. Although the general pattern of developmental change in planktonic foraminiferal morphology was recorded for both fossil and modem populations by several authors (e.g., Rhumbler, 1911; Parker, 1962; Banner and Blow, 1967; Olsson, 1972; Blow, 1979), few detailed ontogenetic studies were pursued until recently. A significant advance was made by Huang (1981) who used a test dissection and SEM observation method to portray the ontogenetic morphology of several Recent and Neogene species. Sverdlove and B6 (1985) subsequently described a method for obtaining ontogenetic morphometric information from light microscopic analysis of planktonic foraminifera embedded in plastic. Their approach is limited to Recent or exceptionally well preserved fossil specimens which are optically transluscent. In a study of the planktonic foraminiferal species Globigerinoides sacculifer (Brady) and G. ruber (d’Orbigny) recovered from surface plankton tows, Brummer et al. (1986, 1987) identified five developmental stages, designated as the prolocular (= embry¬ onic), juvenile, neanic, adult, and terminal (= reproductive) stages. These were defined on the basis of significant quantitative and qualitative changes in test morphology (e.g., test size, chamber inflation, apertural position, etc.), as well as changes in vital behavior observed in laboratory cultures. All of the above authors convincingly demonstrated the importance of ontogenetic analyses in improving taxonomic classification 1 2 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY New FIGURE 1.—Localities of land-based and deep-sea foraminiferal samples discussed in this study. schemes. They further emphasized potential applications of ontogenetic information in phylogenetic reconstructions, test¬ ing of evolutionary models, as well as improving biostratigra- phic resolution, particularly within paleoenvironmentally stressed habitats. A need for extensive revision of taxonomic concepts for several southern high latitude planktonic foraminiferal groups was recognized by Huber (1987, 1988a) in a study of upper Campanian-Maastrichtian assemblages from Seymour Island in the northern Antarctic Peninsula (Figure 1). Species identified by Sliter (1977) as Hedbergella monmouthensis (Olsson), Rugoglobigerina pilula Belford, and Ruglobigerina rotundata Bronnimann from Falkland Plateau Deep Sea Drilling Project (DSDP) Site 327 were found among the shallow marine Antarctic foraminiferal assemblages. However, comparison with type specimens of these species revealed significant morphologic differences. Moreover, comparison of published SEM micrographs from the Cretaceous southern high latitude studies of Sliter (1977), Krasheninnikov and Basov (1983), and Webb (1973) revealed little agreement in species concepts for non-keeled globigerine taxa. Illustrations of the problematic high latitude morphotypes are reproduced in Plate 1. The taxonomic uncertainties were not resolved in the Huber (1988a) Antarctic foraminiferal study, as the problema¬ tic forms were morphologically diverse. Small (<200 |im) normalform specimens with umbilical-extraumbilical apertures (Figure 2 a-d), kummerform specimens with umbilical to slightly extraumbilical apertures (Figures 2e-h), and large normalform specimens with umbilical apertures (Figures 2/-/) were tentatively assigned to Rugoglobigerina ? sp. 1. and Rugoglobigerina ? sp. 2. Analysis of Cretaceous planktonic foraminifera from a number of Ocean Drilling Program (ODP) Sites recently drilled in the circum-Antarctic region (Figure 1) revealed abundant specimens identical to the problematic taxa described from the Falkland Plateau and Antarctic Peninsula with a similar range of morphologic variability. These were formally described as Archaeoglobigerina australis, A. mateola , and Hedbergella sliteri by Huber (1990) and are considered to have been endemic to the Austral Biogeographic Realm during late Campanian-Maastrichtian time (Huber, 1990, 1991a, 1992a; Quilty, 1992). The ontogenetic morphometric approaches described in this study are utilized with several goals in mind. First, the study will verify that the newly described Austral Realm species are not ecophenotypic variants of species previously described from lower latitude regions. The second goal is to establish the range of phenotypic variability of these austral taxa. The morphologies of small forms (referred to as neanic forms or micromorphs) are compared to the interior, pre-adult morphologies of large (gerontic) adults to establish NUMBER 77 3 MICROMORPH (0.162 mm) KUMMERFORM ECOMORPH (0.213 mm) NORMALFORM ECOMORPH (0.410 mm) FIGURE 2. —Micromorph, kummerform adult, and normalform adult planktonic foraminifera from Seymour Island (northern Antarctic Peninsula) previously designated by Huber (1988a:207, figs. 29.1-29.14, 30.5-30.10) as Rugoglobigerinal sp. 1, but presently identified as Archaeoglobigerina australis Huber. Microradiographs of each specimen (b,f, j) show the chamber arrangement in the penultimate and earlier whorls, a-d: micromorph from sample SI-165; e-h: kummerform ecomorph from sample SI-165; i-l: normalform ecomorph from sample SI-415. Maximum test diameters in parentheses. 4 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY that they are conspecific. Finally, topotypes of two Late Cretaceous species that have meridionally costellate ornamen¬ tation will be compared with high-latitude forms that bear faintly similar surface architecture to determine whether their ontogenetic morphologies are similar. Results from this study will lead to a better understanding of the phylogenetic relationships among trochospiral Austral Realm taxa. Ackowledgments. —Part of this study was undertaken while I was a Ph.D. candidate at The Ohio State University. I am very grateful to Peter -N. Webb, William I. Ausich, Stig M. Bergstrom, and Larry Krissek (all at OSU) for their comments on an early draft of this manuscript, and to Kou-Yen Wei (Yale University) and Bill Sliter (USGS) for their careful reviews and helpful sugggestions on a later draft. I would also like to thank Peter-N. Webb for providing the resources to conduct my biometric research and Larry Krissek for making his x-ray machine available for my usage. Sample material was kindly sent to me by George C. Chapronifere (Bureau of Mineral Resources, Australia), Richard K. Olsson (Rutgers University), and the staff at the Deep Sea Drilling Project East Coast Core Repository (Lamont-Doherty Earth Observatory). Many thanks to Liz Valiulis and Chris Hamilton (U.S. National Museum) for their help with preparation of the illustrations and Mary Parrish (U.S. National Museum) for drawing the foraminifera shown in Tables 2 and 3. Financial support from the Friends of Orton Hall Geology Fund (The Ohio State University) and the Geological Society of America is also gratefully acknowl¬ edged. Materials A total of 473 specimens of nine different planktonic foraminiferal species were analysed in this study. The sample localities are shown in Figure 1 and include material from: (1) lower to middle Maastrichtian Samples 113-689B-28X-3, 83-87 cm, 113-18X-2, 119-123 cm, 113-690C-19X-3, 119- 123 cm, and 113-690C-20X-4, 96-98 cm all from ODP Leg 113 Sites 689 and 690, drilled on Maud Rise, Weddell Sea (64°-65°S, 1°-3°E, 2084-2920 m water depth; see Huber, 1990); (2) lower Maastrichtian Sample 71-511-24-5, 69-71 cm, DSDP Site 511, recovered from Falkland Plateau, southern South Atlantic (51°S, 47°E, 2,589 m depth; see Krashenin- nikov and Basov, 1983); (3) lower to middle Maastrichtian Sample 36-327A-10-3, 22-24 cm from DSDP Site 327, from Falkland Plateau, southern South Atlantic (52°S, 46°W, 2410 m depth; see Sliter, 1977); (4) samples 165 and 415 from the lower Maastrichtian of the Lopez de Bertodano Formation on Seymour Island, Antarctic Peninsula (64°S, 57°W; see Huber, 1988a); (5) Maastrichtian samples from the Kemp Clay, Austin County, Texas, (New Zealand Geological Survey samples F101166 and F101167 provided by Dr. P.-N. Webb); (6) lower Maastrichtian Navesink Formation (sample NJK-126), and middle Maastrichtian Redbank Formation, (sample NJK-3) from New Jersey (provided by R.K. Olsson, Rutgers Univer¬ sity); and (7) Santonian Toolonga Calcilutite, sample #71640043, Pillawara Hill, Western Australia (provided by Dr. G. Chaproniere, Bureau of Mineral Resources, Australia). Approach to Study Sample Preparation Sediment samples were dissaggregated in water by gentle stirring over a warm hotplate for five to ten minutes, then ultrasonically cleaned for several seconds to two minutes, stirred again and wet-sieved through a 63 pm screen. The sieved residues were ultrasonically cleaned again for a few seconds, then dried and picked. External Morphology Conventional classification schemes and phylogenetic re¬ constructions of planktonic foraminifera are primarily based on observation of the external morphology of the test (Tables 1-3). Therefore, all foraminiferal groups in this study are illustrated with SEM micrographs showing the standard umbilical, edge, and spiral views and enlarged views of important external structures. Measurements of apertural height/width ratios (A h /A w ) on specimens with extraumbilical apertures and test breadth/diameter ratios (B/D) (Figure 3, Table 4) were taken using a stereomicroscope with a camera lucida attachment, a mouse driver, and a digitizing tablet linked to a personal computer. Bioquant tm and Optimas 1 ™ biometrics software were used to collect measurements from the digitized images. B FIGURE 3.—Biometric variables measured from external views of planktonic foraminifera. Apertural height/width ratios measured only on specimens showing extraumbilical apertures. Variables include: A h = apertural height; A w = apertural width; B = test breadth; D = test diameter. TABLE 1.—Contrasting hierarchical schemes used to taxonomically subdivide the Rotaliporacea and Globotruncanacea (sensu Loeblich and Tappan, 1988). NUMBER 77 oo V oo 3 2 r- r~ O' £ a s r~- \o O' D- i O s 4) § 0' O' UJ .-t .a r~ 7? 3 1 f c vc c 3 O' 6 *1 *5 P c £ :0 O u. u « PQ ■o o c a; 2 . T3 • lis c u-. . «- 1 ° & ° 8 8 £ 8 ■3 q. = O *o • -c a I c 8 « Xl CL n) x . ~-s u ^ a I § I 8 u £5 „ c a £ T3 V3 fc M U 8 8.1 8.1 co *J N (73 e s W e u ; a : E CO C O i il 1 ! 3 "w 3 3 CO 2 Urn c ; Li O Lx C/3 I! c -g « CL u ■c ja o r- 8 £ « o a S oj a Cm O § | 8 T3 2 1 a 1 3* 1 8. *3 • 0 1 2 CO ■5 ■a C 8 0.1 •c £ fill I 11 ? i ■& Q. u 3 ^ C o -5 2 § *CO 2 *• | ■o * • ^ fli 2 2L -c g D " 00 «& .5 O- — o 8 c I ,3 cd _ o u t3 t— IP « T3 u- O ° S £ g E I a w => M 8.! cd *-* i o> .3 ^ 4J 2 o t3 . C V CO a) B- 73 g.i£ cd *0) o c 0-> £ U 3 8 !■ j) l*a s x cS X 00 I U S £ & 8 co 8 8 g.-8 | ^03 o ^ - S o 8 O a F - X C M t 3 a -a s a- S X - £ 0 o. S M§ & jc CO O Z *o o Z 3 CO co 3 O ■3 x c o *♦3 2 c 0) o & 2 a. .S u Tr> V 5 8.1*8 ° 3 -2 § S " CO S tu Q P -d £ o •3 o . _ 8. s Cl 3 O a. o ± a ^ 3 o «- CO w ^ . 3 w c ^ O) O co (U — x r; w u SP a S 8. £ a S _ « O 4) CO > '' *3 2 13 w CO 0> 3 ab«I| o E £ U &b *0 0) o Z o Cl O o "5 3 2 § E s £ O 1 g 1 CO C *3 0 5 >v 3 .2 1 8. (1 c3 JD 3 CO c 3 0 8. on Table 2.—Classification scheme used by Loeblich and Tappan (1988) to distinguish genera included in the Rotaliporacea. 6 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY Table 3.—Classification scheme used by Loeblich and Tappan (1988) to distinguish genera included in the Globotruncanacea. NUMBER 77 7 Table 4. —Biometric data obtained from external observations and microradiographs of species discussed in this study. 8 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY Rugoglobigerina rugosa Texas Kemp Clay r- C cn £ o 00 03 2 CM 4.43 (0.36) 3.75-5.25 5.31 (0.47) 4.50-6.00 98% 55 O i 0.21 (0.06) 0.09-0.34 CD ID CM O 0.64 (0.09) 0.27-0.79 1.29 (0.12) 0.03-1.52 none common Archaeoglob. cretacea DSDP 511, 34-4, 1-3 early Campanian 5 O CO 5.16 (0.39) 4.50-5.75 5.00 (0.37) 4.50-5.75 55 N O) vP 5 s O co j 0.29 (0.04) 0.20-0.36 CD ID CO CO CD 0.47 (0.06) 0.31-0.63 1.11 (0.12) 0.92-1.28 C o E E o o CD C o c Archaeoglob. mateola ODP 690C, 20-4, 96-98 middle Maastrichtian 6 4.23 (0.53) 3.00-5.50 4.43 (0.59) 3.75-5.75 55 CO K 5 s - O co ! 0.19 (0.04) 0.13-0.30 O N- CM ID 960-990 (600) 690 0.99 (0.12) 0.77-1.23 c o E E 8 a> c o c Archaeoglob. bosquensis DSDP 511, 47-5, 27-29 to c <3 'c o c OJ CO 4.23 (0.53) 3.00-5.50 4.64 (0.34) 4.00-5.50 vp 5 s - CO CO 55 m m i 0.19 (0.04) 0.13-0.30 ID CO CM O co 0.68 (0.08) 0.52-0.85 1.03 (0.21) 0.74-1.47 0) o5 k— a> c o c Archaeoglob. australis (adult) DSDP 511, 23-4, 67-69 early Maastricht. 2 O) 4.59 (0.32) 3.75-4.75 4.66 (0.28) 4.00-5.50 VP 0 s - CO 5 s CO CO 1 0.28 (0.06) 0.15-0.50 O CO CM o o 0.55 (0.06) 0.29-0.85 1.16 (0.16) 0.72-1.56 c o E E o o a> 2 Archaeoglob. australis (neanic) DSDP 511, 23-4, 67-69 early Maastricht. 2 CO 4.61 (0.33) 3.75-5.75 4.96 (0.29) 4.25-5.50 55 N- co 55 CO co 0.94 (0.13) 0.72-115 0,25 (0.05) 0.14-0.34 CM CD 0.62 (0.06) 0.44-0.78 1.31 (0.25) 0.80-1.89 c o E E o o a> c o c Costellagerina pilula W. Australia Toolonga Calcil. c o c Hedbergella monmouthensis New Jersey Red Bank Fm. late Maastrichtian 1 CO 5.48 (0.50) 4.75-6.25 5.88 (0.24) 5.50-6.25 55 CD CO 55 CO CM 0.48 (0.12) 0.41-0.62 0.21 (0.01) 0.20-0.21 ID CD o CO CM 0.49 (0.03) 0.47-0.52 o ^ CO CD CD • o V -sS c a> w a> Q. 0) c o c Hedbergella holmdelensis New Jersey Navesink Fm. early Maastrichtian 1 - 5.21 (0.49) 4.50-5.75 6.25 (0.21) 6.00-6.50 55 h- V) 0) Q- 0) c o c SPECIES LOCALITY UJ O < OBSERVATIONS ULTIMATE WHORL CHAMBER NUMBER* PENULTIMATE WHORL CHAMBER NUMBER* PERCENT DEXTRAL PERCENT KUMMERFORM APERTURAL HEIGHT/WIDTH RATIO* UMBILICUS/TEST DIAMETER RATIO* E -3. Q d 3: E -3. < Q 3 5 BREADTH/DIAMETER RATIO OF TEST* PENULT./ANTEPEN. CHAMBER RATIO* o I— GC O CL -J CD LU Values include the population mean, standard deviation (in parentheses), and minimum to maximum range. 'Olsson, 1964; 2 Huber, 1991a; 3 Belford, 1960; 4 Huber, 1988a; 5 Krasheninnikov and Basov, 1983; e Huber, 1990; 7 Pessagno, 1967. NUMBER 77 9 Measurement precision using external views of specimens under the light microscope is considerably less than with the methods described below, particularly for specimens smaller than 200 pm. Although variation about the mean for 20 pm bar scale measurements is ±8 pm at x50 magnification, greater uncertainty (up to ±15 pm) occurs with measurement of three-dimensional images with reflective surfaces, such as foraminiferal shells. Contact Microradiography Methods. —Foraminiferal microradiographs were obtained by adapting the methods described by Arnold (1982). A 2 x 5 inch cardboard sheet with a grid of 30 holes was backed with tracing paper and used to hold the foraminiferal specimens during the x-ray exposure. The tracing paper was coated with gum tragacanth so that the mounted specimens could be oriented to obtain a full axial image. The image was recorded on 2 x 5 inch sheets of High Resolution KODAK Film #SO-343, with the emulsion side placed in contact with the bottom of the cardboard sheets. The film and mounted specimens were placed on the middle shelf of a Hewlitt- Packard Faxitron x-ray unit and exposed at 40 KVP for 40 minutes. The developed film was cut, labelled, mounted on glass slides, and photographed through a Leitz Orthoplan microscope. The best images were obtained from low trochos- piral specimens free of adhering matrix and without infilled chambers. Biometric data were collected from the microradiographs by measuring the x-ray images on a video screen using a video camera mounted on a Leitz Orthoplan microscope, a digitizing tablet linked to a personal computer, and biometrics software. Because vertical portions of the chamber walls are opaque to x-rays, the cross-sectional outline of the axial periphery, chamber sutures, and whorl sutures appear as unexposed curves on the microradiographs (e.g., see Figure 4). Individual distances, size ratios, and area measurements can be rapidly and accurately obtained from the microradiographs using the biometrics software and hardware. Precision in measuring the x-ray images was determined to be within ±2 pm at xl60 magnification. Biometric Variables. —Biometric data collected from x-ray images measurements are portrayed in Figure 4 and listed in Table 4. The number of chambers in the ultimate whorl (U) are calculated by adding the number of whole chambers to the ratio of the distance between the exterior sutural contacts of the first chamber in the ultimate whorl (c,) and the total of Cj + c 2 , the length of the first ultimate whorl chamber overlapped by the final chamber. The same method is used to determine the number of chambers in the penultimate whorl (P). The presence of kummerform (reduced) final chambers was determined based on the ratio of the ultimate chamber width (Uwj) and the penultimate chamber width (Uw 2 ); values of less than one were recorded as kummerform. The ratios of the size of the FIGURE 4.— Biometric variables measured from x-ray images. Initial whorl dimensions were only obtained from the most evolutely coiled specimens. Variables include: c,/(c 2 + g 2 ) = n^ chamber proportion; g,/(g 2 + g 2 ) = umbilicus/test diameter ratio; P = penultimate whorl chambers; U = ultimate whorl chambers; Uw,/Uw 2 = ultimate/penultimate chamber ratio; Uw 2 /Uw 3 = penultimate/antepenultimate chamber ratio. penultimate (Uw 2 ) and antepenultimate (Uw 3 ) chambers are also recorded using this method. The ratio of the umbilical/test diameter is determined by measuring the ratio of the distance from the coiling axis to the umbilical edge of the penultimate chamber (gj) to the total to gj + g 2 , the width between umbilical edge of the penultimate chamber and the chamber’s peripheral edge (Figure 4). Utility and Limitations. —The main advantage to the x-ray method for biometric analysis of foraminifera is the ease and rapidity with which large data sets can be generated. Statistical differences in the number of chambers within the penultimate whorl, chamber size parameters, and position of the generating curve can readily be determined for different species populations of several hundreds to thousands of specimens. The x-radiographs also show accurate detail of ontogenetic changes in chamber and whorl suture morphology particularly among the more evolute coiled taxa. An additional benefit is that the internal morphology of sufficiently preserved holotype or paratype specimens can be observed without recourse to test dissection or thin sectioning. Furthermore, the cost of obtaining the microradiographs is generally limited to the price of the film used, as the necessary equipment is available at most research institutions. This method could not be applied to specimens with coarsely ornamented, heavily encrusted, or infilled tests, as these are opaque to x-rays and thus the chamber sutures cannot be 10 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY differentiated. In addition, several biometric characters are difficult to measure in high-spired specimens because of the weak images produced by strongly overlapping chambers. Chamber overlap prevents accurate total chamber number counts and measurement of morphocharacters within the initial whorl in all but the most evolutely coiled taxa. Attempts at measuring ontogenetic changes in cross-sectional chamber area from the x-ray images were abandoned for all species except the evolutely coiled H. sliteri because of obscured chamber sutures and uncertainty of where in the ontogeny the measurable chambers were positioned. The number of specimen measurements needed to suffi¬ ciently characterize planktonic foraminiferal populations de¬ pends on the morphologic variability of each species group. For example, the mean value for the number of ultimate whorl chambers was determined as 5.28 for the first 20 measurements of Hedbergella sliteri Huber, a morphologically conservative species, and 5.34 for the total population of 52 specimens (Table 4), a difference of less than 2%. On the other hand, the mean value of the first 20 measurements of Archaeoglobiger- ina australis Huber, which shows considerable morphologic variability, differed by 6% from mean values obtained for 52 specimens. The mean values for 42 more specimens of A. australis, changed only by 1% from the values obtained for 20 specimens. Serial Dissections Specimen Preparation. —The procedures for preparing specimens for serial dissection and SEM analysis were modified from methods described by Huang (1981). A small amount of xylol-free Canada balsam is evenly sprinkled on the surface of an SEM stub that is placed on a small lead block and heated on a hotplate at 140°C. When the balsam begins to melt, several drops of xylene are added until the mounting medium homogenizes into a smooth coating about 0.5 mm thick. The stub is removed from the heat after about two minutes. Once cooled, the consistency of the balsam is tested in several areas by the pressure of a needle. The stub must be reheated if the cooled balsam is still soft; otherwise mounted specimens will move while being dissected. About 25 specimens are aligned in several rows with their spiral sides down on the hardened balsam. The stub is then reheated to 150°C while viewed with a microscope. At this temperature, the balsam is too viscous to penetrate the walls of porous specimens, but soft enough to partially emplace the specimens in the medium by lightly pressing with a fine needle. If the specimens sink too far in the embedding medium or become infilled with balsam, they can be reheated, removed with a needle, and cleaned in a small vial of acetone. The stub is removed from the hotplate after all specimens are embedded to their equatorial periphery and adjusted so that their coiling axes are perpendicular to the stub surface. Specimen dissection was made easier by using a device that acts as a universal stage. For this study, a Leitz mechanical micromanipulator was used with a modified attachment for holding an SEM stub. Use of this device allows tilting and rotation of the mounted specimens in any orientation, which is particularly crucial during dissection of moderately to high- spired specimens. Tests are dissected with a fine needle that is sharpened to a wedge about 10 pm in width. The needle is mounted on the end of a micromanipulator, which affords precise three- dimensional movement, enabling dissection of chambers as small as 10 pm in diameter. Foraminiferal tests are dissected under a light microscope with the wedged needle oriented parallel to the plane of the axial periphery. After each whorl is dissected, the specimens are cleaned in a ultrasonic bath and prepared for SEM study. High-spired specimens are the most difficult to dissect as the walls of the adult chambers obscure the view of the test interior. Care must be taken to avoid cutting chambers in the initial whorls beyond their maximum diameter so that accurate measurements can be obtained. The most tedious aspect of this dissection method arises with repeated serial dissection and SEM study of each whorl down to the prolocular chamber. In order to characterize their complete morphology, the umbilical, spiral, and edge views of external morphology are recorded by SEM, before the specimens are mounted in balsam. Specimens chosen for dissection were previously x-rayed to confirm that the test chambers were not infilled. The specimen is photographed on the SEM after each whorl is removed until complete dissection is achieved. If the specimen is damaged during any stage of this process, the goal of illustrating the complete ontogeny of individual specimens cannot be attained. Therefore, several specimens of the same species were serially dissected to improve the odds for complete success. Biometric information from the initial whorl was most rapidly obtained by completely dissecting up to 25 specimens on a single SEM stub immediately after being embedded, without the repeated SEM photography subsequent to each whorl removal. The most cost- and time-efficient way to record the information from the dissected populations is by photo¬ graphing with a 35 mm camera mounted on the SEM. Biometric variables can then be easily measured from proof sheets of the SEM images with the light microscope and the biometrics equipment described above. Biometric Variables.— Qualitative Observa¬ tions: Serial dissection of ventral chamber walls facilitates identification of pre-adult growth stages inside the foraminif¬ eral tests. The exterior of the early formed chambers provides several important criteria that can be used for supraspecific assignment. These include the (1) degree of chamber compres¬ sion, (2) angularity of chamber sutures, (3) changes in apertural position, and (4) surface ornament of the outer walls of interior chambers. NUMBER 77 11 Brummer et al. (1987) cautioned that secondary calcification of earlier formed chambers may obscure their primary surface structure, producing a smoothened surface ornament on the outer wall of interior chambers. The presence of spines and pustules on early formed chambers, however, is considered a primary feature as these are not added after initial chamber calcification (B6 et al., 1979). Quantitative Observations: Biometric data obtained from the initial whorl of planktonic specimens in this study include the diameter of the proloculus (earliest formed chamber), initial whorl diameter, and number of chambers in the initial whorl (Figure 5). Microradiographs of involute taxa do not show this information because of the strong chamber overlap, resulting in blurred images of the initial whorl sutures. Only microradiogra¬ phs of Hedbergella sliteri, a nearly evolute species, recorded accurate detail of the initial whorl chamber sutures. Therefore, the number of measurements for this species (51) far exceeds those for serially dissected specimens, which generally number less than 20 (Table 5). Serial dissections also enable an accurate count of the maximum number of chambers for each species. This information may be obscured in some trochospiral taxa due to secondary calcification on the external surface of earlier formed chambers. A measure of the increase in cross-sectional chamber area per successive chamber is proposed in this study as a means for characterizing the rate of chamber size increase throughout ontogeny. This two-dimensional approach accounts for changes in chamber size and shape, whereas the measure of developmental changes in test diameter used by Brummer et al. (1987) only recognizes growth increase in the direction of coiling. The chamber-by-chamber changes in test porosity were also measured from the serial dissections. The inner shell surfaces provide the best estimation of shell porosity since secondary calcification of chamber walls can greatly reduce or obliterate pore openings on the outer chamber surface (Be, 1968). Diagenetic overgrowths and recrystallization of inner wall surfaces will also reduce the pore number and pore areas, resulting in an underestimation of shell porosity. Thus, care must be taken to use the best preserved specimens available. Although the pore shapes vary between species (Figures 6, 7), all are cylindrical (e.g., Figure 6 d) and most have a funnel-shaped opening (e.g., Figure 6 a). Average diameters of the cylindrical section of the pores were taken for five pores per chamber through the coiling shells of five specimens per species. All pore diameters were measured from the SEM screen at high magnification (x8,000) and converted to pore areas (P A ). Based on the perforation diameters, two major wall types are recognized (after Steinick and Fleisher, 1978; Blow, 1979; Li Qianyu and Radford, 1991): microperforate (<1 pm) and medioperforate (1-4 pm). Macroperforate (>4 pm) walls were not encountered among the species analyzed in this study. P FIGURE 5.—Biometric variables measured from the initial whorl exposed after complete test dissection. The initial whorl chamber number is determined from the sequential count of chambers following the proloculus (P) to the point of overlap with the proloculus-deuteroconch (= First chamber) suture, recorded as 0.25 increments. Pore concentration (P c ) values were determined for five specimens of each species by counting the number of pores per cross-sectional chamber area for the first seven to nine chambers. In the subsequent chambers, pores were counted within a measured area in the central part of the chambers to avoid distortion caused by curvature of the chamber walls. These values were then normalized to an area of 625 pm 2 so that the measurements could be compared with the pore concentrations determined by Be (1968) for several modem planktonic species. Shell porosity (S p ), expressed in percent, is determined by the equation S p = [(P A *P C )/625]*100 for the ontogenetic series of all measured specimens (Tables 6-15). Utility and Limitations. —Serial dissection of ventral chamber surfaces coupled with SEM analysis of test interiors is the best method for characterizing morphologic changes that occur during the ontogeny of trochospirially coiled fossil planktonic foraminifera. Attributes of the pre-adult morphol¬ ogy exposed during test dissection provide a whole new suite of morphocharacters that can be used to supplement observations of the test exterior. The value of this information for improved taxonomic classification is demonstrated in this study, as is the potential for improved phylogenetic and paleoenvironmental reconstructions. The disadvantage of this method is that it is a slow, laborious process requiring equipment not available at many institutions. Careful dissections of the small, interior chambers of numerous specimens could not have been made without the micromanip¬ ulator, a specialized and expensive tool. In addition, the amount of SEM work needed to complete each species analysis adds to the time and expense of this technique. This dissection method TABLE 5. —Biometric and observational data obtained from planktonic foraminiferal serial dissections. 12 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY Values include the population mean, standard deviation (in parentheses), and minimum to maximum range. 'Olsson, 1964; 2 Huber, 1991a; 3 Belford, 1960; 4 Huber, 1990; 5 Krasheninnikov and Basov, 1983; 6 Pessagno, 1967. NUMBER 77 13 FIGURE 6.—Interior views of ventral chamber surfaces showing pore distributions in the twelfth chamber wall of a, Hedbergella sliterr, b, Costellagerina pilula\ and c, Archaeoglobigerina bosquensis. A cross-sectional view of wall pores in the twelfth chamber of A. bosquensis is shown in Figure 6 d. (Scale bar is 20 pm for Figures 6 a-c, 4 pm for Figure 6 d.) can be applied to specimens that are permeated by unconsoli¬ dated sediment, which can be removed in an ultrasonic bath, but it cannot be used on specimens infilled with lithified materials. As with the x-radiographic method, the number of specimens needed to adequately characterize planktonic foraminiferal populations using biometric characters derived from serial dissections depends on the degree of variablity within each species group. One species, Archaeoglobigerina mateola Huber, shows a bimodal distribution of proloculus and initial whorl diameters (see below), but this was only recognized after measurement of the first nine dissected specimens. Addition of the two “megalospheric” specimens to the data set of 11 microspheric proloculus diameters changed the population mean by 9.2%. This total is considered insufficient for an accurate representation of whole population variability. On the other hand, the proloculus diameter means of a less variable species, Costellagerina pilula (Belford) changed by less than 2% after eight specimen measurements were added to the first ten. Data sets of less than 20 specimens presented in this study can be used for preliminary interpretation, but more specimens should be measured to provide a more statistically reliable base for comparison. SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY 20HM FIGURE 7. —Interior views of ventral chamber surfaces showing pore distributions in the twelfth chamber wall of a, Archaeoglobigerina australis ; b, Archaeoglobigerina mateola\ c, Archaeoglobigerina cretacea\ and d, Rugoglobigerina rugosa. (Scale bar is 20 pm for all photographs.) Criteria for Taxonomic Classification Conventional Classification Schemes The standard approach to taxonomic classification of Cretaceous planktonic foraminifera has been based primarily on observations of external features of the foraminiferal shell. Opinions have varied, however, on the hierarchical order of morphological characters that should be used to identify different taxonomic levels (Table 1). Unlike their Cenozoic descendants, Cretaceous planktonic foraminifera with trochos- pirally coiled tests cannot be subdivided into spinose versus non-spinose groups; the earliest known species with true spines probably did not evolve until the early Danian (Olsson et al., 1992). The presence or absence of surface costellae has been proposed as a primary criterion for taxonomic subdivision (Bronnimann and Brown, 1956), but subsequent studies (e.g., Belford, 1983; Petters et al., 1983) have shown that this structural feature appears several times during the Late Cretaceous among distantly related clades, such as Costellager- ina, Rugoglobigerina, and Rugotruncana (see Tables 2, 3). Bolli et al. (1957) considered the position of the primary aperture as the most important morphocharacter for family level classification, whereas Banner and Blow (1959) attached greater significance to the external structural modifications of the aperture (i.e., presence or absence of lips, portici, or tegilla). Since the publication of Loeblich and Tappan’s volume of the Treatise (1964), most authors agree that the presence of an extraumbilical primary aperture and sutural supplementary apertures, and absence of a tegillum are the most important NUMBER 77 15 bases for distinguishing the Rotaliporidae from the Globotrun- canidae. More recently, Loeblich and Tappan (1988) have raised these two families to superfamily rank, using the position of the primary aperture and presence or absence of tegilla as the key discriminating features (Table 1). There is no single morphologic criterion by which all genera of the Rotaliporacea and Globotruncanacea can be distin¬ guished. Although the Globotruncanacea has been defined as having an umbilical primary aperture (Loeblich and Tappan, 1988:467), five genera included in this superfamily ( Glo- botruncanita, Marginotruncana, Sigalitruncana, Globotrun- canella, and Abathomphalus) are characterized by having apertures that extend outside the umbilical region (Table 3). The Globotruncanacea are also stated to have “tegilla of successive chambers covering the umbilical area” (Loeblich and Tappan, 1988:467). However, the genera Contusotruncana (= Rosita defined in Robaszynski et al., 1984), Globotruncan- ita, Kassabiana, Radotruncana, and Sigalitruncana are distin¬ guished from other globotruncanids by having either free or coalescing portici rather than true tegilla. Unfortunately, consistent recognition of the type of umbilical structure present is not as simple as many taxonomic studies imply. Several factors account for this: (1) portici and tegilla are delicate chamber extensions that may suffer taphonomic damage; (2) post-depositional infilling of the umbilicus may obscure identification of umbilical structures; (3) the distinction between coalescing portici and true tegilla is vague; and (4) the expression of lips, portici, or tegilla may change with ontogenetic development. Because of the variability in the preservation or expression of umbilical structures, Weidich (1987) has suggested lessening their relative importance in classification schemes for Cretaceous planktonic foraminifera and abandoning the genera Contusotruncana (= Rosita), Gansserina, and Globotruncanita. Although this view may be considered extreme by some taxonomists, it does correctly point out problems with studies that overemphasize the taxonomic significance of umbilical cover plates. Koutsoukos et al. (1989) determined that ontogenetic polymorphism and ecophenotypic variability has caused much taxonomic confusion within the mid Cretaceous taxon Favusella. These authors found that a morphologic continuum exists between shallow neritic specimens that are small, variable in chamber shape, and bearing surface textures with discontinuous costae or pustules and deeper neritic specimens that are larger, less variable in chamber shape, and with a more coarsely ornamented reticulate surface texture. Determination that the different morphotypes belong to a single broadly defined species was based primarily on comparison of test size, chamber arrangements in spiral view, and relative abundance within various paleobathymetric settings. However, a biometric study of ontogeny within this group was not included in this investigation. Morphologic features that are currently used to characterize planktonic foraminifera appear relatively late in the ontogeny, usually after the beginning of the penultimate whorl. In fact, Brummer et al. (1986, 1987) found that small (<150 |im), pre-adult forms that dominate highly variable and cold surface water environments in the modem ocean bear little resem¬ blance to their adult counterparts. These authors further noted that application of the existing taxonomy to pre-adult ontogen¬ etic stages would result in assignment of the same species to different genera. This also holds true for Cretaceous popula¬ tions. Thus, it is highly desirable to establish an approach to classification that incorporates morphologic changes that occur throughout foraminiferal ontogeny. Ontogenetic Morphology Pessagno (1967:250) stated that “Any study made of Upper Cretaceous planktonic Foraminifera based on external charac¬ teristics alone is hazardous [because] homeomorphy or near homeomorphy is common among many species.” As the SEM was unavailable during preparation of Pessagno’s monograph, and because stereomicroscopes have inadequate optical resolu¬ tion for detailed morphologic study, Pessagno relied on thin sectioning techniques to characterize differences in species’ growth morphologies. This approach has not been widely adopted in taxonomic studies, however, due to the tedium of thin-sectioning foraminifera and limitations of distinguishing growth morphologies based on two-dimensional, rather than three-dimensional views. Few subsequent studies have realized the potential wealth of information revealed by biometric study of planktonic foram¬ iniferal ontogenies. Olsson (1971, 1972, 1974) was one of the first to quantify changes in the pattern of chamber growth in the developmental history of planktonic foraminifera. Within the ontogeny of several subspecies of Globorotalia fohsi, Olsson (1972) identified two phases of geometric growth that are separated by a sudden change in growth allometiy based on measurements of chamber widths plotted against shell radius. Single growth phases were observed by Olsson (1971, 1974) in Globorotalia mayeri and Neogloboquadrina pachyderma and as many as four growth phases were observed in forms identified by Olsson (1974) as Globorotalia pseudopachy- derma. Population statistics were not available in any of these studies, however, as too few specimens were measured. Huang (1981) was the first to systematically employ a method of serial dissection and SEM examination to reveal morphologic differences among planktonic foraminifera. Huang’s method involved the use of a hand-held dissecting needle to crush and remove ventral chamber surfaces and photograph a succession of the newly exposed pre-adult chambers throughout the ontogeny of an individual specimen. This elegant study demonstrated significant differences in the coiling patterns, chamber morphology and ornamentation, proloculus dimensions, and chamber number at successive growth stages within the tests of some modem and late Neogene planktonic foraminifera. Observations from this study 16 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY led Huang (1981) to propose new criteria for supraspecific classification of late Neogene planktonic foraminifera. Following Huang’s (1981) approach, Brummer et al. (1986, 1987) combined information from test dissections of adult specimens with study of pre-adult forms that were recovered from plankton tows. Based on their observations, these authors identified five developmental phases in the ontogeny of modem planktonic foraminifera. These were defined as the prolocular, juvenile, neanic, adult, and terminal stages. Recog¬ nition of these stages was based on sudden shifts in the chamber-by-chamber pattern of (1) test size increase, (2) apertural position, (3) chamber shape, (4) chamber arrange¬ ment, (5) surface ornament (e.g., presence/absence of pore pits, pore distribution, or spine bases), and (6) vital behavior. Pre-adult forms of the same species in plankton tow samples were recognized by back-tracking the morphologic changes that occur within the shells of dissected adult specimens. Abrupt changes in ontogenetic morphology were attributed to changes in trophic behavior (Brummer et al., 1987) and changing physiology of the increasing volume of cell cyto¬ plasm (Brummer, 1988). Brummer et al. (1987) noted that transition from one ontogenetic stage to another depends more on test size than chamber number, shells with large proloculi and initial whorl chambers may reach the adult stage with fewer chambers than a conspecific form with smaller proloculi and initial whorl chambers. Recognition of ontogenetic growth stages among specimens analyzed in this study is based largely on the criteria outlined by Brummer et al. (1986, 1987), with some modifications that are discussed in a later section. Below is a summary of the most important morphological and biological characteristics that distinguish ontogenetic growth stages in planktonic fo¬ raminifera. Prolocular Stage. —The prolocular stage consists of the first chamber formed in the ontogenetic series. The morphol¬ ogy of the proloculi of all species is spherical, except for occasional specimens that show flattening of the wall shared with the deuteroconch. This flattening does not appear to have any taxonomic value, as it occurs in at least one specimen of all species studied. As has been observed previously for modem species (Huang, 1981; Sverdlove and Be, 1985; Brummer etal., 1986, 1987; Brummer, 1988), proloculi are invariably larger than the deuteroconch, and wall pores do not appear until the second or subsequent chambers (Figure 8 a). The size of the proloculus plays an important role in the ontogeny of planktonic foraminifera because it strongly influences the size development and chamber arrangement of the total shell. Generally, the larger the proloculus, the smaller number of chambers needed to reach a certain test size in the initial whorl (Sverdlove and B6, 1985). This holds true for most of the Cretaceous species examined in this study. For example, the species with the smallest mean proloculus diameter, C. pilula, has the greatest number of chambers in a relatively small initial whorl (Table 5). On the other hand, A. cretacea, which has the largest mean proloculus diameter, has fewer initial whorl chambers but a considerably larger initial whorl size. Pores are absent from the proloculi of all species examined in this study, as has been observed in modem and Neogene globigerine taxa (Huang, 1981; Brummer et al., 1986, 1987; Brummer, 1988). According to some authors, differences in the shape and size of prolocular chambers may be used as criteria for distinguish¬ ing supraspecific groups of planktonic foraminifera. Huang (1981) suggested that Globigerina and Globigerinella are unique among late Neogene genera by possessing spherical rather than oval-shaped proloculi. However, Brummer et al. (1987) observed that all globigerinid species have some degree of flattening of the wall between the proloculus and deutero¬ conch. They concluded that proloculus shape is variable both intra- and interspecifically and, thus, does not have any taxonomic value. In a comparative study of 24 species of planktonic foraminifera collected from plankton tows, Sverdlove and B 6 (1985) detected significant size differences between spinose and and non-spinose taxa. They found that with the exception of Globigerina bulloides, all spinose species have a mean proloculus diameter of 15.7 pm, whereas the average proloculi of non-spinose species is greater. A subsequent analysis by Hemleben et al. (1988), on the other hand, revealed much greater overlap in proloculus sizes between modem spinose and non-spinose groups due to wide intraspecific variability. For example, Sverdlove and B6 (1985) estimated the mean proloculus diameter of left coiling Neogloboquadrina pach- yderma at 20.2 pm with a standard deviation of about 4 pm, whereas Hemleben et al. (1988) obtained a mean value of 29 pm and a standard deviation of 10 pm for left coiling forms of the same species. These contrasting results could suggest that the surface water environment may strongly influence prolocu¬ lus and initial whorl dimensions. On the other hand, this variability could be a function of the size distribution among the measured populations; wide variation of sizes will likely yield prolocular measurements that show a high degree of variability. Juvenile Stage. —The deuteroconch denotes the onset of the juvenile stage. According to Brummer et al. (1987), this stage includes a variable, but species-specific, number of chambers coiled in about 1.5 whorls around the proloculus. These chambers show uniform morphologies and a steady rate of size increase. Initial whorl morphologies of all species analyzed in the present study are very similar (Figure 8 c,d); apertures are extraumbilical in position, the umbilical region is relatively broad, the test surface is smooth to finely hispid, and pores are initally rare and initially restricted to the spiral suture. As few as seven or as many as eleven chambers may occur in the juvenile stage, depending on the species. Neanic Stage. —Transition from the juvenile to neanic NUMBER 77 17 FIGURE 8. —Magnified view of the first chambers of the initial whorl in Archaeoglobigerina bosquensis (a) and complete serial dissection of the same specimen of A. bosquensis ( b-g ) revealing morphologic changes associated with transitions from the prolocular, juvenile, neanic, to adult stages. Prolocular stage: note the absence of pores on the wall of the proloculus (P) but presence of pores on the deuteroconch (D) and subsequent chambers (a). Also note that the deuteroconch is always smaller than the proloculus (a,b). Juvenile stage: this includes from chamber 2 up to about chamber 7; note nearly equatorial position of the aperture, presence of narrow lip bordering the aperture, axial compression and smooth surface texture of the chambers, slow rate of chamber size increase, and wide, shallow umbilicus (c,d). Neanic stage: this includes from about chamber 8 through chamber 10; note the umbilical-extraumbilical position of the aperture, widening of the lip bordering the aperture into a narrow flap, appearance of fine, randomly distributed pustules on the chamber surfaces, increase rate of chamber size increase, and narrowing of the umbilicus ( e.f ). Adult stage: this includes the the final three chambers; note the umbilical position of the aperture, increased number and coarsening of surface pustules, further narrowing of the umbilicus, and diminished rate of chamber size increase (g). Presence of a kummerform final chamber may indicate that the terminal stage was reached in this specimen, although this cannot be verified in extinct taxa. stage in modem spinose species typically occurs in test occurrence of an increasingly lobate equatorial outline; (4) diameters between 65 Jim and95jim (Brummer et al., 1987). migration of the aperture from an extraumbilical to an Other developmental changes in this stage that these authors umbilical-extraumbilical position in some species; (5) change have observed include: (1) an inflection in the logarithmic in the number of chambers per whorl to approximately the growth curve followed by increased growth rates in several same as in the final whorl of adult specimens; and (6) an following chambers; (2) the step-wise appearance of about 0.5 increase in the density of surface texture approaching that of to 1.0 whorl of more globular, loosely coiled chambers; (3) adult specimens. ONTOGENETIC STAGES Prolocular Stage Juvenile Stage Neanic Stage Adult Stage 18 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY Most species in the present study do exhibit some or all of the above features by the eighth to ninth chamber (Figure 8 e,f), along with an abrupt increase in shell porosity. However, a neanic stage is not recognized in some species that have uniformly changing morphologies throughout ontogeny. Test size at the onset of the neanic stage generally ranges from 70 to 120 pm among specimens of Costellagerina, Archaeoglobig- erina, and Rugoglobigerina. Pores in most neanic chambers are evenly scattered around the shell wall, from the spiral suture outward toward the axial periphery. Brummer et al. (1987) suggested that morphologic changes occurring in the neanic stage are at least partly related to an increase in trophic activity. This in turn results from a larger cytoplasmic volume and shell size, enabling a greater capabil¬ ity of prey capture. Adult Stage. —The onset of the adult stage occurs at a test diameter between 160 pm and 200 pm in modem globigerine species (Brummer et al., 1987). It is also characterized by the final positioning of the primary aperture and the maturation of the wall texture, surface ornamental features, and chamber shape. From one to several chambers are added in the adult stage before initiation of the terminal stage. Most species analysed in this study attain maximum porosity and show a diminishing rate of chamber size increase by the adult stage (Figure 8g). Adult specimens of H. sliteri, Costellagerina, Archaeoglobigerina, and Rugoglobigerina have diameters that are generally larger than 200 pm, whereas the adult stage in H. holmdelensis and H. monmouthensis is reached in tests of about 150 pm. Terminal Stage. —According to Brummer et al. (1987), the terminal stage occurs at the onset of reproduction, and is characterized by addition of a kummerform, sac-like, or normalform chamber. There is no way to prove that the presence of kummerform or bullate chambers in Cretaceous species necessarily indicates that reproduction has occurred. Because of this, no attempt is made in the present study to identify the terminal stage. Systematic Descriptions and Biometric Data Qualitative observations and biometric data were obtained from test exterior views, microradiographs, and SEM microgra¬ phs of serially dissected tests of H. holmdelensis, H. mon¬ mouthensis, H. sliteri, C. pilula, A. australis, A. bosquensis, A. mateola, A. cretacea, and R. rugosa. The following section includes a brief synonomy list for each species followed by discussion of the principle features that can be used for species identification and a summary of the biometric data. Based on these results, the phylogenetic relationships of the studied taxa are discussed. Genus Hedbergella Bronnimann and Brown, 1958 Type Species. — Anomalina lorneiana var. trochoidea Gan- dolfi, 1942. Description. —Hedbergella is characterized by having a low trochospiral test that is lobate and subcircular in outline, with globular chambers that increase gradually in size throughout ontogeny, a low-arched aperture that is umbilical- extraumbilical in position and bordered by a narrow lip or porticus. The wall is finely perforate and the surface texture is smooth to hispid. Remarks. —Although Loeblich and Tappan (1988:462) have stated that species included in this genus do not have a poreless margin, topotype specimens of H. holmdelensis and H. monmouthensis clearly do have an imperforate equatorial periphery throughout ontogeny (see below). This does not warrant placement of these species in the genus Globotruncan- ella, however, as imperforate carinal bands are absent from H. holmdelensis and H. monmouthensis populations elsewere. Pore distribution within Hedbergella may therefore be environ¬ mentally controlled. Hedbergella holmdelensis Olsson, 1964 Plate 2: figures 1-8 Hedbergella holmdelensis Olsson, 1964:160, pi. 12: figs. 1, 2.—Huber, 1990:503, pi. 2: figs. 2-4, pi. 6: fig. 1. Not Hedbergella holmdelensis Olsson.—Sliter, 1977:542, pi. 3: figs. 1-3. Observations of the Test Exterior. —The test is very low trochospiral, lobate and subovate in outline, and moder¬ ately compressed in the axial direction with a subrounded equatorial periphery. Maximum diameter of the holotype is 190 pm and maximum breadth is 91 pm, and topotypes with tests up to 218 pm and average 163 pm in test diameter, 80 pm breadth, and 0.49 in breadth/diameter ratio (Table 4). The umbilicus is quite small, averaging 19% of the test diameter and tests generally have a total of 14 to 15 chambers, with an average of 5.21 and range of 4.50 to 5.75 chambers occurring in the final whorl. Final whorl chamber size increase is moderate, as indicated by a penultimate/antepenultimate chamber size ratio of 1.25. No kummerform specimens were observed, and about 67% of the population is dextrally coiled. The aperture is a low, extraumbilical or umbilical- extraumbilical arch with a mean height/width ratio of 0.55, and is bordered by a narrow porticus extending from near the umbilicus to the equatorial periphery. The wall is smooth or finely pustulose, sometimes imperforate along the equatorial periphery, and microperforate elsewhere on the test. Observations of the Test Interior.— -Initial Whorl: The smallest size proloculi observed in this study occur in H. holmdelensis, with diameters averaging 10.49 pm and ranging from 9.44 to 11.53 pm (Figures 9-11, Table 5). FIGURE 9 (facing page).—Scatter plots and least squares regression of proloculus and initial whorl diameter measurements for 10 Upper Cretaceous species of planktonic foraminifera. Most species show strong correlation between these two variables. Note the wide scatter of points shown by micromorph specimens of Archaeoglobigerina australis and the strongly bimodal point distribution portrayed by Archaeoglobigerina mateola. Least squares regression line equation, correlation coefficient (r), and number of measured specimens (n) are presented for each species. Initial Whorl Diameter (microns) Initial Whorl Diameter (microns) ^ Initial Whorl Diameter (microns) NUMBER 77 19 ■ Hedbergella holmdelensis & □ Hedbergella monmouthensis Archaeoglobigerina australis 20-i DSDP Site 511 10 J y = 3.47x+19.53 \ r = 0.77 n=19 Archaeoglobigerina mateola 40 H—'—i—'—i—>—i— 1 —i— 1 10 14 18 22 26 Proloculus Diameter (microns) Hedbergella sliteri 10 14 18 22 26 Archaeoglobigerina australis 120-i DSDP Site 511 (neanic) 110- y=5.58x-20.29 r-0.41 n = 24 100 - Archaeoglobigerina cretacea Proloculus Diameter (microns) Costellagerina pilula Archaeoglobigerina bosquensis 120-i DSDP Site 511 110- y=4.08x+12.64 r = 0.67 n = 21 100 Proloculus Diameter (microns) 8 FIGURE 10.—Univariate plots of mean, one standard and initial whorl diameters for the planktonic forami specimens measured for each species. H. sliteri 4- □ © * © □ H. sliteri SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY □ □ o □ o □ o o X o X □ o □ □ o X o □ X 0 X o □ □ o X o □ .CO .CO .CO 1 — 5 IT CO c 05 Cr co V) 3 co ■D CO =3 ® co S O < < -Q < os co CO o 05 05 O co O 05 "co 05 o O cr < < o □ □ o o X □ o □ o o X X □ X © o X o X o 0 □ □ o □ □ + .CO 1 •p* .5%, reaching a maximum of 10%-23% in some specimens. High latitude forms of this species should be studied to determine whether the large porosity values are invariable between contrasting surface water habitats or if they are to some degree controlled by the ambient environment. General Remarks. —The topotypes of R. rugosa selected for dissection and illustrated on Plate 10 are very characteristic of this species; their chambers have a rapid rate of inflation and are slightly compressed in the axial direction, meridionally aligned costellae ornament the surface of final whorl chambers, and their umbilici are covered by tegilla. One of the reasons R. rugosa is included in this biometric study is that it is the type species of the genus Rugoglobigerina Bronnimann (1952). 52 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY Rugoglobigerina rug os a Chamber Number Figure 34.—Arithmetic and logarithmic plots of the chamber-by-chamber increase in cross-sectional chamber area (in pm 2 ) of Rugoglobigerina rugosa. The arithmetic plots show one standard deviation about the mean and the logarithmic plots show only the mean values. The number (n) of specimens analyzed is also shown. Therefore, the obtained ontogenetic data provide additional criteria for comparison with Costellagerina pilula, which is the type species of the only other meridionally costellate genus of the Late Cretaceous (Tables 2, 3). Results demonstrate that the ontogenetic morphologies of these two species are distinctly different. Rugoglobigerina rugosa has (1) fewer chambers in the initial whorl, (2) a more rapid rate of chamber size increase (Figure 26), (3) a reniform rather than rounded cross-sectional chamber morphology, (4) an umbilically positioned aperture in the final whorl chambers, and (5) a tegillum covering the NUMBER 77 53 R. rugosa a> a> E ro ~o 0 ) o CL 4 6 8 10 12 14 16 Chamber number Average pore diameter (pm) b Chamber number 0 2 4 6 8 10 12 14 16 Chamber number d FIGURE 35.—Ontogenetic changes in a, pore diameter; c, pore density; and d, porosity, measured from five adult specimens of Rugoglobigerina rugosa. b, is a linear regression curve calculated from the mean values of pore diameter and pore density of all measured chambers of R. rugosa with bars representing one standard deviation above and below the mean values. A least squares regression line is also shown. Table 15.—Pore diameter, pore density, and porosity data, including averages, standard deviations, and maximum and minimum values, determined for each chamber within five serially dissected specimens of Rugoglobigerina rugosa. Ch. No. AVG DIAMETER STD MAX MIN AVG DENSITY STD MAX MIN AVG POROSITY STD MAX MIN 1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00% 0.00% 0.00% 0.00% 2 0.14 0.31 0.70 0.00 1.55 3.47 7.75 0.00 0.10% 0.21% 0.48% 0.00% 3 0.52 0.49 1.00 0.00 2.50 2.35 4.75 0.00 0.25% 0.27% 0.60% 0.00% 4 0.48 0.48 1.10 0.00 2.15 2.15 5.00 0.00 0.17% 0.19% 0.42% 0.00% 5 0.58 0.53 1.00 0.00 2.85 3.13 7.50 0.00 0.35% 0.40% 0.94% 0.00% 6 0.68 0.41 1.00 0.00 6.30 5.63 14.25 0.00 0.68% 0.72% 1.79% 0.00% 7 0.80 0.50 1.30 0.00 6.30 4.99 12.75 0.00 0.89% 0.82% 1.94% 0.00% 8 1.20 0.23 1.40 0.90 7.65 3.57 12.50 4.00 1.30% 0.53% 2.09% 0.85% 9 1.34 0.59 2.10 0.70 11.00 2.87 13.75 7.00 3.19% 2.79% 6.93% 0.43% 10 1.44 0.50 2.20 0.90 12.60 2.58 15.50 10.25 3.91% 3.28% 9.28% 1.04% 11 1.70 0.79 2.00 1.40 13.63 3.60 15.75 8.25 5.25% 2.42% 7.79% 2.03% 12 2.23 1.19 3.10 1.30 15.06 3.70 19.25 11.25 11.07% 8.75% 23.25% 2.39% 13 2.00 2.00 2.00 10.75 10.75 10.75 5.40% 5.40% 5.40% 14 2.70 2.70 2.70 11.75 11.75 11.75 10.76% 10.76% 10.76% 54 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY umbilical region. Hence, these species were probably not closely related (Figure 18). The morphology of isolated “neanic” specimens of R. rugosa (Plate 10: Figures 1-3) can be identified within the larger shells of adult forms of this species (Plate 10: Figure 12). The surface ornamentation of the neanic forms consists of faint costellae or randomly situated pustules and the final whorl chambers increase quite rapidly in size, giving it a “big-headed” (“macrocephala”) appearance. These pre-adult forms are essentially identical to specimens previously recognized as Rugoglobigerina macrocephala (see Bronnimann, 1952; Ro- baszynski et al., 1984:284, pi. 49: fig. 7a-c). These observa¬ tions suggest that R. macrocephala is a pre-adult form of R. rugosa and, accordingly, R. macrocephala should be treated as a junior synonym. Surface ornamentation is not only variable within the ontogeny of R. rugosa, but it also varies latitudinally. Tropical forms, such as the Kemp Clay specimens illustrated in this study, show a massive development of meridionally arranged costellae on adult chamber surfaces, but middle to high latitude forms are more weakly ornamented with randomly situated pustules and fewer costellae that show a meridional alignment (e.g., Berggren, 1962, pi. xi: figs. la-5b; Olsson, 1964, pi. 7: figs. 2-5; Webb, 1973, pi. 3: figs. 3-9; McNeil and Caldwell, 1981, pi. 2a-3c; Huber, 1991b, pi. 1: fig. 17). Hence, the surface water habitat exerted some control on the architectural features developed on the chamber surface. Temperature was presumably the most significant variable affecting the observed morphologic differences. Ontogenetic Comparisons Criteria used to distinguish transitions from one ontogenetic stage to another within the Cretaceous taxa in this study are based on qualitative observations, such as changes in apertural position, chamber surface ornamentation, width and depth of the umbilicus, and chamber morphology (Figure 9), and quantitative data, including abrupt changes in the rate of chamber size increase (Figure 36). An additional method for characterizing growth transitions is the measurement of ontogenetic changes in mean shell porosity (Figure 37). This is based on the premise that porosity, in combination with the surface area to biomass ratio, is directly related to metabolic activity or growth rates (Bijma, Faber and Hemleben, 1990). Shell porosity is also known to be positively correlated with temperature (Be, 1968; Frerichs et al., 1972). Hence, ontogen¬ etic changes in porosity are constrained by genetic inheritance, but may vary according to: (1) vertical and latitudinal differences in surface water temperature; (2) resource availabil¬ ity (e.g., light, food, oxygen, nutrients); (3) surface water convection; (4) seasonality; and (5) presence or absence of symbionts. Additional study of the same species from different environments will enable a more accurate portrayal of variance in chamber-by-chamber porosity values. Unlike studies of shell porosity in modem species (e.g., Be, 1968; Frerichs et al., 1972; B 6 et al., 1973, 1976; Bijma, Faber, and Hemleben, 1990), pore densities and pore diameters of most of the Cretaceous species studied are positively corre¬ lated, with high correlation coefficients (>0.89) (Figures 20, 24, 25, 28, 31, 33, 35). Exceptions to this are the hedbergellids, which have poor or no correlation between pore diameters and pore density (Figures 12, 13, 17). In most specimens, the ontogenetic change in pore densities is greater than that of pore diameters. Only R. rugosa exhibits a relatively even magnitude of changes in these two variables (Figure 35). Pore densities and pore diameters generally show positive trends throughout ontogeny, although the values for ultimate and penultimate chambers may diminish. Abrupt increases in shell porosity that occur within the first ten chambers of the averaged plots (Figure 37) are used to identify the transition from juvenile to neanic stages. Subse¬ quent escalations to maximum values distinguish the onset of the adult stage. The chamber positions where the developmen¬ tal transitions occur are compared with the chamber growth trajectories of five specimens per species to examine whether changes in growth rates occur at similar positions in the ontogeny (Figure 36). Ontogenetic stages are not recognized in species that do not show significant shifts in growth trajectories and/or porosity values. Hedbergella holmdelensis, H. monmouthensis, and H. sliteri These species exhibit such a remarkably uniform increase in chamber size that only the prolocular stage can be distinguished in the chamber area plots (Figures 12, 36). The surface texture of the hedbergellids also show no abrupt changes during ontogeny (Plate 2: Figures 6, 14, Plate 3: Figure 5). The inflection shown between the twelfth and thirteenth chambers on the mean logarithmic growth curve plot of H. sliteri (Figure 15) is not indicative of transition between developmental stages. Instead, it probably reflects a diminished size increase of terminal chambers that occur from one to four chambers after the twelfth chamber. Pore distributions also show a very gradual dispersal from the spiral suture across the chamber wall (Figure 16a, Plate 2: Figures 7, 8, 15, 16). Porosity values, on the other hand, show a steady increase until about the eleventh to twelfth chamber, where maximum values are attained (Figures 13, 14, 17). Thus, a transition from the juvenile to adult stage is inferred between the tenth and twelfth chambers based only on the porosity data for H. sliteri (Figure 37a), whereas a neanic stage is not recognized. Costellagerina pilula The growth curves of C. pilula are quite uniform in some specimens, but slightly varying in others (Figure 36). The Chamber Area (jam 2 ) Chamber Area (jam 2 ) Chamber Area (jam 2 ) NUMBER 77 55 Hedbergella sliteri Costellagerina pilula Archaeoglobigerina australis 0 2 4 6 8 10 12 14 16 0 2 4 6 8 10 12 14 16 0 2 4 6 8 10 12 14 16 Archaeoglobigerina australis Archaeoglobigerina australis Archaeoglobigerina bosquensis 0 2 4 6 8 10 12 14 16 0 2 4 6 8 10 12 14 16 0 2 4 6 8 10 12 14 16 Archaeoglobigerina mateola Archaeoglobigerina cretacea Rugoglobigerina rugosa 0 2 4 6 8 10 12 14 16 0 2 4 6 8 10 12 14 16 0 2 4 6 8 10 12 14 16 Chamber Number Chamber Number Chamber Number FIGURE 36.—Logarithmic plots of the ontogenetic changes in cross-sectional areas for four specimens of some of the species included in this study. Ontogenetic stages are inferred or determined for each species based on several criteria, including (1) inflections in the growth curves, (2) abrupt changes in shell porosity (see Figure 37), and (3) qualitative observations of serially dissected specimens. See text for further explanation. Average porosity Average porosity Average porosity 56 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY H. sliteri 1 2 3 4 5 6 7 8 9 10111213141516 Chamber number 1 2 3 4 5 6 7 8 910111213141516 Chamber number A. australis 1 2 3 4 5 6 7 8 91011121314 Chamber number A. australis (neanic) 1 234567891011 Chamber number A. mateola 1 2 3 4 5 6 7 8 91011121314 Chamber number 1 2 3 4 5 6 7 8 91011121314 Chamber number 1 23456789101112131415 1 234567891011121314 Chamber number Chamber number NUMBER 77 57 FIGURE 37 (facing page).—Ontogenetic changes in mean porosity for each chamber of five specimens of each species measured. Vertical bars represent one standard deviation from the mean values obtained for each chamber. See Figure 36 and text for explanation of how ontogenetic stages were identified. averaged porosity plots also show a relatively uniform increase throughout ontogeny (Figure 37). The growth stages of this species can only be identified based on SEM observations of the test interior. The juvenile stage is recognized in a series of chambers that lack surface ornament and have a relatively open umbilicus (Plate 4: Figure 3). Neanic chambers are distin¬ guished by development of a pustulose surface texture and tightening of the coil (Plate 4: Figure 8). The onset of the adult stage is identified by the appearance of meridionally aligned pustules on the chamber surface. This usually occurs after the tenth to eleventh chamber in specimens that are larger than 200 (dm (Plate 4: Figures 2, 7, 11). Archaeoglobigerina australis Growth curves for A. australis from Site 511 both show a uniform escalation in chamber size up to the seventh to ninth chamber, where there is a rate increase (Figure 36). The subsequent curves do not show an inflection point that is consistent between specimens until the twelfth to thirteenth chamber. Porosity elevates significantly between the eight and ninth chambers in some specimens, due primarily to an increase in pore concentration (Figure 24), but other specimens show a quite regular increase throughout their ontogeny. Maximum values are attained by about the twelfth chamber (Figure 35). Serial dissection of neanic and adult specimens of A. australis enables visual observation of the juvenile, neanic, and adult stages. Juvenile forms have a low coiling axis, a broad, shallow umbilicus, a nearly smooth surface texture, and apertures that are extraumbilical in position (Plate 6: Figures 17, 18). Chambers formed in the neanic stage, beginning at the seventh to ninth chamber, are more tightly coiled, have a more rapid size expansion, have umbilical to slightly extraumbilical apertures, and show development of a finely to moderately pustulose surface texture (Plate 5: Figure 10). Based on these observations, all of the specimens illustrated in Plate 6: Figures 1-10 are considered to be neanic morphotypes. The adult stage appears by about the twelfth chamber and is characterized by having chambers that slowly increase in size, umbilically positioned apertures, a coarse surface ornament consisting of randomly arranged pustules, and the presence of a portical flap (Plate 5: Figures 5-7, 11, 12). Archaeoglobigerina bosquensis Most of the growth trajectories for A. bosquensis show an increase in growth rates between the seventh and ninth chambers, suggesting onset of the neanic stage (Figure 36). This is followed by a diminished rate of chamber size increase occurring at the tenth to twelfth chamber. The pore density curves show a similar trend, first with a large increase occurring between the seventh to ninth chamber and then reaching a maximum by the eleventh to twelfth chamber (Figure 28). The transition from the juvenile to neanic stage is not so obvious in the porosity plots (Figures 27, 36). Nevertheless, this develop¬ mental phase change is inferred between the seventh to eighth chamber. Maximum porosity is reached by the eleventh chamber, marking the beginning of the adult stage for most specimens. Pre-adult growth stages of A. bosquensis that are revealed by serial dissection are very similar to those of A. australis. Juvenile chambers increase slowly in size and have little in the way of surface ornament, apertures that are positioned near the equatorial periphery, and a broad and shallow umbilicus (Figure 8c, d). Neanic chambers (Figure 8c,/; Plate 7: Figure 5) increase more rapidly in size, have a moderately pustulose surface texture, and umbilical-extraumbilical apertures. The adult stage is characterized by a slowed increase in chamber size, coarsely pustulose surface texture, an umbilically posi¬ tioned aperture, and, frequently, a kummerform ultimate chamber (Figure 8 g,i; Plate 7: Figures 1-3). Archaeoglobigerina cretacea There is no distinct change in the ontogenetic chamber area trajectories for A. cretacea until about the twelfth to thirteenth chamber, where the growth rate gradually diminishes (Figure 36). However, the averaged porosity plots (Figure 37) show significant porosity increases between the seventh and eighth chambers, marking the transition from juvenile to neanic stage, and the tenth and eleventh chambers, marking the transition from neanic to adult stage. Changes in pore distribution do not coincide with these growth stages, as an even scattering of pores is achieved on the ventral chamber wall by the sixth to seventh chamber (Figure 30a,c), before onset of the neanic stage. Serially dissected specimens of A. cretacea reveal no abrupt changes in morphology with increasing ontogeny. Surface ornament is lacking in the early juvenile stage, but is characterized by an increasingly pustulose texture in later chambers (Plate 8: Figures 5, 6). Although the peripheral margin is imperforate throughout ontogeny, faint keels do not develop until late in the neanic stage, and are generally present until the penultimate chamber of adult specimens (Plate 8: Figures 1, 2). The neanic stage is characterized by having a more globular chamber morphology and a smaller umbilical area than in the juvenile and adult stages, but these differences are transitional. Archaeoglobigerina mateola The growth curves for A. mateola are much more erratic than those of the other species. One specimen plot shows a uniform 58 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY log-linear size increase up to the twelfth chamber, while another shows a steady size increase to about the seventh chamber, then a more rapid chamber size increase, until the twelfth chamber which is follow by a size decrease, whereas two others show several chamber size increases and decreases during their developmental history (Figure 36). Interestingly, the seventh chamber of one of the latter specimens is kummerform, suggesting that formation of this chamber type is not always associated with attainment of reproductive maturity. The porosity plots show a much more uniform ontogenetic change than the growth curves (Figures 32, 36). Porosity increase is slow and uniform until about the eighth chamber, where the rate of increase becomes more rapid. This is inferred to be the transition from the juvenile to neanic stage. Maximum porosity is reached by about the eleventh to twelfth chamber, marking the onset of the adult stage. Pre-adult chambers gradually increase in surface ornament density from nearly smooth-walled juveniles (Plate 9: Figure 12), to moderately pustulose neanic forms (Plate 9: Figure 15), to coarsely pustulose, kummerform adults (Plate 9: Figures 10, 11 ). Rugoglobigerina rugosa Transition from the juvenile to neanic stage of R. rugosa shows up as an abrupt chamber size increase between the seventh and ninth chambers (Figure 36). However, only one specimen shows a diminished growth rate that could be interpreted as the onset of the adult stage. This occurs between the twelfth and thirteenth chambers. The other ontogenetic curves have quite uniform rates of chamber size increase after onset of the neanic stage. The averaged porosity data indicate a sudden porosity increase between the eighth and ninth chambers followed by another between the eleventh and twelfth chambers (Figure 37). These denote the transition from juvenile to neanic and neanic to adult stages, respectively. Plots of pore diameters, pore density, and porosity from individual specimens of R. rugosa indicate that the chamber at which these transitions occur (Figure 35) may vary by one or two chambers above or below the growth stage boundaries determined from the averaged plots. Pores are evenly distributed by the end of the juvenile stage in most of the studied specimens, and show no difference in distribution during transition from the neanic to adult stage (Figure 30d). The growth stages are easily differentiated in serially dissected specimens based on changes in surface ornamenta¬ tion and chamber arrangement. Juvenile morphotypes are generally unomamented and gradually increase in size (Plate 10: Figures 5, 12). Neanic morphotypes have an increasingly pustulose surface texture with a faint meridional alignment in the later chambers, a rapid rate of chamber size increase, and are more tightly coiled than juvenile or adult morphotypes (Plate 10: Figures 1-3, 5, 12). Adult morphotypes bear meridionally aligned costellae on the chamber surfaces and a broad, deep umbilicus covered by a tegillum (Plate 10: Figures 8-10). It is not clear from serial dissection as to what stage the tegillum first appears, but this feature has not been observed on isolated specimens smaller than 200 p.m. Summary and Conclusions Previous studies of planktonic foraminifera from upper Campanian-Maastrichtian sequences in the circum-antarctic region (e.g., Webb, 1973; Sliter, 1977; Krasheninnikov and Basov, 1983) have identified a combined total of six non-keeled trochospiral species. Of these, two were included in the genus Hedbergella, four were placed in the genus Rugoglobigerina, and all were assigned pre-existing names of species recorded from low to middle latitude sites. Subsequent examination of coeval foraminifera from the Antarctic Penin¬ sula (Huber, 1988a) and deep-sea sites in the region of the Southern Ocean (Huber, 1990, 1991a, b) revealed that (1) the morphologies of the high-latitude “rugoglobigerine” taxa intergrade and are highly variable, (2) most of the previously illustrated trochospiral morphotypes from the circum-antarctic region were assigned incorrect species names, (3) three of the four “rugoglobigerine” morphotypes could be lumped into the new species Archaeoglobigerina australis, (4) one of the previously identified “ruglobigerine” and one of the hedbergel- lid morphotypes belong to the new species Archaeoglobigerina mateola and Hedbergella sliteri. Currently, a total of seven non-keeled trochospiral species belonging to Hedbergella (H. holmdelensis, H. monmouthensis, H. sliteri ), Archaeoglobiger¬ ina (A. australis, A. mateola), and Rugoglobigerina ( R. pennyi, R. rugosa ) are considered as valid among southern high latitude assemblages of late Campanian-Maastrichtian age. The present study was initiated in an effort to resolve taxonomic uncertainties and clarify phyletic relationships among the Late Cretaceous trochospiral taxa. One major goal was to compare the new high latitude species assigned to Archaeoglobigerina with topotypes of Rugoglobigerina and Costellagerina to establish their proper generic designation. Clearly, a conventional taxonomic approach based on observa¬ tions from adult shells had led to the previous confusion, so a comprehensive analysis of ontogenetic morphometry was deemed necessary to obtain additional criteria for species comparisons. Two methods were employed to acquire these ontogenetic data. Whereas the x-radiograph approach is the simplest, fastest, and least expensive of the two methods, resolution of initial whorl chamber morphologies could only be obtained from the most evolute trochospiral taxa. Another limitation of this method is that it cannot provide information on ontogenetic changes in apertural position and chamber surface ornamentation. Nonetheless, information accurately and efficiently obtained from the microradiographs includes (1) penultimate whorl chamber number, (2) ultimate whorl NUMBER 77 59 chamber number, (3) kummerform frequency, (4) penultimate/ antepenultimate chamber size ratio, and (5) umbilicus/test diameter ratio. The best technique for characterizing planktonic foraminif- eral ontogenies requires whorl-by-whorl dissections of the foraminiferal shells and an SEM micrograph record of each whorl dissection. Although tedious and time-consuming, this approach provides an accurate three-dimensional record of changes in chamber shape, size and ornamentation, coiling arrangement, and apertural position throughout the develop¬ mental history of the foraminiferal shell. Biometric data obtained using this approach include (1) proloculus diameter, (2) initial whorl diameters, (3) number of chambers in the initial whorl, (4) rate of increase in cross-sectional chamber area, (5) total number of chambers in the test, and (6) chamber-by-chamber measurements of pore density, pore diameter, and shell porosity. Comparisons of developmental morphologies were made for five species that inhabited the Austral Realm during the Late Cretaceous. These include Maastrichtian specimens of H. sliteri, A. australis, and A. mateola and Santonian specimens of Archaeoglobigerina bosquensis Pessagno and Archaeoglobig- erina cretacea (d’Orbigny). Topotypes of H. holmdelensis, H. monmouthensis (both of Maastrichtian age), Costellagerina pilula Belford (Santonian age), and Rugoglobigerina rugosa Plummer (Maastrichtian age) were also analyzed. Results indicate that there is a great deal of size and shape variability of test interior morphocharacters among the species populations, and no single character can be used to unequivo¬ cally discriminate between the different taxa. This variability was probably caused by differences in the ambient physico¬ chemical environment from the initial formation of each prolocular chamber throughout the subsequent growth histories of individual specimens. Nevertheless, comparison of popula¬ tion means and standard deviations can have important taxonomic value for discriminating between some homeomor- phic taxa and inferring ancestor-descendant relationships. This was demonstrated by contrasting the initial and penultimate whorl morphologies of Costellagerina pilula with A. australis and R. rugosa. Although A. australis had previously been identified as Rugoglobigerina pilula (= C. pilula ), serial dissection revealed that the latter species has a greater number of chambers in the initial and penultimate whorls and a much more gradual rate of chamber size increase than A. australis. These features similarly distinguish C. pilula from the R. rugosa topotypes, with the additional observation that the chamber morphology of R. rugosa is reniform throughout ontogeny, whereas C. pilula chambers are more spherical. Serial dissection of A. australis, A. mateola, and A. bosquensis revealed nearly identical developmental morpholo¬ gies, demonstrating their close phylogenetic relationship. Differences in coiling pattern and surface ornamentation only become apparent in the final whorl chambers of adult specimens. Exceptions to this include two specimens of A. mateola which have distinctly enlarged proloculi compared to the other archaeoglobigerinids. Based on the observed similari¬ ties and biostratigraphic study of southern high-latitude sites, it is concluded that A. australis descended directly from A. bosquensis sometime during the Campanian and A. mateola descended from A. australis during earliest Maastrichtian time. Because A. cretacea has previously been assigned to Archaeoglobigerina, specimens were analyzed in this study to evaluate similarity in growth morphology to A. australis, A. bosquensis, and A. mateola. Plots of proloculus and initial whorl diameters and observations of ontogenetic changes in chamber shape and ornamentation reveal that the latter species are distinctly different from A. cretacea, and therefore may not be congeneric. However, without comparative data from the type species of Archaeoglobigerina, A. blowi, any revision to the taxonomy and phytogeny of this group would be based more on conjecture than morphologic criteria. Another important problem that has not been resolved in this study is the taxonomic status of high latitude forms that have faint meridional alignment of costellae and umbilical cover plates, as occurs in Rugoglobigerina, but ontogenetic morphol¬ ogies that are identical to A. australis. Are these forms convergent from an ancestral A. australis stock, independently evolving the rugoglobigerinid features on adult chambers, or convergent from an ancestral rugoglobigerinid species, retain¬ ing its ancestral adult features but developing a juvenile morphology similar to A. australisl A more detailed study of these intermediate morphotypes is needed to resolve this question. Ontogenetic changes in pore diameter, pore density, and porosity were measured for all studied species. This approach was used (1) to characterize the intraspecific variability of these parameters, (2) determine their value for discriminating between species groups, and (3) depict changes that occur in these parameters with increasing ontogeny. Results indicate that pore diameters are less variable and generally show a more conservative increase with increasing chamber number than pore density. Contrary to studies of modem planktonic foraminifera, pore diameter and pore density are positively correlated in nearly all species studied, and correlation coefficients for most species are 0.89 or higher. Pore distributions are similar in the early ontogeny of all species, with pores absent from the proloculus, absent or rare in the initial whorl, and initially concentrated near the spiral suture. The chamber number at which pores first appear or become evenly dispersed is quite variable within and between species. Most specimens show even pore distributions by the beginning of the penultimate whorl in adult specimens. Exceptions to this include A. cretacea and topotypes of H. holmdelensis and H. monmouthensis, which have a poreless peripheral margin throughout ontogeny. All specimens of H. holmdelensis, H. monmouthensis, and H. sliteri have a microperforate wall texture throughout ontogeny, with pore diameters less than 1 (im, pore densities of 60 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY 13 pores/625 (im 2 , and porosities generally less than 1% and rarely up to 1.5%. Similar values for pore diameters and pore density were obtained for A. australis, A. mateola, and C. pilula. Porosities of these species generally range below 3%. Archaeoglobigerina bosquensis and A. cretacea both have up to 5%-9% porosity, and specimens of R. rugosa achieve up to 23% porosity. Pore measurements of these taxa from different paleoclimatic settings are needed to evaluate the influence of temperature or other envronmental factors on pore diameter, pore density, and porosity. The shell pore analyses are also useful for characterizing transition from one developmental stage to another within individual specimens. In most cases, abrupt changes in the pore characters coincide with morphological changes. Interestingly, the changes in pore characters of H. sliteri and C. pilula are very uniform during growth, as is the rate of chamber size increase, such that juvenile, neanic, and adult growth stages all intergrade. These growth stages are easier to discern in the other species. The juvenile stage is characterized by a moderately slow and uniform increase in chamber size and shell porosity, an extraumbilical, nearly peripheral, position of the aperture, and smooth wall surface. Following the juvenile chambers are several chambers that increase rapidly in size and porosity. These are included in the neanic stage, and are also characterized by a more nearly umbilical positioning of the aperture, increase in surface ornament density and coarseness, and increase in height of the spiral axis. A faint expression of the ornamental pattern that characterize adult chambers (e.g., meridional costellae in Rugoglobigerina and Costellagerina ) appears in the last one or two chambers of the neanic stage. Onset of the adult stage is typically characterized by attainment of maximum shell porosity, a diminishing rate of chamber size increase, occurrence of umbilical cover plates in some forms, maximum coarsening of surface ornament and, in A. cretacea , appearance of two weakly developed keels on the the axial periphery. Transitions from one growth stage to another may reflect change in metabolic activity and differences in food sources during the growth of individual specimens. Serial dissection of A. australis enabled identification of pre-adult morphologies within the shells of adult specimens, and recognition of these same forms as isolated specimens that either died prematurely or grew under non-optimum environ¬ mental conditions. Because these neanic morphotypes have extraumbilical apertures, adherence to a conventional taxo¬ nomic scheme would suggest that these forms belong in the genus Hedbergella or Globotruncanella. This approach was used by previous authors studying the southern high latitude assemblages (Sliter, 1977; Krasheninnikov and Basov, 1983; Huber, 1988a). Perhaps the most important consequence of this study is the consolidation of a broad range of intergrading morphologies into A. australis. This is an significant step toward revision of taxonomic concepts among Late Cretaceous planktonic foraminiferal assemblages of the circum-Antarctic region. Literature Cited Adelseck, C.G., Jr., and W.H. Berger 1975. On the Dissolution of Planktonic Foraminifera and Associated Microfossils During Settling and on the Sea Floor. In W.V. Sliter, A.W.H. B6, and W.H. Berger, Dissolution of Deep-sea Carbonates. Cushman Foundation for Foraminiferal Research, Special Publica¬ tion, 13:70-81. Anderson, O.R., and W.W. Faber, Jr. 1984. An Estimation of Calcium Carbonate Deposition Rate in a Planktonic Foraminiferal Globigerinoides sacculifer Using 45 Ca as a Tracer: A Recommended Procedure for Improved Accuracy. Journal of Foraminiferal Research, 14:303-308. Arnold, A.J. 1982. Tfechniques for Biometric Analysis of Foraminifera. Proceedings of the Third North American Paleontological Convention, 1:13-15. Banner, F.T. 1982. A Classification and Introduction to the Globigerinacea. In F.T. 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Revue de Micropaleontologie, 30:52-62. Plates 66 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY PLATE 1 Upper Campanian-Maastrichtian planktonic foraminifera from southern, extra-tropical latitudes previously illustrated in Deep Sea Drilling Project reports. The taxonomic classification of these forms is revised in this study. (Scale bars represent 50 pm.) FIGURES 1, 2.— Hedbergella sliteri Huber, previously identified as Hedbergella monmouthensis (Olsson) by Webb (1973, pi. 3: figs. 1, 2) from south Tasman Sea DSDP Site 208. FIGURES 3-5.— Hedbergella sliteri Huber, previously identified as Hedbergella holmdelensis Olsson by Sliter (1977, pi. 2: figs. 1-4) from the Falkland Plateau DSDP Site 327. FIGURES 6, 10, 11.—Micromorph of Archaeoglobigerina australis Huber, previously identified as Hedbergella monmouthensis (Olsson) by Sliter (1977, pi. 3: figs. 1-3) from Falkland Plateau DSDP Site 327. FIGURES 7-9.—Intermediate form between Archaeoglobigerina australis Huber and Rugoglobigerina rugosa Plummer, previously identified as Hedbergella monmouthensis (Olsson) by Krasheninnikov and Basov (1983, pi. 7: figs. 5, 7, 8) from Falkland Plateau DSDP Site 511; note presence of faint meridional costellae in spiral view of antepenultimate chamber. FIGURES 12-14.— Archaeoglobigerina australis Huber (gerontic form), previously identified as Rugoglobiger¬ ina pilula Belford by Sliter (1977, pi. 10: figs. 7-9) from Falkland Plateau DSDP Site 327. FIGURES 15-17.— Archaeoglobigerina australis Huber (gerontic form), previously identified as Rugoglobiger¬ ina pilula by Krasheninnikov and Basov (1983, pi. 11: figs. 4-6) from Falkland Plateau DSDP Site 511. FIGURES 18-20.— Archaeoglobigerina australis Huber (gerontic form), previously identified as Rugoglobiger¬ ina pustulata Bronnimann by Krasheninnikov and Basov (1983, pi. 10: figs. 10-12) from Falkland Plateau DSDP Site 511. FIGURES 21, 22, 26, 27.— Archaeoglobigerina australis Huber (gerontic form), previously identified as Rugoglobigerina rotundata Bronnimann by Krasheninnikov and Basov (1983, pi. 11: figs. 7-11) from Falkland Plateau DSDP Site 511. FIGURES 23-25.— Rugoglobigerina pennyi Bronnimann, previously identified as Rugoglobigerina rotundata Bronnimann by Sliter (1977, pi. 11: figs. 1-3) from Falkland Plateau DSDP Site 327. Note axially compressed final chamber and faint meridional costellae. NUMBER 77 67 ■j L l . m— . 68 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY PLATE 2 External and internal views of topotype specimens of Hedbergella holmdelensis Olsson from the Navesink Formation and Hedbergella monmouthensis (Olsson) from the Red Bank Formation (New Jersey). Maximum test diameter in parentheses. FIGURES 1-3, 6, 7.— Hedbergella holmdelensis Olsson (171 pm): 1, umbilical view; 2, edge view; note chamber compression in the direction of the equatorial plane; 3, spiral view; 6, outer whorl chambers dissected revealing penultimate whorl with aperture that is nearly equatorial in position; 7, complete dissection. FIGURES 4, 5, 8.— Hedbergella holmdelensis Olsson (130 pm): 4, edge view; note chamber compression in the direction of the equatorial plane; 5, umbilical view; 8, complete dissection. FIGURES 9-11, 14, 15.— Hedbergella monmouthensis (Olsson) (140 pm): 9, umbilical view; 10, edge view; 11, spiral view; 14, most outer whorl chambers dissected revealing penultimate whorl; 15, complete dissection. FIGURES 12, 13, 16.— Hedbergella monmouthensis (Olsson) (154 pm): 12, edge view; 13, umbilical view; 16, complete dissection. 70 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY PLATE 3 Serial dissections and x-radiographs of Hedbergella sliteri Huber from the lower Maastrichtian DSDP Site 327 on Falkland Plateau. Maximum test diameter in parentheses. FIGURES 1-4.—External views and x-radiograph of the same specimen (236 pm). Note that the complete ontogenetic series of chamber development is visible in the x-radiograph because of the low trochospire and wide umbilicus. FIGURES 5-7.—Serial dissection of a single specimen (236 pm): 5, specimen with dissected outer whorl; 6, same specimen with all chambers dissected; 7, enlargement of the initial whorl. Note the pattern of pore distribution with increasing ontogeny. Figures 8, 9.—Completely dissected specimen showing entire test and enlargement of the initial whorl (252 pm). NUMBER 77 71 72 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY PLATE 4 Serial dissections and x-radiographs of topotype specimens of Costellagerina pilula (Belford), Toolonga Calcilutite, Pillarawa Hill, Western Australia. Morphologic similarity of the ontogenies revealed by serial dissection of the 4, 5, and 5.5 chambered morphotypes suggests that these are ecophenotypes of a single species. Maximum test diameter in parentheses. FIGURES 1-4.—Four chambered morphotype designated as Rugoglobigerina bulbosa by Belford (1960) and subsequently recognized as Costellagerina bulbosa (Belford) by Petters et al. (1983) (216 pm): 1, x-radiograph; 2, external view; note meridional alignment of costellae; 3, dissected outer whorl revealing smoother-walled penultimate whorl; 4, complete dissection revealing initial whorl morphology. Note similarity of initial whorl in this morphotype to the initial whorls of the five-chambered morphotypes. FIGURES 5-10.—External views, x-radiograph, and serial dissection of larger, 5.5 chambered morphotype (348 pm). Note that meridional costellae are faint or absent on chambers on umbilical side. FIGURES 11-13.—External view, x-radiograph, and complete dissection of a five chambered morphotype (288 pm). NUMBER 77 73 A jwvt X. i V; - ;] [ • > •.: $ ■k, ,v *; •' fflBP 74 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY PLATE 5 Intermediate forms and adult morphotypes of Archaeoglobigerina australis Huber. Maximum test diameter in parentheses. FIGURES 1-4.—Intermediate form between Archaeoglobigerina australis Huber and Rugoglobigerina rugosa (Plummer), (252 pm): 1, external view, showing faintly developed meridional costellae and a weak umbilical tegillum; 2, microradiograph; 3, dissection of outer whorl revealing penultimate whorl chambers with a relatively rapid chamber size increase, a finely pustulose surface texture, and an extraumbilical position of the aperture; 4, enlarged view of portical flap and delicate tegillum attached to final chamber. The presence of meridional costellae and a tegillum suggest affinity with R. rugosa, but the ontogenetic morphology more strongly resembles A. australis. FIGURES 5-9.—External views and complete serial dissection of Archaeoglobigerina australis Huber from Falkland Plateau (316 pm). Note the presence of a broad porticus, but absence of a tegillum. Figure 10.—Oblique view of a partially dissected adult specimen of Archaeoglobigerina australis Huber from Maud Rise (281 pm). Dissection reveals whorl of chambers formed in the neanic stage; note rapid rate of chamber size increase and subcircular aperture that is extraumbilical in position. FIGURES 11-13.—External views and complete dissection of Archaeoglobigerina australis Huber from Maud Rise (230 pm). FIGURE 14.—Complete dissection of Archaeoglobigerina australis Huber from Maud Rise (262 pm). FIGURE 15.—Complete dissection of Archaeoglobigerina australis Huber from Maud Rise (253 pm). FIGURES 16, 17.—Complete dissection of Archaeoglobigerina australis Huber specimen from Falkland Plateau (310 pm): 16, width of photo = 141 pm. 17, whole specimen. FIGURES 18, 19.—External view and complete serial dissection of Archaeoglobigerina australis from Falkland Plateau (362 pm). NUMBER 77 75 76 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY PLATE 6 Micromorphs of Archaeoglobigerina australis Huber from DSDP Site 511, Falkland Plateau. Maximum test diameter in parentheses. Figures 1-6.—External views, x-radiograph, and serial dissections of a single specimen with a total of eight chambers (178 pm). Note the relatively rapid rate of chamber size increase, the extraumbilical position, and subcircular shape of the aperture, as can be observed in pre-adult chambers of gerontic individuals of A. australis (e.g., compare with Plate 5: Figure 10). FIGURES 7, 8.—External view and complete dissection (170 pm). FIGURES 9, 10.—Complete dissection and enlarged view of the initial whorl (181 pm). FIGURES 11-14, 17, 18.—External view, x-radiograph, and serial dissection of a single kummerform specimen (265 pm). Figures 15, 16.—External view and complete dissection of a kummerform specimen (170 pm). NUMBER 77 77 78 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY PLATE 7 Santonian specimens of Archaeoglobigerina bosquensis Pessagno from Falkland Plateau. Maximum test diameter in parentheses. Figures 1-5. —Exterior views, micrograph, and serial dissection of a kummerform adult specimen (355 pm). Figures 6, 7. —Exterior view and complete dissection of a neanic individual (273 pm). Figures 8, 9. —Complete dissection of an adult specimen and enlargment of the initial whorl (288 pm). FIGURE 10.—Complete dissection of an adult specimen (325 pm). FIGURE 11.—Complete dissection of an adult specimen (313 pm). NUMBER 77 79 80 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY PLATE 8 Adult forms of Archaeoglobigerina cretacea (d’Orbigny) and intermediate forms between Rugoglobigerina rugosa (Plummer) and Archaeoglobigerina australis Huber. Maximum test diameter in parentheses. Figures 1-8.—External views, microradiograph, and serial dissections of a single specimen of Archaeoglobigerina cretacea (d’Orbigny) from the Campanian of Falkland Plateau (424 pm). Note the reniform chamber morphology that appears in the initial whorl and continues throughout the ontogeny. Also note that pores are absent from the axial periphery throughout ontogeny. FIGURES 9-15.—External views, microradiograph, and serial dissection of morphotype from Seymour Island that is intermediate between Rugoglobigerina rugosa (Plummer) and Archaeoglobigerina australis Huber (301 pm). Affinity to R. rugosa is indicated by the faint presence of meridional costellae on the penultimate chamber and a thin tegillum (Figures 9, 13). However, serial dissection reveal an ontogenetic morphology that more closely resembles A. australis than R. rugosa (e.g., compare Figure 15 on this plate with Plate 5: Figures 13-17, 19); the early chambers are spherical rather than reniform, and chamber size increase is more rapid in the initial whorl. NUMBER 77 81 t-'-r 1 J Jit '■^v^--* ^ 6 n LW 'JKr 1 c Mt f aB; S; J 82 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY PLATE 9 External views and serial dissections of Archaeoglobigerina mateola from the upper Maastrichtian of Maud Rise. Maximum test diameter in parentheses. FIGURES 1-4.—External views of specimen with an aberrant final chamber and view showing dissected ultimate whorl. Note the smoother surface of the penultimate whorl chambers (280 pm). FIGURE 5.—Complete dissection showing initial whorl morphology (278 pm). FIGURES 6, 7.—Serial dissection of a specimen with elongate pseudospines revealing penultimate whorl chamber and initial whorl mophology (306 pm). FIGURE 8.—Complete dissection of a specimen with a large (28 pm) prolocular chamber (310 pm). Figures 9-12, 17.—External view and serial dissection of specimen with a 27 pm proloculus (253 pm). FIGURES 13-16.—External views and serial dissection of specimen with a 12 pm proloculus (376 pm). NUMBER 77 83 i>~3Ck z m/t^rsk^M Km 84 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY PLATE 10 Neanic and normal-sized adult forms of Rugoglobigerina rugosa (Plummer) from the upper Maastrichtian Kemp Clay (Tfexas) near the location from which this species was originally described. Maximum test diameter in parentheses. FIGURES 1-6.—Exterior, microradiograph, and interior views of a neanic specimen (220 pm). The neanic morphology is characterized by the poor development of meridionally aligned costellae on the antepenultimate and earlier chamber surfaces and the continuing rapid rate of chamber size increase in the final whorl. The magnified view of the tegillum (Figure 6) shows that this structure is more delicate in neanic specimens than in fully mature individuals (e.g., compare with Figure 9 on this plate). FIGURES 7, 8.—Complete serial dissection of a neanic specimen showing the whole specimen and an enlargement of the initial whorl (219 pm). FIGURES 9-13.—Exterior, microradiograph, and complete dissection of an adult specimen (424 pm). Note that the the chambers in the final whorl show a heavy meridional specimens. Figure 14.—Complete serial dissection of adult specimen (404 pm). FIGURES 15, 16.—Complete serial dissection of adult specimen (290 pm). Note the somewhat reniform morphology of the initial whorl chambers (Figure 16). These initial whorl morphologies are identical in neanic specimens (see Figures 5, 7 on this plate). c'+'-f** NUMBER 77 85 REQUIREMENTS FOR SMITHSONIAN SERIES PUBLICATION Manuscripts intended for series publication receive substantive review (conducted by their originating Smithsonian museums or offices) and are submitted to the Smithsonian Institution Press with Form SI-36, which must show the approval of the appropriate authority designated by the sponsoring organizational unit. 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