Download Cenozoic Radiolarian Evolution and

BULLETIN OF MARINE SCIBNCE, 47(1): 221-232,1990
CENOZOIC RADIOLARIAN EVOLUTION AND
ZOOGEOGRAPHY OF THE PACIFIC
Richard E. Casey, Amy L. Weinheimer and CarlO. Nelson
ABSTRACT
Modern day radiolarian distributions can be grossly divided into warm and cold water
spheres separated by the polar convergences and the associated pycnocline. During the Paleogene both warm and cold water sphere radiolarian diversities appear to have been lower
than during the Neogene. One major reason for this difference appears to be the difference
in the number of "packages" of water (water masses essentially) for radiolarians to inhabit
during these times. The number of "packages" or provinces increased in the Neogene due
to the development of polar convergences and their associated polar, shallow subpolar and
intermediate waters, the initiation of the formation of Antarctic (Polar) Bottom Water and
associated Circumpolar Water, and the development of the surface Eastern Tropical Pacific
as a specific "package" of water. Specific examples of radiolarians evolving into these packages
support these contentions. Another Neogene development was the creation of a new "package" that apparently resulted in the evolution, or expansion, of a new niche, that of the
symbiont bearing radiolarians by a variety of taxa. This apparently was preceded by changes
in Antarctic geographies (and perhaps some biological influences) that resulted in Antarctic
glaciation and the development of this niche.
The polycystine radiolarians are chronologically the longest ranging (Cambrian
to Holocene), geographically the greatest ranging (pole to pole, surface to abyss),
and taxonomically the most diverse of the well-preserved microzooplankton. In
the present day oceans there are about 400-500 relatively common polycystine
radiolarian species (Casey et aI., 1983). Approximately 200 live in the shallow
(0-200 m) central and tropical waters (the warm water sphere), 40-50 in high
latitude (poleward of the subtropical or polar convergences) shallow (0-400 m)
waters, 150-200 in deep (greater than 200 m) waters, most of which appear to be
tropical submergent forms, and about 40-50 are eurybathyal forms. Most ofthese
deeper-living forms are vertically stratified as are the shallower forms, with the
main boundaries correlating with water mass boundaries. There appear to have
been cold and warm water spheres each containing endemic radiolarians since
the first appearance of radiolarians in the fossil record in the early Cambrian
(Casey et aI., 1983).
Since about half of the radiolarian species live in deep waters, the study of
radiolarian evolution in an entire ocean (such as the Pacific) should include the
deep forms, and the ability to distinguish them from shallow forms. A method
has been devised to not only distinguish shallow from deep radiolarians but to
place the individual radiolarian taxa into their specific province ("package") in
either the recent or fossil record (at least in the Cenozoic) (Casey et aI., 1983).
METHODS
To investigate the Cenozoic radiolarian evolution in the Pacific, the zoogeographies of radiolarians
through time, in this case the Cenozoic, must be known. The best evidence for the distribution of a
radiolarian taxon comes from collecting living specimens from known oceanographic regimes (such
as specific water masses). This is the case for many of the extant taxa discussed herein; however, this
is impossible for the extinct taxa. The method of inferring the zoogeographies of extinct taxa herein
followed is that described by Casey et al. (1983) where major oceanographic convergences and other
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BULLETIN OF MARINE SCIENCE, VOL. 47, NO. I, 1990
oceanographic phenomena are reconstructed and the relationship of extinct taxa to these reconstructions are used to place them in their correct paleozoogeographic settings.
The construction of the model of modem polycystine radiolarian zoogeography (Casey, 1989)
used these same techniques. Most of the recent sediment samples used were from the Pacific Ocean
so the model is most like the Pacific.
The reconstruction of the number of inferred Cenozoic radiolarian "provinces" (water masses)
through time relies heavily on the published works of Sancetta (1978, 1979). Sancetta used the
microfossil data published in the Initial Reports of the Deep Sea Drilling Project to reconstruct
provinces exhibited by the combined distributions of foraminifera, calcareous nannofossils, radiolarians and diatoms at certain time planes. Sancetta (1978; 1979) also made some original counts in
search of dominant species, and others. We use here only her published data on radiolarians to
reconstruct the number and distribution of shallow provinces. All of her counting groups were used
to reconstruct the number of deep provinces (water masses) using the techniques of Casey et al. (1983).
The water mass reconstructions illustrated in Figure 3 were derived from Sancetta's data using the
technique of Casey et al. (1983). Support for these reconstructions came from appropriately cited
references.
Comparisons between our reconstructed radiolarian provinces and those of Reynolds' (1978) were
done because Reynolds' work provided an independent data set. Reynolds' (1978) relative radiolarian
diversities, relative comutellid "diversity," relative comutellid abundance, and relative "paleo-productivity" were all essentially determined in the same manner; replicate counts of different aliquots
of a sample were made for the various parameters from Deep Sea Drilling Project Hole 77B. These
were then added and compared to the maximum single count ofa value of that sample, and therefore
they are in relative percentages. These comparisons are discussed below.
Specific examples of radiolarians evolving into each of these packages are given, many taken or
modified from previous work. The examples of Antarctic water mass formation, radiolarian occupation
and speciation are new examples and these taxa's zoogeographies were determined in the manner
referred to at the beginning of this methods section.
RESULTS AND DISCUSSION
Model of Modern Polycystine Radiolarian Zoogeography. -Casey (1989) presents a model of modern polycystine radiolarian shallow-water zoogeography. In
this model a hypothetical ocean similar to the Pacific is divided into eight shallowwater provinces (Fig. 1 and Table I). The integrities of these provinces and their
boundaries are mainly established by shallow-water ci- 'ulations as described by
Reid et al. (1978) and McGowan (1974). Herein an attempt is made to incorporate
the deeper-water radiolarian provinces into this modern zoogeography. Studies
by Casey (1971), McMillen and Casey (1978), and Spaw (1979) suggest that water
masses exert a primary control on the distributions of radiolarians in deeper
waters, and that radiolarians are usually endemic to parts of one water mass, or
one, two or more water masses. Therefore, the number of water masses at depth
is a good conservative approximation of the number of radiolarian provinces at
depth. The hypothetical ocean (Fig. 2 after Casey et al., 1983, and Table I herein),
or Pacific, contains two central, two intermediate, one polar circumpolar, one
deep or common, and one bottom water mass for a total of seven deep water
masses or seven deep-water provinces. The total number of present day radiolarian
zoogeographic provinces for the Pacific (or hypothetical ocean) is therefore 15
(eight shallow and seven deep).
Oceanographic and radiolarian characteristics of these fifteen Pacific and hypothetical ocean radiolarian provinces are given in Table I. The characteristics
of primary productivity, degree of stratification, leakage, and neritic influence are
taken from McGowan (1974). The radiolarian characteristics are taken from sediment and plankton samples in the manner described in Casey et al. (1983) and
Casey (1989).
Number of Radiolarian Provinces through the Cenozoic. - The middle Eocene (4446 mya) and late Eocene (40-42 mya) appear to be times oflow cold water sphere
CASEY ET AL.: RADIOLARIAN
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EVOLUTION AND WOGEOGRAPHY
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Figure 1. Model of modem shallow polycystine provinces on a hypothetical ocean similar to the
Pacific (modified from Casey, 1989).
radiolarian diversity (Fig. 3A, Table 2). Nigrini's (1977) work on artostrobid
radiolarian biostratigraphy illustrates few deep living (robust) artostrobids at this
time as does Friend and Riedel's (1967) work on the deep living orosphaerids.
However, in both cases, there appears to be a major evolution within these two
deep living groups in the early Oligocene (34-36 mya). We consider this evolutionary pulse to be related to the increase of Antarctic glaciation, southern hemisphere cooling, and the resulting development of a Paleogene Antarctic Convergence and associated intermediate water and perhaps a "bottom water" (Fig. 3B).
A review of previous considerations of these developments may be found in
Kennett (1982, 1985). This would introduce two new deep water masses and one
new shallow water mass (Antarctic surface water south of the Antarctic Conver-
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BULLETIN OF MARINE SCIENCE, VOL. 47, NO. I, 1990
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BULLETIN OF MARINE SCIENCE, VOL. 47, NO. I, 1990
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water masses in cross-section similar to the modem Pacific (modified from Casey et a!., 1983).
of
gence) thus explaining the relatively high radiolarian diversity illustrated on Table
2. The diversity decrease from early to latest Oligocene probably represents the
establishment of the deep cold water spheres after a considerable period of absence
(perhaps resulting in a greater rate of extinction than evolution of deep adapted
forms causing the decreasl~ in relative radiolarian diversity [Table 2]). The latest
Oligocene (24-26 mya) to the early Miocene (18 to 20 mya) is a period of province
addition with the newly added provinces illustrated as dashed lines in Figure 3C.
In the early Miocene a new intermediate water is formed adding at least one more
deep province (perhaps two if there were no Antarctic Bottom water in the latest
Oligocene) and one more shallow to what there was in the latest Oligocene. There
also is evidence of three radiolarian species, Eucyrtidium inflatum (Kling), E.
CASEY ET AL.: RADIOLARIAN
EVOLUTION
AND ZOOGEOGRAPHY
227
3
4
3
4
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Figure 3. Cross-sectional reconstructions of the Pacific during A = middle Eocene (4~6
mya) and
late Eocene (40-42 mya), B = early Oligocene (34-36 mya), C = late Oligocene (24-26 mya) and early
Miocene (18-20 mya), 0 = middle Miocene (10-12 mya), and E = late Miocene (5-7 mya) and Recent,
AAC = Antarctic Convergence, STC = Subtropical Convergence. All drawings illustrate the crosssectional water masses with solid lines and on the surface of the ocean the convergences with x's and
divergences with dots. In the cross-sectional part of the drawings the x's refer to water movement into
the page and the dots refer to water movement out of the page. The two Australias on drawing C
illustrate the movement of Australia northward from the 24-26 time slice (southernmost Australia)
to the 18-20 my a time slice. Paleotemperatures from Sancetta (1978; 1979), who referenced Savin
(1977); Savin et al. (1975); and Shackleton and Kennett (1975) as her sources.
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Table 2. A comparison of the estimated number of radiolarian provinces deep/shallow (total) to the
relative radiolarian diversities, relative comutellid diversities, relative comutellid abundance and
relative paleoproductivity of Reynolds (1978). These are compared using the time slices (Epoch and
Time) and paleotemperature differences between tropical surface water and bottom water from Sancetta
(1978, 1979)
Epoch
Holocene
Latest Miocene
Middle Miocene
Early Miocene
Latest Oligocene
Early Oligocene
Late and Middle
Eocene
Time
(mya)
2
5-7
10-12
18-20
24-26
34-36
42-44
44-46
"C
dill".
23°e
22°e
23°e
15°e
13°e
14°e
17°e
15°e
Estimated number
radiolarian
provinces
deep/shallow
(total)
7/8(15)
6/7 (13)
5/6(11)
5/4 (9)
3-4/3 (6-7)
5/4 (9)
3/3 (6)
Relative
radiolarian
diversity
Relative
comutellid
diversity
Relative
comutellid
abundance
Relative
paleoproductivity
90
92
80
60
30
60
30
80
95
60
20
20
10
50
25
5
10
10
15
40
7
15
5
15
punctaturn (Ehrenberg), and Siphocarnpe arachnea (Ehrenberg) evolving into what
might be a newly formed intermediate water (Casey, in manuscript, I and Table
3), a water that would be formed at the Antarctic Convergence inferred to be
formed at that time from the work ofSancetta (1978). Major Antarctic glaciation
was initiated at about 15 mya, and with obvious consequences throughout the
Pacific at that time (Weaver et aI., 1981). One of these consequences is reflected
in a reconstruction after that time (Fig. 3D) showing the first true Antarctic Bottom
Water (first shown here, with bottom waters of 2 degrees centigrade, Fig. 3D). A
species that probably evolved into that single pervasive intermediate water of that
time (Fig. 3D and Table 3) was Botryostrobus bramlettei (Campbell and Clark)
which evolved at approximately II my a (Casey, in manuscript).1 All the present
day cold water sphere and warm water sphere packages, except those of the
Circumpolar and the Eastern Tropical Pacific, had been formed by about 6 my a
(Fig. 3E). The radiolarian faunal evidence for the formation of a new North Pacific
Intermediate Water Mass and its associated poleward shallow water mass is from
Casey (1982). The last remaining Pacific radiolarian provinces to form were those
of the Eastern Tropical Pacific and Circumpolar region. The Eastern Tropical
Pacific water is believed to have been formed about 3.5 million years ago due to
the uplift of Panama, with development of this new province indicated by the
evolution of the endemic radiolarian Spongaster pentas (Riedel and Sanfilippo).
The Circumpolar Water is believed to have been formed at about 3 my a related
to northern hemisphere glaciation, the production of new or more North Atlantic
Deep and Bottom Water and therefore the formation of Circumpolar Water by
the mixing of North Atlantic Deep and Bottom Water and Antarctic Bottom
Water (Casey, in manuscript).l
Cenozoic Radiolarian Evolution Related to Zoogeography and Paleoceanography. - The major extinctions of so many taxa including planktonic foraminiferans
and calcareous nannofossils at the Cretaceous-Tertiary boundary are not shared
by radiolarians (from data from Dumitrica, 1973); and it appears that what changes
did occur to the radiolarians at and near the Cretaceous-Tertiary boundary occurred mainly in the warm water sphere and to shallow water forms rather than
to deep water forms (Casey et aI., 1983; herein Table 3). Recently many interesting
theories have been developed to explain the mass and selective extinctions at this
I
R. E. Casey. Radiolarian evolution and the Antarctic. In manuscript.
CASEY ET AL.: RADIOLARIAN
229
EVOLUTION AND ZOOGEOGRAPHY
Table 3. Geologic ranges or radiolarian "family" level groups, arranged by environment. Modified
from, and with additions to, Casey (1987). For EPOCH (or portion of): J = Jurassic, K = Cretaceous,
P = Paleocene, E = Eocene, 0 = Oligocene, M = Miocene, P = Pliocene, P = Pleistocene, and H =
Holocene. The small x (x) is for rare, the big x (X) is for dominant. The "family" level groups are
those of Casey (1987)
Epoch (or portion
of)
Radiolarian groups
Cold water sphere and deep
orosphaerids
spongopylins
sethophormins
artostrobids (robust)
theocalyptrins
Warm water sphere
amphipyndacids
dictyomi trids
Warm water sphere and symbiotic
spongasterins
artiscins
collosphaerids
pylon ids
Radiolarian species
Eucyrtidium injlatum
Eucyrtidium punctaturn
Siphocarnpe arachnea
Botryostrobus brarnlettei
Spongaster pentas
K
P
E
o
M
P
P
H
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boundary. In the late Cretaceous, many extant cold and deep water radiolarian
groups evolved (Table 3). Perhaps this may be associated with a marine cooling
during that time (Savin et al., 1975) and a development of more potential radiolarian cold and deep provinces. Also of interest is the earliest evolution of a
known extant warm water sphere symbiotic radiolarian group (the spongasterins),
suggesting perhaps oceanographic conditions somewhat similar to those of the
Neogene when this "niche" became dominant.
The Paleocene is a period of extinctions for such warm water groups as the
amphipyndacids and dictyomitrids (Table 3). Portions of the Paleocene apparently
exhibited the lowest radiolarian diversities (at least on a "family" level, see the
late Paleocene and early Eocene on Table 3) of the Cenozoic. The warm water
sphere symbiotic collosphaerid and pylonid groups apparently evolved during this
period of low radiolarian diversity, but they did not become dominant until the
Miocene (Table 3). Our estimates of the number of radiolarian provinces through
the Cenozoic, as well as the inferred temperature differences between Pacific
tropical surface and bottom water from Sancetta (1978, 1979), are compared to
Reynolds (1978) data from Deep Sea Drilling Project Hole 77B from the equatorial
Pacific on relative radiolarian diversity, relative comutellid "diversity," relative
comutellid abundance, and relative "paleo-productivity" in Table 2.
There appear to be positive correlations for all of these parameters from the
latest Oligocene to the present (Table 2). As the temperature difference between
surface and bottom waters increases so do the number of radiolarian provinces,
the relative radiolarian diversities, relative comutellid "diversity," relative cornutellid abundance, and relative "paleo-productivity."
The relative radiolarian diversity and abundance includes all radiolarians, shallow and deep forms. The relative comutellid "diversity" and abundance only
refers to the presently deep living, and presumably always deep living, comutellids
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BULLETIN OF MARINE SCIENCE, VOL. 47, NO.1,
1990
(since their origins in the Cretaceous). It appears that there has been almost a
doubling of the number of potential radiolarian provinces since the latest Oligocene. This has led to significant increases (approximately a doubling) in the
relative radiolarian diversities of both shallow and deep water radiolarian species
(or, in the case of cornutellid "morphotypes," they mayor may not be species:
see Reynolds, 1978). The simplest explanation for this is that the increase in the
number of potential radiolarian provinces has allowed more regions or niches for
the radiolarians to invade, and they have then allopatrically evolved into new
species. Specific oceanographic events have caused the development ofthese new
provinces (water masses) in the Neogene. At about 22 my a the Antarctic Convergence may have been formed (Kennett, 1980) and coupled to that formation
would be the initiation of a new water mass, the Antarctic Intermediate waters
(see Table 2 and the dashed lines on Fig. 3C). The radiolarian evidence suggests
that at about 6 my a the development of a northern intermediate water added one
more deep and one more shallow water mass (Table 2). Three more water masses
were added when glaciation in the northern hemisphere (about 3 mya) resulted
in more North Atlantic Deep and Bottom Water and a development of enough
mixing to form Circumpolar Water a secondary (mixing) water mass. The last
Pacific water mass to be formed was the Eastern Tropical Pacific Water which
was formed at about 3.5 my a related to the uplift of the Isthmus of Panama
(Carson and Casey, 1986 and Table 3).
Thus eight or nine new provinces have been added in the Neogene resulting in
a total of fifteen, or twice as many as in the latest Oligocene. These new provinces
have allowed for increases in shallow radiolarian diversities (three or four more
provinces) and deep radiolarian diversities (five more provinces).
One interesting aspect of all this is the why of why did it get cold and produce
more water masses and more radiolarian provinces in the Neogene. Most believe
the isolation of Antarctica by the drifting of Australia and South America northward allowed for the chilling of the Antarctic continent (Kennett, 1980). However,
an interesting proposal by Vincent and Berger (1985) suggests that a carbon sink,
developed by the formation of nearshore marine basins and the trapping of organic
matter, may also be responsible and may have set up the Kennett scenario by
lowering a "greenhouse I~ffect" at that time (the Monterey Effect).
Whatever the scenario" in the middle Miocene a thermocIined ocean developed,
with oligotrophic subtropical anticyclonic gyres and eutrophic boundary current
and other upwelling systems. The strongly thermoclined oligotrophic gyres were
the setting for perhaps a major radiolarian evolution: the evolution of a number
of taxa into a symbiont bearing niche suited to these "new" conditions. The
artiscins, collosphaerids, pylonids and spongasterins groups under the warm water
sphere and symbiotic category on Table 3 either evolved or became dominant in
these oligotrophic gyres during the middle Miocene. There are, however, scattered
prior occurrences of these taxa in the Oligocene (and some before). It may be
more than jest to suggest that the occupation of approximately half of the surface
ofthe earth with a "new photosynthesizer" may have helped lower the Oligocene
greenhouse by tying up carbon dioxide as biomass, and may have aided (or led
to) the Monterey Effect and therefore the Antarctic glaciation and the further
development of their oligotrophic gyres (a Gaian feedback).
CONCLUSIONS
Lipps (1970) reviewed previous hypotheses of mechanisms controlling marine
macroevolution and conduded that they failed to account for modern and past
CASEY ET AL.: RADIOLARIAN
EVOLUTION AND ZOOGEOGRAPHY
231
plankton distributional patterns. He proposed that high-latitude marine climates
regulate the diversity of plankton by creating or eliminating thermally controlled
ecological opportunities and genetic isolation. He cited the appearance and radiation of major new groups of plankton in the fossil record, relating them to his
hypothesis; he also stated that entirely new and different forms developed within
previously existing groups following a similar pattern. In Lipps's model, warm
high-latitude seas eliminate horizontal and particularly vertical habitats and barriers to competition, thus causing plankton extinctions; cool high-latitude seas
create thermal or thermally related barriers to competition and new habitats both
vertically and horizontally, thus increasing opportunities for speciation by isolation of populations.
Reynolds (1978) used Lipps's (1970) model to explain the increase in diversity
of cornutellid radiolarians (deep-living forms) in the Neogene. This study supports
the conclusions of both Lipps and Reynolds. The results herein suggest that the
number of radiolarian provinces is a dominant force in determining the diversity
of radiolarians, more provinces equal more taxa. The number of these provinces
(essentially fairly stable packages of water) appear to be mainly determined by
the complexity of circulation in shallow waters, the presence of convergences in
shallow waters, by the number of water masses in the deep water, and perhaps
by the development of the cold water sphere in deep waters. Deep water radiolarians, as exemplified by the cornutellids, have diversified in direct correlation
to the addition of new deep water masses. One might expect that there should be
a higher cornutellid diversity during the early Oligocene since it had more provinces than the latest Oligocene (Table 2). This may possibly be explained by the
diversification of two other deep water groups at that time, the robust artostrobids
and the orosphaerids. Diversity increases occurred in these groups instead of the
cornutellids. Some type of competition with the orosphaerid group might be the
answer because there has been a decline in orosphaerid diversity since their peak
in the late Oligocene, especially in the middle and late Miocene (orosphaerid data
from Friend and Riedel, 1967) and a steady increase (replacement?) in comutellid
diversity for that same time interval.
We conclude that the increase in the number of water mass regimes in the
Pacific during the Cenozoic (and especially in the Neogene) resulted in the evolution of radiolarians into these new provinces. Our results also suggest that the
development of strongly thermoclined oligotrophic anticyclonic subtropical gyres
presented a niche for the evolution of symbiont bearing radiolarians in the middle
Miocene.
ACKNOWLEDGMENTS
Support for much of the author's and his colleagues' research discussed in this chapter, was provided
by the National Science Foundation, Marine Geology and Geophysics, Grants OCE-74-21805, OCE84-0885 and OCE-86-20446. Acknowledgment is also made to the donors of the Petroleum Research
Fund administered by the American Chemical Society for partial support of these studies. We acknowledge aid from the W. M. Keck Foundation; and from Betsy Colman of the University of San
Diego for editing and typing the manuscript.
LITERATURE
CITED
Carson, T. L. and R. E. Casey. 1986. Zoogeography, paleozoogeography, and evolution of the
radiolarian genus Spongaster in the North Pacific. Pages 97-102 in R. E. Casey and J. A. Barron,
eds. Siliceous microfossil and microplankton studies of the Monterey Formation and modem
analogs. Pacific Sect. Soc. Econ. PaleontoI. Mineral.
Casey, R. E. 1971. Distribution of polycystine radiolarians in the oceans in relation to physical and
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OFMARINESCIENCE,
VOL.47, NO.1, 1990
chemical conditions. Pages 151-159 in B. M. Funnell and W. R. Riedel, eds. The micropalaeontology of oceans. Cambrid~:e University Press.
---.
1982. Lamprocyrtis and Stichocorys lineages: biogeographical and ecological perspectives
relating to the tempo and mode of polycystine radiolarian evolution. Proc. 3d No. Amer. Paleontol.
Conv. 1: 77-82.
--.
1987. Radiolaria. Pages 213-247 in J. H. Lipps and T. W. Broadhead, eds. Fossil prokaryotes
and protists. Dept. Geological Sciences. Univ. of Tennessee.
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DATEACCEPTED: May 12, 1989.
ADDRESS: Marine Studies, Univ. oj San Diego, Alcala Park, San Diego, California 92110.