Download Possible Biological Consequences of Plate Tectonics

Possible Biological Consequences
of Plate Tectonics
Malcolm C. McKenna
PLATE TECTONICS
Hardly anyone nowadays is unaware
of "continental drift," so thorough has
been the coverage of the subject in all
available media. Biologists, however,
may not all be fully familiar with the
basic principles of plate tectonics, of
which "continental drift" is but one
~pect, so it may be useful to attempt to
list the basic principles here. Geophysicists now conclude that these principles
have been in operation for at least the
last three billion years and probably for
the whole history of the earth. A few
authors still dispute these principles
(e.g. Meyerhoff and Meyerhoff 1972),
and no doubt there have been excesses
of enthusiasm by certain proponents of
"the new global tectonics," but even at
this stage in its conceptual development
the generality of plate tectonic theory
has convinced most geologists of its
essential validity.
The author is Frick Curator in the Department
of Vertebrate Paleontology, The American
Museum of Natural History, and Associate
Professor of Geology, Columbia University,
New York, N.Y.
September 1972
The fundamental idea of plate tectonics is that the ocean floor moves.
The lithosphere of the earth (approximately the top 70 km) consists essentially of a system of large, nearly rigid
plates added to by upwelling of new,
relatively hot lithosphere along oceanic
ridges and destroyed by subduction and
remelting of old, relatively cold lithosphere beneath oceanic trenches. Continents float like scum on oceanic lithosphere and may be carried passively
about, sometimes bumping into one
another, sometimes breaking apart and
reforming, but always part of a dynamic
system. Collisions as well as separations
may occur. The continents do not
"drift" through the lower part of the
lithosphere but are carried with it.
Evidence for such a view stems from
many sources; one of the joys of plate
tectonics is how well the concept is
consistent with data from many seemingly unrelated disciplines.
Direct observation of plate creation
and relative motion on the order of a dozen centimeters a year is presently out of
the question along most of the globegirdling length of the mid-ocean ridge
system, but direct measurements in Iceland, where the Atlantic ridge is above
water, have led to the conclusion that
the ridge is indeed spreading there
(Decker, Einarsson, and Mohr 1971).
Another method of direct measurement,
involving laser reflections from corner
reflectors on the moon, may ultimately
enable direct measurement of relative
motion of distant places on the earth's
crust, but in view of the present uncertainties of 30 cm or so in laser ranging
to the moon (Hammond 1970) it may
be some time before the test would
yield usable results.
plausible coastal matches which form an
important body of evidence that separation of some major land areas indeed
occurred, though such fits say nothing
concerning the timing of separation and
contribute no information about continental collisions. Matching geology
along such coasts has added muscle to
the geometric arguments, and has added
information about timing as well,
though at a low power of resolution.
Until the 1960's most non-biological
arguments about "continental drift"
centered about geometrical fits and geological similarities of opposing coasts.
Least-squares fits of either the present
coasts or of various depth contours are
6O"W
",'W
o·
...
AU'H
B
Fig. 1. A. The location of the Reykjanes
Ridge and the area of B. The 1,()()()'fathom
submarine contour is shown together with the
Coastal Matching
S()()'fathom contour for the Rockall Bank. B.
Contoured symmetrical positive magnetic
The classic fit of the southeast coast anomalies recorded over the Reykjanes Ridge.
of South America to the Gulf of Guinea Areas of positive anomaly are shown in black.
and southwest coast of Africa is the (from Vine in Proc. Amer. Phi/os. Soc. 112,5
most obvious of a growing number of after Heirtzler, Le Pinchon and Baron, 1966.)
519
Downloaded from http://bioscience.oxfordjournals.org/ at Penn State University (Paterno Lib) on September 18, 2016
Geology is currently undergoing an
upheaval as profound as Darwin's reorganization of biology in the Nineteenth Century. The purpose of this
essay is to examine briefly the interface
between these two sciences with an eye
toward new possibilities of synthesis
and new ways of viewing the parent
subject, natural history. A current research trend, now accelerating in activity but still inadequately pursued, deals
with the biological consequences of the
geological evolution of the earth as
deduced from recent theoretical advances in geophysics. Inquiry into the
no-man's-land between geophysics and
biology is particularly encouraging at
present: not since Darwin and Wallace
have there been such great opportunities
to mesh geological concepts of the
evolution of the earth with biological
ideas about the evolution of organisms.
now common arguments in the literature (Bullard et a1. 1965, Merservey
1971).
Magnetics
The two most powerful arguments
for large scale plate motions in the
lithosphere are derived from two different aspects of the history of the
earth's magnetic field. These are the
"polar wander paths" and "zebra
stripes" (Fig. 1) of the geophysical
literature.
Measured from each lithosphere
plate, a sequence of rotational pole
positions, each calculated by averaging a
number of relatively contemporaneous
magnetic pole positions, does not fall at
random but rather in a definite "wander
path" progressing in a definite direction
when the calculated rotational positions
are arranged according to geological age
(Irving 1964, Creer 1970). The "wander
paths" are somewhat different for different plates, but parts of the paths
may be indistinguishable. Because the
earth has only one rotational axis,
the conclusion is that the plates have on
occasion moved with respect to each
other, as well as with respect to the
rotational pole. Comparison of the calculated rotational "polar wander paths"
from various plates then generates a
history of plate latitudes and plate
rotations (Fig. 2). The lithosphere as a
whole may also "wander," and a generally westward motion relative to the
deeper interior has been postulated in
theoretical work (Palmer 1968, Bostrom
1971). The Eulerian pole of rotation of
the lithosphere would be expected to
fall close to the rotational pole of the
earth as a whole. However, to the extent
/~
r
o.
\3
®2
~®'
T.
d
I
03
\02
~o'
j
o'
/3
/05
I ; 03I
O.
~o.
\, <:J Y2
D
o~
0'
t
o~.,
Ts
Fig. 2. Plate motions deduced from superposed "polar wander paths;" Left: Both plates move
together from time T1 to\ T4.~producing the same path. Center: Relative motion has separated
the ancient wander paths, but a single position is obtained at time TS' Right: Both paths have
the same shape from Time Tl to T4. but not thereafter. Circles indicate poles calculated from
the square plate; dots indicate poles calculated from the triangular plate.
520
earth's present field, cause the observed
anomalies in the present magnetic field
from place to place. Sequences of Pleistocene and Pliocene oceanic anomalies
can be correlated convincingly with data
sequences of magnetic polarity changes
on continents; older oceanic anomalies
deep under a cover of sediment or
distant from originating ridges must be
identified by extrapolation, or directly
dated with various degrees of resolution
by borehole sampling of the volcanic
basement or by dating the immediately
overlying sedimentary cover. Anomaly
sequences can be and have been extensively correlated from ocean to ocean
and their symmetry on either side o(
originating ridges is truly remarkable
(Fig. 3). At present the ocean floor is
rapidly being mapped at a power of
resolution sufficient to delimit all the
major lithosphere plates and many
minor ones as well.
Transform Faults, Plate Motion,
and Continental Winnowing
Individual plate motions also follow
Eulerian geometry, with instantaneous
poles of rotation for each plate. This is
because plate motions occur on the
surface of a sphere. If angular rotation
tends to be constant, then either the
rate of creation increases as a cosine
function of latitude with respect to the
instantaneous pole of rotation or breaks
occur. Such breaks, the oceanic fracture
zones, fall on arcs centered on the
instantaneous pole of plate rotation and
are at right angles to the "zebra stripes"
of magnetic anomaly maps, i.e. parallel
to the spreading direction. Secondary
creation of new oceanic crust can occur
along fracture zones between plates
with substantially different poles of
rotation. On a global scale, the geometry of plate motion is quite complex
(McKenzie and Morgan 1969, Menard
and Atwater 1969). Fault offsets along
fracture zones between segments of
oceanic ridges where new crust is being
formed have been called ridge-ridge
transform faults (Wilson 1965, McKenzie and Parker 1967, Atwater
1972). Relative motion of the plates on
opposite sides of these faults is the
reverse of that which might have been
expected (rom ridge offset under the
old concept in which the ocean floor
did not spread (Fig. 4). Only with
ocean-floor spreading from each of the
offset oceanic ridge segments do these
reversed offsets make sense. That
BioScience VoL 22 No.9
Downloaded from http://bioscience.oxfordjournals.org/ at Penn State University (Paterno Lib) on September 18, 2016
that in the past the two poles have no~
coincided, a latitudinal component of
"general lithosphere wander" should be
detectable and should have a decipherable history. Relative longitude changes
are not directly determinable by analysis of "polar wander paths" alone, but
are accessible through studies of "hot
spots" (e.g., Morgan 1972). "Hot spots"
are migrating volcanic centers that
appear to overlie rising plumes of material beneath the lithosphere plates.
From time to time vulcanism breaks out
at the surface, but in the meantime the
plate has moved, generating a "wander
path." "Hot spot wander paths" place
important constraints on conjectures of
plate motions.
"Zebra stripes" are patterns appearing on maps which depict contoured magnetic anomaly data derived
from magnetometers towed over oceanic crust. These were at first a great
puzzle, but did not long remain so.
They have turned out to be the result of
alterations of the earth's past magnetic
field polarity, evidence of which is
frozen in new lithosphere as it appears
and solidifies along oceanic ridges (Vine
and Matthews 1963). The remanent
magnetic field of new lithosphere appearing at such ridges reflects the geomagnetic polarity in effect when the
new lithosphere cools below its Curie
point. Because the polarity reverses
often, still younger lithosphere will exhibit the opposite polarity, and so forth,
resulting in bilaterally symmetrical, outward-moving bands of alternatingly polarized lithosphere which, as many authors have remarked, resemble two
nearly identical tape recordings moving
away from a recording head in opposite
directions. These, superposed on the
WEST
KM
200
200
400
•
400
•
EAST
KM
i
r
GAMMAS
GAMMAS
'~t yrvvM
"]
~r
:~
•• 'I'll. I . . . M.'
, . - ...I
r
III M'II
):
,lib.......~"t-........~-"'---jlt-+:"""'-i-:t"2-+:~o4,-~2-+!""'+!~4~--~"""'~-!:-"""~{0 MY
M.Y .•
, I
I~""
I
I
I
GilBERT :GAU S~MATUYAMA:SRU NHES:MA TUYAMA:GAUSS: GllBE RT
REV. !NORM; REV : NORM.: REV. ~ORM.: REV.
Fig. 3. Center and upper magnetic profdes are obselVed, with east on the right, and reversed,
with east on the left, respectively. The lower profde is the theoretical profde over the bodies
shown. Normally magnetized bodies are black and reversely magnetized are white, and all are 2
km thick. With a spreading rate of 4.5 cm/yr the magnetized blocks correlate with the known
history of the reversals to the Gilbert epoch. (from Heirtzler in Phinney: "The History of the
Earth's Crust," 1968. By permission, Princeton University Press.)
present-day motion along such offsets is
indeed opposite in direction to the
offset of the ridge segments has been a
major confirmation by seismology of the
plate tectonics synthesis. First-motion
studies of earthquakes occurring along
ridge-ridge transform faults confirm the
symmetrical spreading of oceanic lithosphere from mid-ocean ridges.
Further evidence of the mobility of
the earth's crust comes from many
additional sources such as studies of
crustal heat flow and petrology. Plate
boundaries and the nature of interaction
at plate boundaries are especially well
shown by seismological studies (Bara~angi and Dorman 1969).
Continental crust, because of its relatively low density, is not so subject to
subduction as is oceanic crust and does
not return permanently below the lithosphere as oceanic plates do at the end of
their conveyor-belt trips along the ocean
floor. If it does descend deeply it tends
to rise again later after remelting and
differentiation, or lifts up continental
crust above it to form exceptionally
high mountain ranges, such as the Himalayas. Continental crust is therefore
winnowed and tends to collect well
away from long established spreading
ridges. On a geological time scale the
conveyor-belt action of the oceanic
crust keeps its surface effectively swept
clean of truly ancient sediments, which
September 1972
explains the lack of rocks older than
Mesozoic on the present deep ocean
floor. The lithosphere of the present
ocean floor, which covers about twothirds of the area of the earth, has been
created in no more than the most recent
5 percent of the earth's history.
. Until the 1960's many geologists,
particularly American geologists, supported a static theory of stable continents, in which the continents had
always been about where they are now.
This was mainly because no mechanism
for "contintneal drift" through oceanic
crust could be envisaged. The current
geological revolution has changed all
this, putting in place of the static theory
a far more general dynamic model which
accounts for a much wider system of
facts and interpretations that either
were unknown or made no sense at all
under the old scheme. It is now time to
investigate how the plate tectonics concept affects biology.
Epicontinental Flooding
and Other Results of
Spreading Maxima
An increasing body of evidence suggests that at times of maximum spreading activity at any particular mid-ocean
ridge more seawater is displaced by the
rising ridge than at other times (Hallam
1963 and 1971, Johnson 1971). Such
eustatic seawater flooding caused by
activity in anyone area of the globe
would tend to flood low sections of all
continents simultaneously, leading to
simultaneous stress in processes of adaptation, extinction, and occupation by
organisms in far-flung areas. Similarly,
cessation of spreading in one area would
also have world-wide eustatic effects.
How all this affects cyclothems and
world climate is just now coming under
review. Expansion and contractions of
ecospace are linked to such episodes;
thus, if spreading is to some extent
episodic, then in some degree so are
some of the major factors in evolution
and extinction (Valentine and Moores
1970).
If world-wide changes in plate tectonic activity are an index of changes in
deep activity beneath the lithosphere
(Nelson and Temple 1972), there may
be an important linkage between oceanfloor spreading, vulcanism, and rates of
polarity switching in the earth's mag-
--=.~------------~j=-----=[- -F
DEXTRAL
TRANSFORM
~~
~~
SINISTRAL
BIOLOGICAL EFFECTS
If we accept the principles and pro-
cess of plate tectonics, then a very great
deal follows, particularly with regard to
the history of environments but also
affecting other aspects of biology. Plate
tectonics theory is not yet complete,
but it is general enough to supplant
SINISTRAL
FAULTS
TRANSCURRENT
DEXTRAL
FAULTS
Fig. 4. Sense of displacements associated with
transform faults and with transcurrent faults.
Double line represents crest of mid-oceanic
ridge; singte line, fracture zone. Terms "dextral" and "sinistral" denote sense of motion
on active portions of faults. (from Sykes in
Phinney: ''1he History of the Earth's Crust",
1968. By permission, Princeton University
Press.)
521
Downloaded from http://bioscience.oxfordjournals.org/ at Penn State University (Paterno Lib) on September 18, 2016
'~J v~J~~~
previous ideas and to provide a firstorder model of the dynamics of the
crust of the earth-the stage for all
biological activity.
netic field. Vulcanism in tum is linked
to atmospheric dust levels, to albedo
changes, and to availability of precipitation nuclei. Polarity reversals, passing
through zero magnetic field as they
must, cause Van Allen Belt collapse and
changes in cosmic ray shielding, especially in the tropics. Quantitative assessments of these factors are still in a
primitive state (Hays 1971).
Separation Effects
522
relics of past continental separations
(Griffiths 1971, Griffiths and Varne
1972).
Collision Effects
Most of us tend to think of "continental drift" as separation of continental masses, but in plate tectonic
theory collision is as likely as separation. Past continental collisions at various times are now postulated by many
geologists as the principal original processes operating in the creation of the
Ural Mountains, the Appalachians, the
Alpine/Himalayan chain, and several
other important past and present mountain chains throughout the world. India
smashed, albeit in very slow motion,
into southern Asia during the Cenozoic;
Australia seems to be colliding with
southeast Asia at present. Many ancient
collisions seems to be indicated by
characteristic ophiolitic and blueschist
suites of rocks that mark the sutures
between former disparate continental
masses.
Two major environmental results of
continental collision are obvious. First,
marine conditions and maritime climate
in the affected area would be profoundly altered and finally destroyed.
Second, a range of mountains, probably
a great one, would be created by marginal crumpling as enormous amounts of
inertial energy were dissipated over
some millions of years. A crude estimate
of such energy under reasonable conditions might be in the neighborhood of
1024 ergs/year over a 2000 km front
(Hales 1969). As much as 10 31 ergs
might be dissipated in this case. The
removal of the ocean and creation of
such a range would have far-reaching
climatic effects. Ecospace would be
generally reduced, even though this
would be partly offset by new ecospace
created by mountain building. Environmental stress would be high and extinctions would be especially common
because of the tremendous alteration of
the environment.
Mixture of terrestrial biotas of colliding land masses would occur, first by
a few "sweepstakes dispersals" (Simpson 1940, 1953) as the coasts neared
one another, then through a filter as
they actually touched somewhere, and
finally by a corridor modulated by the
rising mountains which would act as a
partial barrier. Ecological replacement
of the less successful of similarly
adapted organisms would take place on
a large scale, and the biota, now a single
BioScience VoL 22 No.9
Downloaded from http://bioscience.oxfordjournals.org/ at Penn State University (Paterno Lib) on September 18, 2016
Let us suppose that an originating
ridge appeared or was carried beneath a
continent, rafting away from each other
the two continental halves. I have in
mind the separation of Mrica from the
Americas. The most obvious effect
would be the immediate increase in
length of the total continental coastline.
As the continental fragments were
pulled apart, the new coastlines would
undergo profound environmental evolution as new continental shelves and
slopes formed and as the climate
changed. Expansion of total ecospace
(Valentine 1969) would occur and new
endemism would begin to develop, increasing total world species diversity
(Valentine and Moores 1970).
When the land masses first separated,
a long, narrow, effectively intracontinental arm of the ocean would fill the
developing gap. Evaporation would
likely exceed precipitation and, where
large rivers did not enter, salinity would
be high until the gap widened farther.
The Red Sea is a modem example. Salt
deposition in the nascent split between
eastern North America and the northwest coast of Africa during the Mesozoic seems to have been a similar case,
the salt deposits now being widely
sundered (Rona 1969, Pitman and Talwani 1972, Fig. 2).
The moderating effects of large areas
of water, as well as the changes in
oceanic circulation, would have enormous influence on the climate as the
land mass broke and its parts separated.
As one of my colleagues has aptly
remarked, there couldn't have been a
Gulf Stream before there was an Atlantic Ocean! The eastward moving circumpolar Antarctic Current and its biological effects must also have evolved to the
present situation since the breakup of
the ancient supercontinent of Gondwanaland. Inasmuch as Australia has
moved substantially northward, separating from Antarctica entirely within
the Cenozoic, the evolution of the
Antarctic Current is a Cenozoic event.
Shifts in Arctic oceanic circulation as
connections to other oceans were made
or broken must have once had farreaching climatic effects now only
dimly perceived.
Other climatic changes would occur
if a separating plate moved across climatic zonation, carrying a biota into a
new environment. Ecospace might
either increase or decrease if climatic
belts were crossed. The northward
movement of Australia is a good example because the motion has been
toward the tropics. If Australia had not
moved northward, its terrestrial biota
would have shared to a significant extent the fate of the pre-glacial Antarctic
terrestrial biota.
Although they are probably of very
minor import in paleobiogeography,
guyots and atolls, carried along on the
lava conveyor-belts of spreading plates,
may shift geographic position without
significant change relative to sea level,
or they may be carried to great depths
or, as has occurred in one known area,
the Afar Triangle at the south end of
the Red Sea, even be moved up onto
land. Many of the older guyots and
atolls of the Pacific are calculated to
have moved with a northward component 25-30° or more since their creation (Francheteau et at, 1970). This,
in conjunction with a relative, generally
westward, Eulerian rotation of the lithosphere, is in harmony with various
northwest-southeast lines of Pacific volcanic islands not associated with ridges'
and trenches (Morgan 1972). Palebiological studies of sediment cores from
guyots and atolls should be related to
possible latitudinal components of plate
motion. Some of the island biogeography of MacArthur and Wilson (I967)
takes place on a moving, not a static,
base. Although the time scale of such
motion is long, its potential effects need
to be considered.
Separation of formerly contiguous
areas would lead to disjunct distribution
of organisms, though it is not the only
way to achieve that phenomenon. At
first taxonomic similarities would still
extend to low levels, but with time and
isolation, unless mitigated by dispersal
across or around barriers, similarities
would be confined to higher and higher
taxonomic categories as endemism developed. The evolution in isolation of
• the monotremes, Sphenodon, various
ratite birds, and the southern distribution of various other archaic organisms affected by the fragmentation
of Gondwanaland come to mind as
Noah's Arks
Paleogeography under the stable continent rationale was greatly influenced
and shaped by two Americans, W. D.
Matthew (1915, 1939) and G. G. Simpson (1940, 1943, 1946, 1947a, 1947b,
1952, 1953). Simpson, in particular, did
much to develop the principles of the
subjeCt and the quantify aspects of
dispersal probability. Simpson developed the criteria for recognition of
various types of dispersal routes, ranging
in increasing order of probability from
waif dispersal (or sweepstakes routes)
through the filter bridge to the corridor
(Simpson, 1940, 1953, Hallam, 1967).
Under the stable continent rationale
that was about are far as one could. If
the ocean floor and continents or fragments -of continents move, however,
then large' and small plates carrying
continental crust and even oceanic islands rising above non-continental crust
will make long fourneys if sufficient
time is available, carrying samples of the
biota of one area to disembark eventually at another. En route, evolution in
isolation would occur, to be sure, and
occasional sweepstakes dispersals might
also be expected, depending in part on
the distances to be traversed, but eventually the ark, to use an obvious term,
would dock and the passengers get off
to try to make a new life in a new land.
If its land mass were large enough, say
of nearly continental dimensions, such
an ark might represent a delayed-action
September 1972
one-way corridor. A balanced but consequences for the ark's biota before
evolved sample of the biota would be docking occurred. Australia's rodents
transferred from land mass A on a illustrate this point (Simpson, 1961 ;
fragment of A, A I , to invade land mass Plane, 1967). After docking, one might
B, but the inhabitants of B. could not expect a small ark's biota to be largely
spread back all the way to A in the same swamped; the larger the ark, the more
manner. Such a delayed one-way corri- likely survival would be.
dor, which could also be viewed as a
Motions Along Continental
type of filter, would not be possible
Strike-slip Faults
under the basic premise of stable continents. Because of the distances to be
traversed by large arks, known rates of
Extensive lateral differential motions
plate motion suggest that the time scale occurs in continental crust overlying
of ark journeys would be of Epoch to areas of differentail motion in the lower
Ear magnitude.
lithosphere. The overlying continents
The one-way corridor or filter prin- are fractured and formerly contiguous
ciple is partly illustrated by the col- areas are carried away from each other.
lision, now under way, of Australia The famous right-laterial San Andreas
(once part of Gondwanaland) with Fault system of the North American
southeast Asia (Cox 1970). Also illu- West Coast is an excellent example
strated by the Australian collision is the (Dietz and Holden 1970, Dickinson et
fact that a new corridor between two al. 1972). In this way fossil assemblages
colliding land masses does not develop may be moved significant distances
instantly but first passes through stages away from the locale where they were
of waif dispersal and filter action. To once alive (Addicott 1967). Addicott's
some Ifxtent, also, the more sedentary interpretation suggests a motion of
travelers on an ark, A I , would be met between 190 and 320 km. iri California
on arrival not only by the indigenous since the early Miocene. According to
inhabitants of B but also by somewhat the interpretation presented by Dickinmodified descendants of A l passengers son et a1. (1972) about 300 km of
who managed to jump ship while the movement has taken place there since
ark was still nearing port. Likewise, the early Miocene and perhaps twice
invasion of the ark by inhabitants of the that amount since the beginning of the
port would begin even before docking Cenozoic. A similar right-lateral fault
and conceivably would have far-reaching system in Alaska (Page and Lahr 1971)
Fig. S. Calculated rotational pole positions for the earth in the early Tertiary, uncorrected for
relative plate motions (Based on Creer, 1970, and other sources). All of the calculated
rotational pole positions indicate that, relative to the places yielding the magnetic data utilized,
the rotational pole was nearer Beringia than now. If the earth's rotational axis has not shifted
appreciably, then the plates themselves have shifted positions, both individually and as part of a
more general shift of the lithosphere relative to the deeper earth.
523
Downloaded from http://bioscience.oxfordjournals.org/ at Penn State University (Paterno Lib) on September 18, 2016
biota, would undergo major reorganization. Thus world species diversity
woul,d be reduced by the union of a
major pieces of continental crust.
An important effect of continental
collision, especially if separation occurs
later along the same general trend of the
suture, is that fossil-bearing rocks (and
also rocks from which pole positions
may have been calculated!) of wholly
different geographic origins might be
juxtaposed, as seems to have been the
case along the east coast of North
America (Wilson 1968). Fragments of
continents get left behind, so to speak,
attached like fender paint to the other
party in the collision. The older the
rocks, the greater the chance would be
that the continent to which they now
belong is composite. Unscrambling such
"unnatural" juxtaposition with the aid
of plate tectonic theory may be expected to' have profound effects on
paleogeographic work.
may have moved certain warm temperate early Cenozoic floral localities
farther north than their original positions. Total lateral motion along the
Alpine Fault in New Zealand is interpreted to be as much as 1200 km
(Griffiths and Varne 1972). Although
the distances may not be very great, still
they must be taken into account in
biogeographic reconstructions. If such
motions continue on a time scale
measured in hundreds rather than tens
of millions of years, then distances on
the order of thousands of kilometers are
involved.
"Polar wander paths" for the different plates have done much to confirm differential plate motion, but they
also confirm differential motion of the
lithosphere as a whole (or at least of
groups of plates) with respect to the
earth's rotational axis (Irving 1964,
Creer 1970). Irving (I 964), Irving and
Robertson (I968), Sloan (I 969), Stanley (I 970), Szalay and McKenna
(1971), and others have attempted on
this basis to reconstruct paleolatitudes
for late Cretaceous and early Cenozoic
time, and a number of authors have
done the same for earlier periods in
earth history. The data for early Cenozoic rotational pole positions are still
rather scanty (Fig. 5) but there is little
question that even during that time the
eastern end of Siberia and the Bering
land bridge were nearer the "north"
rotational pole than they are now.
Paleolatitude belts concentric around
such a shifted rotational pole position
relative to the lithosphere make sweeping curves on maps of present latitudes
and vice versa, yet many biogeographic
reconstructions are still made on the
basis of the present polar coordinate
system (e.g., various maps in Middlemiss
et al. 1971). Both aspects of the plate
tectonics systhesis should be reflected in
paleogeographic base maps for biogeographic reconstructions: relative plate
motion should be depicted on a coordinate system compatible with what is
known of the rotational pole position
for the time depicted in each reconstruction. Even as late as the beginning
of the Cenozoic, latitudes were significantly tilted with respect to their present orientation and, to the extent that
latitudes control climatic belts, the climatic belts would have tended to be
similarly tilted with respect to the present coordinate system.
524
This short survey suggests that the
next few years will be exciting ones for
those who wish to synthesize a new
model of biological interaction with the
physical conditions of the earth
throughout its long history. Paleogeography will be profoundly altered and
given a primarily geophysical, rather
than biological, base. Biogeography will,
in general, have to adjust to and test the
validity of that base, and indeed there
will be significant biological constraints
on some geophysical proposals. Biology
will contribute information about the
timing of certain events and the degree
of filtering in dispersal, but will be of
secondary importance in determining
past configurations of the earth's lands
and oceans. The physical sciences will
prQvide a steadily increasing power of
resolution concerning the history of
environmental complexity and physical
environmental stimuli affecting biological evolution.
REFERENCES
Addicott, W. O. 1967. Zoogeographic evidence for late Tertiary laterial slip on the
San Adnreas Fault, California. U.S. Geol.
Surv. Prof, Paper 593-D: D1-D12.
Atwater, T. 1972. Test of New Global Tectonics: discussion. Bull. A mer. Assoc.
PetroL Geol., 56: 385-388.
Barazangi, M., and J. Donnan. 1969. World
seismicity maps compiled from ESSA, Coast
and Geodetic Survey, epicenter data,
1961-1967. Bull. Seismol. Soc. A mer. , 59:
369-380.
Bostrom, R. C. 1971. Westward displacement
of the lithosphere. Nature, 234: 536-538.
Bullard, E., J. E; Everett, and A. G. Smith.
1965. The fit of the continents around the
Atlantic. Phil. Trans. Roy. Soc. London,
258: 41-51.
Cox, C. B. 1970. Migrating marsupials and
drifting continents. Nature, 226: 767-770.
Creer, K. M. 1970. A review of palaeomagnetism. Earth-Sci. Rev., 6: 369466.
Decker, R. W., P. Einarsson, and P. A. Mohr.
1971. Rifting in Iceland: new geodetic data.
Science, 173: 530-533.
Dickinson, W. R., D. S. Cowan, and R. A.
Schweichert. 1972. Test of New Global
Tectonics: discussion. Bull. A mer. Assoc.
Petrol. GeoL, 56: 375-384.
Dietz, R. S., and J. C. Holden. 1970. The
breakup of Pangaea. Sci. Amer., 223(4):
30-41.
Francheteau, J., C. G. A.Harrison, J. G.
Sclater, and M. L. Richards. 1970. Magnetization of Pacific seamounts: a preliminary
polar curve for the northeastern Pacific. J.
Geophys. Res., 75: 2035-2061.
Griffiths, J. R. 1971. Reconstruction of the
south-west Pacific margin of Gondwanaland.
Nature, 234: 203-207.
Griffiths, J. R., and R. Vame. 1972. Evolution of the Tasman Sea, Macquarie Ridge,
and Alpine Fault. Nature (Phys. Sci.), 235:
83-86.
Hales, A. L. 1969. Gravitational sliding and
continental drift. Earth Planet. Sci. Lett., 6:
31-34.
Hallam, A. 1963. Major epeirogenic and
eustatic changes since the Cretaceous, and
their possible relationship to crustal structure.Amer. J. Sci., 261:397423.
_
1967. The bearing of certain palaeozoogeographic data on continental drift.
Palaeogeogr. PalaeoclimatoL Palaeoecol., 3:
210-241.
_
1971. Mesozoic geology and the
opening of the North Atlantic. J. Geol.,
79(2): 129-157.
Hammond, A. L. 1970. Laser ranging: measuring the moon's distance. Science, 170:
1289-1290.
Hays, J. D. 1971. Faunal extinctions and
reversals of the earth's magnetic field. GeoL
Soc. Amer. BulL, 82: 2433-2447.
Heirtzler, J. R. 1968. Evidence for ocean
floor spreading across the ocean basisn. In:
The history of the earth's crust, R. A.
Phinney (ed.). Princeton University Press,
Princeton, p. 90-100.
Irving, E. 1964. Paleomagnetism and its
application to geological and geophysical
problems. John Wiley and Sons, New York.
Irving, E., and W. A. Robertson. 1968. The
distribution of continental crust and its
relation to ice ages. In: The history of the
earth's crust, R. A. Phinney (ed,). Princeton
University Press, Princeton, p. 168-177.
Johnson, J. G. 1971. Timing and coordination
of orogenic, epeirogenic, and eustatic
events. Geol. Soc. A mer. BulL, 82:
3263-3298.
MacArthur, R. H., and E. O. Wilson. 1967.
The theory of island biogeography. Princeont Univ. Press, Princeton.
Matthew, W. D. 1915. Climate and evolution.
Ann. New YorkAcad. Sci.; 24: 171-318.
_
1939.Climate and evolution. Second
edition, revised and enlarged, Spec. Publ.
New York Acad. Sci., 1: 1-223.
McKenzie, D. P;, and W. J. Morgan. 1969.
Evolution of triple junctions. Nature, 224:'
125-133.
McKenzie, D. P., and R. L. Parker. 1967. The
North Pacific: an example of tectonics on a
sphere. Nature, 216: 1276-1280.
Menard, H. W., and T. Atwater. 1969. Origin
of fracture zone topography. Nature, 222:
1037-1040.
Merservey, R. 1971. The coastline fit of
Africa and South America. Palaeogeogr.
PalaeoclimatoL PalaeoecoL, 9: 233-243.
Meryerhoff, A. A., and H. A. Meyerhoff.
1972. "The New Global Tectonics": major
inconsistencies. BulL A mer. Assoc. Petrol.
Geol., 56: 269-336.
Middlemiss, F. A., P. F. Rawson, and G.
Newell (eds.). 1971. Faunal provinces in
space and time. Seel House Press, LiverpooL
Morgan, W. J. 1972. Deep mantle convection
plumes and plate motions. BulL A mer.
Assoc. Petrol. Geol., 56: 203-213.
Nelson, T. H., and P. G. Temple. 1972.
Mainstream mantle convection: a geologic
analysis of plate motion. Bull. Amer. Assoc.
Petrol. Geol., 56: 226-246.
Page, R., and J. Lahr. 1971. Measurements of
fault slip on the Denali, Fairweather, and
Castle Mountain faults, Alaska. J. Geophys.
Res., 76: 8534-8543.
BioScience Vol. 22 No.9
Downloaded from http://bioscience.oxfordjournals.org/ at Penn State University (Paterno Lib) on September 18, 2016
Tilted Latitudes
CONCLUDING REMARKS
Palmer, H. 1968. East Pacific Rise and westward drift of North America. Nature, 220:
341-345.
Pitman, W., and M. Talwani. 1972. Sea-floor
spreading in the North Atlantic. Ceol. Soc.
Amer. BUll., 83: 619-646.
Plane, M. 1967. Stratigraphy and vertebrate
fauna of the Otibanda Fonnation, New
Guinea. Bur. Min. Res. Ceol. Ceophys.
(Aust.) , Bull. 86: VI, 1-64.
Rona, P. A. 1969. Possible salt domes in the
deep A tlantic off North-west Africa. Nature,
224 : 141-143.
Simpson, G. G. 1940. Mammals and land
bridges. J. Wash. Acad. Sci., 30(4): 137-163.
1943. Mannals and the nature of
continents. A mer. J. Sci., 241: 1-31.
__ . 1946. Tertiary land bridges. Trans. New
York A cad. Sci. , 8(8): 255-258.
1947a. Holarctic mammalian faunas
and continental relationships during the
Cenozoic. Ceol. Soc. A mer. Bull., 58:
613-688.
1947b. Evolution, interchange, and
resemblance of hte North American and
Eurasian Cenozoic mammalian faunas.
Evolution, 1(3): 218-220.
1952. Probabilities of dispersal in geologic time. In: The problem of land connections across the South Atlantic, with
special reference to the Mesozoic, E. Mayr
(ed.). Bull. A mer. Mus. Nat. Hist., 99 :
163-176.
1953. Evolution and geography.
Condon Lectures, Oregon State Syst. Higher
Educ., Eugene.
Sloan, R. E. 1969. Cretaceous and Paleocene
terrestrial communities of western North
America. Proc. North A mer. Paleont. Conv.,
September 1969, pt. E, p. 427-453.
Stanley, E. A. 1970. The stratigraphical,
b i 0 ge ographical, paleoau tecological and
evolutionary significance of the fossil pollen
group Triprojectacites. Bull. Ceorgia
Acad.Sci., 28 : 1-44.
Sykes, L. R. 1968. Seismological evidence for
transfonn faults, sea floor spreading, and
continental drift. In: The History of the
earth 's crust, R. A. Phinney (ed.). Princeton
University Press, Princeton, p. 120-150.
Szalay, F. S., and M. C. McKenna. 1971.
Beginning of the Age of Mammals in Asia:
the late Paleocene Gashato Fauna, Mongolia. Bull. A mer. Mus. Nat. Hist. , 144 :
r
I
h
ElIf¥
POLAROIC
•
_ _I
_ _I
_ _I
269~318 ;
Valentine, J. W. 1969. Patterns of taxonomic
and ecological structure of the shelf benthos
during phanerozoic time. Paleontology, 12:
684-709.
Valentine, J. W., and E. M. Moores. 1970.
Plate-tectonic regulation of faunal diversity
and sea level: a model. Nature, 228:
657-659.
Vine, F. J. 1968. Magnetic anomalies associate with mid-ocean ridges. In: The history
of the earth's crust, R. A. Phinney (ed.).
Princeton, p. 73-89.
Vine, F. J, and D. H. Matthews. 1963.
Magnetic anomalies over oceanic ridges.
Nature, 199: 949-949.
Wilson, J. T. 1965. A new class of faults and
their bearing on continental drift. Nature,
207: 343-347.
_ _ 1968, Static or mobile earth: the
current scientific revolution. Proc. A mer.
Phil. Soc., 112(5): 309-320.
September 1972
Shoot round circles
and square squares.
Some extraordinary optics in the new Bausch & Lomb Integrated Camera
Series II produce images freer of distortion than eVer before. Shooting a
properly aligned specimen through a StereoZoom 7 Microscope, Series II
Camera and Camera Adapter, you get a picture that retains the identical
shape. Circles are never out of round. Squares are square-sides don't
cave in or bulge out. Compare results with any other system and
convince yourself.
There's more, too, like a large viewing screen that permits comfortable
group viewing in ambient light. A highly sensitive exposure meter
simplifies picture taking by eliminating guesswork.
Your choice of three interchangeable camera bodies-the 35mm, takes
the full range of 35mm films-BW, color prints and transparencies;
3~" x4~" Polaroid* and 4" x 5" which accepts plates, film packs,
sheets, Polaroid sheets.
Ask for a see-for-yourself, no-obligation demonstration,
or write for our fact-filled Catalog 42-2396.
BAUSCH & LOMB ~
StereoZoom, Reg. T.M. Bausch & Lomb
'Trademark, Polaroid Corp .
SCIENTIFIC INSTRUMENT DIVISION
21609 Bausch Street, Rochester, N.Y. 14602
PLEASE CIRCLE NO.8 ON THE READER'S SERVICE CARD
525
Downloaded from http://bioscience.oxfordjournals.org/ at Penn State University (Paterno Lib) on September 18, 2016
_ _I