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OPEN 3 ACCESS Freely available online
Marine Ostracod Provinciality in the Late Ordovician of
Palaeocontinental Laurentia and Its Environmental and
Geographical Expression
M ohibullah M ohibullah1'2*, Mark W illiam s1, Thijs R. A. V an d en broucke3, Koen S ab b e4, Jan A. Z alasiew icz1
1 D e p a rtm e n t o f G eology, U niversity o f Leicester, Leicester, U nited K ingdom , 2 D e p a rtm e n t o f G eology, U niversity o f B alochistan, Q u etta, Pakistan, 3 G éo sy stèm es,
U niversité Lille 1, Lille, F rance, 4 P rotistology a n d A quatic Ecology, D e p a rtm e n t o f Biology, G h e n t University, G h en t, Belgium
Abstract
Background: We exam ine th e environm ental, climatic and geographical controls on tropical ostracod distribution In th e
marine Ordovician of North America.
Methodology/Principal Findings: Analysis o f th e inter-regional distribution pattern s of Ordovician Laurentian ostracods,
focussing particularly on th e diverse Late Ordovician Sandbian (ca 461 to 456 Ma) faunas, d e m o n strates strong endem icity
at th e species-level. Local endem ism is very p ronounced, ranging from 25% (e.g. Foxe basin) to 75% (e.g. Michigan basin) in
each basin, a p attern th a t is also reflected in o th er benthic faunas such as brachiopods. Multivariate (ordination) analyses of
th e ostracod faunas allow dem arcation of a M idcontinent Province and a so u th ern Marginal Province in Laurentia. While
th ese are m ost clearly differentiated at th e stratigraphical level o f th e bicornis g raptolite biozone, analyses of th e entire
dataset su g g est th a t th ese provinces rem ain distinct th ro u g h o u t th e Sandbian interval. Differences in species com position
betw een th e provinces a p p e a r to have been controlled by changes in physical param eters (e.g. tem p e ra tu re and salinity)
related to w ater d e p th and latitude and a possible regional g eo g rap h ic barrier, and th e se differences persist into th e Katian
and possibly th e Hirnantian. Local environm ental param eters, perhaps o perating at th e m icrohabitat scale, may have been
significant in driving local spéciation events from an cesto r species in each region.
Conclusions/Significance: O ur w ork establishes a refined m eth o d o lo g y for assessing marine benthic arth ro p o d micro­
ben th o s provinciality for th e Early Palaeozoic.
C ita tio n : M ohibullah
M, W illiams M, V an d en b ro u ck e TRA, S a b b e K, Zalasiew icz JA (2012) M arine O straco d Provinciality in th e Late O rdovician o f
P ala eo co n tin en ta l Laurentia a n d Its E nvironm ental a n d G eograp h ical Expression. PLoS ONE 7(8): e41682. do i:1 0 .1 3 7 1 /jo u rn al.p o n e.0 0 4 1 682
E d ito r : A ndrew A. Farke, Raym ond M. Alf M useum o f P aleontolo g y , U nited S tates o f America
R e c e iv e d February 21, 2012; A c c e p te d J u n e 25, 2012; P u b lis h e d A u g u st 10, 2012
C o p y r ig h t: © 2012 M ohibullah e t al. This is an o p en -ac cess article d istrib u ted u n d e r th e te rm s
o f th e C reative C o m m o n s A ttrib u tio n License, w h ich perm its
u n restricted use, distrib u tio n , a n d re p ro d u c tio n in an y m ed iu m , p ro v id ed th e original a u th o r a n d so u rc e a re cred ited .
F u n d in g : This s tu d y w as s u p p o rte d by th e U niversity o f B alochistan, Q u etta, Pakistan (h ttp ://w w w .u o b .e d u .p k /). T h e fu n d ers h ad n o role in s tu d y d esig n , d a ta
collection a n d analysis, decision to publish, o r p rep ara tio n o f th e m an u scrip t.
C o m p e tin g In te re s ts : T he au th o rs h av e d ec lared th a t n o c o m p e tin g in terests exist.
* E-mail: m k241@ le.ac.uk
latitudinal (climatically) controlled biotopes have b e en identified
in C enozoic fossil o stracod faunas [19,21].
In this p a p e r we evaluate the distributional p attern s o f the
O rd o v ician ostracods o f palaeo co n tin en tal L au re n tia [22], focus­
sing particularly on the faunas o f S an d b ian age as these are
am ongst the m ost w idely studied a n d best know n o f all O rdovician
ostracod assem blages (e.g., [17,20,23-27]. L au re n tia n O rdovician
ostracods spanned a p alaeolatitudinal range from 13" N to 25" S,
w hich encom passed tropical a n d sub-tropical clim ate zones
[28,29]; they occupied a range o f m arin e environm ents from
peri-tidal to deep shelf, a n d they occur in b o th c arb o n a te a n d
clastic sedim entary deposits. T h erefo re, potential latitudinal a n d
dep th -related changes in tem p e ra tu re, substrate, productivity,
oxygenation-level a n d salinity m ay be expressed in the different
spatial ranges o f individual tax a a n d ostracod biotopes. A lthough
such p attern s have previously b e en discerned from evaluation o f
ostracod presence-absence d a ta for individual form ations (e.g.,
[17,20], this is the first a tte m p t to integrate d a ta for the w hole
L au re n tia n p alaeo co n tin en t for specific tim e intervals using
m ultivariate statistical techniques.
Introduction
O stracods are small bivalved crustaceans w ith a fossil reco rd
ex tending back to the C a m b ria n [1], T h e y are a diverse class o f
aquatic crustaceans [2], have a w ell-preserved fossil reco rd [3],
a n d are know n from m ore th a n 65,000 living a n d extinct species
[4], O stracods have ad o p te d b o th benthic a n d pelagic lifestyles
[4,5], b u t m ost ostracods in the fossil re co rd are benthic: the
weakly calcified shells o f pelagic form s are n o t frequently preserved
[3]. T h e earliest ostracods occupied shelf m arin e benthic
environm ents d u rin g the O rdovician [6 -9 ]. L ater, they colonised
pelagic environm ents d u rin g the Silurian [10] a n d ra d ia te d into
n o n -m arin e aquatic environm ents du rin g the C arboniferous
[11,12]. O rd o v ician benthic ostracod distribution p a tte rn s have
b e en used to identify biogeographical provinces (e.g., [13-15], to
establish facies-dependent p attern s (e.g., [13] a n d to track the
relative m ovem ent o f p alaeocontinents [16], As well as palaeogeographical controls o n the distribution o f b enthic ostracods,
e nvironm ental effects o f tem p eratu re, substrate, food-supply a n d
w ater d e p th are also influential (e.g., [13,17-21]. D iscrete
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August 2012 | Volume 7 | Issue 8 | e41682
Ordovician Ostracod Provinces o f Laurentia
Graptolites
N o r th
S c o ttis h
A m e ric a n b io z o n e s
re g io n a l
s ta g e s
Conodonts & chitinozoans
N o r th
A m e ric a n
b io z o n e s
W e ls h
b io z o n e s
'5l
M
P u sg illia n
pygm aeus
linearis
linearis
M aysvillian
K atian
(p ars)
o
o
■a
2
ra
o
C hatfieldian
spiniferus
ruedem anni
c a u d a tu s
m orrisi
superbus
confluens
am ericanus
tenuis
bicornis
bicornis
m ultidens
S a n d b ia n
gracilis
gracilis
gracilis
alobatus
gerdae
undatus
com pressa
quadridactylus
aculeata
variabilis
L lanrvirn
M iddle
O rd o ­ D arriw ilian
vician
L landeilian
teretiusculus ter
m urchisoni
A b ereid d ian
artus
cancellata
gracqui
m ultispinata/duplicitas
prim itiva
S. s p . A
hirusta
I
A u relu cian
pygm aea/cristata
spongiosa
caudatus
B urrellian
T urinian
N o r th
A m e ric a n
c h itin o z o a n
b io z o n e
¡
m orrisi
clingani
C heneyan
U p p er
O rd o ­
vician
velicuspis
I
E d en ian
clingani
S tre tfo rd ian
I
Ordovician
(p ars)
\
II
N o r th
N o r th
A m e ric a n
A tla n t ic
c o n o d o n t m id c o n tin e n t
b io z o n e s
conodont
b io z o n e s
tvaerensis
B r it i s h
re g io n a l
s e rie s an d
s ta g e s
I
System
|
Chronostratigraphy
In te r­
In te r­
n a tio n a l n a tio n a l
S e rie s s ta n d a rd
s ta g e s
ansennus
sw eeti
Seera
friendsvillensis
L.sp . A
??
m urchisoni
artus
polonicus
je n k in s i
Figure 1. 'Sandbian tim e slab' (shaded). B e tw e e n th e first a p p e a r a n c e o f N. gracilis a n d th e b e g in n in g o f th e D. clingani g ra p to lite B iozone.
G ra p to lite ra n g e s fo llo w [8 2 -8 6 ], T h e c o n o d o n t d a ta a re fro m [50] a n d c h itin o z o a n s a re fro m [87], T he c o rre la tio n b e tw e e n th e g ra p to lite , c o n o d o n t,
a n d c h itin o z o a n b io z o n e s fo llo w s [63],
d o i:1 0 .1 3 7 1 /jo u rn a l.p o n e .0 0 4 1 6 8 2 .g 0 0 1
T eichert, 1937 [48]; 3, m ost recent descriptions taxonom ically
sound, som e history o f m isidentification (e.g., Eoaquapulex socialis
(Levinson, 1961) [49]; 2, som e history o f m isidentification a n d
d escribed in o p en nom en clatu re (e.g., Krausella? spinosa (H arris,
1957) [23]; a n d 1, sim ple m orphology (i.e. c arap ace w ith few o r no
diagnostic characters, or m orphological v a riation poorly defined
o r poorly described, long history o f open nom en clatu re (e.g.,
Eurychilina? aff. Chilobolbina hyposalenia sensu K raft, 1962 [26], M ost
tax a fell into categories 4 a n d 1. T a x a w ith a w eighting o f ‘1’ w ere
excluded from the analysis. In o u r assessm ent o f the ostracod
assem blage d ataset w e have identified the p rim a ry sedim entary
setting, taphonom y, lithology, p alaeolatitude a n d sam pling points
(sum m arised in T ab le SI).
Results
U nlike fossil O rdovician plankton, w hose distribution p attern s
can b e evaluated from global datasets (e.g., [28-31], ostracods
possessed no pelagic stage in th eir lifecycle a n d th eir prim ary
distribution a t the inter-continental scale was therefore largely
controlled b y geography (e.g., [13,16], N evertheless, distribution
p attern s analysed o n a co n tinent-by-continent basis m ay still
reflect latitudinal o r en v ironm ental signatures. T h e research
m ethodology used here is based o n m ultivariate statistical
assessm ent o f presence-absence d a ta for L au re n tia n species from
w ell-defined tim e intervals w ithin the S andbian, specifically the
gracilis a n d bicornis graptolite biozones [32]. T h e ‘tim e slab’
a p p ro ac h is a co m m o n m eth o d used to deal w ith large fossil
datasets for en v ironm ental reconstruction [33,34] a n d has recently
b e en used for L ate O rdovician Zooplankton o f S an d b ian age [28—
30],
Tim e Slab D e fin itio n
T h e S an d b ian Stage o f the LTpper O rd o v ician has b e en selected
as a tim e slab for this study. It represents a n interval o f rock
deposited from a pproxim ately 461 to 456 m illion years ago [32]
a n d is well defined by the first ap p ea ran c e o f the graptolite
Nemagraptus gracilis. T h e graptolite Ensigraptus caudatus defines the
base o f the succeeding clingani B iozone a n d o f the K a tia n Stage
(Figure 1). T h e S an d b ian is th o u g h t to represent the onset o f a
cooling O rd o v ician clim ate, b u t th ere is no evidence for significant
clim ate fluctuation w ithin the interval itself [28-30], W ith in the
S an d b ian interval som e 229 ostracod tax a are described (from 13
regions; Figure 2), o f w hich 56 tax a are specifically lim ited to the
gracilis B iozone (ca 3 m illion years duration) a n d 117 tax a to the
bicornis B iozone (ca 2 m illion years d uration; see [32] for
chronology). W e have analysed the distribution p attern s o f
ostracods for the gracilis B iozone (5 regions; sam ples la , 2a, 2b,
3a, 8a a n d 13 o n T ab le S I a n d Figures 2, 3) a n d the bicornis
Biozone (11 regions; sam ples lb , 3b, 3c, 4a, 4b, 5 -7 , 8b, 9, 1 0 a 10c, 11 a n d 12 o n T ab le S I a n d Figures 2, 3). Analysis o f the total
(Sandbian) fauna (13 regions) was also u ndertaken.
O stracod Database
A S an d b ian d ataset (for stratigraphical definition see following
section) com prising 13 regions w ith 229 ostracod species from 88
g enera was com piled from p ublished literature (Table S I,
A ppendix SI). T ax o n o m ic filtering o f the original literatu re d a ta
was essential to m inim ise e rro r as species nom en clatu re has
evolved over the 80 years since the first descriptions o f N o rth
A m erican O rdovician ostracods (e.g., [17,20,35^17]. T a x a
described in open no m en clatu re or identified as “ cf.” a n d “ ?”
w ere ex am in ed a n d only those w hich closely resem bled their
holotype w ere included. T a x a described as “ aff.” w ere excluded.
A nd, tax a only identified to genus level w ere also excluded in ord er
to avoid ‘noise’ in the analysis. All o f the species are w eighted from
1 to 4 using the following criteria, w ith 4 b ein g the m ost reliable: 4,
m orphologically distinctive (lobation, m arginal structures etc.),
well described, stable n o m enclatorial history (e.g., Monoceratella teres
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August 2012 | Volume 7 | Issue 8 | e41682
Ordovician Ostracod Provinces o f Laurentia
(brachiopods, trilobites a n d ostracods)
stratigraphie correlation [47].
and
chitinozoans
for
G eographical spread o f data
L au re n tia was selected for analysis because it yields one o f the
m ost diverse a n d geographically w idespread ostracod faunas from
the L ate O rdovician (Sandbian) a n d because it includes a b ro a d
latitudinal range (greater th a n 35"; Figure 3) a n d a w ide range o f
p alaeoenvironm ents [14], W e have also c o m p a red the S andbian
ostracod d ataset from L au re n tia w ith those o f A valonia (for the
gracilis Biozone tim e slab) to show the relevant influence o f in te r­
continental versus intra-co n tin en tal e nvironm ental a n d g e ograph­
ical effects.
O rd in a tio n analysis
lu d
O rd in a tio n is a tool th a t allows the rep resen tatio n o f com plex
m ultivariate datasets in sim ple diagram s in w hich the axes
represent the m ain gradients in species com position in the original
dataset. T hese o rd in atio n axes thus represent environm ental
gradients (ideally the g radient o f a n enviro n m en tal variable, b u t
m ostly a com bination o f several variables) w hich drive the gradient
in species com position. In o rd in atio n diagram s, sam ples are
o rd e re d w ith respect to one a n o th e r o n the basis o f th eir species
com position (occurrence in the sam ple set) [52]. T h e sam ples th at
show m ore taxonom ic resem blance a re p laced m o re closely to
e ach other, w hereas sam ples th a t show greater difference are
placed a p art. As a p relim inary ‘D e tren d e d C o rrespondence
Analysis’ (DCA) using d e tre n d in g by segm ents revealed a strong
tu rn o v er in species com position b etw een the sam ples in all datasets
(length o f g radient > 6 SD , cf. J o n g m a n et al. 1995), we used the
unim odal indirect o rd in atio n m eth o d C o rrespondence Analysis
(CIA) for o u r analyses w ith the software package C A N O C O for
W indow s 4.5 [53]. F o u r datasets w ere analyzed. W e first
p erfo rm ed a test to assess the strength o f the in ter-continental
geographical effect o n the distribution o f ostracods, selecting the
early S an d b ian gracilis B iozone interval (ca 3 m illion years duratio n
from 461 M a), w ith five localities from A valonia a n d six localities
from L aurentia. W e th e n analysed the L au re n tia n d ataset for three
tim e intervals, the gracilis B iozone (ca 3 m illion years), the bicornis
Biozone (ca 2 m illion years), a n d the entire S an d b ian (ca 5 m illion
years). In o rd e r to test w h e th er a significant stratigraphical or
la titu d in a l/g eo g ra p h ic signal was presen t in the entire S andbian
dataset, w e used the direct equivalent o f CIA, viz. C anonical
C o rrespondence Analyses (CCA) w ith stratigraphy (dum m y
variables for gracilis a n d bicornis) a n d palaeolatitude (absolute
values o f degrees palaeolatitude) as the only variables respectively.
Significance was tested using M o n te C arlo p e rm u tatio n tests (4999
unrestricted perm utations, p < 0 ,0 0 1 ).
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Figure 2. O rdovician chronostratigraphy and lith ostratigraph y
fo r N orth Am erica, Canada, and th e Girvan district, southw est
Scotland. T h e N o rth A m e ric a n s tra tig ra p h y fo llo w s [88], C a n a d ia n
D iscussion
s tra tig ra p h y fo llo w s [89] a n d G irvan is b a s e d o n [46,90], T h e S a n d b ia n
s e c tio n s fro m w h ic h o s tra c o d s a re d o c u m e n te d a n d in c lu d e d in th is
s tu d y a re h ig h lig h te d g rey .
d o i:1 0 .1 3 7 1 /jo u rn a l.p o n e .0 0 4 1 6 8 2 .g 0 0 2
In te r-c o n tin e n ta l g e o g ra p h ica l analysis
F o r m u ch o f the O rdovician, L au re n tia was separated by the
Iapetus O c ea n from the p alaeocontinents o f Baltica a n d A valonia,
tho u g h this ocean n arro w ed by the L ate O rd o v ician [54,55].
D u rin g the S an d b ian no species are c o m m o n b etw een L au re n tia
a n d A valonia a n d only a few g enera a re com m on: Eridoconcha
d u rin g the early S an d b ian (gracilis Biozone), a n d Ceratopsis a n d
Easchmidtella du rin g the late S an d b ian (bicornis Biozone; [20,43,56],
O u r results thus support the suggestion th a t p alaeogeography
exerted the strongest control over the global distribution o f
O rd o v ician ostracods (e.g. [16], Evidently, as th ere are no species
in com m on, CIA analysis for the early S an d b ian (gracilis graptolite
Biozone) shows A valonian a n d L au re n tia n localities as two discrete
G raptolites a re the m ain biostratigraphic m arkers used for
correlating o u r chosen rock successions to g eth er w ith the coeval
co n o d o n t biozones [50], H e re the u p p e r Pagodus ansennus a n d
low er Amorphognathus timorensis (Prioniodus variabilis Subzone) c o n o ­
d o n t biozones are considered equivalent to the gracilis graptolite
B iozone, a n d the u p p e r A . tvaerensis B iozone (Prioniodus gerdae a n d
Prioniodus alobatus subzones) as equivalent to the bicornis graptolite
B iozone [50,51]. In som e cases w e have also used shelly fossils
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Ordovician Ostracod Provinces o f Laurentia
I
(Shallow Shelf
Late Ordovician
(Sandbian)
¡Deep Shelf
Ocean
'Equator|
Figure 3. Late O rdovician (Sandbian) palaeo geog rap hy of Laurentia, th e d istrib ution o f ostracod-bearing localities, and th e tw o
faunal provinces (m ap sligh tly m odified a fte r [22]).
d o i:1 0 .1 3 7 1 /jo u rn a l.p o n e .0 0 4 1 6 8 2 .g 0 0 3
clusters o f sam ples (data not shown). O stra co d fauna from the
early K a tia n (clingani Biozone) o f A valonia are sparse, only six
species bein g do cu m en ted a n d none o f these are c om m on to
L au re n tia [56], H ow ever, by the m id-late K a tia n a n d while the
Iapetus O c ea n was closing the A valonian fau n a b e cam e m ore
sim ilar to th a t o f L au re n tia a t the generic level [16] a n d b y the late
K a tia n included the earliest co m m o n species [57].
less interm ediate position o f O k la h o m a is not surprising, as this
was a n aulacogen basin [58] th a t straddled the shelf to basin a n d
therefore con tain ed elem ents th a t are b o th m idcontinent a n d
m arginal. N o significant stratigraphical signal was presen t (CCA,
p > 0 .0 5 ). Indeed, sam ples from regions for w hich b o th gracilis a n d
bicornis m aterials w ere available (Virginia, Pennsylvania a n d
O klahom a) consistently cluster together o n the basis o f region,
n ot stratigraphy (Figure 4a).
Analysis o f th e Sandbian Laurentian dataset
Analysis o f th e bicornis b iozone Laurentian dataset
A p relim in ary CIA analysis (not shown) identified the sam ples
from K entucky (5), M ichigan (7) a n d M ackenzie (13) as outliers.
T hese th ree sam ples are c h aracterized b y the highest percentages
(> 6 5 % ) o f endem ic species in the w hole dataset, a n d w ere
therefore om itted from fu rth er analyses. CIA analysis o f the entire
S an d b ian (gracilis a n d bicornis biozones) o stracod fauna revealed a
clear latitudinal signal, w ith all southern m arginal localities lying
o n the right side o f the first CIA axis, a n d m ost m id continent
localities o n the left (Figure 4a); this relation w ith latitude was
highly significant (CCA, p < 0 .0 0 1 ). T h u s, discrete M idcontinent
a n d M arginal ostracod provinces can b e recognised. T h e m o re or
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As in the entire S an d b ian d ataset analysis (see p a ra g ra p h
above), two ostracod provinces can be distinguished for the bicornis
B iozone tim e slab (Figure 4b). T hese are based o n 173 species
from 11 regions extending from A rctic C a n a d a to O k la h o m a (lb ,
3 b -c , 4 a -b , 5, 6, 7, 8b, 9, lO a-c, 11 & 12 o n Figures 2, 3; T able
SI). T h e ostracod fauna a t the geographical m argins o f L au re n tia
(lb , 3 b -c , 4a—b o n Figures 2, 3) shows considerable taxonom ic
difference from the m idcontinent L au re n tia n fauna (M innesota,
M ichigan, K entucky, O n ta rio , F ranklin D istrict; 5, 6, 7, 9, 10a—c,
11 & 12 o n Figures 2, 3). O k la h o m a (8b o n Figures 2, 3) represents
4
August 2012 | Volume 7 | Issue 8 | e41682
Ordovician Ostracod Provinces o f Laurentia
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V IR G 1 A
0KLA8A
0NT6
ifY2A
•M IN N 1 0 C
Figure 4. Correspondence Analyses (CA) o f th e (a) en tire Sandbian, (b) late Sandbian (bicornis tim e slab) and (c) ea rly Sandbian
[gracilistim e slab). M id c o n tin e n t P ro v in ce lo calities a re s h o w n a s filled circles, s o u th e r n M arginal P ro v in ce lo calities a s e m p ty circles. G rey p o ly g o n s
in d ic a te th e s o u th e r n M arginal P ro v in ce lo calities. For s a m p le lab els, s e e T a b le S1 a n d F igure 2.
d o i:1 0 .1 3 7 1 /jo u rn a l.p o n e .0 0 4 1 6 8 2 .g 0 0 4
the only m idcontinent locality show ing strong sim ilarities w ith the
m arginal L au re n tia n assem blages (cf. 3.2). T h e M idcontinent
Province com prises 48 species th a t are cosm opolitan across this
region, o f w hich 28 are exclusive to this province (e.g. Krausellci
calvini, Winchellatia longispina, Punctaparchites rugosus, Phelobythocypris
cylindrica, Saccaletia buskensis, Tetraciella ulrichi, Tetraciella ellipsilira,
Dicranella bicornis, Pseuclulrichia simplex (and see A ppendix S2;
Figure 5). T h e M id co n tin en t Province also contains 88 species
w hich have occurrences lim ited to a single depositional basin, a n d
are thus endem ic at a local level. T h e southern M arginal Province
com prises 24 species th a t are cosm opolitan across this region, o f
w hich four are exclusive to this region (Eurychilina strasburgensis,
Shenandoia acuminulata, ‘Ctenobolbincc ventrospinosa a n d Platybolbina
punctata). W ith in this province 33 species have occurrences
restricted to a single depositional basin a n d are thus endem ic at
a local level. O k la h o m a (Brom ide Form ation) shares ten species
w ith the southern M arginal Province a n d nine species w ith the
M id co n tin en t Province.
[60]. T h e o stracod distribution p a tte rn s can b e closely co rrelated
w ith those for b rachiopods. T h e M iddle a n d L ate O rdovician
b ra ch io p o d faunas show shallow benthic b ra ch io p o d assem blages
in m id co n tin en t L aurentia, w hereas a b ro a d e r range o f b ra ch io ­
p o d biofacies w ere developed in b o th eastern a n d w estern m argins
o f the p alaeo co n tin en t [64].
T h e factors th a t m ay control the two o stracod provinces are
those associated w ith geography, w ater d e p th (e.g. tem p eratu re,
salinity), latitu d e (climatic), a n d substrate.
G eography
T h e Palaeozoic geography o f L au re n tia has b e en review ed a n d
discussed in detail by piecing together inform ation from
palaeom agnetic studies a n d faunal distribution p attern s [22].
T h ey d e m o n stra ted th a t for m ost o f the O rd o v ician the central
p a rt o f the L au re n tia n c rato n was stable w hereas the m argins w ere
tectonically active. E peiric seas also repeatedly flooded the
L au re n tia n c rato n th a t resulted in thick successions o f O rdovician
c arb o n a te platform s [22,65]. T h e distribution p attern s o f m ost o f
the fossil groups th a t show distinct assem blages in the m arginal
a n d m id co n tin en t regions are widely reg ard ed as differences
betw een depositional environm ents [22,61,62,66], Flowever, a
peninsula lan d m ass existed betw een the different regions a n d
m ay, at least, have p artly separated the southern m arg in from the
m idcontinent a rea (see [22]; figures 8, 11). T h is landm ass m ight
have form ed a geographic b a rrie r for exchange o f ostracods a n d
o th er benthic faunal groups.
Analysis o f th e gracilis bio zo ne Laurentian dataset
T h e ostracod fauna from the gracilis Biozone o f L au re n tia
includes m aterials from V irginia, N ew Y ork, Pennsylvania, the
M ackenzie D istrict (C anada), a n d O k lah o m a (la , 2 a -2 b , 3a, 8a &
13 o n Figures 2, 3). O u t o f 111 species 88 species are endem ic to a
single basin a n d only a few species (23) are co m m o n to several
localities (A ppendix S3). C A analysis o f this lim ited gracilis dataset
suggests the presence o f a latitudinal signal (Figure 4c), b u t m ore
d a ta are need ed to confirm this.
Substrate
'M idcon tinen t:' and 'M a rg in a l' ostracod provinces
S eabed substrate is recognised as a n im p o rta n t factor in the
distribution o f O rd o v ician ostracods at a co n tinental scale [13].
F or exam ple, the c arb o n a te facies o f B altoscandia are d o m in ated
by palaeocope-rich assem blages, w hereas those from the A rm orican M assif are d om inantly m udstone lithofacies w ith binodicoperich assem blages [13]. T h e dom in an ce o f binodicopes is also
noticed in the O rd o v ician m udstones o f S audi A rab ia a n d
southern B ritain [13]. T h e L au re n tia n d ataset includes ostracods
sourced from b o th clastic, c arb o n a te a n d m ixed carbonate-clastic
Ethologies (T able SI). P alaeocopes are the d o m in a n t group (see
A ppendix SI) in b o th the c arbonates a n d m udstones. F or exam ple,
the high diversity fauna o f the shale unit o f the Bucke F o rm atio n o f
explored
T h e m idcontinent was ch aracterised by c arb o n a te platform s,
whilst the m argins w ere typically ra m p settings c haracterised by
c arbonates a n d m udstones w ith a b ro a d e r range o f facies from
peri-tidal to o u ter ra m p settings. Studies o f bryozoans, corals,
conodonts a n d trilobites [59-63] have distinguished discrete
L au re n tia n provinces in the O rdovician, largely controlled by
d ep th -related lithofacies, clim ate a n d sea level change. All the
above m en tio n ed faunal groups b ro ad ly show the sam e distribu­
tion p a tte rn as the ostracods. E ac h displays distinct m arginal
faunas w hich differentiate th em from the m id co n tin en t faunas
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Ordovician Ostracod Provinces o f Laurentia
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Ordovician Ostracod Provinces o f Laurentia
Figure 5. Late O rdovician ostracods o f th e M idcon tin ent and M arginal provinces and w idespread (pandem ic-Laurentian)
assemblages o f palaeocontinental Laurentia. (A-C) S a n d b ia n M id c o n tin e n t P rovince a ss e m b la g e ; (D-L) S a n d b ia n o s tra c o d a s s e m b la g e
w id e s p r e a d in b o th th e M id c o n tin e n t a n d M arginal p ro v in c e s; (M) S a n d b ia n M arginal P rovince a ss e m b la g e ; (N—R) K atian M arginal P rovince
a s s e m b la g e . (A) NMH UK O S 1 3 6 3 4 P u n cta p a rch ite s rugosus (Jo n e s, 1858) [91], c a ra p a c e , rig h t lateral view . (B) NMH UK O S 13479 W in c h e lla tia
lo n g is p in a Kay, 1 9 4 0 [37], te c n o m o rp h ic rig h t v alv e, lateral view . (C) MCZ 4 6 4 6 K rausella c a lv in i (Kay, 1940) [37], c a r a p a c e rig h t lateral view . (D) NMH
UK O S 1 3 5 0 9 E u rych ilin a in d iv is a L evinson, 1961 [49], ju v e n ile te c n o m o rp h ic rig h t valve, lateral view . (E) NHM UK OS 113216 E u ry c h ilin a re tic u la ta
Ulrich, 1 8 8 9 [92], h e te ro m o rp h ic rig h t v alv e, lateral view . (F) NMH UK O S13535 E ia lla tia la b io s a (Ulrich, 1894) [35] te c n o m o rp h ic rig h t valve, lateral
v iew . (G) NMH UK O S 1 3 6 1 7 B a ltice lla decke d (Harris, 1931) [38], c a ra p a c e , rig h t lateral v ie w (H) MCZ 4 5 9 9 b E o h o llin a depressa (Kay, 1940) [37],
te c n o m o rp h ic c a ra p a c e , rig h t lateral v ie w (I) NMH O S 1 3 5 3 8 E u ry b o lb in a b is p in a ta (Harris, 1957) [23], ju v e n ile te c n o m o rp h ic left valve, lateral view . (J)
NMH UK O S 1 3 5 2 6 E o a q u a p u le x so cia lis (L evinson, 1961) [49] te c n o m o rp h ic left v alve, lateral view . (K) BGS GSE 15 3 8 7 B a lto n o te lla p arsisp in o sa (Kraft,
1962) [26], c a ra p a c e , left v alv e, lateral v ie w (L) BGS GSE 15385 K rausella v a ria ta Kraft, 1962 [26], rig h t valve, lateral view . (M) BGS GSE 15384
'C te n o b o lb in a ' ve ntro spin osa Kraft, 1962 [26], h e te ro m o rp h ic , left valve, lateral view . (N) BGS 16E1961 O e p ike lla tu n n ic liffi W illiam s & Floyd, 2 0 0 0 [93],
h e te ro m o rp h ic rig h t v alv e, lateral v iew . (O) M PA 49672, B a ltic e lla sp., c a ra p a c e , left lateral view . (P) BGS G SE 15354 S te u s lo ffin a c u n e a ta (S teusloff, 1895)
[94], c a ra p a c e , left lateral v iew . (Q) BGS G SE15360, L o n g iscula cf. p e rfe c ta M eidla, 1993 [95], c a ra p a c e , left lateral view . (R) BGS G SE15365, Lon g iscula cf.
tersa (N eckaja, 1966) [96], c a ra p a c e , rig h t lateral v iew . F ig u res (A -D , F-H , J) a re fro m th e B rom ide F o rm a tio n o f O k la h o m a ; (E) is fro m St. P aul's
M in n e so ta ; (I) is fro m th e E d in b u rg F o rm a tio n o f V irginia (K-M) a re fro m th e A rdw ell Farm F o rm atio n , G irvan d istric t, S c o tla n d ; (N—R) a re fro m th e
C ra ig h e a d L im esto n e F o rm atio n , G irvan d istric t, S c o tla n d . S cale b a r (A) 2 1 0 p m ; (B) 2 50 p m ; (C) 2 9 4 pm ; (D) 3 3 8 p m ; (E) 3 2 0 p m ; (F) 193 pm ; (G)
20 5 p m ; (H); 3 4 6 p m ; (I) 3 4 6 p m ; (J) 5 4 5 p m ; (K-M, O, P) 5 0 0 p m ; (N) 1000 pm ; (Q, R) 2 0 0 p m . R e p o sito ries fo r s p e c im e n s a re : NHM, N atural H istory
M u se u m , L o n d o n ; MCZ M u se u m o f C o m p a ra tiv e Z o o lo g y , H arvard U niversity; BGS GSE, British G eological S urvey, K eyw orth, N o ttin g h a m .
d o i:1 0 .1 3 7 1 /jo u rn a l.p o n e .0 0 4 1 6 8 2 .g 0 0 5
O n ta rio is d o m in a ted by palaeocopes [27] as are the lim estone
facies o f the H a tte r a n d B enner form ations o f Pennsylvania [25].
T h u s, the dom in an ce a t m id to high palaeolatitude (A rm orican
M assif, S audi A rab ia a n d southern Britain) b y binodicopes, whilst
low palaeolatitudes (Baltoscandia, L aurentia) a re d o m in a ted by
palaeocopes m ay also be related to latitudinal tem p e ra tu re change
a n d n o t to substrate control alone. T herefore, w hile substrate m ay
have affected ostracods a t the very local level, p erh ap s indicated by
the high degree o f species-level endem icity in each basin, it is not
clearly expressed in the distribution p attern s o f binodicope-rich
a n d palaeocope-rich o stracod assem blages a t a provincial scale in
L aurentia.
B rom ide F o rm a tio n is also p re sen t in the shallow to deep shelf
facies o f the low er E sbataottine F o rm atio n o f the M ackenzie
D istrict a n d deep shelf facies o f the L incolnshire a n d E d in b u rg
form ations o f V irginia [17,20,26]. N evertheless, analysis o f the
p a n -L a u ren tian dataset does identify som e diagnostic species th a t
ch aracterize shallow a n d deep shelf facies o f the B rom ide
F o rm atio n in sim ilar settings elsew here. Leperditella rex in peri-tidal
a n d inn erm o st shelf facies o f the B rom ide F o rm a tio n is also
p re sen t only in the peri-tidal facies o f the H a tte r a n d B enner
form ations o f P ennsylvania a n d the in n er shelf facies o f the Bucke
F o rm atio n o f O n ta rio [20,25,27]. T h e distribution p attern s o f the
L au re n tia n ostracod fauna m ay therefore reflect som e depthrelated physical p a ram ete rs b etw een the ‘M a rg in al’ a n d the
‘M id c o n tin e n t’ provinces.
W ater d e p th
In previous studies o f L ate O rd o v ician ostracods w ater d ep th
has b e en considered to have a strong influence o n the distribution
o f ostracods [17,20,67]. T h u s, the two biofacies in the low er
E sbataottine F o rm atio n o f the M ackenzie district, C a n ad a , are
in te rp rete d as a d eep er platform biofacies a n d a shallow shelf
biofacies th a t also has som e elem ents extending into deep er shelf
facies [17]. Sim ilarly, a peri-tidal o stracod biofacies a n d a n openshelf biofacies are recognised in the c arb o n a te ra m p setting o f the
B rom ide F o rm atio n o f O k la h o m a [20]. H ow ever, the shallow a n d
deep shelf assem blages o f the low er E sbataottine F o rm atio n are o f
questionable significance w h en the ostracod fauna is considered on
the continental scale. M ost o f the supposed d eep er platform tax a
o f the low er E sbataottine F o rm atio n are found in shallow m arine
facies elsew here. T hese include species o f the g en era Eohollina,
Platyrhomboides, Dicranella, Ciyptophyllus, Winchellatia, Baltonotella,
Tetradella a n d Euprimitia. T h e form er six o f these are found in
shallow to deep shelf facies o f the B rom ide F o rm atio n o f
O klahom a, w hereas species o f Euprimitia are found in shallow
shelf facies o f the C ro w n P o in t F o rm atio n o f N ew Y ork a n d
species o f Tetradella are p re sen t in the shallow shelf facies o f the
H ull F o rm atio n o f O n ta rio [20,25,36]. T h e w ater d e p th assem ­
blages o f the E sbataottine F o rm a tio n w ere based o n generic-level
assessments, w hich m ay be, a t best, diagnostic only locally a n d
c a n n o t b e trac ed on the p a n -L a u ren tian scale [17]. T h e B rom ide
F o rm a tio n ’s shallow a n d deep shelf assem blages have only a few
species th a t are w idespread elsew here. Som e o f the diagnostic deep
shelf tax a o f the B rom ide F o rm atio n o f O k la h o m a such as
Baltonotella parsispinosa are also p re sen t in the shallow shelf facies o f
the C ro w n P o in t F o rm atio n o f N ew Y ork a n d deep shelf facies o f
the E d in b u rg F o rm atio n o f V irginia [20,25,26]. Sim ilarly,
Eurybolbina bispinata th a t occurs only in the deep shelf o f the
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Latitude
P alaeonvironm ental change associated w ith p alaeolatitude
exerted a strong influence o n the distribution o f fossil m arin e
organism s [21,28,29]. T h e distribution p a tte rn s o f Zooplankton
have already b e en show n to reflect clim ate zones in the Palaeozoic,
M esozoic a n d C enozoic [21,28,29,68-70]. T h e distribution o f
C enozoic b en th ic ostracods have also b e en d e m o n stra ted to be
influenced b y latitu d e [21,71]. T h e sam e p a tte rn o f latitudinalrestricted assem blages m ay also b e reflected in O rdovician
ostracods as the L au re n tia n o stracod provinces identified here
a re restricted to relatively n a rro w latitudinal ranges. T h e southern
M arginal P rovince localities are restricted to latitudes 2 1 -2 5 °S
w hereas the M id c o n tin e n t P rovince is confined to 17°S-5°N a n d
b o th o f these are c h aracterized b y species w ith a restricted
latitudinal range (Figure 2). T hese include Platybolbina punctata,
‘ Ctenobolbina’ centrospinosa,
Shenandoia acuminulata a n d Eurychilina
strasburgensis from the M arginal Province. Also, som e 28 species
(Hyperchilarina bella, Tetradella ellipsura, T. Ulrichi etc.) are restricted
only to the M id co n tin en t P rovince (A ppendix S2). T his suggests
th a t latitudinal te m p e ra tu re v a riation m ay have b e en a factor in
the distribution o f the L au re n tia n o stracod fauna, particularly as
this is also reflected in the b o u n d a ry betw een the tropical a n d
subtropical clim ate zone d e term in ed a t a b o u t 22°S from the
analysis o f Z ooplankton [29].
Trans-lapetus ostracod co n n e ctio n s b e tw e e n Laurentia
and Baltica
Schallreuter a n d Siveter [16] dem o n strated generic-links
betw een L aurentia, B altica a n d A valonia co m m encing du rin g
the late D arriw ilian (late M iddle O rdovician). T h ey arg u ed th a t
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August 2012 | Volume 7 | Issue 8 | e41682
Ordovician Ostracod Provinces o f Laurentia
M iddle O rd o v ician (late-Floian to m id-D arriw ilian) o f S pitsbergen
b e arin g strong generic affinities w ith faunas from the rest o f
L aurentia. H ow ever, a t species-level the Spitsbergen fauna is
do m in a ted by local endem ics, w ith only 13 from 60 species found
elsew here in N o rth A m erica. T h e y also related endem ism to local
environm ental effects influencing the evolution o f tax a th a t h a d
m igrated from elsew here.
faunal sim ilarity from the M iddle to L ate O rdovician was
indicative o f a narro w in g Iapetus O c ea n a n d the ability o f some
species to m igrate across this ocean. By L ate O rdovician tim es,
th ere w ere early species-level links b etw een L aurentia, B altica a n d
A valonia [46,57,67].
T h e southern M arginal P rovince ostracod faunas o f L au re n tia
established the earliest faunal links w ith the Baltic region du rin g
the early D arriw ilian, as seen b y the presence o f species o f Rivillina
a n d Laccochilina in the K an o sh Shale o f U ta h [72], species o f these
g enera bein g also p re sen t in approxim ately contem poraneous
deposits o f the Baltic region (see [13]. By the early L ate
O rd o v ician (bicornis Biozone) b o th the M arginal province faunas
a n d the M id co n tin en t Province faunas possessed generic links w ith
B altica [14] a n d A valonia (this study). T h ere afte r, the M arginal
Province faunas p ro d u c ed the first species-level links w ith B altica
a n d A valonia d u rin g the L ate O rdovician [57,67,73]. M any
species (Longiscula perfecta, L. tersa, Medianella longa, Steuslorfßna cuneata
a n d species o f Hemiaechminoides a n d lannekullea) th a t are restricted to
the M arginal Province o f L au re n tia are also p re sen t in the early
K a tia n o f the Baltic region (Figure 5; [67]. Sim ilar p a tte rn s o f
strong affinities b etw een L au re n tia n m arginal faunas across the
Iapetus O c ea n are also noticed in b rachiopods, trilobites,
conodonts a n d bryozoans [22,61,62,74],
C onclusions
Analysis o f the distribution p a tte rn s
L au re n tia n ostracods dem onstrates that:
Causes o f in tra -c o n tin e n ta l ostracod endem ism in
Laurentia
A t species-level, endem ism am ongst N o rth A m erican S andbianage ostracods is p ro n o u n ced , a n d reflects p attern s th a t w ere
already firm ly established in earlier D ap in g ian a n d D arriw ilian
o stracod faunas [23,72]. O f 229 S an d b ian species do cu m en ted
here, only 65 species occur in m o re th a n one sedim entary basin. A
few S an d b ian tax a are truly p a n d em ic to L au re n tia a n d include
Baltonotella parsispinosa, Hallatia labiosa, Eoaquapulex socialis, Eurychilina
subradiata, E. ventrosa, Macrocyproides trentonensis, Phelobythocypris
cylindrica a n d Cryptophyllus oboloides (A ppendix SI). E ndem ism is
m ost p ro m in e n t in the successions o f O k la h o m a (Southern
O k la h o m a A ulacogen Basin), V irginia (East S h e n a n d o ah V alley
Basin), the M ackenzie D istrict (R oot R iver Basin), M ichigan a n d
Lake T im m iskam ing, O n ta rio , C a n ad a . All o f these areas presen t
m ore th a n 50% endem ic species th a t are restricted to their
p a rticu la r d epo-centre a n d are n o t found elsew here (T able SI).
Sim ilar striking differences a t species level persist into the K a tia n
(clingani graptolite B iozone interval; for w hich see [36,37,67].
T h e strong intra-co n tin en tal endem ism a t the species-level in
the L au re n tia n o stracod fauna suggests th a t ra p id spéciation was
taking place from ancestor tax a in each basin. T h e com parative
ra te o f spéciation is different for different faunal groups [75]. In
m arin e b enthic ostracods the rate o f spéciation can b e com pleted
in less th a n 0.5 m illion years [76-78]. Spéciation m ay have been
driven b y b o th biotic (com petition) a n d abiotic factors such as
geographic h ab itat, geographic isolation, clim ate, tectonics, a n d
sea level change [75,77]. G eographic isolation form ed b y barriers
such as large deep-w ater bodies o r islands m ay result in spéciation
from founder species as noticed across the Isthm us o f P a n a m a for
ostracods [79,80], N otw ithstanding the presence o f a peninsula
betw een the M id co n tin en t a n d M arginal ostracod provinces, th a t
m ay have fostered allopatric spéciation, the p ro fo u n d endem ism o f
o stracod faunas b etw een individual basins in b o th the M id co n ti­
n e n t a n d M arginal provinces suggests en v ironm ental factors
o p eratin g a t the m ic ro -h ab itat scale in each depositional basin
m ay have profoundly influenced the p a th o f o stracod evolution.
Sim ilar p attern s o f strong endem ism a t the species-level are
re p o rte d from o th er O rd o v ician fossil groups. H a n se n a n d H olm er
[81] re p o rte d a diverse b ra ch io p o d fauna from the L ow er a n d
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o f L ate
O rdovician
1)
In ter-co n tin en tal geography exerts the strongest control on
o stracod distribution, the faunas o f L au re n tia a n d A valonia
plotting as discrete entities for the early S andbian, a n d
supporting palaeogeographical reconstructions for this tim e
interval;
2)
W ith in L au re n tia there is strong endem icity a t the specieslevel in each depositional basin, ra nging from 25% (e.g.
Foxe basin) to 75% (e.g. M ichigan basin), w ith the exception
o f G irv an w hich is a n allochthonous fauna;
3)
M ultivariate analyses o f the entire S andbian, gracilis a n d
bicornis tim e slabs allows for d e m a rca tio n o f M id co n tin en t
a n d southern M arginal o stracod provinces;
4)
M id co n tin en t a n d sou th ern M arginal o stracod provinces
a p p e a r to persist from the S a n d b ian into the K a tia n , a n d
faunal contacts w ith B altica a n d A valonia are strongest w ith
the M arginal Province, including the first species-level links,
possibly reflecting greater geographical proxim ity a n d w ater
d e p th tolerance o f these faunas;
5)
T h e M id co n tin en t a n d sou th ern M arginal provinces could,
in p a rt, reflect the T ro p ical a n d Subtropical clim ate belts
th a t have earlier b e e n identified based on Zooplankton
distributions;
6)
T h e strong regional endem icity o f the L au re n tia n ostracod
fauna a t species-level is reflected in o th er faunas such as
b rachiopods. T h e strong endem icity suggests th a t local
e n vironm ental p a ram ete rs o p e ratin g a t the m icro h ab itat
scale m ay have b e e n significant in driving local spéciation
events from ancestor species in each depositional basin.
Supporting Information
Table SI Sandbian ostracod localities o f North Amer­
ica, Canada and southw est Scotland. O straco d distribution
show n by Ethology, depositional setting, palaeolatitude, sam pling
points, taphonom y, total n u m b e r o f species in each F o rm atio n a n d
basin, a n d the n u m b e r a n d percen tag e o f endem ic species in each
depositional basin.
(D O C X )
Appendix SI Entire Sandbian tim e slab ostracod data­
set o f palaeocontinental Laurentia.
(XLSX)
Appendix S2 Sandbian (b ic o r n is ) tim e slab ostracod
dataset o f palaeocontinental Laurentia.
(XLSX)
Appendix S3 Sandbian (g r a c ilis ) tim e slab ostracod
dataset o f palaeocontinental Laurentia.
(XLSX)
8
August 2012 | Volume 7 | Issue 8 | e41682
Ordovician Ostracod Provinces o f Laurentia
A ck n ow led gm en ts
Author Contributions
This is a contribution to IG C P project 591. W e are grateful to Aimal K han
Kasi o f the C entre of Excellence in M ineralogy, University o f Balochistan
for providing literature.
Conceived and designed the experiments: M M M W T V KS JZ . Perform ed
the experiments: M M M W T V KS JZ . Analyzed the data: M M M W T V
KS JZ . C ontributed reagents/m aterials/analysis tools: M M M W T V KS
JZ . W rote the paper: M M M W T V KS JZ .
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