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102
Sponges
12
Marcelo G. Carrera and J. Keith Rigby
Sponges include the most primitive multicellular
organisms and have a record commencing in the
Late Precambrian. All major sponge groups are repre-
sented as Cambrian fossils. Ordovician sponges are
only moderately well known when compared with
other groups of fossils, though they are known from
most continents and 275 species have been described.
This relatively limited known diversity may be due in
part to the scarcity of taxonomic studies and in part
to the phylum’s conservative history.
Ordovician diversification is marked by the ex-
tensive radiation of some groups, whereas others
remained limited and little diversified. Even though
several sponge groups are moderately well known in
the Ordovician, their origins from Cambrian ele-
ments are obscure, largely because of significant breaks
between Middle Cambrian and Lower Ordovician
sponge records.
Ordovician sponge distribution is known in vary-
ing degrees of detail for different areas. The limited
stratigraphic information given in the older literature
makes the assignment of some ranges very difficult.
In addition, a particular problem is the correlation
of northern European sponge associations, which are
largely known only from Quaternary glacial erratic
boulders. Microfossils found in the associated matrix
indicate that most are of early Ashgill age (Hacht and
Rhebergen 1997; Rhebergen et al. 2001). However,
some limestone boulders in the same deposits are mid
to late Caradoc in age. As a consequence, accurate
stratigraphic positions cannot be determined for this
probable carbonate platform association, limiting the
detailed analysis.
We adopted two alternatives: a system in which
the first appearances (FAD) of European sponges are
allocated a range from time slice TS.5c to the last
appearances (LAD) during TS.6a. This system po-
tentially overestimates the real diversity values. The
other alternative is to exclude the European associa-
tion from the database, which considerably under-
estimates the values. The resulting diversity curves,
constructed using normalized diversity measures, are
shown in figure 12.1. The curve showing relative dis-
tribution for the time intervals for the major sponge
groups was calculated based on the first of the alter-
natives data (figure 12.2). The sponge database has
been incorporated into the database managed by
Arnold I. Miller (University of Cincinnati).
■Demosponges
The origin of the class Demospongea is obscured by
the poor record in the Lower Cambrian. Only rela-
tively primitive-appearing sponges with simple, tubu-
lar, thin-walled skeletons made by monaxons have been
reported (Rigby 1991). Similar forms and many addi-
tional monaxonid and probably keratose demosponges
are well represented in the Middle Cambrian of the
Burgess Shale in western Canada and upper Middle
Cambrian rocks in Utah (Rigby 1986). Monaxonid
genera such as Halichondrites and Choia continued to
exist and even proliferated during the Early Ordovician
(Rigby 1991). In the Late Ordovician only two genera
of the order Monaxonida (figure 12.2) have been re-
ported from TS.5b and TS.6a (Rigby 1971). The post-
Cambrian record of nonlithistid demosponges of the
Paleozoic is poor, and so most of the fossils included
within the demosponges belong to the order Lithistida.
Sponges 103
0-
5-
10-
15-
20-
25-
30-
40-
35-
45-
50-
TREMADOCIAN
Tremadoc
Ibexian
489 Ma
1a 1b 1c 1d 2a 2b 2c 3a 3b 4a 4b 4c 5a 5b 5c 5d 6a 6b 6c
472 460.5 44
3
Whiterockian
Species Diversity
Mohawkian Cincinnatian
Arenig Llanvirn Caradoc Ashgill
LOWER ORDOVICIAN MIDDLE ORDOVICIAN UPPER ORDOVICIAN
DARRIWILIAN
FIGURE 12.1. Normalized diversity curve for the Ordovician sponges at species level. Black line with rectangle points indicates diver-
sity including mid Caradoc–early Ashgill northern European sponges. Dashed line with circle points shows diversity minus the northern
European species.
Species Diversity
FIGURE 12.2. Normalized diversity
curve for the Ordovician sponges at
species level and contribution of
major sponge groups to total diver-
sity in the Ordovician. Most of the
sponge groups are shown at suborder
level. However, hexactinellids and
sphinctozoans are different sponge
classes, and monaxonids and heter-
actinids are sponge orders. The lim-
ited variability expressed in classes
such as Sphinctozoa and Hexactinel-
lida, compared with the lithistid
suborders, enforced a differential
comparison of groups.
Orchocladina
Only three genera of orchocladine lithisitids are
known from the Cambrian, but the suborder ex-
panded abruptly to more than 45 genera in the Or-
dovician. Approximately 10 genera are known from
the Silurian and fewer in the Mid Paleozoic. Skele-
tons made principally of dendroclones or chiasto-
clones characterize the Orchocladina. Three families
can be differentiated within the suborder based on
skeletal arrangement. Those considered to be an-
thaspidellids have relatively regular, simple skeletal
structure, typified by such genera as Archaeoscyphia,
Rhopalocoelia, or Calycocoelia. The streptosolenids
have a distinctly less well organized canal system and
skeletal structure. Lissocoelia and Streptosolen charac-
terize this group. The third group is the chiasto-
clonellids and is represented by only two Ordovician
genera.
In the Early Ordovician record, a few genera of the
Anthaspidellidae are associated with reef mounds,
built by microbes, sponges, and calathiid receptaculi-
tids. A sponge-microbial facies forming either bio-
herms or biostromes occurs in Lower Ordovician rocks
deposited around the margins of Laurentia from
Newfoundland to the Great Basin (Alberstadt and
Repetski 1989 and references therein). Other reef
mounds are known from the Argentine Precordillera
(Cañas and Carrera 1993), Hubei Province, South
China (Liu et al. 1997), and Siberia (Webby 1999).
Diversification of orchocladines increased by
TS.2c and is recognized mainly from the Shingle For-
mation of the Egan Range in the Great Basin, west-
ern United States (Bassler 1941; Johns 1994), with
the appearance of 11 species, and in the San Juan
Formation, Argentine Precordillera, with 8 species
(Carrera and Rigby 1999).
The peak of orchocladine diversification during
TS.4b was more significant, given that 20 species
occur in the San Juan Formation, Argentine Pre-
cordillera (Carrera and Rigby 1999), and 31 species
in the Antelope Valley Limestone of Nevada, the Wah
Wah Formation of Utah, and equivalents in the
Mazourka Canyon, California (Bassler 1941; Greife
and Langeheim 1963; Johns 1994).
Both diversification events were recorded in middle
to distal carbonate platform environments and were
coincident with sea level rises during the Oepikodus
evae transgression (TS.2b–c) and Lenodus variabilis–
Eoplacognathus suecicus transgression (TS.4a–b),
respectively.
In the Caradoc (TS.5a–c) the rate of orchocladine
expansion diminished, and only a few new genera
appeared. The majority of Late Ordovician orchocla-
dine genera had their origins in the Early and Mid
Ordovician. No significant expansion in genus diver-
sity occurs in the Late Ordovician; the slight recovery
in diversity values evidenced in TS.5d–6a is mainly
due to the appearance of new species of these older
genera. Upper Ordovician orchocladine occurrences
are localized in midcontinental, eastern, and western
North America (Rigby et al. 1993; Carrera and Rigby
1999 and references therein), in Baltica (Hacht and
Rhebergen 1997; Rhebergen et al. 2001), and in the
Malongulli Formation of New South Wales, Australia
(Rigby and Webby 1988).
Sphaerocladina
The suborder Sphaerocladina appeared in the Cara-
doc as typical spherical forms made of a tridimen-
sional gridwork of sphaerocladine spicules. They are
moderately rare forms in the Ordovician of North
America but are present in great numbers in the Sil-
urian. Abundant occurrences of these genera are re-
ported from the Late Ordovician of northern Europe.
The suborder probably became extinct toward the
end of the Devonian.
Only two genera, Astylospongia and Caryospongia,
appeared in the mid Caradoc of eastern North Amer-
ica, in the St. Lawrence Valley (Wilson 1948). An-
other three genera, Phialaspongia, Camellaspongia, and
Caliculospongia, are recorded as endemic (Rigby and
Bayer 1976) from the late Caradocian of the North
American Midcontinent.
Several species of Caryospongia, two of Astylos-
pongia, a single species of Palaeomanon, and the en-
demic Syltrochos have been reported from the middle
Caradoc–lower Ashgill rocks of northern Europe
(Hacht and Rhebergen 1997; Rhebergen et al. 2001).
In New South Wales, Australia, only the endemic
species Astylostroma micra is recorded from the late
Caradoc–early Ashgill, TS.5d–6a (Rigby and Webby
1988).
104 . .
Tricranocladina
The suborder is a conservative group that appeared
in the Caradocian and existed until the end of the
Permian. In general, outside Australia, the tricrano-
cladines are an exceedingly conservative group. In
the Late Ordovician Malongulli Formation of New
South Wales, however, several species of the endemic
genera Palmatohindia, Arborohindia, Belubulaspon-
gia, Fenestrospongia, and Mamelohindia were recorded
(Rigby and Webby 1988). The widespread species
Hindia sphaeroidalis is also reported. In North Amer-
ica only two species of tricranocladines are recorded
in the Ordovician of the North American Midconti-
nent, H. sphaeroidalis in the mid Caradoc to early
Ashgill and Cotylahindia panaca in the late Caradoc–
early Ashgill (TS.5d–6a). In northern Europe, only
the widespread H. sphaeroidalis is recorded.
Rhizomorina
Until the recent discovery of major sponge faunas
in the Ordovician of Australia (Rigby and Webby
1988) and in the Silurian of Arctic Canada (Rigby
and Chatterton 1989), the Rhizomorina were an ex-
clusively Upper Paleozoic group. Ordovician rhizo-
morines appear restricted in the late Caradoc–early
Ashgill of the Malongulli Formation in New South
Wales, Australia. The endemic genera Lewinia, Boon-
derooia, Taplowia, and Warrigalia and one species of
the genus Haplistion have been recorded from there
(Rigby and Webby 1988).
Megamorina
Discovery of the family Nexospongiidae allows dif-
ferentiation of two lineages within the megamorinids
(Carrera 1996). One line includes the family Sac-
cospongiidae with skeletons typically composed of
tracts of heloclones and monaxons. Rugospongia from
the Argentine Precordillera, Epiplastospongia and Sac-
cospongia from North America, and Cliefdenospongia
from New South Wales, Australia, are included in
this family. The other line has skeletons composed
of irregularly distributed heloclones and monaxons
that are not grouped in tracts. Nexospongia from
TS.2b and 2c of the Argentine Precordillera is to date
the only Paleozoic representative of this lineage. Mega-
morines recorded two small peaks of diversity—in
TS.2c, related to the Argentinian genera, and TS.5b,
related to North America and eastern Australia.
■Hexactinellids
Members of the class Hexactinellida are represented
by entire sponge skeletons in the Lower and Middle
Cambrian (Rigby 1986; Rigby and Hou 1995 and
references therein). The majority of these sponges re-
semble Protospongia and possess a single layer of par-
allel stauractines. Multivasculatus, a still more complex
hexactinellid with two or more layers of parallel hexa-
ctines, appears in the Late Cambrian (Finks 1983).
Hexactinellid sponges are much less diverse than
demosponges in the Ordovician, but they have more
recognizable roots to Cambrian faunas, in that at
least three families have a more continuous record
from the Cambrian to the Ordovician. The Cambrian
and Lower Ordovician families Protospongiidae and
Hintzespongiidae are represented by relatively prim-
itive hexactinellid assemblages, which apparently
thrived in black shales at the margins of Ordovician
continents. Thin-walled species with root tufts, re-
sembling those of the Cambrian, are found in similar
facies of the Ordovician, mainly shales or limestones
of quiet waters. These are more advanced in the sense
that they typically show at least a double layer of
spicules (dermal and gastral).
Species of Protospongia, Cyathophycus, Diagoniella,
Acanthodictya, and Palaeosacus have been described
from the upper Tremadocian black shales of Little
Métis, St. Lawrence Valley, eastern Canada (Dawson
1889). In addition, a more complex pelicaspongiid
hexactinellid has been described recently from the
upper Tremadocian of the Puna Region, northwest-
ern Argentina (Carrera 1998). There are few known
occurrences of Arenig hexactinellids.
Middle and Upper Ordovician records include a
widespread development of the primitive Protospongi-
idae and Hintzespongiidae in North America (Utica
Shale in New York, Trenton Group in Ohio, Ten-
nessee, and Kentucky, as well as the Vinini Formation
in Nevada).
Diversification was more significant in the family
Brachiospongiidae recorded in North America and
Sponges 105
Baltica (Wilson 1948; Hacht and Rhebergen 1997),
in the family Pyruspongiidae from the Williston Basin,
Manitoba (Rigby 1971), New South Wales, Australia
(Rigby and Webby 1988), and in the family Pelicas-
pongiidae, which has one described species from
Anticosti Island, Canada, and four species from New
South Wales, Australia. The families Teganiidae and
Pattersoniidae (e.g., Utica Shale in New York, and
Bigsby and Bellevue limestones in Kentucky) also
appeared in the Middle and Late Ordovician but
overall show only a minor expansion.
Middle and Upper Ordovician hexactinellids
have skeletons that are more complex and three-
dimensional, and some such forms invaded the plat-
form facies (Brachiospongioidea). One type is repre-
sented by Pattersonia, with a stout root tuft and no
central cavity. The other, including Brachiospongia
and Pyruspongia, has flat bottoms without root tufts
and a large central cavity.
Discrete siliceous spicule form genera of mainly
hexactinellid affinity have also been reported. For ex-
ample, the form genera Silicunculus, Kometia, Che-
lispongia, and other problematic forms (e.g., Pseudo-
lancicula) occur in rich and abundant assemblages
of disarticulated spicules in the late Caradoc–early
Ashgill Malongulli Formation of New South Wales,
Australia (Webby and Trotter 1993).
■Heteractinids
The heteractinids are a relatively minor group of
exclusively Paleozoic calcareous sponges with records
that can be traced back to the Early Cambrian, with
Eiffelia from Asia and the same genus in the Middle
Cambrian Burgess Shale of Canada (Rigby 1986).
Jawonya and Wagima (Kruse 1987) from the Middle
Cambrian of Australia were initially considered to
be sphinctozoan genera but are now interpreted as
heteractinids (Rigby 1991; Rigby et al. 1993) or two-
walled sponges with no clear affinities (Kruse 1996;
Debrenne and Reitner 2001).
Rigby (1991) visualized two different lineages for
the evolutionary history of the Heteractinida. One
leads from Eiffelia to the Carboniferous Zangerlispon-
gia, including the Ordovician genera Toquimiella from
North America and Chilcaia from the Argentine Pre-
cordillera (Carrera 1994). The sponges of this lineage
have skeletons that are thin walled, composed of geo-
metrically ranked sexiradiates and mainly diversified
in the Early and Mid Ordovician.
The other lineage, with Jawonya as the stem genus,
includes the Late Ordovician Astraeoconus, Astraeo-
spongium, Asteriospongia, and Constellatospongia (Rigby
1991 and references therein). This group has densely
packed irregularly oriented octactine-based skeletons
and thin walls in Jawonya and Astraeoconus or moder-
ately thick walls in Astraeospongium, Asteriospongia,
and Constellatospongia.
■Sphinctozoans
Sclerosponges of sphinctozoan grade have seg-
mented irregularly proliferated chambers, arranged
around a central cavity. They flourished mainly in the
Late Paleozoic and Early Mesozoic, but the earliest
known sphinctozoans have been reported from the
Middle Cambrian of New South Wales (Pickett and
Jell 1983).
Ordovician sphinctozoan sponges exhibit a dis-
tinctive biogeographic distribution restricted to Upper
Ordovician fold-belt successions of the Paleo-Pacific
Ocean rim. They occur in Alaska and northern Cali-
fornia (Rigby et al. 1988), in New South Wales, Aus-
tralia, and in successions in Asia at the margins of the
North China Platform and the Altai fold-belt region
of northern Xinjiang and the Altai-Sayan mountain
belt of Salair, southwestern Siberia (Pickett and Webby
2000 and references therein).
■Diversification Patterns
Ordovician sponge evolutionary development
shows three major diversification peaks (figures 12.1
and 12.2). A first one, in the Middle Ordovician, oc-
curred on carbonate platforms and includes mainly
the diversification of one group, the lithistid suborder
Orchocladina. However, this expansion in sponge di-
versification involves a more complex array of group
evolutionary patterns. In the Lower and Middle Ordo-
vician, a diversity peak of hexactinellids, monaxonids,
and a few orchocladines occurred in TS.1c. Orcho-
cladine diversity increased slightly in TS.1d–2a, and a
more important rise occurred in TS.2c, with mega-
morinids also appearing as minor components. There
was an important decline in TS.3b–4a before the great
rise near the base of the Darriwilian (TS.4a–b).
106 . .
The second and third diversification peaks (TS.5b
and 6a respectively) in the Late Ordovician are greater
in the sense that they involved not only greater diver-
sity but also a wider range of taxa, the suborders
Rhizomorina, Tricranocladina, Sphaerocladina, and
Megamorina, as well as a main diversification of
sphinctozoan and hexactinellid sponges. The or-
chocladines also recorded important peaks in species
diversity in the mid Caradoc (TS.5a–b) and early
Ashgill (TS.6a). However, diversity values of genera
and species of sphinctozoans, tricranocladines, and
sphaerocladines are more significant. The Late Or-
dovician sponge radiation was associated with mixed
calcareous-siliciclastic platforms, foreland basins, and
island arcs of tropical and subtropical areas.
Early Ordovician
Simple anthaspidellid forms of orchocladines first
appeared in the Early Ordovician. A few widespread
genera were contributors to the development of reef
mounds. The rise of orchocladines coincided with a
worldwide transgression documented in TS.1d–2a.
Sea level rose, and large parts of the low-relief conti-
nental margins were inundated toward the end of the
Early Ordovician (Ross and Ross 1992).
In the Lower Ordovician there was widespread
addition of sponge-bearing reef mounds. Rather
than being purely stromatolitic or thrombolitic, these
bioherms had a sponge-microbial fabric. The hard sub-
strate offered by the microbial structures supported a
diverse metazoan benthic fauna, including lithistid
sponges. After this initial success these lithistid-
microbe reef mounds virtually disappeared at the end
of the Early Ordovician. Only scattered examples
continued to appear in the Mid Ordovician.
The appearance of microbial-sponge mounds had
been favored by the abundance of suitable environ-
ments (carbonate shelf and ramps). The record of
Late Cambrian and Early Ordovician rocks indi-
cates that hard substrates, especially widespread hard-
grounds, had become abundant in shallow-shelf
environments by this time. This increase in hard
substrates has been related to the change in seawater
chemistry (“calcite” seas of Sandberg 1983). Appear-
ance of lithistid sponges in these environments may
also have been related to the late Tremadocian trans-
gression and the incursions of nutrient-rich waters
from deep basin and/or inner platform settings (Brun-
ton and Dixon 1994).
Mid Ordovician
There was a widespread modification in morphol-
ogy and body plans in sponges following the early
Darriwilian (TS.4a–b). The dominant anthaspi-
dellid forms of the Early Ordovician remained im-
portant, but a great variety of canal systems and
complexity of skeletal nets appeared. These latter dis-
coidal, globose, palmate, and digitate forms were all
better adapted to a wide range of carbonate ramp and
platform environments from nearshore to offshore
settings.
This important diversification, which occurred
mainly among the orchocladines, produced no signif-
icant geographic expansion. Until the Late Ordovi-
cian, sponges thrived across the carbonate platform
belt of Laurentia from the Great Basin to the north-
ern Appalachians and on the carbonate platforms in
the Argentine Precordillera and China (figure 12.3).
Faunal exchange between these areas was a common
feature during the Early and Mid Ordovician (Car-
rera and Rigby 1999).
The Mid Ordovician brought about an increasing
complexity in reefs. As a result, new Mid and Late
Ordovician reef associations include a variety of
baffling and encrusting organisms such as bryozoans,
corals, and stromatoporoids, but lithistid sponges
retain an accessory role in these younger bioherms.
Late Ordovician
In the Late Ordovician, sponges underwent maxi-
mum diversification, with the appearance of several
groups of lithistids (suborders Sphaerocladina, Rhi-
zomorina, and Tricranocladina) and of calcareous and
hexactinellid sponges. A high proportion of the gen-
era are endemic, indicating significant isolation and,
as a result, marked provincialism in some areas (Car-
rera and Rigby 1999).
Diversification of lithistid suborders started in the
mid Caradoc (TS.5b), with few representatives of
sphaerocladines and tricranocladines in eastern North
America and Baltica. A minor decrease is evidenced
in TS.5c with a major peak in TS.6a. The suborder
Rhizomorina is a characteristic, widely distributed
Sponges 107
group in the Late Paleozoic, but to date in the Or-
dovician, it is a suborder restricted to Australia. Its
peak of diversification is restricted to TS.5d and 6a.
After their maximum diversity in TS.4b, orcho-
cladines recorded two other maxima in the mid
Caradoc TS.5b and early Ashgill TS.6a, following a
somewhat similar pattern experienced by other lithis-
tid suborders. In a different scenario, and restricted to
western North America and eastern Australia, sphinc-
tozoans registered a diversification peak in the mid
Caradoc TS.5b with a decline in TS.5c–d and a
major peak in TS.6a. Hexactinellids recorded a di-
versification peak with first genera inhabiting shallow
platform facies in TS.4b to TS.5b, with a major peak
in TS.5c and TS.6a.
Late Ordovician sponge radiation occurs predom-
inantly in three main associations localized in Lau-
rentia, Baltica, and island-arc terranes, now located
in eastern Australia and the western North American
Cordillera. Diversification of sponges in Baltica rep-
resents an important event restricted to the mid
Caradoc and early Ashgill (TS.5c–6a); however, un-
certainty of ages of the Baltic faunas prevents precise
analysis. Radiation and migration patterns in Lau-
rentia appear to be well established and provide some
clues about patterns of sponge diversification and
migration across the whole paleocontinent and the
Iapetus Ocean.
The northern Appalachian sections record a long
history of sponge development. Anthaspidellid orcho-
cladines dominated the area from the Tremadocian to
the Darriwilian, for example, in western Newfound-
land, in the Romaine Formation of the Mingan Is-
lands, and in Vermont and New York (Rigby and
Desrochers 1995 and references therein). There was
an addition of possible migrants from the Argentine
Precordillera and the Great Basin in the early Cara-
doc, which raised to 20 the total number of anthas-
pidellid and streptosolenid orchocladines and meg-
amorinids (figures 12.3 and 12.4). The first arrivals
of sphaerocladines (Astylospongia and Caryospongia)
to Laurentia, probably from Baltica, occurred in the
mid Caradoc (TS.5b), in the Ottawa Group, St. Law-
rence Valley (Wilson 1948).
108 . .
4b–4c
3b–4a
2b–3a
1a–1c
FIGURE 12.3. Patterns of geographic distribution, diversification, and major migration routes of Early and Mid Ordovician sponges.
Sizes of circles and numbers indicate the numbers of species, and the relative sizes of the segments show the relative abundances of the
sponge groups. Different arrows indicate possible migration routes of the various groups.
The sponge fauna then migrated to the adjacent
Williston and Illinois basins. This migration was fa-
vored by a transgression that also probably carried
sponge larvae to nearby areas on the craton. Conse-
quently, late Caradoc and early Ashgill faunas are
widely distributed across the midcontinental interior
(figure 12.4). The geographic dispersion of sphaero-
cladines and tricranocladines continued in the Sil-
urian of Arctic Canada (Rigby and Chatterton 1989).
Representatives of tricranocladine and sphaerocla-
dine suborders are, in general, spherical forms with
centripetal skeletons and canal systems. The genus
Hindia and its relatives are the most widely distrib-
uted Paleozoic sponges and commonly occur together,
which suggests that the spherical forms were consid-
erably more mobile than the associated asymmetrical
genera (Rigby 1991; Carrera and Rigby 1999). These
morphologies are best adapted to changing environ-
ments with shifting substrate, which allowed them to
move into a wide range of environments, expanding
geographic distribution of these sponges in the Late
Ordovician.
Radiation and migratory patterns have also been
recognized in the spread of Pacific faunas (Carrera
and Rigby 1999) (figure 12.4). Ordovician sphincto-
zoans in eastern Australia (New South Wales; Pickett
and Webby 2000) occur in an island-arc terrane, as
do those in Alaska and in the Klamath Mountains,
California (Rigby et al. 1988). They also occur in
northwestern China (Chinese Altai Mountains) in
island arcs, and recent finds have been made of
Cliefdenella-like forms in Kazakhstan, also in an
island-arc setting (Webby pers. comm.).
Sphinctozoans are very rare in platform associations
of the world, many of which are still preserved, but
the island-arc terranes have been largely subducted.
Therefore, the positive record of sphinctozoans in the
few preserved island arcs is overwhelming evidence
that they must have diversified and dominated in such
habitats, at least during the Ordovician.
Sponges 109
5c–5d
FIGURE 12.4. Patterns of geographic distribution, diversification, and major migration routes of Mid and Late Ordovician sponges.
Sizes of circles and the numbers indicate the numbers of species, and the relative sizes of the segments represent the relative abundances
of sponge groups. Different arrows indicate possible migration routes of the various groups.
■Concluding Remarks
Globally, the Ordovician was marked by increased
levels of tectonic activity. The Early Ordovician doc-
uments a final stage of extensive tectonism and the
development of vast carbonate platforms. Volcanism
and orogeny (e.g., Taconic Orogeny) increased sub-
stantially during Mid and Late Ordovician time, as-
sociated in part with the closing of the Iapetus Ocean.
Miller and Mao (1995) suggested that tectonic ac-
tivity, mainly volcanism and orogeny, was responsible
for an increase in marine biodiversity. They proposed
that the increment of Mid and Late Ordovician bio-
diversity occurred mainly in tectonic active zones
such as foreland basins and transition zones, whereas
the generic richness of carbonate platforms remained
fairly stable through the entire Ordovician. They based
their assumptions in part on the increase in habitat
partitioning and shifting substrates that developed
during tectonic activity.
The peak of sponge diversity in the Mid Ordovi-
cian, although restricted to the orchocladines, occurred
in carbonate platforms, whereas that of hexactinellids
and monaxonids occurred mainly in deep-water
environments. In the Late Ordovician the lithistid
suborders Sphaerocladina, Rhizomorina, and Tri-
cranocladina, the calcareous sphinctozoans, and the
hexactinellid sponges are main representatives of the
major diversity peak. Late Ordovician sponge radia-
tion was localized in areas of active tectonism and
orogeny (with the probable exception of Baltica, where
sponges were apparently derived from a carbonate
platform).
All these regions (including Baltica) record abun-
dant sponge faunas, along with spicule-rich deposits
or concentrations of opaline silica. They are unusual
in the fossil record and document times and areas of
high productivity. Such areas in modern seas corre-
spond to areas of upwelling (Parrish 1982) where
nutrients are brought up into the photic zone.
More or less contemporaneous sponge associations
from midcontinental North America can be used as
an example of differential diversification of sponges
in two dissimilar geodynamic contexts. These sponge
associations have partially comparable relationships
with coral assemblages from the vast transcontinental
Red River–Stony Mountain Province and, in its
eastern part, the discrete Richmond Province (Elias
1995). The region, especially east of the Transconti-
nental Arch, was influenced by a combination of tec-
tonic activity (Taconic Appalachians) and a related
transgressive-regressive cycle. Within the main western
part of the Red River–Stony Mountain Province,
deposition on the continental shelf and in the epeiric
sea was predominantly of carbonates (Williston and
Hudson Bay basins). Orchocladines and some heter-
actinid sponges mainly occur in these regions, with
only limited diversification. In provincial components
east of the transcontinental arch (Illinois and Michi-
gan basins), however, clastic deposition was signifi-
cant (Elias 1995). It included the Maquoketa Group,
which consists mainly of argillaceous material, prob-
ably principally derived from the Taconic upland.
Diversification of lithistid tricranocladines, sphaero-
cladines, megamorines, and hexactinellids in this
eastern region was important and occurred in a more
tectonically active setting.
Diversification of sponges in the Ordovician shows
a strong geographic and environmental overprint.
Early and Mid Ordovician diversification follows a
worldwide pattern. Curves of diversity peaks in the
Great Basin and in the Appalachians are very similar
to those of the Argentine Precordillera and China. In
the Late Ordovician, however, paleogeography exerted
a more direct influence, with peaks of diversity ap-
pearing to be slightly decoupled between these geo-
graphic regions (see figures 12.3 and 12.4). Ordovician
radiation of sponges appears to be also influenced by
the global sea level pattern (Ross and Ross 1992), with
major peaks coinciding with high sea level intervals.
The sponge decline in Ashgill TS.6b predates the
Hirnantian extinction. Recovery of sponge diversity
in the Lower Silurian involved major groups that
were dominant in the Ashgill diversification peak.
Silurian assemblages are mainly composed of or-
chocladines, sphaerocladines, tricranocladines, and
some hexactinellid groups.
Important changes in sponge classification and
significant recent discoveries have occurred in the
past 20 years. Radiation patterns and the compilation
of sponges according to Sepkoski’s evolutionary fau-
nas (Sepkoski and Sheehan 1983), therefore, should
be revised in light of these new taxonomic studies and
the Ordovician data compiled in this work.
110 . .
We are grateful to John Pickett and Ronald Johns
for their helpful, supportive comments in their re-
views of the chapter. Appreciation is extended to the
editors of the book, especially Barry D. Webby, for
their useful comments on earlier versions of the man-
uscript. MGC acknowledges support from CONICET
and ANPCyT.
Sponges 111
