Benton M.J. Introduction to paleobiology and the fossil record

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(b)

Figure 11.30 (a) Kilbuchophyllum – an Ordovician scleractiniomorph coral (approximately ×10).

(b) Reconstruction of Archisaccophyllia together with lingulid brachiopods, priapulid worms and

tall cylindrical sponges. (a, courtesy of Colin Scrutton; b, courtesy of Hou Xian-guang.)

(a)

THE BASAL METAZOANS: SPONGES AND CORALS 289

(a)

(f)(e)

(b) (c) (d)

Figure 11.31 Some typical scleractinian corals: (a) Hydnophora (Recent); (b) Gablonzeria (Triassic);

(Eocene). All natural size. (From Scrutton & Rosen 1985.)

Box 11.8 Reef building through time

Reefs were not just corals! Throughout geological time, a whole range of mainly modular organisms

have contributed to these calcareous structures (Wood 2001), providing, too, signiﬁ cant carbonate

factories often spalling off the continental shelves into deeper waters. While Early Paleozoic shallow-

marine environments were dominated by various microbes, bryozoans, corals and sponges (including

archaeocyaths and stromatoporoids), the Mesozoic and Cenozoic were characterized by scleractinian

corals (Fig. 11.32). Through time, the more restricted environments were home to stromatolites

during the Paleozoic and early Mesozoic; these too popped up after some extinction events, in for

example the Early Silurian and Early Triassic, as disaster species. The later Mesozoic and Cenozoic

saw the arrival of serpulid and oyster reefs in these more stressed brackish or hypersaline habitats.

Deeper-water environments were the domain of the spicular sponges together with occasional sym-

biotic (ahermatypic) scleractinian corals.

Continued

290 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

Time (Ma)

CenozoicMesozoicPaleozoic

Era Period

Quaternary

Tertiary

Cretaceous

Jurassic

Triassic

Permian

Carboniferous

Devonian

Silurian

Ordovician

Cambrian

Vendian

144

206

251

290

353.7

408.5

439

500

543

565

2500

3600

Deep marine

(aphotic)

Te m p .

–cold

Shallow marine

(photic)

Tropical Subtropical

Restricted marine

(brackish or hypersaline)

Increasing restriction

Asymbiotic

scleractinian

corals

Asymbiotic

scleractinian

corals

Spicular sponges

Microbes

Spicular

sponges

Spicular sponges

Microbes

SPONGES

THROMBOLITES

Rugose

corals

Oysters

Serpulids

Bryozoans–

Serpulids

STROMATOLITES

CYANOBACTERIA

CALCIFIED CYANOBACTERIA

ARCHAEOCYATHS

LITHISTID SPONGES

BRYOZOANS

CORALS

CRINOIDS

MICROBES

STROMATOPOROID SPONGES

MICROBES

TABULATE CORALS

CALCIFIED CYANOBACTERIA

RED ALGAE

STROMATOLITES/THROMBOLITES

Chaetetids

Bryozoans

RUDIST BIVALVES

STROMATOPOROIDS

SCLERACT-

INIAN

CORALS

FRONDOSE BRYOZOANS

Scleractinian corals

PHOTOSYMBIOTIC

SCLERACTINIAN CORALS

MICROBES

PHOTOSYMBIOTIC

SCLERACTINIAN CORALS

CORALLINE

ALGAE

CALCIFIED SPONGES

STROMATOLITES

CALCIFIED SPONGES

Tu bi ph yt es

FRONDOSE & ENCRUSTING BRYOZOANS

PHYLLOID ALGAE

Halimedia

Vermetids

Figure 11.32 Reef building through time. (From Wood 2001.)

THE BASAL METAZOANS: SPONGES AND CORALS 291

Box 11.9 Corals and the Earth’s rotation

Through time, the Earth has changed its rate of rotation, and days have become longer. This extraor-

dinary discovery has come from detailed analysis of the growth bands on coral epithecae. Well-

preserved corals often display ﬁ ne growth lines, grouped together into thicker bands; the former are

thought to reﬂ ect daily growth while the latter bands are monthly growth cycles, controlled by the

lunar orbit. A set of more widely spaced bands may represent yearly growth. In a classic study, John

Wells of Cornell University counted the growth lines on a variety of Devonian corals (Fig. 11.33)

and suggested that the Devonian year had about 400 days. The implication that Devonian days were

shorter suggests the Earth’s rate of rotation is decreasing due to the gravitation pull of the moon.

Ivan Gill of the University of New Orleans and his colleagues (2006) have taken the story much

further. Using a range of more sophisticated techniques, including the scanning electron microscope

and backscattered electron imaging, it is now possible to identify with much more precision microscale

banding in some coral species that could ultimately act as proxies for daily changes in our environ-

ment, highlighting short-term climatic and other events. Moreover, this style of banding can help

decipher a great deal more about the detailed mechanisms and timing of skeletalization within the

corals as a whole.

Figure 11.33 Devonian banded coral, Heliophyllum halli (×3). (Courtesy of Colin Scrutton.)

292 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

(a)

(b)

clusters of crinoids

fasciculate rugose corals

small favositid and

heliolitid tabulate corals

small stromatoporoids

generalist brachiopods

and molluscs

large, platy to domed favositid and

heliolitid tabulate corals

diverse crinoids

massive stromatoporoids

cerioid, astraeoid,

thamnasterioid and

aphroid rugose corals

specialist, small to large brachiopods

and mollusks

Figure 11.34 Pioneer (a) and climax (b) reef communities in Silurian and Devonan reef systems. (From

Copper, P. 1988. Palaios 3.)

long and up to 300 km wide and visible from

space. It is a long-lived structure dating back

to the Miocene. The reef extends from 9˚ to

25˚ south and comprises many multicolored

scleractinian corals together with many other

invertebrates and calcareous algae. The fore-

reef deposits tumble eastwards into the

western Paciﬁ c; landward back-reef lagoons

are developed against eastern Australia. Can

such reef constellations really be recognized

in the fossil record? On the adjacent continent

the Upper Devonian rocks of the Canning

Basin contain fossil barrier reefs dominated

by calcareous algae and tabulate and rugose

corals together with stromatoporoids and

microbiolites. The reef and its associated

facies can be mapped in considerable detail,

as the Windjana Gorge dissects the near-

horizontal strata of the northern margin of

the Canning Basin (Fig. 11.35). An unbedded

core of calcareous algae, corals and stromato-

poroids sheltered a back-reef and lagoonal

environment packed with calcareous algae,

corals, stromatoporoids and crinoids together

with brachiopods, bivalves, cephalopods and

gastropods. In front the fore-reef was steep

and littered by reef talus. However, during the

Late Devonian extinction event, at the end

of the Frasnian, associations dominated by

rugose and tabulate corals together with stro-

matoporoids disappeared; this type of reef

ecosystem never recovered.

THE BASAL METAZOANS: SPONGES AND CORALS 293

Distribution: corals through time

Although some coral-like forms have been

described from the Cambrian, most lack

typical zooantharian structures. Cothonion,

for example, with poorly integrated corallite-

like clusters and opercula was probably a

Cambrian experiment with coralization (Fig.

11.36). The ﬁ rst tabulates appeared during

the Early Ordovician with cerioid growth

modes; tabulae were rare and septa and mural

pores were absent. Nevertheless, by the Mid

and Late Ordovician the more typical charac-

ters of the Tabulata had evolved when they

dominated coral faunas. Some workers have

removed the heliolitids, with individual coral-

lites mutually separated by extensive coenos-

teum, from the Tabulata, as a distinct order.

The group was common until the Early Silu-

rian when the more open structures of the

favositids with massive cerioid colonies began

to dominate, although they were already

abundant in the Ordovician.

The Rugosa appear during the Mid

Ordovician. Many of the evolutionary trends

across the order have been repeated many

times in different families. In general terms the

group evolved more complex, heavier skeletons

prior to extinction at the end of the Permian.

The ﬁ rst scleractinians were established by

the Mid Triassic, derived from multiple ances-

tors among the sea anemones. The Triassic

taxa were probably photosymbiotic, forming

patch reefs in parts of the Tethyan belt. The

group, however, expanded signiﬁ cantly during

the Jurassic with the radiation of both reef-

building and non-reef-building groups in

shallow- and deep-water environments, respec-

tively. Scleractinian evolution was marked by

a number of morphological trends: solitary life

strategies were eventually superseded by a

dominance of colonial forms that display tran-

sitions from low levels of integration in phace-

loid growth modes to higher levels in meandroid

styles, common in modern reefs.

Corals have been used effectively for the

correlation of Silurian (tabulates) and Devo-

nian (rugose) strata but they have been proved

most useful for Carboniferous biostratigra-

phy. During the early 1900s, Arthur Vaughan

studied in detail the distribution of Lower

Carboniferous corals in Belgium and Britain

and he argued they would be of great value

in Carboniferous biostratigraphy. Corals are

very common, often widespread, usually dis-

tinctive, and well preserved in the Lower Car-

boniferous rocks of Europe. However, more

modern studies on Carboniferous biostratig-

raphy using microfossils such as conodonts

and foraminiferans, together with sequence

stratigraphy, have shown that the occurrences

of corals are controlled as much by rock facies

as by time, and so they cannot be used for

global correlation. Nevertheless, many corals

are still useful for local correlations, and

Lower Carboniferous stratigraphy (Fig. 11.37)

has been reﬁ ned on the basis of Vaughan’s

pioneer work and more modern techniques

(Riley 1993).

But was coloniality amongst the bilaterians

a derived condition or, more controversially,

a primitive state (Box 11.10)?

(a) (b)

Figure 11.35 Devonian reefs of the Canning Basin, Australia: (a) main face, and (b) Windjana Gorge.

The fore-reef slope in the foreground has large blocks of unbedded reef material in the background; the

reef is prograding over the fore-reef toward the viewer. (Courtesy of Rachel Wood.)

post-PaleozoicPaleozoicPrecambrian

post TrPCDSOCmETr

Heterocorallia

RugosaCothoniida

Zoanthiniaria

Tabulata

Actiniaria

Corallimorpharia

ScleractiniaKilbuchophyllida

Figure 11.36 Stratigraphic ranges of the main coral groups. Geological period abbreviations are

standard, running from Ediacarian (E) to Triassic (Tr). (Replotted from Clarkson 1998.)

Stages

Brigantian

Asbian

Holkerian

Arundian

Chadian

Courceyan

Dinantian

Vaughan

1905–1906

(Avon Gorge)

Horizon

Seminula

Zone

Dibunophyllum

Zone

Zaphrentis

Zone

Cleistopora

Zone

Modiola Zone

Old Red

Sandstone facies

Clevedonian = Lower Avonian = Tournaisian Kidwellian = Upper Avonian = Viséan

Syringothyris

(Lower

Caninia)

Zone

Figure 11.37 Coral biostratigraphy for the Dinantian. (Redrawn

from various sources.)

THE BASAL METAZOANS: SPONGES AND CORALS 295

Box 11.10 Colonies: the source of the ﬁ rst bilaterians?

Perhaps colonial organisms in the Late Precambrian had a deep signiﬁ cance for animal evolution.

Is it possible that the complex bilateralians we see today originated within a colonial structure prior

to the Cambrian explosion? Ruth Dewel (Appalachian State University, Boone) has developed a

model involving the individuation of colony modules. Colonial organisms tend to develop greater

degrees of integration and internal specialization through time as they begin to function as superor-

ganisms. In this model an organism with bilaterian features, i.e. bilateral symmetry, with three body

regions and epithelium-lined body compartments, can apparently break away from a complex, inte-

grated cnidarian colony to form something like a pennatulacean octocoral that may have formed

the stem group to both the cnidarians and bilateralians (Dewel 2000). A pathway from sponge to

cnidarian to bilateralian body plans in her model is plausible (Fig. 11.38). Pure fantasy? Why then

are outgroups to the early bilaterians large and simple whereas the bilaterians, themselves, are small

and complex? It is an interesting hypothesis; but such hypotheses are there to be rigorously tested

and falsiﬁ ed.

sponge grade

clonal sponge grade

modular sponge

choanoflagellate colony

choanoflagellate

individualized colony

(bilaterian)

colonial cnidarian

(two branches)

Figure 11.38 A possible origin for bilaterians in the colonies? The process involves the

development of multicellularity, followed by multifunctional modules (short arrows) and ﬁ nally a

shift in their functional morphology within the cnidarians and the bilaterians. (From Dewel

2000.)

296 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

Review questions

1 Superﬁ cially sponges seem to be a compact

morphological group but modern molecu-

lar data indicate that they are not mono-

phyletic. Are there in fact morphological

differences between the main sponge

groups that back this up?

2 The archaeocyaths were some of the ﬁ rst

metazoan reef builders, dominating the

Early to Mid Cambrian tropics. How did

their reef communities differ from the pre-

vious buildups of the Late Proterozoic

Namapoikea and those later dominated

by the corals and the stromatoporoids?

3 Tabulate corals were important frame-

building organisms during intervals in the

Paleozoic. Is there any evidence to sug-

gest that they were associated with

zooanthellae?

4 What do aberrant cnidarian taxa such as

Archisaccophyllia and Kilbuchophyllum

tell us about the possible track of coral

evolution?

5 Metazoan reefs have been an important

part of the marine ecosystem since the

Early Cambrian. But during intervals of

extreme stress, for example just after

severe extinction events, such reefs disap-

pear and the planet momentarily returns

to a “stromatolite world”. How can such

an ecosystem, most characteristic of the

Proterozoic, re-establish itself?

Further reading

Clarkson, E.N.K. 1998. Invertebrate Palaeontology and

Evolution, 4th edn. Chapman and Hall, London.

(An excellent, more advanced text, clearly written

and well illustrated.)

Rigby, J.K. 1987. Phylum Porifera. In Boardman, R.S.,

Cheetham, A.H. & Rowell, A.J. (eds) Fossil Inverte-

brates. Blackwell Scientiﬁ c Publications, Oxford,

UK, pp. 116–39. (A comprehensive, more advanced

text with emphasis on taxonomy; extravagantly

illustrated.)

Rigby, J.K. & Gangloff, R.A. 1987. Phylum Archaeocy-

atha. In Boardman, R.S., Cheetham, A.H. and

Rowell, A.J. (eds) Fossil Invertebrates. Blackwell

Scientiﬁ c Publications, Oxford, UK, pp. 107–15. (A

comprehensive, more advanced text with emphasis

on taxonomy; extravagantly illustrated.)

Rigby, J.K. & Scrutton, C.T. 1985. Sponges, chaetetids

and stromatoporoids. In Murray, J.W. (ed.) Atlas of

Invertebrate Macrofossils. Longman, London, pp.

3–10. (A useful, mainly photographic review of the

group.)

Scrutton, C.T. 1997. The Palaeozoic corals, I: origins

and relationships. Proceedings of the Yorkshire Geo-

logical Society 51, 177–208. (First of two useful

review papers.)

Scrutton, C.T. 1998. The Palaeozoic corals, II: structure,

variation and palaeoecology. Proceedings of the

Yorkshire Geological Society 52, 1–57. (Second of

two useful review papers.)

Scrutton, C.T. & Rosen, B.R. 1985. Cnidaria. In Murray,

J.W. (ed.) Atlas of Invertebrate Macrofossils.

Longman, London, pp. 11–46. (A useful, mainly

photographic, review of the group.)

Wood, R. 1999. Reef Evolution. Oxford University

Press, Oxford, UK. (Comprehensive overview of

reefs through time.)

References

Debrenne, F. 2007. Lower Cambrian archeocyathan

bioconstructions. Comptes Rendus Palevol 6, 5–19.

Dewel, R.A. 2000. Colonial origin for Eumetazoa:

major morphological transitions and the origin of

bilateralian complexity. Journal of Morphology 243,

35–74.

Gill, I.P., Dickson, J.A.D. & Hubbard, D.K. 2006. Daily

banding in corals: implications for paleoclimatic

reconstruction and skeletalization. Journal of Sedi-

mentary Research 76, 683–8.

Hammer, Ø. 1998. Regulation of astogeny in halysitid

tabulates. Acta Palaeontologica Polonica 43,

635–51.

Hou Xian-guang, Stanley, G.D. Jr., Zhao Jie & Ma

Xiao-ya 2005. Cambrian anemones with preserved

soft tissue from the Chengjiang biota, China. Lethaia

38, 193–203.

Kershaw, S. 1990. Stromatoporoid palaeobiology and

taphonomy in a Silurian biostrome in Gotland,

Sweden. Palaeontology 33, 681–706.

Riley, N.J. 1993. Dinantian (Lower Carboniferous) bio-

stratigraphy and chronostratigraphy in the British

Isles. Journal of the Geological Society, London 150,

427–46.

Savarese, M. 1992. Functional analysis of archaeocya-

than skeletal morphology and its paleobiological

implications. Paleobiology 18, 464–80.

Sperling, E.A., Pisani, D. & Peterson, K.J. 2007. Porif-

eran paraphyly and its implications for Precambrian

paleobiology. Special Paper Geological Society,

London 286, 355–68.

Wood, R. 1990. Reef-building sponges. American Sci-

entist 78, 224–35.

Wood, R. 2001. Biodiversity and the history of reefs.

Geological Journal 36, 251–63.

Wood, R., Grotzinger, J.P. & Dickson, J.A.D. 2002.

Proterozoic modular biomineralized metazoan from

the Nama Group, Namibia. Science 296, 2383–6.

Wood, R., Zhuravlev, A.Yu., Debrenne, F. 1992. Func-

tional biology and ecology of Archaeocyatha. Palaios

7, 131–56

Chapter 12

Spiralians 1: lophophorates

Key points

• Three spiralian invertebrate groups have lophophores, a ﬁ lamentous feeding organ:

brachiopods, bryozoans and phoronids.

• Brachiopods are twin-valved shellﬁ sh, with a lophophore and usually a pedicle, adapted

to a wide range of life strategies on the seaﬂ oor.

• The phylum Brachiopoda is currently divided into the linguliformeans, with organo-

phosphatic shells, and the craniiformeans and rhynchonelliformeans, both with calcare-

ous shells.

• Paleozoic communities were dominated by orthides and strophomenides, together with

a variety of spire-bearing forms; rhynchonellides and terebratulides are typical of the

lower-diversity post-Paleozoic brachiopod assemblages.

• Brachiopods dominated the ﬁ lter-feeding benthos of the Paleozoic but never fully recov-

ered in abundance or diversity from losses during the end-Permian mass extinction.

• Living brachiopods are relatively rare, occupying mostly cryptic and deep-water

habitats.

• Bryozoans are colonial invertebrates with lophophores, commonly displaying marked

non-genetic variation across a wide range of environments.

• The Stenolaemata dominated Paleozoic bryozoan faunas, with only the cyclostomes

surviving the combined effects of the end-Permian and end-Triassic mass extinctions; as

the cyclostomes continued to decline after the end-Cretaceous extinction event, the

cheilostomes radiated to dominate Cenozoic assemblages.

We may consider here under the name Molluscoidea, the two groups of animals which

are known respectively as the Polyzoa [Bryozoa] and the Brachiopoda. These two

groups, in many respects closely allied to one another, present afﬁ nities on the one

hand to the Worms and on the other hand to the Mollusca . . .

R.A. Nicholson and R. Lydekker (1890) Manual of Palaeontology, 3rd edn