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

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298 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

What do lampshells, moss animals and the

rare tube-dwelling phoronids, or horseshoe

worms, have in common? They may look very

different, but these three phyla, the Brachiop-

oda, Bryozoa and Phoronida, all possess a

complex feeding organ, the lophophore, and

have similar body cavities or celoms. Never-

theless the relationships among the three are

not yet fully resolved, although the phoronids

probably lie close to or may even be part of

the group, the bryozoans are more distantly

related. Our understanding has not changed

much since 1890, but new molecular studies

may help resolve these uncertainties in the

next 10 years.

The phoronids are tube-dwelling, worm-

like lophophorates, with the 10 or so described

species divided between two genera, Phoronis

and Phoronopsis. These animals lack a min-

eralized skeleton and pursue burrowing or

boring life strategies with near-cosmopolitan

distributions. The phylum has a long though

questionable geological history, as some

authors suggest that Precambrian and Lower

Paleozoic records of the vertical burrow

Skolithos (see p. 523) may possibly be the

work of phoronids. The ichnogenus Talpina,

present as borings in both Cretaceous belem-

nite rostra and Tertiary mollusk shells, may

also have been constructed by phoronids.

BRACHIOPODA

It is no valid objection to this conclusion,

that certain brachiopods have been but

slightly modiﬁ ed from an extremely

remote geological epoch; and that certain

land and fresh-water shells have remained

nearly the same, from the time when, as

far as is known, they ﬁ rst appeared.

Charles Darwin (1859)

On the Origin of Species

The brachiopods are one of the most suc-

cessful invertebrate phyla in terms of abun-

dance and diversity. They appeared ﬁ rst in the

Early Cambrian and diversiﬁ ed throughout

the Paleozoic to dominate the low-level, sus-

pension-feeding benthos; a wide range of

shell morphologies and sizes characterize

the phylum, from the tiny acrotretides

(microns in length) to the massive gigantopro-

ductids (nearly 0.5 m wide). Although only

about 120 genera of brachiopods, also known

as lampshells, survive today, they occupy a

wide range of habitats from the intertidal

zone to the abyssal depths. The brachiopods

are entirely marine, bilaterally symmetric

animals with a ciliated feeding organ, or loph-

ophore, contained within a pair of shells or

valves. Internal structures such as teeth and

sockets, cardinal processes and various muscle

scars are all associated with the opening and

closing of the two valves during feeding cycles.

Brachiopods have featured in many paleoeco-

logical studies of Paleozoic faunas, when they

dominated life on the seabed in terms of

numbers of both individuals and species.

Their use in paleobiogeographic analysis is

well documented (see Chapter 4). Neverthe-

less brachiopods have also been widely used

in regional biostratigraphy and, during the

Silurian, a number of orthide, pentameride

and rhynchonellide lineages show good pros-

pects for international correlation.

Despite their relative low diversity today,

living brachiopods are actually quite wide-

spread, represented mainly by forms attached

by pedicles to a variety of substrates across a

spectrum of water depths. At high latitudes

brachiopods range from intertidal to basinal

environments at depths of over 6000 m. They

are most common in fjord settings in Canada,

Norway and Scotland and in the seas around

Antarctica and New Zealand. The associa-

tion of the brachiopod Terebratulina retusa

growing on the horse mussel, Modiolus modi-

olus, a bivalve, is widespread in the northern

hemisphere. In the tropics, however, many

species are minute, exploiting cryptic habi-

tats, hiding in reef crevices or in the shade of

corals and sponges. Larger forms live in

deeper-water environments, out of the range

of predators, like sea urchins, that graze on

the sumptuous meadows of newly attached

larvae.

Morphology: brachiopod animal

The brachiopod soft parts are enclosed by

two morphologically different shells or valves

that are opened and closed by a variety

of muscles; this arrangement is modiﬁ ed

differently across the three subphyla – the

SPIRALIANS 1: LOPHOPHORATES 299

linguliformeans, craniiformeans and rhyn-

chonelliformeans (Fig. 12.1a–f; Box 12.1). In

contrast to the bivalves, where the right valve

is a mirror image of the left, the plane of sym-

metry in brachiopods bisects both valves per-

pendicular to the plane along which the valves

open, or the commissure. The larger of the

two valves is generally the ventral or pedicle

valve; in many brachiopods the ﬂ eshy stalk or

pedicle pokes through the apex of this valve

and attaches the animal to the substrate. The

pedicle can vary from a thick, ﬂ eshy stalk to

a bunch of delicate, thread-like strands, which

can anchor the brachiopod in ﬁ ne mud. Some

extinct brachiopods lost their pedicles during

ontogeny and adopted a free-living mode of

life, lying recumbent on or partially in the

sediments on the seaﬂ oor. The dorsal or bra-

chial valve contains the extendable food-gath-

ering organ or lophophore together with its

supports. A number of types of lophophore

have evolved (Fig. 12.1 g). The earliest growth

stage, the trocholophe, is an incomplete ring

of ﬁ laments, still retained by the pedomorphic

(see p. 146) microbrachiopod Gwynia. By the

schizolophe stage a bilobed outline has devel-

oped, which probably characterized many of

the smaller Paleozoic taxa. The more complex

plectolophe, ptycholophe and spirolophe

styles are characteristic of the articulated

brachiopods.

The linguliformeans (see Fig. 12.1a, b) have

organophosphatic shells with pedicles that

either emerge between both valves or through

an opening called the foramen. The shells

develop from a planktotrophic, or plankton-

feeding, larval stage, and linguliformeans are

characterized by an alimentary tract ending in

an anus. In the lingulates, the opening and

closing of the valves is achieved by a complex

system of muscles and the pedicle emerges

between both valves. Withdrawal of the soft

parts posteriorly causes a space problem that

can force the valves apart; relaxation allows

the animal to expand again forwards allowing

the valves to close. The paterinates are the

oldest group of brachiopods, appearing in the

lowest Cambrian Tommotian Stage. Although

linked to the other linguliformeans on the

basis of an organophosphatic shell substance,

the shell structure of the group is quite differ-

ent and the shells have true interareas, del-

thyria and notothyria and apparently had a

functional diductor muscle system.

The craniiformeans (see Fig. 12.1c) include

a diverse, yet probably monophyletic, group

of morphologies centered on Crania but

including Craniops and the bizarre trimerel-

lids. The shells consist of organocarbonate

and the animal developed separate dorsal and

ventral mantle lobes after the settlement of

the larvae on the seabed during a nektoben-

thonic stage.

The rhynchonelliformeans (see Fig. 12.1d–

f) have a pair of calcitic valves that contain a

ﬁ brous secondary layer, with variable convex-

ity, hinged posteriorly and opening anteriorly

along the commissure. The mantle lobes are

fused posteriorly, where the interareas are

secreted; their margins form the hinge between

the ventral and dorsal valves. Articulation

was achieved by a pair of ventral teeth and

dorsal sockets, and the valves were opened

and closed by opposing diductor and adduc-

tor muscle scars. In the majority of rhyn-

chonelliformeans, the valves were attached to

the substrate by a pedicle, emerging through

a foramen in the delthyrial region. The sub-

phylum contains ﬁ ve classes, the Chileata, the

Obolellata, the Kutorginata, the Strophome-

nata and the Rhynchonellata. Already by the

Early Cambrian, representatives of four of

the ﬁ ve classes were present. However the

two latter classes, containing respectively over

1500 and 2700 genera, dominated Phanero-

zoic brachiopod faunas.

Brachiopods possess both planktotrophic

and lecitotrophic larvae. The planktotrophic

stage may have been the most primitive,

spending some time in the plankton, whereas

lecitotrophic larvae lurking in the benthos

may have developed at least twice. This

obviously has important consequences for

brachiopod dispersion. Since many linguli-

formeans are widespread it is assumed they

had planktotrophic larvae in contrast to the

more endemic rhynchonelliformeans with

possible lecitotrophic larvae (Fig. 12.4).

Brachiopod shells can be very variable in

shape. A single species can even mimic the

outlines of a range of different orders. For

example specimens of Terebratalia transversa

from around the San Juan islands, western

USA, show Spirifer-, Atrypa- and Terebratula-

type morphs with increasing strengths of

currents (Fig. 12.5). Moreover a number of

brachiopods, such as the strophomenides,

especially the productoids, may markedly

300 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

(a)

setae

shell

gut

shell muscles

lophophoral arm

shell

pedicle

mouth

gonad

anus

nephridium

celomic cavity

cuticle

muscle

pedicle

(b)

(c)

median muscle scar

posterior adductor scar

anterior adductor scar

oblique lateral scar

brachial

protractor

muscle scar

(g)

mouth

tips of brachia

trocholophe

zygolophe

schizolophe

plectolophe ptycholophe

spirolophe

early spirolophe

f(ii) Dorsal valve

Adductor

muscle scars

Brachidium

Cardinal process

Socket

(d) Ventral valve

Dorsal valve

Pedicle Lophophore

(e)

Ventral valve

Dorsal valve

Delthyrium

Deltidial

plates

Pedicle foramen

Umbo

Rib

Growth lines

f(i) Ventral valve

Te e t h

Hinge axis

Adjustor

muscle scar

Adductor

muscle scar

Diductor

muscle scar

Figure 12.1 Brachiopod morphologies: (a) internal features of a lingulate, (b) exterior of a burrowing

lingulate, (c) internal terminology of a craniform calciate, (d) internal features of a terebratulide,

(e) external terminology of a typical articulate, (f) internal terminology of both valves of a

terebratulide, and (g) main types of brachiopod lophophore.

SPIRALIANS 1: LOPHOPHORATES 301

Box 12.1 Brachiopod classiﬁ cation

Recent cladistic and molecular phylogenetic analyses have shown that the traditional split of the

phylum Brachiopoda into the Inarticulata and Articulata is incorrect, and instead there are three

subphyla, the Linguliformea, Craniiformea and Rhynchonelliformea. All three have quite different

body plans and shell fabrics (Fig. 12.2). The linguliformeans contain ﬁ ve orders united by organo-

phosphatic shells; the inclusion of the paterinides is the most problematic since the group shares

some morphological characters with the rhynchonelliforms. The craniiformeans include three rather

disparate groups with quite different morphologies but which together possess an organocarbonate

shell. Most scientists now accept 14 articulated orders in the rhynchonelliformeans, not counting

the chileides, dictyonellides, obolellides and kutorginides, mainly based on the nature of the cardi-

nalia and the morphology of the other internal structures associated with the attachment of muscles

and the support of the lophophore. Recently the more deviant chileides, obolellides and kutorginides

have been added to the subphylum. In addition, the articulated taxa have been split into those with

deltidiodont (simple) and cyrtomatodont (complex) dentitions; the former group includes the orthides

and strophomenides whereas the latter include the spire bearers.

Cladistic-based investigations have developed a phylogenetic framework for the phylum (Williams

et al. 1996), supporting the three subphyla (Fig.12.2); their deﬁ ning characters are based on shell

structure and substance. The mutual relationships among these groups are still unclear as are the

relationships between the many primitive articulated and non-articulated groups that appeared

during the Cambrian explosion together with the origin of the phylum as a whole (Box 12.2).

A data matrix containing all the data from Williams et al. (1996) is available at http://www.

blackwellpublishing.com/paleobiology/.

change their shape and life mode during

ontogeny from being attached to the seabed

to lying untethered in the mud.

Ultramorphology: brachiopod shell

The brachiopod shell is a multilayered

complex of both organic and inorganic mate-

rial that has proved of fundamental impor-

tance in classiﬁ cation. The shells of most

rhynchonelliformean brachiopods consist of

three layers (Fig. 12.6). The outer layer (peri-

ostracum) is organic, and underneath are the

mineralized primary and secondary layers.

These layers are sequentially secreted by cells

within the generative zone of the mantle,

forming ﬁ rst a gelatinous sheath followed by

the organic periostracum, and then the granu-

lar calcite of the primary layer. The subse-

quent secondary layer is thicker and composed

of calcite ﬁ bers, and in some brachiopods a

third prismatic layer is secreted. There are a

number of variations of this basic template.

The linguliformeans, for example, have phos-

phatic material as part of their shell fabric.

The shells of rhynchonelliformean brachio-

pods are composed of low-magnesian calcite;

these shells may have ﬁ brous, laminar or

cross-bladed laminar shell fabrics in their sec-

ondary layers. The mineral fabrics themselves,

when investigated at the nanoscale, may be of

particular ecological importance. Those with

calcite seminacre, rather like mother-of-pearl,

can cement directly to the seaﬂ oor whereas

those with ﬁ brous shells can not (Pérez-Huerta

et al. 2007).

Many shells are perforated by small holes

or punctae, in life holding ﬁ nger-like exten-

sions of the mantle or ceca. Their function is

uncertain but they increased the amount of

the brachiopod’s soft tissue. Some strophom-

enates have pseudopunctae, with ﬁ ne inclined

calcite rods or taleolae embedded in the shell

fabric.

The relatively stable brachiopod shell sub-

stance can tell much about the secretion of the

shell but also about environmental conditions

Continued

302 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

Subphylum Order Key characteristics Stratigraphic

range

Linguliformea Lingulida Spatulate valves with pedicle usually

emerging between both shells

Cambrian to

Recent

Acrotretida Micromorphic forms with conical

ventral valve; dorsal valve with

platforms

Cambrian to

Devonian

Discinida Subcircular shells with conical ventral

valve and distinctive pedicle foramen

Ordovician to

Recent

Siphonotretida Subcircular, biconvex valves with spines

and elongate pedicle foramen

Cambrian to

Ordovician

Paterinida Strophic shells with variably developed

interareas

Cambrian to

Ordovician

Craniiformea Craniida Usually attached by ventral valve; dorsal

valve with quadripartite muscle scars

Ordovician to

Recent

Craniopsida Small oval valves with internal platforms

and marked concentric growth lines

Ordovician to

Carboniferous

Trimerellida Commonly gigantic, aragonitic shells,

with platforms and umbonal cavities

Ordovician to

Silurian

Rhynchonelliformea Chileida Strophic shells lacking articulatory

structures but with umbonal

perforation

Cambrian

Dictyonellida Biconvex valves with large umbonal

opening commonly covered by a

colleplax

Ordovician to

Permian

Naukatida Biconvex shells with articulatory

structures and apical foramen

Cambrian

Obolellida Oval valves with primitive articulatory

structures

Cambrian

Kutorginida Strophic valves with interareas but

lacking articulatory structures

Cambrian

Orthotetida Biconvex shells, commonly cemented,

with bilobed cardinal process

Ordovician to

Permian

Billingsellida Usually biconvex with transverse teeth

and simple cardinal process

Cambrian to

Ordovician

Strophomenida Concavoconvex, usually with a bilobed

cardinal process; recumbent life mode;

cross-laminar shell structure with

pseudopunctae

Ordovician to

Permian

Productida Concavoconvex valves with complex

cardinalia; recumbent or cemented life

mode; often with external spines

Ordovician to

Triassic

Protorthida Well-developed interareas, primitive

articulation and ventral free

spondylium

Cambrian to

Devonian

Orthida Biconvex, usually simple cardinal

process; pedunculate; delthyria and

notothyria open

Cambrian to

Permian

Pentamerida Biconvex, rostrate valves with cruralia

and spondylia variably developed

Cambrian to

Devonian

Rhynchonellida Usually biconvex, rostrate valves with

variably developed crurae

Ordovician to

Recent

Atrypida Biconvex valves with dorsally-directed

spiralia and variably developed jugum

Ordovician to

Devonian

Athyridida Usually biconvex valves with short hinge

line and posterolaterally-directed

spiralia

Ordovician to

Jurassic

Spiriferida Wide strophic valves with laterally-

directed spiralia; both punctate and

impunctate taxa

Ordovician to

Jurassic

Thecideida Small, strophic shells with complex

spiralia including brachial ridges and

median septum

Triassic to

Recent

Terebratulida Biconvex valves with variably developed

long or short loops

Devonian to

Recent

SPIRALIANS 1: LOPHOPHORATES 303

at the time of deposition. The ratio of isotopes

within the crystal lattice of the brachiopod

shell was often controlled by the provenance

of the chemical elements (marine or terres-

trial) and temperature and salinity of the sea-

water. Carbon, oxygen and strontium isotopes

are particularly useful. Devonian brachiopod

shells from North America, Spain, Morocco,

Siberia, China and Germany analyzed for

stable isotopes (δ

C, δ

O and

Sr/

Sr) have

provided many new data on the termination

of the Caledonian Orogeny (decrease in the

Sr/

Sr ratio due to limited inﬂ ux of fresh-

water), uplift during the Variscan Orogeny

(increase in

Sr/

Sr ratio due to increased

inﬂ ux of freshwater) and Devonian climate

warming (negative δ

O excursions) together

with increased rates of carbon burial signaled

by positive δ

C excursions (van Geldern

et al. 2006).

PALEOZOIC

Camb Ord Sil Dev Carb Perm Tr Jur Cret

Acrotretida

Lingulida

Craniida

Phoronida

Siphonotretida

Paterinida

Craniopsida

Trimerellida

Obolellida

Naukatida

Chileida

Dictyonellida

Kutorginida

Billingsellida

Orthotetida

Strophomenida

Productida

Protorthida

Orthida

Pentamerida

Rhynchonellida

Terebratulida

Thecideida

Atrypida

Athyridida

Spiriferida

Spiriferinida

CENOZOICMESOZOIC

Figure 12.2 Classiﬁ cation and stratigraphic distribution of the Brachiopoda. (Courtesy of Sandra

Carlson.)

304 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

Box

12.2

The brachiopod fold hypothesis and the search for stem-group brachiopods

Already by the Early Cambrian a range of diverse brachiopods populated nearshore environments.

But where can we ﬁ nd their ancestors and what sort of animals are we looking for? Many have

assumed that a prototype brachiopod probably arose in the Late Precambrian with a phosphatic

shell substance and an apparently simple Lingula-like morphology. But did it evolve from a burrow-

dwelling sessile organism or from a mobile, slug-like ancestor? A careful study of the early develop-

ment of the non-articulated brachiopod Neocrania by Claus Nielsen (University of Copenhagen) has

yielded a few, exciting clues. During ontogeny the embryo actually curls over at both ends (Fig.

12.3). The resulting embryo has the posterior end of the animal forming the dorsal surface (or valve)

and the anterior end, the ventral surface. This process, subsequently called the brachiopod fold

hypothesis (Cohen et al. 2003), provides an elegant model for how a brachiopod could have evolved

from a ﬂ at, possibly worm-like, animal with shells at its anterior and posterior ends. Care must be

taken in locating such possible ancestors. Halkieria, for example, has shells at its anterior and pos-

terior end but is a mollusk (see p. 331); however shells such as Micrina and Mickwitzia may have

belonged to a slug-like stem-group brachiopod. The mystery may be solved only when some excep-

tionally well-preserved fossil is found.

(a)

(b)

Posterior Anterior

Dorsal (brachial) valve

Posterior dorsal (brachial) valve

Anterior dorsal (brachial) valve

Ventral (pedicle) valve

Plane of brachiopod fold

Figure 12.3 (a) The traditional body plan with an upper dorsal and a lower ventral shell. (b) The

brachiopod fold hypothesis plan implies that the brachial valve is the anterior one and the pedicle

posterior – both were previously on the dorsal surface of the animal. (From Cohen et al. 2003.)

(a) (b)

Figure 12.4 Brachiopod larvae. (a) Ventral and (b) dorsal valves of the brachiopod Onniella. Black

arrows indicate the anterior extent of the larval shell. Scale bars, 200 μm. (From Freeman & Lundelius

2005.)

SPIRALIANS 1: LOPHOPHORATES 305

Distribution in time: extinctions and radiations

The make up of the Cambrian, Paleozoic and

Modern brachiopod faunas are fundamen-

tally different, represented by a dominance of

different orders; some key representatives are

illustrated in Fig. 12.7. Cambrian faunas

were dominated by a range of non-articulated

groups together with groups of disparate

articulated taxa such as the chileides, nauka-

tides, obolellides, kutorginides, billingsellides,

protorthides, orthides and pentamerides.

These brachiopods were members of

a variety of loosely-structured, nearshore

paleocommunities.

During the Ordovician radiation, the delti-

diodont orthides and strophomenides domi-

nated faunas. These ﬁ rst evolved around Early

Ordovician island complexes and came to

dominate the shelf benthos, where they began

to move offshore and diversify around

carbonate mounds. These communities

formed the basis of the Paleozoic brachiopod

fauna.

“Spirifer” - type “Atrypa” - type “Terebratula” - type

increasing hydroenergy

frequent variations

Figure 12.5 Morphological variation in Terebratalia from the San Juan islands related to changing

hydrodynamic conditions. (From Schumann 1991.)

External periostracal layer

Inner bounding membrane

Outer bounding membrane

Vacuole

Mucoprotein

Mucopolysaccharide

Protein cement

Secretion droplet

Generative zone

Axis of rotation

Periostracum

Primary shell layer

Secondary shell layer

Nucleus Cellular epithelium

Primary shell

Figure 12.6 Shell secretion at the margins of Notosaria. (Based on Williams, A. 1968. Lethaia 1.)

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

(j)

(k)

(i)

(l)

(m)

(n) (o)

Figure 12.7 Representatives of the main orders of non-articulates and articulates. Non-articulates:

(a) Pseudolingula (Ordovician lingulide), (b) Nushibella (Ordovician siphonotretide), (c) Numericoma

(Ordovician acrotretide), (d) Dinobolus (Silurian trimerellide) and (e) Crania (Paleogene craniide).

Articulates: (f) Sulevorthis (Ordovician orthide), (g) Raﬁ nesquina (Ordovician strophomenide), (h)

Grandaurispina (Permian productide), (i) Marginifera (Permian productide), (j) Cyclacantharia (Permian

richthofeniid), (k) Neospirifera (Permian spiriferide), (l, m) Rostricelulla (Ordovician rhynchonellide)

and (n, o) Tichosina (Pleistocene terebratulide). Magniﬁ cation approximately ×2 (a, e–g, l, m), ×8 (b),

×60 (c), ×1 (d, h–k, n, o). (Courtesy of Lars Holmer (a), Michael Bassett (g), Robin Cocks (j) and

Richard Grant (h, i, k, l).)

SPIRALIANS 1: LOPHOPHORATES 307

The brachiopods experienced ﬁ ve main

extinction events followed by recoveries and

radiations of varying magnitudes. The end-

Ordovician event occurred in two phases

against a background of glaciation and

accounted for the loss of almost 80% of bra-

chiopod families. The recovery and subse-

quent radiation is marked by the decline of

deltidiodont groups such as the orthides and

strophomenides, whereas the spire-bearing

atrypides, athyridides and the spiriferides

with cyrtomatodont dentition (Fig. 12.8),

together with the pentamerides, achieved

greater dominance, particularly in carbonate

environments. Late Devonian events, at the

Frasnian–Famennian Stage boundary, were

also associated with climate change and

removed the atrypides and pentamerides and

severely affected the orthides and stropho-

menides, whereas the spiriferides and

rhynchonellides survived in deeper-water

environments and staged an impressive recov-

ery. A particular feature of the post-Frasnian

fauna was the diversity of recumbent brachio-

pod megaguilds (see p. 91), dominated by the

productides. The Carboniferous and particu-

larly the Permian were intervals of spectacular

experimentation: some brachiopods mim-

icked corals or developed extravagant clusters

of spines while a number of groups reduced

their shells, thus presenting soft tissues to the

outside environment.

Not unexpectedly, the end-Permian mass

extinction saw the demise of over 90% of

brachiopod species, including some of the

most ecologically and taxonomically diverse

groups. The post-extinction fauna was ﬁ rst

dominated by a variety of disaster taxa (see

p. 179), including lingulids; nevertheless the

brachiopod fauna later diversiﬁ ed within a

relatively few clades dominated by the rhyn-

chonellides and terebratulides. The end-Trias-

sic event removed the majority of the remaining

spiriferides and the last strophomenides. The

agenda set by the end-Permian event, involv-

ing the subsequent dominance of rhynchonel-

lide and terebratulide groups, was continued

after the end-Triassic event. The end-Creta-

ceous event may have been responsible for the

loss of about 70% of chalk brachiopod faunas

in northwest Europe; nevertheless, many

genera survived to diversify again in the

Danian limestones. Despite the post-Permian

decline of the phylum, Modern brachiopods

exhibit a remarkable range of adaptations

based on a simple body plan and a well-

deﬁ ned role in the ﬁ xed, low-level benthos.

Ecology: life on the seabed

Living and fossil brachiopods have developed

a wide range of lifestyles (Fig. 12.9). Most

were attached by a pedicle cemented to a hard

substrate or rooted into soft sediment. A

(a)

(b)

Figure 12.8 Teeth of articulated brachiopods: (a) deltidiodont and (b) cyrtomatodont dentition.