Page 322 - Introduction to Paleobiology and The Fossil Record

SPIRALIANS 1: LOPHOPHORATES 309

number of quite different non-articulated and p. 97). The progressive and sequential coloni-
articulated taxa were cemented to the sub- zation of Devonian spiriferids, by Spirorbis,
strate, whereas some groups evolved clasping itself a possible lophophorate (Taylor & Vinn
spines to help stabilize their shells. In a number 2006), Hederella, Paleschara and Aulopora
of groups the pedicle atrophied during ontog- marked the development of an eventual climax
eny. Many taxa thus developed strategies paleocommunity on the actual brachiopod
involving inverted, pseudoinfaunal and recum- shell itself. Were they feeding on incoming
bent life modes; a number lived in cosupport- brachiopod food or just waste? The general
ive clusters and others mimicked corals. Not view is that these animals congregated beside
all brachiopods were sessile; a few, such as the inhalant currents on the median parts of
Lingula, adopted an infaunal lifestyle (Box the anterior commissure, and benefi ted from
12.3), whereas the articulated forms Camer- the indrawn particles of food. An alternative
isma and Magadina were semi-infaunal. view, and it is hard to prove or disprove, is
Throughout the Phanerozoic the brachio- that they were taking advantage of waste
pods have participated in a spectrum of level- being ejected from the brachiopod.
bottom, benthic paleocommunities. Pioneer Brachiopods not only acted as suitable sub-
studies on Silurian brachiopods suggested that strates for an epifauna, they were also prone
their paleocommunities were depth related, to attack (Box 12.4) and drill holes suggest
and a predictable succession of faunas, each predation and in some cases attachment of
characterized by one or more key brachiopods, other brachiopods themselves (Robinson &

has been identified (Fig. 12.11). The onshore– Lee 2008).
offshore assemblages of the Lingula, Eocoelia,
Pentamerus, Stricklandia (or its close relative
Costistricklandia) and Clorinda paleocommu- Brachiopods, functional morphology
nities, fi rst identified in the Silurian of Wales, and paradigms

form the basis of benthic assemblage (BA) Martin Rudwick, an English brachiopod
zones 1–5, ranging from intertidal environ- expert just beginning his career in the 1960s
ments to the edge of the continental slope; (he is now a distinguished historian of
more basinal environments are included in geology), proposed the paradigm approach in
BA6. Parallel studies on Mesozoic brachio- functional interpretation of fossils. His idea
pods have, on the other hand, suggested that was to create an engineering model for a func-
brachiopod-dominated paleocommunities tion, such as water flow in feeding. For

were controlled by substrate rather than depth example, does the costation, the zig-zag
(Fig. 12.12). Clearly, in reality, a combination pattern of ridges and furrows, of the anterior
of these and other factors controlled the distri- commissure of the brachiopod have a real

butions of the Brachiopoda in a complex functional significance? In numerical terms it
system of suspension-feeding guilds. can be shown that costation increases the
Brachiopods have also acted as substrates length of commissure and hence the intake
for a variety of small epifaunal animals (see area that may be held open without increasing

Box 12.3 Chinese lingulides

Did early lingulides live in burrows like many of their descendants? Xianshanella haikouensis from
the Lower Cambrian Chengjiang fauna, South China was a subcircular animal with horny setae and
a massive pedicle. Zhang Zhifei and his colleagues (2006) have shown that these earliest brachiopods
did not live in burrows, but actually attached themselves to the shells of other invertebrates – an
epibenthonic rather than infaunal mode of life (Fig. 12.10). Moreover the Chengjiang lingulide has
a lophophore, a U-shaped digestive tract and an anteriorly-located anus; these advanced features
were already present in the lingulate brachiopod lineage right from the start it seems.

Continued