Adaptations

Attached by pedicle

Epifaunal - hard substrate (1) (plenipedunculate)

Epifaunal - soft substrate (2) (rhizopedunculate)

Cryptic

Interstitial

Cemented

Encrusting (3)

Clasping spines (4)

Mantle fibers

Orthides, rhynchonellides, spiriferides and terabratulides

Chlidonophora and Cryptopora

Argyrotheca and Terebratulina

Acrotretides and Gwynia

Craniops and Schuchertella

Craniids and disciniids

Linoproductus and Tenaspinus

Orthotetoids

Unattached

Cosupportive (5)

Coral-like (6) Recumbent

Pseudofaunal (7) and inverted (8) Free-living (9, 10)

Pentamerids and trimerellids

Gemmellaroids and richthofeniids

Strophomenides

Waagenoconcha and Marginifera

Cyrtia, Chonetes, Neothyris and Terebratella

Mobile

Infaunal (11)

Semi-infaunal (12)

Linguloids

Camerisma and Magadina

Figure 12.9 Brachiopod lifestyles. (Courtesy of David Harper and Roisin Moran.)

number of quite different non-articulated and articulated taxa were cemented to the substrate, whereas some groups evolved clasping spines to help stabilize their shells. In a number of groups the pedicle atrophied during ontogeny. Many taxa thus developed strategies involving inverted, pseudoinfaunal and recumbent life modes; a number lived in cosupport-ive clusters and others mimicked corals. Not all brachiopods were sessile; a few, such as Lingula, adopted an infaunal lifestyle (Box 12.3), whereas the articulated forms Camer-isma and Magadina were semi-infaunal.

Throughout the Phanerozoic the brachio-pods have participated in a spectrum of levelbottom, benthic paleocommunities. Pioneer studies on Silurian brachiopods suggested that their paleocommunities were depth related, and a predictable succession of faunas, each characterized by one or more key brachiopods, has been identified (Fig. 12.11). The onshore-offshore assemblages of the Lingula, Eocoelia, Pentamerus, Stricklandia (or its close relative Costistricklandia) and Clorinda paleocommu-nities, first identified in the Silurian of Wales, form the basis of benthic assemblage (BA) zones 1-5, ranging from intertidal environments to the edge of the continental slope; more basinal environments are included in BA6. Parallel studies on Mesozoic brachio-pods have, on the other hand, suggested that brachiopod-dominated paleocommunities were controlled by substrate rather than depth (Fig. 12.12). Clearly, in reality, a combination of these and other factors controlled the distributions of the Brachiopoda in a complex system of suspension-feeding guilds.

Brachiopods have also acted as substrates for a variety of small epifaunal animals (see p. 97). The progressive and sequential colonization of Devonian spiriferids, by Spirorbis, itself a possible lophophorate (Taylor & Vinn 2006), Hederella, Paleschara and Aulopora marked the development of an eventual climax paleocommunity on the actual brachiopod shell itself. Were they feeding on incoming brachiopod food or just waste? The general view is that these animals congregated beside the inhalant currents on the median parts of the anterior commissure, and benefited from the indrawn particles of food. An alternative view, and it is hard to prove or disprove, is that they were taking advantage of waste being ejected from the brachiopod.

Brachiopods not only acted as suitable substrates for an epifauna, they were also prone to attack (Box 12.4) and drill holes suggest predation and in some cases attachment of other brachiopods themselves (Robinson & Lee 2008).

Brachiopods, functional morphology and paradigms_

Martin Rudwick, an English brachiopod expert just beginning his career in the 1960s (he is now a distinguished historian of geology), proposed the paradigm approach in functional interpretation of fossils. His idea was to create an engineering model for a function, such as water flow in feeding. For example, does the costation, the zig-zag pattern of ridges and furrows, of the anterior commissure of the brachiopod have a real functional significance? In numerical terms it can be shown that costation increases the length of commissure and hence the intake area that may be held open without increasing

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