Comparative analysis of drilling frequencies in Recent brachiopod-mollusk associations from the southern Brazilian shelf

Autor(es)

Simões‚ M.G. ; Rodrigues‚ S.C. ; Kowalewski‚ M.

• Tipo de documento: Artigo Científico
• Fonte: PALAIOS; v. 22, n. 2, p. 143-154, 2007.

Resumo

Over 14,000 specimens-5,204 brachiopods, 9,137 bivalves, and 178 gastropods-acquired from 30 collecting stations (0 to 45 m depth) in the Ubatuba and Picinguaba bays, southern Brazil, were compared for drilling frequencies. Beveled (countersunk) circular-to-subcircular borings (Oichnus-like drill holes) were found in diverse bivalves but also in the rhynchonelliform brachiopod Bouchardia rosea-a small, semi-infaunal to epifaunal, free-lying species that dominates the brachiopod fauna of the southern Brazilian shelf. Drill holes in bivalve mollusks and brachiopods are comparable in their morphology, average diameter, and diameter range, indicating attacks by a single type of drilling organism. Drill holes in brachiopods were rare (0.4%) and found only at five sampling sites. Drillings in bivalves were over 10 times as frequent as in brachiopods, but the average drilling frequency was still low (5.6%) compared to typical boring frequencies of Cenozoic mollusks. Some common bivalve species, however, were drilled at frequencies up to 50 times higher than those observed for shells of B. rosea from the same samples. Due to scarcity of drilled brachiopods, it is not possible to evaluate if the driller displayed a nonrandom (stereotyped) site, size, or valve preference. Drilled brachiopods may record (1) naticid or muricid predation, (2) predation by other drillers, (3) parasitic drillings, and (4) mistaken or opportunistic attacks. Low drilling frequency in brachiopods is consistent with recent reports on ancient and modern examples. The scarcity of drilling in brachiopods, coupled with much higher drilling frequencies observed in sympatric bivalves, suggests that drilling in brachiopods may have been due to facultative or erroneous attacks. The drilling frequencies observed here for the brachiopod-bivalve assemblages are remarkably similar to those reported for Permian brachiopod-bivalves associations. This report adds to the growing evidence for an intriguing macroecological stasis: multiple meta-analytical surveys of present-day and fossil rhynchonelliform brachiopods conducted in recent years also point to persistent scarcity and low intensity of biotic interactions between brachiopods and drilling organisms throughout their evolutionary history. (AU)

• Processo FAPESP: 00/12659-7 - Brachiopod and Bivalve taphonomy in subtropical siliciclastic settings of northern coast of São Paulo State: enviromental variation in taphonomic signatures, biostratinomic style and time-averaging
• Beneficiário: Marcello Guimarães Simões
• Modalidade de apoio: Auxílio à Pesquisa - Regular
• Processo FAPESP: 02/13552-7 - Gradientes tafonômicos em tanatocenoses de moluscos bivalves em baías e na plataforma interna no Norte do estado de São Paulo: implicações no uso de dados tafonômicos para o reconhecimento de tatofácies
• Beneficiário: Sabrina Coelho Rodrigues
• Modalidade de apoio: Bolsas no Brasil - Doutorado