The giants of the phylum Brachiopoda: a matter of diet?

Abstract

The species of the brachiopod Gigantoproductus are giants within the Palaeozoic sedentary benthos. This presents a dilemma as living brachiopods have low‐energy lifestyles. Although brachiopod metabolic rates were probably higher during the Palaeozoic than today, the massive size reached by species of Gigantoproductus is nevertheless unusual. By examining the diet of Gigantoproductus species from the Visean (Mississippian, Carboniferous) of Derbyshire (UK), we seek to understand the mechanisms that enabled those low‐metabolism brachiopod species to become giants. Were they suspension feeders, similar to all other brachiopods, or did endosymbiosis provide a lifestyle that allowed them to have higher metabolic rates and become giants? We suggest that the answer to this conundrum may be solved by the identification of the biogeochemical signatures of symbionts, through combined analyses of the carbon and nitrogen‐isotopic compositions of the occluded organic matrix within their calcite shells. The shells are formed of substructured columnar units that are remarkably long and a few hundreds of microns wide, deemed to be mostly pristine based on multiple analyses (petrography, cathodoluminescence (CL), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM)); they contain occluded organic fractions detected by TEM, nuclear magnetic resonance (NMR) and gas chromatography mass spectrometry (GC‐MS) analyses. We conclude that the gigantic size reached by the species of Gigantoproductus is probably the result of a mixotroph lifestyle, by which they could rely on the energy and nutrients derived both from photosymbiotic microbes and from filtered particulate food.

From shallow to deep water: an ecological study of the Hirnantia brachiopod Fauna (Late Ordovician) and its global implications

“…In the shallow‐water populations, some of the very large specimens in this study are the largest reported for the species. Similar gigantism of brachiopods has been reported (see Rong et al for a brief review), such as Gigantoproductus from the Carboniferous (Qiao & Shen ; Angiolini et al ), suggesting that only the most suitable environments for these populations can promote the largest body size.…”

The shell fabric of Palaeozoic brachiopods: patterns and trends

“…S7C); parallel growth lines were also found in cross‐section, which are comparable with previous observations (Angiolini et al . 2012, 2019; Garbelli 2017). An alternation of secondary and tertiary layer was observed only in Uchtospirifer aff.…”

“…2008), instead, productids show taxa with shell thickened by thin laminae with a sub‐micrometric thickness, as well as producing thick prismatic layers (Angiolini et al . 2012, 2019; Garbelli 2017). In any case, there is never a simple solution such as obtaining a thicker shell by increasing the size of its structural units, as in our data set there is no correlation between shell thickness and fibre/laminae thickness at specific level, nor in most of the orders (Table 5), except for the Orthida which shows a negative correlation at the limit of significance ( p = 0.05).…”

Diagenetic and Biological Overprints in Geochemical Signatures of <em>Gigantoproductus</em> Tertiary Layer (Brachiopoda): Assessing the Paleoclimatological Interpretation

“…Gigantoproductids (tribe Gigantoproductini [30]) are key due to its great potential for paleoclimatological studies because: i) frequent during Carboniferous [28,31,32]; ii) global distribution [30]; iii) large shell thickness and size [33], which allow the extraction of material for geochemical analyses easier than other fossil brachiopods [28,34,35]. Large shell size has been attributed to a possible a chemosymbiotic lifestyle [35]. In spite of these advantages, few studies have been focused on this fossil group for paleoclimatological purposes [9,17,22,28,34].…”

“…Growth rate and stable isotopic fractionation covariation have been identified in δ 18 O and δ 13 C in extant and fossil brachiopods [24,35,40,[49][50][51][52]. δ 18 O and δ 13 C variations between shell layers have been documented in extant and fossil brachiopods, which were considered as kinetic effects of the shell growth [24,43,[49][50][51].…”