Gigantoproductid shell spiral and microstructure of tertiary layer: evaluation as taxonomical characters

Abstract

Brachiopod taxonomy is based on descriptions of shell morphology and key characters, but diagenesis generally modifies or erases some of them, hindering brachiopod identification. Brachiopods that are taxonomically related usually present shells with similar appearance but can differ in size (i.e., Rhynchonellata). Some aspects of morphology – for example the angular measurement of the curvature of the shell or details of shell microstructure – could aid taxonomic identification. Gigantoproductids, which lack a robust taxonomy, have the largest shells among brachiopods and are ideal for this kind of study because of their gigantic size and morphological variability. Furthermore, they have a great abundance and worldwide distribution during the mid-Carboniferous. More than 700 samples have been collected from Sierra Morena (Spain), Montagne Noire (France) and Adarouch (Morocco) identifying up to six gigantoproductid genera: Globosoproductus, Semiplanus, Kansuella?, Latiproductus, Gigantoproductus and Datangia. Microstructural features from 170 thin sections belonging to gigantoproductid ventral valves have been studied, and six crystal morphologies have been distinguished within the tertiary layer: subhorizontal, imbricated, crenulated, acicular, short and long columnar morphologies. Moreover, 23 complete shells from all genera have been selected to investigate shell size and curvature. Results from this study emphasise that shell size, curvature and crystal shape are taxa-related. Finally, a remarkable morphological change in the gigantoproductid populations from the western Palaeo-Tethys occurred during the Viséan–Serpukhovian, from thin-shelled genera with subhorizontal morphology (Viséan) to thick-shelled genera with a tertiary layer consisting of long columnar crystals (Serpukhovian). This study proves that microstructure, maximum thickness and shell spiral characterisation are robust characters when applied to gigantoproductid taxonomy, but also have great potential in other brachiopod groups.

3rd Palaeontological Virtual Congress: palaeontology in the virtual era

“…(2023) review the peptide mass fingerprinting markers in the cave bear Ursus spelaeus ; Ivantsov & Zakrevskaya (2023) describe the body plan of Dickinsonia from materials collected in the south-eastern White Sea; Jiménez-Hidalgo & Carbot-Chanona (2023) report the first Mexican remains of a Anthracotheriidae from the zones of Santiago Yolomécatl and Simojovel de Allende; Kirichenko-Babko & Perkovsky (2023) report the first neotropical carabid beetle from Eocene amber of Ukraine; Mateos-Carralafuente et al . (2023) evaluate the shell spiral and microstructure of tertiary layers in gigantoproductids (Brachiopoda) as taxonomic characters; Luci et al . (2023) describe an Early Cretaceous sponge meadow as an unsuspected host of a dynamic sclerobiont community from the Neuquén Basin (Argentina); Ríos et al .…”

Biomineralización

“…Pero el mayor control en la morfología parece estar condicionado por la genética del organismo en cuestión, ya que muchas morfologías se mantienen a lo largo del registro geológico, transitando entre diferentes familias de un mismo clado (Stolarski, 2000), entre géneros (Mateos-Carralafuente et al, 2022) o entre especies (Coronado et al, 2015) y, por tanto, albergando mucha información evolutiva.…”