DOI: 10.5061/dryad.wpzgmsc25
title: Data from: Microstructural and geochemical evidence offers a solution to the cephalopod cameral deposits riddle

description: Orthoceratoid cephalopods are common in the Palaeozoic rock record but
 became extinct in the Late Triassic. Many orthoceratoids contain cameral
 deposits, which are enigmatic calcareous structures within their chambered
 shell that presumably balanced their straight conchs in a horizontal
 position. Since the mid-19th century, palaeontologists have attempted to
 understand the cameral deposit formation process. The various hypotheses
 include growth from cameral fluids, precipitation by a cameral mantle or
 even their dismissal as post-mortem structures. All of these previous
 interpretations have in common that they are complicated by contradictory
 evidence. Here, we present evidence from well-preserved Trematoceras
 elegans specimens from the Late Triassic St. Cassian Formation (Dolomites,
 northern Italy). We studied the specimens by using optical and electron
 beam microanalysis techniques and argue that the cameral deposits consist
 of primary aragonite and calcite fabrics. A fibrous microstructure, which
 is bilaterally symmetrically arranged with irregularities, is documented.
 Thin organic sheets originally delimited radial growth sectors. Based on
 these observations, we propose a new growth model that explicitly involves
 the cameral sheets. These sheets acted as an extension of the pellicle and
 held a thin film of supersaturated liquid in the otherwise emptied
 chambers by the cameral sheets via the capillary effect. Ions were
 supplied through the siphuncle, such as in living Nautilus, and enabled
 the precipitation of aragonite and calcite fabrics. This model goes beyond
 previous interpretations, resolves contradictory observations and has
 functional implications, suggesting that cameral sheets and deposits were
 an adaptation to increased growth rates.
description: # Data from: Microstructural and geochemical evidence offers a solution to
 the cephalopod cameral deposits riddle Contact: Alexander Pohle, Ruhr
 University Bochum, Germany,
 [alexander.pohle@rub.de](mailto:alexander.pohle@rub.de) This dataset
 contains Electron backscatter diffraction (EBSD) data gathered from thin
 sections of two specimens of *Trematoceras elegans* from the lower Carnian
 (Late Triassic) St. Cassian Formation of northern Italy. The thin sections
 are housed in the Naturmuseum Bozen, South Tyrol, Italy, under the
 repository numbers PZO 16535-01 (cross section) and PZO 16538-02
 (longitudinal section). ## Description of the data and file structure Each
 file contains the prefixes EBSD and the corresponding repository number of
 the specimen. Additionally, the suffix CS indicates a cross section, while
 the suffix LS indicates a longitudinal section. For each specimen, four
 files are included: * A Crystal Project Report (.cpr) file for reloading
 the analysis session in AZtec Crystal. * A Crystal Report Configuration
 (.crc) file storing metadata such as phase information, indexing settings
 and display configurations. AZtec Crystal needed to load the file. * A
 Channel Text File (.ctf) containing raw orientation data, including Euler
 angles, phase IDs, and spatial coordinates. This file contains the main
 results of the analysis. Open format, can be used without AZtec Crystal,
 e.g., using MTEX, an open source Matlab toolbox. * A Text (.txt) file
 containing metadata stored in cpr and crc files for users without access
 to AZtec Crystal. 
 
 Thus, the following files are contained in the dataset: *
 EBSD_PZO_16535-01.cpr * EBSD_PZO_16535-01.crc * EBSD_PZO_16535-01.ctf *
 EBSD_PZO_16535-01.txt * EBSD_PZO_16538-02.cpr * EBSD_PZO_16538-02.crc *
 EBSD_PZO_16538-02.ctf * EBSD_PZO_16538-02.txt