Microstructural and geochemical evidence offers a solution to the cephalopod cameral deposits riddle

bioRxiv (Cold Spring Harbor Laboratory), Journal Year: 2025, Volume and Issue: unknown

Published: Feb. 28, 2025

Abstract Orthoceratoid cephalopods are common in the Palaeozoic rock record but became extinct Late Triassic. Many orthoceratoids contain cameral deposits, which enigmatic calcareous structures within their chambered shell that presumably balanced straight conchs a horizontal position. Since mid-19 th century, palaeontologists have attempted to understand deposit formation process. The various hypotheses include growth from fluids, precipitation by mantle or even dismissal as post-mortem structures. All of these previous interpretations they complicated with contradictory evidence. Here, we present evidence well-preserved Trematoceras elegans specimens Triassic St. Cassian Formation (Dolomites, northern Italy). We studied using optical and electron beam microanalysis techniques argue deposits consist primary aragonite calcite fabrics. A fibrous microstructure, is bilaterally symmetrically arranged irregularities, documented. Thin organic sheets originally delimited radial sectors. Based on observations, propose new model explicitly involves sheets. These acted an extension pellicle held thin film supersaturated liquid otherwise emptied chambers via capillary effect. Ions were supplied through siphuncle, such living Nautilus , enabled This goes beyond interpretations, resolves observations has functional implications, suggesting adaptation increased rates.

Language: Английский

The Lyckholm acme of cephalopods – Review of the late Katian (Vormsi–Pirgu regional stages) Ordovician cephalopods of Estonia

European Journal of Taxonomy, Journal Year: 2025, Volume and Issue: 978

Published: March 3, 2025

A revision of more than 660 specimens fossil cephalopods from the Vormsi–Pirgu regional stages (late Katian Stage), Ordovician Period, Estonia, available Estonian palaeontological collections, reveals extraordinarily high cephalopod-richness this interval, termed “Lyckholm acme cephalopods” herein. Ninety species can be distinguished, belonging to 35 genera, and 17 families. The turnover between assemblages Vormsi Pirgu stage strata is remarkable. Only 16 range through both stages, where former dominated in abundance by tarphycerids orthocerids, latter multiceratoids, probably reflecting pronounced palaeo-environmental changes. Species distributions main collection localities show differences sampling practice give evidence for potential problems delineation. Difficulties delineation of, e.g., Discoceras exist because critical morphological details are commonly not preserved. cluster analysis comparison assemblage with other regions a similarity that Laurentia-palaeocontinent, fact which suggests possible connection Lyckholm-acme “Richmondian Invasion” Laurentia. revision, presented herein, first step toward an in-depth global-scale spatiotemporal patterns cephalopod occurrences, hypothesis could tested. Four genera new: Gorbormoceras gen. nov., Hiiumoceras Hosholmoceras Saxbyoceras nov. 23 Beloitoceras uuemoisense sp. Cyrtorizoceras hariense Danoceras oviforme D. vohilaidense Deckeroceras balticum paopense Dowlingoceras tornense Ephippiorthoceras vormsiense et hiiuense ovalis H. triangulatum Kiaeroceras kaebliki K. ormsoense urgense Redpathoceras saxbyense Rizosceras teres kingpooli Striatocycloceras hosholmense Strandoceras kalevipoegi S. kohilense muhvi sulevipoegi Six placed new combinations: piersalense (Teichert, 1930) comb. Isorthoceras luhai (Stumbur, 1956) saaremense (Balashov, 1959) Gorbyoceras clathratoannulatum (Roemer, 1861) Richardsonoceras priscum (Eichwald, 1860) Schuchertoceras deformis

Language: Английский

Taphonomic and reworking processes isolating cephalopod septa and chamber fillings

Lethaia, Journal Year: 2025, Volume and Issue: 58(2), P. 1 - 18

Published: April 29, 2025

Language: Английский