Beothukis mistakensis from the Ediacaran System of Newfoundland, Canada demonstrates complex fractal-like morphology through the development of primary-, secondary- and tertiary-order Rangea-like units. The primary-order rangeomorph units observed in B. mistakensis are tightly juxtaposed, show no evidence of being independent of one another and are made up of chamber-like secondary-order – probably mesoglea-filled – units. The growth of these rangeomorph units demonstrates that the frond developed from the tip towards the basal region through ontogeny. The tertiary-order units of Beothukis are considered to represent surface morphology on the secondary-order units. This is in contrast to palaeobiological reconstructions of Beothukis that invoke three-dimensional fractal-like branches with independent units, which has been used to infer an osmotrophic mode of life. It is considered here that the fractal-like morphology of the lower surface of B. mistakensis was an adaptation to increase surface area to volume ratio. The quilted morphology of Beothukis proposed here is consistent with a sessile, reclining, phagocytotic and/or chemosymbiotic mode of life similar to that invoked for the reclining rangeomorph Fractofusus.
The assumption that the majority of the Ediacaran fossil taxa on the iconic Mistaken Point E lived erect in the water column underpins inferences concerning: 1) paleoecology of early macrofossil assemblages; 2) how they reproduced; 3) importance of tiering and 4) controls on community dynamics (
The deep marine Ediacaran fossil record of Avalonia is dominated by the Rangeomorpha, a clade characterized by up to four orders of fractal‐like branching. Despite their abundance, morphological diversity and the recent increase in Ediacaran studies, aspects of their palaeobiology, palaeoecology and phylogenetic position in the tree of life are still hotly debated. The clade has traditionally been interpreted as consisting of organisms that lived erect in the water column and tethered to the seafloor, based on the intuitive interpretation of their frondose body plan. However, recent work has challenged this view and instead proposes a reclining mode of life for several rangeomorphs, possibly in symbiosis with chemoautotrophic bacteria. Here, we offer a detailed description of exceptionally preserved specimens of Culmofrons plumosa from the Discovery UNESCO Global Geopark in Newfoundland, Canada. We suggest that Culmofrons plumosa should be reinterpreted as a reclining organism based on taphonomic and morphological evidence. Additionally, reproductive modes and a growth model of the species are here inferred, and they appear to be most consistent with a reclining mode of life, offering a novel palaeobiological reconstruction of the species.
The genus Xenophora comprises species of marine gastropods (Cretaceous-Recent) able to add fragments of various origins to their shells surface. Agglutination potentials vary, from species lacking attachments to species completely covered by agglutinated materials, as in the Mediterranean species Xenophora crispa. Here, we analyse Recent and fossil specimens of Xenophora crispa from the Mediterranean area using SEM and XRD, to better understand their biomineralization patterns and the mechanisms leading to the agglutination of shells, bioclasts and lithoclasts, and their evolution in time. We also provide new data on poorly studied gastropod shell microstructures. We conclude that: a) most of the Xenophora crispa shell consists of an aragonitic crossed lamellar fabric, but fibrous to spherulitic prismatic fabrics, seemingly of calcite, have been found in the columella and peripheral edge (the thickest parts of the shell); b) the objects attachment is mediated by a prismatic microstructure, indicating that this may be the most functional fabric in attachment areas in molluscs; c) the functional purpose of the agglutination in Xenophora crispa may be related to a snowshoe strategy to successfully colonize muddy substrates, coupled with tactile and olfactory camouflage. Indeed, this species secretes in the columella and peripheral edge a less dense and a more organic rich calcitic fabric, possibly to lighten the shell thickest parts in order not to sink in soft sediments and to facilitate the shell raising from the substrate to create a protected feeding area. This behaviour seems to have been maintained by X. crispa over 2 My time span.
Fossils from the deep-sea Ediacaran biotas of Newfoundland are among the oldest architecturally complex soft-bodied macroorganisms on Earth. Most organisms in the Mistaken Point–type biotas of Avalonia—particularly the fractal-branching frondose Rangeomorpha— have been traditionally interpreted as living erect within the water column during life. However, due to the scarcity of documented physical sedimentological proxies associated with fossiliferous beds, Ediacaran paleocurrents have been inferred in some instances from the preferential orientation of fronds. This calls into question the relationship between frond orientation and paleocurrents. In this study, we present an integrated approach from a newly described fossiliferous surface (the “Melrose Surface” in the Fermeuse Formation at Melrose, on the southern portion of the Catalina Dome in the Discovery UNESCO Global Geopark) combining: (1) physical sedimentological evidence for paleocurrent direction in the form of climbing ripple cross-lamination and (2) a series of statistical analyses based on modified polythetic and monothetic clustering techniques reflecting the circular nature of the recorded orientation of Fractofusus misrai specimens. This study demonstrates the reclining rheotropic mode of life of the Ediacaran rangeomorph taxon Fractofusus misrai and presents preliminary inferences suggesting a similar mode of life for Bradgatia sp. and Pectinifrons abyssalis based on qualitative evidence. These results advocate for the consideration of an alternative conceptual hypothesis for position of life of Ediacaran organisms in which they are interpreted as having lived reclined on the seafloor, in the position that they are preserved.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.