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An Eocene orthocone from Antarctica shows convergent evolution of internally shelled cephalopods: -
Swedish Museum of Natural History, Department of Paleobiology. no. (palaeozoology)
Swedish Museum of Natural History, Department of Paleobiology. (palaeozoology)
Division Paleontologia de Vertebrados, Museo de La Plata, Paseo del Bosque s/n, B1900FWA, La Plata, Argentina.
Swedish Museum of Natural History, Department of Paleobiology. (palaeozoology)
2017 (English)In: Plos One, ISSN ISSN 1544-9173Article in journal (Refereed) Published
Abstract [en]

Background: The Subclass Coleoidea (Class Cephalopoda) accommodates the diverse present-day internally-shelled cephalopod mollusks (Spirula, Sepia and octopuses, squids, Vampyroteuthis) and also extinct internally-shelled cephalopods. Recent Spirula represents a unique coleoid retaining shell structures, a narrow marginal siphuncle and globular protoconch that signify the ancestry of the subclass Coleoidea from within the Paleozoic subclass Bactritoidea. This hypothesis has been recently supported by newly recorded diverse bactritoid-like coleoids from the Carboniferous of the USA, but prior to this study no fossil cephalopod indicative of an endochochleate branch with an origin independent from subclass Bactritoidea has been reported.Methodology/Principal Findings: Two orthoconic conchs were recovered from the Early Eocene of Seymour Island in Antarctica. They have loosely mineralized organic-rich chitin-compatible micro-laminated shell walls and broadly expanded central siphuncles. The morphological, ultrustructural and chemical data were determined and characterized through comparisons with extant and extinct taxa using Scanning Electron Microscopy/Energy Dispersive Spectrometry (SEM/EDS).Conclusions/Significance: Our study presents the first evidence for the evolutionary lineage of internally-shelled cephalopods with independent origin from Bactritoidea/Coleoidea. This lineage appears to result from convergent evolution with the subclass Coleoidea. A new subclass Paracoleoidea Doguzhaeva n. subcl. is established for accommodation of orthoconic cephalopods with the internal shell associated with a broadly expanded central siphuncle. Antarcticerida Doguzhaeva n. ord., Antarcticeratidae Doguzhaeva n. fam., Antarcticeras nordenskjoeldi Doguzhaeva n. gen., n. sp. are described within the subclass Paracoleoidea. The analysis of organic-rich shell preservation of A. nordenskjoeldi by use of SEM/EDS techniques revealed fossilization of hypo-septal cameral soft tissues. This suggests that a depositional environment which favouring soft-tissue preservation was the factor enabling conservation of the loosely mineralized shell of A. nordenskjoeldi.

Place, publisher, year, edition, pages
USA, 2017.
Keyword [en]
Cephalopoda, Coleoidea, Paracoleoidea, Convergent Evolution, Eocene, Antarctica
National Category
Natural Sciences
Research subject
Diversity of life
Identifiers
URN: urn:nbn:se:nrm:diva-2355DOI: DOI:10.1371/journal.pone.0172169OAI: oai:DiVA.org:nrm-2355DiVA: diva2:1088393
Projects
Argentine Research Council, PIP 0462
Funder
Swedish Research Council, 2009-4447
Available from: 2017-04-12 Created: 2017-04-12 Last updated: 2017-04-13Bibliographically approved

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