An Eocene orthocone from Antarctica shows convergent evolution of internally shelled cephalopods

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 structu...

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Autores principales: Doguzhaeva, Larisa A., Bengtson, Stefan, Reguero, Marcelo Alfredo, Mörs, Thomas
Formato: Articulo
Lenguaje:Inglés
Publicado: 2017
Materias:
Paleontología
Belemnite
Jurassic
Antarctic
Cephalopod
Acceso en línea:http://sedici.unlp.edu.ar/handle/10915/87083
Aporte de:
SEDICI (UNLP) de Universidad Nacional de La Plata
id I19-R120-10915-87083
record_format dspace
institution Universidad Nacional de La Plata
institution_str I-19
repository_str R-120
collection SEDICI (UNLP)
language Inglés
topic Paleontología
Belemnite
Jurassic
Antarctic
Cephalopod
spellingShingle Paleontología
Belemnite
Jurassic
Antarctic
Cephalopod
Doguzhaeva, Larisa A.
Bengtson, Stefan
Reguero, Marcelo Alfredo
Mörs, Thomas
An Eocene orthocone from Antarctica shows convergent evolution of internally shelled cephalopods
topic_facet Paleontología
Belemnite
Jurassic
Antarctic
Cephalopod
description 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 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 at the tip of the Antarctic Peninsula, Antarctica. They have loosely mineralized organic-rich chitincompatible microlaminated 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 an evolutionary lineage of internally shelled cephalopods with independent origin from Bactritoidea/Coleoidea, indicating 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 hyposeptal cameral soft tissues. This suggests that a depositional environment favoring soft-tissue preservation was the factor enabling conservation of the weakly mineralized shell of A. nordenskjoeldi.
format Articulo
Articulo
author Doguzhaeva, Larisa A.
Bengtson, Stefan
Reguero, Marcelo Alfredo
Mörs, Thomas
author_facet Doguzhaeva, Larisa A.
Bengtson, Stefan
Reguero, Marcelo Alfredo
Mörs, Thomas
author_sort Doguzhaeva, Larisa A.
title An Eocene orthocone from Antarctica shows convergent evolution of internally shelled cephalopods
title_short An Eocene orthocone from Antarctica shows convergent evolution of internally shelled cephalopods
title_full An Eocene orthocone from Antarctica shows convergent evolution of internally shelled cephalopods
title_fullStr An Eocene orthocone from Antarctica shows convergent evolution of internally shelled cephalopods
title_full_unstemmed An Eocene orthocone from Antarctica shows convergent evolution of internally shelled cephalopods
title_sort eocene orthocone from antarctica shows convergent evolution of internally shelled cephalopods
publishDate 2017
url http://sedici.unlp.edu.ar/handle/10915/87083
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