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

ABSTRACT:

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 c

SUBMITTER: Doguzhaeva LA 

PROVIDER: S-EPMC5332165 | biostudies-literature | 2017

REPOSITORIES: biostudies-literature