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Evolution of reproductive strategies in coleoid mollusks

Published online by Cambridge University Press:  31 January 2020

Dirk Fuchs Open the ORCID record for Dirk Fuchs [Opens in a new window] ,
Vladimir Laptikhovsky ,
Svetlana Nikolaeva ,
Alexei Ippolitov  and
Mikhail Rogov
Dirk Fuchs
Affiliation:
Bavarian State Collection for Paleontology and Geology, Richard-Wagner-Strasse 10, 80333Munich, Germany. E-mail: drig.fuchs@gmail.com
Vladimir Laptikhovsky
Affiliation:
Fisheries Division, Cefas, LowestoftNR33 0HT, United Kingdom. E-mail: vladimir.laptikhovsky@cefas.co.uk
Svetlana Nikolaeva
Affiliation:
Natural History Museum, LondonSW7 5BD, United Kingdom; Borissiak Paleontological Institute, Russian Academy of Sciences, Moscow117997, Russia; and Kazan Federal University, Kazan420000, Russia. E-mail: s.nikolaeva@nhm.ac.uk
Alexei Ippolitov
Affiliation:
Department of Stratigraphy Geological Institute, Russian Academy of Sciences, Moscow119017, Russia. E-mail: ippolitov.ap@gmail.com, russianjurassic@gmail.com
Mikhail Rogov
Affiliation:
Department of Stratigraphy Geological Institute, Russian Academy of Sciences, Moscow119017, Russia. E-mail: ippolitov.ap@gmail.com, russianjurassic@gmail.com
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Abstract

Coleoid cephalopods exhibited two distinct reproductive strategies, resulting in small pelagic and large demersal hatchlings, both in the geologic past and recently. In ectocochleate cephalopods, the hatching event is recorded in shell structures (e.g., nepionic constrictions, ultrastructural shifts, or ornamentation differences). In contrast, well-defined hatching markers do not exist on coleoid shells. Changes in septal spacing may be evidence of hatching (e.g., some extant sepiids), but not in all fossil groups. In the present study, we subdivide the early ontogenetic shells of phragmocone-bearing coleoids (belemnoids, spirulids, and sepiids) into key architectural stages and describe their reference to the hatching event. Belemnoids exhibit three key stages, the second of which is here considered to occur shortly before or after hatching. In spirulids and sepiids, there is only one key stage. In Mesozoic belemnoids, spirulids, and sepiids, hatching accordingly occurred with a total shell length of less than 2 mm, which corresponds to mantle lengths of small planktonic hatchlings. Production of small pelagic hatchlings and thus small eggs was therefore the dominant reproductive strategy within the Coleoidea. The first evidence of enlarged hatchlings appeared during the Maastrichtian in Groenlandibelus. During the Eocene, the large-egg strategy apparently became more widespread, particularly in belosaepiids.

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Paleobiology , Volume 46 , Issue 1 , February 2020 , pp. 82 - 103
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Copyright © The Paleontological Society. All rights reserved 2020

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