Spatial distribution of oncocerid cephalopods on a Middle Devonian bedding plane suggests semelparous life cycle

Alexander Pohle,Dirk Fuchs,Dieter Korn,Christian Klug

doi:10.1038/s41598-020-59507-0

Abstract

Reproductive strategies of extinct organisms can only be recognised indirectly and hence, they are exceedingly rarely reported and tend to be speculative. Here, we present a mass-occurrence with common preservation of pairs of late Givetian (Middle Devonian) oncocerid cephalopods from Hamar Laghdad in the Tafilalt (eastern Anti-Atlas, Morocco). We analysed their spatial occurrences with spatial point pattern analysis techniques and Monte Carlo simulations; our results shows that the pairwise clustering is significant, while ammonoids on the same bedding plane reveal a more random distribution. It is possible that processes such as catastrophic mass mortality or post-mortem transport could have produced the pattern. However, we suggest that it is more likely that the oncocerids were semelparous and died shortly after mating. These findings shed new light on the variation and evolution of reproductive strategies in fossil cephalopods and emphasise that they cannot be based on comparisons with extant taxa without question.

Highlights

Among the two major clades of living cephalopods, the Coleoidea and Nautiloidea, there is a broad range of reproductive strategies
Its reproductive biology is still poorly known, Nautilus is unique among living cephalopods in its polycyclic spawning and long life span, in contrast to the monocyclic spawning of the relatively short-lived coleoids[1,2]
Studies of the reproduction strategies of the mostly externally shelled fossil cephalopods are very rare, largely because the scarcity of soft part preservation strongly limits the possibilities of these investigations

Summary

Introduction

Among the two major clades of living cephalopods, the Coleoidea and Nautiloidea, there is a broad range of reproductive strategies. The repeated occurrence of megastriae confined to the adult body chamber of some specimens of the Middle Ordovician tarphycerid Tragoceras falcatum is possibly linked with repeated reproduction cycles and iteroparity[19]; but again, it is currently impossible to say how widespread this strategy was among its relatives. Apart from these few reports, it is difficult to infer the reproductive strategy of many Palaeozoic cephalopods.

Methods

Results

Conclusion