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

Abstract

AbstractReproductive 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.