What do cephalopod beaks tell us about their ecology?

Marjorie Roscian, Anthony Herrel, Paul Zaharias, Raphaël Cornette, Vincent Fernandez, Isabelle Kruta, Yves Cherel, Isabelle Rouget

This is a plain language summary of a Functional Ecology research article which is published here.

In many taxa, such as birds or turtles, a link between jaw shape and diet has been shown to exist. In cephalopods (squids, octopuses etc.) the jaws, called beaks for their apparent resemblance to parrot beaks, are located in the middle of the brachial crown. They are composed of two chitinous parts in the middle of which is positioned the radula, a rasp-like structure common to all molluscs. Cephalopods are active carnivorous predators and mostly nocturnal, making it difficult to observe their food preferences. Stomach content analyses are also complex because the ingestion of hard prey parts is rare and their digestion is rapid. Consequently beaks may be a good alternative to better understand the diet of cephalopods. However, although beaks have been used since the 1960’s for identification, age and size estimations, or even to position these animals in their food web, no one has tested whether their shape is linked with their ecology.

In this paper, we created 3D models of nearly 210 beaks of nearly all known cephalopod families. These models were used to quantify their shape in 3D and to test whether differences exist between species with different ecologies. Our results revealed that not only do closely related species resemble each other, but that animals with different ecologies do indeed have different beak shapes. For example, benthic species like octopuses have rather short, rounded and strong beaks whereas others like some small pelagic squids have more pointed and sharper beaks, ideal for piercing the flesh of fish. These results provide novel avenues to study the relationship between beak shape and function, as well as the possibility of predicting the diet of poorly known extant and extinct species.

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