Geometric morphometrics casts light on phylogenetic relevance of cephalopod beak morphological

The feeding organ of cephalopod species, the beak, can be used to reveal important ecological information. In this study, geometric morphometric approaches were employed to investigate the phylogenetic relevance and classification effect of beak lateral profile shape. The two-dimensional beak morphologies of 1164 pairs of 24 species from 13 genera and five families were constructed, and their evolutionary relationships and taxonomic status were confirmed using geometric morphometrics and molecular biology approaches. We also assessed the phylogenetic signals of beak shape. The analysis results show shape variation in the beak mainly in the rostrum, hood, and lateral wall. The overall shape parameters (all PCs) of the upper and lower beak are more useful for species identification. The shapes of the upper and lower beak show a strong phylogenetic signal, and the phenogram based on the beak shape basically reflected the families' taxonomic positions. We also hypothesized that the shape variation in the beaks of cephalopods may be ascribed to genetic and environmental differences. In summary, beaks are a reliable material for the classification of cephalopod species. Geometric morphometric approaches are a powerful tool to reveal the identification, phylogenetic relevance and phenotypic diversity of beak shape in cephalopods. The feeding organ of cephalopod species, the beak, can be used to reveal important ecological information. In this study, geometric morphometric and phylogenetic analyses were used to explore the diversity and phylogeny in beak shape of 24 species in five families; and to assess whether beak shape contributes to phylogeny and taxonomic studies in cephalopods. This study demonstrates that the species identification results more better based on the shape of the upper and lower beaks as a whole. A strong phylogenetic signal was obtained in the beak shapes of cephalopods. Some evolutionary convergence in cephalopod beaks can be attributed to genetic and environmental differences. image