Divergence time estimates for major cephalopod groups: evidence from multiple genes.

Area of Science:

• * Evolutionary biology
• * Molecular phylogenetics
• * Paleontology

Background:

• * Coleoid cephalopods (octopus, squid, cuttlefish) represent a diverse marine group with an extensive fossil record.
• * Previous studies have not integrated both molecular and fossil data to accurately date their evolutionary divergences.
• * Understanding the evolutionary history of coleoids is crucial for reconstructing marine ecosystem dynamics.

Purpose of the Study:

• * To establish the divergence times of major coleoid cephalopod taxa using a combined molecular and fossil data approach.
• * To investigate the evolutionary history and phylogenetic relationships within the Coleoidea.
• * To compare molecular-based divergence estimates with existing paleontological evidence.

Main Methods:

• * Analysis of molecular sequences from three nuclear and three mitochondrial genes (3415 bp total).
• * Divergence time estimation using the Thorne/Kishino method, incorporating fossil constraints.
• * Phylogenetic analyses allowing for variable rates of molecular evolution across different lineages.

Main Results:

• * The study supports a Paleozoic origin for the Orders Vampyromorpha, Octopoda, and most extant decapodiform taxa.
• * Estimated divergence times are significantly older than previously suggested by paleontological data.
• * Major lineages within the Order Octopoda diverged during the Mesozoic, with a radiation event near the Cretaceous/Cenozoic boundary.

Conclusions:

• * The evolutionary history of coleoid cephalopods is older than previously recognized, with key divergences occurring in the Paleozoic and Mesozoic eras.
• * Molecular data, when combined with robust analytical methods and fossil calibrations, provide crucial insights into deep evolutionary time.
• * Ancient diversification has likely obscured higher-level phylogenetic relationships within the Decapodiformes.