How Squid and Cuttlefish Took Over the Oceans After an Evolutionary Breakthrough

Key Points:

• Squid and cuttlefish, both having 10 appendages and classified as Decapodiforms, differ in internal structures: squid have a feather-like pen for muscle attachment and rapid movement, while cuttlefish possess a porous cuttlebone aiding buoyancy control.
• A new genomic study revealed that squid and cuttlefish diverged into separate evolutionary paths about 100 million years ago during the Mid-Cretaceous period, with rapid diversification following their split.
• The End-Cretaceous extinction event 66 million years ago, caused by an asteroid impact, led to massive marine species loss, but deep-water habitats likely helped squid and cuttlefish ancestors survive harsh surface conditions and ocean acidification.
• Post-extinction ecological recovery allowed soft-bodied cephalopods to exploit new shallow-water niches, leading to rapid diversification, loss or reduction of shells, and the evolution of unique adaptations such as specialized eyes and camouflage.
• Today’s squid and cuttlefish diversity reflects millions of years of adaptation and ecological expansion, with nautiloids as the only remaining shelled cephalopods, confined to deep tropical Indo-Pacific waters.