The Diversification of Squid and Cuttlefish Began 100 Million Years Ago
Image below is from the study of the evolution of decapodiformes (cuttlefish and squid), from the Oceanographic Institute.
An international investigation led by the Japanese Okinawa Institute of Science and Technology (OIST), in collaboration with the Spanish Institute of Oceanography (IEO, CSIC) among others, has shed light on the evolutionary success of squid and cuttlefish. The study, recently published in the prestigious journal Nature ecology & evolution , explains how a group that was on the verge of disappearing or stagnating managed, after millions of years of “waiting” in the depths, to become one of the most diverse and successful groups of marine predators on the planet, according to a press release from the Oceanographic Institute.
To reach these conclusions, the international team sequenced three new squid genomes and used advanced transcriptomic techniques to understand how their organs and internal shell evolved. The analysis combined existing databases with three squid genomes sequenced for the first time to identify the “tipping point” that led to the current diversity of squid and cuttlefish, which together make up the Decapodiformes (ten-limbed) cephalopods. Researchers propose that the massive diversification of modern squid did not occur immediately, but followed a “long fuse” model.
This means that, after an initial separation of lineages about 100 million years ago (in the Cretaceous), there was a long period of little evolutionary change before the diversity of species existing today exploded. “Unlike other groups that diversify rapidly after an environmental change, squid followed a pattern of slow evolution,” highlighted Gustavo Sánchez, leader of the study, who pointed out that “the spark was lit in the explosion of biodiversity, it didn’t happen immediately.”
According to him, after millions of years of stability in the deep waters, the group underwent a rapid expansion into new ecological niches, once conditions on the surface stabilized, resulting in the enormous variety of shapes and sizes that can be seen today. “Cephalopods managed to survive catastrophic events, such as the Cretaceous-Paleogene mass extinction that wiped out non-avian dinosaurs and ammonites, thanks to these refuges in the deep ocean,” explained Fernando Á. Fernández-Álvarez, co-author of the study. “After the great extinction, during the recovery period, squid and cuttlefish underwent rapid diversification to adapt to the new ecosystems and niches that were left empty in the ocean,” he said.
