Cetaceans are a group of animals containing whales, porpoises, and dolphins, including some of our planet’s most iconic aquatic mammals. However, despite living their lives in water, these creatures must breathe air to survive. This seems like a pretty inconvenient way of going about things – especially considering the fact that their ancient ancestors actually lived on land. So why did cetaceans make this evolutionary U-turn and decide to take a permanent dip?
Meet the cetacean family tree
The earliest cetaceans are known from fossils
Then,
Next came Remingtonocetidae, with fossils
Protocetids lived in the middle Eocene,
Basilosaurids emerged
Modern cetaceans emerged around
Why switch from the land to the water?
So why did cetaceans spurn a land-based lifestyle in the first place? As Dr Curt Stager told
“The really kind of the underlying principle here would be that whenever there’s an opportunity, based on your body design for mutations, if there’s an opportunity to make a living, something’s probably gonna move in there and do it,” Stager explained. “And if there was a niche in the water, something that got adaptations that let it survive there, it will survive there.”
One 2018
How cetaceans’ bodies changed for life in the water
First of all: cetaceans are mammals, and mammals nurse their young on milk, so how on earth does this work underwater? Well, their nipples are hidden under folds of skin called
As alluded to before, cetacean nostrils gradually
Toothed whales have evolved echolocation, which
Baleen whales get their name from the comb-like filter-feeding apparatus inside their mouths that they have
How cetaceans’ genes changed during their aquatic metamorphosis was explored in a
The team found 85 inactivated genes, some of which could be related to aquatic adaptations. One of these was SLC4A9, which is involved in the secretion of saliva – food doesn’t really need
A timeline of cetacean evolution
“Within eight million years, the ancestors of whales go from being fully terrestrial, such as the four-legged, furry Pakicetus which lived around the edge of the Tethys Sea, to fully aquatic,” explained cetacean researcher Dr Ellen Coombs in a 2022
Coombs is lead author of a
This data spanned around 53 million years, cetaceans’ whole evolutionary history. This included 88 living species, representing about 95 percent of cetaceans alive today, and 113 fossil species.
“Because the cranium captures many of the most extreme shifts in feeding, respiration, and sensory structures, it is ideal for understanding these rapid and radical changes, but no previous study has reconstructed the evolution of the cetacean cranium through the full breadth of their extinct and living diversity,” added Coombs.
Examining these cetacean noggins revealed that cetaceans evolved in three bursts: one 47.8-42 million years ago in the late Eocene, another around 39 million years ago in the mid to late Oligocene, and finally a lesser one around 18-10 million years ago in the mid Miocene.
The first burst involved ancient cetacean ancestors called archaeocetes first dipping their toes into an aquatic lifestyle alongside walking about on land, doing things such as catching freshwater prey, and adapting accordingly. Their skulls and facial features evolved quickly, which the paper authors attribute either to high productivity prompting rapid change or having little competition.
The second wave involved the origin of neocetes, which is a group that diverged into two sub-groups to suit different niches: mysticetes and odontocetes. The researchers suggest that this fast diversification could have been due to constraints that needed to be overcome via evolution. The skull features of mysticetes were observed to evolve slower than odontocetes. The third wave mostly involved the specialization and diversification of odontocetes.
This incredible example of evolution has resulted in the emergence of many fascinating and beautiful creatures – including the