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You might think that the way mammals eat is not complicated.
They open their mouths, and they bite the thing that they want to eat.
That’s what I do when I see a cupcake.
But there are loads of different feeding strategies out there.
That’s especially true when you live underwater, which is so much thicker than air that
getting a bite to eat can be a bit more complicated than “point yourself at a thing and nom.”
And that means that some marine mammals, like seals and sperm whales,
have had to change their whole approach to getting food.
It doesn’t matter that their distant ancestors were fish.
They’ve had to evolve to eat under water all over again.
On land, biting is the norm.
And it’s definitely still a thing among marine mammals, though it can look a little different.
Dolphins, for example, ram straight towards their food to chomp it.
Okay, so charging at your food face-first isn’t exactly the same as chowing down on a cupcake,
but nevertheless this feeding style isn’t how most marine vertebrates eat.
Because let’s think about water for a second.
It’s viscous enough that grabbing something with your jaws isn’t necessarily efficient.
What you can do, though, is suck food in like a vacuum cleaner – try doing that with air.
Actinopterygian fish, the group that makes up half of all vertebrates,
have specialized jaws ideal for suction feeding.
Helpfully, they also have gills to expel the excess water they take in while sucking.
Us mammals… do not have gills.
And our mouths are full of teeth that seem custom-built for chomping and chewing.
That means that when mammals returned to the water,
evolution had to learn how to suction feed all over again, and without the benefit of gills.
Take sperm whales.
Pygmy and dwarf sperm whales have small snouts and narrow jaws
that don’t look like they’d be good for sucking.
Yet suction feeding is what they do.
You might think of your lips when you suck a milkshake through a straw.
But while those help, it’s mostly the tongue and the throat doing the sucking.
Likewise, in the absence of mobile lips, these whales basically drop their tongues down
and hollow out their cheeks to create negative pressure.
That negative pressure inside the mouth slurps prey right in.
In some ways, it’s actually similar to suckling,
a mammal-specific trick that lets babies drink milk and breathe air at the same time.
Which brings up another drawback when you’ve evolved from a land-dwelling lifestyle.
Suction feeding is a great way to capture food, but it does fill your mouth with water.
Fish, as we said, can clear that water out by expelling it over their gills,
but mammals need to either swallow all that extra water along with all their food…
Or blow the water back out of their mouth without dropping that tasty morsel they just nabbed.
Swallowing salty sea water is costly for the body to process and excrete,
even for marine mammals, so carefully jetting the water out is preferred.
The move is called hydraulic jetting, and it’s sort of like a squirt gun
out of the side of your mouth.
Jetting has been observed in captive pygmy and dwarf sperm whales.
But whales in general don’t do well in captivity,
and observing broader feeding patterns in the wild is pretty logistically challenging.
Seals, though not that closely related to whales, are a bit easier to study in a captive setting.
And it turns out they’re actually great at suction feeding,
raptorial feeding, and hydraulic jetting.
Scientists are still investigating how much different species of seal rely on suction feeding,
but one study with captive harbor seals took a closer look at their preferred feeding styles.
Harbor seals are less specialized for exclusive suction feeding
than some of their relatives, like walruses.
But it seems they still prefer suction to biting when offered prey items
they could get either way.
Underwater food was placed in, or protruding from, a bunch of cylindrical holes.
If the food was poking out of the hole, a seal could opt to just bite down on it with their teeth.
If it was deeper in, suction was called for.
Unlike whales and dolphins, seals and their close relatives have more mobile lips
to help with food capture and manipulation…
but this study confirms
they use the same tongue depression as whales to create suction.
You see, many seals preferred to use suction,
whether the snack was sticking out or fully lodged deeper in the cup.
Scientists also could closely observe how the seals jetted water
out of the sides of their mouths after taking a piece of food.
On occasion, a seal would even blow out a squirt of water
in order to create a vortex that would push the treat out of the tube!
It’s possible that being more flexible in your feeding styles
and using all these different techniques means that you can be more varied in your diet.
And for the mammals that were making the early transition
back into marine environments, that flexibility was probably critical.
Scientists now believe that relearning how to suction feed was an important step
in marine mammal adaptation, paving the way for more sophisticated feeding styles.
Like the baleen that allows for ram-style, and suction-less, filter-feeding in whales.
On top of all the obvious changes to adapt to life in the sea, like limbs becoming flippers,
the change in feeding method is way less obvious, but no less important.
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And thanks so much to the SciShow team for helping us understand how mammals,
when we’re in the water, do suck.
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