In 2019, paleontologists published a new paper on the fossil remains of a whale found near
a creek on the Olympic Peninsula of Washington State.
It was about 28 to 30 million years old and likely an early relative of today’s baleen
whales, though it was probably closer in size to something like a harbor porpoise.
It also appears to have still had teeth, like modern toothed whales, rather than the specialized
baleen plates that are used by today’s baleen whales to strain food from the water.
They named it Borealodon, and while it’s not clear what killed this animal, after it
died, its body fell to the bottom of the ocean, where scavengers started to feed upon it.
Nearly every piece of the skeleton had boreholes from bone-eating worms.
The scientists studying it also found a clam nestled way up inside the animal’s braincase.
The clam was probably a kind of scavenger too, one that lived off of organic compounds
leaching from the whale’s carcass.
In fact, scientists have found other whale fossils from around the same area that also
had clams tucked in among their bones.
And the presence of these clams hints at what may be an interesting evolutionary relationship
— one that we’re still trying to figure out all the details of — but one that could
help us better understand two of the most remarkable habitats on Earth.
Because it looks like the evolution of ocean-going whales like Borealodon may have affected communities
found in the deep ocean, like the ones found around geothermal vents.
And that’s not because of anything the whales did while they were alive.
It turns out that when a whale dies, that’s just the beginning of the story.
Today, whales are classic sea creatures, but they didn’t start out that way.
Early whales, like Pakicetus, lived in what’s now India and Pakistan around 50 to 55 million
years ago.
And they actually seem to have been mostly terrestrial animals that may have hunted in
water kinda like modern crocodiles.
They didn’t stay stuck on land, though.
Over time, these early whales evolved to spend more and more of their lives in the water,
eventually living in shallow, coastal environments like modern seals or sea lions.
Now, as aquatic animals die, their bodies can sometimes sink to the bottom of whatever
body of water they’re living in.
When this happens with whales, it’s called a whale fall
There, scavengers like sharks, hagfish, crustaceans, and worms subsist off the nutrients found
in their bodies.
Scientists have found evidence of scavengers around the bodies of ichthyosaurs and there
are even communities that can live off of plant matter like wood.
With early whales, we can see this too.
They also had mobile scavengers like sharks and whelks.
And at first these whale falls were restricted to shallow environments.
But as time went by, these shallow-water whales continued to expand their reach into the ocean,
evolving to be fully-aquatic by around 40 million years ago.
And by about 37 million years ago, creatures like Basilosaurus were swimming around, with
one particular group of its relatives shifting to open-ocean, deep-diving swimmers.
During this transition, whales’ bodies changed - they lost what remained of their hind limbs
and often got much bigger.
While some, like Borealodon, were only about the size of porpoises, most early whales were
around five meters long, roughly the size of a large Beluga whale today.
And some would get much, much larger.
A modern blue whale, for instance, can be more than 30 meters long and weigh up to 200
tons, making them literally the largest animals to have ever lived.
Their bones changed, too.
They not only got bigger, but the composition also changed.
Over time, what had been dense, heavy bones adapted for shallow-diving became spongier
and rich in lipids.
This could’ve helped them dive deeper, maybe by providing buoyancy or resistance to pressure.
In fact, the sheer amount of lipids found in whale bones makes them unique among vertebrates.
Modern whale bones can be nearly two-thirds lipids.
An adult great whale, which is typically longer than 10 meters, can have 2 to 14 metric tons
of lipids in its skeleton.
Now, lipids are very rich in energy.
And this is interesting because the arrival of these big, ocean-going animals with lipid-rich
bones might have triggered a change in the deep ocean.
That’s because, while some whales may have died at the surface of the ocean, their bodies
didn’t always stay at the surface.
Instead, they could’ve ended up at the abyssal plain, a dark ecosystem at the bottom of the
ocean that’s starved of nutrients.
The whale’s bodies are essentially a buffet for the critters that live there.
Even when the carcass seems like it’s been picked clean, bacteria may still thrive by
digesting chemicals leaching out of the remains, which can support a community for up to 100
years.
If you multiply this by the countless animals that’ve died, whale falls might’ve been
a major and geologically sudden source of nutrients.
And this could’ve affected the creatures that live deep down on the seafloor...
Including those that live at very specific parts of the abyss: hot vents and cold seeps.
These are communities built around chemical sources of energy, like hydrocarbons or sulfites
bubbling up from geologic activity.
Here, microbes break down the chemicals coming up from the rock, which supports a food web
and community.
This process shares a lot of parallels with those microbes found at whale falls.
And it’s been suggested that today, whale falls may be a stepping-stone by which these
vent communities can spread along the seafloor as vents and seeps die off.
This has led to the hypothesis that whale falls could’ve also been evolutionary stepping-stones
for animals to colonize new habitats or they could’ve helped a species expand its range
by being ecological stepping stones.
So paleontologists have started looking back through the fossil record to see if they can
find any evidence of this.
Now, it’s hard to find direct fossil evidence of how these vents and seeps and their communities
may have changed over the years.
We think there was a possible extinction event for them around 90 million years ago, due
to a period of oxygen-poor water in the deep ocean.
But vents don’t really fossilize well, because they usually pop up in areas of the seafloor
crust that are destined to be destroyed by subduction.
Because of this, scientists have turned to phylogenetics - the study of evolutionary
relationships between organisms - to try to piece together how they evolved.
They do this by investigating the genetics and biology of modern species to generate
hypotheses about what their common ancestor was like and how long ago it lived.
For instance, we can compare their genomes and estimate how often mutations have happened
to try to time when one species split from another - a technique often called the molecular
clock.
More changes between two lineages suggest that they diverged earlier in the fossil record.
And doing this for the animals that currently live near vents, seeps, and whale falls reveals
a couple of patterns.
Now, there are two groups that scientists have looked at most closely: a group of mussels
and a group of clams.
The mussels are a diverse group found in deep-sea environments based around chemical sources
of energy, including vents.
And the oldest of their shells appear less than 40 million years ago around Washington
State.
From looking at the DNA of modern ones found in both vents and seeps, as well as those
found at whale and wood falls, it seems like the group didn’t start out as vent creatures.
Instead they were scavengers of falling organic matter that only later invaded vent habitats,
possibly in several different lineages.
Because of the close ecological relationship we see today between whale falls, vents, and
seeps…
And because the timing of when ocean-going whales appear seems to line up with the timing
of when this jump happened...
It’s been suggested that whale falls may have been a stepping stone that helped this
transition take place.
With the clams, on the other hand, phylogenetics suggests that they were probably already vent
or seep specialists by the time ocean-going whales arrived.
The earliest confirmed fossils of these clams occur around 45 million years ago in methane
seeps.
And the clams may have already been found worldwide by the time whale falls started
to really happen.
But!
There seems to have been a burst of diversification that roughly coincided with whale falls potentially
expanding their habitat.
In this case, it’s been suggested that the clams went from vent to whale fall, rather
than the other way.
And the presence of the whale falls may have served as a kind of incubator for natural
selection.
Now, it’s worth pointing out that the connection between ocean-going whales, whale falls, and
changes in deep-sea organisms is still a hypothesis that paleontologists are working to test.
We need a bigger sample size in terms of both the fossil record of vents and ancient whale-falls
in order to say more.
So how strong the connection is here is still being debated, as well as how important whale-falls
are to modern vent organisms.
If it’s true, it not only reinforces how important modern whales are from an ecological
point of view —
As the biggest animals to ever live, often very intelligent, with poop that helps drive
global nutrient cycles —
But it also reveals a really interesting evolutionary relationship, one that links two of the most
remarkable ecosystems on earth: whale falls, and deep-sea vent and seep communities.
It shows how particular adaptations, in this case large bodies and oil-rich bones, in the
evolution of one group can end up affecting evolution in a completely different places,
like the deep sea.
So when we look at fossils like Borealodon and its scavengers, we’re not just looking
at a single evolutionary story, but two intersecting ones.
Before you go, I want to tell you about a new documentary series on PBS Voices, “American
Veteran: Keep It Close.”
Each episode tells the story of a U.S. military veteran and a special object they have from
their time in service — a vial of lip gloss, a small stone, even a microphone — and how
these mementos helped keep them grounded through extreme circumstances.
Check it out, link in our description, and let them know that Eons sent you.
Thanks to this month’s whaley awesome Eontologists: Sean Dennis, Jake Hart, Annie & Eric Higgins,
Luiz Vieira Pinto Neto and John Davison Ng!
By becoming an Eonite at patreon.com/eons, you can get fun perks like submitting a joke
for us to read, like this one from Derek Helling
What do you call a dinosaur that is faking an injury?
A sore-a-fraud!
That one's pretty good. I like that one.
And as always thank you for joining me in the Konstantin Haase studio.
Subscribe at youtube.com/eons for more evolutionary escapades.