The Dinosaurs Too Big To Be Dinosaurs

Big news, dino lovers, and I mean big news.

Walking With Dinosaurs is back on PBS after 25 years,

bringing these iconic creatures to life with the latest research

and state of the art visual effects.

Head to the link in the description to learn more.

In 1842, a new term appeared in the scientific literature: dinosaurs,

maybe you've heard of them.

The term was coined to refer to a collection of strange,

extinct reptilian land animals whose bones

and teeth had been turning up in mines

and quarries in England

as the country rapidly industrialized.

Biologist Richard Owen place these huge,

bizarre animals in a distinct group of their own, which he called dinosauria,

or the terrible lizards.

The first dinosaurs to be recognized in Owen's new grouping included such lumbering giants

as Megalosaurus,

Iguanodon, and Hylaeosaurus.

But there was one type of newly discovered giant reptile

that Owen excluded from dinosauria,

one whose bones seemed so huge that he felt it didn't fit in,

even with this new group of big monsters that were already blowing people's minds.

Today, we know the group Owen left out as the sauropods,

the largest animals that ever walked the Earth.

But for Owen, who was also the first to formally describe a sauropod skeleton,

it was almost impossible to picture something that big walking on land.

So instead of classifying it as a dinosaur, he named it Cetiosaurus,

or whale-lizard, assuming it must have been some kind of gigantic sea monster.

Now, in the years since,

we've learned a lot about these so-called whale-lizards,

including that they really are dinosaurs,

and they really did roam the plains and forests of Mesozoic earth,

smashing through what we once thought were the limits of body size on land.

But we can't judge Owen too hard for getting sauropods so wrong,

because even after all this time,

they still sometimes seem just too big to make sense.

How did these uniquely large land animals actually live with their anatomy

and physiology pushed to such extremes?

Well, sauropods, unprecedented gigantism came with some equally massive costs.

And while we understandably marvel at the grandeur of these titans of the deep

past,

once you dive into the details of what it took to be gigantic,

one thing becomes clear.

It's not easy being big.

Sauropods are in a league entirely their own.

There are no known land animals, living or extinct,

that even come close to the size of the largest sauropod dinosaurs.

The very largest of them, which belong to a group known as the titanosaurs,

are estimated to have pushed up to 35 to 40m in length,

and may be over 70 tons in weight.

For comparison, the next largest non-sauropod land animals in history

that we know of barely approached a third of this size.

So we actually have no good comparisons in any other land animal group before

or since.

Which is extremely unusual in natural history - we often see similar lifestyles

and body plans emerge convergently across even distantly related groups in different places

and at different times.

Like cetaceans and ichthyosaurs, crabs and false crabs, or trees and other trees.

But sauropods are a unique evolutionary case,

and there's probably a reason

that no other animals have ever come close to their proportions.

When you scale up to that degree on land,

your biology has to get pretty weird to cope.

So maybe it's not surprising

that it took a

while for scientists to really accept

that sauropod dinosaurs did,

in fact, somehow haul themselves around on land,

and that they weren't aquatic

or semi-aquatic giant supported by the buoyancy of water around them.

Because merely taking a single step seemed impossible without their legs shattering under their

own weight.

This is simply a problem of physics,

and one of the primary mysteries

that paleontologists have had to grapple with to make sauropods make sense.

And despite all the scientific advances made over the years,

and all the sauropod fossils discovered,

we still struggle to model the biomechanics of such large creatures taking a single

step without breaking apart.

But in 2022, researchers made a pretty important leap in figuring out how on

Earth they walked on Earth.

The scientists decided to test a potential explanation:

built-in feet cushions at the bottom of sauropods huge, column-like legs,

kind of like a larger version of the pads found on the feet of

elephants today.

Seeing as these structures are made entirely of soft tissues, they don't fossilize well,

so they haven't left any proof in the sauropod fossil record.

But by analyzing their foot skeletons and fossil tracks,

the researchers were able to generate 3-D digital models of the feet of various

sauropod species.

This allowed them to test

and compare how the feet behaved under the forces generated by different postures,

both with and without a soft tissue pad included in the model.

They found that without the presence of the pad cushioning

and absorbing the forces bearing

so much weight,

the foot bone simply broke and crumpled, regardless of posture or species.

But with the foot pads,

levels of strain on the foot bones were brought down to safer levels.

And even still, the stress over time would have led to chronic injuries.

Which means it's likely

that their limbs also had other soft tissue structures

that we have no physical evidence of,

but that also helped take some of the load.

So that's at least one problem sauropods seem to have struggled with early on

in their journey towards gigantism,

developing built in biological pillows just to stop their feet from fracturing beneath their

enormous weight.

But their massive bodies didn't just threaten to break their legs,

but also potentially to break their eggs, too.

See, some of the largest animals today are among the most committed parents.

Think whales, elephants, big cats and great apes.

These big animals have just a few offspring at a time,

but personally care for them for years.

But a fully grown 70 ton titanosaur would barely be able to even notice

its own young,

let alone actively care for them.

One researcher described it

as the equivalent of a pigeon trying to care for a baby the size

of an ant.

The fragile sauropod eggs

and the vulnerable hatchlings would have actually been much safer without the parents stomping

around nearby,

and in recent years, the discovery of titanosaur nesting sites around the world,

from South America to Europe to Asia,

have given us a glimpse into how exactly parenting works

when you're almost the size of a 737 airplane.

In 2023, for example,

researchers in central India reported the discovery of a new site containing 256 fossil

eggs belonging to around six species of giant titanosaurs dating back over 66 million

years.

The eggs had been buried in shallow pits along the marshy shores of a

lake,

like the nesting habits of modern crocs.

And the dense, closely spaced clutches of literally hundreds of eggs

that are typical of sites like this suggest

that titanosaurs also nested in big colonies,

similar to many modern turtles and birds.

And also like sea turtles,

Titanosaurs must have had a lay-em and leave-em approach to parenting,

laying a bunch of eggs in

as nice a nest

as you can throw together in an afternoon,

and then skedaddling.

After all, considering their size,

there would just be no way for them to stick around

and navigate through these dense

and fragile nesting sites without accidentally causing damage.

Those titanosaur hatchlings likely had to immediately fend for themselves,

and without any help from mom or dad,

they had to somehow survive their first few years

when they were at their most vulnerable to predators.

Eventually, though, those hatchlings would grow

so big that the fear of predation would only be a distant childhood memory

or trauma.

If they could survive their rocky start, they would become simply untouchable.

But not every part of sauropod anatomy was super sized, though.

In fact, one body part is actually notable for being unusually small, their heads.

Sauropod skulls were so proportionally tiny

that they had the smallest brain size to body ratio of any dinosaur group.

And their brains don't seem to have expanded over the long course of their

evolution either.

Even the latest and largest titanosaur species from right at the end of the

Cretaceous,

over 100 million years after the first sauropods appeared,

still had tiny tennis ball sized brains.

This too may have at least partly been a trade off

that came with their bodies growing

so huge.

See, the evolution of the elongated necks

that sauropods are famous for triggered an array of associated changes in the sauropod

skulls that balanced on the end of them.

This idea is known as the ‘head-neck cascade’,

and it was potentially activated multiple times over the course of sauropod evolution.

Periods of neck elongation seem to be associated with episodes of skull reduction.

The longer the neck became,

the less able it was to support a big

and heavy head at its tip.

So the skull was forced to shrink in proportion to compensate.

Now, size isn't everything when it comes to intelligence,

but those skull size constraints would have put some hard limits on brain power,

limits that other animals, including most other dinosaurs, didn't have to deal with.

Which means that one of the big costs

that sauropods may have paid to get

so uniquely gigantic was to condemn themselves to a path of eternal stupidity.

And surprisingly, this wasn't the only major challenge of the sauropod brain.

They also faced the problem of overheating.

This is because larger animals have lower surface area to volume ratios,

making them worse at shedding heat effectively.

Plus, sauropods were too big to simply scamper into the shade

when they needed to cool down,

like smaller animals easily could in most environments.

If you're a titanosaur 30+ meters long from head to tail,

there generally aren't many things dotted around the landscape that can easily shade you.

This combination of problems was a recurring mystery of sauropod biology.

How are they able to keep cool

and prevent damaging heat sensitive tissues in their brain

and sense organs?

In 2019, researchers argued that they figured out at least part of the answer:

panting, lots and lots of panting.

See, by reconstructing how sauropod blood vessels would have been arranged along the grooves

and canals in their skulls,

the researchers could see how they exchanged heat with their environment to cool off.

And they found that, unlike other dinosaurs they examined,

sauropod blood vessels were clustered in both the nostrils and the mouth.

This suggests that they used panting

as a means to actively cool down

when they approached dangerous levels of overheating,

which may have been pretty often.

So where does that leave our view of sauropods,

nearly 200 years after Owen first described one?

Well, their baffling size has led us on quite a journey.

From reconstructing them as sea monsters to envisioning the iconic,

ground shaking terrestrial dinosaurs that we know them as today.

And it's kind of understandable that science got sauropods so wrong for so long,

because, as we've seen, these animals were barely even possible.

They existed seemingly only to spite physics,

and persisted only thanks to some extreme evolutionary adaptations.

And while we find their record breaking sizes incredibly impressive,

it's important to remember

that living so large would have come with some enormous struggles,

too.

Like shattered legs, vulnerable eggs, an overheating head,

and a brain that was far too small for such big worries.

For more Mesozoic mayhem,

head to the PBS app or PBS.org to watch Walking With Dinosaurs.

Walking With Dinosaurs is back 25 years after the original series brought these icons

of the Mesozoic to life.

The new series uses the latest research to show how these ancient animals behaved

through state of the art visual effects.

Check out the link in the description to watch these new stories from the

deep past.

And a gigantic thanks to this month's Eontologists.

Addie, Annie & Eric Higgins, Carl Woelfel, Jackie Scott-Ralston, Jake Hart, John Davison Ng,

JuanM, Melanie Lam Carnevale, Nico Robin, Raphael Haase, Tony Dai,

and S.T.E.V.E.

Become an Eonite at Patreon.com/eons

and you can get fun perks like access to a digital puzzle of paleoart

commissioned just for Eons.

And as always, thank you for joining me in the Ken Barns Studio.

Subscribe at youtube.com/eons for more Cretaceous creatures.

In fact, one body part is actually notable for being unusually small.

Their heads.....like me....

I have a small head.

Maybe not Sauropod small!

I can wear child hats just fine.

Yes, I have a tiny head.

Sunglasses and?

Sometimes, yeah.

Usually the child-size ones squeeze a bit too much,

but I definitely have to buy, like, the small-sized frames.

Hilarious.

Like, I wore an extra-small helmet in softball.