(host) Around 76 million years ago in what's now Alberta, Canada, there lived an ankylosaur called Dyoplosaurus.

Today, this area is rocky and dry.

But when this animal lived there, it was a lush, coastal environment striped with rivers, perfect for big, plant-eating dinosaurs.

Dyoplosaurus was one of those large herbivores, measuring around four and a half meters long with a wide body covered in thick, bony armor.

And at the end of its tail, there was something that would make it a very special discovery millions of years later: a well-preserved club.

Now, you might think that this piece of equipment is pretty typical for an ankylosaur, but when this dinosaur was first discovered in 1919, nothing like it had ever been seen before because Dyoplosaurus was the first ankylosaur discovered with evidence of a tail club.

And even though we've known about them for more than 100 years, we've only started to get to the bottom of how they worked and how they developed in the first place.

Strangely enough, it looks like the earliest ankylosaur tail clubs actually started out clubless.

Tail clubs are pretty rare in the animal kingdom.

No animals have them today, but they've popped up several times within the evolutionary tree of tetrapods.

For example, some glyptodonts had clubs.

These giant relatives of today's armadillos thrived in the Americas from the Miocene to the Pleistocene epochs.

Some very weird extinct relatives of turtles also developed tail clubs, as did a few groups of dinosaurs.

For example, the sauropods Mamenchisaurus and Shunosaurus both had small clubs.

But the most famous group by far to have this unusual structure is the ankylosaurs, which are my personal favorites because they're just totally metal and eight-year-old me just wants to throw a saddle on one and ride it into battle.

Ankylosaur's tail clubs were the biggest, at least proportionally, and they also required quite a few changes to the dinosaur's anatomy.

And while clubs are practically synonymous with ankylosaurs, most of these dinosaurs didn't actually have them.

True tail clubs were only around for the last 20 million years of the more than 100-million-year reign of these armored dinos.

Now the ankylosaur family tree can be split into two main groups: the ankylosaurids and the nodosaurids.

All of these dinos had impressive armor, but none of the nodosaurids had clubs.

And among the ankylosaurids, only a small derived subset known as the ankylosaurines, had them.

So what were these clubs used for?

Pretty much from the beginning, it was assumed that the club was used as a weapon, either for defending against predators or for fighting with other members of the species.

Some other hypotheses have been suggested over the years, too, like the idea that the club functioned as a false head to confuse would-be predators, or that it could have been used as a sexual display for potential mates.

But the weapon hypothesis always seemed to be the most plausible, based on both the formidable anatomy of the clubs and the fact that other weaponized tails were known from dinosaurs like Stegosaurus .

But no one actually tested this idea for nearly 85 years.

Then in 2009, a paleontologist named Victoria Arbour studied the muscles in ankylosaur tails-- what they looked like and how much force they could generate.

And maybe not surprisingly, those muscles turned out to be pretty extreme.

Arbour studied the tail anatomy of ankylosaurs and compared it to that found in living archosaurs, like crocodilians, and she found that the muscles involved in swinging the tail ran the length of the mobile portion of the tail at the base.

And these were supported by other muscles that were anchored to the dinosaur's wide hips and thigh bones and attached to the tops and bottoms of the tail vertebrae.

Altogether, these muscles gave the tail a massive cross section, which increased the force that the muscles could produce.

Ankylosaurs also had tendons that had effectively turned into bone.

These are known as ossified tendons, and they help support the tail.

So by taking into account this musculature, their range of motion allowed by the tail vertebrae, and the size and weight of the club itself, Arbour was able to calculate the impact force that the club could produce.

We could finally answer with certainty whether ankylosaur tail clubs could have been used as a weapon.

And the answer was a bone-shattering "yes"-- like, literally, The tail club of an adult Euoplocephalus could potentially generate impact forces up to 14,360 newtons.

It was capable not only of breaking but pulverizing bone.

And in fact, further work showed that larger clubs could theoretically generate such a forceful impact that they were at risk of fracturing themselves.

The chunkiest of these boys were not messing around.

So the tail clubs were powerful weapons, although we still don't know whether they were used for defense, to compete for mates or territory, all of the above, or maybe something else.

But while Arbour was working on how these clubs worked, she realized that their evolutionary origin was also a mystery, and it was a mystery with two parts.

Because the clubs of the ankylosaurines are made up of two components: a handle and a knob.

The handle is formed from highly modified and interlocking, or fused, vertebrae that create a rigid structure at the end of the tail.

The knob is made up of enlarged fused osteoderms, or bones found in the dinosaur's skin, that also formed the group's signature body armor.

And this arrangement is really interesting because it combines both the normal internal skeleton of the ankylosaur with their protective dermal skeleton to make it a single structure.

This is part of what I find so fascinating about these guys.

I mean, look at them.

They're like tanks.

So the question Arbour set out to answer was, "Which part of the club evolved first?

The handle, the knob, or both at the same time?"

If the handle evolved first, then the earliest ankylosaurs that began to develop this structure would have had modified rigid vertebrae at the ends of their tails.

But if the knob evolved first, then the tail would have been flexible, like it was in ankylosaurs that didn't have the clubs.

and there would have been some large growth at the tip.

And if the handle and knob evolved together, then the first ankylosaurs with tail clubs would have had evidence of both forming at the same time.

The only way for Arbour to figure out which of these hypotheses was correct was to scour the fossil record for ankylosaurs with tails that matched one of these three options.

And luckily, it turned out that there were a couple that were already in museum collections.

For example, Gobisaurus was an early ankylosaurid that lived around 92 million years ago in what's now China.

It was big, about six meters long and weighing several tons, and it had a very interesting tail indeed.

It had all of the structural support for a tail club, with a stiff handle made of modified vertebrae that looked pretty much the same as the handles of ankylosaurs that had full clubs, but there was no knob at the end and the entire tail was preserved, including the very tip, so we know that it hadn't lost its knob, say, through the process of fossilization.

So Gobisaurus shows that the first hypothesis was correct.

Ankylosaurus developed the handles first.

And there seems to be more evidence even further back in the ankylosaurid family tree in another Chinese ankylosaur called Liaoningosaurus .

This dinosaur lived around 122 million years ago and also has evidence of that stiffening of the tail that formed the handle, though to a lesser extent than Gobisaurus.

The parts of their vertebrae that interlock were much longer than those seen in early ankylosaurs, but there was no sign of fusion between the vertebrae.

However, the only known specimen of this dinosaur with a tail is a tiny juvenile, and the very end is missing.

So it's hard to say for sure whether it really didn't have a knob on its tail or if it just got lost.

Or it may not have grown in yet, because we know that the bony armor and tail clubs of ankylosaurs developed and expanded as the animal grew.

But, given its place in the ankylosaurid family tree and the appearance of the tail vertebrae, it looks like more early evidence that the handle evolved first.

And according to Arbour, it seems that even a stiffened tail alone could still have delivered a painful blow despite the lack of a knob.

It's likely that enlarged osteoderms at the tip of the tail made that blow more effective.

So over time, they were selected for, leading to what we now think of as the typical ankylosaur tail.

So that's how my favorite dinosaur got its club.

The fossil record is full of transitional forms, like Gobisaurus, that can help us solve evolutionary mysteries like this if we just ask the right questions.

In this case, we just had to ask, "Which came first?

The handle or the knob?"

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