Eons

Around 20 million years ago, a group of megaherbivores began to spread across the globe, taking up shop in a huge range of habitats as they spread from Africa and Arabia into Eurasia, and across the Americas.

These were the proboscideans, the group that would eventually include today's elephants.

Though, you might notice something a little off about many of them.

Thats because, for much of their history, they were missing one of the key features of modern elephants: a long, grasping trunk.

Instead, they sported a weirdly long lower jaw, often with a second set of tusks, though the exact look varied dramatically between species.

And these long-jawed proboscideans were doing pretty well for themselves, acting as the dominant herbivore basically everywhere they went That is, until they were all rapidly replaced with proboscideans with long, flexible trunks instead.

Enter the mammoths, mastodons, and our modern elephants.

But what happened?

What suddenly made long jaws such a liability?

Well, it looks like we can thank a changing climate for the evolution of the elephants trunk.

Proboscideans first started popping up in Africa during the early Eocene, around 55 million years ago.

At the time, these regions were similarly tropical to what we experience today.

But unlike modern times, these temperatures stretched to the higher latitudes as well.

Trees and shrubs dominated the vast majority of environments across the globe from Antarctica all the way to what is the northern tundra now.

During this time, and for about half of their existence on Earth, proboscideans were much smaller than elephants, and looked, well, not very elephant-ish.

Take Moeritherium for example, an early genus that stuck around for about 20 million years.

Reaching heights of only 70 centimeters tall and barely 225 kilograms, they looked more like todays tapirs than an elephant.

And for tens of millions of years, proboscideans were only found in Africa and the Arabian peninsula.

But that all started to change around the late Oligocene and early Miocene, between 25 and 20 million years ago, when they started to expand their range.

Thats when proboscideans began to spread across Eurasia.

And by the middle Miocene they found themselves moving into North America, and headed to South America from there.

As they expanded across the world, these megaherbivores diversified dramatically.

In some places, they even filled multiple distinct ecological roles within the same communities.

Most species of proboscideans belonged to a group called gomphotheres.

They arose in the late Oligocene, about 28 million years ago, and were the last common ancestral group to todays elephants.

Not that they looked entirely elephant-y at this stage, given that they were still lacking a very grasping and coiling trunk, which we can identify in the fossil record by looking at specific features of the nasal region.

But they were getting closer.

Because, during this period, many variations of a different, but equally bizarre, facial feature arrived on the scene: elongated upper and lower jaws.

And with longer jaws came a longer trunk to match, even if the trunk itself didnt reach the extreme lengths of the modern elephants just yet.

And this elongated face is a pretty unusual shape, at least from a mammal perspective.

We see really long faces in reptiles, birds, and fishes, but mammals?

Not so much.

Proboscideans broke that mold.

This generally long shape first popped up in species like Palaeomastodon, which had a slightly elongated face and lower jaw, complete with tusks.

And it just kept getting stranger over time.

From there, the diversity of tusk and lower mandible lengthening really took off, with over 20 genera and six families showcasing a huge diversity of form around the middle Miocene, some 20 to 11 million years ago.

In some groups, the lower jaw just kept getting longer and even more dramatic.

Like the appropriately-named shovel-tusked gomphotheres.

Shovel tuskers like Platybelodon, found in Africa and Asia, had an especially extreme mouth shape.

What they lacked in impressive upper tusks they made up for with their long lower jaw, which had short, broad, and flattened lower tusks at the end.

And it was first assumed that they used their strange mandibles to scoop up water plants.

Because, put Platybelodons face side by side with a shovel and you get the idea that it appears to be the role of a scooper.

So on shape alone, scientists made assumptions about what these scoop-faced flat-toothed mammals ate.

But it turns out that didnt paint the full picture.

In one study, a closer look at their teeth using microwear analysis to examine the tiny scratches and patterns left behind, revealed that their diet was a lot more varied than what we first thought.

The wear patterns on their teeth pointed towards a tendency to cut or strip bark, twigs, and leaves, not scoop aquatic plants.

Now, we know that the long-faced gomphotheres were a diverse group that really took off in terms of diversity during the early and middle Miocene.

And this is where at least some proboscideans begin to look like the elephants we know today, because a long nose came hand-in-hand with a long face.

At least, sort of.

Take the likes of Gomphotherium.

This species had extremely silly-looking lower tusks.

Picture the upside-down mouth of a cartoon bunny, and youre getting close.

And while it was a far cry from an elephant jaw, they did have an elongated trunk, based on shared anatomical traits with modern elephants.

There was also Choerolophodon in Africa and Eurasia, which kept the length in the lower jaw but dropped the lower tusks, making it much more elephant-ish looking.

And bringing it back to the shovel-tuskers, Platybelodon not only had a sharp edge on their lower tusks, they also had a trunk that could coil and grasp.

This made them well-adapted for grazing on low, vertically-growing plants, like grasses, grabbing them before cutting them off at ground level which might mean that they were the first proboscidean to use their trunk for grazing.

Around the middle of the Miocene, the climate was getting drier in many regions of the world, and ecosystems were becoming more open and less forested.

So with the range of habitats that existed during this period, from dense humid forests to open, dry areas, there were many different versions of long-faced proboscidean species to fill these niches.

That is, until they started dropping out of the fossil record at a dramatic rate.

For example, Choerolophodon dropped off significantly around 14.5 million years ago, and Gomphotherium was largely gone not long after.

We last see Platybelodon at the end of the middle Miocene.

And across the board, these species were subsequently being replaced by those with more trunk and less lower jaw.

So, something dramatic must have happened along the way that caused this widespread shift from long jaws to extra-long trunks.

Now if youve ever watched an elephant reach up and pull down a branch of tasty leaves, you might think the answer is obvious.

Trunks are just better for reaching up!

But what made a trunk advantageous actually appears to have very little to do with reaching up and browsing on branches.

Instead, it has a lot more to do with reaching down and yanking plants up.

Because, it turns out, this shrinkage of the lower mandibles and tusks that happened across the board in proboscideans actually happened right around the time grasses really took off.

Open grasslands became widespread across the globe in the late Miocene, driven in part by broad climatic factors that increased arid conditions and extreme seasonal fluctuations in rainfall.

Grasping with the trunk likely became the go-to strategy for pulling up these softer stemmed ground cover plants instead of using their teeth to graze on horizontally growing branches, bark, and leaves from trees and bushes in more forested areas.

So as the climate continued to shift ecosystems to more arid conditions, that enabled proboscideans to diversify once again beginning around 8 million years ago in the Late Miocene.

New species popped up around Africa as they abandoned the forest and woodland edges to graze in the growing grassland habitats.

And as these climatic changes become more dramatic and widespread over time, it became the key to their overall survival.

The lower jaw just wasnt cutting it anymore, quite literally, with proboscideans now using the trunk alone to efficiently yank grasses out of the ground, instead of lower tusks to cut off plants at the base.

But it wasnt just the long trunks that clued scientists in on how important grasses were to the proboscideans.

It was partially demonstrated by the evolution of their unique teeth, too.

And, no, were not talking about their tusks again, but about their molars.

Given the abrasive nature of grasses, which use silica in their internal structures that toughens up the leaves, paired with high dust accumulation in a dry environment, you're asking for some serious dental wear and tear.

And as grasslands replaced forests to spread across the globe in the changing climate of the late Miocene, something was happening across many groups of herbivores.

The crowns of their teeth got higher, and their enamel became dramatically folded, creating many ridges across the tooth.

And although this was popping up in a wide range of mammals, some early trunked grazers didn't show much of a change in molar adaptations, at least not in the early days.

It wasnt until around 10 million years ago that the molars of proboscideans like Tetralophodon really started to become specialized.

So what might have started off as a trunk-based dietary change worked for quite a while, and eventually the teeth had to catch up.

But all good things must come to an end.

And although the proboscideans remained very successful and diversified into a wider variety of habitats for a few million more years, they started to drop off globally around 7 million years ago.

Because, the now grabby-nosed, ridge-toothed animals were once again faced with a changing climate.

This time, the consistent, warm temperatures were threatened with an impending ice age.

As a result, the once-productive grasslands were faced with big seasonal shifts, resulting in less food availability to support all of the proboscidean species that had evolved.

Cue the origin of mastodons and wooly mammoths, which helped proboscideans branch out into colder climates and werent limited by grass-feeding specializations.

But then, as climate conditions became more extreme, even those better adapted to life outside of open grasslands began to die off.

In the end, climate change topped off with human hunting pressures that piled on to an already struggling group of mammals would wipe most of them off the face of the Earth.

And today, we are left with only three species of elephants, the last of a long line of once-diverse proboscideans.

Looking back through evolutionary time, we can see how their ancestors and close relatives have had quite the journey, from their humble trunkless beginnings to the wild diversity of the shovel tuskers.

And while long jaws dominated for some time, the rise of grasses prompted trunks to take the dietary reins, leading to the fall of the long-lower-jawed species.

And from there, we eventually got to the trunked elephants we know today.

So, ultimately, climate change drove the expansion of grasslands and the rise of trunksbut when it shifted again, even an adaptation that once changed