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.

That’s 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 elephant’s 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 today’s 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.

That’s 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 today’s 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 didn’t 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 Platybelodon’s 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 didn’t 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 you’re 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 you’ve 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 wasn’t 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 wasn’t 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, we’re 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 wasn’t 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 weren’t  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   trunks…but when it shifted again,  even an adaptation that once changed