If you’ve been on the internet in the past couple of years, you might’ve seen one particular form of convergent evolution pop up over and over again.

Heck, we’ve even talked about it on this channel. It’s called ‘carcinization’ and it’s the process by which many long-bodied lobster- and shrimp-like crustaceans have become short-bodied and crab-like over time.

But what happens when convergent evolution goes the opposite way? Instead of many distinct animal shapes converging on a single form, what if a single ancient animal took on the body shapes of a lot of different critters? [♪♪ INTRO ♪♪] If all crustaceans “want” to look like crabs, then tenrecs “want” to look like basically any other small mammal. There are tenrecs that look a whole lot like hedgehogs, known as hedgehog tenrecs.

And there are tenrecs that are basically impersonating shrews, called shrew tenrecs. And there are even tenrecs that look like wanna-be moles, known as, you guessed it, mole tenrecs. Tenrecs range in size from about 3 grams to up to 2 kilograms, and mostly eat invertebrates, like insects and their larvae.

Some of the bigger species, like the tailless tenrec, will also eat small vertebrates, too. Another bizarre fact about tenrecs is that they’re often said to resemble primitive mammals in some ways. Like, for example, having a cloaca, that’s a single, shared opening for the ends of the digestive, urinary, and reproductive tracts.

And they have this in common with monotremes, like the echidna and platypus, but also with birds and reptiles, so it’s probably a hold-over from the way all ancient mammals did their business. These weird little guys are endemic to Madagascar, they’re native to nowhere else on Earth, though their closest relatives, the also-very-weird otter shrews, live in parts of central and west Africa. And the African mainland is where the ancestors of the tenrecs lived, too, before they got to Madagascar,

sometime between 30 and 56 million years ago.

Now, you probably know that Madagascar is an island. It’s actually the fourth-largest island in the world and you might even be familiar with some of its other charismatic inhabitants, like the lemurs. And the thing about Madagascar is that, even though it’s only 400 kilometers off the coast of Mozambique, the plants and animals that live there are pretty unique.

And that’s because it’s been separated from Africa for something like 160 to 170 million years, and from India for 80 to 88 million years. It’s had a long time to go its own way. But remember how I said the ancestors of tenrecs only got to Madagascar between 30 and 56 million years ago?

While the web-footed tenrec is aquatic, swimming 400 kilometers would be a lot for an animal that’s only about 30 centimeters long. And that species is the only one that’s adapted for an aquatic lifestyle. So, how did tenrecs get to Madagascar in the first place?

It might sound very weird and unlikely, but they probably floated there

on some kind of vegetation that got washed out to sea from somewhere on the east coast of African and was carried by currents to the island. This ancient tenrec, or small group of tenrecs or pregnant female, was probably pretty small, like most of the living tenrecs. All extant tenrecs also have low metabolic rates and low body temperatures relative to their size, which would help make them excellent candidates for surviving an unexpected trip to sea.

Because they wouldn’t need to eat as much as a bigger animal or one with a faster metabolism. Some tenrecs even go into torpor, that hibernation-like state we covered in our fat-tailed dwarf lemur episode. Rafting is also the hypothesis proposed for how lemurs got to Madagascar and how monkeys got to South America, so it’s not totally wild to suggest it for tenrecs, too.

Today, there are only four groups of terrestrial mammals that are native to the island, and when their ancestors made it there, they found that there were a ton of available ecological niches that they could fill. A niche is both a set of conditions within an ecosystem and the role an organism plays within it. So, given all that free ecological real estate, over millions of years, the ancestors of tenrecs evolved into many different species that play many different ecological roles, filling many different ecological niches.

Like, instead of otters on Madagascar, you have got the web-footed tenrec living in rivers and streams. And instead of actual moles, you have mole tenrecs with forelimbs modified for digging. And that brings us back to convergent evolution.

Now, why convergent evolution happens is because similar environmental pressures can have similar solutions, and evolution works with what it has. Mammals that dig end up with strong upper arm bones and big hand-claws, because those are the things that helped their ancestors move dirt effectively. And if both ancient moles and ancient tenrecs were small, terrestrial, quadrupedal mammals, it makes sense that they’d end up looking pretty similar, because they started from similar body plans and were subjected to the same environmental pressures.

Now, none of this is to say that there’s nothing unique about tenrecs. I mentioned earlier their cloaca situation, but one species called the lowland streaked tenrec does something no other mammal does: they stridulate. That’s the technical term for an animal producing sound by rubbing body parts together, like crickets do.

These tenrecs have bodies covered in quills, like hedgehogs and porcupines, and a rad black-and-yellow color scheme. And one set of quills on their back is specialized for making high-pitched, ultrasonic sounds when they vibrate together. They probably use these sounds, along with high-pitched tongue clicks, to either echolocate or communicate with each other.

Which is weird for a mammal! But, I guess, really fits the tenrec theme of convergent evolution and helps make them such bizarre beasts. The Bizarre Beasts pin club subscription window is open from now through the end of April 17th!

The tenrec pin is just really great, they're the little spiky guys, and, they're very cute. If you’d like to support us another way, we also have socks and stickers and other merch available at BizarreBeastsShow.com! And, as always, profits from the pin club and all of our merch go to support our community’s efforts to decrease maternal mortality in Sierra Leone. [♪♪ OUTRO ♪♪]