Welcome to our first episode of season 3 of Bizarre Beasts!
You know we always say that profits from the pin club
and all our merch go to decreasing maternal mortality in Sierra Leone,
so we thought that it would be a good idea to give you an update
on some of the things that you have supported so far:
In April 2021, ground was broken on the Maternal Center of Excellence,
and it’s on track to offer services in 2024,
almost tripling the number of maternal hospital beds in the region.
And with all of your support, that project has expanded in scope to include a dedicated
training center for healthcare workers.
If you want to help us out and get some great pins,
we will be keeping the pin club open for an extra week this month.
We’ll be giving you all those details at the end of the episode.
There are millions of unique species crawling, walking,
flying, and swimming around on our planet,
most of which have yet to be formally described by western science.
And while every species may be unique, not every species is original.
A lot of animals look alike or live in very similar ways.
One example of that: carcinization,
the repeated evolution of crab-like shapes in crustaceans that are not really crabs.
Another example is the scaled reptiles, called squamates,
shrinking or losing their legs over and over again.
Now, snakes might be the most obvious case,
but there are also legless lizards, slowworms, some skinks, and today’s bizarre beast,
which may be the weirdest version of this.
Meet the Mexican mole lizard: a pink, wrinkly,
burrowing creature that is not a mole or a snake or a lizard,
but a truly unique, if not entirely original, combination of traits all its own.
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The Mexican mole lizard is one of around 200 species of a thing you probably have never heard of:
amphisbaenians, a group of scaled, typically-legless reptiles that are neither lizards nor snakes.
Or, at least, we don’t think of them as lizards or snakes.
Squamates are, taxonomically, strangely complicated.
You’ve got what we usually think of as “lizards,” reptiles with four legs,
things like geckos, western fence lizards, chameleons.
And you got snakes, which don’t have legs and seem to be something totally different from lizards.
Like, snakes don’t have real eyelids, while lizards generally do.
And then you’ve got amphisbaenians, which also don’t have legs, except for when they do.
But, here's the weird thing:
when you put these three groups on an evolutionary tree based on their DNA,
you have groups of lizards, like geckos and skinks,
that split off from a lizard ancestor before snakes and amphisbaenians did.
And then you have groups of lizards, like iguanas,
that split off after snakes and amphisbaenians did.
So, from that perspective,
both snakes and amphisbaenians are just different kinds of lizards that have lost their legs,
But, because each group came from its own common ancestor
and the members of each group are more closely related to each other than anything else,
we call them “snakes” and “amphisbaenians.”
Having separate names for them is useful and we’re practical like that.
Now, some research suggests that amphisbaenians got their start in North America
soon after the dinosaur-ending Cretaceous–Paleogene extinction event.
And it looks like the ancestors of the Mexican mole lizard might’ve stuck around that continent,
because today you can find Mexican mole lizards buried
under the shrubland and desert of the Baja peninsula of Mexico.
It's that burrowing lifestyle that may explain why
the Mexican mole lizard is one of only four amphisbaenians to have any legs at all,
as well as one of very few in the group to retain the skeletal scaffolding,
called a pectoral girdle, needed for functional front legs.
Its front legs are strong, with long,
shovel-shaped claws at the end for digging, like a mini-mole,
but Mexican mole lizards don't have back legs for getting around like moles do.
Instead, underground, Mexican mole lizards do what’s called ‘concertina locomotion,’
alternatively bending and straightening their body to inch their way through the sand.
Snakes do this too, usually in tunnels or when climbing up trees.
By bending part of their body into a very tight s-shape,
they anchor themselves in place and avoid slipping backwards
as the other part of their body slowly inches forward.
But for snakes, this takes a lot more energy than other modes of locomotion,
like lateral undulation, which is the classic snake slither.
Mexican mole lizards are much more efficient movers with concertina locomotion than snakes,
and the reason seems to be those front legs.
As the mole lizard pushes its head forward,
it can use its front legs to shovel and sweep dirt out of the way, and to help stabilize its body,
both of which mean more of its energy can be used for forward propulsion.
And concertina locomotion isn’t the only way that Mexican mole lizards get around.
Their scales are arranged in rings around their body,
allowing them to crawl forward with the accordion-like motion that earthworms use.
Also kinda like earthworms,
Mexican mole lizards can lose parts of their body and just keep on going.
They’ve been known to drop their own tail,
in classic lizard fashion, possibly to distract predators.
Unlike many lizards, though, this is a one-time-trick, and the lost tail will not grow back.
But what might be the coolest thing about the Mexican mole lizard
is how it hears, without any external ears.
Which, by the way, is one of the features that usually distinguishes snakes from lizards.
Snakes don’t have holes in their head for hearing, whereas lizards, even legless ones, do.
Now, hearing is when an animal senses vibrations caused by
alternating waves of low and high air pressure
that are interpreted as sounds by the brain.
In reptiles with external ears, those vibrations are picked up by the eardrum,
which transmits them through the middle ear bones, like the columella and extracolumella,
to the cochlea, the part of the ear where the sound-sensing hair cells live.
But because amphisbaenians don’t have external ears,
they’ve adapted to do things a little differently,
think of it as evolution happening to the parts that they do have.
Most amphisbaenians have an unusually large columella and an elongated extracolumella,
but, unlike even other members of this group,
the Mexican mole lizard doesn’t seem to rely on the extracolumella to transmit sounds much at all.
Instead, it uses an inward fold of skin that freely vibrates when exposed to sound waves,
and transmits those sounds directly to the cochlea.
It’s kinda like an alternative eardrum.
The “skin hearing” system is so effective that the
Mexican mole lizard has some of the most sensitive hearing of any amphisbaenian,
but it’s only about as sensitive as that of the average lizard.
Not bad for not having external ears, though!
With its pink, earthworm-y appearance,
lizard-like ability to drop its tail, and mole-esque stubby front arms,
the Mexican mole lizard is definitely unique.
And while its individual adaptations may seem somewhat familiar,
seeing them all on a single animal is what makes this amphisbaenian one Bizarre Beast.
The Bizarre Beasts pin club subscription window will be open for an extra week,
from now through the end of July 10th.
When you sign up, you’ll suddenly have an excuse to tell your friends
all about amphisbaenians when you get your very own in the middle of the month,
and the pins after that around the time each new video goes live.
Check out this squiggly little guy!
He's really good!
For more fun facts about the Mexican mole lizard and other bizarre beasts,
please like and subscribe here,
and follow us on Twitter @BizarreBeasts, and on Instagram and Facebook @BizarreBeastsShow.
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Outro ♪ ]