This episode is supported by the Great Courses Plus. When you think about life before the dinosaurs, if anything comes to your mind at all, chances are the one animal you think of is Dimetrodon. With its lizard-like appearance and that distinctive
sail on it back, Dimetrodon is practically the mascot of the Palaeozoic Era, a time before
flowers, birds, mammals, and even crocodiles. Dimetrodon dominated the last period of the
Palaeozoic, the Permian Period, alongside many other animals that can seem at once familiar
and … not. That’s because these creatures had jumbles
of traits that were partly reptilian and partly mammalian, earning them the paradoxical-sounding
name “mammal-like reptiles.” But these beasts don't belong on the reptile
branch of the Tree of Life. Instead you’ll find them over on the mammal
branch. Because they’re more accurately known as
stem-mammals. Yes, it could easily be mistaken for a primordial
lizard, but Dimetrodon had a bunch of game-changing adaptations that foreshadowed the rise of
mammals millions of years later. One of its most distinctive features? Its weird variety of teeth. Dimetrodon’s name actually means “two-measure
tooth,” because, before it and its kin came along, most animals had rows of teeth that
were basically identical. Meat-eaters, for example, tended to have simple,
pointed teeth that all served the same function -- to pierce through meat. But Dimetrodon had different teeth for different
jobs, turning its mouth into a kind of physiological swiss army knife. Up front, it had long, canine-like teeth for
killing prey, but it also had distinct incisors and teeth in back that pointed backward, perfect
for dismembering carcasses. It was also among the earliest animals to
have serrated teeth, making this stem-mammal the perfect Permian butcher, capable of devouring prey quickly and efficiently. And having more than one kind of tooth is
a hallmark of our own mammal lineage. It eventually led to the diversity of teeth
that we now find throughout the mammalian family -- from the chisel-like incisors of
rodents, to the dagger-shaped canines of cats, to the grinding molars of elephants. Before you eat your prey, though, you have
to catch it. And here, Dimetrodon had a leg up on much
of its quarry. You've probably seen pictures of Dimetrodon,
and odds are those pictures showed the animal in a sprawling posture – kind of like it’s
doing a push up - with its belly and tail dragging on the ground. But fossil tracks found in Oklahoma, which
some experts think were made by Dimetrodon, suggest that the animal was probably capable
of what’s known as a high walk. In this posture, its belly and much of its
tail would have been raised off the ground, with its legs partially straight -- giving
it a stance somewhere between that of a lizard and that of a mammal. This stem-mammal strut would not only have
made Dimetrodon faster and more nimble than its prey, it also would’ve required much
less energy than the sprawling posture used by, say, amphibians. OK. Now, I’m sure you’re wondering: What was
up with that sail? For a long time, the sail of bone and skin
on Dimetrodon’s back was thought to be some kind of temperature regulator. The thinking was that the sail could be turned
toward the sun to absorb heat, while its large surface could release heat quickly when it
was hanging out in the shade. Some experts stick to that theory. But in recent years, others have offered new
ideas about the sail, and what it can tell us about stem-mammals. For one thing, these researchers note, big
animals retain way more heat than small animals. So presumably, bigger Dimetrodons would need
bigger sails. But there are some relatives of Dimetrodon
-- like Sphenacodon here -- that were plenty big, but had tiny sails. Meanwhile, some smaller species had big sails
-- too big to regulate heat for such small animals. And in 2010, a study that compared Dimetrodon
specimens at different ages found that its sail grew really quickly, with juveniles sprouting
sails that were disproportionately large for their body size. This suggested that, rather than serving as
a solar panel, Dimetrodon may have used its sail for something even more crucial to its
survival -- to communicate with others of its kind. And here, too, mammals ended up taking a page
from the book of Dimetrodon. Lots of modern mammals, after all, are known for having flashy features, like the mane on a lion or the antlers of a deer, that advertise
strength to enemies, and help attract mates. Whether the sail of Dimetrodon was used as
a mating display or for threatening rivals is anyone’s guess. But at the very least, this was one stem-mammal
that had something to say to its neighbors, indicating that, as with mammals, communication
was vital to its survival. With unique teeth, extra speed, and a complex
social life, Dimetrodon was able to dominate Early Permian environments. Its success allowed it to spread to many different
habitats, including swamps and deserts, from Canada to Texas to Germany. Alas, the reign of Dimetrodon ended around
270 million years ago. And just 20 million years later, the environmental
catastrophe at end of the Permian, known as the Great Dying, spelled disaster for nearly
all the stem-mammals. But all was not lost for our mammal lineage. The stem-mammals’ ability to adapt -- which
was embodied so well by Dimetrodon -- allowed some to survive. And they went on to diversify over the next
twenty million years -- evolving into a range of forms, from tiny burrowers to saber-toothed
giants, and eventually, you and me. So we can’t claim Dimetrodon as our direct
ancestor. Other stem mammals have earned that title. But still if you take a close look at this
sail-backed animal, you might see a little bit of yourself. Thanks to The Great Courses Plus for sponsoring this episode. The Great Courses Plus is a digital learning service that allows you to learn about a range of topics from educators all over the world including Ivy league professors Go to TheGreatCoursesPlus.com/Eons and get access to a library of different video lectures about science, math, history, literature, or even how to cook, play chess, or become a photographer. New subjects, lectures, and professors are added every month like The Science of Flight taught by Professor James W. Gregory Professor Gregory covers everything from the physics of lift to breaking the sound barrier, which is awesome! With The Great Courses Plus, you can watch as many different lectures as you want – anytime, anywhere without any tests or exams you have to take Help support the series and start your free one month trial by clicking the link below or going to TheGreatCoursesPlus.com/Eons So that's Dimetrodon but we are curious what you want to know about the story of life on Earth? We're always looking topics We've got some in mind but we're looking for yours as well. So leave a comment to let us know And if you want more of this, please go to youtube.com/eons to subscribe! Now do yourself a favor and check out some
of our sister channels from PBS Digital Studios. Your brain will thank you!
What i'd like to know is if the sails could move or were the bones fixed in place along the spine. Seems a rigid structure like that would prevent doing something as simple as rolling over. Was there evidence of musculature or tendons for manipulating the sail position?
Then there's this guy with tree branches: https://en.wikipedia.org/wiki/Edaphosaurus#/media/File:Edaphosaurus.jpg
That was a great video, but the extra stuff at the end is getting a bit excessive. I guess I'm glad it's at the end rather than the beginning, but a solid 20% of the video was an ad/other junk.