Thanks to CuriosityStream for supporting PBS
Digital Studios. It may not surprise you to learn that some
kinds of fossils are more common than others. Most dinosaurs, for instance, are known from
only one or two specimens. Meanwhile, some trilobite species are known
from hundreds or thousands of specimens. But one of the most abundant kinds of fossils
on Earth, numbering in the millions of specimens, came from something most people have never
heard of. And for decades, their identity was a mystery
to paleontologists. But geologists figured out that these mysterious
fossils could basically be used to tell time in the deep past! Please allow me to introduce you to the conodonts. From the time they were first discovered in
the 19th century, and right up until the 1980s, conodonts were only known from isolated hard
parts, called conodont elements. Some of them looked like little fans, or saw
blades, or even barbed wire, but most of them looked like cone-shaped teeth. So they were given the name conodont, which
means “cone tooth.” These elements are all verrry tiny. Most are under one millimeter, and none greater than five millimeters long. And for a long time, paleontologists were
totally stumped about what animals these things belonged to, and where on the Tree of Life
they belonged. Some experts thought that, although they look
kind of like teeth, their similarities to teeth are pretty superficial. But others pointed out that the fossils were
made from a mineral called hydroxylapatite. This is the same mineral that bones and teeth
are made from in vertebrates. So, this led many scientists to think that
they were teeth, maybe from some kind of weird, extinct fish. But while paleontologists were spending a
hundred years or so debating what conodonts were, geologists were discovering what conodonts
could do. When a species is really abundant, widespread,
distinctive, and found in a restricted span of time, their remains can be used as Index
Fossils. These are fossils that help geologists correlate
and date rock layers all over the world. And conodonts were all of those things -- abundant,
widespread, and composed of lots of distinctive species. So they turned out to be some of the most
important index fossils from the whole Paleozoic Era. In fact, many subdivisions of the Paleozoic
are actually defined by when certain conodont species first or last appear. For instance, you know when the Devonian Period
ends and the Carboniferous Period begins, because that’s when you start finding fossils
that belong to a species of conodont known as Siphonodella sulcata. Likewise, in the Triassic Period, nearly every
age is defined by the first appearance of various conodonts. The extinction of Metapolygnathus parvus marks
the end of the Carnian, for example, while the start of the Rhaetian is defined by the
first appearance of the genus Misikella. So, geologists are able to use these fossils
to basically tell time! But conodont elements can do more than just that! They’re also, essentially, geological thermometers! It turns out that conodont elements actually
change color when they’re heated up. And no matter what species they belong to,
they go through the same range of color changes at the same temperatures. Geologists have used these fossils to devise
a six-point scale of how they change from their natural tan color, to brown, then gray,
then black, and finally white, as they get hotter and hotter. With this scale, called the Conodont Alteration
Index, geologists can use the color of a conodont that they find, to figure out how hot the
surrounding rock once was. And this can be really important in fields
like petroleum geology, because it can reveal whether sediments ever got hot enough for
organic hydrocarbons to be converted into oil and gas. So conodont elements quickly became one of
the handiest tools in the geologist toolkit. But meanwhile, paleontologists still had no
idea what kind of animals conodonts were. In the 1970s, fossils of some vaguely fish-like
creatures were found in Montana that were thought to be conodont animals. But further study revealed that the conodont
elements found in those fossils were actually in the animals’ guts. So it turned out that they weren’t conodont
animals; they were fossils of creatures that ate conodont animals! The mystery lingered until 1983, when fossils
were discovered in 350 million year old sediments from Scotland that brilliantly preserved the
soft-bodied animals. And … they were kinda weird, with long eel-like
bodies, tail fins, a stiff rod of tissue down their backs, and giant bulging eyes. Thanks to these beautiful specimens, we were
able to learn that conodont animals were a kind of fish after all! The fossils revealed distinctive, zig-zag-shaped
muscles, known as myomeres, which are still present in fish today. And the rod down its back was a notochord,
an early precursor of the vertebral column seen in vertebrates. Both those features--myomeres and notochords--are
found only in chordates. And the fossils also revealed that the tiny,
tooth-like conodont elements were concentrated in the animal’s mouth -- but also in its
throat! The elements were arranged in a complicated
array of blades and points, like some kind of horror movie monster. Some experts think these spines and barbs
may have been helpful in gripping and slicing tiny prey. But others suggest that they were used to
filter plankton from the water. Either way, the picture of these creatures
was finally coming into focus! Like modern lampreys and hagfish, conodonts
were jawless fish, and they were one of the earliest and most successful groups of vertebrates. And they thrived all over the world throughout
the Paleozoic Era, with many species schooling in the open ocean like modern sardines, while
others stayed closer to shore. Throughout their history, conodonts were affected
by several mass extinctions, including the Great Dying at the end of the Permian Period
252 million years ago. But it wasn’t until the Triassic-Jurassic
Extinction about 200 million years ago that they were finally wiped out. A quick rise in carbon dioxide caused the
climate to warm up, while the acidity, salinity, and oxygen levels in the oceans all began
to change. Their final extinction brought an end to 300
million years of conodonts’ role as a cornerstone of the world’s ocean communities. Sad, I know. But their remains ended up being some of the
most important fossils of the entire Paleozoic Era. They’ve helped geologists find oil and tell
deep time, while allowing paleontologists to understand a whole new type of animal life. Thanks to their success and incredible abundance,
they’re among the most useful fossils in the world. Thanks to CuriosityStream for supporting PBS
Digital Studios. With CuriosityStream you can stream documentary
films, and programs about science, nature, and history, including exclusive originals! For example, you could check out Planet Dinosaur,
a three-part BBC series about the latest discoveries from the days of the non-avian dinos. CuriosityStream offers unlimited streaming,
and for you Eons viewers -- because I like your face! -- the first two months are free
if you sign up at curiositystream.com/eons and use the promo code EONS. Thanks for joining me! I’m always interested in what you want to
learn about! So leave me a comment below with your questions
about ancient life! And be sure to go to youtube.com/eons and
subscribe. Now I’m sure finding out how precise these
tiny teeth fossils are was a bit shocking, but what shouldn’t be surprising is the
preciseness of math. Go learn the language of the universe with
our sister channel Infinite Series and find out what numbers are made of and if there’s
a way to divide by zero.
This video is very well done!
I’m finishing grad school and my head advisor is one of the leading conodont experts of middle Permian conodont faunal successions. Though my personal research doesn’t utilize conodonts, I have learned quite a bit about their usefulness in biostratigraphic correlation and in the establishment of global stratotype sequence boundaries (gssp’s).
I’m glad to see these little buggers are getting some western attention! In China they erect monuments of these microscopic fossils to show their pride for having the Permian-Triassic gssp at the Meishan Section within their borders and here in the west no one has ever even heard of conodonts.
Hindeodus parvus, index for the Permian-Triassic gssp
Edit: spelling