The Most Successful Animals You’ve Never Seen (Spoiler: It’s Trilobites)
[MUSIC]
[Hands open a collections drawer full of small trilobite fossils organized in shallow, open boxes in the Invertebrate Paleontology collections at the American Museum of Natural History.]
MELANIE HOPKINS (CURATOR, DIVISION OF PALEONTOLOGY): Species go extinct all the time.
[The camera slowly moves along a different drawer full of slightly larger trilobite fossils. Then, a series of quick shots of hands holding up distinctive trilobite specimens.]
HOPKINS: In fact, it's estimated that more than 99% of all of the species that have been alive during Earth's history are now extinct.
[A shot of Hopkins picking up a small fossil from a drawer and holding it up near her face to examine more closely.]
HOPKINS: An extinction event is when many species go extinct over a very short period of time.
[Hopkins speaks to camera in a seated interview in a Museum collections space.]
HOPKINS: And if that event is global and affects many, many groups, we call it a mass extinction.
[Fade to black. Three photographs fade up side-by-side, showing Museum dioramas of ancient oceans from different eras.]
HOPKINS: There were three mass extinctions that trilobites experienced.
[A shot of Hopkins holding a trilobite fossil in each hand, comparing them, then speaks to camera.]
HOPKINS: One of the major things that we've learned, I think, from the fossil record is that when species are under stress, there are three things they can do…
[A series of closeup shots highlighting individual trilobite fossil specimens.]
HOPKINS: …they can either adapt, they can move somewhere else, or they can go extinct. Trilobites have done all three.
[Logo]
[Three photographs of trilobite fossil specimens appear side-by-side.]
HOPKINS: Trilobites are arthropods, so they're part of the larger group that includes spiders, scorpions and insects.
[As Hopkins lists each arthropod relative, the photographs are replaced with footage of that animal.]
HOPKINS: But they're an entirely extinct group.
[Shots of trilobite fossil specimens of different shapes and sizes in the Invertebrate Paleontology collections.]
HOPKINS: Trilobites lived from 520 million years ago to 250 million years ago, which means they were around for over 250 million years.
[Hopkins speaks to camera.]
HOPKINS: That's longer than the dinosaurs were around. If you don't include birds.
[Hopkins raises her hand to her chin and looks off-screen, smiling pensively.]
HOPKINS: Well, now actually…it's basically the same amount of time, if you do include birds.
[Hopkins looks back at the camera and LAUGHS.]
HOPKINS: Trilobites were a major component of what we call the Cambrian Explosion or Cambrian Radiation.
[A photograph of a Museum diorama of the Cambrian-era ocean floor.]
HOPKINS: The Cambrian started around 540 million years ago.
[Photographs of two fossils from before the Cambrian era are shown, appearing as abstract shapes and patterns in rocks.]
HOPKINS: And before this, there are some fossils, but it's really hard to tell what they are. And then during the Cambrian, all of a sudden, we see this huge explosion of diversity. Almost every single living group that we see today, we can recognize ancestors in the Cambrian.
[As Hopkins says the above, a series of labelled photographs of Cambrian-era fossils appear in succession.]
[An impression in rock somewhat resembling a branching coral is labelled as “Archaeocyatha: modern sponge ancestor.”]
[A fossil that resembles a modern-day crinoid, or a flower with spindly tentacles for petals, is labelled as “Gogia spiralis: modern echinoderm ancestor.”]
[A photograph of several fossils that resemble the spiral shell of a modern snail is labelled “Aldanella attleborensis: modern mollusk ancestor.”]
HOPKINS: And that happened over a very short period of time.
[Hopkins speaks to camera.]
HOPKINS: Of course, by short I mean geologically speaking, it’s still about 15 million years. But when you’re talking about that much evolution, it’s really remarkable.
[Closeups of a painting depicting trilobites at the bottom of an ancient sea.]
HOPKINS: Trilobites were marine, which means they lived entirely in the ocean.
What we understand about how trilobites lived comes mostly from…
[Fade from a closeup of one of the trilobites in the painting to a similar-looking trilobite fossil in the Museum collections.]
HOPKINS: …their preserved exoskeleton that's left behind in the fossil record,…
[Closeup of fossilized tracks left behind by trilobites in the sea floor.]
HOPKINS: …as well as traces in rocks that indicate the behavior of trilobites.
[Illustrations of the underside of live trilobites with visible legs, somewhat similar to a horseshoe crab’s, appear.]
HOPKINS: So we know that they had a bunch of legs that ran the entire length of their body.
[Footage of model trilobites in a Museum diorama depicting ancient oceans.]
HOPKINS: They spent a lot of time running around the ocean floor, digging through sediment, looking for tasty things to eat, and scavenging wherever they could.
[A series of shots shows many different trilobite specimens of all shapes and sizes from the Museum collection.]
HOPKINS: Over 22,000 trilobite species have been discovered and named, and we're still finding more every year.
Some of them were really bumpy, some of them were really spiny. Some of them were really swollen. Some of them were really flat. Some of them had a lot of segments. Some just had a few segments. Some had really big eyes, some had very little eyes.
They lived everywhere in the ocean.
[A series of natural history illustrations depicting a variety of ancient ocean landscapes appear, with the trilobites in each illustration highlighted.]
HOPKINS: They were in polar regions, tropical regions, shallow water, deep water, water that had lots of nutrients, water that didn't have lots of nutrients. And that makes them really useful for asking questions about biogeography and why species live where they do.
[Fade to white. A timeline appears onscreen beginning with an event labelled “Cambrian Explosion, 540 Million Years Ago” and ending with an event labelled “Present Day.” Close to the “Present Day” event is an event labelled “Dinosaurs Go Extinct, 66 Million Years Ago.” Beneath this, five colorful circles, each with an illustration of a different kind of trilobite.]
HOPKINS: During the evolutionary history of trilobites, there were three major mass extinctions: the End-Ordovician mass extinction…
[An event labelled “End-Ordovician Mass Extinction, 450 Million Years Ago” appears on the timeline]
HOPKINS: …the End-Devonian mass extinction…
[An event labelled “End-Devonian Mass Extinction, 375 Million Years Ago” appears on the timeline]
HOPKINS: …and the End-Permian mass extinction.
[An event labelled “End-Permian Mass Extinction, 250 Million Years Ago” appears on the timeline. The timeline shows that each of these three extinction events happened distantly in the past from the extinction of the dinosaurs.]
HOPKINS: During the End-Ordovician mass extinction, lots of species went extinct, but most major families survived and diversified again. In contrast, during the Devonian, all but one family went extinct. And then finally, at the End-Permian, the entire group went extinct.
[Hopkins speaks to camera.]
HOPKINS: Because every extinction event is different, and every species reacts in a different way to environmental stressors, we can get a sense for the probability that something would go extinct. But, “why did that species go extinct during that time period?” is almost impossible to answer.
[Fade to Black. With a CLICK, lights turn on in a room full of specimen storage cabinets. Hopkins walks into frame and unlocks a cabinet.]
HOPKINS: The fossil record is really important because it's our only way of knowing about organisms that are now completely extinct.
[A series of shots of drawers full of trilobite specimens being pulled out.]
HOPKINS: In the Invertebrate Paleontology collections alone, we have over 5 million specimens.
[Hopkins, speaking from the Museum collections space, takes out a trilobite specimen about the size of a thumb and holds it up for the camera.]
HOPKINS: Here's a very small trilobite. This is a Proetida trilobite from Morocco. But they could also get very big.
[Hopkins pulls open a drawer that contains two trilobite specimens roughly the size of dinner plates.]
HOPKINS: For example, this is a much older trilobite than the little one we just looked at.
[A series of shots showing fragments and pieces of trilobite fossils laid out on a white background.]
HOPKINS (Off-screen): But the fossil record isn't complete. Not everything gets preserved. And the stuff that does get preserved isn't preserved completely.
[In a four-way split-screen grid, footage of Hopkins collecting trilobite fossils in the field is shown alongside footage of trilobite specimens in the Museum collection.]
HOPKINS: And so we have to do a lot of work piecing together these clues from individual beds and then comparing them to other localities to get a more fuller picture of what was living where, at what time.
[A close-up shot of Hopkins in the field, pointing out trilobite fossils in a slab of rock with text on screen reading “Beechers’ Trilobite Bed, Oneida County, New York”]
HOPKINS: We can learn a lot about past ecosystems by simply counting how many different kinds of fossils are at one place.
[A shot of Hopkins in a different field location, using a chisel to point out fossils in rock, with text on screen reading “Wallcott-Rust Quarry, Herkimer County, New York”]
HOPKINS: The diversity and the abundance of those organisms will change from place to place and through time.
[In a third field location, Hopkins examine a rock alongside other scientists on a cliff overlooking a coniferous forest. Text on screen reads, “Anticosti Island, Quebec, Canada.”]
HOPKINS: We can also compare the species that are living in those places to see how they changed.
[Back in the Museum collections, a series of shots of Melanie using her finger to point out the banded segments that make up the middle part of the trilobite’s body between its head, called a cephalon, and its tail, called a pygidium.]
HOPKINS: So, for example, we can count the number of segments in the trilobite body and see how that has changed over time and why it might have changed.
[A series of shots of Hopkins opening collections drawers and pointing out specimens.]
HOPKINS: Comparing within groups and between groups and between extinction events becomes so informative. We start to see patterns.
And it's by comparing those that we can understand better how environments have changed through time, and how species have responded to those changes.
[Hopkins, standing in the collections space and holding up a trilobite specimen, speaks to camera.]
HOPKINS: Being able to look at specimens like this and compare them with one another is really how we answer fundamental questions about evolution and extinction.
[Fade to black. Credits.]
It took three major mass extinctions to end trilobites’ more than 250-year evolutionary lifespan. Today, to understand what these ancient ocean-dwellers can teach us about surviving (and not surviving) mass extinctions, scientists must piece together the clues they left behind in the fossil record—including their hard exoskeletons as well as traces in rock that reveal their behavior.
Join Melanie Hopkins, Curator of Paleontology at the American Museum of Natural History, to explore the history of these many-legged arthropods through the Museum’s collection of more than 5 million trilobite specimens. With scientists finding new species every year—in addition to the 22,000 already discovered—there’s still so much to uncover about these animals that lived even longer than non-avian dinosaurs.