Videos

[LIGHT MARIMBA MUSIC]

[A man in glasses and a floral shirt examines invertebrate fossils in specimen boxes on a table.]

SCOTT EVANS (Assistant Curator, Invertebrate Paleontology): If you have a fossil that's half a billion years old, understanding whether or not that thing could move is a hard question. 

[The same man, Curator Scott Evans, speaks to camera in his office. Many fossils line a desk behind him.]

EVANS: It's easy to tell if something that had legs could probably move around

[In the Museum’s Saurischian Dinosaur Hall, fossil footprints track behind the mounted Apatosaurus.] 

[Evans examines fossils in his office. Close up of a small, narrow, segmented invertebrates.]

EVANS: …and you might ask how, but that's not as difficult, I guess, as something with no legs that left no trails. 

[Evans speaks to camera in his office.]

EVANS: I love big questions that are hard to answer. We have to get pretty creative to try and find out.

[American Museum of Natural History logo appears over footage of Evans and a colleague excavating a fossil bed in a red, rocky area, covered in sparse, but bright green vegetation.]

[Evans works on a laptop in his office. He is surrounded by many fossil specimens of various sizes. On his computer, he manipulates 3D scans of fossil invertebrates.]

EVANS: My name is Scott Evans, and I'm a curator of invertebrate paleontology here at the Museum. I study this time very early in animal evolution, a period known as the Ediacaran, and try to understand how those animals functioned, what they looked like, and ultimately how they might be related to animals today.  

[Animated rendering of the Ediacaran sea floor. A sandy bottom is covered in plume- and leaf-like forms on stalks, and large, flat organisms spread between them. Text reads “Ediacaran Period, 575-538 million years ago.”]

EVANS: The Ediacaran period is a time in Earth's history where we see a shift from life that was largely microscopic to life that was multicellular, big enough to see and could move around. 

[Animation of various Ediacaran organisms: one that looks something like a segmented worm churns forward through the sandy seafloor, some frond-like organisms and a slug-like animal crawling through a greenish organic mat.] 

EVANS: The Ediacara biota are entirely marine organisms, pretty alien creatures that lived on a sea floor covered in this layer of slime that we often call an organic mat. 

[Aerial drone footage of a site in the Australian outback. Excavated fossil beds sit in a sandy, hilly landscape. Text reads “Nilpena Ediacara National Park”.]

EVANS: To study this time period, we have to go to places where the rocks are really old. 

[POV from a dashboard as a car drives over a rocky road that crosses a river. A kangaroo hops through the landscape.]

EVANS: One of the sites that I've been working for over 12 years now is this site called Nilpena Ediacara National Park in the outback of Australia. There are kangaroos, all sorts of fun wildlife.

[The sun sits low on the horizon, lighting an excavated fossil bed. Evans and two colleagues work in a similar site.]

[FLIES BUZZ]

EVANS: But there are also these layers of sediment that preserve Ediacaran fossils. We systematically excavate them. 

[Close-up of fossil bed, made up of broken chunks pieced together. Fossil organisms are tagged and labelled with different colors of tape.]

EVANS: We puzzle piece them back together, and we create these large areas that are literally recreations of the Ediacaran seafloor.

[Evans speaks to camera in his office.]

EVANS: Fossils of the Ediacara biota are what we call external molds. 

[Illustration of an Ediacaran organism on the sea floor. It has a shield-shaped head, and elongated, segmented body that tapers toward the end.]

EVANS: What happens is we have a soft-bodied thing that's sitting on the seafloor. 

[Animated sand layers on top of the organism. Arrows indicated the sediment’s motion. That image dissolves into a transparent view of solidified rock over the organism.]

EVANS: It gets buried by sand and then that sand that buries it becomes rock very quickly. 

[The illustration dissolves into a monotone version of the organism, with a mirrored impression of it in rock opening out like a book.] 

EVANS: Then when the soft-bodied organism decays away what we see is this impression of what the top of the organism would have looked like.

[Evans speaks to camera in his office.]

EVANS: To tell whether an extinct animal could move, we can use lots of different clues. 

[Close-up of a flat, fan-like fossil organism. Text identifies it as “Dickinsonia”.]

EVANS: One of my favorites is Dickinsonia, which is basically this flat pancake that sat on the sea floor. 

[An animated version of a living Dickinsonia on the Ediacaran seafloor. Footage of actual fossil bed with a fan-shaped Dickinsonia fossil impression.]

EVANS: We know it could move. And we know that because it leaves behind traces. 

[Animation of living Dickinsonia with several Dickinsonia-shaped patches appearing behind the organism.]

EVANS: So, Dickinsonia was probably absorbing nutrients through its bottom surface, actually eating that organic mat, creating a Dickinsonia-shaped hole in the seafloor. 

[Evans speaks in his office. A Dicksonia fossil in the pieced-together fossil bed of Nilpena Ediacara National Park. 

EVANS: And we often find sets of those Dickinsonia-shaped holes that end in a Dickinsonia body fossil.

[Close-up of a fossil organism with a shield-shaped head and a tapered, segmented body. Text labels it as “Spriggina”. Various other Spriggina fossils.]

EVANS: Spriggina is also one of these Ediacaran organisms, but Spriggina didn't leave behind something to tell us that it moved. What it did leave behind are different orientations of its body. 

[Various Spriggina fossils with their body forms varying in curvature and orientation. Evans speaks to camera in his office.]

EVANS: Most animals have a very predictable shape, right? 

[A jellyfish swims in the ocean. An earthworm crawls through dirt. Evans speaks to camera in his office.]

EVANS: You know the shape of a jellyfish, you know the shape of a worm. So when you study enough fossils of a particular type of animal, you can understand what the main shape should be, and you can see variations on it that can tell you things like if and how it moved. 

[Anemones sway in the ocean. Their tentacles move as a group as the current changes their orientation.] 

EVANS: If your environment causes your shape to change, then that should be in a predictable way…

[Three fossil organisms labelled as “Aspidella” are oriented in the same way, as indicated by animated arrows.]

EVANS: …and everything in the same environment should change in the same way. 

[On a single fossil slab, three Spriggina fossils of various sizes are oriented in different ways.]

EVANS: But on these beds with lots of different Spriggina, some are perfectly straight, some are totally curved, and the orientation between them doesn't match at all. 

[An animated Spriggina wiggles its body along the sea floor.]

EVANS: And so that really looks like an organism that can move in any different direction it wants, rather than something that's being influenced by some external factor.

[Evans works on a laptop in his office, surrounded by fossil specimens. He manipulates 3D scans of Spriggina fossils.]

EVANS: We examined shape variation in a little over 100 of them. One of the ways that they’re most commonly deformed is that they're bent. 

[Various Spriggina fossils are shown, some bending to the left, and some to the right.]

EVANS: And they can do that in both directions. 

[The animated Spriggina moves by wiggling sinuously.]

EVANS: So that gives you this idea already of them wriggling. 

[Evans talks to camera in his office.]

EVANS: We also see that some Spriggina look like they're missing parts of their side. 

[On photos of fossil Spriggina, arrows indicate sections of their body that are “missing” from a regular silhouette.]

EVANS: Like something that is actually lifting up parts of its body. 

[An illustration of Spriggina in life with a portion of its flexible, segmented body uplifted from the seafloor. Footage of a living marine flatworm as it flows over the ocean floor, lifting up parts of its side in a wave in order to propel itself forward.]

EVANS: Things that move around on the seafloor sometimes spread waves along their outer margins as they move along. 

[Illustration of a living Spriggina with its side lifted dissolves into a version that also shows what its fossil impression would look like—a similar shape to the photos of fossils with missing sections shown earlier.]

EVANS: And so we think that's what Spriggina is doing.

[Photo of a Spriggina fossil with an arrow indicating a “missing” head.]

EVANS: Very rarely, some Spriggina look like they are missing their head totally. 

[Illustration of living Spriggina with its head lifted off the sea floor. Animation of swimming Spriggina, lifting its head off the ground and swimming through the water column.]

EVANS: And we think that's actually because the Spriggina is lifting its head off of the seafloor, which may tell us that it could come up and swim through the water. 

[Evans working at his computer, examining 3D scans of Spriggina fossils.] 

EVANS: When we started looking at all the different examples of Spriggina that were bent one direction over the other…

[Split screen shows, on the left, a Spriggina fossil bending to the left and on the right, a Spriggina fossil bending to the right. Text reads “2:1”.]

EVANS: …about twice as many were bent to the left as were bent to the right.  

[Evans speaks to camera in his office.]

EVANS: Then I started looking at evidence for things having handedness today. 

[Various animals—a parrot eating a piece of fruit held in its left foot, a honey bee flies in slow motion towards the right, an octopus unfurls one of its arms to its right.] 

EVANS: And what we know is that it's not just humans that have a preference for one hand over the other. There are lots of different animals // that turn or move in one direction over the other. 

[Evans speaks to camera in his office.

EVANS: And it turns out that a lot of times that's about this 2 to 1 ratio.

[Close up of a Spriggina fossil with an extreme curve to the left.]

EVANS: Although it is left in the fossils…

[Illustration of the Spriggina organism and its fossil impression opening like pages on either side of a book.]

EVANS: …because those fossils are impressions, they’re actually mirror images. 

[Evans speaks to camera in his office.]

EVANS: So, we know that Spriggina was actually right-handed in life. It preferred to bend to the right.

[Evans examines Spriggina fossil in his office. It is in a reddish rock and small enough to hold the palm of his hand.]

EVANS: This is one of the first things to have left-right symmetry ever in the history of Earth, and immediately it already has this bias. 

[A person writes on a pad of paper, using their left hand.]

EVANS: And so, what we may be learning is that handedness is just a consequence of once you have a left and a right side, you have a preference for one over the other.

[A small primate chews on a piece of bamboo, using its right hand.]

EVANS: A lot of the animals that we see this sort of handedness in have lots of complex sensory abilities. 

[Evans speaks to camera in his office.]

EVANS: And so, this may be telling us that the nervous system of Spriggina was more complex and more similar to those of animals that we know today.

[Animation of the Ediacaran sea floor with frond-like organisms branching up from the seafloor.]

EVANS: One of the other really fun things about studying the Ediacaran is that we are sort of looking at a different planet. 

[Evans speaks to camera in his office.]

EVANS: And so we've actually been funded by NASA to do this work, 

[Animation of Europa and Jupiter as a satellite flies by.]

EVANS: …because if we want to look for complex life on other planets…

[Animation of Ediacaran seafloor where flower-like organisms wave on the sea floor.]

EVANS: …we have to understand the conditions where complex life first evolved on Earth 550 million years ago.

[Production credits]