E14 – Footprints from an Ancient World

Renata analyzes a huge, Pleistocene epoch burrow system of ecosystem engineering callianassid shrimps on the Rio Grande do Sul State Coastal Plain, in the south of Brazil. Renata infers the callianassid species Sergio mirim made these burrows. Credit: Zain Belaústegui

Renata Netto spends a lot of time on beaches. The Brazilian scientist is an ichnologist, a specialist in the traces of ancient animal behaviors preserved in fossilized footprints, trackways, burrows, nests and other impressions. These “trace fossils” do not hold the animal itself, but a kind of geological memory of its presence on Earth, 60,000 or 600,000 or 600 million years ago. Many trace fossils are entombed in cliffs; the fragile fossils cannot come to the lab, so researchers must study them in the field.

In this episode, Renata recounts sharing beaches with surfers and bargaining for paving stones full of trace fossils. She describes the lost world of Earth’s first large multicellular life, the enigmatic Ediacaran Biota, which lived 635–542 million years ago, and the beauty of a shrimp burrow.

This episode was produced by Liza Lester and mixed by Kayla Surrey. 


Episode Transcript

Nanci Bompey:                 Hey, Shane.

Shane Hanlon:                   Hello.

Nanci Bompey:                 Hi. Hi.

Shane Hanlon:                   Hi. Hi.

Nanci Bompey:                 So, today I wanted to ask you a question.

Shane Hanlon:                   Oh boy.

Nanci Bompey:                 Yeah. What are some of your earliest memories, most embarrassing memories kind of thing?

Shane Hanlon:                   As for, so as for embarrassing, most of my embarrassing stuff I think has happened later in life because I care more. So my earlier stuff though is, I have vivid memories of my brother, one of my brothers specifically, at Disney World. We’re at Disney World, and I’m three years old, and I distinctly remember him dragging me up to see, it was Mickey and Minnie Mouse I think. And I am terrified. I am just so terrified. I remember crying. My mother’s yelling at him. He’s just laughing gleefully. Yeah, so that’s-

Nanci Bompey:                 Oh that’s pretty amazing.

Shane Hanlon:                   Yeah. Yeah.

Nanci Bompey:                 That’s a pretty good one.

Shane Hanlon:                   What about you?

Nanci Bompey:                 I don’t know. I don’t feel like, I mean I probably do have memories. Things seem hazy before third grade. But in terms of embarrassing man, we were cleaning out some photos at my mom’s house, wow.

Shane Hanlon:                   Yeah?

Nanci Bompey:                 Wow. That middle school, early high school, is not good.

Shane Hanlon:                   Oh it’s, no.

Nanci Bompey:                 Not good. I was like four foot eight until I was 17 years old I think.

Shane Hanlon:                   Wow.

Nanci Bompey:                 I’m normal height now … but glasses, braces, big hair, the whole deal.

Shane Hanlon:                   Nice.

Nanci Bompey:                 Yeah.

Shane Hanlon:                   Nice. I like it.

Nanci Bompey:                 Anyway. The reason we’re talking about memories today are because we’re gonna talk a little bit about fossils.

Shane Hanlon:                   Oh.

Nanci Bompey:                 So I know memories aren’t fossils, but they’re kind of like emotional fossils that we leave behind perhaps?

Shane Hanlon:                   So very deep.

Nanci Bompey:                 Very deep.

Shane Hanlon:                   Welcome to the American Geophysical Union’s podcast about the scientists and the methods behind the science. These are the stories you won’t read in the manuscript or hear in a lecture. I’m Shane Hanlon.

Nanci Bompey:                 And I’m Nanci Bompey.

Shane Hanlon:                   And this is Third Pod from The Sun.

                                                So Nanci, did you ever collect fossils or anything growing up?

Nanci Bompey:                 No, but I … I don’t know why this reminds me, some random trip that I took to Myrtle Beach, and you can get shark’s teeth on a necklace.

Shane Hanlon:                   Sure.

Nanci Bompey:                 Definitely have one of those. And when we were in Israel when I was, I don’t know, 12, we went on this archeologic dig that my mom was convinced that they just throw things in the dirt so tourists can find them.

Shane Hanlon:                   Nice. Nice.

Nanci Bompey:                 But no fossils.

Shane Hanlon:                   Okay. Yeah.

Nanci Bompey:                 What about you?

Shane Hanlon:                   No, no, not really. But I, as a child, interested in them and stuff. But we talked with an expert in the field. So actually we’re gonna bring in our producer, Liza Lester. Hi Liza.

Liza Lester:                         Hi, guys.

Shane Hanlon:                   So what’d you bring us today?

Liza Lester:                         I talked with Renata Netto. She’s a scientist at Unisinos University, which is a big Jesuit university in the south of Brazil. And she is an ichnologist.

Shane Hanlon:                   Like fish? ichthyology?

Liza Lester:                         Not fish.

Shane Hanlon:                   Not fish?

Liza Lester:                         No, no. ichnology is the study of trace fossils. We’re more familiar with body fossils, which are the shape of the animal itself. Maybe it has the skeleton or the imprint of its skin or its armor. These are more the traces that the animals left behind as it slithered or walked or crawled, or dug burrows or interacted with other animals. So they’re kind of memories that have been preserved for us from hundreds of millions of years ago.

Shane Hanlon:                   Memories. Yeah.

Nanci Bompey:                 That’s so cool. Ancient footprints.

Liza Lester:                         Ancient footprints. And, in fact, ichnos is a Greek word that means “footprint,” so ichnology.

Shane Hanlon:                   Oh. Lovely. So what’s her specialty?

Liza Lester:                         Renata’s specializes in the Ediacaran period, which was a time when animals first appeared I guess you could say. The first large multicellular life was appearing in the fossil record. And it was this very sort of alien, mysterious time. They don’t look anything like the animals that are alive now. But they flourished for almost a hundred million years, about 600 million years ago. And then suddenly, about 542 million years ago, they just vanished from the fossil record. And you see this explosion of diversification of animals that, in the Cambrian period which people may be more familiar with. So she studies these trace fossils from that time.

Shane Hanlon:                   Very cool. Well, let’s get to it.

Renata Netto:                    Well, they don’t look like fossils. You don’t have the body fossil, you have only the trace fossil. The burrow, the trail, the track or trackway, the nest. Some insects make interactions with leaves and so these interactions can be reserved when these leaves are preserved as fossils. Even, it’s rare, but … Oh, poop, it’s very common. And what is rare is, for example, some sort of biogenic structures like a spider’s web, pieces of eggshells.

                                                For example, imagine you go to the beach. You see a lot of small hollows on the beach. You are walking and you see the small hollows, sometimes with bubbles. Beneath the substrate you have a burrow, and you have a clam inside this burrow. And the clam is living in this burrow. They used to live in the burrow for protection, or to get the best position to grab their food, or oxygen when the tides come and the currents bring some new fresh water. So the be in these burrows, for them, it’s a style of life. So when they leave these burrows, these burrows can collapse, be destroyed, or they can be preserved.

                                                They are normally preserved, because most animals interact with the substrate and the surround of their body. They exchange mucus and other biological substances, so these substances react with the physical media. So they start to make a kind of small glue, a kind of bio glue, and this glue promotes a kind of pre cementation. And when this substrate became a rock, these structures tend to be preserved.

                                                So when you go to the field trip you see a lot of rocks, and you see these structures on cliffs or something like this. You have to see them to describe them, to photograph them, to see the details. Most of times you cannot take them, and take it to your lab.

Liza Lester:                         Cause it’s the side of the cliff?

Renata Netto:                    Because they’re inside the cliff, and because you cannot bring the cliff. And maybe when you try to get them out, you destroy them.

Liza Lester:                         Mm.

Renata Netto:                    So ichnologists spend a lot of time in field trips because their object of work, they need to work them in field trips. So there are some samples that you can collect. For example, I used to work with very nice stuff from an ancient glaciation, the Gondwana glaciation that was around 300 million years ago. And this stuff’s pretty pretty nice. The rocks where they are preserved, people used these rocks as slabs for pavement. So these rocks are explored in quarries, and when they open the slabs there’re plenty of trace fossils. So these ones you can collect because they are taking the slabs.

Liza Lester:                         Did you say they’re quarrying it for pavement, or could you see some of these fossils in a countertop or something like that? What are they making-

Renata Netto:                    Well, in the case of these quarries that I mentioned, yes they are used mostly for pavement on the streets.

Liza Lester:                         Okay.

Renata Netto:                    But they also use these slabs to construct walls in pig farms, to separate the pigs. There are plenty of trace fossils, beautiful ones, some that sometimes you see only on the sidewalk. Yes, I had my moments that I saw a trace fossil in the sidewalk, and I said “Oh my God. I don’t have this specimen in my collection yet.” So I tried to negotiate with people to replace, they give me that slab and I replace for a new one. People usually understand, and you’re a scientist, crazy, and they are helpful. Yeah. But the quarries, yes. The pigs come, they live with trace fossils, beautiful ones, beside them.

Nanci Bompey:                 That’s crazy.

Nanci Bompey:                 That is so cool. Have you ever done that, walked by a building and seen impressions of things in there? It’s so cool.

Shane Hanlon:                   Like in the rock, or in the stones? Yeah.

Nanci Bompey:                 Yeah. Yeah.

Shane Hanlon:                   Definitely.

Nanci Bompey:                 That is so cool.

Shane Hanlon:                   Yeah, I do have to say, though, my science background is studying living things. It’s what got me interested in science, why I care about science. So why should we, and I mean the royal “we”, all of us, care about dead stuff and rocks?

Liza Lester:                         Well, besides dead stuff and rocks being really cool.

Shane Hanlon:                   Sure.

Liza Lester:                         These traces can tell us a lot about what life was like 600 million years ago, how these interactions happened between organisms. What they were eating. Was there oxygen in the atmosphere? What was the chemistry of the ocean? It’s really, they can really learn a lot from a whole in the ground that an animal has dug. And this can also tell us about how organisms responded to major climate changes. The Ediacaran was a time of huge geological change. There was the end of this big ice age. There was an asteroid impact. There was the disillusion and reformation of these super continents, and the ocean changed its chemistry. We’re facing some big changes now. Maybe this can tell us a little bit about what happened in the past.

Nanci Bompey:                 Fascinating. See, Shane. You should care.

Shane Hanlon:                   We’ll see.

Renata Netto:                    A lot of interactions that are preserved, and even those interactions made by bacteria, microbial mats on the substrates, they can leave a sort of sedimentary structures, very particular sedimentary structures that reveals that they were present in the ancient substrates. If you have a chance to see the group, or to try to make an approach about the group of bacteria where they are, you can make very valuable interpretations in which conditions that substrates were exposed, or … I don’t know the word in English, but the chemical and physical conditions of the earth’s substrates when the microbial mats were there.

Liza Lester:                         When the bacteria were there, what the conditions were around them?

Renata Netto:                    Yeah.

Liza Lester:                         How old are we talking about here?

Renata Netto:                    Well, I usually work with stuff that has around 600 million years old or 300 million years old. And even with more modern stuff, around 120,000 years old.

Liza Lester:                         Only 120,000. What did the world look like 600 million years ago? What was it like on earth? Was it volcanoes? Was it oxygen in the air? Was the sky blue? What was it like?

Renata Netto:                    No. Apparently 600 million years ago the earth was a little bit more stable than in the beginning. But we don’t have the same extension of continents that we have now. So we had unique continent that was called Rodinia at that time. This continent was really smaller than the Pangaea, for example, that was the biggest continent that we had in the history of earth. At this moment, 600 million years ago more or less, we are talking about, we had a very very huge glaciation in the world. It’s known as the Snowball Wars, and the Snowball Wars it’s because apparently the ice from the poles extended almost all to the equator. So only the equator zone were free of ice at that moment. So when this glacial period finished we had the explosion of pluricellular in Earth. Not the Cambrian explosion, but the Pre-Cambrian explosion. It’s now the Ediacaran fauna, or Ediacaran biota, which is the most correct terminology.

Liza Lester:                         And then the Cambrian is when the trilobites and things like that happened?

Renata Netto:                    Yes.

Liza Lester:                         Okay.

Renata Netto:                    Yes. In the Cambrian, trilobites come to life, and also many other invertebrates that are relatives from the invertebrates that you have now. So almost all the groups, the modern groups of invertebrates that we have now in our biota, modern biota, they have relatives in the Cambrian.

Liza Lester:                         What do these fossils look like from the Ediacaran time? Are they animals, are they plants, what are they?

Renata Netto:                    It’s interesting. Some looks like plants, but they were not plant. There were some very crazy animals with crazy structure.

Shane Hanlon:                   Alright, so, I take back my previous dig. Get it?

Nanci Bompey:                 That was really bad.

Shane Hanlon:                   Speaks the woman who gets up at open mic night at fall meeting every year and just reads terrible science jokes.

Nanci Bompey:                 I tell all terrible jokes.

Shane Hanlon:                   But yeah, this is neat stuff.

Nanci Bompey:                 No, it’s totally cool. So where does she go, I mean other than finding these things in the pavement outside her home, where does she actually go to study all this?

Liza Lester:                         She’s really been all over the world. She’s done a lot of work at Ushuaia, which is at the very tip, southern end of South America. She’s been to Utah. She’s been to Namibia in Southern Africa. She’s been to Denmark. Studied ancient tsunamis in Japan. Just, these fossils are all around the world.

Nanci Bompey:                 So cool.

Renata Netto:                    Also in Portugal, in Nazare Beach, where we have these big waves. You see the surfers go to the biggest waves in the world. Just beside the beach there’s a very very nice outcrop, plenty of beautiful trace fossils. Also in Bahamas, many places, Cuba.

Nanci Bompey:                 One question I had… you said, obviously you can’t take this home. You have to go out there and do all your work in the field. So what is a typical field trip like, your day, and how do you-

Renata Netto:                    Well it depends on the place.

Nanci Bompey:                 Yeah.

Renata Netto:                    There are places that the field trip is very touristic, like in Bahamas, it’s a very nice place. You have, we used to stay in the research center. They give you the facilities, transportation, food. So you go to the beach, you work in sandals, and sometimes maybe in swimming wear. And sometimes you have to dive, which is great also. You have this warm climate, the water is good, so it’s a really really amazing place to work. And very easy to work.

                                                For example, when I was working in Namibia, in the south of Namibia, it was a little bit hard because it was hot. It’s a kind of desert climate, so very hot during the day, cold during the night. The source of water that we had was limited, so we cannot waste water. So the guys cannot wash themselves for two days. I was the only, I was the unique woman and they kept some water for me to wash myself which was great. But the smell of the guys on the second day was not so good in the truck. But it’s part of the work. And you learn to support it, and you take it like “Okay, that’s fun. No worries.”

Shane Hanlon:                   I’m just picturing this strange person on the beach, maybe in field clothes or whatever, digging around, pulling things out of the ground. Does anyone ever ask what she’s doing when she’s on the beach in these gorgeous tourist places, in the Bahamas? Are surfers, or beach goers, or whomever, wondering why she’s there looking through a magnifying glass at this random spot on the beach or in the cliff or something?

Renata Netto:                    Yes. Sometimes, yes. They come, they approach, and they ask what we are doing. We explain, and show them, and they became fascinated because they went to that beach for years and they never never never realized that there was some sort of thing preserved there. So yes, it’s pretty common when you go to these places that are more populated that they ask you what you are doing.

Liza Lester:                         The places you’re looking at, are they fragile? Or are they sturdy, you can go back year after year and see them again? Or is it washing away on the cliffs?

Renata Netto:                    Well, some places are very fragile. There is a place in Argentina, I don’t used to work in this place, but it’s a very famous caves. In this place we have a footprint, and tracks from animals, from the big mammals, from the place to see area. But also human footprints, they are preserved together in the same substrate. These deposits are very close to the beach, and the tide is high. So the tide and the waves are eroding, are weathering the substrates. And also, people that visit the place, because they don’t know the value of that structure so they use to go and walk. It’s a very fragile rock, it’s a carbonate rock, so it’s complicated to be preserved. They tried, there are groups that tried to preserve the place, but sometimes they have big problems.

                                                Where I work, that is in the South of Brazil mostly, we have a problem with the humid climate and the weathering. So it’s pretty … Vegetation grows up very fast, so they used to cover outcrops and sometimes you go and work in the place, and the next year you have to go back there to check some information and you don’t have more the place as it was when we started to work. It’s a big problem. It’s a big challenge.

                                                The other problem are the quarries. Because the quarries are good because they show you the biogenic sedimentary structures due to exploration, but they have commercial intentions so the material, if you are not fast enough to describe all the material in these quarries we can lose a lot of information. Yes, we have problems with our original data.

Liza Lester:                         What’s the most exciting thing that you’ve ever, found when you were in the field, your favorite?

Renata Netto:                    My favorite thing, the most exciting thing that I’ve found was … you see, there are some kinds of shrimps… and they do big burrows. Big, big burrows. The burrows are very extensive, and they used to burrow in the sub tidal area and intertidal area on beaches. And the burrows are very extensive because they live their whole life in the burrow. So they dig, dig, dig, dig, dig, and they are really beautiful burrows because these guys are very nice ecological engineers. They rework the sediment. They have to put the sediment that they excavate in some place, so they use it as a kind of bricks to support the burrow and to keep the flukes the off water inside the gallery. And they live inside there. They make places where they can turn around and go back, and to visit another part of the gallery. They are very smart guys. The most exciting thing was studying some of these structures in places from Brazil.

                                                I found very tiny burrows. Very, very tiny burrows. Baby burrows. Just really really exciting because the baby burrows had almost the same structure as the big ones, but they are really small. Imagine like, toothpick. Yeah, that thing. Really, really, smart. Nice to see on glass, the magnification glass, the neat arrangement of pallets that they have. And it was kind of challenging because we know that the larvae of these animals are mostly planktonic. They live their whole juvenile life on the plankton, and so how they do burrow, and when they start to make that burrow. So it was kind of challenging to learn, and to know when they start to make the burrow, and how. And it’s very very interesting because the phase before they become an adult, they need to go to the benches. And when they reach the bottom, the bottom needs to be composed by a sort of sediment that is sandy size. If the bottom is muddy size, the animal will not survive because he will not be able to excavate and to keep the burrow open, and he needs to do it. So it was really nice work, and really exciting experience to understand what these burrows mean. So you find them laying down, the big ones, like the baby burrows and the mom burrows. It’s really exciting.

                                                I used to say to my students that it’s quite impossible to be a geologist without thinking that the life was present in the history of the earth since the beginning. Since we have crust, earth’s crust, we have life in the way that we know life. And it’s quite impossible to disassociate the life history and the earth’s history. Of course you can study a mineral or seismology or volcanology or whatever, without thinking about life on the earth. But if you really want to be a good geologist you have to consider that they were responsible for many, many transformations in the world. Research people, we focus on this and that and that. But when you see the earth as a kind of unique structure, our home, it’s impossible to disassociate life and earth’s history.

Nanci Bompey:                 See, Shane. It really is all about life.

Shane Hanlon:                   I guess so.

Nanci Bompey:                 Geology and life.

Shane Hanlon:                   Yeah, that’s true.

Nanci Bompey:                 Geology is life!

Shane Hanlon:                   Geology is life, yeah. I’m also just sitting here, just I’m amazed that we haven’t talked about, like brought up a Jurassic Park reference at all. I know that’s a bastardization, but-

Nanci Bompey:                 Like, in regards to fossils?

Shane Hanlon:                   I have no idea, yeah.

Nanci Bompey:                 Oh.

Shane Hanlon:                   This is why I’m a biologist.

Nanci Bompey:                 Sweet. I like that movie.

Shane Hanlon:                   Alright, anyways. That’s all from Third Pod From The Sun.

Nanci Bompey:                 Thanks to Liza for bringing us this story. And for Renata, for sharing her work with us.

Shane Hanlon:                   This podcast is also produced with help from Josh Speiser, Olivia Ambrogio, Laura Lipuma, and Katie Broendel. And thanks to Kayla Surrey for producing this episode.

Nanci Bompey:                 We would love to hear your thoughts.

Shane Hanlon:                   Love.

Nanci Bompey:                 Love to hear your thoughts on our podcast. Please please please rate, review us on iTunes, listen to us wherever you get your podcasts, and of course always at thirdpodfromthesun.com.

Shane Hanlon:                   Alright, thanks all. And we’ll see you next time.

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