February 4, 2019

E14 – Footprints from an Ancient World

Posted by Shane Hanlon

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.

Nanci:   Hey Shane

Shane:  Hello

Nanci:   Hi hi

Shane:  Hi hi

Nanci:   Um, so today I wanted to ask you a question.

Shane:  Oh Boy

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

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

Nanci:   Oh that’s pretty amazing

Shane:  Yeah, yeah

Nanci:   That’s a pretty good one.

Shane:  What about you?

Nanci:   I don’t know, I mean I don’t feel like, I mean I probably do have memories. Things seem hazy before like third grade, but you know. But in terms of embarrassing man, we were like cleaning out some photos at my mom’s house — wow, wow. That middle school, early high school, is not good, not good. I was like four foot eight until I was like 17 years old I think. And like, you know, I’m normal height now, but glasses, braces, big hair, the whole deal.

Shane:  Nice, nice, I like it.

Nanci:   Anyway, um the reason we’re talking about memories today are because we’re going to talk a little bit about fossils

Shane:  Ohhh

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

Shane:  So very deep.

Nanci:   Very deep.


**Music and Intro**

[music starts]

Shane:  Welcome to the American Geophysical Union’s podcast about the scientists and 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:   I’m Nanci Bompey.

Shane:  And this is Third Pod from the Sun.

[music ends]

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

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

Shane:  Sure

Nanci:   Definitely have one of those

And when we were in Israel when I was I don’t know, twelve, we went on this archaeological dig, that my mom was convinced that they just throw things in like the dirt so like tourists can find them.

Shane:  Nice, nice

Nanci:   But no fossils

Shane:  Well okay yeah

Nanci:   What about you?

Shane:  No no not really but as a child I drew sediment stuff, but we talked with an expert in the field, so actually we’re going to bring our producer, Liza Lester, hi Liza

Liza:       Hi guys

Shane:  So what’s, wha’d you bring us today?

Liza:       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:  Like, like fish. Ichnol- ichthyology

Liza:       Not fish!

Shane:  Not fish.

Liza:       No, no ichnology is the study of trace fossils which, we’re more familiar with body fossils, which are the shape of the animal itself, maybe it has a skeleton, or the imprint of it’s skin or it’s armor, and these are more the traces that the animals left behind as it, 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:  Oh, memories

Nanci:   That’s so cool

Shane:  Yeah

Nanci:   Ancient footprints

Liza:       Ancient footprints and in fact ikhnos is a Greek word that means “footprint.” So: ichnology.

Shane:  Oh lovely. So what’s her speciality?

Liza:       Renata specializes in the Ediacaran Period which was a time when animals were first becoming- well 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 about 100 million years about 600 million years ago, and then suddenly in about 542 million years ago they just vanished from the fossil record, and you see this explosion of diversification of animals in the Cambrian period, which people may be more familiar with. So she studies these trace fossils from that time.

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


Renata Netto:                                                    Well, they don’t look like fossils. You don’t have the body fossil, you have only the trace, the burrow, the trail, the track or the track way, the nest. Some insects make interactions with leaves, and so these interactions can be preserved and these leaves are preserved fossils. Even it’s rare but – oh, poop, it’s very common. What is rare is, for example, some sort of biogenic structures like spider’s web, pieces of egg shells.  


Renata Netto:                                                    For example, imagine you go to the beach and so you see a lot of small hollows on the beach, you’re walking, and you see there’s a small hollow, sometimes with bubbles. Beneath the substrate, you have a burrow and you have a clam inside this burrow. 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 to 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 the substances react with the physical media, and so they start to make a kind of small glue. A kind of bioglue and this glue promotes a kind of pre-sedimentation 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. Well, you have to see them, to describe them, to photograph them, to see the details. Most of times, you cannot take them and take them to your lab. 

Nanci Bompey:                                                 The side of a cliff.

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

Nanci Bompey:                                                 Uh-huh (affirmative).

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. This stuff is pretty, pretty nice and the rocks where they are preserved, people use these rocks as slabs for pavement. So these rocks are explored in quarries, and when they open those slabs, plenty of trace fossils. So these ones you can collect because they are taken as slabs. 


Liza Lester:                                                         Did you say they were quarrying it for pavement or could you see some of these fossils in a countertop or something like that? What kind of … where would they be?

Renata Netto:                                                    In the case of these quarries that I mentioned, yes, they are used mostly for pavement on the streets. They also use the slabs to construct walls and pig farms to separate the pigs, you see,

                                                                                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 the trace fossils on a 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 scientifically crazy. They are helpful yeah. But the quarries, the pigs they live with trace fossils, beautiful ones, beside them.

Nanci Bompey:                                                 That’s crazy.


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

Shane: like in the rock, or in the stone? Yeah, yeah

Nanci: yeah!

Shane: 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 that stuff in rocks?

Liza: well, besides dead stuff in rocks being really cool

Shane: sure

Liza: 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. They can really learn a lot from a hole in the ground that an animal has dug. And this can also tell us about how organisms responded to major climate changes. You know, 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 dissolution and reformation of these supercontinents, and the ocean changed its chemistry, so you know we’re facing some big changes now, maybe this can tell us little about what happened in the past.

Shane: Fascinating

Nanci: See Shane, you should care

Shane: We’ll see


Renata Netto:                                                    A lot of interactions that are preserved. Even that the interactions made by bacteria, microbial mats on the substrates, they can leave a sort of sedimentary structures. Very particular sedimentary structures that reveal that they were present in the ancient substrate. If you have a chance to see the group or try to make an approach about the group of bacteria that were there, you can make very valuable interpretations and which conditions that substrates were exposed or I don’t know the word in English but the chemical and physical conditions of their 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. Even with more modern stuff, around 120,000 years old.

Liza Lester:                                                         Only 120,000 years old.

Nanci Bompey:                                                 [inaudible ].


Liza Lester:                                         What did the world look like 600 million years ago? What was it like on Earth? Was it volcanoes, was there oxygen in the air? Was the sky blue? What was it like?

Renata Netto:                                                    Apparently, 6 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, and this continent was really smaller than the Pangea, for example, that was the biggest continent that we’ve had in the history of Earth.

                                                                                At this moment, 6 million years ago, more or less, we’re talking about, we had a very, very huge glaciation in the world.

                                                                                It’s known as the snowball Earth. The snowball Earth, it’s because apparently the ice from the poles extended almost all to the equator. Only the equator zone were free of ice, at that moment.

                                                                                So when this glacial period finished, we had the explosion of pluricellular of life in Earth, not the Cambrian explosion but the pre-Cambrian explosion. It’s now like the Ediacaran fauna or the Ediacaran which is the most correct terminology.


Liza Lester:                                                         Then the Cambrian is when the trilobites and things like that happened.

Renata Netto:                                                    Yes, yes, in the Cambrian trilobites came to life and also many other invertebrates that are relatives from the invertebrates that we 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, what are the animals … were they animals, were they plants? What are they?

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



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

Nanci:    that was really bad

Shane:   speaks the woman who gets up at open mic night at Fall Meeting every year and just reads terrible science jokes

Nanci:    terrible jokes

Shane:   but yeah, this is neat stuff.

Nanci:    it’s totally cool. So where does she go, other than finding these things in the pavement outside her home, where does she go to study all this?

Liza:       She’s really been all over the world. She’s done a lot of work at Ushuaia which is at the very tip of South America, she’s been to Utah, Namibia, Denmark, studied ancient tsunamis in Japan — these fossils are all around the world.

Nanci:   so cool



Renata Netto:                                                    Also in Portugal in the Nosara beach where we have these big waves, you see that surfers go to, the biggest waves in the world. So just beside the beach, there is a very, very nice outgrowth, plenty of beautiful trace fossils. Also in the Bahamas, many places, Cuba.


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

Renata Netto:                                                    It depends on the place. That place is the field trips is very like tourist, you see, like in Bahamas, it’s a very nice place, you have, we used to stay in a research center that give you the facilities, transportation, food. So you go to the beach, you work in sandals. Sometimes maybe in swimming, you swim in swimming wear. Sometimes you have to dive which is great also. You have this warm climate so the water is good so it’s 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, the unique woman and they kept some water for me to wash myself which was great, but the smell from the guys on the second day was not so good in the truck but it’s part of the work. You learn to support it and you take it like, “Okay, that’s fine.” No worries.


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



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


Liza Lester:                                                         Are the places you’re looking at, are they fragile? Are they sturdy, you can go back, year after year and see them again, or do they wash away on the cliffs?

Renata Netto:                                                    Some places are very fragile. There is a place in Argentina I don’t use to work in this place, but it’s a very famous case. In this place, we have a foot prints and tracks from animals from the big mammals from the Pleistocene era, 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 tides and the waves are eroding, weathering the substrates, and also people that visit the place because they don’t know the value of that structure. So they used to go and walk and 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, and so they used to cover outcrops and sometimes you go and work in a place and the next year you need to go back there to check some information and you don’t have more the place as it was when you started 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 a commercial intention 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 ever found 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, we call them callianassid shrimps and they dig burrows. Big burrows and big burrows are very extensive and they used to burrow in the sub-tidal area and inter-tidal area on beaches. The burrows are very extensive because they lived whole life into the burrow. So they dig, dig, dig and they are really beautiful burrows because these guys are very nice ecological engineerings. They re-work 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 their burrow and to keep the flux of water inside the gallery. They live in there.

                                                                                They then make a place 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 and Pleistocene deposits 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 of the big ones, but they’re really small. Imagine like a toothpick.

Nanci Bompey:                                                 That thin?

Renata Netto:                                                    Yeah that thin. Really, really smart, nice to see. Unless the magnifying glass, the neat arrangements of pallets that they have and they throw us a kind of challenge because we know that the larvae of these animals are mostly planktonic. They live their whole juvenile life on the plankton. So how they do burrow, when they start to make that burrow, so it was a kind of challenging to learn and to know when they started to make the burrow and how. It’s very, very interesting because the phase before they become an adult, they need to go to the benthos


Renata Netto:                                                    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 the burrows made. So you find them laying down the big ones, like the baby burrows and the mom burrows, it’s really exciting.

Renata Netto:                                                    I used to say to my students that it’s quite impossible to be a geologist, without think that the life was present in the history of the Earth since the beginning. Since we have Earth’s crust, we have life in the way that we know life. It’s quite impossible to dissociate the life history and the Earth’s history. Of course, you can study a mineral or seismology or volcanology or whatever without think about the life on 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. 


Renata Netto:                                                   For research purpose, we focus on this, on this, on that. But when you see the Earth as a kind of unique structure, our home, it’s impossible to dissociate life on Earth’s history.


Nanci:   See Shane, it really is all about life

Shane:  I guess so

Nanci:   Geology and life

Shane:  Yeah, that’s true

Nanci:    Geology is life!

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

Nanci:   Like that, like in regards to fossils?

Shane:   I have no idea, yeah,

Nanci:    Oh

Shane:   This is why I’m a biologist

Nanci:    Sweet. I like that movie

Shane:   Alright anyways, that’s all from Third Pod from the Sun