Natasha S. Vitek

Topernawi, a new Oligocene site on the western side of Lake Turkana, Kenya

Topernawi, a new site on the western side of Lake Turkana, Kenya, preserves vertebrate, plant, and ichnofossil remains from a period in time that is otherwise unknown in the African paleontological record. Here, recent discoveries, including their effect on our understanding of African faunal communities and evolution of major clades, will be discussed.

FULL TRANSCRIPT 

So, this slide makes it look like it's a single authored talk, and I'd like to correct that immediately. Acknowledging everyone named on this slide should be considered a co-author on this presentation contributing data, contributing ideas, contributing perspective. I'd like to particularly acknowledge Dr. Patricia Princehouse who leads the Topernawi Research Project, who heads it up along with Emmanuel Aoron. And you've heard a lot about the classic strengths of the Turkana Basin and of the Leakey’s research, the Neogene, and the Quaternary, right, the Holocene, Pleistocene, Pliocene, Miocene. For the next hour, we're going to talk about pushing that record back, pushing that richness even further back in time and getting even an even bigger window on the history that we've got in the Turkana Basin and what comes before the Pliocene and the Miocene, it's the Oligocene. And what we know about the Oligocene in Africa is actually fairly sparse. 

We do know that for most of the Paleogene, Pliocene, Oligocene, Africa was an island continent in what you might call splendid isolation in the same way that South America was thought to be splendidly isolated with no land connection to other continents. And that allowed this rich endemic diversity to evolve there on the continent, mostly seen in mammals but in other taxa as well. And our biggest window on that rich and endemic diversity is not unfortunately in East Africa, but in North Africa, in the Fayum and there in the Oligocene, we see a rich record of diverse, long endemic afrotheres, like a whole group of mammals that share an origin on the African continent, including a diversity of hyracoids, proboscideans, so elephants and their relatives taxa that are completely extinct like in embrithopods and taxa that are enigmatic. So, I'm putting them here under hyracoid, but many of you in the audience will know that that's not necessarily settled. 

And other afrotheres too diverse to name and they are living here in the Fayum alongside, more recently arrived laurasiatheres are mammals from northern continents and when I say recently arrived, I mean in the Paleogene geologic continent. So within the past 5 million years or so, just like yesterday. And those are animals like primates, those are animals like rodents, artiodactyls, and carnivorous creodonts. So, for example, (I got to not hit that one, that one) you would have something creodont like here and then these very long extinct, strained arsinoitherium and embrithopods like there. 

And if you're wondering where are the lions and the zebras and the bovids and the hippos, right? They're not here. This is a very different ecosystem and even the things that do have relatives among the fauna today, if you're like, well, we have primates today, we have rodents today. Hippos are artiodactyls on the landscape. Their representatives here are distinctly different and the links between what we have in the Oligocene and what we have today are largely still a mystery to be solved. And so, while it is wonderful that the Fayum fauna is rich and distinctive, it provides only one rich window on an entire continent's worth of diversity. And imagine the entire continent of North America being represented by just what we have here in New York. There's no way it can adequately tell us everything we would want to know. 

There's one other thing that I should mention, keeping the Oligocene pretty mysterious, and that is a pretty big geological event. I won't say too much because the next speaker is one of the world's experts on this period of time. But at around the Paleogene-Neogene transition, so probably very early in the Miocene Africa, Afro-Arabia finally docks with Eurasia and those land bridges open up and animals cross those land bridges back and forth many times. And it has important long-term repercussions for the evolution of Africa's faunas in ways that we are still working out. But to give you a quick sort of sketch of that, if you think about the East African mammalian fauna today, and then you think about that rich diversity of afrotheres in the Eocene and the Oligocene of Fayum, only 5%  of the mammals in East Africa today are afrotheres.

Everything else is a lauresiathere that came down from northern continents at one time or another, which hopefully gives you a sense when I say the Oligocene of Africa, it's fundamentally different, but it's sparsely represented. We do have very interesting pictures on the Oligocene so far as sites like Losodok, like Rukwa, like Chilga, and they are even those are a little bit different from the Fayum, but we're left with a whole bunch of mysteries still. Like how do those differences between these windows that we have accumulate over time and those differences that we do see, are they these massive geological macro scale changes when you have millions of years of evolution or are we also seeing regional differences, right? Like the differences between the fauna of Mexico and Canada, which is a good time to introduce you all to a new site called Torpenawi. It's located on the western side of Lake Turkana in the Ekitale Basin, and its sediments belong to the Torpenawi Formation, which lie atop some turkana volcanics. 

And it's been described in sort of the first and only paper to describe it so far as a micro basin formed very early in the formation of the East African rift system. And I want to introduce that a little bit, spend a little bit of time because it's very different from what you may be used to thinking in the Miocene, Pliocene, Pleistocene. So about 30 million years ago, so a little bit pre Ekitale Basin pre Torpenawi, there was no Turkana depression, there was no lake, there was no rift that was only just getting started. So instead, what you have was this broad volcanic landscape and as rifting begins, as that landscape begins to pull apart, you might imagine pulling apart a sheet of clay or a sheet of say very stiff cookie dough. And as you start seeing these little cracks appear, those would be micro basins in the landscape. 

And where you have micro basins, you have opportunities for sediments to fill, accumulate and be preserved. And so, the current hypothesis is that the Ekitale Basin is one of those micro basins that produces one of these very rare snapshots into this landscape of the early rift, but it hasn't been known for long. Actually, I love that it has a short history because I can put it in entirety on this one slide. Anything in the area to be mentioned at all in publication as far as I can tell is only just over a decade old. And that was a single date from of basalt in the Torpenawi Gorge. The idea that there were sedimentary deposits here at all was only published 2019, 4 years ago. And that publication, there were no vertebrate fossils. That team of geologists noted certainly that there were sedimentary, there's the [00:08:00] opportunity for fossils and they noted that there was abundant fossilized wood but no animals, right? And it turned out actually that same year as the paper actually came out, Patricia Princehouse and team went out looking for vertebrate fossils thinking, well if you've got everything else there, why not? And then found them. So, the Torpenawi Research Project began and then you'll hear much more about the Turkana Miocene Project later in 2020 we joined that team as sort of an Oligocene comparative reference point. 

So you can imagine on a volcanic landscape, pretty much all of the rocks are volcanic in origin of some kind. That would include things that you would normally think of from an intro geology course as volcanic your igneous rocks like your lava flows and your basalts and those are here at the bottom right of the section. But then we also have even our sedimentary structures are volcanically derived. And I also want to spend a little bit of time here, especially because as a vertebrate paleontologist who's used to working in classic lake deposits, river deposits, floodplain deposits, this is very different. Your sedimentary deposits are volcanic classics. They're derived from volcanic activity and so for example, in lower layers we see high density debris flow. So, think of something like a lahar or a mud slide, even if it's not exactly like that, a lot of high energy movement of material. 

And we can tell some of this it's thought to be true because they can see that some of the grains are reworked and transported, these sediments are moving. It doesn't seem like we actually find the fossils in that. And you could imagine it being difficult for a fossil to make it through that kind of high energy environment. What wasn't noted in the original publication that geologists associated with the Turkana Miocene Project, I want to particularly thank Craig here, if I get this wrong, that's not him that's me. We've noticed additional things about the geology of the site. So among these high energy flows, it looks like there may have been some hiatuses where things were relatively quiet, thank goodness for the animals and where weak soils started to form and then were preserved and on that relatively quiet landscape that was an opportunity for animals and plants to be present. 

And then it looks like when the next volcanic event got started, there may have been some air fall ash or something like that burying what animal remains were on the landscape, which might then be covered by the next debris flow or something like that. In upper layers we see something very similar, but instead of a debris flow, it's a pyroclastic flow. So, if you want to think about what buried Pompei or something like that, something similar as what we have here. And again, we're not so much sure that in something like a pyroclastic flow that we're getting the fossils, but again, these hiatuses, these relatively quiet temporally localized sections seem to be where the fossils are coming from. Although you can imagine a site that's only been known for four years or so, there's still a lot of work to do on this interpretation and on the geology and we're excited to be conducting it. 

And then at the very top we have another, another flavor of pyroclastic flow. And you might, but this is a very hot pyroclastic flow. We find wood in there, but not much else but what is very nice about having an ignimbrite, this kind of hot pyroclastic flow at the top and basalts at the bottom is that if all the fossils that we find are in between those two, and they are all the red dots on this wonderful map that Maggie Gaiku made as part of her master's project with Turkana University College master's program seem to be in these middle U3, U4 layers. 

The geologists on the team have been able to get radiometric dates from the ignimbrites and from the basalts and that allows us to wonderfully constrain the age of these fossils very tightly within only about an 800,000 year window. So, we think these things are between 29.2 and 30 million years old which means we can now put Torpenawi in this collection of Oligocene sites and say that it provides the oldest at least independently dated right there. Some of these you can see Lokone like we're not quite sure and it could be even older than what I've put here. But Torpenawi is dated independently of the fauna, and it puts it as such one of the oldest vertebrate bearing sites in the Turkana basin to date, which like all of these other windows allows this wonderful rare window into the flora and fauna of that time in East Africa. 

But what I actually think is really exciting here is the fact that it is very similar, almost overlapping in age with the Fayum means that we get an opportunity that no other Oligocene site has as far as I can tell to really look at that regional versus time hypothesis. They're so similar in time that it's quite possible that any differences are just due to the fact that we're sampling another part of the continent. I should mention what's also very cool is in addition to the vertebrates and the plants I'm about to tell you about, we also have trace fossils. We've got burrows in some of these sandstones, but many of you are here for the fauna. The most common taxa that we find on the landscape are hyracoids so hyraxes and their relatives, and I show this, I like to show this image is first in terms of deposition and recovery you can see, (let me switch) a lot of our fines are isolated.

We don't have beautiful mandibles let alone complete beautiful skeletons. We get often this is a collection of one tooth at a time for the most part, even with that challenge that it comes from associating specimens into species, the hyracoids are so abundant on the landscape that we've been able to get representatives of most of the tooth positions along the tooth row and even multiples so that we can start to assess within species variation and really try to make sure that we're getting our identifications right. But I know this isn't really helpful, everything's not to scale. So let me switch to this. With the hyracoids, we think we've got five taxa, so they're pretty diverse here and they come in a range of body size from the smallest we've reconstructed to be about eight kilograms. So think of the size of a small terrier, maybe like a porcupine or a badger, or sorry, a small spaniel. The largest being 150 to 175 kilograms. So here in North America things that size might be like a black bear in Africa you're thinking maybe like a waterbuck or a gemsbok or something like that. 

So these are ranging across the landscape and what has been really wonderful is working with collaborators in particular the stable isotope geochemist. And I apologize, I noticed this while practicing last night. I forgot Ashley House, Daniel Green and Kevin Uno's name on this slide, but this is their work and it's been incredible. They've looked at the stable isotopes across these five species. So, in addition to the range of body sizes across the landscape, there's range of isotopic use on the landscape potentially indicating different parts of the habitat or different water use just within the hyracoids don't worry, there are other animals that I will talk about. So, there are these long extinct embrithopods that we've got, Arsinotherium we have these enigmatic ptolemias which have been argued by some to be relatives of the aardvark just with much more of a radiation than aardvarks would let you appreciate. 

But that's going to take a lot more work to figure out and I should acknowledge Erik Seifert and Matt Borths are really providing a lot of the taxonomic expertise on some of these animals. We've got ongoing work again; you could imagine only having found fossils in 2019. Those of you're familiar with the length of time it takes taxonomic work to do. We've got some ongoing identifications. And so, in addition to Eric and Matt, Winnie, Winfred Mbogo is helping us out with the anthracotheres this summer. We also have rodents we're getting some small fossils here, so some of some really characteristic and very interesting African rodents like scaly tailed squirrels. We've got some of those unambiguously, lots of fayamin rodents. So that picture is of Metis, which is a common animal in the Fayum. Erik's particularly excited to be working on these. And we do have primates, we have a few kinds of primates. And all I have on here is catarrhine, as I'm sure much as you say. And we're doing that because one of the other things that's very cool about Torpenawi is that it's right within this credible interval for the crown catarrhine divergence. And so, whether or not these are stem or crown catarrhines, we want to be very careful. We want to dot all of our i's and cross all of our T's getting these identifications right and when we have all of the evidence assembled, we are very excited to share it with you. So please be patient. 

And to give you kind of a sense of where we're at so far in early 2021, I put together this preliminary species accumulation curve of what we had at the time. And so on the left was sort of the preliminary. We know we've got some rodents, primates, and all of this stuff on the right, we made kind of a wish list. Here's what we'd like to see if we collected more. At the time we had about 150 identified specimens. We thought, okay, we've collected more fossils than that if we can identify what we've already gotten in the collections, maybe we'll get to like 250. With continued collections and continued identifications, not only have we blown bright faster, we're now well over 400 specimens, but it's been very exciting to be able to cross off the wish list sort of one at a time, some of the new things. So, we now have, like I said, the ptolemaiid, the anomaluroid that we were hoping to find that they're there. Some of these we don't know if we find, right there may not be carnivores there to find and that would be very interesting too. I should mention actually even just yesterday, Erik sent me an email that macroscelid is not tentative he said it's unambiguous, we can change, change is constantly happening. 

I got to make sure I'm moving on time. I cannot forget the flora because as you heard earlier, we knew there was fossil wood there, both small and big large chunks of wood. they were not kidding about that. What we didn't know we would find would be beautifully preserved leaves and beautifully preserved fossil fruits. This is all these photos, and this work is credit to Rahab Kinyanjui who is conducting this research currently. It looks like it's preserved in a very fine grained, sort of like siltstone or mudstone. And these fossils themselves also come in kind of distinctive layers within here. And so we think it was a relatively shallow, very low energy environment like a pond or a swamp or something. You see the preservation's beautiful. She's found not only those macro flora but has processed some of the sediments, especially on sites like Blue Hill looking for phytoliths and pollen and has found them. 

And both the leaves, the fruits, the phytoliths suggest a woody environment potentially relatively closed. And as Rahab has been working on the reconstruction, she says information from the leaf physiognomy and things like that suggest precipitation of roughly 2000 millimeters yeah, millimeters per year. A mean annual temperature range of maybe 18 to 28 degrees celsius and a suggestion of a seasonal tropical forest present at to Torpenawi. And so if you look up seasonal tropical forests today, what are their modern analogs? What do they look like? They look like potentially these kind of seasonal tropical forests in Bangladesh where during the rainy season it is very, very green and during the dry season, not so much. Some of the isotopic data that's coming back from, again, our colleagues (all right, and I got their names there at least) sort of are consistent with the botanical work in that Torpenawi is isotopically pretty distinct from later sites, including both some later Oligocene and Miocene sites. 

I should note on this plot, Torpenawi is down here in the purple. And so the isotopes are also consistent with this idea of potentially much more water, potentially a more closed environment forest. And the carbon here on the x axis is giving us the sense that there is not that kind of open C4 grassland that you might expect instead it's a lot of C3 and C3 plants can be a lot of things, but some of those things are more forested woody environments (there we go). So, to give you sort of an overall, even at this early date, we can say Torpenawi is distinctive, right? It's botanically distinct from earlier and later communities. It's faunally distinct and given that things are ongoing all, again, I'll illustrate this with the hyracoids because they're some of the ones that we understand the best in ongoing years we hope you can see this in a lot of other ways.

So for example, you saw the five hyracoids at a range of body size among those five, only one genus in that is shared with the Fayum. So the Fayum, I've colored here, the latest Fayum genera I've colored here in pink to match sort of the pink arrow here and also at the Fayum but in many other sites is the itty bitty thyrohyrax and that's the only one. Everything else that's there in the Fayum is not here at Torpenawi. And then also in comparison on the other side, these later Oligocene and Miocene assemblage, there's also some shared those I've colored in blue here. And so some things that we have at Torpenawi are also shared with later sites, but only about half. And some of the really characteristic hyracoid taxa that some of you working in the Miocene may be used to seeing like Afrohyrax and Meroehyrax, they're not here. So we have a lot to do. There's an incredible and a very exciting long-term future for this site and I look forward to being part of the team that shares these developments with you in the future. Thank you all for your time and attention.

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