Ellen Miller

The Buluk primates in their environment

Buluk is well-known in paleoanthropology for the recovery of primitive apes and monkeys, from a time period after the divergence of the two lineages but before the evolution of modern forms. New discoveries provide additional insights into the early phases of African ape and monkey evolution, and these findings are discussed in light of current work reconstructing the Buluk paleoenvironment.

FULL TRANSCRIPT 

What is new with the Buluk primates in their environment. And I have added Ellis Locke and John Kelly, J Kelly as we all know him because they have been doing the heavy lifting on the apes. So this is a lot of it is their work. Buluk is located on the eastern part of Lake Turkana and geographically Buluk is really important because it is the easternmost of all of the Miocene localities. And if you want to know what your monkeys and apes are doing, you have to include information from the furthest reaches of their known adaptive zones. Temporally Buluk is also really important because it's now most of the fossils come from about 16.7 million years ago, and that sits be look inside the mid-Miocene climatic optimum. That is the last time that the planet was as hot as it is now, and for the same reason a carbon excursion which exceeds equilibrium. 

A little bit of the history of work at Buluk, not very many of you have been there. It's hard to get to. So in the 1970s, Ron Watkins was mapping the volcanics out there for his dissertation and he came across some fossils. So he published those with John Harris in 1974. And I don't have a picture of Ron out at the type site, but this is members of the Turkana Miocene Project visiting the Buluk type site last summer. The first fossil exploration was a short one in 1978 by Kamoya Kimeu. In the 1980s, 1983, Richard Leakey, Meave Leakey and Alan Walker do a field season out there. And in 1985, Leakey and Walker published a description of the fauna, including new higher primates, that's apes from the early Miocene. And Meave publishes a very important paper on the Buluk monkeys. There was almost, there was no work at Buluk then for almost 20 years until I bounced up there in 2004 with Ron Watkins. 

And one of the things that was clear right away is there was going to be absolutely no way to logistically work out at Buluk. It was just too remote. But in 2007 when they started to build TBI Ileret, we bounced out there again in 2008 and 2009 for two short exploratory seasons. In 2013, I was joined by Isaiah Nengo and the work continues today with Gabrielle Russo, Tara Smiley, and the Turkana Miocene Project. So, this is a simplified stratigraphic section through Buluk. Very simply, the Irile basalt is at the bottom. Then there's a series of sandstones, clay stones, silt stones, lots of silicified wood, including some very, very large logs. And all of the fossil vertebrates come from this part of the section. Then a big volcano blue ends the river system. So, there's a whole series of reworked pantelleritic tuffs, and then the Il-Jimma basalt caps it. 

So keep your eye on that little finger of basalt with the two stars there. That is this which was dated, we got the date back 10 days ago courtesy of the Turkana Miocene Project that's now dated to 16.7 and almost all of our fossil localities are from just below this layer. So, thanks for having those dates rolling guys. The deposition al environment at the time the animals were living there, just for reference, the yellow arrow is that little finger of basalt and the blue arrow is us excavating of what we call the dead elephant bone bed. And this is a panorama through dead elephant valley. At the time that the animals were living there, Buluk would've been a mature river system, very likely with gallery forest and all of the fossils come from the channel sands. You can see that this important bone bed is sitting right in the middle of the channel. 

This is dead elephant bone bed on the first day. So we were like, we should go to that place where all this bone is coming out. And we just took brushes and glue and this was an afternoon's work. And you can see just one afternoon of brushing, no excavating at all. And we were like, whoa, this is a lot of bone upon bone going directly into the hill. So this has been one of the richest areas. All of the fossils come from channel sand deposits, but those channel sands are associated with these very thick red clay floodplain deposits. And the paleosols indicate a very strongly seasonal sub-humid to semi-arid climate. Note that there's no inter fingering of the floodplain in the ash when that volcano blew it absolutely ended the river system. And as Ron Watkins, I do have a picture of him here, pointed out to me that the topography of the landscape at the time the animals were living here would've been relatively flat because the ash is uniformly thick in most places. So that was sort of a cool thing to learn. 

Slightly stratigraphically above the dead elephant bone bed. We have another locality we call Richard’s, for those of you that can see bone, you've already noticed this, but there is bone coming out all along here Richard and Alan described a wall of bone with four feet of basalt sitting on top of it. Here is the same bone bed with the four feet of basalt demonstrated. The good thing about having four feet of basalt on top of your bone bed is we should be able to get a really good date on this because the basalt rolled right on top of the channel. The bad thing about having four feet of basalt on top of your bone bed is that you have four feet of basalt on top of your bone bed. So what we think we should do is get an explosives expert, somebody. These guys are really good, just enough to put in some small enough charges just to crack the basalt so we can carry it away. 

And truthfully, I think we all know this would be a wonderful tribute to Richard who was famous for finding the right tool for the job and not being afraid to use that correct tool. Even slightly stratigraphically higher we have a locality we call Valley of the Moon. We have fossils coming from the very bottom of this locality, and this is a super interesting place. The ash here is not water carried, that's a gas powered flow. So we are really close to the blowhole and the flow is northwest to southeast also in this same valley as a series of trees with Troy and Kevin posed there. And the trees also seem to be all blown over northwest to southeast. This is something we're going to double check and actually measure this year, but that's sort of cool also. So just to recap, we know where the dead elephant bone bed is in the sequence. 

We are not exactly sure yet where Richard's bone bed is or where Valley of the Moon falls exactly, but we are going to have excellent stratigraphic control because each of our fossil localities is so closely associated with a dateable layer. So onto the fauna itself, we now have about 34 species in 31 genera. And the ones colored in black are ones that Richard and Meave and Alan Walker would have known. The names have likely changed, but they would've known about those animals. The ones in white are ones that we have recovered since then. I will just point out the unusual diversity relative to a modern fauna. Those are six species of elephant of Proboscidean in three different families. There are four Rhinoceros, no modern landscape supports, such a large number of herbivores. Also, of the eight Carnivorans, three of them are a very, very large body size. So as people that know me are fond of me saying, uniformitarianism only gets you so far because in the Miocene you really have to think outside the box. 

Buluk is famous for having very large mammals. We have elephant bones. This is a rhinoceros jaw upside down, a lovely tusk bean plastered. The smallest animals we ever found were monkeys and occasional isolated ape tooth, a tragulid, a little mouse deer sized thing. But we never had anything smaller than that. We never had any rodents, insectivores, we never even had anything the size of a rabbit. So, I had always wondered if we really, really concentrated and wet sieved all summer, could we get micro mammals? So, in 2021 we spent three months, seven days a week, sunup to sundown wet sieving about 25 giant bags of sediment from each of the bone beds. And we do have micro mammals. You might even get this is one of the larger ones. So they're only only about two millimeters across. And these are getting imaged as we speak. We have about 150 teeth and over a thousand postcrania. So we do have small things at Buluk,.Another thing that we can know from the fauna, of course this is the Oman audience, we don't need to explain this to that plants get when they take in CO2, then the animals eat those plants and you can see the carbon in their dental enamel and all, to make a long story short, this is the work of Erisa Arney. And all of the Buluk fauna falls in between -12.5 and -9. So very clearly sort of an open woodland habitat. 

Just to make that even clearer comparison with Thure’s work from 1997, Fort Ternan was always considered to be sort of an open woodland, open canopy site. And Buluk is even more open woodland than Fort Ternan. 

So this is, you guys know what I'm going to say, geo-fabulous. This is a Proboscidean centrum from a vertebra and those I think are beetle holes. And it was suggested to me that they were likely dermestids. And if that's the case, then at least at some point during the year, the temperature was between about 65- and 85-degrees Fahrenheit because that's the optimum temperature for dermestids. They don't like it too cold, they don't like it too hot. Although I will bow to Dino's superior knowledge who suggested it's unlikely to be dermestids, but a soldier beetle? 

Which also have a very specific…

My point exactly there we are still going to learn something about the climate from this. So I love these sort of fossilized behaviors, this sort of moment in time. So that's the geofabulous part of it. The monkeys, so Meave published to the first monkeys 16 specimens in 1985. This was a really important paper. It really put Buluk on the map. At that time, not very many localities had monkeys and she put all of them in an indeterminate species of prohylobates largely because early cercopithecoids, systematics was a disaster and Prohylobates was the genus with priority. So she thought when they got redone, this was a great insurance policy. It was very smart. We came along in 2009, a bunch of us and redid early Cercopithecoid systematics noting that the monkeys from Buluk belonged in their own genus Noropithecus bulukensis because Noro is monkeys in Daasanach. 

And then in 2020, Ellis Locke, as part of his dissertation published 91 new specimens, 91 new Monkeys from Buluk including new tooth positions. Long story short, this is just a sample of some of the monkeys discussed by Ellis in 2020, and they're just really variations on a theme. They're not that different from Victoriapithecus or other monkeys. They have slightly longer sheer crests, but it's interesting that the monkeys are really quite generalists. And this is a slide I shared with John Kappleman. So you've seen it mostly this morning and he was focusing on Alophe. I will just say that with Noropithecus, we are helping to trace the order in which these primitive features are lost and the modern features of modern Old-World Monkeys are gained, including their signature feature bilophodonty. So Noropithecus is part of that story.  And now the apes, so Leakey and Walker, 1985, these are the apes that they knew and the taxonomic assignment, Shivapithecus, Kenyapithecus, Micropithecus for the most part. I will begin with Micropithecus. 

We really don't know what to make of this. That is really a rotten little jaw, and that femoral shaft has neither proximal nor a distal end. So you know what I know about that. But in 2022, just last year, Nishimura et al, published on the phylogenetic affinities of a fossil ulna from Buluk. And this clearly belongs to a small suspensory ape. So, we are not sure what the relationship is between this small suspensory ape and the original maybe Micropithecus specimens, but there is at least one small bodied ape, maybe two. And in 2021, we also found one tooth of something that's likely Nyanzapithecus. So we could have one small bodied ape, we could have two, we could have three. This is an area that really needs a lot more work. The rest of the material that Leakey and Walker published in 1985 was all put in Afropithecus turkanensis

So, some key new specimens from Buluk. I will begin all the way on the end with cf. Limnopithecus cf. Limnopithecus, we have put, we are going to put in cf. Limnopithecus because the canine is pretty close to a female Limnopithecus legetet, but this is the only specimen we have. It's not in great shape. So it is what it is. The very large Proconsul, we are getting more and more comfortable that it is probably Proconsul gitongai, this is gitongai from Kipsaraman known from the middle Miocene site. The proportions aren't exactly right, but the morphology of the tooth, that's a really good match. And then we have this lovely juvenile mandible of Afro Pitus and I'm about to let you in on some news that Afropithecus. Afropithecus is a textbook example of every thorny problem a paleontologist can possibly face separating what is individual variation from what is species level variation from what is sexual dimorphism from what is idiosyncratic variation. 

So, we do think that this is a juvenile mandible of Afropithecus because that M3 when we had its CT scanned is a pretty good match for Afropithecus. There's a large number of features, the metaconid fold among other things. The premolars are also very consistent with Afropithecus. But here's the rub. So, these are the associated maxilla and mandible found by Leakey and Walker published in 1985. And when you use J Kelly's quantitative shape method for sexing the canines, the lower canine falls in the range for extant female apes. But it is the largest canine in the entire hypodigm. The upper canine falls in the range for males. So this is an unusual, it's a bit of a head scratcher. We have only one new Afropithecus canine that we've discovered and it's a dead ringer for the males, so that's not very much help. 

One possibility is that the two specimens are not actually associated, very possible. Another possibility is that the male and female of Afropithecus have more monomorphic canines because their diet has been reconstructed as this very, very special sclero. I've never been able to pronounce that. Well, sclerocarp feeding, which is a very strange kind of seed predation that involves use of the canines. So this is part of the head scratcher. It doesn't get any better when you get to the maxilla. Rossie and McClatchy in 2013 rightly described that there are four different recognizable patterns in the maxilla of things attributed to Afropithecus. And it doesn't get any better when you get to the mandible because there are three additional patterns. And if we add that Buluk mandible, if that really is Afropithecus, it introduces yet a fourth combination of the relationship between premolar and molar size. 

So we have our work really cut out for us and just getting towards the end. So soon it will be cocktail hour. This is the work of Daniel Green and Kevin Uno. This is the oxygen values and bear with me. This is very, very cool. So, these tell you something about where the animals are getting their water from, and it is really normal for anthracotheres to have low oxygen values because mostly they're considered semi-aquatic or at least hydrophilic, right? They love the water, and it is normal for things like giraffes, which are getting a lot of their water from browsing to have high oxygen values. At all of the other sites Daniel Green has found that in the Hominoidea here is largely driven by Afropithecus. That Afropithecus at Kalodirr and Locherengan, the value was up there with the giraffes. But Buluk is an anomaly where the monkey and the ape are probably getting their water from drinking right out of the river. 

And so this is very strange. This is unique to Buluk as far as we know. Unique to Buluk so far. One of the things that Dan and I were just talking about casually over coffee, so I don't want you to attribute too much to this, it's just an idea. But  we were thinking that having these very low oxygen values for the monkey and the ape, but Buluk, maybe it has something to do with the fact that the planet is heating up and the leaves are getting much better at preventing themselves from desiccation and maybe the leaves and the fruits available are really not able to provide enough water for something like a monkey or an ape. And so they are getting their water from the river rather than from fruits and leaves. Just an idea that we're throwing out there because it does seem like Buluk is quite an arid environment. 

Well-watered only because such a major river system runs through it. So, what we know, a large mature river system, very likely with gallery forest, remember we have a suspensory ape. So there has to be at least enough tree cover for the ape to go tree to tree. But very largely that is probably set in an open canopy woodland. The climate would've been strongly seasonal, sub-humid to semi-arid. The mammalian fauna is diverse by any measure. But one of the things that's interesting is all of the herbivores are browsers. We have no grazers at all. The Buluk monkey like the other early monkeys, probably more terrestrial and less folivorous than the modern forms. And we at have a minimum of five different ape taxa, which is fairly similar taxonomic and adaptive diversity to other early myosin sites. More interesting than what we know is what we are working on. 

So, work in progress includes, we are still working on incorporating dates from the Valley of the Moon and Richard's bone bed into the sequence. There is still continuing work going on, on all of the environmental proxies. This is the Turkana Miocene Project. So still working on the soil carbonates, the biomarkers, the phytoliths. There's more comparative isotope work coming starting next week. We are still describing some of the new aspects of the fauna. There's a manuscript on the Proboscideans in the works. We still are working on describing new pigs and the rhinos and we are very interested in the taxonomy of these bone beds. One of them in particular, the one dead elephant is interesting. All of the animals are at stage zero or stage one where, so these are not animals that have been rotting out on the floodplain for a long time. So, something interesting is going on and we're very interested in the taphonomy. Not every bone bed has this, but the one that dead elephant does. So a lot of work still to be done. We know how those bone beds formed. We just don't know why the animals are in them. 

There's still additional isotope work on the Buluk monkeys, especially comparing them with Victoriapithecus. I'm very curious whether Victoriapithecus, which is middle Miocene, is also drinking meteoric water. And of course, there is describing the new Buluk apes and interpreting the isotope results. And then the thorny problem that is Afropithecus. And there was one more really important work in progress. This I'm doing in conjunction with Gabrielle Russo and Tara Smiley. We are right now working on a grant proposal on the early middle Miocene transition because the mid-Miocene climatic optimum corresponds with a very large turnover event. And fortunately, Buluk at 16.7 is right at the beginning of this rise in climate. And Napudet at 13 million years old is a locality in the aftermath of global warming. So, we have two localities in the Turkana basin that essentially bookend the mid-Miocene climatic optimum and the faunal transition. 

And in between there are the sites of Kipsaraman and Maboko and Fort Ternan. And so, we should be able to look at faunal change through the mid-Miocene climatic optimum. And it's always good to point this out to people that are paleontology affiliates, that one of the things that we provide is we really provide the long view and the work in the middle Miocene, particularly across the early middle Miocene transition, is very relevant for climate change today because we know what happens. We can see who wins and who loses. We've been through this before, we've been through this in the early Miocene. And one of the things that we see is just within the primates, for example, the monkeys make it through pretty much unscathed. The monkeys make it through. There’re some changes in cusp size, there's changes in crest length, but really that body plan and that adaptation makes it through the mid-Miocene climatic optimum pretty well.

Apes on the other hand, the entire early middle, early Miocene, sort of above branch quadrupedal walking, that whole adaptation goes away, and you have a hundred percent replacement by apes that are capable of more orthograde climbing. You get the first long forearms relative to hind limbs. So the entire new, you lose one entire body plan and get a totally different body plan. So this is one of the things that we are interested in investigating. So, I will just say that this is a picture from the early days of Ileret in 2008 and a very, very deep bow of gratitude to Louise and Richard and Meave. None of this was possible without you and asante sana from team Buluk.

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