Gabrielle A. Russo

Middle Miocene primates from Napudet, Kenya

Napudet is a Middle Miocene locality in the Turkana Basin well known for yielding ape fossils, including an infant cranium of Nyanzapithecus alesi. This talk focuses on primate fossils that the Napudet Research Project has since discovered, including an ape partial postcranial skeleton, highlighting the continued importance of Napudet for contributing to our understanding of primate evolution.

FULL TRANSCRIPT 

Thank you. What a wonderful past few days it's been. I'm delighted to have been asked to come to talk to you about Napa debt, but of course what I'll show and talk about today is no single author effort. So, the Napudet Research Project is a huge collaborative effort. There are researchers, colleagues, museum staff, students, fossil hunters, communities that are all a part of that. And so I want to begin by acknowledging the many individuals who are all co-authors of this talk. And of course, no talk about Napudet can be had without acknowledging and taking a moment to remember my former co-director, Isaiah Nengo, who passed shortly after Richard early last year. Isaiah was passionately dedicated to the work at Napudet, his work at TBI and the communities and the surrounding areas. He made numerous discoveries including some of which I'll talk about today and I want to just express my immense gratitude for the invitation, encouragement and support by Isaiah, Lawrence, and Richard, who was Isaiah's very close mentor. As we've seen, one important part of honoring their legacy is carrying on our work in the basin and it's a real privilege that I have that honor at Napudet. 

So today I want to introduce you to Napudet, which is perhaps a relatively noose locality compared to some of those we've already talked about. I will provide an overview of the paleontological and geological investigations there. Discuss the fauna and specifically Middle Miocene primates, including some new discoveries and I will focus in particular on the functional and evolutionary anatomy as well as the significance of an ape partial skeleton. And with a few moments left, I hope discuss some new directions for the project. So Napudet is paleontological locality in northern Kenya on the west side of Lake Turkana. It is just south of TBI Turkwel and the Turkwel River and just west of Lothagam. A series of fossiliferous areas were discovered during survey by the Koobi Fora Research project in the early 1990s. They were looking for Pliocene sites and wandered into what we now know as the red series. It's been worked ever since. It was returned to in 2013 by the KFRP, along with Isaiah Nengo and since then Isaiah and a moment to acknowledge the contributions, especially by Craig Feibel, Ellen Miller, and Tara Smiley and more recently, Napudet has held a central position as one of the only Middle Miocene sites in the area that's involved in the Turkana Miocene project. 

While its paleontological investigation really started in the early nineties, the hills were part of reconnaissance geological work in 1959 to 1960 later reported on by Dodson. In that report, he noted sedimentary strata of interest including tuffs and ashes in the areas surrounding the hills. McDougall and Brown provided a date on a columnar basalt, we now know is part of the lower basalt in the series, a date of 12.8 and Craig Feibel since at least 2013, I think perhaps earlier, has been a really key figure in understanding the quite complex geology of Napudet. Additional key pieces of information including forthcoming dates on previously undated basalts dates on the petrified wood that you've heard about yesterday are all being generated more recently by the Turkana Miocene Project. So the stratigraphy of Napudet is published in the 2017 Nengo et al Nature paper. There are three primary fossil bearing intervals of interest, Pliocene sediments of the Nachukui formation, and you can see there at 4.1 the base of Lake Lonyumun. Beneath that is what we've informally termed the “Red Series” and then the Emunyan beds, and I'll talk a little bit about each of these. So we warmly refer to the areas north and west of central Napudet as the “Pliocene Leakey Sites”. We need to clearly distinguish these from the Miocene sediments at Napudet. They do also though cap areas of the “Red Series”, as you'll see in a moment. Roughly 90% of our fauna are identified to the family level or below. And among primates are primarily cercopithecoids though there is also some very fragmentary hominin material. 

Underlying the lake is again informally the “Red Series”. There are places north and south as shown in the map there comprised of red sandstones and conglomerates. Thus far it doesn't yield any dateable materials, but we know it has to be older than 4.1 as it lies below the lake and probably younger than the middle Micoene. So possibly containing sediments spanning Mid-Late-Miocene perhaps Pliocene. Given the possible late Miocene date, the fossils are of considerable interest. The fossils from the strata though however, are also considerably beat up. So they are currently under study. We're continuing investigation working in these series and are obviously keen on finding or identifying anything that'll help us nail down that late Miocene date, including taxa that don't cross that Miocene-Pliocene boundary. And of course, what Napudet is best known for are the Emunyan beds located centrally. These fossil bearing strata are dominated by bedded and polychrome tuffs underlain by columnar basalt flow that was dated in the 2017 paper to 13.3. Roughly 70% of our fauna derived from these beds, a number of the fossils are under study, and some are published. We recently published work in Journal of Vertebrate Paleontology earlier this year was led by Michael Morlo on the carnivores from Napudet showing we have a new species of giant amphicyonid. 

The Emunyan beds are also well-known for our fossil forest. These beds preserve fossil wood and there are several areas where the fossil trees are preserved upright in situ. Trees along with the phytolith data from the site tell us that forested and woodland habitats probably existed on the landscape. A number of important primate fossils derived from the Emunyan beds. Of course, it's best known for the nearly complete infant cranium of Nyanzapithecus alesi. This was described in 2017, but what I want to focus on today are the primates that have been discovered since 

Many of these come from a site we call “Red Hill”. You can see it's there located in sort of the lower part of those upper polychrome tuffs. This is an incredibly important site. It documents quite a bit of primate taxonomic and ecological diversity. It's also known for the first primate discovery at Napudet, a pretty beat up ape canine. However, more recent “Red Hill” work has actually yielded adult alesi including an upper and a lower M3, and that lower M3 is going to be the first known for that species. These teeth corroborate the impression from that type specimen that the species size is slightly larger than Nyanzapithecus pickfordi. The lower M3 is very derived actually resembling Oreopithecus, which also in that regard shows us that N. alesi is more advanced than N. pickfordi. From “Red Hill” there are also two lower molars, an M3 and probably an M2 of what appears to be Kenyapithecus. It largely resembles the Fort Ternan material and given the sort of scant and finite Fort Ternan sample, these teeth from Napudet are going to be both important and exciting in providing new information and a new opportunity to learn about this taxon. 

We also have a Galagid mandible. This preserves the M3 and an unassociated distal humerus. The mandible tentatively shows affinities with Komba, which we know from early and middle Miocene sites, also including Maboko. But what I want to provide detail about today with you is an ape partial skeleton that we have from a different site in the Emunyan beds “Hallelujah hill”. You can see it's just north of the bedded tuffs from which you find alesi in those polychrome tuffs in that same section.

Why I want to focus on the ape partial skeleton is to highlight the importance of continuing to search for Middle Micoene localities in the Basin and elsewhere. The middle, Middle Miocene is a very important time period in ape evolution. It's when we start to see a move away from pronograde adapted predominantly quadrupedal positional behaviors of early Miocene taxa like Proconsul and Ekembo toward more fore limb dominated behaviors that are later found among some late Miocene apes and of course crown apes. However, there are few post crania from East African Middle Miocene hominids. It includes scant remains attributed to Kenyapithecus from Fort Ternan and partial skeletons of Nacholapithecus from Nachola and Equatorias from Kipsaraman. However, the two partial skeletons of these latter are considerably damaged and distorted precluding comparisons, particularly quantitative ones. These aside, there are no other reported ape post cranial specimens from East Africa between 15 and 7 million years. Enter Napudet, in 2015 we discovered elements of an ape partial post cranial skeleton at and since then, as you can imagine, a considerable amount of our fieldwork has been dedicated to recovering that skeleton. Here's what we have for the skeleton KNM-NP 64631. The panel on the right show some of the more functionally and informative pieces, but there are more than 70 post cranial specimens representing the vertebral column, shoulder, hip, elbow, ankle joints, as well as the hands and feet. There are no cranio-dental remains. 

What I'd like to focus on is the comparative and functional anatomy of this skeleton of some of the more recent finds.  We make comparisons to extant anthropoids and some extinct, mostly African Miocene apes. 

Of the femur shown on the right in the red box now is all we have preserved as the femoral head and partial neck. However, the femoral head is quite spherical and projects proximally from the neck as in other hominids and unlike in monkeys indicating there was probably good overall hip joint mobility in multiple planes. Of course, from the femoral head we can glean important body size information. We use published regression equations to estimate body size from the super inferior diameter of the femoral head and the estimated body size of the Napudet ape is roughly between 13.5 to 16.5 kilograms. This is comparable for reference to ranges for some baboon species, some large bodied colobines and is a bit bigger than siamangs. Here's a bi-variate plot of log radial head max diameter against log mid lumbar medial lateral breadth. The Napudet ape is shown by two stars, one for each lumbar vertebra, platyrrhines are in purple cercopithecoids in blue and hominoids in red. And the takeaway here is that forward's vertebral size, the Napudet ape has a large radial head falling above the hominoid line along which Ekembo falls. 

Here we've quantified the bevel angle of the radial head. A larger angle shown as values to the right and is exhibited by most monkeys indicates less radial head beveling reflecting a shallower corresponding humeral Zona conoidea. That together will provide stability at the elbow joint, especially in pronated arms positions as is assumed during quadrupedal locomotion. A smaller angle shown as values to the left and is exhibited by most extant apes, extant apes, and it tallies indicates more radial head beveling, which articulates with a deeper humeral Zona conoidea and provides stability as the radial head as it moves and rotates through pronation and supination movements as during four limb dominated activities. The value for the Napudet ape radius shown as that star falls within the lower range of the extant ape distribution as well as Ateles. This reflects a more derived elbow condition compared to cercopithecoids, and in this way also differs from a Ekembo and Epipliopithecus, which have relatively less beveled radial heads. Here's a comparative panel of lumbar vertebrae shown from top to bottom, ventral cranial and lateral views. There's extant Papio on the left, extant Pongo on the right, sandwiching Ekembo, Nacholapithecus, the Napudet ape, one of the Morotopithecus vertebrae. 

The Nadudet ape lumbar vertebrae are most similar in their size shown here highlighted as cranial articular surface area. Their body proportions and their shape to those of Nacholapithecus, and those are all outlined in that red box. In particular, the Napudet specimen, NP 66 resembles quite a bit the 35250 skeleton lumbar vertebra are shown there right next to it, and that's really evident in a cranial view. 

These box plots show variation in an index of transverse process position relative to the medial lateral breadth of the cranial articular surface, which in our sample scales isometrically both within and among the primate clade sampled. Values for the Napudet ape fall between the values for mid lumbar verts for cercopithecoids on one hand shown toward the left, which have more ventrally positioned transverse processes reflecting an emphasis on spinal flexion during quadrupedal walking and running. And on the other hand, toward the right exhibited by Ateles, Aluotta, Gibbons Hylobatids in general and especially the great apes, all have more dorsally positioned transverse processes associated with a more dorsal stable spine as would be needed during upright positional behaviors. And the transverse processes of the Napudet Ape you can see are not as dorsally positioned as those of the one, Morotopithecus lumbar vertebra, but perhaps are slightly more dorsally positioned than a Ekembo or Nacholapithecus. Though all of that variation for those latter taxa could probably be sampled within a taxon. 

There are two fragments of pollical proximal phalanx that we were able to join in order to estimate some length. These box plot show variation in a ratio of pollical proximal phalanx length relative to the supero-inferior diameter of the femoral head. Values to the left indicate relatively short thumbs, values to the right indicate relatively long thumbs. The Napudet specimen shown as the star has a relatively long thumb falling within the range of Hylobatids and platyrrhines and near Ekembo. And for most Miocene apes, a long thumb has been associated with assisting and powerful grasping during our arboreal locomotion. We have a left medial cuneiform bone of the foot shown here in medial and distal views compared to a selection of other Miocene hominids. The first metatarsal facet was able to be segmented from the medial cuneiform and its curvature was quantified. These box plots show variation in that curvature with values to the left showing less medial-laterally curved first metatarsal facets and values to the right, showing more medial-laterally curved first metatarsal facets. Hominoids tend to have increased curvature compared to cercopithecoids, and the Napudet specimen has marked medial lateral curvature falling within the ranges of variation for hominoid and Aluotta and situated within the range of a Ekembo variation. Interestingly, the Nacholapithecus specimen appears to have a somewhat flattened for flattened reduced curvature. However, as you can see with extant Pan, all of the variation for those Miocene hominids could be sampled within a single taxon. 

Overall, the Napudet ape exhibits mobile joints indicated by sphericity and projection of that femoral head and will not be shown today, a very globular humeral capitulate with a deep Zona conoidea that's going to articulate with that very beveled radial head I showed earlier, all of which are pronounced to earlier Micoene apes. The bones of the elbow joint in particular are quite large relative to some other skeletal elements, and there's a long first ray and the curved, very curved medial cuneiform. MT1 facet implies well-developed grasping of the hands and feet like other Micoene hominoids not shown today, but there's also part of the talocrural joint that shows consistency with mobility and dorsiflexion and inversion that would be associated with climbing. All of the above support an inference of a reliance on more four limb dominated activities such as perhaps vertical climbing or orthograde clambering with the forelimbs playing a more important role in body support compared to earlier Miocene apes. 

In its morphology and inferred functional anatomy the Napudet ape most clearly or most closely resembles Middle Miocene ape Nacholapithecus from Nachola also in Kenya, but south of Napudet. There are slight differences including body size estimates. While the Napudet ape resembles perhaps a small bodied Nacholapithecus, without cranial remains, cranial dental remains the null hypothesis of what it might be still has to include other taxa known from Napudet from which we only know from teeth, cranial dental remains. The Napudet ape post cranial skeleton is much smaller bodied than Equatorius or Kenyapithecus that lacks any sort of terrestrial adaptations as well so it's unlikely to be that. Could it be alesi? Well, little post cranial are known from Nyanzapithecus, however, body size reconstructions from the infant cranium and the adult Nyanzapithecus alesi specimens yield body sizes of around 9-11 kilograms. So that would be smaller than our estimated ranges for the Napudet ape, but further Nyanzapithecine post crania are needed.

Though its attribution remains unclear at present the Napudet ape post cranial skeleton has great importance as the only other post cranial skeletons known from East African Middle Miocene, hominoids, Nacholapithecus, and Equatorius are crushed and distorted. So the relatively well-preserved morphology of the Napudet ape is going to provide key information about the body plan and evolution of Middle Miocene apes. Since the Middle Miocene is also the time about which we start to see an increase in four limb dominated behaviors, the skeleton serves as important data point in the fossil record against which we can test hypotheses about the evolution of more upright positional behaviors that are later characteristic of crown apes. So additional work at Napudet and new Middle Miocene localities in the Basin and elsewhere are needed to help understand the pathway by which we get the body plans of modern apes. And to take this one step further, the Middle Miocene is important because it tells us about what comes in time period right before appearance of hominins. In other words, the Middle Miocene and its ape players set the stage for the rise of hominins. 

With my remaining few moments, I want to quickly turn to situate this transition documented, documented by the Napudet ape post cranial skeleton in a larger evolutionary context, and to do so, just briefly mention a project in collaboration with Ellen Miller and Tara Smiley that harnesses the strengths of two Miocene localities in the Basin, Napudet in the much more scenic locality of Buluk. Our forthcoming work will examine faunal evolution among the Middle Miocene Climatic Optimum (MMCO), which represents one of these major warming interruptions and what is otherwise sort of a long-term cooling trend in the last 50 million years. The Middle Miocene climatic optimum or warming occurred around 17 to 14 and a half, and past research has demonstrated that this seems to corresponded with a large turnover faunal turnover events informally referred to as the Early Middle Miocene Transition. Buluk and Napudet are excellent localities for which to take at this faunal change, take a look at this faunal change because at roughly 17, Buluk sits documents a fauna that sits on the cusp of this MMCO and at 13 Napudet documents a fauna in the aftermath of that warming event.

In other words, they bookend the MMCO. We'll put this together with published faunal data from regional localities, including Kipsaraman at 15.5, Maboko at 15, and capture faunal change at roughly 500,000-year increments. We'll integrate taxonomic and ecological data to test hypotheses about lineage specific changes, including, for example, major transformations in the catarrhine body plan as well as first and last appearances all within a comparative framework. And as the MMCO has been touted as the best analog for current day climate change, the results of our work will have importance for a number of fields beyond paleontology and paleoanthropology, including conservation. And with a project that has significance for both paleontology and modern-day mammalian conservation. We'd like to think that this is one that Richard would approve of. With that, I'd like to thank Lawrence, Fred, Alicia, and the other conference organizers as well as Stony Brook, TBI and National Geographic for putting on this truly wonderful event. And of course, the various museums and funding bodies that make our work at Napudet debt possible. Thank you.

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