CARTA: Bipedalism and Human Origins-Comparative Anatomy from Australopithecus to Gorillas

this ucsd-tv program is a presentation of university of california television for educational and non-commercial use only check out the new youtube original channel you see TV prime at youtube.com slash you see TV prime subscribe today to get new programs every week you for at least 50 years has been realized that uprightness or bipedality is really of all the characteristics that define humans and our immediate ancestors or hominins bipedality is really probably the most distinctive that is from the beginning and continuing into the present day it's standing and walking moving locomoting on to lower limbs which really sets us apart more than anything else really from the beginning from our closest relatives now of course the human family tree has expanded a lot in the last 50 years this is actually taken from a figure from wood and Richmond Brian Richmond is one of our speakers today from about 11 years ago and I had to add a few more tracks to it for today so new attacks are being added all the time and are thinking about these taxes changing all the time with the discovery of new material I think most people would agree that most people in the field would agree that bipedalism was a part of the normal locomotor repertoire from the beginning in fact by definition that almost has to be the case if you're a hominin bipedalism must be at least the part of your locomotor repertoire and we can call this facultative which just means that you could do it somewhere even down here there's evidence that some bipedality was practiced and I think we had also people in the field would agree and everybody else that by later Homo erectus and certainly homo sapiens that we had exclusively bipedal behavior or committed or obligatory so those things are not really in question what is in question is what happened in between the two that is do we have a progression even progression through the years of gradually increasing sophistication of bipedal gait gradual perfection of bipedal gait what kinds of variations in bipedal gait might we have where their possible regression to a less bipedal locomotive repertoire do different parts of the body evolve at the same rate if you're becoming better a biped allottee there's still lots of questions here that are up in the air and it partly depends on what skeletal features you look at so even within this one fairly circumscribed group so had our hominids the skeletons have been interpreted in very different ways in the past depending on which features you concentrate on certain features in decayed and arboreal locomotor repertoire at least in part others have been interpreted as indicating committed and exclusive bipedality so really which traits you use and what the constraints on those traits are and how they reflect what an animal was capable of doing what it actually did do are all very important questions for interpreting the skeletal record and we're going to be talking about lots of parts of that skeletal record today beginning with talk on the pelvis which is the next talk obviously pelvis a very critical part of the skeleton for bipedal locomotion lots of changes have taken place on the pelvis as you can see just from a quick comparison of a human and a gorilla pelvis so I hope you enjoy the talks I think there's really quite a variety here represented in terms of topics and in terms of approaches hopefully by the end of it we'll have if not a clearer view of how bipedality evolved at least a more complete or complex view without further ado I'm going to invite our next speaker our first speaker to come up Steve Churchill from Duke University who's going to talk about pelvic architecture of Australopithecus sediba and Jesus Homo thank you Chris so as the co-chair of the of the symposium I also want to extend a welcome to you I think we're going to have a fantastic afternoon of talks I want to kick things off by talking about pelvic architecture and if you look at the last four and a half million years of the evolution of the human pelvis I think all paleoanthropologists would would agree that you see some major architecture architectural changes here which reflect an improvement in the ability of this structure to engage in bipedal locomotion so you know most notably the pelvis gets shorter from top to bottom the iliac blades or hip blades become more flaring and more lateral so everybody would agree this is probably about bipedalism but that's really where the the agreement ends and when you get down to the differences between the australopiths like Lucy as a group here's a reconstruction of Lucy's pelvis and members of the genus Homo whether it's early homo like Homo erectus or later homo like us there are some major structural changes here and there's not very much agreement about what those changes mean so for instance in the pelvis of the genus Homo you find that the hip blades are more vertically oriented they're they're more curved the birth canal is rounder and larger the pelvis itself is more robust its stouter the the pubic bones are more upturned the the ischium in the back of the pelvis is shorter so what are these these differences between Australopithecus homo mean well Chris talked about the fact that there are sort of two major views of locomotion in the australopiths and depending on which of those two views you subscribe to depends on how you interpret these changes in the pelvis from the australopiths to the genus Homo so by one model which we might call the arboreal model the australopiths were for sure they were bipeds when they were on the ground but the argument is that they didn't spend all of their time on the ground that they were still climbing trees maybe to get away from carnivores this guy looks like he's not doing too good a job of that but to get away from carnivores or they're sleeping up in the trees or they're going up there after food resources and they're feeding up there or whatever but for some reason it's important to their adaptation that they're still climbing and because they're still climbing they're spending some of their time on the ground some other time on the trees they've got to have a locomotor skeleton which is competent at both of those things and therefore there have to be compromises that are made so according to this model lucy and other australopiths basically selection was constrained to the extent to which it could could improve their skeleton for bipedalism because they had to be competent climbers and because of this it's been suggested that when they did walk to rest early they walked with a different kinematic gait that they probably walked more like a chimpanzee walks bipedally with a flexed a partially flexed hip and a flexed knee so the argument goes that with the origins of the genus Homo like this early Homo erectus skeleton from Africa that the genus Homo was fully terrestrial and now this constraint is lifted and now selection really can fine-tune the skeleton for bipedal locomotion we get changes in the pelvis and other changes in the lower limb and our kind of bipedal ism full striding bipedalism on an extended hip and an extended knee comes about so by this model that would explain the differences in the pelvis between these two groups and then as Chris said there's also some scientists who think no Lucy was a dedicated terrestrial biped the amount of time that she spent the trees was minimal and in fact the adaptations of her lower limb for bipedal locomotion kind of ruined her for climbing the the changes down here made her an incompetent climber and so we're looking at a fully terrestrial animal here so then the question becomes well why does the hip change and in fact it's been suggested that Lucy was not only a good biped but she was a better biped than us that her pelvis is better adapted for bipedalism than ours and that should always sort of raise a question for people because why should selection ever favor the worsening of a structure for the job that it's intended to do well the argument goes that the the difference is between the the pelvis of these australopiths and our pelvis has not to do with locomotor changes but with the fact that brains got big in the genus Homo and we have to pass I say we but fortunately I don't actually have to do this but some of us in here have have done this have got to pass a large brain baby through this bony bony birth canal and so in order to accomplish that as brains expanded in the genus Homo the hip blades had to be moved or the hip joints had to be moved farther and farther apart and there was some sort of constraint operating on the total width of the pelvis and so that requires an architectural change overall in the pelvis so according to Owen Lovejoy who's the major proponent of this model the differences in the pelvis between Australopithecus homo aren't about locomotion they're about big brain babies and the architectural changes that you need to accomplish that in a couple of papers Lovejoy actually laid out a model explaining how these changes came about and he basically said there are three large scale architectural changes that occurred going from Australopithecus to the genus Homo the first is that the birth canal got rounder the second is that it got larger and the third is that there was an upward rotation of the pubis in the front of the pelvis a downward rotation of the ischium in the back of the pelvis in order to increase space in the birth canal and then he said that because of the way that the pelvis develops to to get these kinds of architectural changes you're going to get some second very changes the the pubic ramus in front becomes shorter the iliac blades have got to become more vertical and less laterally flared these features called iliac pillars sort of changed position and become more robust I'll talk about those in a second the the ilium itself the upper part of the pelvis becomes more robust and the ischium shortens all as developmental consequences of these major architectural changes well we have some new specimens from South Africa which shed a little bit of light on this question of was it a locomotor shift or was it some sort of obstetric shift that explains the differences in the pelvis of these two groups this is a new species of Australopithecus Australopithecus sediba from a site called malapa outside of Johannesburg we have two partial skeletons this is MH one he's a sub-adult male he's the type specimen of the the species this is MH to an adult female she's the para type and they're about 1.98 million years old which is a really interesting time because that's around the time that the last australopiths are disappearing from the fossil record and early members of the genus Homo are starting to become more abundant in the fossil record and as you can see we've got some pelvic remains from both of these individuals represented when we announced the species a year ago all we had reports of the juvenile male pelvis we had the left hip blade and ischium and we had a portion of the right hip blade but even with those parts we could tell that there were a number of derived features of Homo like features in the pelvis that were more similar to what we saw in things like Homo erectus than they were to what we saw in other australopiths like Lucy or like STS 14 which represents Australopithecus africanus from South Africa so we're starting to see some of these features and some of the things that Lovejoy had argued were a function of large brains in this australopith but what's interesting is this is a small brain species the juvenile male has a brain size of about 420 pick centimeters he's almost a dolt so if the brain were to get bigger it wouldn't get much bigger and that's on the low end of the range for australopiths so we're seeing these changes before brain size expansion and that suggested to us that there was something wrong with the obstetric model now you can say well this is a juvenile male it's a male to juvenile what would an adult female look like well about a month after we announced the species we began to recover parts of the female's pelvis we actually had the pubis at the time that we announced the species but we found her hip the upper part of her hip laid the ilium and we found her sacrum and that allowed us to reconstruct half of her pelvis which we could then mirror image now there is unfortunately the anterior part of the hip blade is missing and that required a little bit of interpretation but we had some nice curvatures there that we could work with to kind of guide the reconstruction and here's her reconstructed pelvis mirror image this is a virtual reconstruction of the South African STS 14 australopiths pesum on and here's mh1 the juvenile male we reconstructed him - although we have a lot less to work with and so we're not as confident in the reconstruction of him but you can see that there are some real architectural differences here between sediba and Australopithecus africanus the same would be true if I put Lucy's pelvis up there and again this is a small brained species so here's a chart with some of the obstetric diameters and other diameters this column is mh2 from malapa this is that africanus specimen STS 14 here's a reconstruction of Lucy's pelvis and this is a specimen from Ghana Theo Pia which has been attributed to Homo erectus but it's it's taxonomic placement isn't a hundred percent certain and I just want to point out two things the first is if we take the ratio of the width across the hip blades relative to the width between the hip joints this small number in sediba relative to the Australopithecus an indication of how vertically set those hip hip blades are and the second thing is highlighted in yellow here is just the ratio between the diameters of the the pelvic Inlet in two directions and this this number here tells you relative to Lucy that this is a rounder birth canal than we find in Lucy Lucy's is very oval and long from side to side but the same is true of this Africana specimen from east africa and this isn't as round as you get in later homo but it is certainly a rounder birth canal now this is a the iliac angle which is the measure between the the pubic ramus here and the front of the iliac blade here and you can see in the genus Homo that the angle tends to be relatively small both because the pubic symphysis is superior oriented and because the iliac blades are fairly vertical when you get to the australopiths here's leucine here's SDS 14 that angle tends to be fairly open because the pubic ramus are horizontal and the iliac blades are more flaring here's MH 2 this is a Neanderthal which is like other homo and you can see that MH 2 has got an iliac angle which is lower than what we're seeing in in the australopiths and it's still high for what we tend to see in in modern humans but certainly within the range of variation of modern humans I mentioned that iliac pillar in MH 1 we see a very homo like iliac pillar at least in some respects it's a very distinct iliac pillar whereas an MH 2 it looks much more like the australopith condition it's an indistinct pillar seems to be very anteriorly positioned so there's some variation here where one of them looks a bit more homo like the other looks very primitive very Australopithecus going on with that and then I also mentioned that one of the things the secondary changes is an increase in the robusticity of the the pelvis and this is just a measure of the stoutness of this area right here where loads are transferred from the sacroiliac joint to the hip joint and what you can see is that members of the genus Homo whether they're modern humans or archaic humans like Homo erectus and Neanderthals tend to have a very thick very robust area here you can tell also that this area is shortened relative to what you see in Lucy and this is despite the fact that mh1 is a little bit larger in body size than than Lucy Australopithecus Oort of Grass Isle area and again both of our our hominins from malapa fall with the modern humans rather than or with the genus Homo rather than with the australopiths and then the last feature that I'm going to talk about is this little groove or sulcus right here between the hip joint and the the ischial tuberosity in the genus Homo it tends to be a very narrow groove so what we've done here is we've simply divided it by the diameter of the hip joint to control for body size and you can see in modern humans and archaic humans that it tends to be a very very narrow groove relative to body size in the australopiths it tends to be very large long groove and that's a reflection of the the reduction in the size of the ischium the lower part of the pelvis in the genus Homo and again the our single specimen mh1 from malapa we can evaluate this in again it looks like homo rather than like Australopithecus and this is just to illustrate this feature here are two specimens of Australopithecus afarensis from had our and you can see this this sort of great distance here between the hip joint and the ischial tuberosity and here's mh1 these have all been scaled to the same size and here's mh1 to show you how much narrower this this groove is now again you can say well he's a juvenile and who knows maybe with a couple additional years of growth the ischium would really really grow and this sulcus would become a lot larger well in response to that I can show you a juvenile Australopithecus africanus specimen from mock upon Scott M LD eight this individual is of a much younger developmental age than MH one and the groove so here's the bottom of the acetabulum here and here's the top of the ischium here this this sulcus is actually already absolutely larger than it is in nm h1 so I don't think this is a developmental thing I think the ischium really is shorter in M h1 so going back to these things which are argued to be about brain size expansion in Australopithecus sediba we are seeing a rounder birth canal we are not yet seeing an increase in the absolute diameters of the birth canal we are seeing an upward rotation of the pubis unfortunately we don't have the the parts that we need in order to tell whether we've got the downward rotation of the issue so that remains an open question with respect to the secondary changes we are not seeing a reduction in the length of the superior pubic ramus it's still very australopith but we are seeing more vertical and less laterally flared iliac blades we are seeing sort of what appears to be a more robust iliac pillar in one specimen but not the other so that's variable so again we don't know what to make of that we are definitely seeing greater robusticity of the ileum and we are seeing this reduced distance from the acetabulum to the ischial tuberosity so to me it really seems like the obstetric model seems to be problematic we're seeing a lot of these changes which are argued to be the function of brain size expansion and the need to enlarge the birth canal in a species which has got a small adult brain size now does that mean that the arboreal model is correct it doesn't de-facto mean that the arboreal model is right it simply means that there's there's a problem with this obstetric explanation for the differences between Australopithecus and Homo however to my way of thinking it's sort of hard to to imagine why we're seeing these changes in the pelvis if it doesn't reflect uh some sort of change in the way that the pelvis is bearing loads and operating during locomotion to me it suggests that there is some sort of kinematic shift going on thank you our next speaker is dr. Jeremy's de Silva from Boston University who is going to talk about Foot and Ankle diversity in Australopithecus well thank you all very much for the invitation to come here and speak I'd like to move the conversation south a bit from the pelvis down to the foot and talk about as Chris said foot Knakal diversity in Australopithecus it really does need saying that there is no other mammal on earth that walks quite the way we do so of course scientists have tried to figure this out when did upright walking evolve why did it evolve and how how have we acquired our bipedal adaptations and central to this argument as Chris and Steve have pointed out has been the genus Australopithecus Australopithecus lived in Africa from two to four million years ago you've already been introduced to it Lucy the new specimens of Australopithecus sediba from malapa caves which I'll discuss at the very end of my talk and again as Chris and Steve already nicely laid out for me there have been a number of different hypotheses to explain the locomotion in these creatures the first is that they watched walked with a crouched gait what some called the the groucho gait the bent hip the bent knee and that they had not yet acquired full upright striding bipedalism like you see in humans today others interpret the very same fossils differently that these were capable upright walkers and that human-like bipedalism has deep roots in our in our past and others say it depends on the species you're talking about that there might actually be a mosaic or different ways of moving on two legs throughout the past I'd like to examine these three ideas from the point of view of the foot the human foot is strikingly different from the foot of our ape relatives there are a number of differences but in in my view these are the biggies apes have a very very small heel they have an ankle that's well adapted for climbing they have a flexible mid foot something called the mid tarsal break that I'll talk about in just a moment and they have a big toe that can they can grasp with in stark contrast humans have a large heel to deal with the forces of heel strike during upright walking we have an ankle well adapted for walking for climbing we have a stiff mid foot that allows us some propulsion rather than grasping abilities in our mid foot and we have a big toe in line with the other toes well how did this all happen that's of course the million-dollar question and what do we rely on to figure this out well we look at fossils we relied very heavily on fossils but unfortunately for those of us that study fossil feet there have been very very few fossil foot pounds over 50 years ago Louis Leakey working in Olduvai Gorge made a pretty phenomenal discovery a partial foot of a single individual this is the very famous ator although I hominid 8 foot which consists of all of the left foot - the heel and the toes and over the course of the next 50 years a whole lot of people have had a whole lot to say about this foot if I miss your name I apologize well if you wanted to study foot evolution this is pretty much the only game in town for a long time I've even throw my hat in the ring recently as well and you would think that with such a complete foot there would be some consensus and there's not we can't agree as a field what species this foot belongs to we can't agree whether it's an adult or juvenile I happen to think this is in the foot of an old female robust Australopithecus something it's the foot of a juvenile Homo habilis we can't agree on the function of this foot so we desperately need more foot fossils I suppose well researchers working in these East African deposits 2 million years old or so have made extraordinary discoveries these partial skulls illustrated here are just a few of what was found but the foot bones found in those very same deposits could fit into the palm of your hand very very few foot bones found from Olduvai Gorge and from Koobi fora Don Johanson working in 3 million year old sediments had our well he had a little bit more luck I suppose he found Lucy but he also found many fossilized foot pounds including this partial foot skeleton shown on the on the lower right right here shown as that I'm going to refer to as the hat our foot ha but the paleoanthropology oh gods can be cruel sometimes what is preserved of the hat our foot is not preserved of the each foot and vice versa and so one cannot infer the remaining anatomy of one foot from the other unfortunately these bones as well are from different species and from things that lived over a million years apart in time now fortunately during those very same years Mary Leakey and colleagues on earth this really extraordinary set of track put prints of an early species of human that lived over three and a half million years ago the Laetoli footprints I'll return to these in a moment now as extraordinary as these are and they certainly are extraordinary it sure would be nice to know more about the skeleton of the foot that made this that would fit into this slipper if you will so of course in the 1970s and 80s researchers continue to look for these fossilized bones and they found remarkable partial skeletons Lucy shown on the left there and the one and a half million year old juvenile Homo erectus from Mary kotomi shown on the right but what I'll point out to you is no feet or very few feet Lucy has three foot bones of the fifty-two she would have had in life and then Erika Tom a skeleton preserves maybe one there's one that could be first metatarsal in fact the most complete foot of any partial skeleton found into up into the mid-1990s in East Africa is this eight bones of a very fragmentary Homo erectus skeleton that has been unceremoniously named K and M ER 803 very little has been done with this foot by the way it's actually a lot more interesting than I think I'm presenting as it here now the other window into human evolution is South Africa of course but it is fared no better in our quest for understanding foot evolution great skulls even a couple of partial skeletons but again no feet now there are plenty of foot bones that have been recovered from South Africa but these are isolated finds almost all are from different individuals many of which probably from different species call me crazy but I like to think that in order to really understand foot evolution we need feet not just isolated foot bones but of course you work with what you have and I do believe that every fossil no no matter how small or how fragmentary how isolated has an interesting story to tell I also really think that every fossil deserves to have its story told so we do work with these fossilized bones usually asking the question whether the more human-like or more ape-like in the ways that are functionally relevant so we can return to that list again as we already mentioned humans and apes a very very different fee so what about Australopithecus are they more human-like or they more ape-like for these particular characters or they somewhere in between the two or do we see a mosaic with some being more human-like and others being more ape-like well let's start with that large heel unfortunately once again very few heel heel bones calcaneal but there are a couple from Hadar and these fall well within the human range of distribution for the size of their heel these are big heel striking individuals in my opinion so we can check that I believe in the human column although it'd be nice to have a few more what about the ankle now well some of my research has looked into how the ankle is adapted for climbing in non-human Apes so here's a chimpanzee climbing a tree Figo's and what really struck me when these guys were climbing is not that they climb backwards but that they had an incredible range of flexion at the ankle joint they could flex their ankle about 45 degrees when they were climbing so pretty much they could take the top of their foot and shove it up against their shin that's pretty remarkable next slide if I did that you'd be driving me to the hospital right now now notice that this is going to leave its effect on the butt on the bones this is the ankle from the point of view of the foot on the left is action pansy on the right is a human and notice that humans have a very square shaped ankle joint chimpanzees and contrast have a trapezoid shaped joint and this helps with the the forces of climbing on a highly flexed foot notice is well illustrated with the red arrows here something called the medial malleolus that's the chunk of bone on the inside of your ankle in Apes it's quite large in humans it's quite small and this I thought was reflecting climbing on a twisted in or inverted foot okay what about Australopithecus well we've got four ankles from Australopithecus and early members of genus Homo and they're all strikingly human-like they all have a square-shaped ankle joint and in a reasonably thin medial malleolus I think Australopithecus ankles are well adapted for walking now what this means to me is that if they were still climbing trees which many people suspect that they were as we've heard about they weren't doing it like any modern ape climbs so what about the mid foot region now this stiff mid foot that humans have versus the mobile mid foot you see in Apes this is something called the mid tarsal break when Apes lift their heel they establish a new fulcrum right in the middle of their foot they have a floppy foot they can kind of fold their foot in half humans don't have this at all we have a very stiff rigid mid foot because we have ligaments in the bottom of the foot that present and prevent this and we also have bones that lock together that produce a very rigid bottom of the foot so how can we tell about Australopithecus whether they had a rigid foot or not well one of the bones that indicates to us that an animal has a rigid Midford or not is the bone that's illustrated here this is called the more this is the fourth metatarsal and the base of the fourth metatarsal and animals that have mid foot mobility and can kind of flip fold their foot in half have a very convex or curved fourth metatarsal base humans in contrast have a very flat fourth metatarsal base there are now four Australopithecus fourth metatarsal 's and they all look strikingly human-like they're not halfway between human and ape they're quite human-like for this particular character so it suggests to me that they didn't have a floppy foot mid foot either now finally while some would certainly disagree with me on this one I interpret the very few isolated foot bones that we have that are relevant to the question of whether there was a grasping big toe or not in Australopithecus as strong evidence that they did not have a grasping big toe and central to this issue of the footprints the Laetoli footprints that show at least in my opinion prominent heel strike the lack of mid foot flexibility and a big toe in line with the others and there been two recent studies pretty sophisticated analyses looking at these Laetoli footprints suggesting that they walked whoever made these walked with a very human-like gait now I'm not arguing that Australopithecus walked exactly like you and I do their foot bones were not exactly like yours in mine they had longer more curved toes than we did and they had a little more mobility in certain joints of their feet so why well they may very well have still been climbing trees to some degree maybe they were building night nests especially to stay away from those predators or perhaps the infant's had more grasping ability to hold on to their moms prior to the invention of strollers and baby Bjorn's that may been a really important driving factor here so central to the to the argument of course are these australopithecines getting at the question of whether there was more of a gradual evolutionary change in upright walking or whether these things were good obligate upright right walkers and as you can probably tell at least from the point of view of the foot and the ankle I tend to support this middle hypothesis that these things were quite good upright walkers however this was all based on those isolated foot bones it would be really nice again to have some feet with associated skeletons and again right up until the mid-1990s all we had were these isolated foot bones and then and then the floodgates opened first little foot little foot was discovered in South Africa and announced in 1995 it's a nearly three million year old Australopithecus partial skeleton remarkable specimen it was originally published in 1995 as possessing a grasping toe grasping big toe and certainly if you only have these four bones you can arrange these in a way that suggests that there is a grasping big toe there are more bones that have been found and when they fit in like a puzzle piece the first toe and the second toe right in line with each other I don't think this thing had a grasping toe at least in my judgment it refutes the hypothesis of a grasping big toe in little foot but this thing did have a grasping big toe Ardipithecus ramidus a four and a half million year old skeleton from Ethiopia a remarkable specimen living a million years prior to Lucy showing a just amazing foot skeleton in attach to a partial skeleton of this female art epatha kiss in the year 2000 the suraíh limbs again found the skeleton of a three-year-old female Australopithecus afarensis the de Keiko child a magnificent specimen quite complete and she has a foot and this foot here is shown as it was published in 2006 still within its matrix it has now been fully prepped out and I can assure you it is absolutely magnificent the Dmanisi fossils from the former Soviet republic of Georgia 1.8 million years old which means we finally know a little bit more about what the foot of Homo erectus looks like and on the island of Flores the feet of the puzzling Homo floresiensis found an association with this really unusual and amazing skeleton lb-1 of a female hobbit so in just 15 years we've gone from having essentially no skeletons with associated feet to having five and now six and seven the specimens from malapa South Africa have feet associated with their skeletons and these are bound to get more complete as more and more fossil material is pulled from this cave site but as exciting as these new skeletons are and they certainly are incredibly exciting we already know what the foot of Australopithecus looks like right it has a large heel and ankle adapted for walking a stiff mid foot for propulsion and it's big toe in line with the other digits so we already know what the foot of Australopithecus sediba should look like and plus these are only two million years old and as Steve already illustrated in many ways these look more human-like than than than previous australopithecines so if anything these feet should look more like yours in mind and they don't they don't at all first the heel the Australopithecus sediba heel is incredibly small and it has this hook like beak on the bottom quite reminiscent of what we see in a chimpanzee what we see in a gorilla this does not have a big large heel that you see in things that live a million years prior to this what about the ankle remember humans have a square-shaped ankle joint in a thin medial malleolus a chunk of bone in the inside of your foot as all australopithecines do as well except for sediba which has a square-shaped ankle joint and this incredibly thick medial malleolus so it's human-like in one respect but then quite ape-like in the thickness of the medial malleolus suggesting it was climbing with a bit of an inverted foot this hasn't been published yet but I'm really excited about this the stiff mid-foot that we discussed that you see in Australopithecus they align themselves with humans is not found in Australopithecus sediba it tends to have a convex or at least the specimen has a convex base suggesting quite a bit of mid foot mobility in this particular species we don't know about the big toe yet but for all of the features that we said Australopithecus was a human like this foot is not it's decidedly not at all so this suggests to me that the hominids from malapa could not possibly be walking in the same way that humans walk today and probably was not walking in the same way that earlier australopithecines or even australopithecines living at the same time we're walking either unfortunately we don't just have the foot but there's the the hip as you heard about and there's the knee and and soon we're going to present a hypothesis for how we think this thing was actually moving around its landscape so what does this all mean well it suggested me two things first the malapa hominids demonstrate two steel line from a colleague of ours Bruce Latimer who's a foot guy he said impress recently that based on these fossils there is more than one way to skin the bipedal cat and I think he's probably right that the sediba material and the other material of australopithecines suggests that there must have been different ways at least two different ways of moving around between 2 and 4 million years ago and second I'm going to end on this note perhaps I'm being a little overly optimistic here but I like to think that we're entering a golden age of paleoanthropology isolated bones are wonderful and they're really really important but for the first time we have the opportunity to study not just isolated bones but partial skeletons not just a few of them but seven of them now we've got RT and the Dmanisi fossils and littlefoot and the de child and the hobbit from Flores and now the Australopithecus sediba material and they're certain to be more that's going to be discovered and going to be published soon this is a really exciting time for our field a time when we're going to be able to answer some of the old questions that we've had but we're going to be able to generate a whole barrage of new questions that we never even thought to ask prior to having these in hand this is going to be a lot of fun thank you all very much my next speaker is Matt door cherry from Smithsonian Institution and he's going to talk about insights into hominin bipedalism from gorilla anatomy hi how is everybody doing here today I'm really excited to be here so why gorillas why am I talking about gorillas well as humans so we all know we like to study ourselves and so we we seem to know an incredible amount about our own evolutionary history and some of the faces and skeleton and body shapes and body sizes that are in our own evolutionary family but you know too bad if you're an African ape or a gorilla because if there were any gorillas sitting in the audience today they probably wouldn't be too impressed because all we really have are possibly about 3 teeth that might represent a 10 million year old gorilla ancestor and so I think if if there were guerrillas in the audience here and in particular silverback we'd probably hear something like which is their throat growl to basically get other members of their group in line and stepping up to it and so I think we'd be hearing something like that in terms to pull up our socks and start looking at what we have in extant groups a little bit more carefully because they're not all the same and they're not just we can't just lump them together and I think in terms of what Jeremy was just talking about I think we have a lot to learn from them still and one of the reasons why this is interesting is because we've actually known for a long time that there are differences among different gorillas and this goes all the way back to the 1930s when the great primate anatomist and anthropologist Adolph Schultz published this paper on differences in between mountain gorillas and Western gorillas now mountain gorillas live in high-altitude habitats and Schultz knew this whereas Western gorillas lived down near the coast or in lowland forests so you have very different ecological habitats but what Schultz was so excited about was that he seemed to see that in mountain gorillas that there their big toe was more in line entirely human-like and he certainly didn't make that argument but in comparison to the other great apes and particularly other gorillas they were more reminiscent they were approaching what we see in humans and you can see that here where he was illustrating these are mountain gorillas on the top and these are Western gorillas and he made a lot of he highlighted the fact that the toe lengths were different you had lots of things going on and in particular again this this big Alex being slightly more in line with the other with the other toes now we've come a long way since Shultz and we know a lot more about the different habitats and the ecology the ecological habitats that these gorillas inhabit we also know that they don't just grade from one end to the other in terms of their their habitat structure they are separated and this they have been separated for long periods of time and as an example we have Western gorillas here which are known as gorilla gorilla and Eastern gorillas over here and they're separated by quite an expanse not to mention the Congo River which is a not an easy barrier to cross but as you go from these Western gorillas that are in lowland habitats we have these Eastern gorillas that some inhabit strictly Highland habitats which is the mountain gorillas but then you also have growl gorillas which used to be known as eastern lowland gorillas but they inhabit both the highland area of East Central Africa here as well that they've expanded out into this huge lowland forest area and that's all happened fairly recently which makes them very interesting as models to look at how differences in these ecological habitats and in particular trees you know how big are the trees are their fruits and that sort of thing how these things can influence the morphology in terms of you know no one would argue that they're all terrestrial knuckle walkers just like we probably don't argue that all hominins aside from say Ardipithecus are bipeds but they do differ subtly in the frequencies of our boreal 'ti and maybe there's something that we can see in the skeleton of gorillas now earlier this year I know you've all read this I'm sure everyone's already read this paper but no as a musician I know you know you you write a song you make an album you still got to go out and push it so I am pushing this one a little bit this is a paper myself and my colleagues published earlier this year in Journal of human evolution where we tried to re-examine what Shultz had did now this is actually from Shultz his original publication and this was his entire sample where he tried to look at the medial cuneiform which is the bone at the base of your big toe and he tried to look at the angles of that relationship to see whether or not their toe was more like ours and more in front and in line with the other feet or was it more diverged right and so I had developed a series of techniques doing my dissertation to look at morphology and wrist bones that seemed to be perfect to looking at this because what we do is we basically are able to fit planes to three-dimensional models that we acquire from from scanning technologies and we can begin to quantify these ways in very easily and we can look at the distribution of these features and so it's very technical you you get a scan model and then you color in the lines I learned this in kindergarten I think I finally was able to do it by about grade four some of you probably could do it a lot earlier and and this is what we do we we take the three-dimensional models and we just color in the articular surfaces and this does provide a little bit of slop because we might all color them in a slightly different way but generally it has little effect on the quantitative metrics that we're looking at and we're able to fit planes and things like that to the surfaces and get a very very easily quantify how these facets how these articulations are oriented relative to another as well as sort of their relative size and curvatures so what's really fascinating is if we look at this bone at the base of the hallux that has a big impact on whether our big toe is more divergent or more in line with the other toes what we see is very interesting where we have these Eastern gorillas in this case mountain and growl our grill is over here and then we have Western gorillas as the black triangles and then the x's and the o's are chimpanzees so what we can see is that Western gorillas like chimpanzees and bonobos actually have a more divergent big toe right which is not unsurprising because we know that they live in more forested habitats then these Eastern gorillas that live in these Highland habitats now initially I thought we were expecting to see a little bit more variation here because perhaps growler gorillas were going to be somewhat in between because they inhabit both Highland and lowland habitats but I never get it right the first time and I and I screwed up because when I went back and then looked you know at the time when we started this I didn't really know that much about gorillas and it turned out that almost all of these gorillas are highland growl gorillas and so I got back on the plane and I I went back over to Europe and I hunted down as many lowland growl gorilla skeletons as I could find and just to give you a little tease of how exciting I think this is here are some of the three variables that really distinguish between the the gorillas and chimps I showed you on the previous slide and what's really fascinating is the lowland growl gorillas are beginning to show similarities with the western lowland growers and so even though this change is very recent because we know from genetic and other morphological data that eastern and western gorillas began diverging somewhere between a million and a million and a half years ago and there's been low levels of gene flow up until probably even the last twenty to fifty thousand years right but we've had these Highland gorillas diverging in this respect and yet now as broward gorillas became separated from mountain gorillas probably around 20,000 years ago it's only within the last ten thousand years that forests have returned in this part of Africa and crept up and made connections to these Highland habitats so Grauer lowland growl gorillas have basically expanded and and dispersed into this area within the last ten thousand years and we're already beginning to pick up these subtle variations related to grasping because they're climbing more and they're going after more fruits now so I even I just want to tell a quick story because I'm fascinated by this and unfortunately we don't have a lot of these lowland ours skeletons in the world and so I even made a trip to Rwanda to then try and cross the border to get into Goma and write down Leakey vu and go into here just a few months ago and unfortunately because I'm Canadian there's been a bit of a diplomatic spat or something going on and so Canadians can't get entry visas into Rwanda very easily and even though I had a visa to go into DRC the Rwandan said well no you've already entered Rwanda we may not let you back in and so I was kind of stuck because my departing flight was going to be from Rwanda so I didn't get in to the DRC to look at more lowland growers but I will trust me so instead I've started to look at some other bones and one I think that's very important as Jeremy touched on is is the tailless because it can help tell us whether you have more of an inverted set to the foot where the sole is more oriented like this or a more even it set where it's more like an us where it's straight underneath our knees and again Eastern gorillas have been kind of ignored in this respect and here's an example of what a Western gorilla or a chimp for instance tailless looks like and so here you can see it's very uneven and more curved this is a inverted set to the foot well this is a mountain gorilla okay and you can see the the rims on both sides are very even and you're getting a much flatter surface right this is very much looks a lot more human-like for those of you that know this morphology what's also interesting you may note that Eastern gorillas seemed to have slightly higher degree of torsion of the of the Taylor head which is also more human-like you can also see that a little bit in this specimen so we can take these these bones and again by doing the color in the lines method we can then export the surfaces and fit quadratic equations to them to try and quantify the curvature in a way that's replicable and so what's really fascinating I think is that we can see that hey Western gorillas are far more curved than our mountain gorillas okay and also you may also note that when you change the relative height over here this whole lateral side of the foot gets bigger okay so we can use that facet that articulates with the fibula and also we can see that that facet is getting larger is larger in western gorillas than it is in mountain gorillas now I know I'm excited enough already but it gets even better because when you look at grauer gorillas you can see that lowland Grauer gorillas are beginning to diverge from the Highlander hours even though you know these are still connected biologically but as humans have gone in there in the several last few hundred years you know they're there those corridors are getting less and less but because the lowland growers have expanded into thousands of gorillas over the past 10,000 years Highland growers have been more restricted they haven't increased in numbers but I think that increase in numbers coupled with the different habitats you're beginning to see selection tinker with this morphology now what's fascinating is you can see in terms of that lateral side they look like they're doing it a slightly different way than how Western gorillas have done it relative to mountain gorillas in general and that these two features aren't always going together but you can begin to tweak the anatomy not because they're no longer terrestrial but because the frequency of their or boreal behaviors is going up and so when you just look at these two variables never mind a multivariate analysis getting all fancy just curvature of the trochlea on the x axis and the relative size of the fibular facet on the lateral side you can see Eastern gorillas particularly the Highland growers and the mountain gorillas over here Western gorillas the triangles way up here and lowland growers beginning to invade that morphological ecological space that is shared with Western gorillas so again why I think this is so fascinating and relevant to our discussions about the evolution of hominin bipedality is because gorillas are still here we know what they look like we can get their genetics we know how they're related you know there's still a lot to work out on how that that's all happened over the past several hundred thousand years but we have a good enough idea and the fact that we agree that they're all terrestrial knuckle walkers I mean maybe they do not go walk a little bit differently from one another but I don't think we need to say that the different ways that hominins walk bipedally probably weren't all that different at least in the sense that when we look at it we might want to look at how ecology and how the paleo ecology and the paleo environment may be sort of obscuring and giving us some noise when we look at these more this morphology because if we can see it in gorillas at least over the last million years in terms of Eastern versus Western but when we can begin to pick it up within something that has likely occurred only within the past five to ten thousand years I think it's really exciting to see how morphology can be tweaked along an ecological morphic line and I doubt that hominins are any different now I borrowed Jeremie slide from the the sediba paper to highlight this and so I hope I hope you don't mind but I I I thought this slide really illustrates it well and this was in the supplementary material of their paper showing a number of hominin tailai and noting that hey there's tremendous variation in the torsion angle of the head which in part is related to when you look at these lateral and medial rims you have to orient them so they're in the same plane so when one is higher than the other it does kind of it influences this a little bit but in particular in the grooving of the trochlea again which relates to more pronounced or less pronounced curvature now we can throw our hands up in the air and say things like you know Taylor morphology is so variable it doesn't tell us anything or we can say you know what when we actually look across Apes and within Apes maybe there are signals there that tell us something about this now this is not saying you know just like I wouldn't argue that a an Eastern Western gorilla is not a terrestrial knuckle Walker but I might argue that hey you know what there's tweaking going on there that's related to a higher frequency of climbing and we may we may argue again you know based on this sort of gorilla model of whether or not it what its relevance is for looking at-at hominin bipedality because let's admit it bipedality is very different from knuckle-walking but at least they're both terrestrial and at the very least i know if there were a gorilla in the audience he'd probably say at least an encouraging so thank you very much you you

Channel: University of California Television (UCTV)

Views: 69,135

Rating: 4.7796144 out of 5

Keywords: Steven Churchill, Jeremy DeSilva, Matt Tocheri, bipedalism, evolution, hominid

Id: I2jo719D3Zw

Length: 58min 29sec (3509 seconds)

Published: Thu Feb 23 2012