CARTA: The Upright Ape: Bipedalism and Human Origins -Footprints Body Form and Locomotion

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 to 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 tacks 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 bike it ilysm must be at least the part of your local motor 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 home 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 great gait what kinds of variations in bipedal gait might we have where they're possible regressions to a less bipedal locomotive repertoire do different parts of the body all of at the same rate if you're becoming better a buy PA tality 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 groups I had our hominids the skeletons have been interpreted in very different ways in the past depending on which features you concentrate on certain features indicate and our boreal 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 our next talk is by Brian Richmond from George Washington University entitled Pleistocene footprints and the evolution of human bipedal ISM ok well thank you very much for the invitation I'd like to thank the members of Carta the organizers and D Churchill and Chris ruff and for all of you for coming today I'm following up on a number of good talks it's hard to follow an act like that but I wanted to to echo their sentiments that that the evolution of human gait has long been central to understanding of human origins and it's led to a conic images that are in the in the public today and even led to public commentary about where we are today or where we're headed I won't won't go into that today that's that's above my pay grade so but many of those reconstructions were initially based on at a time when we didn't have a very complete fossil record and as several speakers have noted that fossil record is growing and it's growing at an increasing pace which is really exciting for us and so at this point in time we have upwards of 20 or more species in the human fossil record that represent our ancestors and relatives and they're bound to be more especially down in this area so it's a very rich fossil record I'm not going to talk about all of that today but I'm going to point out that in addition to fairly maybe subtle variation among species we have at least several major transitions from well the jury is still out on what article is what the morphology means but certainly we have an increasing understanding of the anatomy of Australopithecus afarensis and now sediba as well that represents really interesting wrinkles in the evolution of anatomy and there's a at least at least one major transition people can agree on between australopithecines such as Australia's afarensis and africanus and what we see in early homo erectus and that occurs at a time indicated in orange when there were dramatic changes in the in the environment where east africa saw just a wholesale change towards much drier conditions and the first expansion of the first really true savanna grasslands the way we see today it probably had something to do with that transition but now the anatomy though has led to an immense amount of debate about what exactly was the gate like of early hominins and I think now the question has changed - what were early hominin gates like that they're they're bound to be these subtle variations as well but I would argue to that to really test these hypotheses that they're generated from the anatomy so we need some kind of evidence of past behavior one way we can look at that is look at the way bones respond to changes in exercise and that could give us some direct evidence of how individuals acted during their lifetime and we also have a few cases like like this where we have footprints in the ground those represent fossilized behavior that was something that was that records an event of the behavior of some individuals walking across that landscape it tells us about gait it's also led to some very creative and popular notions about what the what the social behavior might have been like if these early hominins so you'll note that here are three different reconstructions of this fossil trail and here the females walking in front the males I don't know if he's following or stalking her I'm not sure here we have the the male taking the lead to his pregnant partner and here they're walking an arm in arm-- which is very cute what's what's interesting though is these are all just I can't believe how fundamentally wrong there are because they are because if you look at the trails the one on the Left represents one individual if this was another individual it would be twice as big and if you look closely there are actually three different individuals making tracks in that track way so there are three of them walking behind each other and one walking to the side so none of these really have it quite right but certainly this is this was and still is a very exciting discovery that's still debated today but until recently we haven't had really anything to compare it to this this was a singular discovery and there wasn't there were there were not footprints from other species and other times to be able to compare to look at the evolution of of these kinds of fossilized behavior so what I'm going to briefly mention today is is our discovery of a new collection of footprints and what that is starting to tell us about the evolution of human gait so that takes us here to Eastern Africa to Kenya up here to Lake Turkana if we blow up this picture of Lake Turkana we're working right up here near the ethiopian border near a town called illa ret just right there and now the site looks something like this and we have we were digging at the site because we've been finding some fossil hominin arm bones and hand bones that would be for another talk but as we were digging here we ended up discovering something we didn't expect first let me point out that we're fortunate here in this part of East Africa to have a rich fossil deposit that's full of volcanic ashes so here's the volcano ash volcanic ash here in white there's another one here in gray can just seek outcropping there's another lighter one right up here so there's three volcanic ashes interbedded in this one hillside and we know from a lot of geological work that's been done in the area that those three represent the northern illa Allah Rhett and lower illa at tuff that have been dated to within about ten to fifteen thousand years of each other so it's remarkable that this whole hillside represents somewhere the vicinity of ten to fifteen thousand years of time one and a half million years ago so but this also complicates things having such a rich fossil record also means that at any one time there's more than one species living at that time and we know that one and a half million years ago at least four species were present in Africa and three of these species this parenthesis eaj Homo habilis and Homo erectus or early African Homo erectus they were all present in fact they're all three of those are known within a mile of the site so so we don't know which species are represented the site yet now what like draw your attention to is that we were we were down here excavating for fragments of a partial skeleton when some geologists were studying the hillside and I'm going to zoom in right here on this backpack and this picture here you see the backpack and you can see in cross-section this nice we see this nice sedimentary layer here and there's some sand with a little bit of cross bedding here there's another sort of muddy silty package and more sand and I'm not a geologist so I thought well that's really neat you know but my geologist colleagues who are studying this and a couple of them pointed out and he said you know this is really unusual to have this really irregular surface you know we don't know of any physical processes that would give you that those could be footprints like huh so what we did is we excavated laterally to the side and in this picture you can see this is where we were standing before and look this whole layer is just full of footprints which we wouldn't have this girl that discovered otherwise and here's why when fossils which are basically bones have turned into rocks when they finally emerge on the surface and weather out in the surface that they're there to be found so when you walk along looking for fossils you're looking for the things that have eroded out to the surface when a footprint erodes onto the surface it's just dirt so people don't go prospecting for footprints key you'll find them that way so once once we were clued into what were the kinds of interfaces of a basically a fine packed silt mud buried in sand if we knew we could find those combinations then there was a good chance that the sand had buried some kind of surface at that time so we started looking for that and in this one hillside we've now found upwards of twelve land surfaces with prints in them just in in nine meters within that ten ten fifteen thousand years and some of them have really exquisite preservation and we were fortunate enough I also thought when we found this is like well hominin fossils represents somewhere in the vicinity of 1% of the of the macro macro fauna and the fossil record so I was trying to imagine how much of the hill you'd have to dig till you find one person the one percent that represents hominins fortunately they happen to like this environment so we have lots of footprints of large birds like this thing that was probably a fossil stork we have fossil bavitz lots of them fossil hippos we also found some fossil hominin prints and here some of them with really exquisite anatomical detail like here you can see the big toe the second third fourth fifth toes as the foot sunk into the mud here's another one where you can really see all the toes nicely lined up and here's a nice little footprint so this is really exciting because it gives us a whole new a time period new line of inquiry to ask questions about in the fossil record so this is actually from a couple years ago but we've done more since then is we found at least two different layers in that one Hill hominin footprints in fact last summer we continued this trail on some more and we also continued this trail on some more this upper surface had a lot of hominin footprints in it again these represent these represent two different surfaces separated by five to ten thousand years in this particular instance so they're not the same individuals and same instance so what we did to record and analyze those is use a method called photogrammetry which it's nice and easy all you need is a camera although you also need shade which is not easy when you're near the equator in the desert in Africa so I have a team that that created shade forests for these pictures and what we do is take a whole repeated series of photos that overlap and just like your eye sees two images and interpolate that into three dimensions we did that with the photographs and so each purple box represents where the camera was when we took a picture and we get an entire land surface in two dimensions and we can even get it in three dimensions as well so and then we can do something like this where we have a hominin print here's a modern foot for scale here then you get you get a nice three-dimensional capture of that of that topography now what's exciting about that is that it not only gives us a nice color picture but it it actually it gives us contours where we can look at not just the shape of the outer outer contour of the print we can look at the the depths within a print and we we suspect that the depths or print are related to how you're mechanically using your foot on the substrate so here on this upper surface it's there's a lot of prints in here but here for example is a right foot print left right left right left right left and you can see here's the the 3d capture of that trail and we've done some things like look at some stride lengths and step lengths once we found these footprints we were also struck by how little data that we're out there on how to interpret footprints there hasn't been a lot of need to do that I think so we've we set up a hold experiment out in the field with local people who thankfully grew up without wearing shoes so we had some habitually unshod folks and we had them walk jog and run through mud palette and also on a pressure pad which measures your foot function as you land and try to look at things like speed and stature and foot length and so forth so with those modern footprints and with the fossil footprints we set about to measure anatomical landmarks now this is not the same thing as the foot itself because the same foot making a series of footprints will make slightly different footprints every time so one foot that doesn't change its shape much it can still make different kinds of footprints and that's what we're trying to do we think that the slop if you will the variation in different footprints turning gait that's a lot of the sorts of interesting information it's not it's not noise it's the signal so what we're trying to do is figure out what that signal is and how it varies with speed and how muddy it is and and also your gait how whether you walk with extended limbs or flexed limbs and so forth so we said about digitize some of the these landmarks and I'm just going to point out a few things that we found so far the first thing is these fossil footprints are big they are as big as most modern footprints and that's that's not quite what we expected based on based on fossils the best body size estimates of early Homo erectus or Prentice Boise or Homo habilis tend to be on the smaller side so these are really large prints and you can pair them to the typical Laetoli print so these are much larger individuals than what you see in an afro ANSYS we also looked at something that's of interest which is how how divergent is that big toe it's going to be a little bit different looking at bones you can look at how they might articulate but here's how they're actually functioning on a substrate and what we did is we simply measured that big toe and extrapolated it back to where intersected with the axis of the foot and we have two different modern groups one was the sample I showed you of those local - niche folks in Kenya another one was a set of holocene modern human prints now what we see is that the lie atole prints have a much more divergent toe now this is not as divergent as what you saw in some previous slides with chimpanzees or gorillas they would be out here so we don't think that I totally the the makers of the live totally prints had a grasping toe but there is evidence that there's more there's just still more of a gap between the big toe and other toes interestingly in three different surfaces we're seeing sort of an intermediate we're seeing a more or thing a toe more in line with the other toes but not completely we still don't know whether some of this might be due to variation in the mud type or something like that but it is it is interesting that maybe even hominins at one and a half million years ago didn't have a big toe that was quite as fully adducted or brought in line as as ours another measure of great interest is whether these hominids had have really well-developed longitudinal arch so what we did try to measure that is is measure the the broadest point on the ball of the foot which we show here and the narrowest point on the instep those with high arches tend to have a very narrow strip here a flat foot you'd see a lot of you see a lot of depression down here and what we found basically is in blue the lie atole prints for a given width of the ball of the foot they had a much broader instep meaning that there wasn't much of a list of tissue arch there and the green and grey represent our modern sample and the red represent one of the fossil samples interestingly one of the other layers we have a couple of individuals that have what looked like a much more primitive kind of arch shape it's possible we have two different species represented here again we can't tell what species the printmakers are yet but we're ideally we're going to find three different foot shapes that would be ideal I don't know if I can put that order in to the paleoanthropology gods or not actually my what I really want if I get to put one order in I really want one to walk along and then trip do a whole body plant you get a whole you know that's what I will be a true believer there but that's what I tell everyone I like please that's what I want that's facial expression to be great but ok we'll keep looking so finally one last thing we did too is that we wanted to see if the deepest point under the underneath the underneath the footprint where that was especially where that was under the ball of the foot so if we take a lie atole footprint and we warp it into one of these one and a half million year old prints one of the things we see is that this medial part of the foot moves over which reflecting that arch measurement and then the deepest point of the ball the foot moves towards the big toe that's interesting because that's one of the hallmarks about of the way we walk however as a caveat if we warp one of these one-and-a-half million old prints into a modern human prints it moves over even further and the arch moves over even further so we don't know whether this represents just different foot morphologies at this point or possibly differences in gait or substrate or what but what it does suggest the fact that this deepest point in the footprint that's something that that is typical of a human way of walking well we land on our heel like this the path of pressure goes along the outside of our foot and right near the end of our stance phase-in of our of our support we shift all that weight over to the big toe or towards the big toe and we push off and we propel ourselves and that's part of our efficient way of walking that makes our walking more efficient than that of other mammals apes tend to land on their heel the path of pressure goes along the outside of the foot but then they just lift their foot up they don't push in with with their the strongest tow their big toe so the fact that this this the deepest point is farther over towards the midline towards the medial side that suggests us that we're seeing this more modern type way of walking at one-and-a-half million years ago so here we are we we don't know yet whether that represents Homo erectus Homo habilis or boy Zi based just on the sheer size of the prints we don't we have no Homo habilis that are big enough to be good candidates right now would either be male paranthesis boy Zi or Homo erectus or both if if the footprints are indistinguishable it would suggest that the common ancestor of those had a foot morphology kind of like this so it's still early days because we we have a limited sample so far but I would say that the coup before formation is an enormous place full of exposures and we've already identified a half a dozen other sites kilometers away from our site where we have some kind of footprints of bavitz or something else so I think this is opening up it's really exciting it's opening up a whole new line of inquiry about looking at variation across landscapes and over time they can help answer some of these questions and test some of these models about how our early ancestors walked long ago so thank you very much and I'd like to thank you all for coming my next speaker is dr. Carol Ward from the University of Missouri talking about early hominid body form hello I'd like to thank also Chris and Steve and carta and the organizers for inviting us all here and enough of the feet already they're interesting but we're going to move things back north for a little while I'm going to talk about body form specifically the torso because that actually has quite a bit to say about how our ancestors may have moved and walked what I'm going to give you today is sort of the simplified view because I only have a little bit of time but I hope it gives you a sense that when we look at not just the limbs and the lower limbs and the feet that we tend to focus on it's really quite a bit more information we can put to the question about how our ancestors moved around now why do we really care actually how someone like Lucy here the poster child for human evolution moved around well this not only tells us about the origins of bipedality and the origins of hominids and the early evolution of hominins but also we have to remember that natural selection can only act on last year's model on the variation that's present so the more that we know about early hominins in their body form and their locomotion more we understand about the kind of natural selection are the kind of material selection had to work on to produce our genus Homo so it's a really important question and aren't you tired of seeing this diagram today we've been seeing this diagram since about 1973 when this article was published in Time Life and even though we put it up here we talked about it this is an iconic image and thank you very much dr. Richmond for stealing my joke we all have t-shirts things on the walls of our cubicles that parody this picture it's funny it's everywhere everyone I think in the country has seen this image or used it but it also plays into I think our perceptions and our ideals of actually how human evolution evolve you have these knuckle-walking creatures that slowly start standing up in a shuffling way and they move around and they finally get better and better at it until the or us today I think this colors a lot of the public perceptions of human evolution and I think it's in the back of our minds even as I it says we're looking at the fossil record because we have a feeling of this is kind of how it happened and I think there's time with the growing fossil record I think you've all seen here today we're getting a much better appreciation of variation a much more complete picture of the anatomy of all these different species of hominids that are live that maybe this picture although it makes a wickedly funny t-shirt is maybe something that we should stop paying so much attention to you so what I hope to talk about today is some of the evidence that's come to light in the last I don't know 10 20 30 years that really should make us question perhaps whether or not the earliest part of our lineage these australopithecines were in fact shuffling around like they are they have been since 1973 in this time life diagram and you wouldn't think that we'd have a whole lot to say about the torso in the body form of these creatures because vertebrae and ribs and things are fragmentary they don't preserve very well but in fact paleontologists have been dutifully out there in East Africa and South Africa finding fossils and we actually as you seen today have quite a number of skeletons which we can put to bear on the question of what these animals look like I'm going to talk to you today about really just the vertebral column pelvis and the torso here of most of these of Australopithecus afarensis and Africanness and even Homo erectus these fellows are too new and I haven't put them in my analysis but they're going to have a lot to say as well so we actually have some material to work with now when an animal stands upright like a human for example we have a particularly unique not just lower limb but by fidelity is manifest throughout our skeletons particularly in our vertebral column and if you look at the side view of human and a chimpanzee you see some notable differences in the spine chimpanzees are like your pick your favorite Quadra pet here the spine is evolved to be sort of a uniform arch structure with a series of vertebral bodies and they have a fairly even concave forwardly concave curvature to them when humans stand upright and this develops throughout our ontogeny from the beginning we've been to hold their head upright the beginning to sit upright and stand we have a series of sinusoidal curvatures in our spine that allows us to get our center of gravity up over our supporting limbs we don't walk found like this poor chimpanzee is here I was challenging my students to see you know you know like the spinal curves just try walking around for a couple of days like this come back on Monday and tell me how your back feels it doesn't work very well this is a very mechanically efficient way to balance our weight right over our supporting lower limbs and it's distinctive of humans we do not see these curvatures and other animals even trained monkeys that walk upright on two feet in the circuses and zoos and so forth so this is a distinguishing human feature so we might ask when we look back at those early Australopithecus skeletons did they have curvatures like this because that might tell us if they're standing upright or if they're shuffling in a bent-over posture so the vertebral column actually here is a series of wedge-shaped blocks and a lot of the curvatures come from stacking up a series of wedge-shaped blocks and there's other things involved too but in the thoracic or the rib bearing region this is the front of this person in the back the spine curves forward and these are wedge-shaped blocks that are shorter in the front than in the back in the lumbar or lower back region as well as in the neck the back of the vertebra is shorter than the front so we can measure this wedge shape of individual bones and say something about the curvature of the whole column put together so bear with me for a moment on this graph we can number the vertebra from the bottom up to the top and we can measure this wedge shape how short is this angle so this on this side positive numbers would have shorter in the front and on this side you'd have shorter in the back and you can put a chimpanzee on here and they wiggle around a little bit but all of their vertebrae are wedged forward because that's fine is curved forward all the way through the column you put a human on here and you see actually two peaks this is very distinctive of anterior wedging and then boom in the lower back this is where it hurts for those of you older people like myself the wedging is posterior and that gives you that backward curvature the cost of the problems now we can put some fossils on here here's our Homo erectus boy and there's not quite as complete but you can kind of imagine two peaks but sure enough in the lower lumbar region he's wedged we can put Lucy on here she doesn't have very many vertebrae but you sort of get a two peaks we can put a stroke because Africanness the dinked of two peaks and sure enough negative down in the bottom we can put another Australopithecus africanus negative in the bottom and if we slap them all on here at one time you can see all of them have the hint at these two distinctive peaks but notably they have this posterior wedging at the bottom so we can see that the distinctive human spinal curvatures are with us even as early as Australopithecus afarensis and based on these guys we don't seem to see a heck of a lot of variation in this pattern of curvatures so rather than thinking of these creatures as hunched over we can go back to our diagram and maybe put a big X through this portion of it they weren't probably hunched forward like this and they're actually when you walk with bent knees and bent hips if you walk around like this you will naturally lean forward and flatten out your curvatures when you're walking over bent knees and bent hips we've done a little bit of kinematic day that aren't quite ready to publish or show you yet but in fact we think this note suggests not only is your torso upright but your lower limbs would have been pretty well extended too so even in the beginning of our time life diagrams you got a fairly upright posture to the spine so that's something that we can learn about posture from the torso but if you look for example at the gorilla and the human here and you look at this region you see that they're pretty different and other speakers have alluded to this today the humans have the short distinctive pelvis we have a fairly long lumbar spine and a waist and the sort of barrel shaped ribcage and there's a real difference here so can we see anything about that when we look at these fossils on this picture I took from Leslie Aiello's paper it's a very nice diagram showing the chimp and the human you see this cone-shaped ribcage here in the chimp and a barrel shape and a human now the ribcage in the torso is made up of a whole lot of little bones put together and it's very you don't ever find them all laid there together in the fossil record so you have to try to make inferences from bits and pieces of the whole this is hard to do and again as other speakers have mentioned until recently we haven't had a lot of partial skeletons to work with so in the early 80s this was the reconstruction of Australopithecus that was made and I'll show you how it was done but you can see this rib shape here is very cone shaped and very much like an ape and particularly much like yours or mine there's another picture that reconstruction of Lucy this reconstruction was based on Lucy and the brown parts here in this reconstruction of the parts that are fossils in the white parts of the parts are kind of made up and you'll notice if you look at the ribcage as a heck of a lot of white parts so when this reconstruction was made there wasn't really a whole lot to go on and it was really the best game in town and it was going but this cone-shaped ribcage has had actually quite a lot of influence on our biological interpretations of our ancestors for more even than just locomotion if you imagine if you take your eye and you sort of connect the dots through here what you get is sort of what would look like a really big belly no waist kind of a shape maybe more like our friend ambam the gorilla here that we've all seen on YouTube and not particularly human-like and from this we have made inferences about the biology and locomotion of Australopithecus for example there's not a lot of a waste here in a waist of something you use to rotate your pelvis and move your spine when you're walking in efficient bipedal gait without a waist you've watched an ape walk there kind of torso stiff and they move back and forth not nearly as fluid and efficient as our gait we can also imagine if you dot the line so there's a huge area here for a gut and apes have very large guts we have smaller guts and it seems to have been a change in human evolution but a lot of our inference of what it would have been like an Australopithecus comes in fact from this reconstruction also this is very narrow at the top unlike ours and that has also been linked perhaps to tree climbing or Arbaugh reality getting at the locomotor hypotheses for Australopithecus locomotion and a lot of that is in fact based on this reconstruction which I said was the best game in town going but there are new fossils that have been found since the early the 80s and 90s when this was published so for example I'll just weave through some of the evidence here and some of this is older some of this is newer but it's been accumulating over time this is the lower part of the vertebral column of your neck and in a human here you can see where the rib attaches to the vertebra here so your very first rib this is a neck vertebra this is a chest vertebra here the rib attaches at the vertebral body and again out here in a human the first rib attached was the first thoracic vertebra and you can see the facet joints here where they articulate and the chimpanzee on the other hand the rib actually sits higher so the whole chest cavity sits a little bit higher up on the neck and you can see on the head of the first rib of a chimp two distinct articular facets one for this vertebra one for this one in Jim omen in 1986 published these pictures of Lucy and in fact there's only one Fassett if you look more closely at some of the Australopithecus fossils there is only one Fassett here so the rib is sitting not between these vertebrae but down lower in a slightly more human-like position if you take a bird's eye view of the rib cage this is a thoracic vertebra this is the spinous process as those bumps that run up and down your back back here you can see the spinous process back here so this is the back the person's belly would be up in the ceiling in a human the ribs arc from the vertebra back around up towards your chest in a chimpanzee the ribs kind of shoots straight out from the vertebral column and this is so the vertebral body is less pushed into the thoracic cavity is lessened vagine' ated in a human you have much greater in vagine' a shin here there's more leverage for the extensor muscles to hold up the spine etc etc and that's rather different from a chimpanzee now we don't have whole articulated rib cages in the fossil record but you can see the transverse process here and where this rube would attach to the vertebra and humans it's swinging way back and a chimpanzee is kind of sticking out to the side and that's something we can measure because we have these vertebrae this is a new one from the hauteur site and that's been found is found in the 90s and this is Lucy and we can actually measure the attachment of where this rib would attach and take a look at it and if you do that for the middle thoracic vertebrae these are separate vertebrae we can measure this angle in an 8 the angle is larger because the process is where the ribs attach is sticking out to the side all the way through in a human they tend to be lower in an Australopithecus both offer Ensis and Africanness they're really low which shows that this does transverse process we're very dorsally inclined that vertebral column is quite invaginate 'add and that is associated again with that upright posture so if we looked at Australopithecus they would have looked much more human-like Fincham like in that cross-sectional shape of that ribcage so the ribs are a little bit lower and they're more the vertebral columns more infatuated on top of that more curved spine now in 2010 a second Australopithecus afarensis skull was published this is called um caught a new mu it was from posted by Johannes haile selassie and its colleagues it's bigger than Lucy it is a nice big male and wonderfully it has some reasonably complete ribs including this complete second rib this is the first complete one we've had Lucy's just got little bits and pieces and they're not very easy to work with so what haile selassie and the colleagues did is they measured the neck of the rib here's where it attaches to the spine they took the neck here and then they measured the distance how far it flares out how far it curves around the front of the rib cage and you can make a little ratio of these and tell how curved they are here's a picture of a human rib so here's the neck and here's this blue line sitting way back here as these ribs are curving around the gorilla not so much this thing just heads right out here and right back up to the midline so they published this graph so here's humans and cut a new moves vertebrae down here they're very curved this ratio is very low where's the chimpanzee no gorillas are not and so they could say AHA the upper part of the ribcage where the second rib is is not ape like and this might have to do with either knuckle walking because chimps and girls are knuckle walkers or I wondered if this had to do in fact with the shape of the rib cage when you put it together so my undergraduate student Sara Bartlett sat there and drew blue and red lines on pictures of ribs for about three weeks and we was able to measure these not just in chimps and gorillas but in other specimens and here's what you see Gibbons look like humans and Gibbons have a barrel shaped ribcage on top orangutans look like chimpanzees and gorillas they have a cone-shaped ribcage on top and siamangs interestingly are somewhat in between so what this seems to reflect is not necessarily our boreal 'ti because gibbons are sure pretty good in the trees with their hand and radiation but in fact perhaps ribcage shape suggesting perhaps that at least this Australopithecus afarensis individual had a more dome-shaped ribcage up near the top than we had suspected previously so not only the top of the ribcage show a little bit less great ape-like cone shape than we thought the bottom of the ribcage does it well if you look again where these ribs attach to the vertebrae they attach at the body and they also touch on this transverse process and if you look at the last three ribs of a human you can see ribs 11 and 12 or floating ribs these are the ones that people like cher and Scarlett O'Hara get removed so they have nice small waists but this 10th rib has a big fat articulation for the transverse process if you look at a chimpanzee on the other hand you see these big articulations all the way down the lower ribs are big and they're attached tightly to that rib cage so they can't wiggle around in a soft tissue like our floating ribs can when we look at Lucy she doesn't have all of them but we can see this is thought to be a 10th rib with a big articulation and it has at least one rib here with no articulation at all so there's at least one floating rib so the bottom half of the rib cage wasn't attached maybe quite as tightly and immovably to the vertebral column and Lucy as it would be in a chimpanzee so when we go back again to this reconstruction I think that there is enough new fossil evidence that we can perhaps put an X through exactly this reconstruction as well now if I were really artistic and clever I would draw what I think Lucy looked like but I'm not very good artistically so I'm sorry to have done this to your diagram dan is a picture from the Dan Lee Berman's papers a few years ago and it shows a chimp and a human and a Lucy skeleton using this reconstruction that was published at the time and I'm afraid all I can do is use Photoshop pretty well so I'm afraid a Photoshop tear your Lucy here to give what I would consider a new and improved Lucy based on some of this new evidence the number of changes include a rib cage that really is broader up at the top then we have seen perhaps in the reconstructions beforehand and you know still fairly wide at the bottom he's our wide-body little individuals but also perhaps a more of a waste than we might have suspected given the fact that there are quite a number of lumbar vertebrae haven't showed you the evidence but they have at least as many as us and they would have been bear HAP's more mobile with more floating ribs here so maybe they would have had more of a waist now it may not be exactly like you and me but it's also not exactly like a chimpanzee either and I think we need to think of this evidence when we're thinking about the biology and the locomotion of these animals based on what we can see from bits and pieces of the ribcage so we can go back to our early time life diagram and we can see these hunched over creatures that maybe wouldn't have had much way to move their ways they would have been bent forward and I think we can now understand that perhaps when we look at Lucy perhaps we might think of creatures that were walking fully upright like we are whether or not they still climb trees whether or not there was a shift in the bending of the trees when we to homo or something else going on this doesn't necessarily speak to that because we can also look back in the fossil record that I don't have time to talk about and see that maybe our ancestors weren't exactly like chimps either but when we have a picture of Lucy in our minds will be picture these australopithecines walking around the landscape we need to be thinking of them perhaps as moving and looking a little bit more human-like than maybe we thought of in 1973 so thank you very much our next speaker is dr. Chris ruff from Johns Hopkins University and he's giving a talk entitled limb strength proportions and locomotion in early hominins all right as a number of speakers have already noted including myself in the introduction bipedalism trusty old bipedalism hasn't considered the definitive hominin trait the thing that really sets us apart but of course we know that humans can still climb trees and that other primates can adopt bipedal postures like this capuchin monkey who's breaking a nut with a stone here and doing very well at it what makes human bipedal gait special though is that it's very efficient modern human bipedal gait so if we look at this experiment bare-metal study from a few years ago if we look at the cost of transport that is how much it cost in terms of oxygen consumption to move a certain mass a certain distance you find that humans are down here walking humans these are chimpanzees bipedal and quadrupedal so obviously much less efficient than humans and in fact humans are more efficient even than your sort of average quadruped Eddie so very efficient what makes it efficient well lots of the things that we've been hearing about today restructuring of the vertebral column bring the body center of gravity over the hip joints in the lower limb and the foot the restructuring of the pelvis for more efficient weight transfer changes in the foot quite important so we heard many times today and lengthening of the lower limb which we haven't heard about but increasing the length of the limb that you're walking on because of our pendulum mechanics of walking increases efficiency in fact relative limb lengths that is the length of the for limb to hind limb or individual bones making up the limbs have long been used to categorize and describe locomotor differences at primates so this slide from Schultz is no Schultz his name showing up quite a bit today did some of the fundamental work back in the early mid 1900s in this area and we can see this is a ratio of four limb length to hind limb length we could see humans down here and that a quadrupedal primate and then finally working our way up through the great apes and then the most arboreal lesser apes and orangutangs with the highest ratio of foreland hind limb lays a pretty good correlation with locomotion so of course this is something that paleoanthropologists have spent quite a bit of time studying however relative limb length is not necessarily as simple as would be indicated in the previous graph it varies at a complex way in early hominins not all the elements of the limb change in length in in tandem you can have situations where one part of the limb is increasing in length and the other is not situations where it's very hard actually to work out sort of the allama tree of what's changing is that the hind limb getting longer or the four limb staying becoming relatively shorter or what what exactly is driving these things there's also been some suggestions especially recently that relative limb length may be a very conserved kind of characteristic that is it doesn't change very quickly necessarily with a change in locomotion so you can have primitive retentions where an animal might be completely bipedal but retain for example a longer upper lamb or for limb if it's not selected against so it's actually been suggested that relative limb length is not a particularly good or very precise characteristic to evaluate locomotion with in Hammad's primitive retentions or functionally significant or but this is really the important part what we really want to do is distinguish between characteristics that can tell us what early hominids actually did as opposed to what they could do okay so relative limb length might tell you what they could do but we're looking for traits tell us what they actually did and this requires a more direct evidence of you something that's really going to reflect what they did during their lifetime as opposed to a possible primitive retention and the characteristics that I study are structural features of long bones the geometric distribution of bone in the cross which can be analyzed using an engineering model to tell us how strong those bones are and we know from various experimental and observational studies like this famous study of tennis players here was carried out actually by my undergraduate advisor at Stanford a long time ago I had nothing to do with a study but I did look at the data later on and finding that the playing arm of tennis players whether it's right or left side these are professional tennis players with some forty to sixty percent stronger than the non playing arm and conversely if you reduce the mechanical loading on a limb bone it will reduce its cross-sectional strength and we also notice from ontogenetic studies which I think are very interesting natural experiments because you're in this case we're actually following a longitudinal sample of individuals so each one of these points is a mean for a sample of 20 individuals that's being followed longitudinally part of the Denver growth study and this is the ratio of femoral to humeral strength okay and it it's I've compared it here to a baboon sample which was a cross-sectional sample wild shot baboons and you can see that at six months to a year of age humans have limb strength proportions identical to an adult baboon which makes perfect sense because we're quadrupeds at that age it's only after you begin walking that the femur increases in relative strength until it's vastly different from the baboon as an adult so this is a natural experiment of an actual change in local motor behavior creating a change in bone strength now very recently we've been starting a study similar kind of study with gorillas and I was very happy to see Matt talking about mountain versus lowland gorillas today because that is actually the contrast that we're looking at mountain gorillas we know are less arboreal lowland gorillas are more arboreal and we know that they have different strengths proportions which I kind of show you in a minute but we've also just recently gotten some data on young mountain gorillas who we know are actually more arboreal than their adult family members and find some very interesting results here this is actually humour over several strengths here are chimpanzees and lowland gorillas is relatively stronger upper limbs because they climb or mountain gorillas are significantly lower okay they have less strong four limbs but here our juvenile mountain gorillas these are very young ones and they look much more like lowland gorillas and chimpanzees and we know that they climb or so even in this close phylogenetically close comparison we're finding some really distinctive changes that correlate with local motor behavior in in bone straight so we think these are good characteristics for determining what an animal was actually doing at that point in its life okay here's the the same hominin phylogeny and what I'm going to do is go through a few comparisons within this phylogeny of actually lower limb to upper limb bone strength and see whether actually we can say something about what these animals were actually doing it that at that point in time so the first comparison I'm going to carry out is between some of these early homo taxa now at this point we're almost to the exclusively bipedal portion of the hominid tree so the question would be are all these fellows here actually bipedal committed bipeds or is there some variation we have three associated skeletons with skulls that we can taxonomically group Homo habilis H 62 and a couple of early Homo erectus or gastrous specimens an adult and it's famous juvenile and arakata b-boy that you've seen several times already today and we were able to obtain cross sections from the humerus and the femur for each of these if we look at femoral the humeral strength in modern humans and chimpanzees as expected humans have greater femoral strength relative to humeral strength the chimpanzees there is no overlap here between the distributions and if we add those specimens in we find 1808 that was the adult early Homo erectus falls right within modern humans the dairy economy boy also right within modern humans his slightly lower position here could actually be explained by the fact that he's an adolescent adolescents don't quite have the modern proportions adult proportions but Oh age 62 does not Homo habilis I like the Chuckle Homo habilis falls in within the chimpanzee distribution quite quite obviously well below the human distribution indicating that's different we have two different to me at least two different forms of mechanical loadings of the limbs here strongly suggesting to me that Homo habilis whether or not it was completely modern in terms of bipedality went on the ground was using the trees was using its upper limbs in a chimp like manner what about AI Francis the taxon at Lucy belongs to well we have Lucy okay so one really associated specimen that we have that we can do this analysis on we were not able to get cross sections of this for a long time but just recently with the help of John Capel Minh and his crew down to Texas of CT scans actually were taken that were interpreted and we were able to add her to the chart here and she falls in between humans and chimpanzees actually so not human-like but more human-like that oh-6 t2 which in itself is a very interesting observation but my interpretation would be relatively stronger humerus okay and in fact from other isolated specimens just humor I we know that ah Francis did have an extremely strong humerus by any measure here a huge muscle crests etc so unfortunately we don't have associated femoral but that is certainly consistent with the evidence from these isolated bones what about africanus well unfortunately we don't have any associated humour i humeral femoral specimens but we do have one specimen from sterk fontaine 431 where we have a good distal half of a humerus and we have a hip bone with the acetabulum or the hip bone side of the hip joint which we can measure and we can use to estimate body size we have a couple of different estimates because actually this acetabulum slightly distorted but we can get a fairly good estimate of body size that way and then we can compare humor strength relative to body size which is not as good as relative femur but it is one measure of relative humoral strength this is what we come up with we do that first of all okay this is humoral strength body mass here are modern humans here are chimpanzees these are a couple of modern chimpanzees with known body weights we have others with estimated body weights see the chimpanzees have much stronger humor I relative to their body size and modern humans and this Australopithecus africanus Falls with chimpanzees even above chimpanzees is a very strong humerus relative to its body size and so does Lucy actually Lucy on the same chart here so a africanus also had a extremely strong humerus this is a sediba and you've seen this before okay recently you came available and through the help of Steve Churchill and Chris Carlson and Lee Berger it's able to look at cross sections from the humorous humor I have these two individuals there is a femur but the distal end of the femur here is rather worn and broken up and so the cross sections are not completely trustworthy yet at least they're still being worked on but I was able to estimate body mass from the femoral heads heads of these two individuals one of these is a juvenile one as an adult and again look at relative humeral strength and this is where it comes out this is very interesting given the information we just had on the foot earlier today in fact sediba looks more modern than these others in terms of relative humoral strength and I put WT 15,000 there nary a kata me boy on here also just kind of for for comparison so the implication being that in fact it was not loading its upper limbs in the same way as these earlier australopithecines were how about ramidus well very interesting skeleton obviously people have said a few words about it today not too much unfortunately we don't have cross-section from it yet all I assume that they will be coming and we don't have a humerus okay we have partial femoral shaft tibia we have four limb bones we can look at the length of the radius versus a tibia for example and it falls right in next to chimpanzees and not near modern humans and I think just even looking at these comparisons here you can see that the strength of the forearm versus the leg here is probably not going to be very human-like you know will have to be quantified and we also know from other features such as the a ducted big abducted big toe and a long curved digits etc that are ramidus has many indications of a harbor reality I don't think that's really in question from anyone so if we look at this chart again here here's what we find a rabbit a significant arboreal component Gale Francis also evidence for a significant our boreal behavior upper limb loading africanus the same Homo habilis is same actually and then once we get through our gas here at erectus we have evidence for completely modern behavior but until that point all these forms to my mind at least show that there was in addition to whatever bipedalism was practiced on the ground who also had significantly higher loadings of the upper limb relative to the lower limb which to me indicates that it was also being used in an arboreal context so I think these data and other data indicate that among early hominids terrestrial bipedality coexisted with arboreal climbing for millions of years terrestrial bipedality did not become obligatory until latest Australopithecus or or Homo ergaster erectus and that adoption of terrestrial bipedality was a gradual process with many intermediate experiments and I think that's also the message we're getting from most of the other Talk's today and I would like to thank everyone here for their work on this thank you you

Channel: University of California Television (UCTV)

Views: 29,767

Rating: 4.8482757 out of 5

Keywords: Brian Richmond, Carol Ward, Chris Ruff, bipedalism, evolution, hominid

Id: DCPQK7OdhUY

Length: 59min 44sec (3584 seconds)

Published: Thu Mar 01 2012

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Why are we the only two-legged creature to develop an exclusively upright gait? And what did it mean to the development of the human species? CARTA brings you foremost experts to explore the many facets of these questions in this fascinating series with presentations from Brian Richmond, Carol Ward and Chris Ruff that compare different evidence and aspects of hominid body form and what those tell us about upright locomotion in hominids.