"Sauropod Dinosaurs: Long Neck and Peculiar Claws"

Case Western Reserve University's Institute for the science of origins proudly presents the origin science Scholars Program the Institute advances the scientific understanding and application of the origins and evolution of human and natural systems the origin science scholars lectures are presented with the assistance of Case Western Reserve University Segal lifelong learning program College of Arts and Sciences and media vision my pleasure tonight to introduce dr. Lee Hall who is a vertebrate paleontologist at the Cleveland Museum of Natural History his research focuses on two main groups of fossil animals a group of huge armored fish that includes the famous Dunkleosteus and the phylogenetic Sand functional morphology of dinosaurs please join me in welcoming dr. Lee Hall thank you for the introduction Glenn and thank you to you and Patricia for the invite to be part of this fantastic series I've attended several of these over the years and these have always been so informative so I hope to do right by that so my name is Lee Hall and I'm a paleontologist at the Cleveland Museum of Natural History and the photo above you I think by the end of this lecture will hopefully give you pause give you something interesting to think about because as many times in paleontology and I suppose other science is something it can seem rather innocuous and something that maybe you don't even pay much attention to can end up taking up a significant portion of your time as you do research and it's always fascinating to me because you end up learning so much about something that otherwise beforehand you may not have even given a second thought to and that's what we're talking about tonight a sauropod feet so I work over at the Natural History Museum a few blocks from here and I'm my title is prepared or so my job is essentially to run the fossil lab so we have a fossil lab in the basement of the museum and doing some consolidation treatments to an ancient camel they're called steno Milas my day-to-day activities involve putting fossils back together or conserving them for future generations but some of the most fun that I have is actually getting to collaborate with Case Western Reserve doing presentations like this or training students some of whom are in the audience tonight so don't be too hard on me guys please so this study was made possible with the help of two people I need to to mention so dr. Denver Fowler and the cowboy hat there who initially drummed up the concept for this research project back in 2009 and we presented this first part at a conference called the International Conference on dinosaur eggs and babies and we turned that presentation into a paper and on the right there is mrs. Ashley Hall now she is my wife so she's here tonight and I gotta say hi dear thanks for being here very support but yeah so without Denver without her work on the second half of the research you know we wouldn't be I wouldn't be standing here with you tonight so I just want to make sure that they are properly acknowledged and thanked for their help in 2011 the first paper came out in the journal historical biology and the second half of the study came out in 2016 and a specialty publication called dinosaur tracks the next steps which is a richly illustrated book that focuses on learning from dinosaur track ways or footprints and doing more than just measuring stride and gait but trying to figure out paleo biological hypotheses of behavior and using new methods in paleontology and after I made that sound very juicy and interesting I'm only going to be talking about the first paper tonight so you have to come back in November for part two so tonight we're gonna go through three sections the first one we will talk about sauropod dinosaurs in general don't worry if you have never heard that word before or you don't notice or but it is because we're all gonna be on the same page after the first section then we'll jump into the sort of the meat of the research and talk about a couple of hypotheses involving sauropod claws and and we will finish it off by trying to understand these interesting anatomical features by looking at evolutionary trends in the group of sword I know sores as well as trying to figure out if we can look at modern biology of living animals to help understand what they use these claws for we all in the same page very good part one sauropods so there in the image behind me our sauropod dinosaurs and pretty much everything everyone whether they intended to or not at some point and their life has probably seen something representing a sauropod dinosaur if you've ever driven by sinless Sinclair oil station you've seen a sauropod silhouetted they're pretty hard to avoid especially after all the Jurassic Park in Jurassic world movies and King Kong and everything else sauropods were one of the most successful groups of dinosaurs they evolved early in the Mesozoic and as you can see here they have a very healthy span throughout pretty much the entirety of the what's called the age of dinosaurs and they had a fairly healthy diversity too and one of the really interesting things about sauropods is that yes even though they all have basically long necks and long tails and are really big they go about getting those things in slightly different ways oh and interestingly so the classic distribution or division of dinosaur taxonomy has had sauropods nested with the saurischians or the lizard hipped dinosaurs which means that these giant herbivores are more closely related to velociraptor and t-rex than they are to things like Stegosaurus or Triceratops which belongs in the ornithischians this has been thrown topsy turvy more recently as phylogenetic analyses are often you know responsible for doing but for now we'll just stick with sort of the classic division and you have sauropods grouped in with the saurians so if we look at a geologic column as represented here by Rachel's artwork the Mesozoic here the middle area life will zoom in it spans from roughly 250 to 66 million years ago and sauropods really evolved at the end of the Triassic so that first third of the age of dinosaurs and once you get into the Jurassic they explode in diversity and that's when you hear of some of the classic and most famous species of sauropod dinosaurs like brontosaurus and Brachiosaurus and Diplodocus and interpretations you have diversification of a group of dinosaurs called titanosaurs which are include which include things like Pataca titan which is on display at the Field Museum now and at the American Museum some of the absolutely largest terrestrial animals to ever walk the earth this is a image representing the diversity of sauropods there are several groups and you can see they all have in common that classic feature of relatively long necks and long tails but again some of them are held a little loftier than others you can see in the middle of the screen the titanosaurs have rather long forearms so their vertebrae sort of tilt upward towards the shoulder and then the heads are lofted high into the air the diploid acids down in the bottom left they are some of the longest dinosaurs and they are essentially cantilever it over the shoulders and the hips they of necks that are just about as long as their tails and then up in the upper right or some of the weirdest sauropods the Rebecca sword a which had the the front of their skulls were flattened out they almost looked like like a how a vacuum cleaner with brushes flattens out and the deck Chris or a day which had neural spines that grew out of the skin and they so that essentially the top was a vertebrae projected out of the neck about three feet or so so sauropods you know actually turns out they have a lot more morphological diversity than you know typically you'd be familiar with in pop culture and then there's Camaro swords down in the bottom right which are sort of another classic Jurassic 9 or type and we're gonna not really focus on any one of those particular groups so don't worry about trying to memorize all these something a days and something add on because we're really just looking at broad evolutionary patterns which is why I like this study because you can just kind of pull back and just see where things are trending and where they're going another thing that's significant about sauropod so there's a Camarasaurus a skull on the upper left which once upon a time was thought to be the skull of brontosaurus and we can talk about that and they were in the QA if anyone's curious but you see in the jaws in the upper right there they have large and flat spatulate teeth they're very rounded they're they're big they're bigger than most people's thumbs would be and then in the bottom there's the skull of a Diplodocus which is one of the longer sauropods and the teeth at the front of the mouth are more pencil or peg like and what's going on here is essentially you have many of these gigantic animals living in the same environments at the same time and you want to be able to exist happily without having to compete with one another for the same food resource so you're essentially seeing niche partitioning in the dentition where the chimera sores or the spatula toothed sauropods were browsing higher up in trees and things like Diplodocus with a peg like teeth were raking in vegetation from the lower trophic levels in the firm forests and what-have-you and just in case you don't know where the teeth are I made a graph okay so there's gonna be a few cladograms in the talk and if you're not familiar with a cladogram it's essentially a very simple diagram that shows you degrees of relatedness among animals it doesn't necessarily show you ancestor descendant relationships so these two cladograms are saying the exact same thing if we press this is called a node this is essentially an area where there is a branching event you could hypothesize that there is a common ancestor shared between all three and as you move up the tree perhaps a common ancestor shared between a and B but we're not putting any animal names there so now that we have that out of the way we can move into something a little bit more in-depth so this would be sort of a classic example where you have fish now amphibians did did evolve from a an ancestor in the ocean right a fish ancestor but when you group reptiles and amphibians those two will be more closely related probably than either of them would be to fish we're clear okay so same thing there it doesn't matter to matter the direction this is probably even too much information because we're not actually going to use this for much other than to look at this diagram now I'm not usually a fan of pictures with a lot of small stuff for a presentation but essentially what this is showing you is a couple of things this is what we talk about when we're talking about sauropod uh so all these animals I'm talking about all these names they exist on this tree somewhere some of the more basal forms are up here and more derived forms meaning you know maybe they showed up a little bit later in the Mesozoic in the Jurassic and Cretaceous will show up as you move up to the crown of the tree and if you're curious that's where our museum logo applicantís Oris comes from right there so hafla cancer soars is still kind of weird we don't have a skull for it and that makes it pretty difficult to figure out where it sits within the overall sauropod group we'll see this diagram again and it's just important that you sort of understand that as we move from sort of the upper left of the bottom right we're sort of seeing a trend and evolution and evolutionary relationships in these animals so background into the history of sauropod discoveries in the eighteen 1880s 1870s 80s anyway a long time ago and has stayed far far away there was a geologist named Arthur Lakes and Arthur lakes actually would go out and while he was doing sections and drawing up geologic columns he he you'd find fossils and so what was sort of the norm back then was you'd have people out doing work on geology in the West and then you had paleontologists back east at Yale or Harvard and when people would find things out west they would mail them or shipping my train out east and and and write letters back and forth when they find these things so Arthur lakes as a geologist he's also famous because he would paint watercolors when in do pastel work when he was out in the field so here they here he is reclining at Como Bluff Wyoming there's records of people getting kind of irritated with him because when they'd be working and moving rocks he'd be painting a picture but we're really glad we have these color representations of fieldwork from the sort of the early days of dinosaur paleontology so one day Arthur Lakes in 1877 he's out southwest of Denver Colorado in a town called Morrison and he he discovers what he calls the bones of some gigantic saurian upper arm bone and a backbone and he sends this letter to a guy named OC Marsh who if you've ever heard of the bone Wars was one of the pivotal players it's a fascinating time in American history and I wish I had time to get into it now but it's worth looking up an arrow and there's several good books so this is the Denver area there we go and if you've ever flown in to the airport the airport's right up there and this little red dot down here that's Morrison and then here's a little here's a map map shot of it so we're in southwestern Denver there's Red Rocks Amphitheatre anyone ever go see the Grateful Dead there go see a show well it turns out Red Rocks is right across a canyon from where the bone wars began so that entire Ridge system that cuts across like a scar is called dinosaur ridge and that is where these fossils were first found so the first fossils of brownness brontosaurus and some of the first examples of Stegosaurus and Allosaurus were discovered right here it's a fascinating historical site to visit so they start digging and they find bones and they start putting them together these are our earliest sort of attempts at reconstructing sauropod dinosaurs and as you can see here in ten years you know they were able to put together a little bit more of the skull fill a little bit more of the ribcage and whatnot but our earliest ideas of these animals whether they were sluggish and slow and lizard-like and the tails were dying on the ground if they could barely walk on the ground and then they were they were hanging out the swamps if they were doing anything and so a few years later you know we're still looking at lethargic animals they're still hanging out in the swamps you know it's walking around on the ground but this this tail doesn't really have any structure to it it's very loose and lizard-like so this is kind of indicative of early misunderstandings with the anatomy of dinosaurs and sauropods and why we have these erroneous ideas that are still propagated into modern pop culture and then moving forward into the mid 20th century finally by the 1980s and 90s if we have a better understanding of the anatomy of these animals so this is sort of our current understanding you know we know that they're active and they're warm-blooded and they're getting around so we can start looking at some of the more interesting aspects of of their behavior questions so far your diagram I guess you call it a cladogram yep is that based solely on DNA DNA analysis or I wish muscles or oh so we don't have DNA with Dinosaurs because the molecule of DNA is completely obliterated after you know a few tens of thousands of years so going back a hundred million years or 220 million years is gone the way that these diagrams are assembled is through careful scrutiny of the skeletal anatomy of these animals and it's initially determining what features of the skeletons are significant for determining a genus or species level separation and that's difficult because when you're just looking at bones and bones that have often you know they've been crushed and you don't necessarily have a complete skeleton you might not even have a skull where a lot of that important information lies those diagrams get changed up a lot every year so it's all hypothetical it's all based on our best current understanding of you know the anatomy of these fossils but but it's always changing so the other based on essentially analysis of the anatomy how they reproduce well when a mommy dinosaurs and a daddy dinosaur that's a really good question and sometimes those basic questions are the most difficult questions to answer because what can you learn from you know a skeleton so we're actually going to talk a little bit about that later on in the presentation and I think part of your question will be answered so I don't you know spoiler warning I don't want to give anything away but as far as the physics I mean at least half the population had to get up on two legs once a year and that's that's about all we don't mean just lay eggs so dinosaurs yeah dinosaurs did lay eggs and and so we have evidence of nests and eggs from from pretty much every major clade of dinosaurs from the meat-eaters and the sauropods and the duck-billed dinosaurs know eggs are nests for horned dinosaurs yet and in armored dinosaurs either if I'm remembering correctly but they did lay eggs hard shelled eggs how do you know they were warm-blooded one of the interesting things with that question and how do we know they were warm-blooded there are a few different definitions in a few different ways to become warm-blooded were they necessarily warm-blooded like you or I think we're homeo thermic endotherms we essentially generate our own body heat and then we maintain that body heat with our metabolism and I don't think dinosaurs all maintained their body temperatures the same way and you know if you're a sauropod and you to be a hundred feet long once you heat up it's really hard to dump that heat off to the the reason we know so much about dinosaur physiology is because the bones although they fossilized retain internal tissues so the bone tissues the structure micro structure of bone tells us a lot about dinosaur metabolism so when you cut open a dinosaur leg you can see the different layers of deposited bone that were essentially laid down like tree rings as the animal grew and you can calculate growth rates from that and there's a bunch of fancy statistics you can do that I don't necessarily know how to do or explain however the the basic answer is that the bones we can do histology on those bones and out of the microscope they reveal quite a bit of information about their physiology and from that we know that that many of them were very fast growing fast maturing animals which is indicative of a high metabolism much like modern birds thank you for joining us you have been watching Lee hall discussing sauropods the iconic long necked long-tailed dinosaurs among whom were the largest animals to ever walk the earth for more information on the origin science Scholars Program please visit the institute's website at origins dot case dot edu in the next part of the talk mr. hall will focus on competing hypotheses digging and walking for the shape of sauropods feet and claws now back to the talk we're gonna talk about a couple of hypotheses with dinosaur claws scratch digging versus substrate grip so what's in a name I always like to throw I don't realize that's Shakespeare I think but so what's in a name well this is the guy OC Marsh he's the guy who started the bone wars against Edward Koch who also has wonderfully crazy facial hair Pro PT of the period he coined the name Sorrell pota and 1878 now when you take a look at the anatomical features of your typical sauropod skeleton what's gonna stand out right away I mean they're big they've got massively long necks with proportionately small heads although these skulls were at least the size of a horse skull on the small end and usually larger than that long tails they have these massive massive hips that are about the size of the engine block of a pickup truck but for four from Marsh he was really interested I guess in in their feet because the name sauropod means lizard foot it was very vogue in the late 1800s to name groups of dinosaurs based on their feet theropod dinosaurs which include t-rex and other meat-eaters that means beast foot and then sauropod means lizard foot and then duck-billed dinosaurs belong in a group called ornithopods which means bird foot and so when when you look at their feet well if you look at a lizard foot there is there's some blue similarities between like this variant of lizard foot and the foot of some early early sauropod uh morphs from the Triassic Triassic around 200 million years ago and you just you just have to take my word for it but beyond that there's there's really not a whole lot going on there where I would say well this is you know something that would be indicative of calling it a lizard footed animal when when you look at the sauropod foot skeleton that's the hand on the left and the foot on the right and so if we go back and forth between the lizard sauropod lizard sauropod so I'm not sure what was going through Marcia's mind at the time and I wasn't able to dig up anything but I'm sure he had a good reason for it at the time so just take a moment and look at those look at those things so there's no bones missing from that from that hand so what you're looking at is from a fairly derived sauropod so this is something like like a Brachiosaurus or an Apatosaurus essentially if you if you take all your distal fingertips off and just leave that first digit and then stick your thumb out you've made a sauropod hand congratulations now now walk around on that and with the foot or the Pez they've retained these three large claws and they've gotten rid of sort of two of the outer claws the one thing in common in these two limbs is that you'll see the both the metacarpals and the metatarsals or the long bones of the hand they're arranged in a semicircular column they're very stout these bones are bigger than bigger than bread loaves each so in there they're massive they could be as big as your torso in some of these dinosaurs and this is where things kind of get interesting because if you look at the foot of a sauropod you can sort of key the bones and so the blue those are the metatarsals the long bones under the ankle the green those are your phalanges for the toe bones and then the yellow those are the specialised toe bones that have been essentially modified into a big claw and if you're wondering what your foot how that would compare I'll do that for you right now with a little bit of a PowerPoint magic there we go and so again blue that's the long bones your foot so if you get if you have a fallen arch you can blame that blue group in there and then our toe tips I mean they're not giant claws but we have these thin little collages that sort of stick out of the skin they're on their distal phalanges so now that you're all experts in sauropod foot anatomy we can learn about feet and what they tell us so feet are very informative and turns out when you look at if you compare any particular piece of anatomy from one animal across several animal groups you'll see that they sort of vary based on evolutionary heritage but also you know what's how these animals make a living so you know predators have sharp claws then sec Tavor primate up there in the upper right the eye eyes got this long weird finger for poking tapping trees and fishing grubs out of holes a sloth obviously has claws that look really vicious but they're meant for climbing trees geckos have these really wild feet that they used to cling on to in climb and then you know amphibians like frogs have the webbed feet for swimming so I think that sort of drives the point home over and over again you can learn a lot from feet so this is the front foot of a sauropod as you can see it's very stout and again there's one thumb claw and the rest of the tips of those toes are gone so by the time you get into the Jurassic this is kind of what sauropod feet look like and this is from our own applicantís source at the Natural History Museum so you can come and see these yourself in person oh my gosh that's amazing and this is the sauropod pest and if you look that's my shoe so you've to give you an idea of how big these animals are so and this isn't even the biggest of big sauropods so there's an interesting sort of arrangement if you look right overhead you can see the claws so they have sort of an initial on overlapping pattern held in a neutral position they sort of tip towards the inside of the foot and so medially the claws we say they're there canted medially or they tip kind of medially that the bottoms of them kind of spread out towards the side away from the center of the body and they make this there's a really interesting angle there I just want to drive that point home because we're going to be looking at this and what's really interesting about those claws is that they have a what's called an offset flexor tubercle now to simplify that your body is essentially a bunch of pulley systems with muscles and tendons and you're making your skeleton move and so for a sauropod whenever they wanted to flex their feet down so if you imagine trying to pick up a marble with your toes everyone's probably flexing their toes down into the ground you know your tendons are pulling your toes and your toes are going straight down okay perpendicular to the surface of the earth but with sauropods they're flexor tubercle or the little part of the bone where the tendon would attach to pole the claw down was offset kind of medially or toward the midline of the body so when they flex their foot the claws would actually and I'll do my animation again here they would actually kind of tip over and fold over and stack across the front of the foot in a really really bizarre articular arrangement which is completely unique to this this group of dinosaurs so we call this plantar flexion and there's some someone doing some exercises but in the bottom there plantar flexion is essentially when you tip your foot away from your body and curl your toes down so we're gonna be talking about this particular behavior in sauropods and this is just about as Nicias I think you can get in any study I mean it's like who thought we'd be talking about feet moving down you know you're like I want to hear about dinosaurs and we're talking about feet what's going on here so plantar flexion is essentially going to give you an arrangement and I've Illustrated it here with the claws sort of folding down and overlapping this is such a bizarre articulation and movement that it's even do it was difficult for me after several attempts to to draw to some satisfaction but the important thing is that we're looking at what happens when these claws are flexed and they end up overlapping and forming more or less one continuous surface perpendicular to the to the front of the foot so what's going on here you know sauropod feet are weird that's that's one thing they should be called weird foot right instead of lizard flight well here are the hypotheses so number one substrate grip so maybe when they're there walking around maybe they're walking through mud it's a little slippery maybe they're walking through some loose sediment the feet engage this this flexion and the claws help keep a grip on the ground you don't want to fall down if you weigh 40 tons or whatever so we would be familiar with off-road tread on vehicles or or cleats on athletic shoes you know or hiking shoes that helps us essentially keep a grip on the ground when we're climbing around artificially and so in sauropods it may have presented prevent it slipping and provided traction and prevented something like this from happening that's terrible but the issue with as dramatic as seen is that this is is we actually have fossil sites where all we find our sauropod feet or all we find are essentially the legs preserved because they got stuck in the mud and the top parts of the skeletons just eroded away so it leaves a little bit to be desired as far as trying to explain what selection pressure was significant enough to essential across the board you know create the this feature hypothesis number to scratch taking if anyone's ever had a dog or maybe a plot problematic wrote in their garden essentially just use your paws of your hands to digging into the ground and probably not for burrowing and sauropods this seems a little bit unrealistic so what good is it to have a digging implement on your hind foot if you're 100 feet long perhaps nest excavation so we're going to talk a little bit about reproduction well how do you go about determining one way or the other which of these is you know more more valid than the other if if it's possible well so we do have fossils from sauropod nests and we can we can probably look at some of those we have nesting grounds especially famously down in South America and we're going to talk about that in the next section but we're just going to take a few questions now so happy to answer questions from the last session or questions about sauropod foot anatomy and I'm running a little bit quick here so make them good were these creatures North America or were they all over the entire world global they've been found on every continent including Antarctica and kudos to the paleontologists who went to Antarctica to look for fossils and dug up a sauropod are they still discovering this species of dinosaurs and when was the last one if know when was the last one that's covered it seems just about once a month there's some there's some new species of dinosaur coming out one of the most recent major species of sauropods from the last year would have been dreadnought us brontosaurus has been an off again on again species and paleontology for like over a hundred years and and this is because back in the 1800s Marsh you know these big bones were found we were finding lots of big bones all over and these guys marsh and cope were really fighting each other in the press and in the scientific publications to see who could get the most publications and they even they took out ads in major newspapers insulting each other for several years and it really soured a lot of relationships but they were so fixated on on trying to out publish the other person that a lot of times they got sloppy and so the slightest perceived difference in fossils meant there was a new species and so this was sort of the case with something called brontosaurus excel SiC Celsius which stands for the the Regal Thunder lizard so as it turns out upon closer inspection after these guys died in the early 1900s other paleontologists were trying to sort through the mess and it turns out that the bones of brontosaurus were really similar to a already described animal named Apatosaurus and so they ended up lumping brontosaurus back into a pata source but by that point there were already museum exhibits up and there was this movie called King Kong that had come out and there was a brontosaurus in there so it was in the popular culture so for many many years brontosaurus has essentially been considered well like a wastebasket taxon it's been it's been you know in the graveyard of scientific names until more recently a publication came out in like 2015 I think where it was resurrected as a valid genus and there are currently three proposed species of brontosaurus so you can get it's cool to be brontosaurus again but you know the point being there's so many different species of dinosaurs being published annually that sometimes it's hard to keep track how old did these guys get roughly so using histology you can count the growth rings inside the bone and get a rough estimate for age and with most dinosaurs when you are pushing your 30s here up there so we're not looking at like a hundred years you know not like tortoises they they sort of they lived fast and died youngish but I mean 30 years for a giant animal in the wild it's kind of you know it's I think that's rather typical but what's really amazing is how big these animals got in that amount of time you know averaging anywhere from 10 to 20 feet upwards to over 100 feet long in some of those groups I want to go back to the overlapping Clause for a minute does that not by constitute a blade-like action a blade like yes loud blade or as far as weaponry you know that's that's an interesting it's an interesting thought and and to use that hindfoot like a weapon you'd animal would have to be in pretty dire straits I think that at a certain point a sauropod probably whether intentionally or not kicked something whether it was walking or if there was a predator trying to get up at its belly but you know these limbs are huge and you know the animals he they're heavy and so you don't want to be removing one of your main supports if you don't have to so as far as evolving things for a weaponry it's really hard to show that and that's another thing that goes back to like early 20th century paleontologists you know writing popular press books and saying oh everything's about tooth and claw and blood and gore and Triceratops horns are strictly for defense and it had a shield and we know now that we and we have the benefit of knowing more because they did the work before us so I don't want to pooh-pooh the work I just we know enough now that a lot of these crazy features and dinosaurs like the armor and the spikes I'm sure some of it was useful in a combative situation but we're seeing more evidence for sexual selection and species recognition being the driving force of a lot of these crazy skeletal features so what dinosaurs did with their bones it's kind of what birds do with their feathers and their plumage today so if you see a triceratops skull with that big frill think of you know the peacock throwing its tail up and and showing off so we have explanations for what was going on with the claws on the back feet but what do we have any like big theories on why they just have the one claw on the front so the thing about dividing a presentation up into into the thirds and sections is you're trying to anticipate like a narrative and and inevitably a clever audience will always be thinking ahead which is which is great it's just I haven't shown you some pictures yet but as far as like the cell and pressures for that I mean it could have been useful if they were asking bark off trees or for the for the well for the males it probably was good to have once a year you know like I said earlier but so far we don't really understand sexual dimorphism and dinosaurs or if it even exists so at this point it's it's all still largely speculative so if you're looking for something to do in grad school there's a project we hope you've been enjoying the origin science Scholars Program with Lee Hall mr. Hall is preparator of vertebrate paleontology at the Cleveland Museum of Natural History his excavated Troodon nests from Montana Megalodon teeth from beneath the streets of downtown Los Angeles sea caves in Alaska and late cretaceous dinosaurs in southern Alberta Canada in the second part of our talk we discussed how useful sauropods claws would be for digging holes in the dirt versus for providing traction on slippery surfaces in our final segment mr. Hall will talk about how we can study modern animals to learn about dinosaurs now back to our talk part three trends and analogs and evolution and living clues so this is my favorite part of the talk because this is sort of the payoff for sitting patiently and we start to see some neat ideas being discussed so we're gonna look at the evolution of sauropod feet going sort of up the tree here and I'll do that again just so everyone can see because I spent a lot of time on this arrow so yeah we're basically we want to understand okay if these claws are important feature and we're trying to figure out what they were used for we want to try and understand maybe what selection pressures are driving the evolution of these features well if we start at the beginning sauropods got big pretty early on so there's gonna be some external constraints they're big they're they're heavy so the limbs are gonna be fairly columnar the the feet and hands are gonna be stout and number one they have to be able to support a lot of weight but number two they're doing something with their claws so we'll start with the feet so there's sort of that lizard footed sort of Pro sauropod low finkasaurus on the far and as we march up sort of the evolutionary ladder you can see that they lose the two outermost claws and then they hypertrophy or enlarge the first the claws in the first three toes so the big toes is truly a big toe here so they get bigger and bigger and bigger now if we look at the hands and this is really crucial we'll see that they started off with a fairly large manis with with fairly sizable claws on them and then as you move up the tree they actually lose them altogether and a few select groups so that epistle katia on the far right that's not a mistake it completely lost every single bone passed past the knuckle so if you've ever walked around on your fists I mean you're walking like one of these animals would have so the question then becomes we look at these hypotheses of scratch taking and substrate grip and we try to analyze them now with an understanding of the evolutionary context of these features and so if you look across these animals they're getting bigger and bigger foot claws and they're retaining the foot claws so clearly the foot claws are important but in a lot of cases they're removing most of the claws from the hand except for a mysterious thumb claw or in some cases getting rid of them entirely so back in 1989 mark Gallup published an interesting paper about the foot of a dinosaur and this paper it's called pluralists it's been lumped in with another dinosaur called Astrid on whatever it's a big sauropod but he he talked about this idea of scratch sticking now he wasn't the first person to bring it up but this was the most thorough discussion about it that had happened and I think he mentions it like three or four times in the paper but you can see a foot is mentioned there and essentially his arguing was that there is a special articulate relationship when you look at these foot claws there's actually quite a bit of range of motion possible and the toes of the hind feet even though there would have been a big fleshy pad for standing and a lot of muscle tissue the claws were still capable of a great range of motion so they were mobile so we know that they weren't just kind of sitting doing nothing and in a study by Matt bond in 2005 he again looked at the articulate relationship of the anatomy in the clause and said yeah they can do this cool movement and they can fold over and form sort of a blade across the front of the foot but he didn't think scratch digging was viable because as he says here they did the closet not appear to penetrate the soil parallel with the feet as they do in digging mammals so what he means is if you were to dig a hole with your hand okay the direction of your limbs motion you know if you had a big claw coming off the front of your fingernails were really long the broadest part of your fingernail would be utilized properly for digging okay if you tried moving your hands sideways to the soil you're gonna slice through so what what Bannen is saying here is that because while the sauropod foot is sort of held in a neutral position the claws are not oriented ideally for for digging but he says like they are in digging mammals and again he says they twisted and flexed into the soil perpendicular to the direction of locomotion and then he kind of left it at that and I can understand because the study was mostly about the physiology of sauropod hands and feet it was a big paper and this was just sort of him of a minor note so I don't want to you know be too hard on him about that so we need to look at some modern analogues and let's start with an elephant because sauropods are big and a lot of times when you see sauropods in popular culture or toys of these things their feet look just like elephants if we compare the hand skeleton of the sauropod to an elephant you know you have these big Medic metacarpals and then you have a reduction in the limbs but this is actually not a bad not a bad analogy - the giant claw however there's a marked difference in V in the footprint so an elephant foot both the front feet in the back feet are there just like sewer lids they're big in their round sauropod front feet have these big fat fleshy pads on them but on a sauropod front foot if we look at a track here of an up of a right and a left or a right forefoot in hind foot or Hanan of what i could just say the easy words you can see that there's a sort of a being shaped or kind of a semi lunate crest so sauropods didn't have a fleshy heel on their hand when we have tens of thousands of trackways that tell us that this isn't an anomaly so right there the analogy with elephant feet breaks down and again the sauropod feet some of those are about a meter long and you can see some of the impressions from the claws there we won't get into this too much this time but for the next lecture we certainly are gonna dive into trackways so if you look at the hind foot I think it's pretty apparent that you can't make much of a comparison there because elephants don't have claws they have nails okay so that's that's not gonna work well let's look at digging mammals now because that was mentioned in one of the studies and well so there's a wombat on the left and you can see it's got these flat broad claws that stick out straight from the front of the foot same thing with the mole there so his argument is essentially saying that you know sauropods don't move their claws like mammals so they couldn't have dug like mammals which is which is true they're not mammals but the analogy's falls apart because he's not considering the the motion of the foot with the flexion of the claws engaged so and in the initial idea the broad claws of moles are great for digging but sauropods you know this is a cross-section through the claw mind you so if we were to be really cruel and chopped through the middle of the claws of these animals that's what the cross-section would look like moles are good for digging structurally sauropods not so much when they move into the soil sauropod claws aren't very efficient for digging in this position so mole wins however if we consider the flexion of the sauropod claws and the angle that they'd be laying at once that anatomical anomaly the mechanism was engaged it's a different picture entirely and they become actually rather efficient and they become a great like a hoe for like a garden hoe yeah I see some of that ha I told you so yeah so what's really interesting is not only would these make something like a like a good scraper but if you've worked in industry like I have for a little bit as a paleontologist I watched a lot of holes get drilled for solar fields and for power lines and things and they use these things called rock augers which is on the right there and it turns out that the little teeth that are on those auger flights when they move they're overlapped and shaped not so dissimilar from sauropod claws so sauropod feet might be a good analogy for you know looking at rock augers instead of digging mammals but this is actually the best modern analog for a sauropod foot this is a gopher tortoise which is a beautiful animal and you can see that there's a little dirt on top of the shell of this I I think I think that's a male you can tell because they'll have a usually males might have a long what's called a cooler horn so the bottom part of the shell where the collar bone is in us has a long stem that kind of sticks out and so they can use it for fighting other tortoises you know for them is very serious but for us it's something that's cute look at their fighting so these are these are tortoise feet and at the top there they are with the flesh on on a on the top is the hand and see on the bottom is a hand they're flipped but as you can see they have fairly stout phalanges or finger bones and they have fairly broad claws and this is good because you know Turtles being reptiles are more closely related to sauropods than mammals are and turns out of all the animals so here again showing you the sauropod foot compared to towards claws this is where in our study we're seeing more similarities and we're kind of going mmm now if only only tortoises did something really interesting with their foot claws like burrow which they do and of all the animals in the animal kingdom that you would look at and say yeah that's a burrow where I'm tortoises or at the bottom of the list with that big shell it's just nuts but they actually dig very long and elaborate burrows they can be several meters deep and and I mean like 20 feet long and there's they're good habitat for a lot of animals and snakes and owls and rodents or squatters as the tortoises probably call them but tortoises are really really good diggers and they actually dig with their hind feet and there's actually a little bit more to it so we know that the sauropods probably aren't burrowing with their feet so what else could be doing with those feet and digging well so when tortoises lay eggs the females they dig a nest so in this image here you can see that she's using her right foot to scrape dirt out of the hole and spread it away from where she's going to deposit her eggs and then she will switch over and the left foot comes in reaches down digs in and starts to remove sediment so this is making us wonder if there might be something something relatable here with sauropods because that's a pretty important thing to be able to do if you want to keep you know if you want to keep the the the pack live in so diagrammed here the tortoise foot plus towards the stick one foot into the ground excavate some sediment pile it in a pile or flick it away and then put the other foot into the ground to excavate until the Burrow is several tens of centimeters deep and then the other interesting factoid is that they will urinate on to the soil and pack it down in order to keep the Burrow the nest from collapsing before they lay their eggs and then they use their feet to to bury it again so I mean they can't see what they're doing I don't know if you can tell about the picture but it's they don't have a rear view mirror on their shell so they're doing this all by feel and they've got the clumsiness of that big shell and and so what we're curious about is like well what does the sauropod nest look like so this is a sauropod nest here as you can see it's not made of sticks and twigs like a bird nest but it's actually excavated into the ground and it's a somewhat oblong shape and if we look at publication images from a site called la cama Wavell in South America in the center of each of those pictures you'll see this circular or a spherical sauropod eggs those two scattering of them there so that's probably the most round of the nests but you can see the sort of elongated way the things are deposited into a trough and that's a that's a scientific illustration so there's a rim around the nest as well so there's soil that's been piled up around here which lends evidence to excavation and then if we look at pictures of the nests taken in the field after they remove the eggs in the back walls of the excavations you can actually see that the sauropods dug deep enough and this was in all the nests a look at the sauropods excavated into the ground deep enough to expose cross bedded strata that had been deposited in the soil before they got there so sauropod nests are not built in this case on top of the ground surface they are there's evidence for them actually being excavated into the soil and that would look something like this where the sauropod comes along and in deposits the eggs into the trough were they capable of excavating the nests themselves well we think so because the trough like elongate structure of the nest seems to lend itself to a big animal using its hind legs maybe one maybe wolf switching and then probably doing a little bit of a crouching probably not letting the eggs drop ten feet into the nest but as this figure here shows you the nests are stratigraphically there's stratigraphic evidence and now potentially to anatomical evidence for scratch diggin being adaptation for nesting so there's our there's our current understanding that's scratch digging helps life find a way as it were and so that is end of part 1 of this lecture of the study and we're going to look into trackways in the second part because as it turns out if you want to figure out what sauropod feet were doing in the mud and those slippery's substrates there's fossil evidence for that in thousands of tract ways across the world and that is a that's a child sitting in a footprint full of water taking a bath Texas right any evidence that they would bury the eggs then cover them I see the pictures kind of showing them visible but then they would be vulnerable to predators yeah so and the interesting thing is that sauropods are thought to essentially have lay the eggs and then left them so they weren't really other than making the nests they weren't doing any monitoring so when the young hatch they had to sort of figure things out on their own and the evidence for whether or not the eggs were buried comes from looking at the microstructure of the eggshell because not all dinosaur eggshell is created the same and looking at little pores in the eggshell you can determine the gas conductance efficiency of the of the egg as a whole so if an eggshell is well how does this work if it's porous or if it's not porous yeah so without I don't want to misspeak here but essentially sauropod eggshell gas conductance based on porosity tells us that they would have probably been partially buried in vegetation and so there's so sort of like what you see with crocodiles and so I think when something when the eggs are buried under vegetation they need a higher porosity because you need to have oxygen supply and coming into the egg whereas if the eggs are exposed so very early on the surface you don't need as many pores because you're exposed to the air which would have been the case in theropod dinosaurs which which would have some of them would have brooded on top of the eggs the origin science scholars lectures are presented by Case Western Reserve University's Institute for the science of origins with the assistance of the Siegel lifelong learning program the College of Arts and Sciences and Media vision for more information on the origin science Scholars Program including a full video archive please visit the institute's website at origins dot case dot edu

Channel: Case Western Reserve University

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Keywords: case, western, reserve, university, science, origins

Id: 442r6ocCI_0

Length: 53min 38sec (3218 seconds)

Published: Wed Mar 18 2020