howdy in this class we'll be focused on dinosaurs but what exactly is a dinosaur if we find a fossil how do we know whether that fossil's a dinosaur and not some other animal there are many ways that the word dinosaur is used in the popular media and there are many misconceptions about what is called a dinosaur the origin of the word dinosaur is also full of confusion about what these bones we find embedded in rocks could even be and some of that confusion continues to influence public ideas of what a dinosaur is even today we did the word da when did the word Dinosauria was first defined in 1841 there were only three dinosaurs that were known then to Western scientists the first of these species was the carnivorous megalosaur reported in 1824 by William Buckland however Buckland didn't see Megalosaurus really being any different from Modern reptilian predators and maybe just a bit bigger something like a crocodile is basically what he thought megalosaur looked like the second dinosaur to be coined was Iguanodon originally identified from teeth found in a quarry by Marianne mantel and her husband The Physician Gideon mantel Gideon sort of Saw himself as being more important than just a doctor as something sort of a a scientist and so he took he became a bit obsessed with the teeth and he took them and showed them to bucklet Buckland however told him they were just fish teeth well undeterred Gideon nailed them to France to show them to the famous anatomist Georges couvier George's mailed them right back to Gideon with a note saying that they were just Rhino teeth nothing remarkable but Gideon was not convinced unrelentless he went to London and he spent a lot of time there in the collections of the Royal College of Surgeons which he was a member of he was looking through the collections of Bones Etc various species of animals trying to find teeth that looked like the teeth that had come from the Quarry the curator of the collections William Clift glanced at them and said well they look like iguana teeth just 20 times the size and indeed when Gideon compared them to Modern iguanity that is exactly how they were they were like much larger iguana teeth and so that cracked the case for Gideon he imagined that the teeth and some other assorted bones that he had found from the Quarry all together came from some very large iguana-like animal and about 20 times the size of a modern iguana something that was really quite strange and very unlike anything that was alive today he decided to name this animal iguanasaur a close friend of his in a letter said that that was a little redundant since iguanasaur in Greek just means iguana lizard and so Gideon actually changed it before publication to Iguanodon meaning to go on a tooth Gideon's claims of these giant prehistoric reptiles sparked the public interest and Gideon and his fellow fossil collectors searched the Quarry that the Iguana teeth had come from for more In 1832 Gideon described the third dinosaur species from fragments of a large armored reptile that he named haileosor this was fragmentory because Quarry workers had used explosives to extract its remains however no matter how fragmentory it was now clear that there was some lost variety of gigantic reptile-like animals that once lived had gone extinct this led into early theories about organic transmutation what we now call Evolution the changing of species from one to another however this was still years before Charles Darwin published his ideas on natural selection in 1859 and many of these early ideas about transmutation were not well thought out and we're very much scorned by high-ranking scientists speaking of high-ranking scientists Richard Owen and Aristocrat an anatomist who had a high paying University professorship and was much more higher ranking in society than either Gideon mantel or William Buckland he decided that he would coin the word Dinosauria to include these three particular animals Owens did not agree with those various unscientific claims of transmutation with species evolving in its new species on their own and so he sought to interpret the giant reptiles in his worldview as terrible lizards or as he named them dinosaurs Owen established this name in fact by inserting the term into the transcript of a speech that he had given the year before in 1840. which was about to be published in written for this is rather unusual even back then for a scientist to do and some have wondered if Owens did this because he had heard that Gideon mantel intended to name the group himself once Gideon heard of that Owens had established a name though he gave up Owens dinosaurs were terrible in the sense of the Greek dinos meaning terrible potent or fearfully great by which Owens didn't mean that they were horrible but that they were reptiles of great awesome and god-like Power you could describe the ancient Greek God Zeus as terrible in that sense same sense applies to the dinosaurs what Owen saw them as was that they they had a strange combination of reptilian bird and mammal-like characteristics from which he inferred that this was evidence that they were some sort of lineage of reptiles that had been uplifted by Divine Force gifted with mammal-like characteristics in some interval before the creation of true mammals for his role in coining the term dinosaur which would increase the public frenzy over dinosaurs Owens became involved in dictating the look of several dinosaur sculptures for the Crystal Palace grounds in London working closely with the sculptor Benjamin Waterhouse Hawkins these sculptures which opened to the public in 1854 were based on the incomplete specimens that Gideon mentel and Buckland had found and they looked very different than the dinosaurs we know today exemplifying Owen's view of dinosaurs as these enormous reptiles endowed with mammal-like characteristics via divine intervention following Owen the exact traits of what defined a dinosaur remained unclear but broadly the word King to mean reptiles of unusual size that were terrestrial the dumb land as opposed to being aquatic that they walked upright like a mammal or a bird and were extinct furthermore although Owen saw the dinosaurs as filled with great potency and strength the sculptures of the crystal Garden were instead received by the public as looking rather lazy and slow and said in their mind that dinosaurs were slow-moving Giants not competitive with modern mammals lazing in streams and easily replaced by humanity and other mammals that image largely stayed in the public mind for over a century even though paleontologists were making constant discoveries between scientists to have a somewhat different and evolving view which changed very rapidly at the end of the last century for example this T-Rex toy is from the mid-1980s and looks very different from the way that same species was depicted in a 1992 movie Jurassic Park this toy rather more closely captures that depiction that film really changed the public perception of dinosaurs and moved most folks away from the misconception Owen's initial definition of dinosaurs is terrible lizards leaves a lot to be desired in science today we build definitions based upon observable facts but not all facts are equally useful we also need to be very specific in our definitions and science because we need to communicate precisely so now that we know more than Owens and other early dinosaur work from 180 years ago how might we go about developing this definition sometimes folks use dinosaur just to mean something old like that class is taught by a dinosaur so how long ago did a group of animals lived could be a way to Define diet to define the group dinosaurs let's consider that if we Define a dinosaur as anything we only know about through fossils that they are so old that we have no living individuals we have a really broad definition animals like this trilobite that would extinct 250 million years ago is certainly not a dinosaur but that definition would make them dinosaurs we need to get more specific and say that it is only one fossil from the Mesozoic a specific time period between about 250 million years ago and 65 million years ago but fossil organisms like say an ammonite would then be dinosaurs as well so I've just given two extinct invertebrate organisms animals lacking a backbone and you're probably thinking well that if we'd also included that they had an internal skeleton and that they had a backbone the definition would work out better so uh say what about a mosasaur then if we allow if it was alive during the Mesozoic and mosasaur's avertebrates but this is still not something scientists would consider to be a dinosaur why not nor are other vertebrate organisms that we find as fossils in the Mesozoic like small mammals that were only the size of a paper clip so if being a vertebrate and having bones and a backbone on land living the mozoic is still not enough of a specific definition uh to include dinosaurs and exclude everything that's not a dinosaur we still aren't specific enough fossil bones footprints in the mud and other types of fossils give us information about the physical anatomical forms of organisms that we can use to group them we can then look at multiple detailed characteristics of the fossil and infer things about their shape or how they walked by putting together the fossil bones we find to visualize the complete organism so we might look at something we've reconstructed that had four legs walks with its feet under its body and has scaly skin and say well now I've got a good list this must be a dinosaur but we'd still fall short because because ancient relatives of today's crocodiles that lived in the Mesozoic did not have them odds brawling body Dragon walk that alligators and crocodiles have today these ancient crocodilians actually also evolve the ability to walk with their legs under their body walking with your legs under your body makes an animal a lot faster on land than if it Waddles with its limbs out as being able to do so is useful to multiple animals and could evolve in different groups because it gives them an advantage over those other sprawling animals I mean would you say that a bird is human just because we both walk on two legs or that a snake must be a worm because they all lack limbs anatomical characteristics that help animals function in the world and live their particular lifestyle can show up in lots of different unrelated groups and can cause us to put organisms in the same box so to speak even when they aren't all that similar even though Anatomy is probably the best way to define a group not all anatomical characteristics will be equally useful for creating that definition in science we've realized that simply listing characteristics and placing organisms in boxes with similar looking characteristics leads us to make some pretty poor definitions but one thing we can piece together through the anatomy of organisms is how they are genetically related to each other these definitions that rely on The evolutionary or genetic relationships among organisms are called phylogenetic definitions and we use particular anatomical characteristics of the organisms to build evolutionary trees and know their phylogenetic positions these characteristics are influenced by the lifestyle of organisms but are instead features that an organism has simply because it was passed to them from their ancestors we then Define groups based on shared ancestry inferred from anatomical similarity these groups that we Define based on shared ancestry are called clades and a clade includes the most common ancestor of the group and all of its descendants no matter how distant when in geologic time the organism lived is not relevant and whether it later evolved one or more characteristics that made it very different from the original ancestor perhaps more adapted for some particular lifestyle that doesn't matter either in this class we are primarily Examining The clade Dinosauria by which we mean the group containing the last common ancestor of all dinosaurs so the species that is the ancestor of everything that we could call a dinosaur and the descendant of that particular ancestor no matter how distant all the descendants we'll talk later in the class about how we determine these relationships and test different hypotheses of who is more related to whom but for now know that we Define these groups based on their shared ancestry there is a common ancestor of all life on our planet there is a common ancestor of all animals there is a common ancestor of all vertebrates and a common ancestor of all dinosaurs and these various clades are nested within each other such that all dinosaurs are also animals all dinosaurs are also vertebrates but not all vertebrates are dinosaurs and not all animals are vertebrates there are other groups of vertebrates with their own shared ancestors such as mammals for example oh take uh take this dimetrodon for example if you want to find a toy dimetrodon like this well you will almost certainly have to go to a toy store and walk down the aisle where the toy dinosaurs are and that's where you will probably find a toy dimitrodon and superficially well a dimetrodon looks a lot like a dinosaur but if we look at particular skeletal characteristics of dimetrodon we find some really striking differences from it and say oh a Tyrannosaurus Rex one of the obvious is looking at the skulls and with the dimitragon skull we'll see that there's actually just one hole here where the jaw muscles attach however if we look at dinosaurs like the T-Rex we see that there are actually two holes one above the eye and one below for those jaw muscles to attach if we keep looking at other fossils and at more at other modern organisms we'll find that there's lots of things that share these two different ways of attaching a jaw to a skull and will realize that we can actually group many organisms into how exactly the jaw attaches to the skull in fact having just one Hall in a skull is a feature shared by all mammals including us whereas having two holes in the skull is a trait shared by all ARCA source the clay that includes dinosaurs crocodiles and birds so this dimetrodon it turns out based upon the shared anatomical characteristics with other mammals and other species that are closely related to mammals is part of this mammal Group which we call synapses and so it's more closely related to us than it is to the Tyrannosaurus Rex and it is not a dinosaur so that is to say that we share a common ancestor with Dimetrodon and that common ancestor is shared with Dimetrodon that common ancestor does not lead to Tyrannosaurus Rex and that's a way of thinking about what is more related to what the the Tyrannosaurus Rex and crocodiles share a common ancestor which isn't in that Shane of common ancestors that leads to us in Dimetrodon ah this phylogenetic definition of dinosaurs also leads us to realize that well birds are actually Dinosaurs the Tyrannosaurus Rex and say your common chicken actually share a common ancestor that really is quite close in time that that common ancestor was probably alive sometime in the Triassic or the Jurassic the idea that dinosaurs are extinct or restricted to the Mesozoic is a misconception due to having an incomplete definition of what a dinosaur is birds have anatomical characteristics that they inherited from their ancestors characteristics that are shared with Dinosaurs but are not shared with other groups of vertebrates one aspect and you'll learn more about this later is that all dinosaurs starting right from the the most common ancestor of dinosaurs seem to have a hole through their hip that same hole is also present in today's modern chicken mentioned Hawks and ducks and ostriches so just like some vertebrates are dinosaurs some dinosaurs are birds and all birds are dinosaurs such that dinosaurs are very much alive today in this class we will often use the phrase non-avian dinosaurs two mean all the dinosaurs that are not Birds Dinosauria the clade of dinosaurs actually has Birds nested within it the non-avian dinosaurs are extinct meaning they are no longer living on our planet but birds are Extant and still living and evolving on Earth we'll use these terms often particularly we will say extinct to mean clades that are no longer living and extant to mean clades that are still with us extent can also mean that you are not extinct at that time T-Rex and Triceratops were extant at the same time in the fossil record for example as we find new fossils we try to fit them into this phylogenetic framework by integrating the anatomical characteristics of those fossils sometimes this new information fits in really neatly and we immediately know where that fossil fits in the phylogenetic tree The evolutionary relationships of all the organisms we're interested in and what it's most closely related to other times the particular mix of characteristics that we see in a fossil maybe something that we've never seen before and this new combination May alter our understanding of the relationships that we infer the big groups what is a vertebrate what is a dinosaur what is a mammal those are really well supported unlikely to change but we'll see that for smaller groups nested within dinosaurs for example there's sometimes uncertainty in those relationships and uncertainty that we will need new fossil fines and more careful study to resolve moving forward we'll use phylogenetic definitions of groups of organisms these groups are determined using characteristics that the organism have due to their shared common ancestry given everything we know about dinosaurs and their anatomical characters come from fossils we will next talk about how fossils are preserved and what processes control the fossil record beginning in the next video segment