[MUSIC] I'm Carly Miller from the University of Illinois and here we are at the field museum in Chicago, Illinois in the dinosaur hall in the exhibit Evolving Planet. So what we want to cover today is the specific sub groups of dinosaurs. Once again, are probably our favorite extinct reptiles. So the dinosaurs are split up into two different groups and those groups are differentiated by their hip structure, which seems rather specific but it is a distinguishing feature here. The two groups are the Saurischians and the Ornithischians. Saurischians are named such because their hip structure is an analog to modern day lizards. So, Saurischian, that's lizard hip and then Ornithischian. Ornith is bird, ischian refers to the hip bone as well. All right, so let's take a look a little bit more closely at this distinguishing feature or morphology of the hip structure that separates dinosaurs into two different groups, the Saurischians, or the lizard hipped dinosaurs, and the Ornithischians, the bird hipped dinosaurs. The first group, the Saurischians, are called that because that actually means lizard hipped, saur isch. So, the Ischium is a bone in that pelvic girdle. So we have the Ilium, the Ischium, and the Pubis. That's the technical information that you're going to need to remember. So the Ornithischians are actually termed bird hipped. And so, again, we're talking about the Ischium, the Ilium and the Pubis. So that actual distinction is that the ischium and the pubis are arranged differently in those two groups. So in the Saurischian groups, the lizard hips again, the ischium and the pubis are actually perpendicular to one another. So the pubic bone actually hangs down, if you will, into the stomach of these large Saurischians. The Ornithischians, or bird hips, the ischium and the pubic bone are parallel to one another. And again, dinosaurs are broken up into these two big groups based on just their hip structure. Pretty interesting information. If we can go into the Saurischians a little bit more in detail, I'm sure you're familiar with these. The theropods or T Rex, those guys are actually bipedal, they run on two legs and they're carnivorous. Again we're focusing in on the hip structure here so that we can distinguish between two groups of dinosaurs, Saurischians and Ornithischians. What you can see here is you can kind of see a big blade like structure which is the two pubic bones, on this Therapod, hanging down into the stomach and it's perpendicular to the ischium bones which are pointing back towards the tail. So what we're looking at here is a precursor to actual modern day birds. Just to remind you, they're still grouped in the Saurischian group of dinosaurs with lizard hip structure. Again, this is a little bit misleading because these are the precursors to modern day birds, and yet they're exhibiting the lizard hipped structure. Actually, something to remember is that Saurischian's are the ones, and specifically the theropods, that gave rise to modern day birds. So this nomenclature is somewhat misleading because the bird hipped dinosaurs actually didn't give rise to modern day birds. The Saurischians or the lizard hipped dinosaurs are the ones that actually, were the precursors to modern day birds. And the second group is the Sauropodomorpha, it's a large word, it's a mouthful. But those are the really really large, large dinosaurs. They have barrel-like bodies. They're huge organisms, but they eat grass, [LAUGH] more or less. They're herbivorous. Take a look at this sauropodomorph behind me. The scale of this reptile is astounding. So again, I'm about 6' tall, almost, and I only reach up to this animal's knee, his lower leg bone, the tibia. That's amazing. Look at his hip structure. He has a nice lizard hip structure here, with the pubic bone pointing down towards the stomach and the ischium pointing back towards the tail, kind of in this perpendicular composition here. But look at the scale of this Sauropodomorpha. That is amazing. All right, there are five groups within the Ornithischian group, and those are, again, the bird-hipped dinosaurs. The first one that we'll talk about is the Stegosaur, which is here behind me. You can tell it's a Stegosaur by a series of vertical triangular plates that extend parallel to the backbone bone and run from head to tail. Again, this organism is quadrupedal and it's herbivorous. The second group is the Ankylosaurus. Ankylosaurus are a heavily armored quadruped, but again they're herbivorous, but you can tell it's an Ankylosaur by a series of plates all on the back. It's heavily armored and it's got spikes projecting from it's sides. Very protective organism there. The third group is the Ornithopods. Ornithopods is a very diverse group of dinosaurs. There's many different morphologies there. But the things to remember are that they might have walk quadrupedally and ran bipedally to flee from their predators. Again they're herbivorous organisms. It's a very diverse group. So this Hadrosaur clearly exhibits the bird-hip orientation that defines the Ornithischians, which are the bird-hip dinosaurs. So what we can see here is the pubic bone running this way and the ischium running back towards the tail, so they're almost in a parallel orientation here, and that's the definition of an Ornithischian. So here we have a gorgeous example of the dinosaur group, Ceratopsia. You'll notice that it's quadrupedal. It's herbivorous which is great. Not too scary here. And you can see the protective measures that this dinosaur has developed. It has a huge sweeping plate coming off the back of the skull and you can see these three projecting horns coming off the front of the skull. One, two and three here. The last group of Ornithischian's are the Pachycephalosauria, and they're named that because of this thick dome that actually has grown into a big, bony, protective structure on the top of their head. These guys are actually bipedal, a change there, but they still are abiverous. We're wrapping up here in the dinosaur hall at the field museum in Chicago, Illinois and something that's just shocking that we're noticing looking around at these dinosaurs is one, just the number of dinosaur bones that have survived so long since the Mesozoic Era. So we're talking tens of millions of years ago. [LAUGH] Up to hundreds of millions of years ago, that is shocking to me. And, but they have such robust skeletons that a lot of those hard parts have survived that long, and we can piece together those skeletons and learn a lot about how they ate, how they hunted, how they interacted with one another and the environments in which they live. So if you have a chance, check out your local museum. And even if it's just a piece of a dinosaur you will be shocked an excited by just these amazing reptiles. [MUSIC]
