Dinosaur Family Tree-Ornithiscians

When we construct our dinosaur family tree, we are going to stick to most of the major branches.  Most of the branches can be subdivided even further or branched out into yet more directions, but we're going to keep this simple for now.

OK. Lets start with the ornithischian branch. Now if you remember from our topic on What is a dinosaur? all dinosaurs that belong to the ornithischian group are plant-eaters. Some of these dinosaurs are quadrupedal (walk on all fours, like our dog or cat), some bipedal (walk on two hind legs), and some switch from four-legged to two-legged depending on the situation.

Some of the branches have a representative dinosaur for that branch. The branch itself is usually named after that particular dinosaur. There are several reasons for this. The dinosaur may be the first discovered for that particular branch. It may be the oldest representative of that branch. Or, it may be the only member of that branch, but it is significantly different enough to not fit into any other category.

So, we said we're starting with ornithischia. From there, the first level branches are, thyreophorans, ornithopods, and marginocephalians. Wow, are they a mouthful or what? Well, scientists like to use big words. Thyreophorans is the main group that contains all the armored dinosaurs. These were dinosaurs like scelidosaurus, ankylosaurus and stegosaurus. You've probably seen a picture of an Ankylosaurus. They look like little tanks with four legs. They had bony protuberances over their entire bodies, even their eyelids! Stegosaurus is the dinosaur with huge plates running down it's back with a spiked tail. Stegosaurs were the animals walking through the stream in The Lost World: Jurassic Park 2. Scelidosaurus is not so well-known. They were the precursors to stegosaurs and ankylosaurs.

The next branches to come from ornithischia are ornithopods and marginocephalians. Yikes! The words are getting bigger. Not to fear. We'll take them one at a time.

Ornithopods further break down into hypsilophodontids, iguanodontids, and hadrosaurs. Hypsilophodontids are represented by, none other than: Hypsilophodon. big surprise, eh? They were small (7.5 feet long), bipedal, plant-eater with large eyes and a beak. Iguanodontids are represented by Iguanodon. See how easy this is? They were one of the first dinosaurs discovered. They were quite large (20-30 feet long). They walked on two feet or four, whichever was required. And they had a spike where their thumb would be. Hadrosaurs are commonly called "duck-billed" dinosaurs. They are broken down into crested and non-crested types. Hadrosaurus, the first dinosaur to be discovered in North America (in New Jersey, in fact...woo hoo) is a member of the hadrosaur group. They are the non-crested group. A parasaurolophus, with it's long bony head gear is a member of the crested group (separated out as lambeosaurines)

The last group branching out from ornithopods that we are going to talk about are the marginocephalians. These were the group sporting the fanciest headgear around. This group is further broken down into pachycephalosaurs and ceratopsians. Pachycephalosaurs are affectionately called boneheads.They had a thick bony skull which scientists are still debating on what it was used for. That group is represented by Pachycephalosaurus. Ceratopsians were the horned dinosaurs. They came in various sizes (some up to 30 feet in length) and all had an array of frills, horns, and bony protrusions on their skulls. Triceratops, from this group, is quite well known with it's large frill and three horns on it's skull.

That was a basic description of some of the major groups in the ornithischian branch. There are many more subgroups and off shoots that are changing all the time. Some are being added, some are being combined, and yet others are being eliminated.

So, now lets take a look at the saurischian group and its many branches.


Next-Dinosaur Family Tree-Saurischians.