Unlike the Ornithischian dinosaurs, Saurischia vary greatly in their body plan. So rather than just giving you a handful of subgroups to look at, we have to further break lizard-hipped dinosaurs into more manageable groups. The first group we will look at is the sauropods.
Sauropod (if you haven't pieced it together from all the fancy lingo you are picking up), means "lizard foot", though most people will identify them by their more Land-Before-Time-ish name of 'long-necks'. This group contains the largest dinosaurs that ever lived and are probably the most recognizable group.
We can break up the sauropods into three major groups (again there are others, but this is just easier right?), Diplodocoids, Brachiosaurs, and Titanosaurs. These are among the most distinguishable of the sauropods, though it is really only a sampling of the later forms. The easiest way two distinguish the Diplodocoids from the other two is that they tended to grow horizontally, while the Brachiosaurs and Titanosaurs grew vertically. The former group contained genera like Apatosaurs, Diplodocus, and Brontosaurus, while the latter two had Brachiosaurus and Giraffatitan.
(Saltasaurus would be an easy exception to this rule as its body plan was more horizontal despite being part of the Titanosaur clade. But a closer look at how the neck attaches to the body, shows its separation from the Diplodocoid groups).
As an additional note, because I think everyone gets the hang of the long-necks, I wanted to broach the issue of some of these weird terms. Specifically, the 'saurids' vs. 'sauroids' suffix, thing. I have to reiterate that I am not a scientist and I only grasp a basic knowledge of these things myself from my own exploration, but you aren't alone when it comes to the confusion of all the variations on a name. Sometimes you see Diplodocus, other times it is Diplodocids, and what the heck is a Brachiosauroid?
Okay, if you see a dinosaur name and it ends with 'us', odds are you are looking at a very specific dinosaur. Diplodocus, refers to a genus of sauropod dinosaurs. If we said Diplodocus carnegii or D. carnegii, we are referring to a specific species of Diplodocus (remember all that Linnaean chart stuff from Part 1?). If we use the suffix 'id', we are referring to the larger group. Diplodocid, refers to the Family which contains all the various genera and species that branch from it. To use our initial example, it would be the Ursid family of the bears.
Now, the 'oid' suffix is a bit more difficult. This is used to refer to a group that is similar to the named group, but not actually found within it. If I have the Diplodocoid group, I am refering to the family that contains Diplodocus (the genus). If I have a dinosaur that is a Diplodocoid, let's say Haplocanthosaurus, it is not quite part of that family, but it is close enough to still be grouped somehow. Check out this classification map and find Haplocanthosaurus (part of the Diplodocoids) and then find Diplodocus (part of the more specific Diplodocids). It looks like it should belong, but it sits just outside that latter set of branches.
Next time: Part 5 - Saurischian Dinosaurs - Therapods