Much of my memories of dinosaurs are fuzzed with time. However, they’re still clear enough for me to inflict them upon you in the form of random trivia and griping, aided by the Wikimapedius. That’ll teach you to use the internet, you danged kids.
First of all, there is no Brontosaurus. Your parents lied to you, they brought down the presents after you were asleep and ate the milk and conifer leaves themselves. Time to grow up and move on.
NOT BRONTOSAURUS.
What there WAS is Apatosaurus. Yes, “Deceptive Lizard” sounds much less cool as a scientific name than “Thunder Lizard,” but there you have it. Othniel Marsh screwed up and named the same genus of animal under two separate names, first Apatosaurus in 1877, then Brontosaurus in 1879. The only time on earth at which Brontosaurus existed was between the years of 1879-1903, when a man named Elmer Riggs politely pointed out that the skeletons were too similar for that shit to fly, and so they now are as one under the original genus: Apatosaurus
Secondly, dinosaurs were reptiles. Taxonomic classification of our “terrible lizards” is as follows: Kingdom Animalia (animals), Phylum Chordata (things with some kind of cartilege rod and nerves along their backs), Subphylum Vertebrata (things with backbones), Superclass Tetrapoda (they gots four legs, or limbs, or whatever), Class Reptilia Sauropsidia (our lovable scaly scallawags, the reptiles, and the birds), Subclass Diapsida (reptiles that gots two holes on either side of their skull), Infraclass Archosauromorpha (“ruling lizard forms,” containing, among still-living things, crocodiles). Superorder Dinosauria (and very super indeed, good sir). There will be an exam.
Now that we’ve established the reptilehood of dinosaurs, it’s time to state this: being a reptile does NOT equal being cold-blooded and covered in scales (in fact, since cold-blooded and warm-blooded are widely derided as inaccurate, half-formed concepts with many grey areas and fuzzy thinking, very little equals being cold-blooded). It goes something like this:
- –Dinosaurs are a subgroup of reptiles.
- -Some dinosaurs evolved into birds.
- -Therefore birds are a subgrouping of dinosaurs, which also makes them a subgroup of reptiles.
- -Therefore being a reptile does not mean you have to be scaly and ectothermic (dependant upon your environment for heat regulation, or “cold blooded”).
This duck has tried passing as non-reptillian. It's only lying to itself.
At this point it should be mentioned that by now pretty much absolutely everybody accepts that birds are dinosaurs, taxonomically speaking. Once you’ve found fossilized feather imprints and/or evidence of quill knobs in more than twenty species of dinosaur, you shouldn’t really still be skeptical about any sort of possible relationship between the two groups.
As to the dinosaur’s own means of body heat, it’s one of the biggest debates in paleontology, and it’s still being argued about, although they’re widely regarded as endothermic nowadays (Endothermic: controlling their body heat from within, such as via retaining heat through sheer bulk or burning energy to produce your own, like mammals or birds). Nowadays a lot of the arguing is over exactly how they did it, because it isn’t science if you aren’t constantly trying to tear each other’s and your own theories apart. No, really, that’s how it works.
Thirdly, allow me to present you with the following incredibly simplistic dinosaur division guide.
-The Superorder Dinosauria (still totally super) is divided into the two Orders Ornithischia (bird-hipped) and Saurischia (lizard-hipped) based upon, well, the appearance of their hips.
- The Saurischia contains the suborders Sauropodomorpha (sauropods and prosauropods, aka “the big dudes with really long tails and necks”) and Theropoda (therapods, aka “those two-legged, meat-eating guys with the sharp pointy teethings”).
- The Ornithischia contains, well, almost everything else, pretty much all herbivores. The ceratopsians (horned guys), ornithopods (“duckbilled dinosaurs”), stegosaurs and ankylosaurs. Funnily enough, given the naming, birds came from the Saurischia, not the Ornithischia (too bad – winged Triceratops would be awesome).
There you have it, your incredibly simplistic dinosaur classification guide. Now, for my last trick of presenting old and stale information….
All together now: MARINE REPTILES AND PTEROSAURS! WERE! NOT! DINOSAURS!
NOT A DINOSAUR.
ALSO NOT A DINOSAUR
Use the following rule-of-thumb flowchart if you grow confused with these simple, simple facts when confronted with a Mesozoic Era beastie. 
Now I’m going to go regret that I will not see a human being devoured by a Tyrannosaurus in my lifetime.
Updated on June 29th, 2009 with some added taxonomy, because I am slow and stupid.
All original material copyright Jamie Proctor, 2009.
Picture Credits:
- Brontosaurus: Public Domain image from Wikipedia.
- Mandarin Duck: Public Domain image from Wikipedia.
- Mosasaurus: Public Domain image from Wikipedia, defaced in Microsoft Paint.
- Ramphorhynchus: Public Domain image from Wikipedia, defiled in Microsoft Paint.
- Dinosaur Flowchart: Myself, once again in Paint.