First of all...

       Don't forget that no one, including me, knows everything about dinosaurs.  Many things are open to different interpretations than I have given them, so it is best, if you are researching something, to check several other print sources and websites for information.  What you see on these pages is a sort of distillation of information acquired over the years, constantly (well, as often as I can) updated to reflect changing views.  For my website recommendations, my links page has several very good sources.  For excellent print resources, please check out my sources page.  If you enjoy looking at the historical science, I can't help too much, because I was born in 1981, but if you're interested in the ideas from the transitional period of dinosaur science (late 1970s-mid 1980s), David Norman's 1983 Illustrated Encyclopedia of Dinosaurs and Robert Bakker's 1986 The Dinosaur Heresies are two classics, and Glut's two earlier encyclopedias (I forget what years they were, but the first was early 1970s, while the second was early 1980s) can give you a glimpse at the changing taxonomy and thought of the times.

    Let's get the abbreviations and other such information out of the way quickly:
    Because I'd rather not write genus, genera, and species all the time, I'll sometimes refer to them as either taxa, when the situation is plural, or taxon, when the situation is singular.  There are a few acronyms used in describing genera and species, and I use some of them pretty often.  Here they are:
        N.D.=nomen dubium, which for this page's purposes means that a certain taxon is based on such poor material it is unlikely anyone will be able to further assign material to it, leaving that taxon at best a historical curiosity.
        N.N.=nomen nudum, which means a name has been given but material has not been assigned.  Basically, the name is informal, and may or may not be expanded upon in the future.
        I.S.=incertae sedis, meaning I have a general idea where this taxon belongs, but not enough to pin it down well; thus the position is uncertain.

    There are a few more "nomen" phrases, but these are the most important for reading this page.  Some others, for when you want to impress someone at a party by using big words from dead languages, include: nomen oblitum, which means a name has been discarded through long disuse or a taxonomical challenge; nomen validum, which means a valid name (all names I don't have an N.N. or N.D. on are valid, but I've been terribly lazy and decided not to put little N.V.s after all the valid names); nomen conservandum, which means this name had been challenged, but it has been redefined and its validity upheld; and nomen vanum, which means it's missing something, but I can't remember for the life of me what.  Nomen "nonexistum" is a joke I came up with for a couple of entries in the alphabetical index, where somehow a broad term was thought to refer to a genus ("Coelurosaurus", "Carnosaurus", and "Tyreophorus"; no points for guessing what they probably refer to).  
    If you see the word "type" in parentheses after a species name, it doesn't mean I forgot to write something there, but that the particular species indicated is the type species, or the species on which the whole genus is based on.  A type species is based on a type specimen, which is supposed to include distinctive characteristics that separate that organism from all other organisms.  The words "type specimen" are usually shorthand for "holotype specimen," but there are a number of other "type" terms, indicating various conditions, that are not important for this semi-technical website to describe.  
    Another Latin word that pops up from time to time is Vide, which roughly means through; for example, Abbott vide Costello, 1999 means the name was first published in Costello, 1999, but described in Abbott's work.
    Also, I am in the habit of overusing quotation marks.  When I think it has been shown that a certain species does not belong in the genus it is assigned to, either through strong difference or dubious nature, I enclose the generic name in quotation marks and do not italicize it, i.e. "Omeisaurus" tianfuensis.  This is not standard format, but I like to use it in this informal setting to provide a good visual cue as to what's going on.

    Next, I'm not going to use time definitions like "early Cretaceous", because that's just too vague a time length, unless that's as far as a timespan  has been narrowed down to.  I prefer using ages, which typically vary in length between five and ten million years.  I will, however, put time abbreviations behind the ages I give, because even the best of us get our Berriasians and Barremiams mixed up at times.  Note, though, that you use "lower" or "upper" instead of "early" or "late" when describing formations, but "early" or "late" with the ages.  The abbreviations are as follows:

    Cretaceous (K): Late Cretaceous=LK, L for late and K for Cretaceous (C not being available)
                             Early Cretaceous=EK, E for early (note that due to a tragic oversight, there is no true Middle K)
Although there is no officially-recognized Middle Cretaceous at this time, some workers have taken to referring to the Albian-Cenomanian as a "Middle Cretaceous".

    Jurassic (J): Late Jurassic=LJ
                      Middle Jurassic=MJ, M for Middle
                      Early Jurassic=EJ

    Triassic (Tr): Late Triassic=LTr (again, plain T was occupied, so the little "r" was grafted on)
                       Middle Triassic=MTr
                       Early Triassic=ETr (which won't show up again on these pages, but it can't hurt to know)

    Time Chart: MA=mega-annum; for our purposes, the same as million years ago.  Bear in mind that all of these dates are somewhat approximate, and are typically more accurate the closer they are to us, meaning we are sure the Mesozoic ended 65 million years ago plus or minus a little relative error.  I'd like to thank T. Mike Keesey, of the Dinosauricon (a vastly superior dinosaur website-if you like dinosaurs get there immediately!) for letting me use a format very similar to his time chart.  What you see below is the most recent edition of the time chart.  The dates for the ages themselves are always in a bit of flux, giving or taking a million years here or there; while the dates come from various combined radioactive isotope dating techniques (Ar-Ar, K-Ar, several U-Pb systems, etc.), the ages are typically based on marine biostratigraphy of common, widespread, but short-lived things like types and assemblages of shelled organisms. 

Now, the famous ages:

Finally, a little bit about the little graphs on the top of each dinosaur page:
Cladistics looks for MONOPHYLETIC clades based on shared derived anatomical characteristics (known as synapomorphies), which means all of the descendants of a certain common ancestor are included.  If some are missing, the clade is PARAPHYLETIC.  These groupings are allowed in Linnean taxonomy, but not cladistics.  Even worse, if we have a situation like grouping dolphins with pikes but not including the dolphins' and pikes' common ancestor, we have what is known as a POLYPHYLETIC clade.  I generally go with cladistic usage, but will use terms like prosauropod, iguanodont, and hypsilophodont, which are not monophyletic clades, but are useful terms denoting certain general types of dinosaur.  I also don't believe in the practice of making families for one genus, and avoid it like the plague.  Thus, no Archaeopterygidae.  Similarly, I don't believe if you make one subfamily, you should need to make another when it would contain only one taxon.  For example, in Dromaeosauridae I used to have Velociraptorinae but not Dromaeosaurinae, because I consider it redundant to have Dromaeosaurus alone in Dromaeosaurinae (then they expanded Dromaeosaurinae).  What follows is a way of reading the little diagrams I make at the start of pages.  If it could be followed legibly, I would use diagonals, as the cladograms are supposed to be done, but back and forward slash keys can only do so much, so I went with vertical and horizontal lines instead.  You should take some (actually, most) of what I say with a grain of salt, because I really don't understand all of cladistics yet (maybe later).  This is sort of quasi-cladistics.  The diagrams I show have not technically been tested, but are a sort of composite of what other people have found, with some of my own opinions thrown in (so it's best to look at a few different sources, instead of relying on just me).  (I apologize now if your computer doesn't show my spacing correctly)

Disclaimer: I am not what you would call a good systemist.  I'm not even sure if that should be systemist or systematist, and I'm not sure why I'm telling you this.  So, I rely on what others have done, mixed with my own knowledge.  I am mostly interested in the genera and species, so I use my "phylogenies" as frameworks on which to hang them.  In addition, unlike most dinosaur specialists, I am not a theropod person; I'm more an ornithischian person who will muck about in the sauropodomorphs and basal theropods, and I tend to avoid the heated coelurosaurian stuff altogether.

Note: the dinosaurs in this next diagram do not exist.

<--Samplesauria=this becomes just a basal level with its Linnean meaning stripped away.  A
     |                       dinosaur in this clade can be referred to as a samplesaurian, and if it also
     |                       fits the characters assigned to Stoogesauroidea it can be referred to as a
     |                       stoogesauroid.  You will also find a link here to the previous page (that's
     |                       what the "<" means-also, a ">" tells you where to go to see the next
     |                       page:-->Somethingsauridae).
     `--Stoogesauroidea=the suffixes "oid" and "oidea" refer to superfamilies, more basal than
          |                           families.
          `--+--Howardosauridae=the suffixes "id" and "idae" refer to families.
               |     `--+--Curleyia=this genus is a howardosaurid stoogesosauroid more basal than
               |          |                     Howardosaurinae.
               |          `--Howardosaurinae=this subfamily is more derived than Curleyia, but is
               |               |                            still in the same family.  The fact that it comes off of a
               |               |                            plus sign from Curleyia's line means it is the sister
               |               |                            taxon to Curleyia, and not a direct descendant.
               |               |--Moeia
               |               `--Shempia=the fact both of these taxa are on the same down line means
               |                                    they are roughly equal in advancement (neither shows any
               |                                    character that would allow one to be seen as more derived
               |                                    than the other).  In this situation, I'll usually list alphabetically.
               `--Finesauridae=from the line, you can tell Finesauridae is a distinct family not
                    |                    descended from Howardosauridae, but sharing a common ancestor
                    |                    with it in Stoogesauroidea.  Howardosauridae and Finesauridae are
                    |                    sister groups.
                    `--Larriia=If you see a single member in a family, it is likely there are dubious
                                      members or members whose placement is uncertain (incertae sedis)
                                      within the clade.  I never list either of these two categories on the
                                      diagrams.           

Now, because the fossil record is incomplete (to say the least!), it is misleading to say that X taxon is the ancestor of Y taxon.  It may have been, but this cannot be tested in any way short of a time machine.  Instead, X taxon can be linked with Y taxon through study of its remains, but the actual relationship between the two remains unknown.