What are the differences between all these names?
Each of these names describes a taxonomic group, or ``taxon'' (plural ``taxa''). They are progressively less inclusive - that is, the groups at the bottom of the list include fewer specimens than those at the top. At the lowest level listed here, Tyrannosaurus is a genus - the type genus of all the other taxa.
We'll start by dealing with the most familiar of these terms, then move onto the more obscure ones.
The dinosaur names that we're all familiar with - Diplodocus, Tyrannosaurus, Velociraptor, etc. - are all genus names. A genus (the plural is ``genera'') is a group of one or more species. Genus names are always written with an initial capital letter (Diplodocus, never diplodocus), and are set in italics for valid genera (those which have been properly described.)
Species names always appear together with their genus name (or its one-letter abbreviation) - a species name alone is not meaningful. Like genus names, valid species names are set in italics (Diplodocus carnegiei or D. carnegiei, never Diplodocus Carnegiei or D. Carnegiei.)
In non-technical writing, dinosaurs are nearly always referred to at the genus level - everyone talks about Velociraptor, no-one about Velociraptor mongoliensis. For some reason, there's one big exception to this: there's something irresistible about the name T. rex!
To go with the tyrannosaur example, there is a single genus, Tyrannosaurus, which is generally considered to include three species: Tyrannosaurus rex, Tyrannosaurus bataar and Tyrannosaurus efremovi. (Although some people place T. bataar in its own genus, Tarbosaurus; and some think that T. efremovi also belongs there, while others don't think it's valid at all.)
You won't see these too often, but some people like to have a classification level intermediate between genus and species (that's a subgenus) and one even more specific than species (that's subspecies.) For example, some workers consider Giraffatitan to be subgenus of Brachiosaurus (while, predictably, others consider it a genus in its own right, and others consider it a mistake, referring the species brancai to Brachiosaurus. But that's neither here nor there.)
When a subgenus name is used, it appears in parentheses after the genus name; and like a genus name, it is both italicised (when valid) and capitalised. It looks like this: Brachiosaurus (Giraffatitan) brancai.
Subspecies names are not generally used in dinosaur palaeontology; but it's a given that someone will come out with one the moment I put this statement up on the web :-)
Subspecies names, when they are used, appear immediately after the species name, but not in parentheses. (You want consistency? Go study pure maths instead!) Like species names, they are not capitalised, but are set in italics when valid. The best-known example of subspecies is probably that of humans: orthodoxy changes, of course, but there was a time when Neanderthal man and modern man were considered subspecies of Homo sapiens - they were known as Homo sapiens neanderthalensis and Homo sapiens sapiens respectively. And a good one to irritate people with at parties is the case of the two subspecies of gorilla: the type subspecies is Gorilla gorilla gorilla (Yes! Really!), the lowland gorilla; and there also Gorilla gorilla beringei, the mountain gorilla.
We sometimes wish to talk about a group of related dinosaurs - a family. Families are named after their ``type genus'' - usually either the first one to be named, or ``the most important'' genus, in some sense. The family name is made replacing the genus name's ending with the suffix ``idae''. For example, the family containing Tyrannosaurus, together with similar genera such as Alectrosaurus, Gorgosaurus and Daspletosaurus, is called the ``Tyrannosauridae''.
Like genus names - and indeed all other group names - family names are capitalised. Unlike genus names, but again like all other group names, they are not set in italics. So it's ``Tyrannosauridae'', not ``tyrannosauridae'' or ``Tyrannosauridae''.
In some cases, it's useful to break a family down further, into sub-families. Subfamily names are made by replacing the ending of the type genus name with the suffix ``inae'' (so that they are distressingly similar to family names.)
For example, the subfamily Tyrannosaurinae contains Tyrannosaurus itself along with Gorgosaurus and Daspletosaurus (and others). Some workers consider that the family Tyrannosauridae also contains another subfamily, Aublysodontidae, which contains Aublysodon and Alectrosaurus.
And sure enough, sometimes we want to talk about a group larger than a family: for example, the group containing the family Tyrannosauridae together with some other related genera. Such a grouping is called a superfamily, and its name is made by replacing the ending of the type genus name by the suffix ``oidea'' (which, yes, is also painfully easy to misread as a family name.)
Unfortunately, the superfamily Tyrannosauroidea is not a very interesting example, since no genus outside of the Tyrannosauridae is known to be inside it - although several, such as Stokesosaurus and Siamotyrannus are candidates for this classification. (A better example of a superfamily is the Hadrosauroidea, which contains the genera Ouranosaurus, Altirhinus and Nanyangosaurus as well as the Hadrosauridae.)
Of course, this isn't the end of the story. On occasion people like to talk about smaller-than-subfamily groupings such as ``tribes''. An example tribe would be the Tyrannosaurini, which has never been formally defined but might include Tyrannosaurus and Tarbosaurus, if the latter is indeed a separate genus. There are also such nonsensical groupings as Hyperfamilies, Grandfamilies, Megafamilies and even Gigafamilies. I am not making these groupings up.
Fortunately, you can ignore these. Pretty much no-one uses them any more.
Even the individual grouping names are not used that often. Consider the case of everyone's favourite duck-bill, Parasaurolophus. It's a member of the tribe Parasaurolophini, which is contained in the subfamily Lambeosaurinae, which in turn is contained in the Euhadrosauria, then the Hadrosauridae, Hadrosauroidea, Iguanodontoidea, Styracosterna, Ankylopollexia, Dryomorpha, Euiguanodontia, Iguanodontia and Euornithopoda. Which is, of course, contained in the sub-order Ornithopoda.
Who needs all that? No-one. Don't let it bother you. Once you're down beyond the sub-order level, families, subfamilies and superfamilies are 99% of the game.
When we want to say that an animal is a member of a superfamily Somethingidae, we describe it as being a somethingid (not capitalised.) Similar rules exist for the other groups, as follows:
So, for example, we can say that an Alectrosaurus is a tyrannosauroid and also a tyrannosaurid, but not a tyrannosaurine nor a tyrannosaurin.
The group types genus, species, family, subfamily etc. are called ``ranks''. They come from the old-fashioned Linean system of taxonomy. When the more modern cladistic system is used strictly, ranks other than genus and species are not used (although the groups themselves - Tyrannosauridae etc - are.)
For a much more complete and scholarly treatment of tyrannosaur relationships, see Thomas R. Holtz Jr.'s Tyrannosauroidea page in the the Tree Of Life: ag.arizona.edu/tree/eukaryotes/animals/chordata/dinosauria/tyrannosauroidea/tyrannosauroidea.html
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