|The Linnaean System|
|In the Linnaean system (and taxonomic systems based on it), the Genus is the first grouping of species, the ranking between Family or Tribe and Species. Only very closely related species are grouped together in a single genus. The genus is sort of like the surname, whereas the species is the first name. So Canis lupus, the wolf, is distinguished from Canis familiaris, the domesticated dog. Although very similar they are still distinct species, but belong to the same genus. Or in man, Homo erectus and Homo sapiens. Note that the higher ranking genus) name is written first. This is like the Chinese system of names where the family (sur-)name comes before the individual name. e.g. Kung-fu-tze (Confucius) was literally "Mr Kung" (Kung being the family name). As a formality the genus name, like the species name, has to be written in italics. Where that is not possible it should underlined, e.g. Homo erectus (that one is not a link ;-) ).|
|Subgenus||Genus (Subgenus) species|
Note that the genus name is only one half of the scientific name. That is why it is called the binomial system - there is genus and species. Many books on dinosaurs and prehistoric life (and also web sites) only give the genus name as if that was the complete name. But in fact it is actually, to give an example, Triceratops horridus, not just Triceratops. The only prehistoric animal in which the species name is usually given is of course the famous Tyrannosaurus rex. There are actually several species of Tyrannosaurus though, the species found in Mongolia is known as Tyrannosaurus bataar.
There is a regrettable tendency though to split up vertebrate especially dinosaurian) genera so that each genus only has a single species - e.g. T. bataar is often called Tarbosaurus, despite being so similar to Tyrannosaurus it is not funny.Such oversplitting also occurs among fossil invertebrates, groups like the Nautiloidea mollusks) are serious oversplit with much too many genera - especially if you compare them to recent mollusks.