ICZN or NOT!!!

[Steven Mahon <floridamahon@yahoo.com>]

Hello Again,

I have another question. (Which probably has an easy
answer). I know alot of people, in accordance to ICZN,
use the first-named genus to name the family etc..
Well, I've that some families do not follow this.
(With the exception of Nomen Dubia).
For example:

Stegoceras 1902 > Pachycephalosaurus 1943
Lycorhinus 1924 > Heterodontosaurus 1962
Hypacrosaurus 1913 > Lambeosaurus 1923
Yangchuanosaurus 1978 > Sinraptor 1994

Those are only a handful out all the families I've
noticed. Could anyone tell me why the second names are
used over the first?

    Thanks Again,
        Steven Mahon

s/n's/dinoboy219 & stevensaurusrex
site/http://www.geocities.com/floridamahon/Classifosauria.html?1054160741913
title/aspiring paleontologist

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