@article {7555,
	title = {Generation and maintenance of gradients in taxonomic diversity},
	journal = {Science},
	volume = {164},
	year = {1969},
	note = {reprint},
	pages = {947-949},
	keywords = {diversification, fossil record, gradients, paleontology, taxonomy},
	author = {Stehli, Francis G. and Douglas, Robert G. and Newell, Norman D.}
}
