Because of preservational bias, most fairly complete specimens have been found in the chalks of Kansas which represent a marine setting well out from shore.

see Oceans of kansas

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(By the way, I hate it that so many papers in the areas of planetary science and geology are not easily available to the dreaded "non-subscribers". It is like they are screaming at me: "YOU CAN'T HANDLE THE TRUTH". Good, I feel better now.)

"Quaerendo inventis"