cast are sunk in
It is called a mold fossil, which can become a cast fossil. After the soft parts of the animal rot away, a cavity remains (the mold fossil) which becomes filled with hardened sand or mud (the cast fossil).
cast
A replica of a fossil produced by filling a mold with sediment or crystals is called a cast fossil. It provides a detailed three-dimensional representation of the original fossil and is often used in scientific research and educational settings.
Bing's picture yesturday was of a living fossil I really didn't look into it but maybe you should.
The key difference between the shell on the left and the cast fossil on the right lies in their formation. The shell is a physical structure that was once part of a living organism, while the cast fossil represents a replica of the original shell's shape created by sediment filling in the mold left behind after the shell decayed or was removed. Essentially, the shell is the original material, whereas the cast fossil is a mineralized impression.
The cast of Picture Show - 2013 includes: Allene Lindsey as Marion
The cast of The Big Picture Show - 1994 includes: Ken Kirkby as himself
The cast of The Oddville Picture Show - 2009 includes: Steven Morel Jenny Parsons
The cast of First Picture Show - 1975 includes: Gavin Millar as Himself - Presenter
The cast of The Stanley Baxter Picture Show - 1972 includes: Stanley Baxter as Various Roles
The cast of The Golden Oldie Picture Show - 1985 includes: Dave Lee Travis as Himself - Presenter
The cast of The Last Horror Picture Show - 2005 includes: Robert Englund as The Janitor Kane Hodder
The cast of Picture Show at the End of the World - 2009 includes: Peter Barron as Bk Jeff Brownrigg as The Barber
The cast of Uncle Josh at the Moving Picture Show - 1902 includes: Charles Manley as Uncle Josh
The cast of The Silent Horror Picture Show - 2008 includes: Soumita Acharya as Monster Pablo Bubar as Victim
The cast of The Last Picture Show Re-Release Promo - 1971 includes: Peter Bogdanovich as himself
See one by clicking on the link below: