A Important Cretaceous Ammonite in Concretion
Lot 2090W
Slash - Singular Ammonite with Mysterious Slash Mark
US$ 80,000 - 90,000
£50,000 - 56,000

Lot Details
Slash - Singular Ammonite with Mysterious Slash Mark
Placenticeras costatum
Cretaceous
Pierre Shale, South Dakota

Discovered in the Baculites compressus zone of the Pierre Shale in a dry creek bed in Western South Dakota, this extraordinary fossil ammonite was freed from a 600-pound calcareous concretion. As the ammonite was uncovered, an extraordinary feature was revealed – a straight-line slash across the ammonite's shell, hence, the nickname, Slash. Though mosasaur bite marks have been observed in ammonites, never has a scar of this type been seen.

Fortuitously, the piece presents as part and counterpart, displaying both a "positive" and "negative" portion. The "negative" side exhibits the presence of over 150 limpet home scars immaculately preserved. Also visible are its umbilical tubercles, intricately preserved. The shell boasts a rainbow of iridescent colors including red, green, pink, yellow and blue.

Perhaps a prehistoric sawfish produced the scar. One scientist suggested that the "Cretaceous equivalent of a swordfish" might have been the attacker. Mosasaurs and giant turtle species are also known to have lived as contemporaries to Placenticeras costatum. The question of what caused the unusual marking remains the central mystery to this singularly fascinating specimen. Part and counterpart are offered on custom wooden tree portions. (2) Overall ammonite shell measures 27 ½ x 22 x 7in
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    Auction Administration - Natural History
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