Eubostrychoceras
Corkscrew-shaped heteromorph ammonite from the Upper Cretaceous.
Eubostrychoceras is a genus of heteromorph ammonite with a corkscrew-shaped shell that coils helically, leaving an open, empty umbilicus at the center. Its coiling is usually right-handed (dextral), and the shell is covered with moderately strong, straight ribs that run across the whorls. The aperture, or opening, reverses direction near the end, pointing upward or back toward the apex. The sutures are moderately complex, and the siphuncle is positioned at the middle of the flank. This genus lived during the Upper Cretaceous, from the Middle Turonian to the Campanian, and belongs to the ancycleratid family Nostoceratidae. Fossils have been found across a wide geographic range, including Antarctica, Japan, Spain, the far east of Russia, Alaska, Vancouver Island, the U.S. Western Interior Seaway, Germany, and Madagascar. A 2001 report also documented it from Alaska’s Matanuska Formation. The species *E. japonicum* is Turonian in age, likely restricted to the middle Turonian, and based on shell texture, coiling, and stratigraphic relationships, *E. valdelaxum* from Japan probably evolved from it. Related genera include *Anaklinoceras*, *Bostrychoceras*, *Didymoceras*, and *Nostoceras*.
Quick Facts
- Taxon
- Eubostrychoceras
Facts from the source article.
Lore & Background
Eubostrychoceras is characterized by a loosely to tightly wound spiral forming a corkscrew with an open, empty umbilicus in the middle. Coiling is commonly dextral (right hand), and the shell is covered by moderately strong, straight transverse ribs. The aperture reverses general direction and points upwards or back towards the apex, while sutures are moderately complex and the siphuncle is located mid flank.
Reader's Guide
Eubostrychoceras is significant for its unusual corkscrew morphology among heteromorph ammonites, providing insight into the diversity of shell forms during the Upper Cretaceous. Its widespread distribution across multiple continents and marine deposits, including the U.S. Western Interior Seaway and the Matanuska Formation in Alaska, makes it a useful index fossil for correlating Middle Turonian to Campanian strata. The evolutionary relationship between E. japonicum and E. valdelaxum, based on shell texture and stratigraphic position, highlights patterns of speciation within the Nostoceratidae family. The genus contributes to understanding the adaptive radiation of heteromorph ammonites in Cretaceous seas.
Did You Know?
- Eubostrychoceras has a corkscrew shell with an open, empty umbilicus in the middle.
- E. valdelaxum from Japan likely evolved from E. japonicum based on shell texture and stratigraphy.
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