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RARE Aulacostephanus pseudomutabilis Ammonite Fossil Block Elsworth Rock Upper Kimmeridgian Jurassic UK
RARE Aulacostephanus pseudomutabilis Ammonite Fossil Block Elsworth Rock Upper Kimmeridgian Jurassic UK - Image 2

RARE Aulacostephanus pseudomutabilis Ammonite Fossil Block Elsworth Rock Upper Kimmeridgian Jurassic UK

£60.00

A rare and scientifically significant ammonite fossil block featuring Aulacostephanus pseudomutabilis, from the Upper Kimmeridgian stage of the Late Jurassic, discovered in the Elsworth Rock Formation at Elsworth, Cambridgeshire, United Kingdom. This is an uncommon and visually impressive specimen showcasing one of the key ammonite genera used in high-resolution Jurassic biostratigraphy.

  • Fossil Type: Ammonite (extinct marine cephalopod)
  • Species: Aulacostephanus pseudomutabilis
  • Format: Fossil block with visible shell detail
  • Size: See photo with 1cm scale cube for full sizing
  • Geological Period: Jurassic
  • Stage: Upper Kimmeridgian (~156–152 million years ago)
  • Formation: Elsworth Rock (part of the Ampthill Clay / Kimmeridge Clay group)
  • Locality: Elsworth, Cambridgeshire, England, UK
  • Family: Aulacostephanidae
  • Superfamily: Perisphinctoidea
  • Order: Ammonitida
  • Depositional Environment: Quiet marine basin with clay-rich sedimentation, part of the Late Jurassic epeiric sea system of southern Britain

Geological & Scientific Significance:

Aulacostephanus pseudomutabilis is a key zonal species for the Upper Kimmeridgian and is widely used in regional and intercontinental ammonite zonation schemes. It is known for its strongly ribbed shell with bifurcating ribs and distinctive outer whorls.

This specimen comes from the Elsworth Rock, a compact, fossiliferous layer rich in ammonites and bivalves, within the broader Kimmeridge Clay Formation. These marine deposits were laid down during high global sea levels, forming part of one of the best-known Late Jurassic marine successions in Europe.

The ammonite’s shell features—such as its open umbilicus, pronounced ribbing, and planispiral coiling—reflect an active, nektonic lifestyle in open marine settings.

Notable Features:

  • Classic ribbed morphology of Aulacostephanus with strong bifurcating ribs
  • From a rare fossiliferous layer in Cambridgeshire’s Upper Jurassic beds
  • Excellent preservation and stratigraphic value
  • Ideal for collectors, educators, and Jurassic fossil specialists

Authenticity Guaranteed: All of our fossils are 100% genuine. This ammonite block is provided with a Certificate of Authenticity, verifying scientific identification and provenance.

Photo Disclosure: The exact specimen shown in the images is what you will receive. A scale cube with 1cm squares is shown for sizing accuracy.

This Aulacostephanus pseudomutabilis fossil block is a superb and rare example from England’s Late Jurassic seas—perfect for display, study, or collection.

(Actual as seen)

Only 1 left in stock

SKU: UF4579 Category:

Description

A rare and scientifically significant ammonite fossil block featuring Aulacostephanus pseudomutabilis, from the Upper Kimmeridgian stage of the Late Jurassic, discovered in the Elsworth Rock Formation at Elsworth, Cambridgeshire, United Kingdom. This is an uncommon and visually impressive specimen showcasing one of the key ammonite genera used in high-resolution Jurassic biostratigraphy.

  • Fossil Type: Ammonite (extinct marine cephalopod)
  • Species: Aulacostephanus pseudomutabilis
  • Format: Fossil block with visible shell detail
  • Size: See photo with 1cm scale cube for full sizing
  • Geological Period: Jurassic
  • Stage: Upper Kimmeridgian (~156–152 million years ago)
  • Formation: Elsworth Rock (part of the Ampthill Clay / Kimmeridge Clay group)
  • Locality: Elsworth, Cambridgeshire, England, UK
  • Family: Aulacostephanidae
  • Superfamily: Perisphinctoidea
  • Order: Ammonitida
  • Depositional Environment: Quiet marine basin with clay-rich sedimentation, part of the Late Jurassic epeiric sea system of southern Britain

Geological & Scientific Significance:

Aulacostephanus pseudomutabilis is a key zonal species for the Upper Kimmeridgian and is widely used in regional and intercontinental ammonite zonation schemes. It is known for its strongly ribbed shell with bifurcating ribs and distinctive outer whorls.

This specimen comes from the Elsworth Rock, a compact, fossiliferous layer rich in ammonites and bivalves, within the broader Kimmeridge Clay Formation. These marine deposits were laid down during high global sea levels, forming part of one of the best-known Late Jurassic marine successions in Europe.

The ammonite’s shell features—such as its open umbilicus, pronounced ribbing, and planispiral coiling—reflect an active, nektonic lifestyle in open marine settings.

Notable Features:

  • Classic ribbed morphology of Aulacostephanus with strong bifurcating ribs
  • From a rare fossiliferous layer in Cambridgeshire’s Upper Jurassic beds
  • Excellent preservation and stratigraphic value
  • Ideal for collectors, educators, and Jurassic fossil specialists

Authenticity Guaranteed: All of our fossils are 100% genuine. This ammonite block is provided with a Certificate of Authenticity, verifying scientific identification and provenance.

Photo Disclosure: The exact specimen shown in the images is what you will receive. A scale cube with 1cm squares is shown for sizing accuracy.

This Aulacostephanus pseudomutabilis fossil block is a superb and rare example from England’s Late Jurassic seas—perfect for display, study, or collection.

Additional information

Era

Jurassic
Origin

United Kingdom

Jurassic Information

The Jurassic Period (201–145 million years ago) was the golden age of dinosaurs, with iconic species like Brachiosaurus, Stegosaurus, and Allosaurus dominating the land. It was a time of warm, humid climates, with high sea levels that created vast shallow seas, supporting abundant marine reptiles, ammonites, and early coral reefs. The first birds, such as Archaeopteryx, evolved from small theropod dinosaurs, while early mammals remained small and nocturnal. Lush forests of cycads, conifers, and ferns covered the land, providing food for giant herbivores. The breakup of the supercontinent Pangaea accelerated, shaping Earth's geography and setting the stage for the diverse ecosystems of the Cretaceous.

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