Description
Polished Dactylioceras Ammonite Fossil from Whitby, North Yorkshire
This genuine polished ammonite fossil of the genus Dactylioceras originates from the famous Lower Jurassic deposits of Whitby on the Yorkshire coast of England. Preserved within the Whitby Mudstone Formation, the fossil dates to the Toarcian stage of the Lower Jurassic, approximately 182–174 million years ago.
Whitby is internationally renowned for its fossil-rich Jurassic cliffs, which have produced some of the most iconic ammonite fossils in Britain. The specimen has been carefully selected and professionally polished to reveal the intricate internal chamber structure of the ammonite shell. The photographs show the exact fossil specimen you will receive.
This fossil includes a Certificate of Authenticity lifetime guarantee generic card, confirming that it is a genuine fossil specimen. Full sizing can be seen in the accompanying photographs.
Dactylioceras – A Classic Jurassic Ammonite
Dactylioceras is a well-known genus of ammonite belonging to the order Ammonitida, an extinct group of marine cephalopods related to modern squids, octopuses, and cuttlefish. These animals lived in the oceans for hundreds of millions of years and were among the most abundant marine invertebrates during the Jurassic period.
Within the ammonite classification, Dactylioceras belongs to the family Dactylioceratidae, a group characterised by strongly ribbed shells and open spiral coiling. These ammonites possessed a planispiral shell composed of a series of chambers separated by complex internal walls known as septa.
As the ammonite grew, it built new chambers at the front of the shell, sealing off older chambers behind it. These chambers were connected by a tube-like structure called the siphuncle, which allowed the animal to regulate buoyancy within the water column.
The shell of Dactylioceras is typically recognised by its evenly spaced radial ribs that extend across the whorls, creating a distinctive and visually striking spiral pattern.
Polished Fossil Preparation
This specimen has been cut and polished to reveal the internal chamber structure of the ammonite shell. Polishing exposes the fossilised septa and chamber walls that once helped the animal control its buoyancy while swimming.
The internal chambers may display natural mineralisation that developed during fossilisation. These minerals can create attractive natural patterns and colours within the fossil, making polished ammonites particularly popular display specimens.
The polishing process highlights the natural geometry of the shell while preserving the fossil’s original structure.
Geological Formation – Whitby Mudstone Formation
This fossil originates from the Whitby Mudstone Formation, an Early Jurassic geological unit exposed along the cliffs of the Yorkshire coast. The formation is composed primarily of dark marine mudstones and shales that accumulated in a relatively deep marine environment during the Toarcian stage.
At this time, much of Britain was covered by a warm epicontinental sea connected to the broader Tethys Ocean. Fine sediments settled slowly on the seabed, preserving marine organisms that lived within the water column.
The Whitby Mudstone Formation is famous for its exceptional fossil preservation. In addition to ammonites, the formation has produced fossils of belemnites, marine reptiles such as ichthyosaurs and plesiosaurs, crinoids, and numerous other marine invertebrates.
Ammonites such as Dactylioceras are particularly important in geology because they serve as index fossils, allowing scientists to identify and correlate rock layers of the same age across different regions.
Morphology and Shell Features
The shell of Dactylioceras is characterised by a tightly coiled spiral with pronounced ribbing across each whorl. These ribs likely helped strengthen the shell structure while also contributing to the animal’s hydrodynamic profile.
Inside the shell, the chambered structure provided buoyancy control, allowing the ammonite to maintain its position in the water column. The outermost chamber housed the living animal, while the older chambers served as buoyancy compartments.
The distinctive ribbing and coiling pattern make Dactylioceras one of the most recognisable ammonite genera from the Early Jurassic of the United Kingdom.
Jurassic Marine Environment of Whitby
During the Toarcian stage, the seas covering what is now northern England were home to a diverse range of marine life. Ammonites such as Dactylioceras swam through the water column alongside belemnites, fish, and other cephalopods.
Predators such as ichthyosaurs and plesiosaurs hunted in these waters, forming a complex marine ecosystem that thrived in the warm Jurassic seas.
When ammonites died, their shells often sank to the seafloor where they became buried in fine mud sediments. Over millions of years these sediments hardened into rock while the shells mineralised, preserving them as fossils.
Authenticity and Collector Information
This fossil is a genuine specimen from the Lower Jurassic Whitby Mudstone Formation of Whitby, North Yorkshire, UK. The photograph shows the exact fossil you will receive, providing collectors with complete transparency.
Each fossil includes a Certificate of Authenticity lifetime guarantee generic card, confirming its genuine geological origin.
Polished Dactylioceras ammonites from Whitby are among the most recognisable and historically significant fossils from the British Jurassic. This specimen makes an excellent addition to any fossil collection, natural history display, educational geology set, or cabinet of classic Jurassic ammonites.
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