Description
Cymbites Ammonites in Fossil Woodstone from the Jurassic Coast
This genuine Cymbites sp. ammonite fossil preserved within fossil woodstone originates from the Charmouth Mudstone Formation at Lyme Regis, Dorset, United Kingdom, part of the world-famous Jurassic Coast UNESCO World Heritage Site. These fossils date to the Lower Jurassic Period during the Sinemurian–Pliensbachian stages, approximately 199 to 183 million years ago, when southern Britain was submerged beneath warm shallow seas.
This unusual specimen combines ammonite fossils with fossilised woodstone, creating a striking and scientifically interesting association between marine life and transported terrestrial plant material. Ammonites such as Cymbites were free-swimming marine cephalopods that inhabited Jurassic oceans, while the fossil wood represents plant material carried from nearby land into the marine environment where it eventually became fossilised alongside marine organisms.
Specimens preserving both ammonites and fossilised wood are particularly interesting because they illustrate the interaction between terrestrial and marine ecosystems during the Early Jurassic.
Geological Setting of the Charmouth Mudstone Formation
The Charmouth Mudstone Formation forms part of the Lower Lias Group, a sequence of marine mudstones and shales deposited in an offshore marine basin during the Early Jurassic. These rocks are widely exposed along the coast between Lyme Regis and Charmouth in Dorset, an area renowned for its exceptional fossil preservation.
During the Sinemurian and Pliensbachian stages, the region lay beneath a relatively deep marine shelf connected to the Tethys Ocean. Fine sediment accumulated slowly on the seabed, creating conditions that allowed the preservation of delicate fossils including ammonites, fish remains, marine reptiles, and plant debris transported from nearby land.
Storm events and river systems occasionally washed driftwood and plant fragments into the sea, where they settled on the seabed. Over time, these materials were buried by mud and mineralised to form fossil woodstone, sometimes preserving marine organisms that settled nearby.
Classification of Cymbites Ammonites
Cymbites belongs to the phylum Mollusca, class Cephalopoda, subclass Ammonoidea, an extinct group of marine animals related to modern squid and octopus.
Ammonites possessed tightly coiled shells divided into chambers separated by complex septa. These chambers were connected by a tube-like structure called the siphuncle, which allowed the animal to regulate buoyancy by controlling gas and fluid within the shell.
Members of the genus Cymbites are early Jurassic ammonites recognised by their relatively smooth shells and gently rounded whorls. These animals were active marine predators or scavengers, feeding on small marine organisms while swimming in the open ocean.
Ammonites are among the most important index fossils used by geologists to identify and date Jurassic rock layers because they evolved rapidly and had wide geographic distribution.
Morphology and Notable Features
Cymbites ammonites typically display several distinctive morphological characteristics that allow identification within fossil assemblages.
Common features include:
- Coiled shell with rounded whorls
- Smooth or lightly ornamented shell surface
- Narrow umbilicus where inner whorls remain visible
- Chambered shell interior divided by septa
- Symmetrical spiral growth pattern
These shells provided protection while also functioning as buoyancy control devices, enabling the animal to move vertically within the water column.
When preserved in rock, ammonite fossils may appear as internal moulds, mineralised shells, or impressions within the surrounding matrix.
Fossil Woodstone Formation
The presence of fossil woodstone in this specimen indicates that plant material from nearby land entered the marine environment and became preserved within the sediment. Over time, the organic structure of the wood was replaced by minerals through a process known as permineralisation, resulting in a stone-like preservation of the original material.
Woodstone within Jurassic marine sediments often forms dense, dark, mineralised pieces embedded within mudstone or limestone. These fossil wood fragments sometimes act as substrates around which marine organisms settled or were buried.
The association of ammonites with fossil wood provides valuable insight into the dynamic coastal environments that existed during the Early Jurassic.
Early Jurassic Marine Ecosystem
During the Lower Jurassic, the seas surrounding what is now Dorset were rich with marine life. These waters supported diverse ecosystems that included:
- Ammonites and belemnites
- Marine bivalves and gastropods
- Fish and sharks
- Marine reptiles such as ichthyosaurs and plesiosaurs
- Crustaceans and other invertebrates
Floating driftwood occasionally served as temporary habitats for marine organisms before sinking to the seafloor, where both plant material and marine shells could become preserved together.
Authentic Fossil Specimen
This fossil is a genuine Cymbites ammonite specimen preserved in fossil woodstone from the Charmouth Mudstone Formation, Lower Jurassic of Lyme Regis, Dorset, UK. The specimen has been carefully selected for quality and display appeal.
The photograph shows the actual fossil specimen you will receive, allowing collectors to clearly examine both the ammonite fossils and the surrounding woodstone matrix.
Full sizing please see photo.
Certificate of Authenticity
This fossil includes a Certificate of Authenticity lifetime guarantee generic card, confirming that the specimen is a genuine natural fossil.
Ammonites from the Jurassic Coast are among the most iconic fossils in the world. A specimen combining Cymbites ammonites with fossil woodstone represents a particularly interesting geological association and makes a striking addition to any fossil collection, geological display, or educational exhibit.
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