Caenisites Fossil Ammonite Blue Lias Jurassic Coast Monmouth Beach Lyme Regis Dorset UK

Authentic Caenisites Fossil Ammonite from the Jurassic Coast

This striking Caenisites Fossil Ammonite is a genuine and beautifully preserved specimen from the Blue Lias Formation, discovered on the Jurassic Coast at Monmouth Beach, Lyme Regis, Dorset, UK. Dating to the Early Jurassic period (approximately 199–200 million years ago), this ammonite represents an early stage in ammonite evolution following the Triassic–Jurassic boundary event.

Your specimen was discovered by our team members, Alister and Alison, on 27 February 2024, and has been expertly cleaned, prepped, and treated by Alison to reveal its fine natural detail and shell structure. The photograph shows the actual specimen you will receive, ensuring complete authenticity and provenance.

Geological Context and Origin

This fossil originates from the Blue Lias Formation, an iconic sequence of alternating limestone and shale layers that extends along the UNESCO World Heritage-listed Jurassic Coast of southern England. The Monmouth Beach locality near Lyme Regis is world-renowned for its rich fossil record, providing exceptional examples of ammonites, marine reptiles, and other early Jurassic marine fauna.

The Blue Lias represents deposition in a calm, shallow marine environment approximately 195–200 million years ago, during the Hettangian to Sinemurian Stages of the Early Jurassic. The sediments accumulated in an anoxic (oxygen-poor) seabed, which greatly reduced decomposition and allowed fine preservation of shells and skeletons. These conditions, combined with periodic sediment influxes, created ideal layers for fossilisation, giving rise to the extraordinary abundance and detail seen in specimens like this Caenisites ammonite.

Scientific Classification

• Kingdom: Animalia
• Phylum: Mollusca
• Class: Cephalopoda
• Subclass: Ammonoidea
• Order: Ammonitida
• Superfamily: Psiloceratoidea
• Family: Arietitidae
• Genus: Caenisites
• Age: Early Jurassic (Hettangian–Sinemurian)
• Formation: Blue Lias Formation
• Locality: Monmouth Beach, Lyme Regis, Dorset, UK

Caenisites is an important index fossil for the lower part of the Blue Lias sequence, particularly within the Caenisites turneri Biozone. Its distribution across Europe makes it vital for correlating lower Jurassic rock strata and understanding ammonite evolution in the aftermath of the Triassic extinction.

Morphological Features and Preservation

This Caenisites ammonite displays the genus’s typical evolute coiling, with all whorls visible from the side and a moderately wide umbilicus. The shell ornamentation is characterised by strong, evenly spaced ribs that radiate outward and gently curve toward the venter (outer rim), where they often form a subtle keel. The ribs are slightly raised, giving the fossil a distinct three-dimensional relief that is beautifully accentuated in the natural limestone matrix.

The fossil’s preservation is excellent, with fine details of the ribbing and whorl structure visible. In some areas, natural calcite infill highlights internal chambers (phragmocone sections), creating a soft contrast between the ammonite and its matrix. The scale cube (1 cm) in the photo provides accurate size reference, and full dimensions are listed in the accompanying images.

The slab has been carefully trimmed and stabilised for display, making it a superb collector-grade specimen that showcases both scientific value and aesthetic appeal.

Palaeobiological and Scientific Significance

Caenisites represents one of the earliest post-extinction ammonite genera to diversify in the Jurassic seas. As a nektonic marine cephalopod, it was an agile swimmer, related to modern squids and cuttlefish. Its chambered shell allowed buoyancy control through a system of interconnected gas-filled chambers, enabling it to move efficiently through the open water column.

The widespread occurrence of Caenisites fossils in the Blue Lias reflects a thriving early Jurassic marine ecosystem dominated by ammonites, belemnites, and early fish species. Its abundance and preservation provide important clues about the recovery of marine ecosystems after the end-Triassic mass extinction, marking the dawn of the Jurassic era of marine life.

Authenticity and Provenance

All of our fossils are 100% genuine specimens and come complete with a Certificate of Authenticity. Each piece is responsibly collected, professionally prepared, and carefully treated to ensure long-term stability and presentation quality. No artificial enhancements or replicas are ever used — the fossil shown is the actual piece you will receive.

This Caenisites Fossil Ammonite from the Blue Lias Formation is an outstanding example of Britain’s early Jurassic heritage — a scientifically important and visually striking specimen from the legendary fossil beds of Monmouth Beach, Lyme Regis, Dorset, where the story of palaeontology itself began.