Dactylioceras tenuicostatum Fossil Ammonite Jurassic Whitby Runswich Bay UK Middle Lias

Description

Authentic Dactylioceras tenuicostatum Fossil Ammonite from Whitby, UK

Presented here is a superb specimen of Dactylioceras tenuicostatum, a fossil ammonite from the Middle Lias (Lower Jurassic) deposits of Runswick Bay, near Whitby, United Kingdom. This ammonite is an iconic fossil from the Yorkshire Coast, well known among collectors and geologists alike. The exact fossil shown in the photographs is the piece you will receive, and it comes with a Certificate of Authenticity to guarantee its genuineness.

Geological Context and Age

This specimen originates from the Lower Jurassic, Toarcian Stage, dating back approximately 180–174 million years. The coastal exposures around Whitby and Runswick Bay are internationally recognised for their exceptional fossiliferous deposits, which represent the sediments of a shallow epicontinental sea. Layers of fine shales and mudstones, laid down in low-oxygen environments, preserved marine fauna in remarkable detail.

Scientific Classification

• Species: Dactylioceras tenuicostatum
• Genus: Dactylioceras
• Family: Dactylioceratidae
• Superfamily: Eoderoceratoidea
• Order: Ammonitida
• Class: Cephalopoda
• Age: Middle Lias, Lower Jurassic
• Locality: Runswick Bay, Whitby, North Yorkshire, UK

Dactylioceras tenuicostatum was first described in the 19th century and remains one of the most scientifically important ammonites of the Toarcian, serving as a guide fossil for dating rock layers across Europe.

Morphological Features

The Dactylioceras tenuicostatum ammonite is characterised by:

• A tightly coiled, planispiral shell with consistent whorl expansion.
• Fine, dense ribbing that runs across the flanks and continues cleanly over the venter.
• Typically small to medium adult size, but with elegant shell ornamentation that makes it highly recognisable.
• A keel that enhances the streamlined hydrodynamic shape, reflecting its life as an active swimmer in the open seas.

The slender ribbing of D. tenuicostatum is what gives it its species name, derived from the Latin “tenuis” (fine) and “costa” (rib).

Stratigraphic and Biozone Importance

This ammonite defines the Tenuicostatum Biozone, which marks the base of the Toarcian Stage in the Lower Jurassic. As such, Dactylioceras tenuicostatum is not only a collector’s fossil but also a critical biostratigraphic marker used by geologists to precisely correlate and date rock layers worldwide. Its abundance and distinctive features make it invaluable for palaeontological research.

Depositional Environment

During the Early Jurassic, the area that is now Whitby was covered by warm, shallow seas rich in marine life. Periods of low oxygen in the seabed environment allowed for excellent preservation of ammonites, belemnites, fish, and marine reptiles. Over millions of years, these sediments hardened into the shales and nodules that today erode from the cliffs and shorelines of the Yorkshire Coast, releasing beautifully preserved fossils like this one.

Collector’s Significance

This specimen of Dactylioceras tenuicostatum is not only aesthetically striking but also historically and scientifically significant. Its clear ribbing and classic coiled form make it an excellent display piece, while its role as a stratigraphic index fossil makes it an important addition to any serious fossil collection. Fossils from Whitby are especially prized for their preservation and their role in the history of palaeontology.

Item Details

• Fossil Type: Ammonite – Dactylioceras tenuicostatum
• Age: Middle Lias, Lower Jurassic (approx. 180–174 million years)
• Location: Runswick Bay, Whitby, United Kingdom
• Condition: Well-preserved with fine ribbing and coiling visible
• Scale: Rule squares/cube = 1 cm (see photographs for full sizing)
• Certificate: Includes a Certificate of Authenticity
• Specimen Shown: The exact fossil photographed is the one supplied

This Dactylioceras tenuicostatum ammonite fossil from the Jurassic of Whitby is a remarkable specimen combining natural history, beauty, and scientific value. A genuine treasure of Britain’s Jurassic Coast, it is ideal for collectors, educators, or anyone with a passion for fossils.