Dactylioceras tenuicostatum Fossil Ammonite Jurassic Middle Lias Whitby UK Genuine

Description

Authentic Dactylioceras tenuicostatum Ammonite from Whitby, United Kingdom

This superb Dactylioceras tenuicostatum fossil ammonite originates from the world-famous fossil beds of Runswick Bay, near Whitby, North Yorkshire, United Kingdom. Dating to the Middle Lias of the Lower Jurassic Period, approximately 183 million years ago, this specimen represents one of Britain’s most iconic and scientifically significant ammonites. The Whitby coastal exposures have long been celebrated for their exceptional preservation of marine fossils, particularly ammonites, which serve as key index fossils for dating Jurassic strata. This genuine Dactylioceras specimen displays exquisite ribbing, symmetry, and shell detail typical of the species, making it both a highly collectable display piece and a fine example of early Jurassic marine life.

Geological and Stratigraphic Context – Middle Lias, Toarcian Stage

The fossil was discovered within the shales and mudstones of the Middle Lias (Lower Jurassic), specifically the tenuicostatum Zone of the Toarcian Stage. These rocks were deposited in a shallow epicontinental sea that once covered large parts of northern England during the early Jurassic, when the region lay closer to the equator under a warm, subtropical climate. The fine-grained sediments of the Whitby Mudstone Formation allowed for exceptional fossil preservation, often capturing minute shell structures in remarkable detail. This formation, stretching along the Yorkshire coast, is globally recognised for its fossil richness and has contributed significantly to paleontological research and ammonite zonation used in Jurassic stratigraphy.

Species Information – Dactylioceras tenuicostatum

Belonging to the family Dactylioceratidae within the order Ammonitida, Dactylioceras tenuicostatum is one of the most characteristic ammonite species of the early Toarcian. It is typified by its thin, tightly coiled planispiral shell, with fine, evenly spaced ribs that run uninterrupted across the whorls. The ribs are delicate but sharply defined, giving the species its name “tenuicostatum,” meaning “fine-ribbed.” The shell exhibits a pronounced keel along the outer whorl, a hydrodynamic feature that aided buoyancy control and stability as the ammonite navigated ancient Jurassic seas. These ammonites were nektonic carnivores, related to modern cephalopods such as squids and cuttlefish, feeding on small crustaceans and planktonic organisms.

Palaeoenvironment and Scientific Importance

During the Early Jurassic, the area around modern-day Whitby formed part of a broad marine shelf bordering the proto-North Atlantic Ocean. The depositional environment of the Middle Lias was a calm, low-energy seabed where fine sediments settled gently, burying and preserving the shells of marine organisms in anoxic conditions that inhibited decay. Dactylioceras tenuicostatum is a critical index fossil used globally to define the base of the Toarcian Stage, marking a key interval in Earth’s geological history that saw significant oceanic and climatic changes. The species is one of the most precisely dated ammonites known, helping geologists correlate rock layers across Europe and beyond.

Preservation, Authenticity, and Display

This genuine ammonite fossil from Runswick Bay displays beautiful natural preservation, showing fine ribbing, suture detail, and curvature of the whorls. The fossil’s surface may exhibit natural mineralisation from iron pyrite or calcite replacement, typical of Whitby ammonites, which gives them their distinctive metallic or stone-like sheen. It has been carefully cleaned and stabilised to protect the fine detail of the fossil while maintaining its natural authenticity. The specimen shown in the photographs is the actual fossil you will receive. A 1 cm scale cube is included for accurate size reference.

Each specimen comes professionally selected for quality and scientific value and includes a Certificate of Authenticity, confirming it as a genuine fossil from the Jurassic strata of Whitby, England.

All of our Fossils are 100% Genuine Specimens and come with a Certificate of Authenticity.

Scale Rule Squares / Cube = 1 cm. Full sizing details are shown in the photo. The specimen pictured is the exact fossil you will receive, chosen for its exceptional preservation and display appeal.