Dactylioceras tenuicostatum Ammonite Block Whitby Jurassic Fossil Multi Specimen

Description

Dactylioceras tenuicostatum Multi Ammonite Block with Phragmocone from Whitby

This impressive fossil specimen is a multi ammonite block containing several examples of Dactylioceras tenuicostatum preserved within the natural rock matrix. The specimen also displays a visible phragmocone section, revealing part of the internal chamber structure of the ammonite shell. The fossil originates from the famous Lower Jurassic deposits of Saltwick Bay near Whitby, Yorkshire, United Kingdom, one of the most renowned ammonite fossil localities in the world.

This specimen was discovered by our own team members, Alister and Alison, on 23 February 2026 along the Yorkshire coastline. After recovery, the fossil block was carefully cleaned, prepared, and treated by Alison, allowing the ammonite shells and internal chamber structures to be clearly visible while preserving the natural character of the specimen.

The photographs in the listing show the exact fossil block you will receive, making this a unique display specimen. The fossil includes a fully hand-signed Premium Certificate of Authenticity, confirming the specimen’s authenticity and provenance.

Full sizing of the specimen can be seen in the listing photographs.

Geological Origin – Lower Jurassic Deposits of Whitby

This ammonite block originates from the Lower Jurassic strata exposed at Saltwick Bay near Whitby, part of the classic fossil-bearing cliffs of the Yorkshire Coast. These rocks date to approximately 183 million years ago during the Early Jurassic Period, when the region was covered by a shallow marine basin connected to the ancient Tethys Ocean.

The sedimentary rocks in this area consist primarily of marine shales and mudstones, which formed as fine sediment slowly settled on the seabed. These low-energy depositional conditions allowed delicate marine organisms to be preserved in remarkable detail.

Saltwick Bay is internationally recognised for producing abundant ammonite fossils and has been studied for centuries by geologists and palaeontologists. The deposits are especially famous for preserving Dactylioceras ammonites, which occur in large numbers and are used to define important stratigraphic zones within the Jurassic.

Dactylioceras tenuicostatum – Index Ammonite of the Early Jurassic

The ammonites preserved in this fossil block belong to the species Dactylioceras tenuicostatum, a well-known Early Jurassic ammonite widely used in geological dating.

Taxonomic classification:

• Phylum: Mollusca
• Class: Cephalopoda
• Subclass: Ammonoidea
• Order: Ammonitida
• Superfamily: Dactylioceratoidea
• Family: Dactylioceratidae
• Genus: Dactylioceras
• Species: Dactylioceras tenuicostatum

This species is particularly important in geology because it defines the Tenuicostatum Biozone, a key stratigraphic interval within the Lower Jurassic Toarcian Stage.

Dactylioceras ammonites were abundant in Early Jurassic seas and are among the most recognisable ammonites from the Yorkshire Coast.

Morphology and Shell Structure

Dactylioceras ammonites are known for their strong ribbed shell ornamentation, which gives the fossil a distinctive textured appearance.

Characteristic features of Dactylioceras tenuicostatum include:

• A tightly coiled planispiral shell
• Numerous fine ribs radiating from the inner whorl across the shell
• A relatively evolute shell with visible inner whorls
• Fine ribbing that continues across the venter
• Internal chambered shell structure

The presence of a phragmocone within this specimen reveals part of the ammonite’s internal buoyancy system. The phragmocone consists of a series of gas-filled chambers separated by thin septa, connected by a tube known as the siphuncle.

This structure allowed the ammonite to regulate its buoyancy while swimming within the water column.

Early Jurassic Marine Ecosystem of Whitby

During the Early Jurassic, the seas covering what is now Yorkshire supported a rich and diverse marine ecosystem. The environment was populated by numerous marine organisms including:

• Ammonites such as Dactylioceras
• Belemnites
• Marine reptiles including ichthyosaurs and plesiosaurs
• Bivalves and gastropods
• Crinoids and other echinoderms

Ammonites were active marine predators and swimmers, using jet propulsion to move through the water. Their shells allowed them to maintain buoyancy while hunting small prey such as crustaceans and planktonic organisms.

When these animals died, their shells sank to the seabed where they could become buried by sediment and preserved within the shale layers.

Authentic Whitby Fossil Discovered by Our Team

This specimen represents a genuine ammonite block collected from one of the most famous fossil localities in the United Kingdom. Fossils from Whitby are highly valued by collectors due to their scientific importance and distinctive appearance.

Key features of this specimen include:

• Genuine Dactylioceras tenuicostatum multi ammonite fossil block
• Visible phragmocone internal chamber structure
• From the Lower Jurassic deposits of Saltwick Bay
• Early Jurassic Period
• Collected at Saltwick Bay, Whitby, Yorkshire, UK
• Discovered by Alister and Alison on 23 February 2026
• Cleaned, prepared, and treated by Alison
• Photographs show the exact fossil specimen you will receive
• Supplied with a fully hand-signed Premium Certificate of Authenticity

This impressive ammonite block makes an outstanding addition to Jurassic fossil collections, ammonite displays, geology collections, and natural history exhibits, offering a remarkable snapshot of marine life from the ancient Jurassic seas of the Yorkshire Coast.