Rare Harpoceratoides alternatus Ammonite Fossil, Lower Toarcian Stage Jurassic, Authentic Italian Collectors Specimen with COA

Description

Genuine Jurassic Ammonite Fossil

This listing offers a genuine Harpoceratoides alternatus Ammonite Fossil from the Lower Toarcian Stage of the Early Jurassic period, discovered in Italy. Ammonites were extinct marine cephalopods of the subclass Ammonoidea, related to squid and cuttlefish. Their beautifully coiled shells are among the most iconic fossils, prized for their natural beauty and vital role in paleontological research. This specimen has been carefully chosen for its preservation and detail, with photographs showing the exact fossil you will receive. A 1 cm scale cube is included for accurate sizing.

Geological Context – Lower Toarcian, Jurassic

The Lower Toarcian, approximately 182 million years ago, is a key interval within the Early Jurassic. It is closely associated with the Toarcian Oceanic Anoxic Event, a time of dramatic global change in ocean chemistry and marine ecosystems. Fossil-bearing strata from this stage in Italy preserve ammonites in remarkable detail, providing important insights into Jurassic marine life.

Ammonites from this stage are particularly important as index fossils, meaning they allow geologists to precisely date and correlate rock layers across wide geographic regions. Specimens such as Harpoceratoides alternatus are therefore highly valuable not only to collectors but also to scientific study.

Species Profile – Harpoceratoides alternatus

The species Harpoceratoides alternatus belongs to the family Hildoceratidae, within the superfamily Hildoceratoidea and order Ammonitida. This genus is distinguished by its sharp ribbing, compressed shell form, and distinct keel.

Key features of Harpoceratoides alternatus include:

• A compressed, planispiral shell with moderately involute coiling.
• Alternating strong and weaker ribs, a defining characteristic that gives the species its name.
• A sharp keel running along the venter, typical of the genus.
• Complex suture lines visible in well-preserved specimens, marking the internal septal divisions of the shell chambers.

These diagnostic traits make Harpoceratoides alternatus highly distinctive, allowing for precise identification and biostratigraphic use.

Paleoenvironment and Scientific Value

During the Early Jurassic, the region that is now Italy was covered by shallow epicontinental seas, rich with marine life including ammonites, belemnites, and early marine reptiles. Ammonites such as Harpoceratoides alternatus were nektonic predators, actively swimming and feeding in the open waters. After death, their shells settled onto the seabed, where they were rapidly buried by fine sediments, preserving them for millions of years.

The presence of Harpoceratoides alternatus is crucial for defining ammonite biozones within the Lower Toarcian. Their restricted stratigraphic range allows paleontologists to establish precise correlations between different fossil localities. Collectors value these specimens not only for their ribbed elegance but also for their contribution to our understanding of Jurassic stratigraphy.

100% Genuine with Certificate of Authenticity

All of our fossils are guaranteed 100% genuine specimens and include a Certificate of Authenticity. This ammonite is not a cast or reproduction but an authentic relic of the Jurassic seas of Italy, preserved for nearly 182 million years.

A Collector’s and Display Fossil

This Harpoceratoides alternatus ammonite fossil from Italy is an exceptional specimen for fossil enthusiasts, geology students, and natural history collectors. Its combination of scientific importance, geological provenance, and striking ribbed morphology ensures it will be a highlight of any collection or display.

Scale Rule Squares / Cube = 1 cm. Please see listing photos for the full sizing of this exact specimen.