Macrocephalites subcompressus Ammonite Fossil from Chari Formation Lower Callovian Jurassic Jumara Dome Cutch India

Description

Geological Context and Provenance

This rare Macrocephalites subcompressus ammonite fossil comes from the Chari Formation, Middle Macrocephalus Beds, Lower Callovian Stage of the Jurassic Period, approximately 166 – 163 million years ago. The specimen originates from the Jumara Dome in Kutch (Cutch), India, one of the most important Jurassic fossil localities in South Asia. This area exposes richly fossiliferous sediments that have been studied extensively for their exceptional ammonite faunas, which serve as key reference points for global biostratigraphy.

The Callovian is a significant stage within the Middle Jurassic, and the Jumara Dome deposits are particularly renowned for their diverse and well-preserved ammonite assemblages. These fossils allow scientists to refine the regional and international stratigraphic framework, making specimens from this locality both scientifically valuable and highly collectible.

Fossil Type and Species Information

Macrocephalites subcompressus is a member of the Order Ammonitida, Superfamily Perisphinctoidea, and Family Macrocephalitidae. The genus Macrocephalites is particularly well known in the Callovian for its large, strongly ribbed shells, which occur widely across Tethyan marine deposits. This species, subcompressus, is an important biostratigraphic indicator, often used to define the Macrocephalus Zone, a key interval in the Jurassic time scale.

As an index fossil, Macrocephalites subcompressus provides a valuable reference for correlating rock layers in different regions of the world, demonstrating its dual significance for both collectors and geologists.

Morphological Features and Identification

This specimen exhibits the diagnostic features of Macrocephalites subcompressus:

• Compressed Whorl Section – A flattened, subrectangular to suboval profile typical of the species.
• Evolute Coiling – Earlier whorls remain visible, creating an open appearance.
• Strong Ribbing – Prominent ribs radiate across the flanks and curve elegantly over the venter, giving the fossil a striking aesthetic.
• Size and Presence – Often comparatively large ammonites, their ribbing and symmetry make them particularly attractive display pieces.

The shell’s suture lines would have been highly complex, reflecting the animal’s adaptation for withstanding pressure at varying ocean depths. Like other ammonites, the internal chambers of the shell allowed for buoyancy control, enabling the animal to move vertically within the water column in search of prey.

Depositional Environment

During the Callovian, the Kutch Basin was part of the Tethyan seaway, a warm shallow marine environment connected to global Jurassic oceans. Sediments of the Chari Formation primarily consist of marls, shales, and limestones, which were deposited under stable marine conditions. These fine sediments provided excellent conditions for the preservation of ammonites, often retaining exquisite detail in their ribbing and shell morphology.

The ammonites of the Jumara Dome, including Macrocephalites subcompressus, lived in an ecosystem rich with other marine life, including bivalves, gastropods, belemnites, brachiopods, and marine reptiles. The abundance and diversity of fossils from this area make it one of the premier fossil localities for Jurassic palaeontology.

Collector Appeal and Authenticity

This Macrocephalites subcompressus ammonite fossil is a rare and desirable specimen from a classic Jurassic locality. Its combination of scientific importance and striking natural beauty makes it a valuable addition to both private and institutional collections.

• 100% Genuine Specimen – Supplied with a Certificate of Authenticity.
• Exact Fossil Shown – Photographs show the actual specimen you will receive.
• Scale Reference – Scale rule squares / cube = 1 cm. Please consult photos for full sizing.

A carefully chosen piece, this Macrocephalites subcompressus ammonite fossil from the Jumara Dome, India, represents both the grandeur of Jurassic ammonites and the exceptional geological heritage of one of the world’s most important fossil localities.