Description
This listing features a RARE and exceptionally large 12-inch Mortoniceras rostratum fossil ammonite from the Upper Albian stage of the Cretaceous Period, found in Cooke County near Fort Worth, Texas, USA. A classic and highly desirable specimen from one of the most important Lower Cretaceous ammonite sites in North America.
This is a 100% genuine fossil, carefully selected and accompanied by a Certificate of Authenticity. You will receive the exact fossil shown in the photographs. Refer to the photo with the scale cube (1cm squares) for full sizing.
Fossil Overview:
- Species: Mortoniceras rostratum
- Common Name: Fossil Ammonite
- Geological Period: Cretaceous
- Stage: Upper Albian (~105–100 million years ago)
- Formation: Duck Creek Formation (part of the Washita Group)
- Locality: Cooke County, near Fort Worth, Texas, USA
- Preservation: Excellent external mould with some natural shell detail preserved
Geological & Depositional Environment:
The Duck Creek Formation was deposited in a warm, shallow marine sea that covered much of what is now Texas during the mid-Cretaceous. These sediments were laid down in the Western Interior Seaway, an epicontinental sea that split North America.
The Albian was a time of major diversification for ammonites, and Mortoniceras is a key marker genus for this period. These ammonites are important index fossils used to date Upper Albian marine strata in North America and beyond.
Biozone & Zonal Significance:
Mortoniceras rostratum is associated with the Mortoniceras (Mortoniceras) inflatum Zone, a globally recognised ammonite biozone of the Upper Albian. This species is used in correlation of marine Albian strata across Europe, North Africa, and North America, highlighting its significance in biostratigraphy.
Taxonomy & Classification:
- Phylum: Mollusca
- Class: Cephalopoda
- Subclass: Ammonoidea
- Order: Ammonitida
- Superfamily: Acanthoceratoidea
- Family: Brancoceratidae
- Genus: Mortoniceras
- Species: rostratum
Morphological Features:
- Robust shell with strongly ribbed whorls
- Distinctive tuberculate ornamentation (nodes and spines on ribs)
- Typical evolute coiling – all earlier whorls visible
- Deeply incised suture lines
- Rostrate (beaked) ventral lobe gives the species its name
The dramatic ornamentation and large size suggest it was a strong swimmer in the open sea, possibly a predator or opportunistic feeder.
Notable Points:
- Specimens of this size are uncommon and highly collectible
- Represents a key taxon for dating Upper Albian marine rocks
- Excellent preservation with visible diagnostic features
- Collected from a classic American fossil locality
- A centrepiece ammonite for any fossil collection or educational display
Why Buy From Us?
- Every fossil is 100% authentic, no replicas or reconstructions
- Includes a Certificate of Authenticity
- The exact specimen in the photos is what you’ll receive
- Professionally packaged for safe shipping and rapid dispatch
Bring home a piece of the ancient Cretaceous sea with this extraordinary Mortoniceras rostratum ammonite – a stunning fossil with both scientific and display value.
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