Description
Genuine Catacoeloceras crassum Juvenile Ammonite Fossil
This genuine juvenile ammonite fossil is identified as Catacoeloceras crassum and originates from Caen in Normandy, France. It dates from the Toarcian Stage of the Lower Jurassic, preserving the shell of a young marine cephalopod that lived in European seas approximately 180 million years ago.
Juvenile ammonites are particularly interesting because they preserve an early stage in shell development. Their whorl proportions, ribbing and ornamentation can differ noticeably from those of fully grown adults, providing an insight into how the shell changed as the animal matured.
This carefully selected fossil is the exact specimen shown in the listing photographs. Its natural shape, preservation, colour, matrix and individual geological characteristics can therefore be examined before purchase. Full sizing and scale information are provided in the photographs.
Catacoeloceras Classification and Palaeontology
Catacoeloceras crassum belongs to a distinctive group of strongly ornamented ammonites that inhabited Early Jurassic seas. Its broad scientific classification includes:
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida
Superfamily: Eoderoceratoidea
Family: Dactylioceratidae
Genus: Catacoeloceras
Species: Catacoeloceras crassum
Ammonites were extinct marine molluscs related to living squid, cuttlefish, octopuses and nautiluses. They possessed chambered external shells and became exceptionally abundant and diverse throughout the Jurassic Period.
The family Dactylioceratidae includes many characteristic Toarcian ammonites with evolute coiling and prominent radial ribbing. These ammonites are important to palaeontologists because their rapidly changing forms help date and correlate Lower Jurassic marine rocks across Europe.
Juvenile Shell Morphology
As a juvenile specimen, this ammonite represents an early part of the animal’s growth history. The shell developed as a planispiral coil, with successive whorls added around a central umbilicus within the same plane.
Catacoeloceras commonly displays evolute coiling, meaning that the earlier whorls remain relatively exposed rather than being deeply concealed by later growth. This produces a broad central umbilicus and allows much of the shell’s developmental sequence to remain visible.
The shell ornament typically consists of strong primary ribs extending outwards from the umbilical region. These may strengthen, divide or change direction as they cross the flanks towards the venter, or outer edge of the shell. Depending on the growth stage, some specimens may also show small nodes or tubercle-like swellings where the ribs divide.
The species name crassum refers to a comparatively robust or thick form. Even in a juvenile example, the shell may show the beginnings of the sturdy whorl proportions and pronounced ornamentation associated with the species.
The exact features visible depend on preservation. The fossil may retain portions of the original shell surface, mineral replacement, a sediment-filled internal mould or a combination of these forms.
Growth Stages and Ammonite Development
Ammonites grew continuously throughout life by adding new shell material at the aperture. As the animal increased in size, the body chamber expanded and the shell’s proportions and ornamentation could change.
Young ammonites were not always miniature copies of adults. Rib density, whorl thickness, tubercle development and shell curvature could alter substantially during growth. These developmental changes are known as ontogenetic variation and are important when identifying juvenile fossils.
A juvenile Catacoeloceras crassum may therefore display finer or more closely spaced ornamentation than a mature example. The preserved shell offers a snapshot of the ammonite before it reached full adult size, making it a scientifically engaging specimen for anyone interested in ammonite growth and evolution.
Chambered Shell and Buoyancy
Internally, the ammonite shell was divided by curved partitions called septa. These formed a sequence of chambers connected by a narrow tube known as the siphuncle.
The living animal occupied only the final and largest body chamber. The earlier chambers were abandoned as the ammonite grew and became part of its buoyancy system. By adjusting the balance of liquid and gas within these chambers, the animal could regulate its position in the water.
The intricate lines formed where the septa met the outer shell wall are known as sutures. Although these patterns may not always be exposed on a fossil, they are important anatomical features used in ammonite classification.
The living animal would have extended its head, eyes and muscular arms from the shell opening. It likely fed on small marine organisms and organic material within the Jurassic water column.
Toarcian Lower Jurassic Age
This specimen dates from the Toarcian Stage, the final stage of the Lower Jurassic. The Toarcian followed the Pliensbachian and preceded the Aalenian, representing an interval approximately 184 to 174 million years ago.
The Toarcian was a period of major environmental change and ammonite diversification. Extensive seas covered large parts of western Europe, producing fossil-rich marine sediments in France, Britain, Germany and neighbouring regions.
Ammonites are among the most useful index fossils from these deposits. Many genera and species appeared, evolved and disappeared over comparatively short intervals, allowing geologists to divide Toarcian rocks into detailed ammonite zones and subzones.
Dactylioceratid ammonites are especially characteristic of the Toarcian. Their widespread occurrence allows sedimentary rocks from different European basins to be compared with considerable precision.
Early Jurassic Marine Environment
During the Toarcian, the area now forming Normandy lay beneath a warm epicontinental sea. This marine environment was connected to wider European and Tethyan waters and supported a varied ecosystem.
The sea contained ammonites, belemnites, nautiloids, bivalves, gastropods, brachiopods, crustaceans, fish and marine reptiles. Microscopic plankton formed an important part of the food web and contributed organic and calcareous material to the seabed.
Fine mud, clay, carbonate sediment and shell debris accumulated over time. Changes in water depth, oxygen levels, current strength and sediment supply produced different rock types and influenced how fossils were preserved.
This juvenile ammonite lived within that marine ecosystem before its shell ultimately became part of the sedimentary record.
Fossilisation and Natural Preservation
After the young ammonite died, its shell descended to the seabed. Currents, scavenging organisms and sediment movement may have affected it before final burial.
Fine sediment entered the empty shell and accumulated around the exterior. As further layers were deposited, pressure compacted the sediment and gradually transformed it into rock.
The original shell was composed largely of aragonite, a form of calcium carbonate that can dissolve or alter during fossilisation. Mineral-rich groundwater may have replaced or recrystallised the shell, while hardened sediment inside the chambers preserved the ammonite as an internal mould.
Natural fractures, worn ribbing, incomplete edges, matrix deposits, mineral markings, irregular surfaces and variations in colour are authentic results of fossilisation and geological exposure. These characteristics form part of the specimen’s individual history and ensure that every fossil is unique.
Caen, Normandy Fossil Provenance
Caen and the surrounding Normandy region are renowned for their Jurassic sedimentary rocks and long history of geological study. Extensive limestone and marine deposits in the area preserve evidence of the seas that repeatedly covered northern France during the Jurassic Period.
Normandy has produced numerous ammonites, bivalves, brachiopods, echinoids and other marine fossils. Specimens with recorded locality and geological-age information are especially desirable because their original palaeontological context has been retained.
The combination of species identification, juvenile growth stage, Toarcian age and Caen provenance gives this fossil strong scientific, educational and collecting interest.
Actual Specimen and Certificate of Authenticity
This is a genuine fossil specimen and not a cast, replica or artificial reproduction. The listing photographs show the exact Catacoeloceras crassum juvenile ammonite that will be supplied, allowing you to inspect its natural shell profile, ribbing, matrix, colour and individual preservation before purchasing.
Full sizing is shown in the photographs.
The fossil includes a generic Certificate of Authenticity card carrying a lifetime guarantee. Its distinctive dactylioceratid morphology, juvenile growth stage, Lower Jurassic age and documented Normandy provenance make it an excellent addition to an ammonite collection, French fossil display, natural-history cabinet or educational geological collection.
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