Dorset Inferior Oolite

Introduction to Burton Bradstock Inferior Oolite Ammonites

Burton Bradstock, located on the Jurassic Coast of Dorset, England, is well-known for its rich deposits of Inferior Oolite, a Middle Jurassic limestone formation that contains a variety of fossil ammonites. These ammonites provide valuable insights into the marine environments of the Middle Jurassic period, approximately 174 to 163 million years ago. The Inferior Oolite at Burton Bradstock is famous for producing well-preserved ammonites with distinct morphological features and intricate suture patterns, making them of great interest to both paleontologists and fossil collectors.

The fossils from Burton Bradstock are often found in limestone and oolitic ironstones, where they have been preserved in fine detail. Species such as *Dumortieria*, *Stephanoceras*, and *Parkinsonia* are commonly found in this area, offering insights into the evolution of ammonites during the Middle Jurassic.

Geological Occurrences of Burton Bradstock Inferior Oolite Ammonites
Burton Bradstock is part of the famous Jurassic Coast of southern England, a UNESCO World Heritage Site known for its outstanding fossil record. The Inferior Oolite, which forms part of the Middle Jurassic strata, is particularly well-exposed in the cliffs around Burton Bradstock. Key fossil sites include:

Burton Bradstock Cliffs

Inferior Oolite Formation: The Inferior Oolite at Burton Bradstock consists of limestone and oolitic ironstone beds that date to the Bajocian stage of the Middle Jurassic. These rocks contain an abundance of fossil ammonites, which are often found in limestone nodules or as impressions in the oolitic rock. The ammonites from this formation are typically well-preserved, with fine details of their shells and suture patterns intact.

Other Notable Locations

West Bay: Just to the east of Burton Bradstock, the cliffs at West Bay also expose layers of the Inferior Oolite, where ammonite fossils are commonly found. The rocks in this area are part of the same geological formation as Burton Bradstock and contain similar species of ammonites.

Detailed Information about Burton Bradstock Inferior Oolite Ammonites
The fossil ammonites from Burton Bradstock’s Inferior Oolite are an important source of information about the diversity and evolution of Middle Jurassic cephalopods. Below is a detailed exploration of their anatomy, preservation, evolutionary significance, and ecological roles:

Anatomy and Structure

Anatomy of Ammonites: The ammonites from Burton Bradstock exhibit the typical coiled, chambered shells that are characteristic of ammonites. Their shells are often ribbed or ornamented with nodules, and they possess complex suture patterns that help paleontologists identify different species. These ammonites used their internal chambers to control buoyancy, allowing them to move through the water column in pursuit of prey.

Preservation of Ammonites: Fossils from the Inferior Oolite at Burton Bradstock are often preserved as internal molds within limestone or oolitic ironstone. In many cases, the original shell material has been replaced by minerals such as calcite, which enhances the visibility of the shell’s intricate details, including the ribs and suture lines.

Evolutionary Significance of Burton Bradstock Ammonites

Middle Jurassic Radiation: The ammonites of Burton Bradstock represent a period of significant diversification during the Middle Jurassic. This was a time when many new genera and species of ammonites evolved, adapting to different marine environments. The fossils from this area provide valuable information about the evolutionary trends that shaped ammonite diversity during this period.

Biostratigraphy and Index Fossils: Ammonites from the Inferior Oolite are important index fossils for dating rock layers in the Middle Jurassic. The rapid evolution of ammonite species during this time makes them ideal for correlating rock layers across different regions. Species such as *Dumortieria* and *Stephanoceras* are often used for biostratigraphic purposes.

Ecological Role and Adaptations

Marine Predators: The ammonites of Burton Bradstock were likely active predators in the Middle Jurassic seas, feeding on small marine animals such as crustaceans, fish, and other mollusks. Their beak-like jaws and tentacles would have allowed them to capture prey, while their coiled shells provided protection from larger predators.

Adaptations to Marine Environments: The ammonites from this region evolved various shell morphologies and suture patterns that helped them adapt to different marine environments. Some species had thicker, more robust shells for protection, while others had streamlined forms for greater mobility in the water.

Key Species of Burton Bradstock Ammonites
The ammonites found in the Inferior Oolite of Burton Bradstock represent a diverse array of species from the Middle Jurassic. These species are significant for understanding the evolutionary trends of ammonites during this period. Some of the key species include:

Middle Jurassic Species

*Dumortieria* (Bajocian, Burton Bradstock): *Dumortieria* is a genus of ammonites known for its ribbed, coiled shell with intricate suture patterns. Fossils of *Dumortieria* are commonly found in the Inferior Oolite and serve as important index fossils for the Bajocian stage of the Middle Jurassic.

*Stephanoceras* (Bajocian, Burton Bradstock): *Stephanoceras* is a genus of ammonites characterized by its ornate, ribbed shell with prominent nodules. Fossils of *Stephanoceras* are often found in the oolitic limestone of Burton Bradstock and are prized for their aesthetic appeal and scientific value.

*Parkinsonia* (Bajocian, Burton Bradstock): *Parkinsonia* is another common genus of ammonites from the Inferior Oolite. Its shell is typically smooth with faint ribbing and prominent suture patterns. Fossils of *Parkinsonia* are used as index fossils for the Middle Jurassic and provide insights into ammonite evolution during this period.

Significance of Burton Bradstock Inferior Oolite Ammonites

The ammonites from Burton Bradstock are of great scientific importance due to their excellent preservation, diversity, and value for biostratigraphy. Key areas of significance include:

Scientific Importance: The fossils from Burton Bradstock provide valuable information about the evolution of marine life during the Middle Jurassic. These ammonites help paleontologists understand the evolutionary trends and morphological adaptations that allowed ammonites to thrive in ancient marine ecosystems.

Biostratigraphy and Geological Correlation: The ammonites of the Inferior Oolite are essential for dating Jurassic rock layers and correlating them with other fossil sites across Europe. Their use as index fossils makes them crucial tools for understanding the geological history of the Middle Jurassic.

Paleobiogeography: The ammonites found at Burton Bradstock provide insights into the paleogeography of the Middle Jurassic seas and help scientists reconstruct ancient marine environments. These fossils illustrate the widespread distribution of ammonites and their adaptation to different ecological niches.

Conclusion

The fossil ammonites from Burton Bradstock’s Inferior Oolite represent some of the most scientifically significant and well-preserved examples of Middle Jurassic cephalopods. Their intricate suture patterns, diversity, and role as index fossils make them a valuable focus of paleontological research.

By studying these fossils, scientists gain valuable insights into the evolution of marine ecosystems during the Jurassic period, the biostratigraphy of Jurassic rock formations, and the adaptation of ammonites to ancient marine environments. Burton Bradstock’s ammonites continue to captivate both scientists and fossil collectors, offering a glimpse into the ancient seas of the Middle Jurassic.