WHEN SPONGES LEAVE THEIR MARK: CLIONA PERFORATIONS IN THE FOSSIL RECORD

 

                   Pliocene bivalve Glycymeris sp Da Costa 1778 from Italy with small holes in the shell (Photo by Jordi Sanchez).

The small perforations you observe in some fossils, attributable to sponges of the genus Cliona, are the result of their bioerosion mechanism. These sponges are known as "boring sponges" due to their ability to excavate calcareous substrates, such as mollusk shells, coral skeletons, and limestone rocks, to create galleries and chambers where they live.

The boring process of Cliona is not carried out by a mechanical scraping action, as might be the case with some predatory mollusks. Instead, these sponges use a chemical and cellular method to dissolve the calcium carbonate of the substrate.

 Detail of the perforations (Photo by Jordi Sanchez).

The presence of Cliona sponge perforations in fossils is a well-documented phenomenon that provides valuable information about the paleoecology and evolution of these organisms. Here are some key points:

1. Bioerosive Activity:

• Sponges of the genus Cliona are known for their ability to bore into calcareous substrates, such as mollusk shells, corals, and rocks. This activity, called bioerosion, leaves characteristic traces in fossils.
• These fossil traces, known as ichnofossils, are classified under the ichnogenus Entobia. Entobia cretacea is a common ichnospecies that is attributed to Cliona sponge activity.

2. Fossil Record:

• Cliona perforations are found in the fossil record from the Mesozoic and cenozoic, indicating that this bioerosive activity has been common for millions of years.
• The presence of these perforations in fossils of different marine organisms provides evidence of the ecological interactions that occurred in the past.

 Miocene gastropod Melongena lainei Basterot 1825 with small holes (Photo by Jordi Sanchez).

3. Paleoecological Importance:

• The study of Cliona perforations in fossils allows paleontologists to reconstruct past marine ecosystems and understand the relationships between different organisms.
• The presence and distribution of these perforations can provide information about the abundance and diversity of Cliona sponges and their host organisms in different geological periods.

Additional Information:

• Cliona perforations can affect the preservation of fossils, as they weaken the structure of calcareous substrates.
• The study of Cliona perforations in fossils is an important tool for research in paleontology, geology, and marine biology.