UNRAVELING THE MYSTERY OF REVERSE DRILL HOLES IN NEOGENE BIVALVES

Predatory common drill holes on a miocene Turritella terebralis Lamarck, 1799 from Leognan (France).

In a fascinating study, researchers have uncovered a unique predation behavior exhibited by gastropod predators on Neogene bivalves from the Netherlands. This behavior, termed "reverse drill holes," provides insight into the challenges predators face when distinguishing between live and dead prey. Here are the key points from the research:

·      Definition of Reverse Drill Holes: Reverse drill holes are unique in that they are created from the inner side of the bivalve's shell, indicating a predation attempt that did not effectively utilize the predator's sensory capabilities to differentiate between live and dead prey.

      (1–3) A valve of Astarte incerta Wood, 1850, fromthe lower Pliocene Oosterhout Formation of Langenboomin the Netherlands (MAB 4685) exhibiting a reverse naticid drill hole. Views: outer (1), inner (2), and detail (3). (4–6) A valve of Astarte goldfussi Hinsch, 1952, from the lower to middle Miocene Miste Bed (Aalten Member, Breda Formation) of Miste in the Netherlands (RGM.783230) exhibiting a reverse drill hole. Views: outer (4), inner (5), and detail (6) (From Klompmaker & Dietl, 2024)

·      Chemical Cues as a Trigger: The study proposes that chemical cues released by nearby living prey may have confused the gastropods, leading them to mistakenly drill into empty shells. This hypothesis suggests that the presence of these cues can significantly influence predator behavior.

·    Rarity of Reverse Drill Holes: The research found that reverse drill holes are quite rare, accounting for less than 1% of all drill holes observed in the studied assemblages. This contrasts with other forms of unsuccessful predation, such as incomplete drill holes and multiply-drilled specimens, which are more common.

·      First Fossil Evidence: This study marks the first documented instances of reverse gastropod drill holes in the fossil record, highlighting a previously unrecognized aspect of predator-prey interactions in ancient ecosystems.

·        Implications for Predator Behavior: The findings suggest that while predators generally have effective sensory and decision-making processes, there are instances where these processes can fail, leading to mistakes in prey selection. This has broader implications for understanding predator behavior and the evolutionary pressures that shape these interactions.

 

Common drilling holes in Anadara diluvii (Lamarck, 1805), a bivalve (clam) of the family Arcidae from the pliocene of Barcelona.

This research not only sheds light on the complexities of ancient predation but also emphasizes the importance of chemical communication in ecological interactions. The study opens new avenues for exploring how predators adapt their hunting strategies in response to environmental cues.

Reference: Klompmaker, A. A., & Dietl, G. P. (2024). Reverse drill holes: remarkable mistakes made by gastropod predators attacking Neogene bivalve prey. Journal of Paleontology, 1–7. doi:10.1017/jpa.2024.36

 

UNDERSTANDING AMMONOIDS: THE ANCIENT MASTERS OF BUOYANCY

 

What are ammonoids?: Ammonoids are a group of extinct marine animals related to modern squids and octopuses. They are best known for their spiral-shaped shells, which are often found as fossils. These creatures lived in the oceans for over 300 million years and are considered iconic fossils due to their unique shell structures and evolutionary history.

The structure of their shells: The shells of ammonoids are divided into chambers, which are separated by walls called septa. These septa have complex internal architectures that evolved over time, becoming more intricate as ammonoids adapted to their environments. The complexity of these structures is a key feature that scientists study to understand their biology and evolution.

 

Buoyancy control: One of the most fascinating aspects of ammonoid biology is how they controlled their buoyancy. The septa within their shells are not just for structure; they play a crucial role in helping the animal float and move in the water. The folds and shapes of these septa can retain liquid, which is essential for buoyancy regulation. This means that ammonoids could adjust their position in the water column, helping them to avoid predators and find food.

 

Recent research findings: Recent studies using 3D-printed models have shown that ammonoids with more complex septa can hold more liquid due to better surface tension. This ability to retain liquid is vital for buoyancy control, allowing these ancient creatures to thrive in various marine environments. The research suggests that ammonoids with intricate shell designs had a significant advantage over those with simpler structures.

Creation of cylindrical shells models (a–c) and chamber models (d–f) used in liquid retention experiments. (a) Wireframe view showing the suture (orange) wrapped around the internal whorl section. (b)   Extruded, virtual model with the cylindrical shell and septum unied together. (c) Final 3D printed model used to measure the liquid retained by surface tension in the septal recesses. (d) Virtual model of a single chamber (camera). (e) Virtual model of the camera subtracted from a bounding volume.(f) Final, 3D printed model with empty chamber inside and holes for drainage on the adoral, adapical, and ventral sides of the model (Peterman et al, 2021)

Ecological Importance: Understanding how ammonoids managed their buoyancy provides insights into their ecological roles in ancient marine ecosystems. Their adaptations allowed them to survive and flourish during significant evolutionary changes, making them key players in the history of life on Earth.

In summary, ammonoids are remarkable examples of evolutionary success, showcasing how complex structures can lead to better survival strategies in changing environments. Their story continues to captivate scientists and enthusiasts alike!

More info: David, J., Peterman., Kathleen, A., Ritterbush., Charles, N., Ciampaglio., Erynn, H., Johnson., Shinya, Inoue., Tomoyuki, Mikami., Thomas, Linn. (2021). Buoyancy control in ammonoid cephalopods refined by complex internal shell architecture.. Scientific Reports, 11(1):8055-8055. doi: 10.1038/S41598-021-87379-5.