FLOATING OR ANCHORING: EXPLORING THE FUNCTIONAL ROLE OF SCYPHOCRINOID LOBOLITHS

 

Silurian crinoid Scyphocrinites elegans Zenker, 1833 (about 419-425 million years) from #Erfoud (#Morocco) (Photo: Jordi Sànchez)

In the fascinating world of paleontology, the study of ancient organisms like scyphocrinoids offers insights into their ecological roles and adaptations. Recent research (*) has reassessed the functional role of loboliths, the gas-filled structures associated with these crinoids, challenging previous assumptions about their buoyancy and feeding strategies.

Scyphocrinoids, which thrived during the middle Paleozoic, were once thought to be planktonic organisms that used their loboliths for buoyancy, allowing them to float while feeding. However, this hypothesis is now under scrutiny.

A, Example of traditional reconstruction of scyphocrinoid as a pelagic, floating crinoid along with reconstructions of cirrus (B) and plate (C) loboliths (*).

The study examined the skeletal structure of loboliths, revealing that they are primarily composed of labyrinthic stereom. Notably, there are no adaptations observed that would prevent gas leaks or water ingress, which raises questions about their buoyancy function.

The research suggests that the hypothesized tow-net feeding mode of scyphocrinoids would have resulted in low relative velocities between the filter and the surrounding water, making it an ineffective method for passive filter feeding.

Instead of serving as a buoy, the loboliths likely functioned as modified holdfasts. Their shape and microspines may have helped scyphocrinoids anchor themselves in soft sediments, similar to strategies used by some modern mollusks and brachiopods.

Maintaining an upright position with a long stalk (up to 3 meters) would have been challenging. The study proposes that scyphocrinoids may have extended the distal part of their stalk along the substrate for stability, allowing them to feed effectively while anchored.

 Reconstruction of scyphocrinoids as benthic crinoids with nearly vertical stalks (*).

This research not only reshapes our understanding of scyphocrinoid biology but also highlights the diversity of adaptations that ancient organisms developed to thrive in their environments. The findings suggest that these crinoids occupied a significant ecological niche in the Paleozoic seas, potentially influencing the structure of marine communities.

In conclusion, the reassessment of scyphocrinoid loboliths reveals a complex interplay between structure and function, emphasizing the need for continuous exploration in paleobiology to uncover the mysteries of ancient life.

(*) More info:  Gorzelak, P., Kołbuk, D., Salamon, M. A., Łukowiak, M., Ausich, W. I., & Baumiller, T. K. (2020). Bringing planktonic crinoids back to the bottom: Reassessment of the functional role of scyphocrinoid loboliths. Paleobiology, 46(1), 104-122.

UNVEILING THE WORLD OF SCLEROBIONTS IN MICRASTER ECHINOIDS

 

Cretaceous (~ 85 million years old) sea urchin Micraster coranguinum Leske, 1778 from Lleida (Catalonia) (Photo: Jordi Sánchez).

The study of sclerobionts—organisms that attach to hard surfaces—provides a unique window into ancient marine ecosystems. Recent research (*) focusing on Micraster and Gibbaster echinoids from the Upper Cretaceous of northern Spain has revealed a wealth of information about these interactions. Here are some expanded insights:

• Rich Biodiversity: The research highlights a diverse array of sclerobionts associated with Micraster echinoids. This includes various bivalves (such as Dimyidae, Anomiidae, and Plicatulidae), polychaete annelids, bryozoans, and lituolid foraminiferans. The presence of such a variety of organisms indicates a complex and thriving ecosystem in the ancient marine environment, showcasing the intricate relationships that existed among different species.

 

Sclerobiont traces: 1- Valve of Atreta sp. (bivalve mollusc): 2- Spirorbis sp. (carcareous tube-form), attached to the test of a cretaceous (~ 85 Myo) sea urchin Gibbaster brevis Desor, 1847 from Lleida (Catalonia) (Photo: Jordi Sánchez).

• Dominance of Encrusting Bivalves: Encrusting bivalves were found to be particularly prevalent, appearing in approximately 90% of the studied echinoid specimens. This suggests that these bivalves played a significant role in the ecological dynamics of the time, potentially influencing the survival and behavior of the echinoids they inhabited.
• Bioerosion and Epibiosis: The study emphasizes the significance of bioerosion—where organisms bore into the echinoid tests—and epibiosis, where organisms live on the surface. Structures such as Oichnus simplex and Trypanites solitarius were identified as bioerosion indicators. These interactions not only provide insights into the ecological relationships of the time but also inform us about the processes that lead to fossilization.
• Patterns of Preservation: The preservation of sclerobionts is often seen as calcified or pyritized internal molds. Their distribution tends to be concentrated on the apical side of the echinoid tests, particularly in the interambulacra regions. This pattern can reveal important information about the living conditions and ecological preferences of these organisms during their life.

 

Large Spiraserpula sp.Regenhardt, 1961 (Polychaete worm) encrusting in a cretaceous (~ 86 Myo) seaurchin Gibbaster brevis Desor, 1847 from Olazti (Nafarroa) (Photo: Jordi Sánchez).

• Taphonomic Pathways: The presence of sclerobionts on Micraster tests allows researchers to analyze taphonomic pathways, distinguishing between accumulated and non-accumulated fossils. This analysis is crucial for understanding fossil preservation processes and the ecological interactions that occurred during the life of these organisms. The study concludes that the taphonomic history observed is common among infaunal echinoid populations living in organic-rich, mixed sediments during the Mesozoic era.

In summary, the exploration of sclerobionts associated with Micraster and Gibbaster echinoids not only enhances our understanding of past marine ecosystems but also provides essential insights into the taphonomic processes that shape the fossil record. These findings contribute to a deeper appreciation of the intricate relationships that existed in ancient marine environments, revealing the complexity and richness of life in the Upper Cretaceous seas.

(*) Zamora, S., Mayoral, E., Vintaned, J. A. G., Bajo, S., & Espílez, E. (2008). The infaunal echinoid Micraster: taphonomic pathways indicated by sclerozoan trace and body fossils from the Upper Cretaceous of northern Spain. Geobios, 41(1), 15-29.