Starfish and Brittlestars

What Are Fossil Starfish and Brittlestars?

Fossil starfish (Asteroidea) and brittlestars (Ophiuroidea) are the preserved remains of ancient echinoderms that lived in marine environments. These creatures, with their radial symmetry and distinctive arms, have existed for hundreds of millions of years, dating back to the Ordovician period. Starfish and brittlestars belong to the phylum *Echinodermata*, which also includes sea urchins and crinoids. Their fossils are found in sedimentary rocks, often preserved in stunning detail, revealing the complex anatomy of these ancient marine organisms.

Fossil starfish and brittlestars provide valuable insights into ancient marine ecosystems, the evolution of echinoderms, and the environmental conditions that shaped the seas of the past. Their delicate structures are often preserved in fossil beds where rapid burial helped protect them from decomposition.

Types of Fossil Starfish and Brittlestars
Fossil starfish and brittlestars exhibit a range of forms, reflecting their adaptations to different environments over geological time. Here are some of the most notable types:

Fossil Starfish (Asteroidea):

*Petraster*: This extinct genus of starfish is known from the Ordovician to Devonian periods. *Petraster* fossils often exhibit five arms and show the characteristic central disc of starfish, preserved in detail.

*Palasterina*: Found in rocks dating to the Ordovician period, *Palasterina* is an early example of a starfish, with well-preserved fossils showing the arm structure and ambulacral grooves used for feeding.

*Calliderma*: A genus of fossil starfish from the Jurassic period, *Calliderma* fossils are known for their intricate arm structure and central body, often found in shallow marine deposits.

*Astropecten*: Modern and fossil species of *Astropecten* date from the Jurassic to the present. Fossils of this genus often show the unique marginal plates of the arms, with detailed preservation of their spiny surfaces.

Fossil Brittlestars (Ophiuroidea):

*Ophiura*: Fossils of *Ophiura* are found in Jurassic and Cretaceous deposits. This genus of brittlestar is characterized by its slender arms, which are often preserved in various positions due to their flexibility.

*Eurypalaeaster*: Dating back to the Ordovician period, *Eurypalaeaster* is one of the earliest known brittlestars, with fossils that display the typical long, flexible arms radiating from a central disc.

*Amphipholis*: This genus of brittlestar has been found in fossil deposits ranging from the Jurassic period to the present. Fossils of *Amphipholis* are known for their small, fragile bodies, often preserved in fine-grained sediment.

*Furcaster*: Fossils of this extinct genus are found in Paleozoic rocks, particularly from the Silurian to Devonian periods. *Furcaster* is characterized by its long, flexible arms and small central disc.

How Fossil Starfish and Brittlestars Are Formed

The fossilization of starfish and brittlestars is a rare event due to their delicate and flexible bodies, which are prone to disintegration after death. However, under favorable conditions, their fossils can be exquisitely preserved. The key processes involved in their fossilization include:

Death and Rapid Burial: After a starfish or brittlestar dies, it must be rapidly buried by sediment, such as mud, silt, or fine sand, to prevent decomposition and disarticulation of its body. Rapid burial is often associated with storm events, underwater landslides, or shifts in sediment in quiet marine environments.

Mineralization: Over time, minerals from the surrounding sediment infiltrate the buried remains. The original organic material is replaced or supplemented by minerals such as calcite, preserving the intricate details of the skeleton, including the arms and central disc.

Impression Fossils: In some cases, the body of a starfish or brittlestar may decay, leaving behind an impression or mold in the surrounding sediment. This impression can later be filled with minerals, creating a cast fossil that replicates the external shape of the organism.

Calcification: The skeletons of starfish and brittlestars are composed of calcite plates called ossicles. During fossilization, these ossicles can become calcified and preserved in their original form, allowing paleontologists to study the detailed structure of these ancient echinoderms.

Importance of Fossil Starfish and Brittlestars

Fossil starfish and brittlestars are important for understanding the evolution of echinoderms and the dynamics of ancient marine ecosystems. Their fossils provide valuable insights into:

Evolution of Echinoderms: Fossil starfish and brittlestars help trace the evolutionary history of echinoderms, showing how these animals adapted to different marine environments over hundreds of millions of years.

Marine Ecosystem Reconstruction: Fossil starfish and brittlestars provide evidence of ancient marine ecosystems, including reef environments, shallow seas, and deep ocean floors. Their presence in the fossil record helps reconstruct the biodiversity and ecological interactions in these environments.

Environmental Indicators: The specific types of starfish and brittlestars found in fossil beds can serve as indicators of ancient environmental conditions, such as water depth, temperature, and sediment type. They are valuable tools for interpreting past marine environments.

Preservation of Soft-Bodied Organisms: The fossilization of delicate organisms like starfish and brittlestars highlights the exceptional conditions required for the preservation of soft-bodied and flexible creatures in the fossil record.

Mass Extinction Events: Fossil starfish and brittlestars provide evidence of how marine life was affected by mass extinction events, such as the Permian-Triassic extinction, and how these echinoderms recovered in the aftermath of global environmental changes.

Conclusion

Fossil starfish and brittlestars offer a unique and detailed view of ancient marine life, providing valuable information about the evolution of echinoderms and the structure of ancient ecosystems. These fossils reveal how starfish and brittlestars adapted to different environmental conditions, survived mass extinction events, and played important roles in marine food webs throughout Earth’s history.

Their delicate and often intricately preserved fossils are not only beautiful but also scientifically significant, helping paleontologists piece together the history of life in the oceans. Fossil starfish and brittlestars continue to be a key resource for understanding the diversity of ancient marine life and the processes that shaped the evolution of the modern oceans.