A study published in PeerJ Life and Environment has reshaped our understanding of the evolutionary history of sea stars, particularly the family Asteriidae. The study, titled Phylogenetic and taxonomic revisions of Jurassic sea stars support a delayed evolutionary origin of the Asteriidae, introduces new findings that challenge longstanding assumptions about the evolutionary timeline of these marine invertebrates.
Sea stars of the superorder Forcipulatacea, comprising approximately 400 species, are integral to marine ecosystems. Over the past century, scientists have debated the systematics of this group, leading to varying classifications. This new research reassesses six well-preserved Jurassic sea star fossils and reveals that none of these Jurassic taxa belong to modern families like Asteriidae. Instead, they represent stem-forcipulatids, suggesting that Asteriidae likely originated later in the Late Cretaceous, rather than the Jurassic, as previously thought.
Key Findings:
- Comprehensive Phylogenetic Reassessment: The study employed cutting-edge phylogenetic methods to analyses 42 fossil and extant sea star species, creating the largest phylogenetic dataset for Forcipulatacea to date. This comprehensive matrix of 120 morphological traits provided a fresh perspective on the evolution of this group.
- Discovery of New Genera: Researchers described two new Jurassic sea star genera, Forbesasterias and Marbleaster, which contribute to our understanding of early sea star diversity and morphology.
- Delayed Origin of Asteriidae: The research concludes that Asteriidae, the largest family within Forcipulatacea, and the third largest family of sea stars, likely evolved during the Late Cretaceous, up to100 million of years after the Jurassic species analyzed in this study. This contradicts previous assumptions that placed the origin of Asteriidae in the Triassic or Early Jurassic.
- Early Diversity of Forcipulatacea: The findings also suggest that Forcipulatacea was more diverse in its early evolutionary stages than previously believed, providing new insights into the adaptive radiation of these species.
Methodology:
The research utilized a Bayesian tip-dating analysis incorporating the fossilized birth-death process to estimate evolutionary relationships and timelines. This method enabled the time calibration of the phylogenetic tree, resulting in a more accurate representation of the evolutionary history of the group.
Lead author Dr. Marine Fau noted, "Our study reshapes how we think about the evolutionary trajectory of one of the most significant clades of sea stars. The delayed origin of Asteriidae has major implications for understanding the diversification of marine species in the Mesozoic era."
Implications for Marine Biology:
The findings from this research have wide-ranging implications for the field of marine biology, especially for paleontologists and evolutionary biologists. By identifying these Jurassic sea stars as stem-forcipulatids, the study pushes back the timeline for the evolution of modern sea star families and opens new avenues for future research into how these ancient species adapted to their environments.
