Molecular phylogeny and fossil records reveal the origin and evolutionary history of deep-sea Ophiuroidea

IntroductionThe evolutionary history and biogeographic assembly of deep-sea Ophiuroidea remain incompletely understood. This study aimed to clarify the origin, spatial evolution, and long-term assembly of deep-sea ophiuroid diversity through an integrative framework.MethodsWe integrated multiple lines of evidence, including fossil paleogeography, taphonomic-control analyses, global biogeographic regionalization, directional dispersal asymmetry, time-calibrated molecular phylogenetic analysis, quantitative assessment of species diversification rates, and ancestral-area reconstruction.ResultsFossil paleogeographic reconstructions reveal that early ophiuroid occurrences were mainly associated with shallow continental margins at low to middle paleolatitudes, followed by broader spatial expansion during the Paleozoic and a pronounced western Tethyan signal during key Mesozoic intervals. Taphonomic-control analyses show that this western Tethyan concentration remained evident after accounting for preservation opportunity, supporting the importance of this region in the historical distribution of Ophiuroidea. Analyses of extant deep-sea Ophiuroidea show that modern diversity is concentrated mainly in the Indo-Pacific, southwestern Pacific region, and the Gulf of Mexico tropical western Atlantic. Directional dispersal analyses further indicate compositional asymmetry among regions, with a strong western southern Pacific influence at the whole deep-sea scale. Depth-stratified regionalization reveals marked faunal differentiation in the mid-bathyal zone, followed by broader cross-basin connectivity in the lower bathyal and abyssal zones. Molecular dating suggests that deep-sea-associated ophiuroid lineages began to diverge in the late Paleozoic, whereas ancestral-area reconstruction highlights the importance of the Indo-Pacific region in the later biogeographic history of the sampled taxa. Diversification analyses indicate a non-constant evolutionary tempo, with temporal signals broadly consistent with repeated environmental restructuring and post-extinction ecological recovery.ConclusionOverall, these results suggest that deep-sea ophiuroid diversity was assembled through a multi-stage and multi-regional process involving ancient Tethyan historical signals, later Indo-Pacific and Pacific-centered accumulation, depth-dependent connectivity, and recurrent ecological reorganization through geological time.