Abstract
Understanding of the evolutionary history of the ophiuroids, or brittle stars, is hampered by a patchy knowledge of the fossil record. Especially, the stem members of the living clades are poorly known, resulting in blurry concepts of the early clade evolution and imprecise estimates of divergence ages. Here, we describe new ophiuroid fossil from the Lower Jurassic of France, Luxembourg and Austria and introduce the new taxa Ophiogojira labadiei gen. et sp. nov. from lower Pliensbachian shallow sublittoral deposits, Ophiogojira andreui gen. et sp. nov. from lower Toarcian shallow sublittoral deposits and Ophioduplantiera noctiluca gen. et sp. nov. from late Sinemurian to lower Pliensbachian bathyal deposits. A Bayesian morphological phylogenetic analysis shows that Ophiogojira holds a basal position within the order Ophiurida, whereas Ophioduplantiera has a more crownward position within the ophiurid family Ophiuridae. The position of Ophioduplantiera in the evolutionary tree suggests that family-level divergences within the Ophiurida must have occurred before the late Sinemurian, and that ancient slope environments played an important role in fostering early clade evolution.
Highlights
Earth’s ecosystems are so complex and diverse that their scientific assessment is generally done using model organisms as a manageable subset representative for the whole
We show that the new fossils are part of the ancient stock of the living ophiurid families Ophiuridae and Ophiopyrgidae
The new fossil ophiuroids described in the present paper provide novel insights into the early evolution of the order Ophiurida
Summary
Earth’s ecosystems are so complex and diverse that their scientific assessment is generally done using model organisms as a manageable subset representative for the whole. One of the groups that recently emerged as a promising model organism to explore marine biodiversity and evolution are the ophiuroids, the slender-armed cousins of the starfish. Phylogenetic estimates have recently progressed to the point that the molecular data available are among the most exhaustive in marine invertebrates [5] but agree with morphological estimates [6]. Despite these advances, the deep divergences are still poorly understood. The fragmentary knowledge of the fossil record, hampers the use of the Ophiuroidea as a model organism to explore deep-time biodiversity patterns
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