Fossil evidence for the ancient link between clonal fragmentation, six-fold symmetry and an epizoic lifestyle in asterozoan echinoderms.

Asexual reproduction by means of splitting, also called fissiparity, is a common feature in some asterozoan groups, especially in ophiactid brittle stars. Most fissiparous brittle stars show six instead of the usual five rays, live as epibionts on host organisms, and use clonal fragmentation to rapidly colonize secluded habitats and effectively expand the margins of their distribution area. While the biology and ecology of clonal fragmentation are comparatively well understood, virtually nothing is known about the evolution and geological history of that phenomenon.

New fossils of Jurassic ophiurid brittle stars (Ophiuroidea; Ophiurida) provide evidence for early clade evolution in the deep sea.

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 gen.

A new bathyal ophiacanthid brittle star (Ophiuroidea: Ophiacanthidae) with Caribbean affinities from the Plio-Pleistocene of the Mediterranean.

Identifiable remains of large deep-sea invertebrates are exceedingly rare in the fossil record. Thus, every new discovery adds to a better understanding of ancient deep-sea environments based on direct fossil evidence. Here we describe a collection of dissociated skeletal parts of ophiuroids (brittle stars) from the latest Pliocene to earliest Pleistocene of Sicily, Italy, preserved as microfossils in sediments deposited at shallow bathyal depths.

Brittle-star mass occurrence on a Late Cretaceous methane seep from South Dakota, USA.

Articulated brittle stars are rare fossils because the skeleton rapidly disintegrates after death and only fossilises intact under special conditions. Here, we describe an extraordinary mass occurrence of the ophiacanthid ophiuroid Brezinacantha tolis gen. et sp.

First glimpse into Lower Jurassic deep-sea biodiversity: in situ diversification and resilience against extinction.

Owing to the assumed lack of deep-sea macrofossils older than the Late Cretaceous, very little is known about the geological history of deep-sea communities, and most inference-based hypotheses argue for repeated recolonizations of the deep sea from shelf habitats following major palaeoceanographic perturbations. We present a fossil deep-sea assemblage of echinoderms, gastropods, brachiopods and ostracods, from the Early Jurassic of the Glasenbach Gorge, Austria, which includes the oldest known representatives of a number of extant deep-sea groups, and thus implies that in situ diversification, in contrast to immigration from shelf habitats, played a much greater role in shaping modern deep-sea biodiversity than previously thought. A comparison with coeval shelf assemblages reveals that, at least in some of the analysed groups, significantly more extant families/superfamilies have endured in the deep sea since the Early Jurassic than in the shelf seas, which suggests that deep-sea biota are more resilient against extinction than shallow-water ones.

Ancient origin of the modern deep-sea fauna.

The origin and possible antiquity of the spectacularly diverse modern deep-sea fauna has been debated since the beginning of deep-sea research in the mid-nineteenth century. Recent hypotheses, based on biogeographic patterns and molecular clock estimates, support a latest Mesozoic or early Cenozoic date for the origin of key groups of the present deep-sea fauna (echinoids, octopods). This relatively young age is consistent with hypotheses that argue for extensive extinction during Jurassic and Cretaceous Oceanic Anoxic Events (OAEs) and the mid-Cenozoic cooling of deep-water masses, implying repeated re-colonization by immigration of taxa from shallow-water habitats.