Early Miocene stalked crinoids (Echinodermata) from the southern Rhodanian basin (southeastern France). Paleoenvironments and taxonomy

Using recent samplings and specimens from ancient collections, 14 sites and five species of stalked crinoids have been listed in the Miocene of the southern Rhodanian basin (southeastern France). Three species and two genera are new for science: Papacrinus avignonensis n. gen., n sp. (Balanocrininae), Paraconocrinus rhodanicus n. sp. (Rhizocrinidae) and Gastecrinus vinealis n. gen., n. sp. (Incertae sedis). The identification among the Mediterranean Miocene fauna of the genus Metacrinus, now confined to the Indo-Pacific province, was confirmed by the discovery of brachial ossicles attributed to Metacrinus berthei. The richest and most diversified site was exposed during temporal excavations at the Place du Palais des Papes in Avignon. Four out of the five stalked crinoid species were found in this fossil assemblage in which M. berthei predominates. ?Endoxocrinus gastaldii is associated with M. berthei in several sites. Using dissociated ossicles, differences in quantitative and qualitative characters between these two species are deeply analyzed with their taphonomical, taxonomical and paleoecological consequences. Paleoreliefs and valleys, which had been incised during the Burdigalian, channeled currents. They favored stalked crinoid settlement on various substrates during the late Burdigalian—Lower Langhian transgression. Comparison with the extant fauna allows us to estimate the depth range of the biotopes with stalked crinoids from 100 to 250 m. These estimates are in agreement with those deduced from other paleontological studies.

A new ophiacanthid brittle star (Echinodermata, Ophiuroidea) from sublittoral crinoid and seagrass communities of late Maastrichtian age in the southeast Netherlands

A new species of brittle star, Ophiomitrella floorae, is recorded from the lower two meters of the Gronsveld Member (Maastricht Formation), of late Maastrichtian age (c. 66.7 Ma). These relatively fine-grained biocalcarenites reflect shallow-water deposition in a sheltered setting with a relatively firm sea floor and clear waters, under middle sublittoral and subtropical conditions. Associated echinoderm taxa comprise more robust, sturdy-plated ophiomusaid and ophiodermatid brittle stars and numerous bourgueticrinine sea lilies. The new brittle star described herein belongs to a family whose present-day members are predominantly restricted to bathyal depths. Its small size and the exceptional preservation of a single articulated specimen partially wrapped around the stalk of a bourgueticrinine suggest that O. floorae n. sp. was probably epizoic and specifically associated with stalked crinoids.

Low predation intensity on the stalked crinoid Democrinus sp. (Echinodermata) in Roatán, Honduras reveals deep water as likely predation refuge

Predation has been hypothesized to play a key role in the evolutionary and ecological history of crinoids. Whereas evidence of predation on crinoids in the form of injuries can be common, quantifying predation intensity, which is critical for properly evaluating such hypotheses, has proven challenging. Here, we used a longitudinal approach to quantify predation intensity on the extant, deep-water, stalked crinoid, Democrinus sp. The quantitative estimates are based on data collected from a manned submersible during expeditions conducted over a 3-yr span. These results indicate that this deep-water crinoid is subject to much lower predation intensity than are crinoids living in shallow water, consistent with (1) an inverse relationship between predation intensity and depth, and (2) the hypothesis that for stalked crinoids, which are unable to handle high predation intensity, deep water is a refugium.

PALEOENVIRONMENTAL AND BIOSTRATIGRAPHIC IMPLICATIONS OF ECHINODERM OSSICLES TRAPPED WITHIN BURMESE AMBER

ABSTRACT Marine organisms are uncommonly preserved in amber. Recently, they were reported to be associated with Burmese amber. However, most of specimens from previous reports were preserved on the amber surface or within the sediment surrounding the amber. Based on X-ray tomography and thin-section optical microscopy of Burmese amber, we report here the first genuine and unambiguous evidence of inclusion of crinoid ossicles preserved in the fossil resin. Preservation of this exclusively marine group in amber gives insights into the paleoenvironment of the crinoid-amber association and provides additional evidence to support previous observations of shallow-water stalked crinoids from the mid-Cretaceous, when many stalked crinoids started to shift offshore due to increased predation pressure during the Mesozoic Marine Revolution. Crinoid remains, represented by disarticulated stem and arm ossicles assignable to Isocrinus cf. legeri (Repelin), point to a mid-Cretaceous age for the Burmese amber and support some previous hypotheses suggesting a close proximity between the resin-producing trees and seawater.

Crinoid respiration and the distribution of energetic strategies among marine invertebrates

During the Mesozoic, the radiation of durophagous marine predators caused the ecological and evolutionary diminution of once-successful groups, including stalked, suspension-feeding echinoderms known as crinoids. Featherstars, crinoids that shed the stalk during development and exhibit anti-predatory adaptations such as high motility, defied this trend, and today they are widespread and diverse across ocean depths. As a ‘success story’ of the Mesozoic Marine Revolution, featherstars could be used to reveal how some marine lineages succeeded in the face of increased predation over geological time. However, current limited understanding of crinoid functional anatomy has inhibited such study. Using microphotography, scanning electron microscopy and computed tomography, I characterize the structure and variation of crinoid circulatory anatomy and explore differences between featherstars and stalked forms. Contrary to previous accounts, I find support for the role of coelomic circulation in crinoid respiration. This includes a previously undocumented case of positive allometry: larger crinoids have more complex circulatory anatomy. Moreover, quantitative analysis of coelomic anatomy shows that the circulatory system is generally more complex in featherstars than in stalked crinoids. The adaptations that allowed featherstars to persist in shallow water apparently entailed an increase in the functional capacity of the circulatory system, possibly due to consistently greater metabolic rates.

Predation on feather stars by regular echinoids as evidenced by laboratory and field observations and its paleobiological implications

Among extant crinoids, the feather stars are the most diverse and occupy the greatest bathymetric range, being especially common in reef environments. Feather stars possess a variety of morphological, behavioral and physiological traits that have been hypothesized to be critical to their success, especially in their ability to cope with predation. However, knowledge of their predators is exceptionally scant, consisting primarily of circumstantial evidence of attacks by fishes. In this study the question whether regular echinoids, recently shown to consume stalked crinoids, also consume feather stars is explored. Aquarium observations indicate that regular echinoids find feather stars palatable, including feather stars known to be distasteful to fish, and that regular echinoids can capture and eat live feather stars, including those known to swim. Gut-content analyses of the echinoidAraeosoma fenestratum(Thomson, 1872), which is commonly observed with large populations of the feather starKoehlermetra porrecta(Carpenter, 1888) in video transects from marine canyons off the coast of France, revealed elements of feather stars in the guts of 6 of 13 individuals. The high proportion of crinoid material (up to 90%), and the presence of articulated crinoid skeletal elements in the gut ofA. fenestratum, suggest that these echinoids consumed at least some live crinoids, although they may have also ingested some postmortem remains found in the sediment. Additionally, photographic evidence from the northeast Atlantic suggests that another regular echinoid,Cidaris cidaris(Linnaeus, 1758), preys on feather stars. Thus in spite of the broad suite of antipredatory adaptations, feather stars are today subject to predation by regular echinoids and may have been since the Mesozoic, when this group of crinoids first appeared.