Earth ocean Sciences

A single specimen of the protasterid ophiuroid Protasterina flexuosa from the Kope Formation (Cincinnatian, Upper Or− dovician) of Kentucky exhibits three−dimensionally pyritized tube feet. This represents the first report of soft−tissue pres− ervation in an echinoderm from the type−Cincinnatian series. The tube feet are solid and lack all internal structure. They consist of aggregated masses of small euhedral to subhedral pyrite crystals suggesting that pyritization, although de− cay−induced and mediated, did not necessarily replicate soft−tissues but might instead have formed inside the void−spaces left behind during the decay process. The discovery of pyritized soft−tissue as delicate as ophiuroid tube feet suggests that similar forms of soft−tissue preservation might be found in other taxa in the Kope Formation. Perhaps much more impor− tantly, this unexpected occurrence demonstrates the incompleteness of our knowledge of permissible conditions for the preservation of soft−tissu...

A single specimen of the protasterid ophiuroid Protasterina flexuosa from the Kope Formation (Cincinnatian, Upper Or− dovician) of Kentucky exhibits three−dimensionally pyritized tube feet. This represents the first report of soft−tissue pres− ervation in an echinoderm from the type−Cincinnatian series. The tube feet are solid and lack all internal structure. They consist of aggregated masses of small euhedral to subhedral pyrite crystals suggesting that pyritization, although de− cay−induced and mediated, did not necessarily replicate soft−tissues but might instead have formed inside the void−spaces left behind during the decay process. The discovery of pyritized soft−tissue as delicate as ophiuroid tube feet suggests that similar forms of soft−tissue preservation might be found in other taxa in the Kope Formation. Perhaps much more impor− tantly, this unexpected occurrence demonstrates the incompleteness of our knowledge of permissible conditions for the preservation of soft−tissu...

Background: As Earth warms, temperate and subpolar marine species will increasingly shift their geographic ranges poleward. The endemic shelf fauna of Antarctica is especially vulnerable to climate-mediated biological invasions because cold temperatures currently exclude the durophagous (shell-breaking) predators that structure shallow-benthic communities elsewhere. Methodology/Principal Findings: We used the Eocene fossil record from Seymour Island, Antarctic Peninsula, to project specifically how global warming will reorganize the nearshore benthos of Antarctica. A long-term cooling trend, which began with a sharp temperature drop ,41 Ma (million years ago), eliminated durophagous predators-teleosts (modern bony fish), decapod crustaceans (crabs and lobsters) and almost all neoselachian elasmobranchs (modern sharks and rays)from Antarctic nearshore waters after the Eocene. Even prior to those extinctions, durophagous predators became less active as coastal sea temperatures declined from 41 Ma to the end of the Eocene, ,33.5 Ma. In response, dense populations of suspension-feeding ophiuroids and crinoids abruptly appeared. Dense aggregations of brachiopods transcended the cooling event with no apparent change in predation pressure, nor were there changes in the frequency of shell-drilling predation on venerid bivalves. Conclusions/Significance: Rapid warming in the Southern Ocean is now removing the physiological barriers to shellbreaking predators, and crabs are returning to the Antarctic Peninsula. Over the coming decades to centuries, we predict a rapid reversal of the Eocene trends. Increasing predation will reduce or eliminate extant dense populations of suspensionfeeding echinoderms from nearshore habitats along the Peninsula while brachiopods will continue to form large populations, and the intensity of shell-drilling predation on infaunal bivalves will not change appreciably. In time the ecological effects of global warming could spread to other portions of the Antarctic coast. The differential responses of faunal components will reduce the endemic character of Antarctic subtidal communities, homogenizing them with nearshore communities at lower latitudes.

Onychaster is prominent in discussions on the ancestry of crown group ophiuroids because about half of researchers have classified Onychaster as a Palaeozoic representative of the living Order Euryalida. With this classification there is a Mis­sissippian to Cretaceous gap in the euryalid fossil record. Other researchers have classified Onychaster as non-euryalid, in which case there is no such gap. This undecided status is an important reason to review the classification of Onychaster using new observations. In Onychaster the lateral plates are strictly on the underside of the arm where they form a double row and nearly touch midventrally; there are no mid-ventral underarm plates. The undersurface-laterals bear a transverse row of spines that point proximally (in retro-direction). The disk in large specimens bulges interradially such that the arms insert subambitally. The morphology of Onychaster vertebrae is documented anew in SEM stereo-pair images. Distinc­tive features include: ...

A single specimen of the protasterid ophiuroid Protasterina flexuosa from the Kope Formation (Cincinnatian, Upper Or− dovician) of Kentucky exhibits three−dimensionally pyritized tube feet. This represents the first report of soft−tissue pres− ervation in an echinoderm from the type−Cincinnatian series. The tube feet are solid and lack all internal structure. They consist of aggregated masses of small euhedral to subhedral pyrite crystals suggesting that pyritization, although de− cay−induced and mediated, did not necessarily replicate soft−tissues but might instead have formed inside the void−spaces left behind during the decay process. The discovery of pyritized soft−tissue as delicate as ophiuroid tube feet suggests that similar forms of soft−tissue preservation might be found in other taxa in the Kope Formation. Perhaps much more impor− tantly, this unexpected occurrence demonstrates the incompleteness of our knowledge of permissible conditions for the preservation of soft−tissu...

Onychaster is prominent in discussions on the ancestry of crown group ophiuroids because about half of researchers have classified Onychaster as a Palaeozoic representative of the living Order Euryalida. With this classification there is a Mis-sissippian to Cretaceous gap in the euryalid fossil record. Other researchers have classified Onychaster as non-euryalid, in which case there is no such gap. This undecided status is an important reason to review the classification of Onychaster using new observations. In Onychaster the lateral plates are strictly on the underside of the arm where they form a double row and nearly touch midventrally; there are no mid-ventral underarm plates. The undersurface-laterals bear a transverse row of spines that point proximally (in retro-direction). The disk in large specimens bulges interradially such that the arms insert subambitally. The morphology of Onychaster vertebrae is documented anew in SEM stereo-pair images. Distinc-tive features include: ...