Environmental distribution of post-Palaeozoic crinoids from the Iberian and south-Pyrenean basins, NE Spain

Post-Palaeozoic crinoids from northeast Spain ranging from the Ladinian (Middle Triassic) to the Ilerdian (lower Ypresian, early Eocene) are documented. Here we provide the first attempt to reconstruct the environmental distribution of these crinoids based on relatively complete material (mostly cups). Triassic forms are dominated by encrinids from outer carbonate ramps. Late Jurassic crinoids are dominated by cyrtocrinids, comatulids, millericrinids, and isocrinids, occurring either on sponge mounds and meadows or on soft substrates within middle to outer carbonate ramps. Aptian (Early Cretaceous) forms include nearly complete isocrinids which are found in extremely shallow environments represented by bioclastic carbonates and interspersed oyster-rich layers. Other Aptian occurrences come from more distal and deep environments and are composed solely of comatulids. Albian forms are dominated by cyrtocrinids and isocrinids associated with coral reefs. Late Cretaceous and Eocene crinoids include mostly bourgueticrinids (Comatulida) that are found either in outer ramp facies or associated with mid-ramp reef complexes. The later corresponds to one of the shallowest occurrence of bourgueticrinids in the Cenozoic. The palaeoecological data for fossil crinoids of northeast Spain contributes to reconstructing the history of the bathymetric distribution of articulate crinoids, supporting the idea that stalked crinoids were able to inhabit a wide range of shallow marine environments in the late Mesozoic and early Cenozoic

Palaeoenvironmental control on distribution of crinoids in the Bathonian (Middle Jurassic) of England and France

Bulk sampling of a number of different marine and marginal marine lithofacies in the British Bathonian has allowed us to assess the palaeoenvironmental distribution of crinoids for the first time. Although remains are largely fragmentary, many species have been identified by comparison with articulated specimens from elsewhere, whilst the large and unbiased sample sizes allowed assessment of relative proportions of different taxa. Results indicate that distribution of crinoids well corresponds to particular facies. Ossicles of Chariocrinus and Balanocrinus dominate in deeper-water and lower-energy facies,with the former extending further into shallower-water facies than the latter. Isocrinus dominates in shallower water carbonate facies, accompanied by rarer comatulids, and was also present in the more marine parts of lagoons. Pentacrinites remains are abundant in very high-energy oolite shoal lithofacies. The presence of millericrinids within one, partly allochthonous lithofacies suggests the presence of an otherwise unknown hard substrate from which they have been transported. These results are compared to crinoid assemblages from other Mesozoic localities, and it is evident that the same morphological ad-aptations are present within crinoids from similar lithofacies throughout the Jurassic and Early Cretaceous

Additional evidence for the drilling behavior of Paleozoic gastropods

Although the record of Paleozoic drillholes is long and extensive, evidence pertaining to the identity of the drillers is sparse. The most conclusive evidence, a driller “caught in the act”, has been documented only once (Baumiller 1990). In that example, a drillhole in the calyx of a crinoid was found directly beneath an attached platyceratid gastropod. Additional evidence for drilling by platyceratids has been circumstantial, i.e., based on the association of platyceratids with certain blastoids and crinoids, and the presence of drillholes in other crinoid and blastoid taxa. To a skeptic, the lack of congruence between drilled and platyceratidinfested crinoids and blastoids is not sufficient evidence that platyceratids were the drillers. More conclusive evidence requires examples of drillholes in taxa that are known to have been platyceratid−infested, preferably from localities where both infested specimens and drilled specimens co−occur

Drilling predation on Permian brachiopods and bivalves from the Glass Mountains, West Texas

Although bored invertebrates have been described from every period of the Paleozoic, little information on the frequency and nature of Late Paleozoic drill holes exists. Our examination of the Permian silicified fossils, which were bulk collected by G.A. Cooper from the Glass Mountains of west Texas, revealed numerous drilled brachiopods and bivalve mollusks. Drill holes are perpendicular to the shell, smooth sided, sometimes beveled, and have other characteristics consistent with a predatory/parasitic origin. The frequency of drilling is significantly lower (p ≤ 0.05) for brachiopods (1.07%, n = 7597) than for bivalves (7.43%, n = 619). This study confirms that drilling predators and/or parasites were present in the Late Paleozoic. However, the drilling frequencies reported here—rarely exceeding 5%—are much lower than those reported for the Late Mesozoic and Cenozoic, which typically exceed 20%. The low Late Paleozoic frequencies are consistent with a majority of estimates reported previously for the older periods of the Paleozoic and suggest that the intensity of drilling predation/parasitism in marine benthic ecosystems remained low throughout the Paleozoic and did not increase until some time in the Mesozoic. Our data suggest that prey/host types with a higher nutritional return (bivalve mollusks) may have been preferentially selected for attack by predator(s)/parasites(s) already in the Permian

Fossilized soft tissues in a Silurian platyceratid gastropod

Gastropod shells are common in the fossil record, but their fossil soft tissues are almost unknown, and have not been reported previously from the Palaeozoic. Here, we describe a Silurian (approx. 425 Myr) platyceratid gastropod from the Herefordshire Lagerstätte that preserves the oldest soft tissues yet reported from an undoubted crown-group mollusc. The digestive system is preserved in detail, and morphological data on the gonads, digestive gland, pedal muscle, radula, mouth and foot are also available. The specimen is preserved three-dimensionally, and has been reconstructed digitally following serial grinding. Platyceratids are often found attached to echinoderms, and have been interpreted as either commensal coprophages or kleptoparasites. The new data provide support for an attached mode of life, and are suggestive of a coprophagous feeding strategy. The affinities of the platyceratids are uncertain; they have been compared to both the patellogastropods and the neritopsines. Analysis of the new material suggests that a patellogastropod affinity is the more plausible of these hypotheses

Crinoid stalk flexibility: theoretical predictions and fossil stalk postures

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75286/1/j.1502-3931.1996.tb01836.x.pd