Presumed postlarval pentacrinoids from the Lower Devonian Hunsrück Slate, Germany

Abstract

Several tiny crinoids with crowns as small as 1 mm, or less, in width are newly recognized from the Hunsrück Slate of southwestern Germany. The presence of erect arms above an amorphous calyx in some specimens can be inferred. Based on comparison with the size and gross morphology of developmental stages in living crinoids, these tiny Hunsrück crinoids are judged to be at an early postlarval stage that is analogous to the pentacrinoid stage just after development from the stalked, but armless, smaller cystidean larval stage found in both living comatulids and isocrinids. Some of these tiny crinoids have a stalk up to 4 mm long attached to a now pyritized former substrate. Their clustered occurrence suggests gregarious settlement of larvae. Taxonomic identification of these presumed pentacrinoids is not possible, even to the sub‐class level, although they are preserved with larger juveniles of the cladids Propoteriocrinus and Lasiocrinus. These larger juveniles exhibit 3‐D pyritized calcite plates, whereas the probable pentacrinoids appear to be preserved as flattened, micro‐crystalline pyritized dermal tissues that enclosed lightly calcified, porous ossicles. The pentacrinoids were likely buried within weeks or months of hatching, based on developmental stages in similar‐sized living crinoids. These tiny crinoids, presumably pentacrinoids, are a further example of the extraordinarily detailed preservation of delicate tissues in pyrite from the Hunsrück Slate. They are most likely the pentacrinoid stage from one or more of the crinoid taxa (30 genera) present in the Hunsrück Slate. Assuming these are not microcrinoids, they are the first report of pentacrinoids from the fossil record and document that a Palaeozoic sister group to modern crinoids had similar developmental stages.

Catalogue of living crinoids (Echinodermata: Crinoidea) from Brazil

“…-Souto et al 2014: 279.-Clouse et al 2015. -Kammer et al 2015: 310, fig. 2a-d.-Pertossi et al 2019, fig.…”

Biogenic Iron Preserves Structures during Fossilization: A Hypothesis

“…Although fossil mineralization is common in the geological record, [ 52–57 ] little work has been done to investigate the role of tissue chemistry during the mineralization process. Recently, it was suggested that the recurrent association of particular mineralogical phases such as fluorapatite, or Fe‐sulfides (pyrite, pyrrhotite) with specific tissues in crustacean fossils preserved within carbonate‐rich concretions from the Jurassic exceptionally preserved biota of La Voulte‐sur‐Rhône (Ardèche, France) were linked to differences in the original biochemical signal of the organic matter.…”

Early post-metamorphic, Carboniferous blastoid reveals the evolution and development of the digestive system in echinoderms

“…However, living echinoderms have diverged greatly from the latest common ancestor they share with all deuterostomes and, hence, might not closely reflect developmental processes in the earliest forms. Study of the extensive Palaeozoic fossil record of echinoderms could shed light on the early evolution of development in the phylum, but such work is hampered by the scarcity of fossilized early ontogenetic stages (although see [4]). Here, we report an extremely well-preserved, early postmetamorphic echinoderm from the Carboniferous (approx.…”