File:Seirocrinus subangularis (fossil crinoid) (Posidonia Shale, Lower Jurassic; Holzmaden area, Germany) 1 (35674916591).jpg

Seirocrinus subangularis (Miller, 1821) - fossil crinoid from the Jurassic of Germany. (CM 34210, Carnegie Museum of Natural History, Pittsburgh, Pennsylvania, USA)

Crinoids (sea lilies) are sessile, benthic, filter-feeding, stalked echinoderms that are relatively common in the marine fossil record. Crinoids are also a living group, but are relatively uncommon in modern oceans. A crinoid is essentially a starfish-on-a-stick. The stick, or stem, is composed of numerous stacked columnals, like small poker chips. Stems and individual columnals are the most commonly encountered crinoid fossils in the field. Intact, fossilized crinoid heads (crowns, calices, cups) are unusual. Why? Upon death, the crinoid body starts disintegrating very rapidly. The soft tissues holding the skeletal pieces together decay and the skeleton falls apart.

The specimen shown above is from the famous Holzmaden Lagerstätte, a Jurassic-aged soft-bodied fossil deposit in Germany. The deposit consists of marine black shales and has produced many complete vertebrate skeletons, many of which have a carbonized halo/outline of skin. The latter is seen in sharks, bony fish, crocodilians, pterosaurs, plesiosaurs, and ichthyosaurs. Many female ichthyosaurs are fossilized with embryos in their bodies, or in the apparent act of giving birth. An alternative interpretation of the latter is that such fossils represent post-mortem abortions due to compression from burial in sediments. The Holzmaden deposit also has fossil logs with encrusting crinoids, plus ammonites & belemnites (both cephalopods) with soft tissues preserved - including ink sacs, tentacles, and hooks.

From museum signage:

Holzmaden

Fossils from a Jurassic sea

The bottom waters of the seas covering southern Germany during the Early Jurassic often lacked oxygen, so when a dead organism sank to the seabed, there were few bacteria around to decompose it. These conditions are the main reason for the exquisite preservation of Holzmaden's fossils, which include rarely preserved soft tissues such as ichthyosaur fins and cephalopod ink sacs. Such finds have revealed fundamental aspects of these animals' anatomy and behavior that could not have been determined from hard parts alone.

As in the Triassic, crinoids (“sea lilies”) remained abundant in Jurassic seas, and were more diverse than today. Unlike all modern crinoids, which live anchored to the seafloor, Seirocrinus probably drifted the open ocean attached to floating logs. This crinoid reached gigantic sizes, with stalks stretching up to 65 feet (20 meters) long.

Classification: Animalia, Echinodermata, Crinoidea, Articulata, Isocrinida, Pentacrinitidae

Stratigraphy: Holzmaden Lagerstätte, Posidonia Shale, Toarcian Stage, upper Lower Jurassic

Locality: unrecorded/undisclosed site at or near the town of Holzmaden, southwestern Germany

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