- Saccocoma pectinata
- Jurassic Age
- Solnhofen Limestone
- Near Hienheim, Germany
- This specimen will come in the 6.25″ x 8.25″ Riker Mount with Label as Shown
Saccocoma is an extinct genus of Comatulida crinoid that lived from the Late Jurassic to the Early Cretaceous in Europe and North America. It contains at least two species.
This is a pelagic (free-floating) crinoid from the Jurassic (150 million year old) Solnhofen Limestone in Germany. It’s of the species Saccocoma pectinata.
They are from a group of crinoid echinoderms, in which the adults are free-swimming
Comatulida is an order of crinoids. Members of this order are known as feather stars and mostly do not have a stalk as adults. The oral surface with the mouth is facing upwards and is surrounded by five, often divided rays with feathery pinnules. Comatulids live on the seabed and on reefs in tropical and temperate waters.
Like other echinoids, comatulids have pentamerous symmetry as adults though the larvae have bilateral symmetry. Late in their development, the larvae are attached to the seabed by a stalk, but this is broken at metamorphosis and the juvenile crinoid is free living. The body has an endoskeleton made from a number of articulated calcareous plates known as ossicles covered by a thin epidermis. It is in the shape of a cup (the calyx) with a lid (the tegmen) which has a central mouth and an anus near the edge, the gut being U-shaped. There is a ring of clawlike appendages (the cirri) near the base of the aboral underside; these grip the substrate to keep the feather star in place.
There are five long, often branched, rays attached round the edge of the tegmen. Each of these is further subdivided into branchlets (the pinnules). Most comatulids originally have 10 arms, each ray being subdivided once. The arms are fragile, and if one is broken off, at least two grow in its place; in this way the number of arms can increase. The arms are composed of articulating ossicles held together by ligaments, and the pinnules have a similar structure. The arms are very flexible and can be spread widely or coiled up. An ambulacral groove starts on each pinnule and joins with others to form grooves on the arms all leading to grooves on the tegmen ending at the mouth. These food-collecting grooves are overhung by calcareous plates (the lappets) and have a lining of fine cilia.
The Solnhofen Plattenkalk, or Solnhofen limestone, is a Jurassic Konservat-Lagerstätte that preserves a rare assemblage of fossilized organisms, including highly detailed imprints of soft bodied organisms such as sea jellies. The most familiar fossils of the Solnhofen Plattenkalk include the early feathered theropod dinosaur Archaeopteryx preserved in such detail that they are among the most famous and most beautiful fossils in the world. The Solnhofen beds lie in the German state of Bavaria (Bayern), halfway between Nuremberg (Nürnberg) and Munich (München) and were originally quarried as a source of Lithographic limestone.
During the Late Jurassic, this area was an archipelago at the edge of the Tethys Sea. This included placid lagoons that had limited access to the open sea and where salinity rose high enough that the resulting brine could not support life. Since the lowest water was devoid of oxygen, many ordinary scavengers were absent. Any organism that fell, drifted, or was washed into the lagoons from the ocean or the land became buried in soft carbonate mud. Thus, many delicate creatures avoided consumption by scavengers or being torn apart by currents. The wings of dragonflies, the imprints of stray feathers, and terrestrial plants that washed into the lagoons were all preserved. The fossils are not numerous, but some of them are spectacular, and their range gives a comprehensive picture of a local Jurassic ecosystem. At times, the lagoons almost dried out, exposing sticky carbonate muds that trapped insects and a few small dinosaurs. Over 600 species have been identified, including twenty-nine kinds of pterosaur ranging from the size of a sparrow to 1.2 m (4 ft) in length. The fine-grained texture of the mud silt forming the limestone from the Solnhofen area (which is composed mainly of the towns of Solnhofen and Eichstätt is ideal for making lithographic plates, and extensive quarrying in the 19th century revealed many fossil finds, as commemorated in the name Archaeopteryx lithographica, all the specimens of which come from these deposits.