What are Crinoidea, Camerata?
Crinoids are ancient organisms Crinoidea, Camerata, having lineages appearing in the fossil record in the Burgess shale some 508 million years ago. Crinoidea echinoderms developed in and are found commonly from the Ordovician period 486 to 445 m.y.a., through the Silurian, Devonian and Carboniferous periods, eventually suffering mass extinctions in the ‘great extinction’ event of Permian period. Some still surviving through to the modern day, in differing forms in our oceans. These marine sub species have been discovered in shallow seas to the deepest oceans. The enigmatic and most fascinating fossil sub species intrigues palaeontologist and continues to have a mysterious ecology since its earliest origins.
Where did Crinoids Exist?
Fossil Crinoids have been found anchored to driftwood, these psuedoplanktonic organisms from the Jurassic period of Germany have been discovered in colonies of individuals attached to huge fossilised tree trunks, flotsam from those ancient seas. Some like the Scyphocrinus elegans of Morocco, North Africa, had large root balls, which are believed to be a flotation or buoyancy aid, some simply rooted themselves to the seafloor or onto rock outcrops, others were pelagic having large ovoid heads which floated above the seabed moving in sea currents, while others may have dredged along the seafloor. Some modern varieties walk on cirri, a type of appendage to the columnar stem, having an appearance of legs or arms lined with tube feet, using them in a similar fashion as an octopus might appear to do with its tentacles, moving over the ocean floor.
Where are Crinoids found?
We find the best fossil specimens in Morocco. Here is a rich vein of Devonian red limestone which produces wonderfully preserved examples of dark grey calcified individuals, along with mass mortality beds. Flowery heads on long segmented stems seemingly sway, orientated as the last sea current lay them down moments before some catastrophe covered them with localised mineral rich silts. Mass extinction events, undersea shelf slips, reef collapses or tsunami's did probably contributed to thousands or millions of individuals being covered in this way. Later through a process of precipitated calcite fossilisation metamorphosed into the fossil limestone plates unearthed today. From millions upon millions of deposited individuals, only a few survive in the fossil record in a good preserved state. In this geographical region of Africa palaeontologists are lucky to be able to have access to the desert regions where fossils may be foraged more easily.
How are Crinoids found?
The process of finding and excavating the Crinoids of Morocco is one which is riddled with hazards because of the remoteness of the fossil bearing layers that reside in the desert ténéré or wilderness. The uninhabited space offers unrestricted access to the fossil beds on one hand, on the other hand makes the collecting process arduous, the remoteness and extreme heat and cold play a part in the discomforts of professional fossil digging. In flat open spaces of the ténéré the diggers sink large square pits into the desert floor, sometimes up to 20ft or 30ft deep. These pits in the main are not shored, timber being in short supply in the seemingly lifeless ténéré. Also the ténéré making the transporting of mechanical excavation equipment to the sites prohibitive, these flat areas are often circled by mountains ranges.
With picks and shovel the holes are opened to the rock levels below, where the Crinoids may be found. With every blow of the pick the walls of the sandstone pit shudder, causing sandy debris to fall to the floor of the excavated hole. Once a rock layer (4ins to 6ins in thickness), is struck it is broken up with sledge hammers, each piece is turned over in the hope Crinoids may be present in the limestone. Not always is the gift a Crinoid fossil, sometimes layers contain no fossil Crinoids and the pit is abandoned. In these remote areas one will see many abandoned excavations, broken slabs of limestone viewed from the rim’s of fruitless pit’s, piled in heaps many feet below.
The Crinoid anatomy
Has not changed much since the their early development. Although some may have attached themselves to driftwood many types held a holdfast to the sea bed. Some may have been up to 40 metres in overall length, this was mainly the stem or columnar stalk eminating from the radix or holdfast. The stem was formed of disc like plates, liken to vertebrate disc’s, these segments fixed together with ossicles, the stem supported the head or crown of the Crinoid. The crown consisted of the aboral cup, this inverted pyramid shaped cup termed a calyx was made up of fixed brachial plates. Feathery pinnule arms were connected to the calyx, the arms made up of ossicles, attached to these were the cilia, the filter feeding process end of the Crinoid.
The calyx or crown was where all the dynamic action took place. Brachial plates of the Tegmen, a slightly inverted dome structure with a central point rising up into a pyramid of further brachial plates, resided in the calyx, this opened when the Crinoid was feeding. Here was located the mouth and anus side by side, the cilia passed filtered organisms via ciliated ambulacral grooves along the pinnule arms transporting food to the mouth. A series of intestinal tubes passed these nutrients to the gut and back up to the anus, the Crinoid having no stomach.
Crinoids have been likened to feathery plants, when seen swaying in the current this is entirely a feasible impression and apt description. Sea lilies, feather stars are all terms associated with the Devonian fossil Crinoids. All our team at The Fossil Store are in agreement that the existence and demise of the Crinoids is intriguing and equally fascinating.