THE FOSSIL STORE™; The anatomy of the Crinoidea

THE FOSSIL STORE™; Crinoidea, Camerata; Crinoids are ancient organisms scientifically named Crinoidea, Camerata. The Crinoidea lineage made its first appearance in the fossil record some 508 million years ago.

The Burgess shale famously carries many soft-bodied life forms, newly discovered species when in 1909 Charles Walcott first discovered the fossil site in the Canadian Rockies.

Crinoidea are echinoderms and developed fully in and are found commonly from the Ordovician period 486 to 445 million years ago, through the Silurian, Devonian and Carboniferous periods, eventually suffering mass extinctions in the ‘great extinction’ event of the Permian period.

Some have survived in various forms through to today in our oceans. These marine subspecies have been discovered in shallow seas to the deepest oceans. The enigmatic and most fascinating fossil species intrigues palaeontologist and continues to have a mysterious ecology from its earliest origins.

 

 

Crinoid habitats

Where did Crinoids live; Jurassic fossil Crinoids have been found anchored to driftwood, these pseudoplanktonic organisms evolved in the Jurassic period of Germany and have been discovered in colonies of individuals attached to huge fossilised tree trunks, natural flotsam of those ancient seas. Some like the Devonian period Scyphocrinus elegans of North Africa had large root balls, which are theorised to be a flotation or buoyancy aids.

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.

 

Crinoid Discovery + Excavation

How are Crinoids found; The process of finding and excavating the Crinoids of Morocco is one which is peppered 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 fossil sites prohibitive, these flat areas are often circled by mountains ranges.

With basic tools, pick axes and shovels, the diggers open up the pits to the limestone fossil bedrock levels below, where the Scyphocrinites Crinoids may be hoped to be discovered. Once at the rock level and with every stone splitting 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 sledgehammers, each newly created slab is turned over in the hope Crinoids may be present in the limestone. Not always is this the case a Crinoid fossil, some layers contain no fossil at all and the pit is then abandoned and the diggers move on. 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.

 

Crinoidea Anatomy Development + Form

The Crinoids anatomy; As seen in THE FOSSIL STORE™ photography, the Crinoidea has not changed that much since their early development some 500 million years ago, they are still as fascinating as ever and definitely an enigmatic creature today as they are in the fossil record.

Although some may have attached themselves to driftwood many types held a holdfast to the seabed. Some may have been up to 40 metres in overall length, this was mainly the stem or columnar stalk emanating 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 consists of the aboral cup, this inverted pyramid-shaped cup termed a calyx was made up of fixed brachial plates.

Calyx is named from the Greek (a Greek slender stemmed cup), it has also been used in botany to name the part of flower head which covers the bud and later supports the opened petals. 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, a pyramid of further brachial plates, these opened when the Crinoid was feeding. Here under the Tegmen were located the mouth and anus side by side. Arms covered in 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 real stomach. Crinoids have been likened to feathery plants, when seen swaying in sea currents, this is an entirely 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.

 

 

 

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