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About Graptolite

Where does the name 'Graptolite' come from? Good question. I think it must have come from wanting a geological-sounding name for the boat as a sort of tribute to my academic and work years as a rock-basher. Not much came to mind though until I was reminded of my old friend John Rigby's PhD thesis on the subject of graptolites, an unassuming fossil that I had also studied a little at university. 

Graptolites were colonies of marine creatures that quietly floated about from place to place. It felt right for a boat name at the time.

Here is more information about fossil graptolites than you could possibly want to know.

Graptolite Taxonomy

Graptolite's were early inhabitants of the worlds seas and were known chiefly from the Upper Cambrian through the Lower Carboniferous. The name comes from the Greek graptos, meaning "written", and lithos, meaning "rock", as many graptolite fossils resemble pencil marks on the rock.

The name originates from the genus Graptolithus, which was used by Linneus in 1735 for inorganic mineralizations which resembled actual fossils. Later workers used the name to refer to a specific group of organisms. Graptolithus was officially abandoned in 1954, partly because of its original purpose as a grouping for inorganic mimicries of fossils.

Since the 1970s, as a result of advances in electron microscopy, graptolites have generally been thought to be most closely allied to the pterobranchs, a rare group of modern marine animals belonging to the phylum Hemichordata.

Graptolite Morphology

Each graptolite colony (known as a rhabdosome) has a variable number of branches (called stipes) originating from an initial individual (called a sicula). Each subsequent individual (zooid) was housed within a tubular or cup-like structure (called a theca). The number of branches and the arrangement of the thecae are important features in the identification of graptolite fossils.

Most of the dendritic or many-branched types are classified as dendroid graptolites (order Dendroidea). They appear earlier in the fossil record (in the Cambrian period), and were generally benthic animals (attached to the sea-floor by a root-like base). Graptolites with relatively few branches were derived from the dendroid graptolites at the beginning of the Ordivician period. This latter type (order Graptoloidea) were pelagic, drifting freely on the surface of ancient seas or attached to floating seaweed by means of a slender thread. They were a successful and prolific group, being the most important animal members of the plankton until they died out in the early part of the Devonian period. The dendroid graptolites survived until the Carboniferous period.

Graptolites as Zone Fossils

Graptolites are common fossils and have a worldwide distribution. They are important index fossils for dating Palaeozoic rocks as they evolved rapidly with time and formed many different species. British geologists divide the rocks of the Ordovician and Silurian periods into graptolite biozones; these are generally less than one million years in duration.

Graptolite Preservation

Graptolite fossils are often found in shales and mud rocks where sea-bed fossils are rare, this type of rock having formed from sediment deposited in relatively deep water that had poor bottom circulation, was deficient in oxygen, and had no scavengers. The dead planktonic graptolites, having sunk to the sea-floor, would eventually become entombed in the sediment and are thus well preserved.

Graptolite fossils are often found flattened along the bedding plane of the rocks in which they occur, though may be found in three dimensions when they are infilled by iron pyrite. They vary in shape, but are most commonly dedritic or branching (such as Dictoyonema), saw-blade like, or "tuning fork" shaped (such as Didymograptus murchisoni). Their remains may be mistaken for fossil plants by the casual observer.

Graptolites are normally preserved as a black carbonized film on the rock's surface. They may be sometimes difficult to see, but by slanting the specimen to the light or covering it with a film of oil they reveal themselves as a shiny marking.

Graptolite The Yacht

Yacht Graptolite is not a fossil yet, being built only in 2002. The design is a Bavaria '44', almost 14 metres long with a beam of 4.25 metres and a draught of 1.65 metres. She is a sloop rig with an in-mast furling mainsail. There is a fin and bulb iron keel and a spade rudder. She has three double cabins and two shower/heads and can sleep up to seven although the usual crew is three or four.

She's a fairly typical, production cruising boat but there have been a number of additions to make her suitable for blue-water cruising including additional navigation instruments, a diesel generator, a combined wind/towed generator, a reverse osmosis watermaker and an SSB radio.

 

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Last Update 16/07/2009