Complete Fossil Helps Palaeontologists Piece Together Worm Evolution

A tiny fossil of an armoured marine worm may not be everyone’s idea of a museum show stopper but for scientists attempting to understand the evolution of Annelids in the Palaeozoic era the finding of a complete fossilised animal represents an important breakthrough.

Discovered in Morocco by a graduate of the Dutch Ghent University – Peter Van Roy this fossil represents a complete specimen which previously had only been known from fossilised fragments of dermal armour.  The work carried out by Peter, in collaboration with Yale University geologist Derek Briggs and his graduate student, Jakob Vinther will help scientists to better understand annelid evolution.

The Annelids are segmented worms; they are represented by the phylum Annelida and include about 15,000 modern species of worms and leeches.  The name Annelida was first applied to this group of worms by the famous French scientist and pioneer of evolutionary theory, Jean-Baptiste de Lamarck in 1809.  The genus to which this fossil belongs had been described back in the 19th Century but it was only known from small pieces and up until now scientists could only guess at what the animal looked like.

The worm is believed to be a Machaeridian an armoured segmented worm, with rows of scales on the back and sides of the animal.

The Fossil and an Illustration of the Machaeridian Segmented Worm

Picture Credit: Science Daily
Illustration Key:
Length of worm = approximately 25 mm
Trunk = yellow
Limbs = red
Bristles = grey
Attachment for Shell Plates (armour) = green
Digestive Tract = purple
Dorsal Linear Structure = blue

Machaeridians evolved during the Cambrian period and survived for around 180 million years before finally becoming extinct during the Carboniferous.  Scientists cannot be sure about when they first appeared as the fossil record for soft-bodied animals is extremely sparse.  Conditions have to be absolutely right to permit the preservation of soft body parts, the carcase has to be buried quickly in fine sediments and mineralisation must start to allow the outline of the body to be preserved before the soft tissue decays.

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