Paisley Museum’s Fossil Collection Review


Paisley Museum’s Fossil Collection Review

Paisley museum is one of 10 partner museums in the Leeds Geoblitz project and the only Scottish participant.

As a partner, Paisley Museum was lucky enough to host Neil Owen, the Curator of Geology at Leeds Museum, who spent a week with us reviewing and researching our collections.

One of the outcomes of what was a very quick review for such a large collection of many thousand geology specimens was a list of fossils highlighting the wealth and diversity of the fossil collection.

This review will be covered in a series of blog posts. The aim is to raise awareness of one of the natural history collections hidden away in the museum stores, to unearth evidence of ancient life hidden in those collections and to highlight individual specimens of interest.

Life on Earth began about 3.8 billion years ago, initially with single-celled organisms such as bacteria, eventually evolving into multi-cellular organisms around 800 million years ago. However, it is not until around 542 million years ago, over a relatively short period of time known as the Cambrian explosion that most of the life forms that we are familiar with began to evolve.

This blog will feature specimens from both well-known and not so well-known plant and animal groups. Although starting quite a bit into the history of life on Earth, at the Ordovician some 485 to 443 million years ago, the museum’s collection contains a more diverse representation of ancient life from this period onwards.

 

Ordovician Period (485 – 443 million years ago)

During the Ordovician marine life increased and diversified significantly with the seas dominated by molluscs (bivalves, sea snails and straight nautilus) along with arthropods  (arthropod meaning jointed leg and which included: shrimps, sea scorpions and trilobites). However, the end of this period was characterised by a series of devastating mass extinctions.

Trilobite Shale from Ontario, Canada

 

Trilobites, a class of arthropods, thrived during this period. So named due to the division of their body plan into three longitudinal lobes all trilobites show a slightly raised central lobe with two flatter lobes either side.

Despite the variety of trilobites, all followed the same body structure with a cephalon (head), segmented thorax (chest area just behind head) and pygidium (tail piece). Incomplete trilobite fossils are common, because most of these fossils are actually moults of the carapace (shell), shed during the trilobite’s growth stage; a feature still retained by modern insects and crustaceans. These brittle shell moults are often broken apart and become fossilised, as illustrated in this example which is composed of a multitude of trilobite pygidiums.

This trilobite-rich layer of shale records a mass death event. Whatever happened did so quickly, one possible explanation being a mud slide burying both living and dead animals in a disorganised group. 

Climacograptus bicornis from Dob’s Linn, near Moffat, Dumfries & Galloway, Scotland

This strange looking fossil is a graptolite. Normally found on dark mudstones and shale, graptolites can easily be mistaken for pencil markings on rock. In fact this is what graptolite means “written on the rock” from the Greek graptos meaning “written” and lithos meaning “rock”.

Graptolites were colonial marine creatures (like corals) made up of many tiny individual animals linked together. Most floated freely in the sea, probably resembling seaweeds. Graptolite fossils represent the animals dwelling place, and consists of numerous short burrows strung together in a long chains. The actual zooid animals are rarely preserved, leaving behind their delicate “plant like” burrow structures.      

Graptolites formed in the Cambrian period (542 – 485 million years ago) but thrived during the Ordovician, evolving into many different forms and eventually becoming extinct during the Carboniferous period, around 315 million years ago.

 

Silurian Period (443 – 419 million years ago)

The Silurian was a “greenhouse” period with warm, tropical seas home to a rich variety of animal life. This was a period of great adaptation for marine invertebrates (animals without a backbone) as well as the time when some invertebrate groups began to make the transition from sea to land.

Calymene blumenbachii  

   

Trilobites were still a common animal during this period, only entering a decline and eventual extinction during the Devonian (419 – to 359 million years ago).

Calymene blumenbachii, a familiar trilobite was first discovered in the limestone quarries of Wren’s Nest Hill in Dudley, England and so has been nicknamed the “Dudley Bug”.

Like most trilobites this species could roll up into a ball, most probably for defence.

 

Eurypterid (Sea-scorpion) claw

 

Eurypterids are an extinct group of scorpion-like animals. Although closely related to scorpions they were not true scorpions. They were formidable predators that existed from the mid-Ordovician (470 – 458 million years ago) to the Permian (299 – 252 million years ago) and thrived in mainly brackish or freshwaters, although the earliest groups may have lived in the sea.

The largest eurypterids reached lengths of over 2 metres making them the largest marine arthropods to have ever lived but most were less than 20 centimetres. In some, including this specimen, the first pair of limbs ended in pincers armed with sharp pointed teeth on the inner edges.

 

By Nicola Macintyre at Paisley Museum 


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