This is the third in our series of blogs delving into the fossil collection at Paisley Museum. This blog will concentrate on the Carboniferous period, a time when Britain lay at the equator and is named for the rich deposits of coal formed by lush swamps that dominated areas of what is now North America and Europe.
A large part of the fossil collection at Paisley Museum is from the Carboniferous period and from the local vicinity which is not surprising as Paisley sits in the central belt of Scotland, one of the main coal bearing areas of Britain.
This blog will focus on some of the animal life that thrived during this period, whilst the following blog will look at the plant life.
Carboniferous Period (359 – 299 million years ago)
Gigantoproductus giganteus from Muirkirk, East Ayrshire, Scotland
Gigantoproductus giganteus is an extinct species of brachiopod or lamp shell. It was a two-shelled marine invertebrate (animal without a backbone), not to be confused with bivalves to which it is not related, found on the seabed, partially buried in sand or mud, in shallow seas.
This species could grow to 30cm (12 inches) in length making it one of the largest brachiopod species to have ever lived.
Brachiopods were the most abundant and diverse marine invertebrate of the Paleozoic Era (542 – 252 million years ago), originating in the early Cambrian (542 – 521 million years ago), diversifying in the Ordovician (485 – 443 million years ago), but crashing during the end-Permian mass extinction (252 million years ago) with over 95% of all brachiopod genera (groups) becoming extinct.
The fossil record suggests that Gigantoproductus giganteus was most common during the early Carboniferous period, 359 to 323 million years ago.
Sanguinolites costellatus from Gurdy Cut, North Ayrshire, Scotland
This bivalve (two-shelled) shellfish, similar to modern-day mussels, lived in burrows on the sea floor. Like most modern-day bivalves, Sanguinolites was a filter-feeder, using its gills to trap small food particles from sea water.
Found in the Carboniferous coal sediments of North Ayrshire, this specimen was deposited at a time when the Midland Valley (geological area underlying the central belt of Scotland from Girvan to Greenock in the west and Dunbar to Stonehaven in the east) was covered in tropical rainforests surrounded by tropical seas. It most probably died in its burrow as both of its shells have remained joined together.
Like brachiopods, bivalves originated in the early Cambrian, diversified in the Ordovician and suffered huge losses during the end-Permian mass extinction event. But, unlike brachiopods, bivalves then experienced a second major period of diversification where they gained an evolutionary advantage over brachiopods resulting in the diversity and abundance of this invertebrate type that we see today.
Nautilus ingens from Lugton, East Ayrshire, Scotland
Nautilus ingens, a nautiloid, was a member of a diverse group of marine cephalopods that evolved in the Late Cambrian (497 – 485 million years ago) to become one of the main predatory marine animals of the Paleozoic Era.
Some 2,500 species of nautiloid are known from the fossil record, including forms with straight or partially coiled shells. Today, only a handful of species survive.
Present day cephalopods include animals such as octopus, where the shell is absent, and squid and cuttlefish, where the shell is internal and straight. Only in nautilus is the shell external and coiled.
Gyracanthus formosus from Dalry, North Ayrshire, Scotland
Belonging to the extinct class of fish, the acanthodii (also known as “spiny sharks”, although they were not sharks), Gyracanthus is found in both Devonian and Carboniferous-aged rocks.
The acanthodii had a cartilaginous skeleton, the same as sharks and their relatives, but their fins were supported by bony spines.
A bit of a mystery, Gyracanthus is only known from isolated fin spines like the one photographed, and other fragmented bones. The function of the fin spines is still not fully understood but it may be that they kept the fins rigid to help stabilise and provide lift as the animal moved through the water or that they were used in defence.
Trace fossil - tridactyl footprint from Cardowan, Stepps, North Lanarkshire, Scotland
Evolving from lobe-finned fish in the late Devonian (370 – 359 million years ago) tetrapods (four-limbed, land vertebrates) underwent their first major diversification in the early Carboniferous (359 – 323 million years ago), followed by a second in the late Carboniferous (323 – 299 million years ago).
Trace fossils are the preserved sign of an activity such as footprints, tracks, worm burrows, root cavities, etc and provide important information about an organism’s lifestyle, providing clues to diet or behaviour. However, unless the body fossil of the organism is preserved along with the trace fossil it is difficult to determine what made the trace fossil and for this reason many trace fossils are given their own scientific names.