Invertebrate Palaeontology

Invertebrate palaeontology is the study of fossils of animals with no backbone or spine.

Introduction

Fossils are the remains or impressions of a once-living plant or animal found in rock and often hardened through natural processes. Invertebrates, as the name suggests, are animals that do not possess a vertebral column and this also applies to the soft-bodied and smaller invertebrates such as worms and amoebae, whose remains are poorly fossilised. Hard-bodied and larger invertebrates are better preserved as a result of their hard shells, bones and teeth. More often than not, it is the very hard calcareous shells of, for instance, molluscs such as snails, mussels and oysters that are best preserved. The Invertebrate Palaeontology Collections at Iziko South African Museum reflects this chequered fossilisation record. Nonetheless, thanks to the hard work of the museum’s researchers and other contributors, this collection is still a sizeable and important one.

Middle Devonian fossils

The fossils in this collection represent the Middle Devonian Period, which lasted from 393 to about 382 million years ago. The material was mostly recovered from the Bokkeveld Group, rock strata (or layers) that forms part of the sequence of rocks known as the Cape Supergroup which stretches across most of the Southwestern part of South Africa. The collection holds fossils of bivalves, brachiopods, starfish, trilobites, ophiuroids, crinoid and sponges.

Trace Fossil Collection

This collection is mostly made up of some 300 trace fossils, which are mainly arthropod trackways from the Lower Ecca varved shales of Early Permian age.

Cretaceous Fossil Collection

This collection holds specimens dating back to the Cretaceous Period (145 to 65.5 million years ago). It was a period with a relatively warm climate and high sea levels that created numerous but shallow inland seas. The end of the Cretaceous saw many faunas going extinct which included the dinosaurs (vertebrates) and ammonoids. The collection comprises several thousand ammoniod specimens. These ammonoids are mostly keeled – i.e. shells that had ridges running lengthwise down the back – although there are also some good examples of heteromorph ammonoids, so called because of their varied coiled shells. The collection also holds a number of specimens named after Dr ECN van Hoepen, the first full-time director of the National Museum in Bloemfontein, from which they are on permanent loan. Much of the Cretaceous collection was contributed by the previous curator Dr Herbert Klinger who has been a driving force in ammonite research in South Africa for the past few decades.

Cretaceous to Recent Microfossil Collection

There are over 1,000 microfossil specimens in the collections, covering marine and freshwater Ostracods, and Foraminifera (marine only). These microfossils are small (smaller than 1 mm in diameter) and require a microscope to study their structure and to identify them. Most of the ostracods were contributed to the collection by Dr Richard Dingle and the foraminifera by Dr Ian McMillan.

Pleistocene Fossils

These collections include fossil and subfossil terrestrial, marine and freshwater vertebrates and invertebrates representing approximately the past two million years, i.e. the Pleistocene epoch, which started about 2.5 million years ago to around 11,700 years ago. This period also covers much of the development of early human ancestors. The collections provide environmental and ecological contexts for the faunal evolution and biodiversity over this time, as well as for the development of human behaviour. These observations also contribute to our knowledge of long-term environmental change and the understanding of modern issues such as global warming.

Keywords

Ammonoids: An extinct group of marine invertebrates with distinct spiral shells.
Arthropod: An invertebrate animal with an exoskeleton (external skeleton), a segmented body, and jointed appendages (limbs), which makes up over 80% of described living animal species. It includes scorpions and spiders.
Bivalves: Or bivalvia, a class of freshwater and marine molluscs with shells protecting the left and right parts of the body.
Brachiopods: Marine animals with shells on the top and bottom.
Calcareous: To be made mostly or partly the chemical compound known as calcium carbonate; it is the main component of the shells of marine organisms and snails, for example.
Chemofossil: A fossil comprised only of chemicals remaining from the decomposition of a living organism.
Crinoids: Marine animals characterised by a mouth on its top surface, surrounded by feeding arms
Epoch: In geochronology, i.e. the science for dating rocks, fossils and sediments (solid material that is moved and deposited in a new location), an epoch is a subdivision of the geologic timescale; it is longer than an ‘age’, but shorter than a ‘period’.
Ecological: Regarding the relation of living organisms to one another, and to their environment.
Exoskeleton: The hard and inflexible covering for the body of some invertebrate animals, such as grasshoppers, cockroaches, crabs and lobsters.
Faunal: Adjective for fauna, or animal life.
Foraminifera: Or ‘forams’, small marine organisms with either a single or multi-chambered shell, with both extinct and living forms.
Fossil: The remains or impression of a prehistoric organism that has been preserved in ‘petrified form’ (in which its organic remains have been replaced by minerals that slowly turn to rock) or as a mould or cast in rock.
Invertebrate: An animal with no vertebral column (backbone/spine).
Macrofossil: Fossils large enough to be visible to the naked eye.
Microfossil: A fossil or fossil fragment that can only be seen, examined or studied with a microscope.
Molluscs: A large group of marine invertebrates that include snails and octopus, known for their soft bodies and (mostly) hard shells.