Name: The Soom Shale
Location: Cape Province, South Africa
Age: Late Ordovician (Ashgill)


Fauna of the Soom Shale


The biota of the Soom Shale is characterised by nektonic (free swimming), and nektobenthic (limited swimming, mostly bottom-dwelling) faunas. The fauna shows a top-heavy trophic structure, with many predators and few prey.

1. Eurypterids:

The Soom Shale eurypterid Onychopterella augusti occurs as a few exceptionally preserved specimens. These are from the Kerbos locality (location). Onychopterella is the first Ordovician eurypterid found in a Gondwanan deposit. Specimens show superb detail, including lamellate book-gills, evidence linking them to modern-day scorpions. The specimens average 100-120 mm in length.

Eurypterid Onychopterella augusti (Braddy et al. 1995). Photo used with permission of The Palaeontological Association. Reconstruction of Onychopterella augusti (Braddy et al. 1995). Photo used with permission of The Palaeontological Association.

2. Conodonts

The Soom Shale was only the third location in the world to show soft-tissue preservation of conodonts. This is most commonly in the form of eye musculature in association with the feeding elements, but in one specimen body muscle blocks are also found. As well as showing soft tissue preservation, the conodont Promissum pulcrum is the largest ever found. Its body length during life has been estimated at 400 mm, an order of magnitude bigger than any conodont previously found.

Schematic illustration of cConodont feeding apparatus. Author's own rendering. Conodont animal reconstruction. Author's own rendering.

3. Orthoconic Cephalopods

Orthoconic cephalopods from the Soom Shale show exceptional preservation. The feeding apparatus, or radulae are seen in four specimens, suggesting the affinity of orthocones is closer to ammonoids than nautiloids, as previously thought. The orthocone conchs show colonisation by orbiculoid brachiopods, which probably occurred during life, not after death, as in previous examples.

Orthocone fossil showing orbiculoid brachiopods on the conch and surrounding sediment (Gabbott 1999). Photo used with permission of The Palaeontological Association. Reconstruction of orthoconic cephalopod. Author's own rendering.

4. Brachiopods

Two brachiopod groups are represented in the Soom Shale, orbiculoids and trematids. The orbiculoids have been found in association with orthocone conchs. Trematid brachiopods are found as isolated specimens, much fewer in number than the orbiculoids.

Orbiculoid brachiopod showing growth rings (Gabbott 1999). Photo used with permission of The Palaeontological Association. Group of orbiculoid brachiopods crushed in sediment, found in association with orthocone to left (Gabbott 1999). Photo used with permission of The Palaeontological Association.

5. Naraoiid Trilobites

Naraoiid trilobites, unlike other trilobites, are soft boddied. They show no biomineralised carapace, and inlude some of the most primitive forms. The Soom Shale naraoiid Soomaspis slendida shows very good preservation, mostly as internal moulds. It is a small animal, around 10 mm wide.

Naraoiid Soomaspis splendida (Fortey & Theron 1994). Photo used with permission of The Palaeontological Association. Internal mould of pygidium of Soomaspis sp. (Fortey & Theron). Photo used with permission of The Palaeontological Association.

6. Chitinozoa

Chitinozoa are organic-walled microfossils with unknown biological affinities. They are vesicular-shaped fossils with one open end and a body cavity. They usually occur as individuals, but can sometimes be found in complex structures such as chains. In the Soom Shale, chitinozoans are visible on bedding surfaces, as individuals, chains, aggregated masses, or associated with organic envelopes. The aggregtaed masses can reach numbers in the thousands, with the largest mass measuring 52 mm by 12 mm.

Chain of chitinozoan vesicles (Gabbott et al. 1998). Photo used with permission of The Palaeontological Association. Camera lucida drawing of chitinozoan chain. (Gabbott et al. 1998). Photo used with permission of The Palaeontological Association.

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