Article

Environmental stress five million years ago on the West Coast of South Africa?

Tamara Franz-Odendaal, Department of Zoology, University of Cape Town, South Africa
Email: tfranz@botzoo.uct.ac.za

Among the many fossils palaeontolgists find are some particularly interesting variations on mammals found in the present time -  ever heard of a two-toed horse or, a short-necked giraffe or a two-tusked elephant? What about the specimens with pathologies? Box them and forget about it?  A UCT scientist explains how these specimens can give us clues about the health of animals that lived millions of years ago.

The West Coast Fossil Park at Langebaanweg (LBW) is one of the largest Early Pliocene (5 Ma) deposits in South Africa. This locality is unique because of its incredibly diverse range of fossils. Amongst the carnivores: the first sub-Saharan African bear (Agriotherium africanum), sabre-toothed cats and a new species of hyaena were found. New herbivores include gomphotheres (early elephants with two pairs of tusks), a three-toed horse and a short-necked giraffe (Sivatherium hendeyi) to name just a few. Fossil birds are extremely well represented and include several different species of freshwater birds, seabirds, songbirds, birds of prey and even an ostrich! Interestingly, it is thought that subtropical forests and a river were present at this locality 5 million years ago (mya), yet no crocodiles, only one primate and only a few tropical birds have been found. Apart from these new species, several modern vertebrates were also found - these include hippos, white rhinos, bush pigs, several antelopes, tortoises, frogs, snakes, seals, sharks, and of course an array of micromammals. 

Apart from the extremely diverse fossil fauna, a large number of fossils (bones and teeth) with defects and pathologies have been found. In the past such material was simply labelled as such, boxed, and added to the collection without any further study. However, in recent years it is increasingly recognised that pathological specimens can provide a host of information about the health of extinct populations.

This is why this scientist has set out to firstly investigate the palaeoenvironment at LBW and secondly to try to understand the nature of the pathologies present in the fossil animals. Little is known about the palaeoenvironment of the Southwestern Cape during the last 20 million years. Except that at around 17-13 Ma (Miocene epoch) there were some major global environmental changes that resulted in expanding grasslands and diminishing trees/forests. In addition the presence of burnt bones and catastrophic mortality profiles of some of the LBW animals indicate that fires and floods were a common occurrence. A solitary pollen study on the deposit underlying the main fossil bed, done by Prof Joey Coetzee (Dept. of Botany, University of Free State) almost 20 years ago, indicates the presence of marshes and subtropical forests during the Miocene period. Interestingly, a few fynbos pollens were found indicating that fynbos was beginning to establish itself at this time. More detailed analysis of the flora during the Early Pliocene is desperately required, but few peat deposits with preserved pollens have been found. The fossil fauna provide us with more solid clues about the environment at LBW 5 mya. The kinds of animals found show that both browsing and grazing animals, many of them very large animals, co-existed. In order to better understand the palaeoenvironment of the West Coast of South Africa during this time period, stable carbon and oxygen isotope analyses were conducted on dental enamel from several of the herbivores. Results show that the grasses were all temperate (cool growing season) varieties and not savanna (warm growing season) varieties. That is C3 and not C4 grasses dominated the area. What this means is that the climate in this region 5mya was very similar to what is experienced today.

A second thrust of her research focuses on the short-necked giraffid or sivathere. A large percentage of the teeth of this animal have a dental defect known as enamel hypoplasia. Since enamel is not remodelled over time, unlike bone and dentine, the study of enamel defects is an ideal tool to investigate events that occurred during the first few years of an animal's life. Thus enamel has an advantage over bone in that early developmental stress events can be investigated. Such information would otherwise be unavailable. Enamel hypoplasia can occur either as linear grooves or bands of pits on the tooth surface or as single pits. Linear enamel hypoplasia is known to occur as a result of physiological stress such as weaning stress, nutritional stress, traumatic calf-cow separations, fevers during illness, etc. Her particular quest is to understand under what circumstances the enamel hypoplasia in the sivathere population occurred and to investigate whether such defects reflect the changing environmental conditions. It is likely that with the diminishing woodlands and expanding grasslands, there was a decrease in the amount or quality of food available for the sivatheres. Detailed analyses (currently underway) will elucidate the extent of these defects and which, if any, other groups of animals are afflicted with the same dental defects. Abnormal tooth wear has also been observed in several fossil herbivore teeth suggesting that these animals were not eating their usual diet. In addition, skeletal pathologies have been identified in many of the carnivores, some herbivores and a few birds.

It is believed that the study of dental and skeletal defects as well as stable isotope analyses will help build a better understanding of the palaeoecology of the West Coast of South Africa five million years ago.

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