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From the wet clays of Peterborough to the sunny Caatinga of Brazil

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David M Martill (UK)

After several gruelling years of working in the sticky wet Jurassic clay pits of the Peterborough district for their gigantic marine reptiles and even more massive fishes, it was a refreshing change to fly south and investigate the sun-baked Caatinga of South America. The Chapada do Araripe, on the borders of the Brazilian states of Ceará, Pernambuco and Piaui, had always fascinated me (Fig. 1).

Fig. 1a (left). A map showing the location of the Chapada do Araripe in the northeast of Brazil. Fig. 1b (above). Detail of the Chapada do Araripe. This is one of the most important sites in the world for Cretaceous Gondwanan fossil fauna and flora.

I had seen specimens of the fabulous fossil fishes (I hope you like the alliteration) in limestone concretions (Fig. 2) that kept turning up in European fossil shops, but what had really caught my eye was a short letter to the scientific journal Nature that described fossil ostracods from those very same concretion horizons.

Fig. 2. A typical concretion from the Santana Formation, with a not so typical fish. This is one of the rare fossil rays.

I am not an aficionado of ostracods: who is? They mostly look like small baked beans, and it is so tedious trying to mount them on stubs so that you can see them under the electron microscope. No, it was the remarkable quality of their preservation that caught my eye. The specimens in question were described by Ray Bate, who had noticed that it was not only the shell preserved, but the entire animal (Fig. 3), all the soft parts, including their enormous genitalia (ostracods only claim to fame …. hung like stallions, then some).

Fig. 3. Fossil ostracod with its naughty bits preserved. This exceptionally delicate fossil was obtained by immersing a concretion in 10% acetic acid and searching through the insoluble residue under a binocular microscope. The specimen is approximately 1mm high.

Such remarkable preservation was at that time (1970) almost unheard of. Even amber inclusions were considered then to represent nothing more than the husks of the entombed insects and spiders. This exquisite preservation fascinated me and I was determined to go and see these wonderfully fossiliferous concretions in the field, for myself, first hand. I undertook background research while working at the Field Museum in Chicago. Chicago in the 1980s was arguably the centre of the universe for palaeontological research and it still is to some degree. Much more important though was the wonderful library in the Field, including its collection of often difficult to source Brazilian journals.

With the background reading done and a plane ticket in my hand, I set off for Brazil. I remember doing so with some trepidation as a fish worker at the Natural History Museum in New York had told me how dangerous the area was, and how treacherous travel in the area could be. I teamed up with Brazilian palaeoichthyologist Paulo Brito, now at the State University in Rio, but then, like me, a student of palaeontology.

Getting to the area couldn’t have been easier. The roads are excellent, express buses run regularly and taxi vans can be found to take you into the remotest of areas. And what is more, everyone is so friendly and helpful. I think that that this particular fish worker was probably trying to keep the area to himself. My first field season in Brazil was the stuff of palaeontological dreams.

We discovered new localities where the ground was littered with concretions, nearly every one containing a complete fossil fish. We even found some of the ‘fish mines’ (Fig. 4) where illegal fossil traffickers had been digging (Fig. 5).

Fig. 4. Possibly the site where botanist and explorer George Gardner first found fossil fishes on the flanks of the Chapada do Araripe. This locality is near the pretty little town of Jardim on the south east flank of the giant plateau.
Fig. 5. Fossil fish mines. These are the places where the fossils that can be bought in fossil shops around the world come from.

The material they had smashed to smithereens was depressing, but then again, collecting from their ‘leftover’ piles was in fact quite productive (Fig. 6).

Fig. 6. A ‘left over’ pile from the fossil miners. Many interesting discoveries can be made on the ‘waste’ dumps.

The fossils that I wanted were examples where I could see high concentrations of phosphatic material (Fig. 7).

Fig. 7. A fossil fish from the Santana Formation in which much of the body musculature has been preserved in white calcium phosphate. The concretions can provide rich pickings of exceptionally well-preserved small invertebrates, often within the stomach of the fish. The fish miners often discard these specimens as visually unattractive, at least in their eyes, but not in mine.

Mostly these were recognised as concretions containing a fish and large patches of fine white material. This material was actually the fossilised muscle tissues of the fish and under the electron microscope remarkable detail can be seen; including cell nuclei, mitochondria and the banding patterns of striated muscle fibres (Fig. 8). In these very same concretions are also found the little ostracods with their preserved naughty bits and often other animals as well.

Fig. 8. Detail of the soft tissues as photographed under the scanning electron microscope. Fig. on the left shows two muscle fibres (each approximately 10-15 microns across) with the banding characteristic of striated muscle. The picture on the right shows a number of mitochondria or nuclei on the surface of the muscle, each of which is approximately 1 micron long. Such preservation by mineral replacement is truly remarkable, though not rare.

These fish nodules all come from a rock unit known as the Santana Formation (Fig. 9) and in particular from a layer known as the Romualdo Member.

Fig. 9. Simplified stratigraphic log showing the fossiliferous units present in the Araripe Basin of the Chapada do Araripe.

Fossil collecting from this layer is so easy it almost takes the fun out of it. But while on my first trip, I learnt of another fossiliferous unit, the Crato Formation, a few tens of metres below the nodules (Fig. 10).

Fig. 10. A typical exposure of the richly fossiliferous Nova Olinda Member, the basal unit of the Crato Formation.

This rock unit comprises a series of finely laminated limestones with hundreds of small fishes called Dastilbe (Fig. 11) interbedded with sands and silts.

Fig. 11. The small gonorhynchiform fish Dastilbe. This is the most common vertebrate fossil, perhaps even the most common fossil, of the Nova Olinda Member. Specimens vary in length from 10mm to 300mm.

The lowest of the limestone units is now called the Nova Olinda Member and commonly yields the remains of fish, insects (Figs. 12 and 13) and plants (Fig. 14) and, more rarely, scorpions, frogs (Fig. 15) pterosaurs (Fig. 16), turtles, lizards, and even a few feathers from time to time.

Fig. 12. This beautiful dragonfly from the Nova Olinda Member is on display in the museum at Santana do Cariri.
Fig. 13. This is the larva of a mayfly. These are abundant in the Nova Olinda Member, and occasionally the adults are found.
Fig. 14. Fragments of the gymnosperm tree Brachyphyllum are often found on the cut slabs in the stone yards.
Fig. 15. This spectacular frog represents an extremely rare discovery for the Nova Olinda Member.
Fig. 16. A remarkable ornithocheirid pterosaur cf. Ludodactylus sp. from the Nova Olinda Member.

In fact, the fossils from this unit are more diverse and often almost as well preserved as the fishes from the famous nodules, although preservation of soft tissues is not nearly as common. The Nova Olinda limestone of the Crato Formation is quarried for paving slabs (Fig. 17) and because it has to be cut by hand many of the quarry workers discover fossils, thus a cottage industry selling fossils has developed in the region.

Fig. 17. These quarry workers find hundreds of fossils every year. However, technically Brazilian law prevents them from selling the fossils and very often an important specimen will be discarded.

The fossils eventually find their way (usually illegally) into the fossil shops of North America, Europe and Japan. Don’t feel guilty about buying these fossils though, the people of the region need every opportunity they can to earn a bit of extra cash. I find it surprising that the trade hasn’t been legalised and some sort of co-operative set up to develop the trade for the local people. Such a scheme would have benefits for the locals, Brazilian scientists and science as a whole. Every now and then a local government clamp down halts the activities of the dealers, but when this happens the fossils are often just thrown away… what a sad loss.

One of the really nice things about doing any scientific fieldwork based in Brazil is the friendliness of the people. In the north east of Brazil people are very laid back, enjoy life and will party at any excuse.

The local sugar cane, when not being used for car fuel, is converted into a wicked drink called Cachaça. This is fall over juice, but when mixed with a little tonic and a bit of sugar and lime, the Caiprinha is an excellent way to wind down from a baking hot day in the field bashing nodules.

Visiting this region of Brazil is dead easy. Buses from Rio de Janeiro to Fortaleza actually drive across the Chapada do Araripe and stop in Crato, one of the local towns. There are good hotels in Crato and Juazeiro do Norte and the area has excellent opportunities for tourism. There are country parks with lakes fed from freshwater springs… swimming in Perrier. There are natural parks with a wealth of birdlife… if you like hummingbirds and there are artefacts and lithoglyphs aplenty. Two museums are dedicated to fossils, one at Crato and one in Santana do Cariri, while at Jardim a small museum is dedicated to the early history of the region (Fig. 18). The area was first explored by westerners in the 1830s when George Gardner based himself at Crato on his big plant hunting expedition and it is still possible to trace his original route if you can get hold of the detailed maps.

Fig. 18. The area is becoming a popular visitor destination, and a number of small museums have opened up in the region. This one at Jardim is dedicated to Scottish explorer and botanist George Gardner.

The tropical and exotic Val do Cariri and the Chapada do Araripe are a far cry from the wet and sticky Oxford Clay pits of central England and one soon loses interest in the Jurassic once you set foot on the fossil-rich South American Cretaceous.

Photographs by Robert F. Loveridge

About the author

At the time this article was written, the author was at the Palaeobiology Research Group at the School of Earth and Environmental Sciences, University of Portsmouth.

Portsmouth PO1 3QL United Kingdom

Further reading

Fossils of the Oxford Clay: Palaeontological Association Guide No 4, edited by David M Martill and John D Hudson, The Palaeontological Association, London (1991), 286 pages (Paperback), ISBN: 0901702463.

Fossils of the Santana and Crato Formations: Palaeontological Association Guide No 5, by David M Martill, The Palaeontological Association, London (1993), 158 pages (softback), ISBN: 0901702463.

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