Large Jurassic ammonites from Madagascar are often seen in European and North American fossil and mineral fairs. They come in a variety of preservations, from brown internal moulds with fractal-like sutures to specimens that retain the nacreous shell. They range from small specimens to large ones that can exceed 70 cm in diameter. Species of the families Phylloceratidae, Lytoceratidae, Aspidoceratidae and Perisphinctidae are the most common. The late Maurice Collignon, a French career military officer, collected the first specimens during four field campaigns in the fifties, and described a number of species in his Atlas des fossiles caractéristiques de Madagascar [1].
During one of our trips to Madagascar, we had the opportunity to visit one of the localities where these ammonites are collected. We had already seen plenty of polished specimens in the crafts markets in Madagascar’s capital Antananarivo, and we wanted to have a look at the place and the rocks they are found in. All sources pointed to an area in the Atsimo-Andrefana region, that is southwestern Madagascar. We were already in the region when we heard about the exact whereabouts of the place. The fossils occur in a remote locality that can be accessed after a 1h30 hike and the crossing of a 100 meters wide, shallow river. In this part of the country, the rain season is short and the climate dry, i.e. favourable conditions to the growth of bushes and shrubs, and the presence of natural rock outcrops.
Locally, the Upper Jurassic consists of a succession of soft brown fossiliferous oolithic limestone overlain by several meters of grey-blueish marls. Initially, ammonites used to be found lying on the ground or just beneath the ground surface. Such places are still found occasionally, and one of them was dug during our visit. Once these are exhausted, all that remains is a vast area with piles of oolithic limestone with fossil remains.
Then, diggers start working towards the hill summit, where the bed is concealed by meters of an unfossiliferous unit of marl. After selecting a place, quarrymen dig square pits varying from 1.5 to 4 meters, working with picks, shovels and crowbars made of concrete iron, alone or by teams of two to four men. During our visit, efforts were concentrated on one such pit, which required the removal of 6 metres of marls to reach the fossiliferous bed. As the men were approaching the fossiliferous level in the largest pit, small ammonites could be seen in the hands of those working in smaller pits where the oolithic layer had been reached. Sometimes, when the fossiliferous bed is dug out, the men dig horizontally, below the marls. Needless to say that proceeding this way is prone to dangerous working conditions. We weren’t told if accidents happen. As seen from the fractures in the marls, it is likely that pits collapse faster than the horizontal expansion of the workings.
Ammonites are in important source of income for the inhabitants, as their main revenue arise from the cultivation of rice and small red peppers. Purchasing one of these ammonites is the last link of a business that involves villagers, a number of brokers, exporters and sellers like us at Gondwana Fossils. Have a look at our selection of Jurassic ammonites from Madagascar for sale.
[1] Collignon M. 1959. Atlas des fossiles caractéristiques de Madagascar (Ammonites). IV (Argovien–Rauracien). – Service géologique, Tananarive, pls. 47–95. [PDF Scribd] [PDF ginras.ru]
