 |
| Aioloceras besairiei (Collingnon, 1949) |
This is specimen #00783B in the collections of the Vancouver Palaeontological Society, (VIPS). The chambers have a wonderful calcite filling best viewed by carefully slicing these specimens in two.
There is a small imperfection near the centre that renders this ammonite its signature mark of perfection. This lovely is in my care as a study specimen.
Madagascar is an island country is about 400 kilometres off the coast of East Africa in the Indian Ocean and a wonderful place to explore off the beaten track. Exotic, beautiful and geologically interesting — it remains high on my bucket list to explore.
Madagascar has some of the most pleasing of all the fossil specimens I have ever seen. This beauty is no exception. The shell has a generally small umbilicus, arched to acute centre and falcoid ribs that spring in pairs from the umbilical tubercles then disappear on the outer whorls. Take that magical body plan with its pleasing symmetry and add an infilling with spectacular calcite — spectacular!
It is rightfully Aioloceras besairiei — and correctly labelled as such by the VIPS — but some specimens I have looked at earlier were marked as a Cleoniceras besairiei. This is impossible, of course, as Cleoniceras and Grycia are not present in Madagascar. This lovely, seen in cross-section, is now far from home and in my collection to enjoy for a time before returning to Courtenay on Vancouver Island.
Aioloceras besairiei are within beudanticeratinae. Cleoniceras and Grycia are the boreal genera. If you would like to see — or argue — the rationale on the name, consider reading Riccardi and Medina's riveting work from back in 2002, or Collingnon from 1949.
The beauty you see here measures in at a whopping 23 cm. It hails from the youngest or uppermost subdivision of the Lower Cretaceous. I had originally thought this locality was older, but dating reveals it to be from the Lower Albian, approximately 113.0 ± 1.0 Ma to 100.5 ± 0.9 Ma. This locality produces ammonites that are beyond measure in their singular beauty.
Aioloceras are found in the Cretaceous of Madagascar at geo coordinates 16.5° S, 45.9° E: paleo-coordinates 40.5° S, 29.3° E.; and in four localities in South Africa: at locality 36, near the Mzinene River at 28.0° S, 32.3° E: paleo-coordinates 48.6° S, 7.6° E.
We find them near the Mziene River, at a second locality north of Hluhluwe where the Mzinene Formation overlies the Aptian-Albian Makatini Formation at 28.0° S, 32.3° E: paleo-coordinates 48.6° S, 7.6° E; and at Haughton Z18, on the Pongola River in the Albian III, Tegoceras mosense beds at 27.3° S, 32.2° E: paleo-coordinates 48.0° S, 7.8° E.
If you happen to be trekking to Madagascar, know that it's big. It is 592,800 square kilometres (or 226,917 square miles), making it the fourth-largest island on the planet — bigger than Spain, Thailand, Sweden and Germany. So, enjoy your time and wear comfortable shoes.
If you are interested in learning more about this species, check out the Treatise on Invertebrate Paleontology, Part L (Ammonoidea). R.C. Moore (ed). Geological Soc of America and Univ. Kansas Press (1957), p L394. Or head over to look at the 2002 paper from Riccardi and Medina. 2002. Riccardi, A., C. & Medina, F., A. The Beudanticeratinae and Cleoniceratinae (Ammonitina) from the Lower Albian of Patagonia in Revue de Paléobiologie - 21(1) - Muséum d’Histoire Naturelle de la ville de Genève, p 313-314 (=Aioloceras besairiei (COLLIGNON, 1949). You have Bertrand Matrion to thank for the naming correction. Good to have friends in geeky places!
Collignon, M., 1933, Fossiles cenomaniens d’Antmahavelona (Province d’ Analalave, Madagascar), Ann. Geol. Serv. Min. Madagascar, III, 1934 Les Cephalopods du Trias inferieur de Madagascar, Ann. Paleont. XXII 3 and 4, XXII 1.
Besairie, H., 1971, Geologie de Madagascar, 1. Les terrains sedimentaires, Ann. Geol. Madagascar, 35, p. 463.
J. Boast A. and E. M. Nairn collaborated on a chapter in An Outline of the Geology of Madagascar, that is very readable and cites most of the available geologic research papers. It is an excellent place to begin a paleo exploration of the island.
If you happen to parle français, check out: Madagascar ammonites: http://www.ammonites.fr/Geo/Madagascar.htm
