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Wooster’s Fossil of the Week: A juvenile conch from the Upper Pleistocene (Eemian) of The Bahamas

Thursday, November 17, 2016 21:25
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(Before It's News)

inagua-lobatus-gigasI collected this beautiful shell from a seashore exposure of Pleistocene sediments on Great Inagua, the third largest island of The Bahamas. I was on an epic expedition to this bit of paradise with Al Curran and Brian White of Smith College in March 2006. We were pursuing evidence for a sea-level change event in the Eemian, about 125,000 years ago. This was some of the most exciting scientific work I’ve done, so this little shell brings back many memories. I found it loosely cemented into a small patch of carbonate sediments inside a hollow of an ancient coral reef. This shell and numerous other samples were basic data for a rapid rise and fall of sea level during the last interglacial interval. The project is summarized in the Thompson et al. (2011) reference below.

This is a juvenile of the common Queen Conch Lobatus gigas (Linnaeus, 1758). In its adult form with a flared aperture it is one of the most recognizable modern shells in the world. Some of you may be surprised by the generic name. I was. I knew this shell as Strombus gigas, the original name given to it by the sainted father of taxonomy Carolus Linnaeus in 1758. After several adventures in the literature, Landau et al. (2008) placed the species in the genus Lobatus Swainson 1837.

salvador-lobatus-gigas-1The species looks exactly the same today, at least in its shell. This is a similar modern Queen Conch juvenile collected from San Salvador Island in The Bahamas. Note the color patterns which are lost in the fossil.

salvador-lobatus-gigas-2This is the apertural view of the same modern shell. With time it would have grown a much thicker apertural margin to protect it from predators.

buonanni-strombus-gigas-figureThis is the earliest image known of the Queen Conch (Buonanni, 1684). For a long time the type specimen (the specimen of record defining the taxon) of Strombus gigas (the older Linnaeus name) was missing. In 1941 this figure — the figure itself — was designated a neotype (a replacement type) of the species. (First time I’ve heard of that move.) The original type specimen, though, was found in Sweden in 1953, so there is an actual shell in the collections and no need for this neotype.

bonanno-coverThat first figure of Lobatus gigas was drawn by Filippo Bonanni (1638-1723), a remarkable Italian Jesuit scholar. It is found in the book above, which is the first known guide to seashells for collectors. (Note the “SUPERIORUM PERMISSU”, meaning he published with the permission of his Jesuit superiors.) Bonanni was one of the first to suggest fossils had at least some organic origins, speculating that they were either organism remains or “products of natural powers.”

References:

Buonanni, F. 1684. Recreatio mentis, et oculi in observatione animalium testaceorum curiosis naturae inspectoribus italico sermone primum proposita. p. Philippo Bonanno . Nunc denuo ab eodem latine oblata, centum additis testaceorum iconibus, circaquae varia problemata proponuntur. Ex typographia Varesij, Romae, xvi + 270 + [10] pp., 139 pls.

Landau, B.M., Kronenberg G.C. and Herbert, G.S. 2008. A large new species of Lobatus (Gastropoda: Strombidae) from the Neogene of the Dominican Republic, with notes on the genus. The Veliger 50: 31–38.

Thompson, W.G., Curran, H.A., Wilson, M.A. and White, B. 2011. Sea-level oscillations during the Last Interglacial highstand recorded by Bahamas corals. Nature Geoscience 4: 684–687.

White, B.H., Curran, H.A. and Wilson, M.A. 2001. A sea-level lowstand (Devil’s Point Event) recorded in Bahamian reefs: comparison with other Last Interglacial climate proxies; In: Greenstein, B.J. and Carney, C., (editors), Proceedings of the 10th Symposium on the Geology of the Bahamas: Bahamian Field Station, San Salvador Island, p. 109-128.

Wilson, M.A., Curran, H.A. and White, B. 1998. Paleontological evidence of a brief global sea-level event during the last interglacial. Lethaia 31: 241-250.

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