Post by Joe Botting on Apr 22, 2011 23:29:05 GMT -5
Hi All,
I've been away on fieldwork in Anhui Province, working on an Early Cambrian sponge fauna. It was an extremely fruitful few days (a lot of new species, and interesting ones at that), but I thought I'd share a bit about what is (allegedly) one of the most common Cambrian sponges: Protospongia.
Protospongia? sp. by joe with a camera, on Flickr
It was originally described from South Wales by Salter in 1864, based on fragments of a large, probably bowl-shaped sponge with a regular square grid made of cross-shaped spicules. The spaces between the largest spicules were subdivided by smaller ones, and still smaller ones, and so on, and the entire sponge was probably over a metre across, but the wall only a millimetre thick. So far, no-one has excavataed a complete one - they may have found them, but getting them out of the rock intact is probably almost impossible!
The problem is, with a name like "Protospongia" it's inevitable it will get used too widely. (Someone finds a primitive sponge? It's got a square-ish grid? Got to be Protospongia!) As a result, there are loads and loads of alleged species from the Precambrian to the Silurian that have been put into it. It's a perfect case of a "dustbin genus".
If you look for genuine Protospongia among the records, you find something remarkable - it's very limited. It's really known for certain only from South Wales, Ireland, and the US/Canada - all from the Middle Cambrian. There are some possible examples from Argentina and China of a similar age (the Chinese ones slightly older), but most of the records are of things that should be other genera. So we're left with a genus that appeared in the late Early or early Middle Cambrian, was common around the Iapetus Ocean (the ocean that used to be equivalent to the North Atlantic, but in a slightly different place, so Scotland was part of North America) and may have made it further afield... and then died out. There are no definite records I have found from after the Middle Cambrian.
What this tells us I'm not quite sure. For one thing, though, the view that early sponges just appeared and didn't change much is clearly wrong - they had complex and dynamic distribution patterns that we don't at this stage understand. But perhaps the most important lesson is the importance of good taxonomy...
I've been away on fieldwork in Anhui Province, working on an Early Cambrian sponge fauna. It was an extremely fruitful few days (a lot of new species, and interesting ones at that), but I thought I'd share a bit about what is (allegedly) one of the most common Cambrian sponges: Protospongia.
Protospongia? sp. by joe with a camera, on Flickr
It was originally described from South Wales by Salter in 1864, based on fragments of a large, probably bowl-shaped sponge with a regular square grid made of cross-shaped spicules. The spaces between the largest spicules were subdivided by smaller ones, and still smaller ones, and so on, and the entire sponge was probably over a metre across, but the wall only a millimetre thick. So far, no-one has excavataed a complete one - they may have found them, but getting them out of the rock intact is probably almost impossible!
The problem is, with a name like "Protospongia" it's inevitable it will get used too widely. (Someone finds a primitive sponge? It's got a square-ish grid? Got to be Protospongia!) As a result, there are loads and loads of alleged species from the Precambrian to the Silurian that have been put into it. It's a perfect case of a "dustbin genus".
If you look for genuine Protospongia among the records, you find something remarkable - it's very limited. It's really known for certain only from South Wales, Ireland, and the US/Canada - all from the Middle Cambrian. There are some possible examples from Argentina and China of a similar age (the Chinese ones slightly older), but most of the records are of things that should be other genera. So we're left with a genus that appeared in the late Early or early Middle Cambrian, was common around the Iapetus Ocean (the ocean that used to be equivalent to the North Atlantic, but in a slightly different place, so Scotland was part of North America) and may have made it further afield... and then died out. There are no definite records I have found from after the Middle Cambrian.
What this tells us I'm not quite sure. For one thing, though, the view that early sponges just appeared and didn't change much is clearly wrong - they had complex and dynamic distribution patterns that we don't at this stage understand. But perhaps the most important lesson is the importance of good taxonomy...
