Post by Joe Botting on Feb 4, 2012 8:23:05 GMT -5
A bit of a different one today: shrimps. Well, kind of.
We've been sorting out the Tonggau Biota (Lucy's new Lagerstatte in South China), and are getting our heads around the diversity so far. It's getting quite ridiculous - there seem to be at least 20 species of dendroid graptolites, 20 species of trilobites, twenty brachiopods... and so on. And we've barely started collecting yet.
One of the big surprises was the ceratiocarid fauna. These are little shrimp-like crustaceans that are very widespread in the Early and Middle Ordovician worldwide. They're normally found in graptolitic shales, and you often get one or two species in abundance if they're there. We certainly get that at Tonggau:
ceratiocarid by joe with a camera, on Flickr
What we've been finding, though, is that there's a lot more too them than we expected. There are some 'typical' sorts of an ceratiocarid, which form dense layers and are quite widespread, and then there are others. Mostly they're only at one or two horizons, and rare even when we find them, but they're strikingly different. This one is similar (but not identical) to a well-known species called Caryocaris curvilata, and the critical thing to look at is the array of spines along the left edge:
aff. Caryocaris curvilata by joe with a camera, on Flickr
There are also others, with more impressive spines:
ceratiocarid by joe with a camera, on Flickr
That one also has spines at the right side, much smaller but also more robust, and there seems to be a pair of them. These ones with spines are probably easily described, but the ones without are trickier - especially as they're often preserved at odd angles, so you're not even sure of the outline. We think the crease along this one is actually the hingeline:
ceratiocarid indet. by joe with a camera, on Flickr
Basically, they're diverse. Without even really trying, we've got perhaps ten or twelve species. In Wales we've had a few but it's not as many as that. In the Fezouata... there are none. Not a single little carapace, despite there being bigger bivalved carapaces, and all manner of unmineralised arthropods. This is a bit of a baffling mystery at the moment, as all these faunas are from a similar age. However, the Tonngau was roughly equatorial at the time, Wales was high southern latitude, and Fezouata was virtually polar. Does the latitude dictate the diversity of bivalved crustaceans? Who knows?
Rather like sponges and dendroid graptolites, we know far too little, because so few people have been studying the group. There are abundant fossils, but few specialists, and that makes them rather appealing. It's always good to study a group where almost everything you find is new...
That might be tempting if we run out of sponges, worms, dendroids... well, you never know. ;D
We've been sorting out the Tonggau Biota (Lucy's new Lagerstatte in South China), and are getting our heads around the diversity so far. It's getting quite ridiculous - there seem to be at least 20 species of dendroid graptolites, 20 species of trilobites, twenty brachiopods... and so on. And we've barely started collecting yet.
One of the big surprises was the ceratiocarid fauna. These are little shrimp-like crustaceans that are very widespread in the Early and Middle Ordovician worldwide. They're normally found in graptolitic shales, and you often get one or two species in abundance if they're there. We certainly get that at Tonggau:
ceratiocarid by joe with a camera, on Flickr
What we've been finding, though, is that there's a lot more too them than we expected. There are some 'typical' sorts of an ceratiocarid, which form dense layers and are quite widespread, and then there are others. Mostly they're only at one or two horizons, and rare even when we find them, but they're strikingly different. This one is similar (but not identical) to a well-known species called Caryocaris curvilata, and the critical thing to look at is the array of spines along the left edge:
aff. Caryocaris curvilata by joe with a camera, on Flickr
There are also others, with more impressive spines:
ceratiocarid by joe with a camera, on Flickr
That one also has spines at the right side, much smaller but also more robust, and there seems to be a pair of them. These ones with spines are probably easily described, but the ones without are trickier - especially as they're often preserved at odd angles, so you're not even sure of the outline. We think the crease along this one is actually the hingeline:
ceratiocarid indet. by joe with a camera, on Flickr
Basically, they're diverse. Without even really trying, we've got perhaps ten or twelve species. In Wales we've had a few but it's not as many as that. In the Fezouata... there are none. Not a single little carapace, despite there being bigger bivalved carapaces, and all manner of unmineralised arthropods. This is a bit of a baffling mystery at the moment, as all these faunas are from a similar age. However, the Tonngau was roughly equatorial at the time, Wales was high southern latitude, and Fezouata was virtually polar. Does the latitude dictate the diversity of bivalved crustaceans? Who knows?
Rather like sponges and dendroid graptolites, we know far too little, because so few people have been studying the group. There are abundant fossils, but few specialists, and that makes them rather appealing. It's always good to study a group where almost everything you find is new...
That might be tempting if we run out of sponges, worms, dendroids... well, you never know. ;D
