Wednesday, 5 May 2010

Today's Critter: Bomakellia

Today I spent most of my time looking at Cretaceous rocks, so it would not be surprising if I said this critter was Cretaceous. It wasn't. Not even close. Bomakellia kelleri is another fascinating fossil of the Ediacaran fauna, dated to 555 million years old. It is known only from this 9cm long specimen:
It was originally classified as a potential arthropod, possibly even a primitive trilobite or anomalocarid. If it had arthropod affinities then it was certainly primitive. The possible semicircular cephalon and tri-lobed appearance may link it to trilobites, though it does not have segmented limbs or antennae (which may be due to its primitive nature or due to preservation as these parts often do not fossilise in trilobites). Trilobites also have gills on the body, which Bomakellia may be sporting, though this has been a possible connection with the anomalocarids. Below is a reconstruction which fits with the arthropod interpretation:
More recently, as with many of the Ediacaran fauna, it has been interpreted as a possible rangeomorph. The most famous rangeomorph is perhaps Charnia. Rangeomorphs have a frond like structure and were possibly colonial animals, attaching themselves to the sea floor by a hold-fast (interpreted as the head when classed as a proto-arthropod). Spriggina is another Ediacaran organism which has been seen as both a possible arthropod with trilobite affinities and a rangeomorph. Below is Bomakellia reconstructed as a rangeomorph:

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