Sunday, May 12, 2013

Opabinia and Tullimonstrum

A silly little doodle of Opabinia (on the left) and Tullimonstrum (on the right).

Opabinia is known from the 505-million-year-old Burgess Shale fossil beds in Canada, one of the oldest sites with well-preserved imprints of soft body parts. It has some bizarre anatomy — most notably five eyes and a trunk-like proboscis — and its exact evolutionary relationships are still debated. It’s most likely closely related to the ancestors of arthropods, and one study has suggested that its closest living relatives might even betardigrades.

Tullimonstrum, meanwhile, comes from the 300-million-year-old Mazon Creek fossil beds in Illinois, USA. It’s found quite commonly there, to the point that it’s the official state fossil — and yet nobody knows just what type of animal it is! The overall rarity of soft-bodied creatures in the fossil record makes it impossible to tell what it might be related to. And while its proboscis does have a surprising similarity to that of Opabinia, that’s probably more due to convergent evolution than any actual relation.

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