Here’s Lookin’ at You, Dollocaris

I’ve never been particularly interested in space. I think the fossil record is to blame. Not because paleontology takes up all the compartments in my brain for wonder or anything like that. It’s more that I don’t really care all that much about distant planets that may or may not harbor life when we have a fantastic record of strange creatures right here on Earth.

Just look at Dollocaris. I hadn’t even heard of the little Jurassic invertebrate until a few months ago, when paleontologist Jean Vannier and colleagues published a new analysis on the critter, but it immediately made me think of a little spacecraft. The small body, big eyes, and grappling appendages make the small arthropod look like one of the little repair ships you might see mending the surface of larger starcraft in the background of a big-budget scifi epic. But this was nothing alien or that we had to conjure through CGI. Dollocaris was real, and lived on our planet around 160 million years ago.

Exactly what Dollocaris was, no one really knows. The most specific paleontologists can get is somewhere in the realm of arthropods. But from there the spineless fossil has been associated with everything from mantis shrimp to remipedes – blind, worm-like crustaceans that live in the darkness of aquatic caves. If nothing else, this shows that having a complete fossil doesn’t always yield all the answers we want. The fossils of Dollocaris Vannier and coauthors present are stunning in their detail, but the little hunter is so odd that it falls into the big folder of Problematica that paleontologists regularly scratch their heads over.

Affinities aside, however, paleontologists have been able to work out a bit about this critter’s biology. For example, the eyes of Dollocaris are huge. Each bulb is about a quarter of the arthropod’s body length, with Vannier and colleagues estimating around 18,000 lenses on each of those eyes. Better still, the eyes of Dollocaris specimens found in southern France are among the best invertebrate eyes ever preserved, their detail intact down to the receptor cells. These show that Dollocaris was a highly-visual predator, Vannier and coauthors write, watching for movement to launch its spiky appendages forward and snag smaller arthropods, some of which were preserved in the gut contents of the precious fossils.

But the eyes of Dollocaris also raise a paradox. Vannier and coauthors report that its visual detection system would have been best near the surface in brighter water. Yet the Jurassic rock in which it was found has often been considered to be a darker place, primarily on the presence of creatures like vampire squid, deep-sea crinoids, and other other invertebrates found in dim waters today. The problem is that this is reconstruction by association, Vannier and colleagues point out, and perhaps these “deep sea” animals lived in shallower habitats in the past, only later rolling downslope into the abyss. Weird as Dollocaris is by itself, the invertebrate may have just made an entire window into the past a little stranger still.

Reference:

Vannier, J., Schoenemann, B., Gillot, T., Charbonnier, S., Clarkson, E. 2015. Exceptional preservation of eye structure in arthropod visual predators from the Middle Jurassic. Nature Communications. doi: 10.1038/ncomms10320