ETA: OK, technically it should be “suspension-feeding”, because there’s a good chance that its feeding mechanics involved more than simple filtering (see comments). I hate retconning, so I’ll leave the post as it is aside from this addendum. Thanks for the heads-up, Dave Bapst 🙂
This is when I put everything resembling work aside to squee madly over a fossil.
(Imagine me grinning like crazy and probably bouncing up and down a bit in my seat)
Tamisiocaris is a newly “updated” beast from the Cambrian, and the coolest thing I’ve seen since that helicoplacoid on a stalk (most cool things come from the Cambrian, right?). It is the Cambrian equivalent of a baleen whale.
Anomalocaridids were close relatives of arthropods and are among the most iconic creatures of the Cambrian. Most anomalocaridids we know of were large, swimming predators with large head appendages bearing sturdy spines to grab prey and bring it to that trilobite-crunching pineapple slice mouth. Going with the whale analogy, they were more like the killer whales of their time (although they would be easy snacks for an actual killer whale). In fact, when the putative head appendage of Tamisiocaris was originally described by Daley and Peel (2010), the only odd thing they noted about it was that it was not hardened or obviously segmented the way those of Anomalocaris were.*
Tamisiocaris was already cool back then, because it was the first animal of its kind found at Sirius Passet in Northern Greenland, one of the lesser known treasure troves of fabulous Cambrian fossils. However, since then, more appendages have been found, and it turns out that those long spines had been hiding a fascinating secret.
They were… kind of hairy.
Closer examination of the appendages shows that their long, slender spines bore closely spaced bristles, making each spine look like a fine comb (whole appendage and close-up of a spine above from Vinther et al. ). With all the spines next to each other, the bristles would have formed a fine mesh suitable for catching prey smaller than a millimetre. Compared with modern filter-feeding animals, Tamisiocaris fits right in – it would have “fished” in a similar size range as a greater flamingo. Vinther et al. (2014) suggest that Tamisiocaris would have brought its appendages to its mouth (which isn’t among the known fossils) one at a time to suck all the yummies off.
These guys are tremendously interesting for more than one reason, as the new study points out. First, HOLY SHIT FILTER FEEDING ANOMALOCARIDIDS! (Sorry. I’m kind of excited about this.) Second, the mere existence of large** filter feeders implies a richness of plankton people hadn’t thought existed at the time. Third, there is some remarkable convergent evolution going on here.
Often, really big plankton eaters evolve from really big predators – see baleen whales, basking sharks, and these humongous fish for example. It’s not an already filter-feeding animal growing bigger and bigger, it’s an already big animal taking up filter-feeding. The interrelationships of anomalocaridids suggest the same story played out among them – ferocious hunters begetting “gentle giants” in a group with a totally different body plan from big vertebrates. For all the dazzling variety evolution can produce, sometimes, it really rhymes.
And finally, Vinther et al. did something really cool that tickles my geeky side in a most pleasant way. In their phylogenetic analysis that they did to find out where in anomalocaridid evolution this plankton-eating habit came along, they found that Tamisiocaris was closely related to another anomalocaridid with (on a second look) not dissimilar appendages. They named the group formed by the two the cetiocarids – after an imaginary filter-feeding anomalocaridid created by artist John Meszaros for the awesome All Your Yesterdays project.
Man. That’s definitely worth some squee.
*Disclaimer: I’m basing this on the abstract only, since palaeontological journals are one of the unfortunate holes in my university library’s otherwise extensive subscriptions.
**For Cambrian values of “large” – based on the size of the appendages, this creature would have been something like two feet long.
Daley AC & Peel JS (2010) A possible anomalocaridid from the Cambrian Sirius Passet Lagerstätte, North Greenland. Journal of Palaeontology 84:352-355
Vinther J et al. (2014) A suspension-feeding anomalocarid from the Early Cambrian. Nature 507:496-499