These fossil echinoderms are not ONLY freakishly BIG, BUT to add a little "weird" to it...THEY FLOAT!!! (most echinoderms almost always live on the sea bottom)
So, that you can see how different these critters are relative to the "normal" ones... some introductory crinoid background.
Here is what the most commonly encountered "feather star" aka an "unstalked crinoid" looks like...
...and here's some basic anatomy and etc. about the other body form of crinoids with a stalk. These "stalked" crinoids are the ancestral forms and are what you see in the fossil record.
Most of them live on the sea bottom. Sometimes attached and sometimes with a long tail. Go HERE to an older blog I wrote, which has a little bit about their ecology.
What I'm about to say may turn what you know...UPSIDE DOWN!!!
It turns out FOSSIL crinoids from the Jurassic (about 145-200 Mya) and the Devonian (360-416 Mya) did something that NO modern crinoids are known to do!! They were PELAGIC.
in other words...THEY COULD "SWIM". (well..some only float) :-)
Much of the info for this section is from this paper by Seilacher & Hauff 2004.
Basically, there were FOUR kinds of floating crinoids. Here is a handy guide from Seilacher & Hauff (Fig. 1) with the water current flow (added in blue) for emphasis.
Crinoids are all filter feeders.
So, those big cups with all of the arms on them??
They hold them into the water current and food as the water passes through them. The crinoids that float do essentially the same thing but sit in the middle or the top of the water column instead of the bottom.
Here's the different kinds of floating aka pelagic crinoids.
1. "Floaty" crinoids that float on driftwood.
These are the best known planktonic crinoid and occur in the Jurassic (145-200 mya) rocks of Germany but have also been collected from China.
They are often preserved attached to driftwood. The stalks were thought to be kind of elastic and used as sort of a filter-feeding "drag net" as they floated through the water..
The fossil deposits of these animals are often excellently preserved.
The other really obvious thing about these floating crinoids is that they are HUGE!! They are probably the LARGEST crinoids known!!
IN FACT, they are probably the largest (or at least the longest) ECHINODERMS that the world has ever seen!
See the slab above? There must be at least 50 individual animals (counting the filter feeding cups) on this floating log.
How big are they?? The stalks on these crinoids can approach TWENTY METERS (60 FEET!). The filter feeding cups get to be easily a METER (about 3 feet) in diameter. Here's ME next to a single fossil of Seilocrinus in the museum for scale. Its not as big as some..but STILL....its LARGE.
2. Crinoids with BUOYANT floats!
These are interpreted as actually having a FLOAT!!!
They are positively BUOYANT. Similar to the ones above, these were thought to drag their feeding arms, sort of like a tow-net, filtering food from the water.
These were called Scyphocrinites and they were from the Lower Devonian. The big "floats" of these animals are actually fossils called loboliths. They're filled with big porous, presumably air or gas filled calcium carbonate balls. Wow.
3. Stemless floaty crinoids!
These are unusual STEMLESS crinoids..but they aren't comatulid crinoids (i.e., not the same as the ones around today)
Genus name is Saccocoma and these fossils are found from the Upper Jurassic Solnhofen limestone in Germany. Its thought by some that these were free-swimming..possibly floating in the water column.
4. Floating Bottom "dredge" crinoids!
This is one is just crazy (or at least the interpretation is!).
This one is called Uintacrinus from the Upper Cretaceous and its thought that these had a gas or air-filled cup and that they DRAGGED their arms along the bottom.
Functionally, this makes for one of the strangest terms I've ever heard.."Hemipelagic dredger".
A swimming bottom, deposit feeder. The arms DRAG along the bottom like a frakkin' DREDGE net!!!
Do ya' see that big mess behind my head?? That's because my mind is BLOWN!
(Thanks to Mary Sangrey and the IZ Paleontology department for assistance with photography and specimens!)