When Sea Urchins ATTACK!!! Crinoid EVASION=Crinoid EVOLUTION!!

(image courtesy of T. Baumiller)

Ya' know what I love about today's post? When ya' got two great things that go great together!!!

Deep Sea Biology and Paleobiology!!!

This article is based on this brand spanking NEW paper by Tomasz Baumiller along with his colleagues in the new Proceedings of the National Academy of Science. Go here for the citation.

and has already gotten some play in Astrobiology Magazine....
You may recall, early in the Echinoblog, I wrote about the predation on stalked crinoids (above) by cidaroid sea urchins. (Click to see!)

To recap, both cidaroids and stalked crinoids are "living fossils", a term used to describe living animals that closely resemble (or are related to) critters that we are accustomed to seeing only as FOSSILS.

This makes them good analogs for inferring past ecological interpretations.

(Calocidaris image courtesy-D. Pawson, NMNH)

A few years ago Tomasz Baumiller and his colleagues, found that these sea urchins actually ATE stalked crinoids!!

This was surprising! Urchins as carnivores???? We generally think of sea urchins as algae-grazing, poop-producing, spiny balls. Sort of like the cows of the sea.

So, they pursued the matter!! Seeking out evidence from all corners of the EARTH that these Urchins were not cows, but the marine equivalent of ravenous, bloodthirsty BEASTS! And that evidence was FOUND!

1. Living Evidence. The authors looked at the shallow-water tropical urchin Eucidaris which was examined live in aquaria alongside the shallo-water crinoid Lamprometra palmata (along with some deep-sea crinoid bits as a further test of whether they would be appealing!)

Do the urchins go for it??

(image courtesy of T. Baumiller)

They DO indeed go for it!! Now, Eucidaris doesn't exclusively go after crinoids-but it DOES indeed like eating them up!!!

The picture above shows part of a crinoid (the small white bit) being devoured by the cidaroid urchin Eucidaris.

You can click here to see the movie at the PNAS website of this beast feeding!

Here's some pix!! Here's what's called a brachial-essentially one of the arms off the "chewed on" crinoid. (see here to see where a brachial goes)

(image courtesy of T. Baumiller)

..and a close up of the cidaroid POOP! An arm segment that's been digested and passed!

(image courtesy of T. Baumiller)

See the notches on that bottom segment?? Those are made by the JAWS on the urchin!

They leave a mark. This is important....

2. FOSSIL Evidence!!
The authors wanted to see how far into the history of these animals this relationship may have lasted.

(image courtesy of T. Baumiller)

How could they tell? They looked for the NOTCH (from above).

They looked through 2,500 fragments of fossil crinoid stalks from five Triassic (Mesozoic) sites in Poland. More then 500 of these pieces (about 20% of the total) had these scratches and notches!!

(image courtesy of T. Baumiller)

Its entirely possible these marks could be explained through other reasons. Scavengers or perhaps environmental factors that erode or deform the remains?

But they argue that these fossil deposits were buried quickly-suggesting that the marks were made when they were alive as opposed to scavengers.

They also found that cidaroid spines and test fragments were present around damaged crinoid body parts at these Triassic fossil sites.

So, Yeah. They ATE them.

3. So, WHY IS THIS IMPORTANT???

So both crinoids and sea urchins (as well as most other marine animals) undergo a massive extinction event at the end of the Paleozoic.

The great end-Permian event (click here to get more info) resulted in near-extinction of most Paleozoic crinoids and sea urchins.

(this image from the Earth Through Time website)

But this was followed by a BIG rebound. In otherwords, they survived and RE-DIVERSIFIED.

Many of the older taxa went away-and this was followed by new body forms, which exploited those which had gone extinct. This "re-set" of animal diversity is called the Mesozoic Marine Revolution.

So what happens to the cidaroid urchins? They started getting STRONGER and more effective jaws.
And Crinoids?? CRINOIDS BECOME MORE MOBILE!!!

Some got into FLOATING....(see here for more on this-not everyone agrees on interpretation of these)

(this image modified from Seilacher & Hauff, 2004)

how to CRAWL....

Some lost the stalk and learned how to SWIM....


Based on this, the authors suggest that there was a sort of "escalation of arms". Armament went "up" in the predator and so Defense correspondingly rises in they prey. A sort of Mesozoic Arms Race is at play.... One driving the other.

Thus, the GREATER mobility seen in crinoids was A REACTION TO THEIR PREDATORS...Namely...cidaroid sea urchins!!!

You get a bigger jaw? We're gonna swim away! Get armor! Whatever it takes.

Thus, this relatively straightforward predator/prey relationship has conceivably driven the evolution of this group for hundreds of millions of years.

Wow. Tasty.