Part praying mantis, part flatworm, part geminating snuffleupagus: Model of Anomalocaris from the Natural History Museum, London. Creative Commons Gaetan Lee.

On the list of hallucinatory animals, the Cambrian creation known as Anomalocaris has held a particular grasp on natural history buffs’ imagination. Its name (essentially “weirdo shrimp”), its fascinating path to discovery, and its use as a Cambrian fall guy in Burgess Shale recreations have all contributed to this. Natural history documentaries, in particular, have tended to portray this thing patrolling the Cambrian oceans and harassing helpless trilobites with the cool assurance of a Great White Shark. In my copy of “Prehistoric Life: The Definitive Visual History of Life on Earth” published by DK just last year (and highly recommended), the caption of the beautiful full-color page describing Anomalocaris declares “3 ft 3 in The length of the largest Anolmalocaris specimens. Its size and formidable mouthparts made it a top predator of the Cambrian seas.”

Before I come to the current study, it’s worth knowing something about the history of this thing. In the world of Cambrian paleontology, Anomalocaris is a superstar. Life’s first big multicellular experiment (that we know about) — the Ediacaran — was mostly about soft-bodied life. Its second great multicellular experiment is the one that gave rise to most of the major groups we recognize today. This was the community of organisms famously discovered in the Canadian Burgess Shale, and it is the one in which Anomalocaris was found. The only problem was that when scientists first found it, they thought they had three separate living things — a real life enactment of the story of the blind men and the elephant.

First found was a shrimp’s tail — but only the tail. It was this that was named Anomalocaris.

A proboscis of Anomalocaris. On first glance, they thought it was a weird shrimp because its little "appendages" were not jointed, unlike modern shrimp. As it turns out, it was a weirdo shrimp because it wasn't a shrimp.

Next found was a pineapple ring — or what looked like a pineapple ring. Captain Morgan notwithstanding, scientists interpreted this as a squashed jellyfish and named it Peytoia. Finally, scientists found a fossil they judged to be a sponge, and named it Laggania. The pineapple ring was attached, but was interpreted as a jelly fish that had just happened to settle on top of the sponge and got squashed into place. Finally, the scientist Harry Whittington at last found a fossil in which the shrimp hinder was attached to the pineapple ring. No, really? What the heck was this thing? A few years later, they put it all together: the sponge was the body, the pineapple ring the mouth, and the cocktail shrimp was one of a pair of probosci of this titanically large (for the Cambrian) animal. Anomalocaris, they called it, since earliest taxonomic names have precedence, and judged it to be the terror of the Burgess Shale fauna.

For the Cambrian, this thing was big. At about one meter (three feet) it dwarfed the other species we typically find in the ecosystem. But it turns out that titanism may have been the size enhancement that comes with being a whale shark, not a white shark. Scientists at the Denver Museum of Nature and Science conducted computer studies of Anomalocaris‘s bizarre mouthparts and found that it was extremely unlikely it was capable of crushing much more than a gummy bear, much less an armor-plated trilobite. Supporting their study, they examined some 400 fossil Anomalocaris mouthparts — and found nary a chip or scratch. Considering how soft our fingernails are and how frequently they get chipped or scratched, I’m afraid it appears Anomalocaris must have been chowing down on something either very soft or tiny indeed. Soft worms, they suggest — or plankton.

So the vicious predator may have been a gentle, harmless (unless you happen to be a plankter) filter feeder. At least — that’s the tale now! With as many twists and turns as this story has taken, I wouldn’t be surprised if another surprise lies in wait. For instance . . . scientists have actually found and identified fecal pellets of this thing. That’s one study I, for one, will be glad not to have to do . . .

This is a little animal called a water bear, or tardigrade. On the mosses, lichens, forest litter, ponds, beaches, snowbanks (and even hot springs) of the world, this little guy plods along, oblivious to the larger world. At just 100 micrometers (.1 mm) to 1.5 mm long, they are cute on paws. Did you notice the little fingers?

Hug me! The caterpillar from Alice in Wonderland meets Heimlich from A Bug's Life? Creative Commons Rpgch

Discovered in the 18th century, these little guys were named water bears for their trundling, bear-like gait — that is, if can you imagine a bear with *four* pairs of legs and a penchant for shriveling up in winter rather than curling up in a cave. Tardigrade, in fact, just means “slow walker”.

Water bears exist at a strange junction between the world of the large and the world of the small. They are multicellular organisms with intestines, brains, eyes, fingers, and a chitinous cuticle that they shed, but in many ways they behave like protists, which are also microorganisms but not animals at all. Some tardigrades don’t defecate until they moult. Others don’t mate until that happens. The fertilized eggs stay behind in the moulted skin and incubate there, or sometimes adhere to a nearby surface. They are also eutelic (you-tell-ik), which just means that every water bear grows exactly the same number of cells, and once that number is reached, they can grow larger only by growing those cells. This isn’t uncommon for microbial life. Their mouths are armed with stylets with which they pierce and suck the delicious contents of plant cells, algae, and small invertebrates.

Creative Commons Rpgch

As for their bizarre survivalism streak, withstanding the vacuum and scorching solar radiation of space seems to be a byproduct of their ability to survive dry spells (they can go for a decade without water), just as it is for the bdelloid rotifers, whom I’ve also covered here. They can reversibly enter a state of suspended animation called cryptobiosis, in which their metabolism screeches to a halt and their water content plunges to a hundredth of normal. This helps protect their DNA, and a sugar called trehalose helps protect their membranes. For further information, see here. In 1997, they were launched into low-earth orbit and survived the vacuum of space for 10 days. Yes, Tardigrades . . . in . . . Space! Several went on to lay and hatch eggs normally. Interestingly, there is even a sci-fi sounding word for their state of suspended animation: when so ensconced, they are called a “tun”.

Taxonomically, water bears are most closely related to arthropods, or all the crustaceans and insects of the world, and onychophorans, the velvet worms. Biologists would say they are one of the bilaterian crown groups, or one of the earliest lineages to split into their own group after animals developed mirror-image symmetry. Other early-diverging animals either had no symmetry (sponges) or were radially symmetrical (jellyfish et al.) You can check out their neighborhood of the life family tree here (look for tardigrada). You may notice they’re also in a group called “ecdysozoa”, which is just a code word for “all the organisms that moult exoskeletons”, which actually does seem to be a true, historical, one-time evolutionary inovation (i.e., synapomorphy in bio-speak), and thus make it a taxonomically valid group.

Final cool factoid: few tardigrades have fossilized, but of those that have, one was named Beorn leggi, which will be delightful to those of you who have read The Hobbit. And in case you were wondering if someone actually had the chutzpah to do it, yes, yes someone did. It was screaming to be done. Behold the plush tardigrade.