So, assuming you're not a cleverclogs who already knows what Anomalocaris is. When you saw the title did you expect it to refer to the jigsaw from the workbench, or the puzzle in the box on top of the wardrobe? The one from the wardrobe is most relevant, but the idea of expectations met or unmet is an essential part of the story here. As, of course, is Anomalocaris: one particular jigsaw from a whole set made somewhere around 500 million years ago. A jigsaw that took some very fine minds over one hundred years to solve.

The Jigsaw Pieces

Moving more speedily on to look at the jigsaw pieces: these are cool jigsaws, very minimalist chic. Each piece is made from a black slab of rock from the ancient¹ seabed shales on Mount Stephen in the Canadian Rockies. The images on the black rock, imprints from Earth's earliest animals, appear in a shiny film when the light catches them at certain angles.

In the Anomalocaris jigsaw box there are four pieces:

• Anomalocaris the Odd Prawn

  Piece one shows an imprint a bit like what anyone unfamiliar with the actual make up of a shrimp would think of as its tail. It's an arc of segments, 8.5cm across. The segments are wider at one end of the arc, taper to a point at the other end and have small spikes on the inner side. The first person whose thoughts on this piece are recorded is a JF Whiteaves, who in 1892 thought it to be the abdomen (the bit that looks like a tail in a lobster or a prawn) of a crustacean. He named it 'Anomalocaris', the strange shrimp, which suggests at least some uncertainty on his part.

• Peytoia the Jellyfish-Like-No-Other-Jellyfish

  Piece two shows a complete ring of segments, around 6 to 7cm in diameter. It looks like four quarter-circle arches, each with a keystone, joined together to form a flattened ring around a hollow centre, with sharp teeth added to the inner edge of each keystone. This one was first named by a Charles Walcott in 1911. He thought it to be a jellyfish of some sort and called it Peytoia. It didn't look like any known jellyfish, but jellyfish are common today and there was an expectation that they would be found among these pieces of shale from the floor of a long-gone ocean. None had so far been identified.

• Laggania the Possible Sea Cucumber

  Piece three has an imprint of an elongated, vaguely oval, mass about 25cm long with a line of overlapped lobes on each side. It's a poor imprint and it's understandable that it was at first supposed to be an indistinct animal such as sea cucumber by its first finder, Charles Walcott again, in the early 1900s.

• Tuzoia the Red Herring

  Piece four was found in 1928 and was described as the head of Anomalocaris, the Odd Prawn. As events transpired, see below, this piece turned out not to belong in the Anomalocaris jigsaw box at all and should have been discarded. It had stood to reason that there must be a head to go with the tail, so when a piece was found showing a head-like shape at the head end of the shrimp the obvious connections were made. It was in fact the carapace of Tuzoia the Crustacean, and neither prawn nor herring.

Reviewing the Pieces – the Centipedish Arthropod and the Amorphous Sponge

Pieces from the shales were studied by waves of Professors over the next decades. Walcott, the first to extensively examine the shales in situ, had shipped bits of the puzzle to museums all round the world. The slabs contained the prints of many more creatures than the ones in the Anomalocaris jigsaw box. The thing about these shales was that the life trapped in their forming sediments was covered so quickly and so closely that the soft tissues of animals from hundreds of millennia ago, from the time when animal life began to develop beyond its earlier simple forms², were preserved. Flattened but preserved. New techniques meant better analysis; new discoveries were made and pieces were reallocated to different boxes.

In the 1970s and 80s in the Sedgwick Museum in Cambridge, Professor Harry Whittington, taken with the oddity of the animals, set his students to work poring over boxes of pieces to re-examine them. Two of them came up with re-interpretations of the pieces in the Anomalocaris box. In 1978 Simon Conway Morris took another look at piece three and suggested Laggania change from Possible Sea Cucumber to Amorphous Sponge. In 1979 Derek Briggs put forward that rather than being a crustacean abdomen, Anomalocaris was in fact a limb of a large Arthropod: one that might look quite like a big centipede. The review continued.

Finding the Picture on the Top of the Box

In 1981 Whittington and Briggs took a look at one of Walcott's slabs, previously taken to be an imprint of Peytoia lying over Laggania. On close examination they not only discovered that the two pieces actually fitted together as part of one creature but, when they delved further, piece one, Anomalocaris, was found to be there too and to be part of the same animal. The new creature retained the name Anomalocaris. Far from being a relatively uninteresting collection of an odd prawn or centipede, an unusual jellyfish and a possible sea cucumber or strange sponge, it was in fact a gloriously ridiculous looking, never-seen-before, 60cm long predator of the Cambrian seas: the largest such known to date. The Odd Prawn's segmented arc was one of a pair of clawed arms with which it could grasp its prey to shove it into the teethed ring of its mouth, formerly known as Peytoia the Jellyfish. It had eyes on stalks and its long, 'sea cucumber' body, formerly known as Laggania, was lined down either side with winged lobes for swimming and it looked like nothing living in today's world.

Which may be why it took 100 years to see it for what it was. Assuming, that is, that the paleontologist interpreters have got it right now. There were other equally, or even more fantastically shaped creatures found in the Ogygopsis and Burgess Shales on Mount Stephen. Like Hallucigenia, named, you might think, in despair at ever being able to make head or tail of it. The current interpretation is that it's a seabed scavenger, and it does have a slight look of the hyena about it. Albeit a hyena with seven paired spines along its back and a series of flagellating limbs for legs. Until recently, it was not quite certain which way up the creature stood and there's still no certainty which end is head and which is tail.

Initially, the scientists (paleontologists Whiteaves, Walcott, Whittington, Conway Morris, Briggs and colleagues) interpreted what they saw according to their expectations, past understanding and what they were familiar with in today's oceans. Understanding life in the Cambrian seas took and takes knowledge, imagination and an openness to new ideas, new creatures, new interpretations and to less certainty: like all life, really. Nobody, not scientists nor poets, Presidents or Popes, not even mother-in-laws, should be certain they've got the pieces of the jigsaw right, or that they're seeing the whole picture, or that there aren't presently inconceivable truths out there.

More Findings for the Interested

In the 1990s more work on the Burgess Shale fossils and new examples found in the Chengjiang shales and the Emu Bay Shale in Australia have led to the identification of several species of Anomalocaris and possible relatives. They have a variety of claw/eating-appendages which suggest some may simply have swept plankton into the mouth while others were capable of preying on Trilobites. Their tails vary too, from long and thin to fan-shaped, and a variation from Chengjiang shows a line of legs below the lobes. There are some beautiful pictures of them, and more information, on The Anomalocaris Homepage.

For those who want some scientific detail, Anomalocaris now belongs to the group of Anomalocarids in which three genera: Anomalocaris, Laggania³, and Amplectobelua, have been identified. They are usually regarded as belonging to the Arthropod group, although arguments have been made in the past that they belong in their own phylum, Dinocarida.