Complexity Puzzle, Revealed

I had so many creative guesses for the complexity puzzle posted the other day, that I decided to pull them altogether into one mosaic:

So... who was right?

I tried to include every answer, adding a few of my own "guesses" as well, to show more similar forms. Thanks to everyone who added their input. Both Chris and kimball had the correct answer, kimball being slightly more specific. The pattern (shown second from the upper left in the mosaic) was taken from a baculite fossil, showing the suture lines, and a fraction of shell. The baculites were a straight-shelled cousin to the ammonites, both displaying these complex patterns.

The sutures are found where the septum (the wall separating the inner chambers) met the shell. In the picture on the right, you can see a fossil of a single chamber from a rather large baculite. The complex suture patterns follow along the edge, where the shell coated the animal, but disappear into smoothness near the center.

Here's the fossil I took the pattern from, shown front and back:

When I first got this specimen at a mineral auction, it was unlabeled in a cardboard box with a variety of other fossils. As a result, I have no idea where it came from, or what species it might be. It isn't a very spectacular specimen, but I like it--it shows quite a bit of baculite anatomy. Not only can you see the suture lines, but some of the nacre shell remains, with an iridescent shine. On the "top" of the fossil (shown on the right, above) you can see the siphuncle, a small tube through which air and water passed in order to control buoyancy.

In living species of nautili and their extinct relatives, suture lines are, at most, wavy. The suture patterns found in ammonite and baculite fossils, on the other hand, are quite complex. They exhibit a sort of fractal geometry, similar to the Koch Curve, a repeating fractal pattern that resembles a snowflake. (See image, above.) Were they simply flowery ornamentation for the mollusk? Or did they offer some evolutionary advantage? Recent research shows that the complexity of the sutures may have increased the ammonoid's ability to withstand hydrostatic pressure. The patterns are also quite useful to paleontologists, allowing them to identify specific species of ammonoids. (The patterns are complex enough that, these days, some geoscientists are using GIS mapping software to chart the lines.)

These patterns aren't just visually useful and appealing, however. In the geophysics department at the University of Utah, students have experienced the patterns in a different fashion--creating audio representations of nautiloid suture lines:

Students were asked to try to recognize the various genera of ammonoids that were provided in lab by listening to their sonified sutures. Also, they experimented with the theremin in an attempt to sonify the sutures of the three principle kinds of ammonoids (goniatites, ceratites and ammonites). First, computer-generated suture lines of a dozen common genera of shelled cephalopods were played for the class on an audio CD player, so that the students could hear what a sonified suture might sound like. By simply listening, everyone in the class was able to distinguish between the general categories of goniatitic, ceratitic and ammonitic suture patterns with 100 per cent accuracy. Further, they were able to identify the particular genera of ammonoids with an accuracy of about two out of three.

The biggest drawback of examining a fossil is that it doesn't quite look like the animal once did. For an extinct creature like a baculite, picturing the animal is part science, part guesswork. I came up with my own drawing of a "living" baculite, but rather than focus on specific details, I went for a cartoonish style. (I based the drawing off of two fossils that couldn't possibly have existed at the same place or time, so I used a fair bit of creative license.) I do like to imagine the shell of the baculite shining with an iridescent glow, compared to the dark, dull shell of the trilobite. Also, I like to fancy that the baculites were an intelligent species, perhaps sentient enough to consider keeping a pet... or not:

Pet or Lunch? Pencil drawing, colored in photoshop (KLF 11/22/2006)

Image credits: Suture lines diagram by Kevin Bylund via Tonmo.com. Answer mosaic images: Oysters shells by bibliona via flickr; Baculite sutures by author; Violet branched coral fungus (Clavaria amethystina) by DSutherland via flickr; Satellite photo of Atcama Desert in Chilie via the European Space Agency; White branching coral by emblatame via flickr; Petticoat from Renoir painting Dance at Bougival via the Gallery of Art; Back of a weasel (Mustela franata) via Rachael Pettry, Pensacola Junior College; Lichen by JavaJane; Budding leaf by tanakawho via flickr; Snowflake on a leaf by csavules via flickr; dusty miller by Lynnmar via flickr; ice on chain by Happy.Phantom via flickr. All other images created by the author.