I visited the Field Museum of Natural History in Chicago with my father back in 1969. We especially enjoyed the paleontology dioramas - I being a newly-declared geology major. As we strolled past millions of years of history from about 500 to 400 million years ago (no land animals appearing for a long time yet) the animals that most struck our fancy were the Nautiloids. My dad described them as "ice-cream cone creatures". They were the top predator of the day and reached lengths of 13 feet or more.
These phenomenally successful creatures are represented today by the Nautilus, which as we know is tightly coiled, (as well as more distantly related squid and octopus.) Starting some 400 million years ago, relatives of the nautiloids appeared called ammonoids - these were also coiled.
Both the straight and the coiled animals start out very small. As they grow, they construct a larger shell section, walling off and abandoning the old one (except for a very nifty little tube that allowed them to adjust their buoyancy by adding or removing gas from the empty chambers.) Oliver Wendell Holmes described this in The Chambered Nautilus:
Year after year beheld the silent toil
That spread his lustrous coil:
Still, as the spiral grew,
He left the past year's dwelling for the new,
Built up its idle door,
Stretched in his last-found home, and knew the old no more.
As the ammonoids evolved, they began to make more and more complicated boundaries between the old and new chambers - we call these sutures. The complexity of the sutures is used by paleontologists to determine the age of the fossil. The photos below show simple and extremely intricate suture patterns. For those of you inclined toward math, the complex ones are fractal.
We as humans are short-lived creatures and tend to ignore the vastness and wonder of earth's history-book. These beautiful fossils open my mind to unimaginably ancient chapters.
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