Dive Dry with Dr. Bill

#313: You Old Fossil

No, that isn't what some lovely young woman yelled at me when I whistled at her. Besides, I don't whistle at women... I try to win them over with my mind. Yes, I know... it hasn't worked very well, has it? The "old fossil" I'm going to write about today is much older than I am... by about 525 million years! Although this species has been extinct for over 500 million years (and I'm not!), and certainly is no longer seen in our waters, it once lived in the early Paleozoic seas of the Cambrian from what is now California to British Columbia. At the time this region was known as Laurentia, although that's a name given it by modern scientists since humans wouldn't appear on the scene until 150-200,000 years ago, and they apparently evolved in Africa.

This fossil belongs to the scientific genus Helicoplacus and was a member of the helicoplacoids. This early group of echinoderms is referred to as a stem group since they are among the most primitive of the spiny skinned animals. These are the first echinoderms that left relatively intact fossils that could be carefully studied. Eventually more familiar forms like starfish (or sea stars if you prefer), brittlestars, sea cucumbers and sea urchins evolved from these primitive forms. It is believed these early ancestors were probably rather sedentary critters that suspension fed on plankton and organic material drifting to the ocean floor.

This strange group was first revealed to the scientific world in 1963 by Drs. J. Wyatt Durham of UC Berkeley and K. E. Caster from the University of Cincinnati. They described these weird critters as having round, spindle-shaped bodies with rows of calcium carbonate plates spiraling around their bodies. The genus name Helicoplacus means "spiral plates." Durham and Caster believed these loose rows of plates allowed the external skeleton or test to expand and contract. In that sense they resembled the far more evolutionarily advanced critter DrBillicus bushingianus, although that the stomach of that species generally only expands and rarely contracts.

Helicoplacoids were small bottom dwellers about two inches long. Paleontologists, the folks who study fossils, now believe they lived on the bottom in an upright position with the spindle end down. Their mouth was located about 2/3rds of the way up the body on the side. Food was captured from the surrounding waters and transferred by tube feet in the spiral groves to the mouth. In this early period of life on Earth, conditions at the ocean floor were very different. Soft sediment environments like sand or silt bottoms were not very dynamic. There were almost no organisms burrowing into the bottom or forming mound-like homes. Instead the soft substrate was covered in a film of microbes such as bacteria.

Some scientists believe that when burrowing forms evolved, they began turning the soft bottom over, creating water currents with particles in them. This change in the nature of soft bottom habitats may have caused the extinction of the helicoplacoids within just 15 million years. They were just too specialized in their morphology and feeding methods to adapt to these new conditions.

So what is this old fossil's connection with Helicoplacus? When I was an undergraduate at Harvard, I took a course in invertebrate paleontology so I could study the evolutionary origins of the marine invertebrates. I knew it would be good to better understanding how our current marine critters evolved over hundreds of millions of years. I was sorting through loose fossils stuffed in a drawer in Harvard's Museum of Comparative Zoology when I came across one fossil that clearly resembled nothing else I'd seen or heard about. I was sure I had a "find..." maybe I would even get it named after me and establish my place in biology forever.

Dr. Bernie Kummel was the class professor, and at the time he seemed somewhat "fossilized" and aloof to me. However, his assistant was a fresh young Ph.D. who often had a smiling face and was pretty receptive to student questions. I took my fossil find to this assistant, who immediately recognized it was something unique and took it to Dr. Kummel. The professor concurred, but said I couldn't name the species unless I wrote up and published the scientific description. Ugh... sounded worse than another term paper. Dr. Kummel ended up sending "my" specimen to Dr. Durham at Berkeley who described and named the species. So much for my eternal recognition in the scientific world! As it was, the several species of Helicoplacus initially described were eventually merged into one, Helicoplacus gilberti, so even if it had been named for me that name would have disappeared with barely a trace.

That young assistant professor was none other than Dr. Steven Jay Gould. Dr. Gould was known scientifically for his theory of punctuated equilibrium. It hypothesized that there were long periods of evolutionary stability broken by infrequent episodes of rapid divergence of new species. My readers may know him far better as one of the most influential and widely read authors of popular science. His works in this area include The Panda's Thumb, The Flamingo's Smile, Bully for Brontosaurus, The Mismeasure of Man and Ever Since Darwin.

You may ask why we should worry about extinctions occurring today if many species of past epochs became extinct. Yes, extinctions are a natural element in dynamically changing environments. Species usually only have a short lifespan (if you consider millions of years short) in the eco-evolutionary play. However, extinctions today are occurring at very rapid rates. It took Helicoplacus 15 million years to fade away. Many species are disappearing within decades, often tied to changes induced in ecosystems by human activity. This is why we are concerned... so many species are disappearing in such a short time. Of course there have been periods in Earth's history when global catastrophes caused large numbers of species to die off quickly. For example, it is believed the impact of a cosmic body with the Earth was responsible for the disappearance of the dinosaurs, 96% of then living marine species and about 70% of all land vertebrate species about 251 million years ago. Do we really want to be the cause of another mass extinction episode?

© 2008 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

The fossil Helicoplacus that I found in a pile of unexamined fossils at the Museum of Comparative Zoology.

This document maintained by Dr. Bill Bushing.
Material and images © 2008 Star Thrower Educational Multimedia