Thursday, March 12, 2009

Taphonomy -- It's Difficult to Survive the End

. . . the report of my death was an exaggeration.

~Mark Twain, note written May 31, 1897
[for the story behind this quip see Lighting Out for the Territory by Shelley Fisher Fishkin (1998)]

On Wednesday, March 11, 2009, the House of Representatives failed to pass S. 22, the Omnibus Public Land Management Act of 2009, under suspension of the rules (requiring a 2/3rds vote in favor). This is disappointing because I favor the Paleontological Resources Preservation provisions that are a very small part of this complex, massive bill. (Background on the Paleontological Resources Preservation provisions can be found in previous posts in this blog, and recent action on the legislation is described in the column on the right.)

This legislative comment is not really what I intended to start this post with, but it will certainly do as a segue. Some folks who have engaged in debate over provisions appear to consider them dead as a result of this vote. Wait, I say, “The report of its death is an exaggeration" (slightly misquoting Twain, but not nearly as greatly as others have). There were 282 members of the House who voted in favor of the omnibus bill, much more than enough to pass the whole bill under normal procedures. So, I anticipate that these provisions will survive their "death" and come back before the House later. (Until then, a less-than-productive debate will continue.)

Death and what survives death are in fact what I was intending to write about. I went on a hunt earlier this week for fossilized teeth from two sharks, the Otodus obliquus and the Palaeocarcharodon orientalis, teeth from the latter seemingly so rare as to have attained near mythic status in these parts. The venue was a Paleocene formation that sheds its fossils onto the shore and into the murky waters of the Potomac River.

It was one of those early Spring days after a front has passed through and we’re treated to deep blue skies and a good wind.

As I walked north, I experienced that curious phenomenon in which some things in my environment suddenly stand out in stark relief. It’s not a matter of being present in the moment which implies being sharply aware of all that is transpiring around me. No, it’s a very selective awareness, it’s the donning of 3-D glasses causing a blurry red-cyan picture to suddenly shoot objects toward my face. In this case, what came rushing toward me out of the background of the river, shore, cliffs, and woods was the mortality of living creatures.

I have to blame it on Donald Prothero’s engaging textbook Bringing Fossils to Life: An Introduction to Paleobiology (1998). The night before, I read the first chapter about taphonomy, the study of the processes by which organisms become fossils. In essence, it’s the study of what happens to organisms after death, revealing the incredibly long odds against the creation of fossils from any assembly of living entities, odds that are even longer for some creatures, such as those with only soft body parts, than for others. So much happens to breakup and destroy the once living being. These processes impose harsh, effective filters that militate against fossil creation – there isn’t much, if anything, left to fossilize. The agents of this destruction include, among others, predators, scavengers, bacteria, and the weather. In this environment, wave action works a great power.

There I was, scanning the shore line for fossilized teeth, while evidence of the breakup of the once living began standing out against the background – a dead fish in the early stages of decay and one scavenged to its bare essence; the ravaged pelt and hooves of a dead deer, its bones long destroyed or scattered. The message was clear, these were not fossils in the making. Most death is not. Fossilization, as Prothero describes, entails some very special circumstances.

Still, despite the unlikelihood of fossilization and subsequent discovery, abundant fossilized shark teeth did roll in the surf, being briefly exposed and then covered, while others lay baking in the sun where waves had left or revealed them. I spotted part of a tooth root in the wet sand and made my day when I pulled out a nice Otodus obliquus (1 ¼ inches on the slant) with possibly a pathological kink up near the tip.

Later, it occurred to me, as I considered the juxtaposition of the decayed and scattered bodies of fish and deer with the fossilized teeth that littered the beach that day, that shark teeth may constitute some sort of special case in taphonomy because it’s highly unlikely that the tooth I found came from a dead O. obliquus. No, sharks lose teeth repeatedly throughout their lives, in the tens of thousands over the course of a lifetime. So, nearly all of the fossilized shark teeth found by collectors are those lost by sharks living at the time the teeth separated from the jaw. Ironically, while alive, sharks shed abundantly the one component of their anatomy that is most likely to fossilize – their enameloid-covered teeth. Sharks are cartilaginous creatures after all. And these teeth are lost in bodies of water where they fall to the bottom and may potentially encounter an environment that nurtures their fossilization. From the perspective of this collector, it’s a most excellent process that may better the odds of survival as a fossil.

No comments:

Post a Comment

Nature Blog Network