Posted by: Rob Viens | September 24, 2012

A Fossil Primer I

September 24th found Darwin packing up the treasure trove of fossils he had collected the day before:

“Employed in carefully packing up the prizes of yesterday.— In the morning one of the Schooners arrived & the other is shortly expected. They have had a very bad passage of 6 days.— Mr Rowlett brings back an excellent account of Rio Negro.— Nothing could exceed the civility of the Governor & the inhabitants.— It was rendered the more striking from the contrast of our reception at the fort of Baia Blanca.” (Sept 24)

It turns out that fossils have a long and interesting history, so I thought I’d write a little “fossil primer” over the next couple of days. Today – the “discovery of fossils”.

As with so many great scientific ideas, Darwin came to his at a time when several other scientific pieces were falling into place.  The significance of fossils, for example, was just being recognized by the scientific community in the early 1800’s. This was important because fossils became a key piece of evidence for Darwin.

But fossils were not always that well understood.  In ancient times they were thought to be left my mythical beasts – in fact, many of the “monsters” of Greek mythology were born in the fossil record.  There were also a few accounts suggesting that sea shells found on mountaintops came from a time when the sea covered the land.  This idea took hold and was applied during the Middle Ages to suggest that fossils were left by Noah’s flood.

But there was more to the story than that.  “Fossil” comes from the Latin for “dug up” and in those days the term represented any strange curios that were dug out of the rocks – including “true fossils” (as we know them today), as well as crystals and concretions.  They were thought to be things that “grew” in the rocks.  That doesn’t seem to strange when you also remember that the origin of rocks was also not well known at the time.  If you assume that rocks had been in place since the beginning of the Earth, it became difficult to explain how a solid fossil could somehow be entombed in a solid rock, unless it grew in place.

This brings us back to our friend Nicholas Steno who, during the 1600’s, helped determine the basic rules of relative dating (see Relative Dating with Darwin Part I and Part II).  Steno was the first real modern thinker to get a handle on what fossils were – essentially the remains of once living things entombed in the rocks.  It helps that he was also one of the first people to really understand that sedimentary rock was made of “petrified” sediments.  This was important because it meant that the rock had once been loose material that could have buried organic remains and later been turned into rock.  Hence, the answer to how one solid gets embedded into another solid was revealed (Steno’s book on this translates as  “Forerunner to a dissertation on a solid naturally contained in another solid”)

As the physician to the Grand Duke of Tuscany, Steno also had access to a lot of unusual finds.  One day some fishermen brought him a “week-old” giant shark carcass caught in the Mediterranean.  In dissenting the specimen (hopefully with good ventilation), Steno realized that the teeth of the shark were a perfect match with strange “fossils” uncovered in rocks in the surrounding mountains. (These fossils were called “tongue stones” – thought to be the tongues of ancient dragons.) Putting two and two together, Steno concluded that these fossils were the remains of once living sharks. The true nature of fossils was emerging.

Steno’s sketch of a modern shark and some “tongue stones”:

Steno's shark sketch

Steno moved on to life in the church (and has since been beatified) but others followed up with this idea – including Robert Hooke and Johann Scheuchzer. However, the idea took a while (100 to 150 years) to gain any sort of acceptance. I suppose it did not help that there where a lot of misinterpretations along the way. Scheuchzer, for instance, identified a fossil “human” called Homo diluuvii.  It turned out to be a giant salamander (Salamandra scheuchzeri) from the Miocene.

Scheuchzer’s Homo Diluvii
Homo diluvii

Around 1800 all of that changed with the work of the French naturalist Baron Georges Cuvier. Cuvier was an anatomist, and a darn good one at that.  He was one of the first to actually correctly identify specific fossils for what they were, including identifying bones from mastodons as being similar to modern elephants. Since animals such as mastodons were no longer around (at least in Europe where the bones were found), it also suggested that life in the past was not necessarily the same as life today.  Hence, Cuvier’s work led to the idea of extinction.

Baron Cuvier:

Baron Cuvier

Lastly, around this same time, William Smith was realizing that there was a pattern to the fossil record. (See details in Relative Dating with Darwin Part II)   This completed the picture, adding the idea not only did fossils represent animals that no longer existed but that those animals changed through time. Powerful ideas indeed.

All of this was happening just 25 years or so before Darwin set sail on the Beagle.  Had his trip been 25 years earlier, he might not have even realized the significant of the bones in the cliffs of Punta Alta. Luckily, he did. (RJV)

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Responses

  1. […] Eyewitness to Evolution. For more on Darwin and fossils, you can also see A Fossil Primer (Part I and Part […]


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