24 March 2009

Note from the Lone Male Excavator:

What is a fossil? One of our readers, "Duys" in Belgium recently reminded me of how one can determine a fossil and I thought it a good time to bring it up. I'll meet that idea in a round about way here:

The other day, I held the back door for a family visiting the museum. One of them was in a wheel-chair and since the back (staff) door is nearest the parking lot, could enter there. Anyway, I was heading into the lab and so held that door open too so that they could get a peek inside at Shelley and the volunteers eating lunch and glimpse behind the scenes fossil workstations. The older gentleman pushing the wheelchair asked me if I was a fossil... "I'm getting there," I replied. (Yes, the LME turns 30 in less than a month.) This question the gentleman asked was not one we get often, but we are very often asked if the bones and other previously living materials we dig out are, in fact, "fossils."

Strictly speaking, it depends on your definition of the word fossil. When I took Invertebrate Paleontology, my professor, in the first week, was discussing some common mistakes & misconceptions in word definitions. One he mentioned was archaeology vs. paleontology, between which this blogs readers surely already distinguish the differences and similarities (yes?). Another he discussed was the difference between "fossil remains" and "recent remains," as well as how to tell if what you have is a fossil. Being a geologist, he discussed the difference in whether or not the remains had undergone mineralization. He noted that a fossil will not smell if you hold fire to it. Furthermore, if you stick your tongue to a "recent" bone it will stick a bit, but it won't with a "fossil" bone.

Geologists and dinosaur paleontologists often use this sort of "mineralisation" definition, but how do La Brea bones hold up to it? Since they do still contain collagen, Rancho La Brea bones would, hypothetically, still produce a burning organic smell if we held them to fire. And, yes, ones tongue would likely stick to them if tried, but that may be more due to the asphalt than the collagen.

So I've decided to test these hypotheses with a personal experiment. (Of course, I am not serious.) We don't need to burn or lick these bones to determine that they have collagen, as studies have already used collagen samples from many of the bones in attempts to extract proteins and DNA.

So, are they not fossils?
A 30,000 year old bone is a fossil, no matter how you slice it. Ancient Rancho La Brea bones, plant, shells, and insect parts all fall under the more encompassing definition of fossil provided to us by thefreedictionary.com:
"A remnant or trace of an organism of a past geologic age, such as a skeleton or leaf imprint, embedded and preserved in the earth's crust."

The Rancholabrean North American Land Mammal Age (named for our site) spans from
300,000 to 11,000 years BP, so being of a past geologic age, our remains in this time frame are fossils.

Here is a question for you all:
Are the bones, plants, shells, insect parts, etc., that we find and can date to less than 11,000 YBP fossils? Pit 10 contained a vent of remains, for example, dated at around 9,000 years. So these are not technically from "a past geologic age." Are these bones not fossils?

Since Andrea alluded to it in a previous post, I have to mention that a month ago I sprained my left wrist when I rode the top of a ladder to the ground...backwards and downwards, and slam. I have missed my left hand terribly and promise to never take it for granted again if it works with me on the physical therapy and retains full functioning.
Lawyers need not contact me, as the staff here and NHM human resources department have been caring and accommodating.

Oh, and FYI:
We've completed excavation of Box/deposit 10B; our first box finished. It went pretty fast because it was a disturbed (mostly fallen apart) deposit and we did not measure out any bones or use a grid system on it. We will not, be changing the project name to Project 22, but the thought crossed our minds.


Doug said...

Archeology/ Paleontology. I have heard that my whole life. People were always asking me " you want to be a archeologist, right?" Likely just general confusion. Or could be because I love Indiana Jones. Or maybe a bit of both.

I have heard many times that fossil means "dug up". Under that definition, the roots belonging to that lemon tree I tore out of our backyard qualify as "fossils". About the mineralization: so that's why giant lemur bones from Madagascar and moa bones from New Zealand are referred to as sub-fossils.

Also, Ryan, I finally got all my pictures from our tour if you want to see them. Just follow the link in my name.

Ryan said...

Thank you Doug! Great Pics! You should be proud of yourself...you are the only reader so far with an attention span strong enough to have gotten through that whole post and reply to my question.

Doug said...

You're welcome Ryan! If I can get through Tetrapod Zoology, your posts are a walk in the park. Anyways,I also sent Andy a link to those pictures. As you may have been able to tell, I had a lot of fun with the pirate flag.

John Scanlon FCD said...

Permineralization occurs at different rates in different conditions so isn't necessary for any reasonable definition of a 'fossil'. The best thing might be to say that fossils are whatever palaeontologists work on (including trackways, buried soil horizons, chemical signatures, and a lot of other stuff apart from bones and shells). Or, remembering that most vertebrate remains are reduced to splinters or less in a few years after death: anything that (without artificial preservation techniques)remains of once-living organisms more than a decade or so after their death. I sometimes explain this to visitors on laboraotory tours here in Mount Isa (Queensland, Australia) but always add something like "but anything less than half a million years is too young to be interesting".

I work mostly with bones 15-25 million years old preserved in crystalline limestone which we remove with acetic acid (a bit like using a heat-gun, but it keeps working while you sleep). No collagen left, and some recrystallization may have occurred, but once the calcite is dissolved out we're back to the original bone mineral.

Regarding the tongue-test: that magnet-like sticking sensation is a test for apatite, which is the mineral component of bone and still often present in fossils. Collagen and fat interfere with it, so fresh bones don't stick, but it will work on older material if the bone is not actually replaced by a different mineral. First time I experienced it was at one of the late Triassic Plateosaurus excavations in southern Germany, where there were just a few chips of sky-blue fossil bone left on the surface, over 200 million years old. Definitely fossil.

Spencer said...

Archaeology vs. paleontology...sigh...I do get so tired of hearing that.

I propose we keep both sides happy and call it Project 23 most of the time, but when we get down to it possibly we can call it Project 23-22, etc. etc. Haha, not really, but still....

Hope your hand gets better. It still hasn't fully healed?