This project was born from the practical need to be able to maximize our ability to learn about past environments using the geochemistry of fossil teeth. There have been a few studies, some published and some student projects, that have examined whole jaws, but nothing sufficiently systematic or with enough samples that we can apply statistical analysis. And in most cases, the focus is on the cheek teeth and does not include the incisors. Such studies are interesting and worthwhile and I’ll be outlining some of them here in the lab notes. They are an important component of doing this project in the most objective and usable way possible.
I’ve worked in many places globally, with most of my research taking place in the Rocky Mountains region of the United States. And I’ve never NOT picked up skulls whenever I found them. These specimens represent a skull I collected sometime in the last century (wink) when I was working on my PhD (studying 60 million year old mammals in Wyoming).
Even though I collected the skull and jaw for the pronghorn pictured above 20+ years ago, this is still a perfect specimen for use in this project. Most importantly, I know that both teeth came from the same jaw (I removed them myself), which means I can directly compare the chemistry of the teeth and understand where they are similar and where they are different. With the additional knowledge of its age (modern) and where it came from (the Hanna Basin), data collected from this jaw can be used in related studies of how environment is reflected in tooth chemistry.
In 2019, I collected bulk samples from both the third molar and the incisor and analysed them. Above are my notes from when I collected the samples.
So what is all that nonsense written there?
“Rm3” and “Ri1” refer to the exact tooth position. These are the right lower third molar and the right lower first incisor. R (or L) indicates if it came from the right or left side of the jaw. The M and I indicate the tooth positions (Molar, Incisor, Canine, and Premolar). The lower case “m” and “i” indicate these teeth came from the lower jaw.
“PH-SIR-19-53” and “PH-SIR-19-54” are numbers that I assigned to the powdered samples when I collected them and put them into tiny vials. The PH is for me, Penny Higgins. SIR stands for “Stable Isotope Ratios” which is what I use when I’m collecting a sample that doesn’t belong to any particular project. Samples collected specifically for this project will be denoted “JP” for Jaw Prawject, so I can remember why I collected the sample. “19” stands for the year that I collected the sample, in this case 2019. 53 and 54 are for the number of samples I collected that year. So PH-SIR-19-54 is the 54th sample that I collected in 2019 that was not associated with any particular project. I collected these samples because I was already thinking about this research question, but hadn’t framed it into a formal project yet.
The term “bulk” written beside the sample number tells me that I collected a bulk sample from the tooth. That is, I collected only one sample representing an average of the entire tooth.
I always include a drawing of the specimen before I sample it for two reasons. One is so that I can make note of where I took the sample. It’s not always obvious when your finished, so it’s helpful to have a drawing. Two is so that I have a visual record of what the tooth looked like before sampling. Sometimes teeth shatter during sampling. And occasionally a tooth gets misplaced. If they’re not labeled, sometimes the only way to connect a sample to its tooth is through this drawing.
The moral of that story is to not be afraid to draw in your notes, even if you think your draawings are bad. But I digress.
Beneath my drawing of the Rm3 is says (sloppily) “broken & glued”. This is important for me to make note of, because I might have accidentally included some of the glue in with the enamel sample, which could affect the chemical analysis results.
In pen beneath each tooth is written a number that starts with “G-“. The G- numbers are assigned to the samples when they’re analyzed in the lab where I ran them. If I want to connect the results of the chemical analysis with the samples and ultimately back to the teeth, I have to know the G-numbers.
OK Penny. That’s great. So…? What did you learn?
We are measuring the relative amounts of stable (i.e. not radioactive) isotopes of carbon and oxygen in the tooth enamel. From the analysis, we get what are called “delta values,” one for carbon (δ13C) and one for oxygen (δ18O). The units of delta values is “per mil” and is denoted as ‰. In a future post, I’ll explain what this is about. For the moment, it is sufficient to say that we hope the delta values for carbon and oxygen are the same for the incisor and the molar. “The same” means that the values would be within 0.2‰ of each other.
Here are the results. I was able to analyze the molar sample once and the incisor sample twice:
Lab ID Sample Tooth δ13C δ18O G-7648 PH-SIR-19-53 Rm3 -11.2‰ -9.7‰ G-7649 PH-SIR-19-54 Ri1 -12.2‰ -3.5‰ G-7649 PH-SIR-19-54 Ri1 -12.3‰ -3.4‰
What we see is that where we analyzed the same sample (the Ri1) twice, we got the same answer for both δ13C and δ18O. But, between the two teeth, the results are very different, especially for δ18O.
Rats. I guess my hypotheses that they’d be the same is wrong. Phooey.
This is science. We don’t fling our hands in the air and quit. There are multitudes of reasons why this may be the case. δ18O is affected by season. What if the teeth grew at different times of the year? What if the glue on the Rm3 messed everything up? What if the analysis for the Rm3 was bad? We only ran it once before we ran out of sample, so we can’t be sure.
This is where you come in! We need more samples. We need to run enough analyses to confidently draw any conclusions. I still have these teeth, so I can resample and run them again. Or we can run a whole bunch of pronghorn teeth. Or horse teeth. Or cattle teeth. Or badgers, because why not?
There are far more questions than answers right now. Your support of this project will help us answer some questions, and will help us ask better questions in the future!