Peer Review and Iron Age Fossil Shark Teeth Collecting

Earlier this year, public health experts Nason Maani and Sandro Galea cautioned that a public policy for the pandemic promising to “follow the science” misconstrued science and the role it can and should play in the public arena.  (What Science Can and Cannot Do in a Time of Pandemic, Scientific American, February 3, 2021.)  The details of their cogent arguments aren’t relevant to this present post, but their comment about peer review is:

Peer review, designed to catch our mistakes at the best of times, can suffer from in-group bias and in any case has been put aside to an unprecedented degree in the explosion of preprint research during the pandemic.

And, so, when policymakers (at least, some) are claiming to be subordinating their actions to guidance from science, one of the safeguards that is intended to minimize egregious errors in scientific research is being relaxed.  Of course, it is.

I hadn’t thought much recently about scientific peer review until I came across some archaeological research on an Iron Age (8-9th century BCE) site in Jerusalem.  (Thomas Tütken, et al., Strontium and Oxygen Isotope Analyses Reveal Late Cretaceous Shark Teeth in Iron Age Strata in the Southern Levant, Frontiers in Ecology and Evolution, Volume 8, December, 2020.)  It’s quite a remarkable story about the potential good that peer review can do, and about the role serendipity can play in the scientific endeavor.

Tütken and his colleagues had prepared a research article on a multitude of fish teeth (over 10,000) they had found in the fill dumped into a pool to create the foundation for a private house built in Jerusalem some 2,900 years ago.  Their focus was on what these teeth could reveal about the trade in fish at the time.  As they write, “Identification of fish trade in antiquity is traditionally based on the presence of ‘exotic’ fish remains in archaeological sites, which are distantly located from the original habitat of the fish.”

Among the thousands of fish teeth the authors analyzed were 29 shark teeth.  Not surprisingly, in drafting their article, the authors operated on the logical assumption that any remains, such as the shark teeth, discovered in archaeological layers had a provenance contemporaneous with other remains and objects found at the site.

Then came the peer review process.  One reviewer spotted something curious about the shark teeth depicted in the original piece.  As Tütken said,

We had at first assumed that the shark teeth were remains of the food dumped nearly 3000 years ago, but when we submitted a paper for publication, one of the reviewers pointed out that one of the teeth could only have come from a Late Cretaceous shark that had been extinct for at least 66 million years.  (As quoted in The City of David and Sharks’ Teeth Mystery, Goldschmidt Conference, Phys.Org, July 4, 2021.)

How fortunate that one of the reviewers of the original paper had some exposure to fossil shark teeth and was brought up short by the distinctive shape of a shark tooth among those depicted in the original article draft.  I assume the tooth that sparked this realization was from the genus Squalicorax (I don’t think that’s made clear in anything I’ve read, but, as I note below, it’s a safe assumption).  Ah, the value of a breadth of knowledge among peer reviewers, knowledge that ranges beyond the narrow focus of the paper under review, thus avoiding what Maani and Galea describe as “in-group bias.”

A bit of paleontological understanding is useful to appreciate the impact that this Iron Age research story has had on me and why I think the Squalicorax teeth saved the day.  This genus of sharks, which existed in the Late Cretaceous (from roughly 100 to 66 million years ago), sported teeth so distinctive that they are very easily recognized by even the least experienced collector of fossil shark teeth.  These shark are commonly known as Crow sharks.  Pictured below is a specimen of S. kaupi I found many years ago in Big Brook, New Jersey.  It is 15 mm on its longest axis.

Tütken and his colleagues, using data on the strontium isotope ratios and oxygen isotope ratios found in the teeth of extant fish from different bodies of water in the eastern part of the Mediterranean, determined that all of the shark teeth in their study were not contemporaneous with the Iron Age structure.  Indeed, the isotope ratios in those teeth matched those determined by others for Late Cretaceous fossil shark teeth found in Israel and Jordan.  (Fish teeth retain the isotope ratios present in the waters when the fish were alive.  Thus, a time signature is carried by the teeth and, if read, can separate contemporary from ancient teeth.)

The researchers largely ruled out the possibility that these Cretaceous teeth weathered out of local formations.  Instead, it appears likely they were discovered and removed from a site some 80 kilometers away.  Which raises the key question:  Why were these fossil shark teeth here at this Jerusalem site?  A question to which the authors do not have an answer.  There is no evidence these were being used as ornaments or as tools.  As a result, Tütken has said,

Our “working hypothesis is that the teeth were brought together by collectors, but we don’t have anything to confirm that. . . .  We know that there is a market for shark’s teeth even today, so it may be that there was an Iron Age trend for collecting such items. . . .  However, it’s too easy to put 2 and 2 together to make 5.  We’ll probably never really be sure.  (As quoted in Phys.Org.)

Fossil shark tooth collectors at work three millennia ago?  Amen to that, I’d like to think so.

I am puzzled by one aspect of the discussion in the paper as published.  Tütken et al. write that, at archaeological sites in the area, shark vertebrae are the primary shark remains that are found, not teeth.  That just doesn’t square with my experience working geologic formations that contain shark fossils because teeth vastly outnumber vertebrae.  Even if the research being cited applies to sites to which contemporary sharks were brought, teeth in the specimens would still grossly outnumber vertebrae.  Were sharks decapitated and only their bodies transported to other sites?  Quite curious.

Anyway, score a big one for peer review.  Tütken and his colleagues are quite gracious in their comments in the published paper about the impact of the reviewer’s observation about a Cretaceous fossil tooth which they label a “game changer.”

It led us to perform additional analysis and, ultimately, to rework the narrative of the manuscript, changing the story from shark exportation from the Nile delta to fossil shark finds in cultural layers.  This was a textbook example how a good review should work and we are very appreciative.