The “Oldest” Object in our Collection: A Natural History Mystery
By Clare Sully-Stendahl

If you’ve been following our Instagram page, you’ll know that we just posed a big question: What is the oldest object in our collection?

You may have guessed a fragment from an old ship; or pictured one of our antique sextants. And we do indeed have some incredibly old artifacts and documents (including a book published in 1691!). But it’s not all just ships and navigational tools at the Maritime Museum – and if some of those are already a few hundred years old, we also have some items that are old on a completely different timescale. We have several fossils in our collection, including three that are estimated to be 380 million years old.

 I was very excited to learn we had fossils at the museum, and turned to our old catalogue cards to learn more about these three specimens in particular. But I was left with more questions than answers…

The catalogue cards describe the fossils as being approximately 380 million years old, and as each being an “ammonite-orthoconic” (straight-shelled ammonites). Something immediately seemed not quite right. Ammonites appeared only around 240 million years ago – and “heteromorph ammonites,” (which include the non-spiralled “orthoconic” ammonites) really only diversified during the Cretaceous period around 150 million years ago.

Based on dates alone, therefore, it didn’t seem possible that these specimens could be 380 million years old and ammonites. Before concluding that they weren’t ammonites, however, I had to address an important question: how did we know they were actually 380 million years old? It seemed to me there were two possible situations: either the fossils were as old as the catalogue card said they were, and not ammonites; or they were ammonites, and millions of years younger than the date we had recorded. To get to the bottom of the fossil mystery, I got in touch with the very helpful “specimen identification” folks at UBC’s Pacific Museum of the Earth.

They confirmed that my hunch was correct – these fossils are almost certainly not of orthoconic ammonites. Instead, they suggested that they are orthoconic nautiloids, a related group of straight-shelled cephalopods that emerged almost 500 million years ago and that were very common throughout the Paleozoic Era.

They explained that the best way to differentiate between fossil ammonoids and nautiloids is to look at the septa – the lines that divide the animal into chambers. In nautiloids, the septa are concave to the body chamber (where the soft body and head of the animal is), and in ammonoids the septa are convex to the body chamber. Can you spot the difference in the photo below? I’ve placed one of the “mystery” fossils beside a known ammonite from our collection, for comparison.
Notice how in the “mystery” fossil, the septa lines curve away from the head end – but in the ammonite, they curve towards the head end.

It seems, therefore, that these three mystery fossils had been identified as the wrong species – they’re likely orthoconic nautiloids, which means that the date estimate of 380 million years is certainly reasonable since they’ve been around for almost 500 million years! Indeed, nautiloids have a fascinating evolutionary history. Although they’re the earliest cephalopods found in the fossil record, they still have a living member: the nautilus.

Why does a maritime museum have natural history objects like these? Some of our fossils (and other animal parts like tusks or skulls) were collected on maritime journeys such as the St. Roch expedition. In the case of the three fossils discussed today, we don’t know exactly where they’re from or who collected them, but we do know that at least one of them came from Fort Ross, Nunavut. Millions of years before people lived and sailed in the Arctic, animals such as these constituted a different side of maritime history – that of the creatures that lived in the sea a long, long time ago.

References

National Geographic. “Ammonite.” https://www.nationalgeographic.com/animals/prehistoric/ammonites/.

Deposits Magazine. “Understanding Heteromorph Ammonites.” https://depositsmag.com/2017/03/16/understanding-heteromorph-ammonites/.

University of California Museum of Paleontology. “The Cephalopoda.” http://www.ucmp.berkeley.edu/taxa/inverts/mollusca/cephalopoda.php.

Thanks to the “Specimen Identification” team at the Pacific Museum of the Earth! http://pme.ubc.ca/visit/specimen-identification/.