New Species of Jurassic Mammal from Scotland

This week my colleagues and I published a new species of fossil mammal, found in the Jurassic-aged rocks on the Isle of Skye. It's a sister to Scotland's first Jurassic mammal, Borealestes serendipitus, but is smaller, with differences in the upper teeth and bones of the skull. We named it for the stewards of the landscape, the Cuillin mountains, that watch over our team during fieldwork. We named it, Borealestes cuillinensis.

This is a publication I've been working towards for a long time. It incorporates some material from my PhD, which included mammal material from the richest vertebrate fossil site on the Isle of Skye, on the Strathaird Peninsula. The main specimen I was interested in was a fossil mammal skeleton, found in 1972 (collected in 1973) by Dr Michael Waldman (Stowe School) and Prof Robert Savage (University of Bristol), and their fieldwork team. Despite it being the most complete mammal from the Mesozoic known in the UK, this skeleton wasn't studied, but remained in the collections at National Museums Scotland (NMS). In the 1990s researchers at the museum rediscovered it, and then Drs Nick Fraser and Stig Walsh at NMS later teamed up with Dr Stephen Brusatte at the University of Edinburgh to offer a PhD on the fossil. I was the lucky candidate.

The skeleton belonged to B. serendipitus. It proved difficult to CT scan due to the size of the rock that contained it, so Stig and I (along with Dr Ian Corfe) took it to the European Synchrotron Radiation Facility (ESRF), where Dr Vincent Fernandez obtained amazing scans of the fossil. I've now used those to study the skeleton. With my co-authors I've gone on to publish papers on its ear bones, jaws, and now the skull.

The fossils of Borealestes serendipitus (left), and Borealestes cuillinensis (right). Above are digital reconstructions from ct and synchrotron scans, showing the skull bones inside the rock. Below are the skull reconstructions. The coloured areas (blue and green) show which bits are preserved in the specimens.

But there is a lot more to our new paper than just this specimen. The team I work with on the Isle of Skye - comprising researchers from National Museums Scotland and the Universities of Oxford and Birmingham - discovered another amazing mammal skeleton from the same locality. It was found by Prof Richard Butler (University of Birmingham) in 2018, and upon first examination appeared to be another B. serendipitus skeleton. But when we CT scanned it, I realised this was a new species of Borealestes. The upper teeth were slightly differently shaped, and in the skull the sutures between the very front of the upper jaw (premaxilla) and the main part of the upper jaw (maxilla) were in a different position. Along with other minor differences, and the smaller size of the animal, we realised we had a new species!

The fossil of Borealestes cuillinensis, moments after discovery. Only the tiny jaw was visible on the surface, Richard has great eyesight to spot such a wee beastie! (Photo by Elsa Panciroli)

The rest of the skeleton is still being studied, but the skulls are now published in the Zoological Journal of the Linnean Society. In the paper we outline the diagnostic features for the two species, and use the jigsaw of the broken skull to reconstruct the crania. As well as erecting this new species, we also realised that a species previously assigned to Borealestes, 'B.' mussettae, doesn't belong in that genus at all, so we renamed it Dobunnodon mussettae, after the Iron Age Celtic tribe that occupied the area in Oxfordshire where it was found, the Dobunni.

The molar tooth of Dobunnodon mussettae (previously 'Borealestes' mussettae), the new genus named for the Celtic tribe, the Dobunni.

One thing that threw us at first, is that the lower teeth of these two species are incredibly similar. Usually, we expect lower molar teeth (the ones at the back) to be different, which helps us name new species. But these are almost indistinguishable. We are certain the new specimen is a new species though, as I said previously, because the upper teeth are different, and the sutures in the skull are not the same. Also, we know the new fossil is an adult because it has all of it's teeth fully erupted, so it's not just a young serendipitus! This discovery teaches us that we might not be making accurate estimates of the number of species at a locality if all we have to go on are isolated fossil lower teeth and jaw fragments. Only with more complete skeletons can we be sure... but they are so rare, so we just have to do our best!

The digital reconstructions by Matt Humpage are exceptional. They show Borealestes serendipitus (left) and Borealestes cuillinensis (right), with a 5 pence coin for scale.

The incredible digital reconstructions are by Matt Humpage, and they really blow all my amateurish attempts at drawing extinct animals (as I did for previous publications) out of the water! I highly recommend you check his work out. He also does beautiful digital renders of plants, and he produces videos (including the one for this paper) - plus he's open for commissions!

Stay tuned for more wonderful fossil discoveries from Scotland!

 

Reference

Panciroli E, Benson R, Fernandez,V, Butler RJ, Fraser NC, Luo Z-X and Walsh S. 2021. New species of mammaliaform and the cranium of Borealestes (Mammaliformes: Docodonta) from the Middle Jurassic of the British Isles. Zoological Journal of the Linnean Society [online].