American Moles in a Spanish Crater

Eastern mole

Moles are unusual animals. Most species are highly adapted for digging, spending almost all their lives underground, making them vulnerable to predators when they have to venture onto the surface. One might think, therefore, that they would not have dispersed widely across the globe and that it should be easy to trace their evolutionary history.

However, this is not the case. For one thing, moles are found across the Northern Hemisphere, in Europe, Asia, and North America. A million years is, after all, a very long time and moles have been around far longer than that - including some times when the Bering Straits were dry land. 

Traditionally, the mole family has been divided into three subfamilies, two of which are almost entirely unique to Eurasia, and one to North America.

Leaving aside the fact that "almost entirely" is a rather key caveat here, more modern genetic studies have indicated that the reality is, in any event, more complex. One of the original three subfamilies is still considered valid, consisting of a group of mysterious forest-dwelling animals unique to China and Myanmar that don't seem especially adapted for burrowing. We know almost nothing about them, but so far as we can tell, they forage in leaf litter rather than digging, and it's often thought that they still resemble the original mole ancestor. Given this, it's perhaps less surprising that they were once more widespread, with fossils known, for example, from Slovakia.

Second are the desmans, which have been split off from the Old World mole subfamily to be given one of their own. Also unlike what we would immediately think of as "moles", they are semiaquatic, living in rivers and spending most of their time swimming. They appear to have originated in Iberia, where one species still lives, but at one point lived across much of Europe and present-day Turkey. Today there are just two species, with the second one living in Russia, Ukraine, and Kazakhstan.

There is, however, rather more debate about the others, due in part to relatively few detailed genetic studies having been carried out. Some studies do at least come close to the traditional view, but others veer further away, suggesting that there is no clear split between the Old World and New World species, suggesting considerably more migration between different continents than we might have expected.

The oldest mole fossil known belongs to Eotalpa, which lived in southern England in the Late Eocene, over 35 million years ago. Surprisingly, it is better adapted to digging than the living shrew-moles of China, which might suggest that the latter are not so primitive as usually thought, having lost the ability rather than never possessing it. But, with moles already being widespread not much later, it would be a stretch to say that moles originated in Britain, or even in Europe. The picture is too complex from too early on for us to know where they first evolved.

Part of the problem is that mole fossils are generally very incomplete. As with many other small mammals, often all we have are teeth and arm bones (the humerus of moles, being adapted for vigorous digging, is highly distinctive). The requirement to dig and the relative uniformity of the underground environment, free from many of the effects of climate and weather, also means that moles don't really change all that much. As a result, one fossil may look much like another, making it hard to determine how many really belong to new species.

This would be less of a problem if we had more complete fossils. And, while it isn't going to solve the mystery of the geographic origin of the first moles, just such a fossil has been recently described. It was discovered in a lagerstätte near Girona in northeastern Spain. Although the exact definition can be debated, in general terms, lagerstätten are fossil sites that preserve remains in an unusually complete form and that are especially useful to palaeontologists. (I'm a little surprised that I've never had cause to use this word on the blog before, but apparently, I haven't).

There are many ways that they can form, but this particular one was originally a crater formed when water came into contact with volcanic magma and exploded, creating a wider, flatter bowl than one normally associates with eruptions. Once it cooled, the crater filled with water to form a lake, eventually laying down stable layers of silt and clay that kept out oxygen, thus preventing worms or other invertebrates from reaching carcasses and disrupting their skeletons while feeding. The lake is long gone, but the rock layers it created remain intact.

The deposits from which this fossil was discovered have been dated to at least 3.25 million years ago, placing them in the Late Pliocene, the long autumnal period that immediately preceded the Ice Ages. That's a minimum age, however, with as yet unpublished research apparently suggesting an older date, closer to 5 million years ago - the Early, rather than Late, Pliocene.

N American species in blue - all others are Eurasian

The fossil consists of the skull, jaw, forelimbs, ribs and part of the backbone, all still connected to one another, and a detached hind limb. Although parts of it are badly damaged, this is already more than we would expect from most mole fossils, and the jaws and forelimbs are particularly well preserved. Originally thought to be a close relative of the living European mole, like all other known Spanish moles from the Pliocene, the fossil is complete enough that more recent analysis has shown it to be something else entirely.

Named Vulcanoscaptor because of its discovery in a former volcanic crater, comparison with other living and extinct mole species showed that its closest known relative was likely the living eastern mole (Scalopus aquaticus). 

This is significant because the eastern mole lives, not in eastern Europe, or even Asia, but in the eastern US, from Massachusetts and Florida to Nebraska and Texas, with some populations straddling the Canadian and Mexican borders. Its own closest living relatives live on the other side of the continent, from Vancouver to the far north of Baja California. Their ancestors are thought to have been there since the middle Miocene, over 10 million years ago, so what, one might ask, was Vulcanoscaptor doing in Spain so much later?

There are a couple of possibilities. Perhaps the simplest is that, as proposed by a study in 2015, the lineage first evolved in Eurasia before it moved to North America. If this is the case, perhaps some population remained behind, isolated from their kin and struggling on in an isolated region until the Pliocene. But, then again, we already know that the geographic history of the moles is a complex one, so it's possible that the animals migrated back to Eurasia at a later time, with Vulcanoscaptor being an offshoot of one of these groups. 

Here, it's worth noting that the closest living relative of the hairy-tailed mole (Parascalops breweri) of New England, the Appalachians, and southeastern Canada is, surprisingly, the Gansu mole (Scapanulus oweni) of central China. Moles do get about.

As one might expect, given its close relationship, Vulcanoscaptor had the same adaptations for digging that American moles do today. This might lead one to question how this particular individual ended up in the anoxic mud at the bottom of a volcanic lake. It's possible that it was semi-aquatic, since the star-nosed mole (Condylura cristata) is both semi-aquatic and adapted for digging, proving that the two are not incompatible. More likely, however, it was dropped by a predatory bird flying over the lake, or it had fallen in and drowned, possibly during a flood.

Either way, since it clearly lived locally, and Spain isn't exactly close to Massachusetts, it's another piece of evidence that moles have travelled extensively in the last few million years. While it can't be easy for them, it may help that they have few direct competitors, given their unusual lifestyle. They have travelled between Eurasia and North America three or four times just since the modern subfamily arose, leading to the complex patchwork we have today.

[Photo by Bert Cash, from Wikimedia Commons. Cladogram adapted from Linares-Martín, et al. 2025.]