Ancient Otters of Idaho

The common river otters of Eurasia and North America are remarkably similar animals. If you placed them side by side you might notice that the Americans ones are (on average) slightly larger, and have a slightly more bland colour to their coat... but, really, it's not easy. I, for one, wouldn't claim to be able to tell which species a particular photograph was of without additional evidence (most obviously, where it was taken).

It was therefore assumed for a long time, not unreasonably, that they had to be very close relatives. As early as 1843, they had been placed in separate genera, as Lutra lutra and Lontra canadensis, respectively. However, it's worth noting that this is 16 years before the publication of On the Origin of Species, so, when he did so, it's isn't obvious that John Edward Gray was necessarily thinking about how "related" they might be. Indeed, for much of the 20th century it was common to ignore Gray and place all of the fairly typical looking clawed otters together into the genus Lutra.

Weasels in Cool Rivers: The Common Otters

Eurasian otter

The otters are, arguably, the least weasel-like of all the members of the weasel family. Although the relationship has been clear for a long time - the first scientific description of an otter, by Linnaeus in 1758, actually placed it in the genus Mustela, to which stoats and weasels belong - so have the differences. As early as 1771, Danish zoologist Morten Thrane Brünnich split them off from their fellow mustelids, erecting the new genus Lutra to describe them.

By 1838, at least three genera of otter had been described, and the group were raised to 'subfamily' status to distinguish them from their terrestrial kin. Other subfamilies were erected later, largely to distinguish the badgers, but the otters have remained as a clearly distinct group within the overall weasel family.

Genetic studies in the last four years have given us a much clearer picture of how the various kinds of mustelid are related to one another, and it turns out to be more complicated than we thought. For example, martens turn out to have been around longer than otters have, which was something of a surprise. The otters, however, survived the revision unscathed, confirmed as a genuine evolutionary group, albeit one that is younger than we might have guessed. Their closest relatives within the family turn out to be the mustelines, the group that, among others, includes the semi-aquatic mink.