MAMMAL NAMES | Moustachioed Marine Monsters:

Ireland's Baleen Whales

Close-up of baleen from a humpback whale, showing the moustache-like bristles at the ends, which are the reason baleen whales are sometimes referred to as the 'moustached whales'

For the last few months we have plunged into Ireland’s seas to delve into the deeper meanings of the names of Ireland’s many toothed whales. So, for the next few months we will remain in these same waters to plumb the depths of meaning in the names of their relatives who occupy the other side of the divide in the order Cetacea – the baleen whales. As we will see, even when we only skim the surface as regards the names of these moustachioed marine monsters, we already find ourselves in the deep, inundated by a flood of fascinating appellations, epithets, and pseudonyms, many of which relate to that hallmark feature to which they owe their name – baleen.


In terms of species numbers, the baleen whales are certainly the poor relation in the order Cetacea, having only 14 species versus the toothed whales’ 72. However, they are far better represented in Ireland’s seas as a group than their toothed kin, with seven species, or fully half their number, having been spotted in Irish waters compared to only a quarter of toothed whale species (18 out of 72).


And though this still means that they are greatly outnumbered by the toothed whales, who can claim 11 more species in Irish seas than them, what they lack in species numbers is more than made up for by the sheer magnitude of their presence, with many of them being larger than the largest toothed whale that shares these waters – the sperm whale.


As we saw a few months ago, the sperm whale can weigh up to a staggering 57 tonnes, but even such a jaw-dropping weight cannot match that of the baleen whales in Irish seas, with all except two of them capable of reaching an astonishing 60 tonnes or more. These include forms such as the northern right whale, bowhead whale, humpback whale, fin whale, as well as that giant among giants that can claim the title of ‘the largest animal to ever live’ – the blue whale.

The blue whale can claim the title not only of 'the largest baleen whale on Earth', but of 'the largest animal to ever live'

The baleen whales, then, are generally far larger than the toothed whales in Ireland’s seas. Indeed, some even reserve the term 'whale' almost entirely for the baleen whales because of their great size, but this is confusing for any number of reasons. For instance, according to this view, the order Cetacea is generally divided up into whales, dolphins, and porpoises, but this division does not actually encompass all cetaceans. Furthermore, killer whales and sperm whales are accorded the title of 'whale' purely based on size, but, as we have seen, they are more closely related to other toothed whales like the dolphins. Finally, to insist that smaller cetaceans such as dolphins and porpoises should not be referred to as 'whales', while simultaneously referring to them as toothed whales is patently ridiculous.


In any case, in terms of their names as a group, it is not size which distinguishes the baleen whales, but how they are adapted to feed. Unlike the toothed whales, adult baleen whales have no teeth, their mouths instead filled with baleen plates that descend from the upper jaw and together act like a brushy sieve, allowing them to trap fish and krill after gulping in vast amounts of water and straining it.


Recent discoveries have even revealed just how baleen may have evolved in the baleen whales, and, fascinatingly, that their earliest ancestors could also claim the title of ‘toothed whales’.


The last common ancestor the baleen whales shared with the toothed whales, that lived around 39–38 million years ago, was itself a toothed cetacean, and after the subsequent split in the order Cetacea, the earliest members of the line leading to today’s baleen whales would have been toothed also. However, while their sister line, the toothed whales, have retained teeth to the modern day, the evolutionary journey of the whales on the baleen whale line obviously took a different turn.


In 2017, the discovery of a 36-million-year-old fossil in Peru of an early member of the baleen whale lineage, Mystacodon selenensis, was announced, and it lent crucial support to a theory about how these whales had evolved from being toothed forms to baleen forms.


This early whale still sported a mouthful of teeth, but the evidence suggested that it did not capture prey with its teeth, like the common ancestor it shared with the toothed whales did and many toothed whales do today. Instead, this ancient whale is thought to have fed by suction feeding, ‘hoovering up’ its prey by drawing water into its mouth through lowering the pressure inside it with the movement of its tongue, before expelling the water again. Eventually, the teeth became redundant altogether, and it is now thought only after they were lost did baleen evolve from the gums to more effectively trap prey drawn in by suction feeding. Thus emerged baleen whales like those that sail Ireland’s seas today, who still retain remnants of their toothy ancestry in the vestigial teeth that develop in the embryo but subsequently disappear.

In any case, it is to this wondrous feeding structure, this baleen, that the baleen whales owe their common name, but it is also the source for the scientific name for their group.


The scientific name of the toothed whales is very straightforward, being Odontoceti, which simply means ‘toothed whales’, derived from the Greek odontos, meaning ‘tooth’ (as we saw in last month’s blog on the beaked whales), and the plural form of the Latin cetus, meaning ‘whale’. However, the scientific name for the baleen whale group is far more obscure, the name Mysticeti appearing to derive from a transmission error in older editions of Aristotle’s Historia Animalium which in modern editions translates as ‘the mouse, i.e., the whale so called’, which is possibly an iconic reference to the great size of many baleen whales.


But there is, in fact, a lesser known and far more suitable alternative scientific name for the baleen whales and this is Mystacoceti, meaning the ‘moustached whales’, derived from the Greek mystakos, meaning ‘moustache’ (as we saw when we met Ireland’s whiskered bat a few months back) and, again, the plural of cetus, meaning ‘whale’. This refers to the bristles on the baleen plates, which do indeed have a moustache-like appearance.

Another image of a baleen plate from a humpback whale, which more clearly displays the moustache-like appearance of the bristles

So, Mystacoceti would appear to be a far more accurate scientific name for the baleen whales than the garbled Mysticeti. However, this latter name is not alone in being an inaccurate name associated with the baleen whales, as an alternative name for baleen also does not accurately represent the true nature of this feature. Baleen is also referred to as ‘whalebone’, but this is quite misleading as baleen is not composed of bone at all but of keratin – the same material that human fingernails are made from.


Anyway, thankfully, the word ‘baleen’ itself comes from a very simple and straightforward source, derived as it is from the Latin balaena/ballaena, another word meaning ‘whale’. And, interestingly, balaena itself is derived from the Greek word phallaina, which is thought to come from the Greek phallos, meaning ‘swollen penis’, and thus may be a reference to the body shape of a whale.


And this point brings us neatly along to the two groups of baleen whales that are found in Ireland’s seas, which each display a distinctive body shape and incorporate the word balaena in their respective titles.


The first of these is the family Balaenopteridae, which is the best-represented baleen whale group in Irish waters, accounting for five species, namely, the blue whale, fin whale, sei whale, northern minke whale, and humpback whale. The family name Balaenopteridae is derived from the genus Balaenoptera, to which all species in Irish seas bar the humpback whale belong. Balaenoptera comes from balaena, which, as we’ve just seen, means ‘whale’, and the Greek word pteron, which, as we have seen in previous blogs, means ‘wing’. In this case, this is a reference to the presence of a dorsal fin in the members of this baleen whale family, in contrast to the other baleen whale family in Irish waters, Balaenidae, represented by the northern right whale and the bowhead whale, in which a dorsal fin is conspicuously absent.

Illustration of a northern right whale, showing the obvious absence of a dorsal fin, in contrast to the members of the family Balaenopteridae who owe their name to the presence of one

But there are yet more differences between the members of the two baleen whale families in Ireland’s seas, and one of these is reflected in the common name for the Balaenopteridae species – rorqual.


‘Rorqual’ is a name that derives from the Norwegian language and means ‘furrow whale’, referring to the grooves, or longitudinal folds of skin, which extend from the chin backwards on the underside of the mouth, reaching behind the mouth in all species, and as far as the naval in all species except the sei whale. These grooves can expand when these baleen whales are feeding, allowing their mouths to become far larger in size, facilitating the straining of krill and fish from a far greater volume of water.

Humpback whale displaying the longitudinal folds of skin on its underside from which the name rorqual, meaning 'furrow whale', is derived

Like their toothed relatives that comprise the other branch of the whale order, then, the baleen whales in Ireland's seas display marked differences in form when compared to one another, and this will become even clearer as we take a closer look at the various species in the months to come. And yet, fundamentally, these moustachioed marine monsters stand (or float) united, all sporting in their mouths a feature which none of their toothed relatives possesses and which defines their nature as whales and many of the names that are associated with them – that briliant brush-like baleen.

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