National Geographic

There’s Something about Caperea marginata

Of all the baleen whales in the sea, the pygmy right whale is arguably the most mysterious. Technically-known as Caperea marginata, this 20-foot cetacean is rarely seen in its South Ocean habitat. And even when a stranded specimen turns up, the whale continues to vex scientists. Molecular and anatomical data conflict about just what sort of baleen whale Caperea marginata actually is, and the frustrating marine mammal has often been regarded as the sole member of its own subfamily. Yet University of Otago whale experts Ewan Fordyce and Felix Marx have proposed a startling solution to the question of the pygmy right whale’s identity.

Zoologists have long known that “pygmy right whale” is a misnomer. As Fordyce and Marx point out in the paper, Caperea marginata “differs from right whales … in its external form and osteological features in all parts of the skeleton.” The small, southern whale just happens to superficially resemble the larger, better-known right and bowhead whales. Indeed, as Fordyce and Marx found when they reviewed a “wealth” of Caperea marginata in New Zealand museum collections, the whale appears to be a cetothere – a variety of baleen whale that was thought to have gone extinct about 2 million years ago.

In particular, the cryptic whale has two distinct ear characteristics that have are only seen among a recently-extinct group of whales called herpetocetines, themselves part of the larger cetothere group. Indeed, when Fordyce and Marx ran an analysis of whale relationships drawing from 166 traits among 23 taxa, Caperea marginata fell out among the cetotheres. A switch in our understanding has resurrected a lineage of whales that was thought to have entirely disappeared.

When cetotheres first evolved is a sticky problem. Their fossil record goes back at least 12 million years, Fordyce and Marx note, but, based on estimates from molecular data, they may have emerged even earlier. Future fossil finds will test the timing estimates. Still, based upon the divergence of other cetotheres, Fordyce and Marx propose that the Caperea marginata lineage split from its relatives around 9 million years ago. Given the general lack of Caperea fossils, they expect that the ancient whales also inhabited the southern hemisphere, where the marine record is patchy and not as well-studied.

But what did Caperea marginata survive while its relatives perished? A significant clue, Fordyce and Marx suggest, may be that the rare whale is a case of evolutionary convergence with true right whales. Caperea marginata didn’t look like other cetotheres and presumably had different habits. This shift in diet and behavior away from its close relatives might have allowed the marine mammal to survive. Even though Fordyce and Marx have discerned the place of Caperea marginata in the whale family tree, paleontologists and zoologists are faced with the new enigma of how this exceptionally rare whale persisted through the climatic and oceanic changes that wiped out its kin.

[Check out this video of a Caperea marginata dissection, featuring Ewan Fordyce.]

Reference:

Fordyce, R., Marx, F. 2012. The pygmy right whale Caprea marginata: the last of the cetotheres. Proceedings of the Royal Society B. http://dx.doi.org/ 10.1098/rspb.2012.2645

There are 7 Comments. Add Yours.

  1. Mike Keesey
    December 20, 2012

    Very cool. Note that Cetotheriidae Brandt 1872 has priority over Neobalaenidae Miller 1923, but Neobalaeninae Miller 1923 has priority over Herpetocetinae Steeman 2007.

  2. Boesse
    December 20, 2012

    Mike – in the paper, the analysis by Fordyce and Marx doesn’t include Caperea within the Herpetocetinae. They defined Herpetocetinae as the Herpetocetus + Nannocetus clade; Caperea came out as the sister taxon to the Herpetocetinae, and they retained it in the Neobalaeninae, which is a good conservative taxonomic decision on their part.

  3. Nick
    December 22, 2012

    Hi Bobby (@Boesse), how does their proposal line up against molecular analyses of cetacean phylogeny? I don’t have their paper yet sadly due to no access and I’m not super familiar with molecular phylogenies of Cetacea, but I just wondered if this confirmed or went against the existing molecular topology and how well supported those topologies were from different lines of evidence.

    Nick

  4. Nick
    December 23, 2012

    To answer my question, and as pointed out in the paper itself (having just received it courtesy of Marx), this topology is pretty much 100% congruent with the largest molecular analyses published for cetaceans.

    McGowen et al. 2009. Divergence
    date estimation and a omprehensive molecular tree of extant cetaceans.Mol. Phylogenet. Evol.53, 891–906.
    Geisler et al. 2011. http://www.biomedcentral.com/1471-2148/11/112

  5. Boesse
    December 23, 2012

    That’s pretty much what I was going to say. In most morphological analyses, the Cetotheriidae is occupies an intermediate position between balaenids and balaenopteroids – which is the position of Caperea in nearly all molecular analyses.

  6. Nick
    December 23, 2012

    How affected do you think prior morphological analyses would be by the inclusion of more basal mysticetes towards recovering the topology found in molecular analyses?

    In areas where I am currently working (paper submitted), I found character construction and taxon selection can be highly responsible for influencing noncongruence.

  7. Boesse
    December 23, 2012

    A prior analysis by Marx (2011) included all described toothed mysticetes as well as many other toothless mysticetes. The topology isn’t that different; most of the changes in topology are due to the addition of new characters, new observations on character states, and reinterpetation/redefinition of previously established characters. I wrote a little bit about it here:

    http://coastalpaleo.blogspot.co.nz/2012/12/evolution-of-pygmy-right-whale-caperea.html

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