Friday, October 13, 2023

Did Cetothere Whales Go Extinct?

 The evolutionary history and relationships of whales has long fascinated scientists for decades. The fossil record of whales is deep and expansive with many bizarre bauplans (body-plans) that are unlike anything alive today. Presently whales can be divided into two broad taxonomic groups, the odontocetes (toothed whales, dolphins, and porpoises) and the mysticetes (baleen whales). The extant  mysticetes are traditionally divided into the following three taxonomic families, Balaenopteridae, Balaenidae, and Eschrichtiidae. Two additional families within the mysticeti clade are recognized, Eomystecidae and Cetotheriidae but both of these families are extinct and represented solely by fossils... Or are they?

Illustration of a Pygmy Right Whale Source: Wikipedia Commons

The Pygmy Right Whale Carpera marginata is an elusive mysticete found throughout the world's southern oceans. As the common name would imply, it was traditionally thought to be closely related to Right Whales (Balaena spp.), which belong to the family Balaenidae. Superficially Pygmy Right Whales do appear to be a Right Whale that decided to stop growing halfway through their pubescence. Looks however can be deceiving and the apparent relationship between the full-sized and the pygmy right whales is quite literally skin-deep. Ewan Fordyce and Felix Marx published a paper in 2013 re-assessing the skeletal morphology and taxonomy of Pygmy Right Whales and found something interesting. By comparing the skull and ear-bones of fossilized Cetotheres to those of Pygmy Right Whales they concluded that the Pygmy Right Whales were Cetotheres. 

Phylogenetic Tree of Extant Mysticetes. Note how the Pygmy Right Whale is the sister group to Balaenopteroidea and only distantly related to the true Right Whales (Balaenidae).
 Source: Wikipedia (note this phylogeny was made four years prior to this study and is subject to change)

While the shape and position of bony features is highly revealing of evolutionary relationships, morphology alone is an incomplete dataset. Genetic material such as DNA or other related proteins provide clearer and far more complete pictures of an organisms taxonomy. Luckily for fans of Cetotheres, genetic studies published this year provide further lines of evidence that their lineage may still persist to this day in the form of Pygmy Right Whales. 

It is incredibly important to note that the debate itself is still not settled as to whether or not Pygmy Right Whales are true Cetotheres or a lineage that diverged early during the evolution of  Balaenopteroidea and is nested within that clade instead. The article presents this evidence as "Putting the Debate to Rest" whereas the study it draws from is far more tentative in its conclusion as to whether or not Pygmy Right Whales represent the last of the Cetotheres or are a strange, persistent, and early offshoot of Balaenopteroidea. This kind of scientific journalism that presents phylogenetic datasets as solved/absolute disservice the public in two ways. Firstly, it is outright dishonest and misrepresents the work of the authors, giving the general population an overconfidence in our understanding of complex evolutionary relationships. It also harms the publics' understanding of the scientific process of developing taxonomic as these models of relationships are constantly changing with new data points and new statistical computational models.

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