Whales are among the most fascinating and diverse animals on the planet. They belong to a group of mammals called cetaceans, which includes dolphins and porpoises.
Cetaceans have a long and complex evolutionary history, dating back to about 50 million years ago, when they diverged from their land-dwelling ancestors and adapted to life in the water.
However, not all cetaceans are equally well-known or understood.
One of the most mysterious and elusive species is the pygmy right whale, which has puzzled scientists for decades with its unique features and uncertain origins.
In a recent study, researchers have finally settled this whale of a debate by using genomic, morphological, and paleontological evidence.
What is the pygmy right whale?
JOSEPH PREZIOSO/AFP via Getty Images
The pygmy right whale (Caperea marginata) is the smallest of the living baleen whales, measuring only about six meters in length and weighing up to 3.5 tons, as per Phys.org.
Baleen whales are cetaceans that feed by filtering plankton and small fish from the water using comb-like structures called baleen plates in their mouths.
The pygmy right whale is found in temperate and subpolar waters of the Southern Hemisphere, but its ecology and behavior remain virtually unknown.
It is rarely seen at sea and seldom strands on shore, making it one of the least studied whales in the world.
The pygmy right whale is also remarkable for its tank-like skeleton, which is unlike any other living cetacean. It has a short and blunt head, a narrow and arched lower jaw, a curved dorsal fin, and a V-shaped blowhole.
Its skull shape seems to be adapted for skim-feeding, where a whale swims at the water's surface with its mouth open to collect food.
This is very similar to the larger true right whales, such as the North Atlantic right whale (Eubalaena glacialis) and the Southern right whale (Eubalaena australis), which also have arched lower jaws and skim-feed on plankton.
How is the pygmy right whale related to other whales?
Because of its resemblance to the true right whales, some scientists have long believed that the pygmy right whale is closely related to them, hence their similar names.
However, others have argued that the pygmy right whale is more closely related to species like the blue whale (Balaenoptera musculus) and the humpback whale (Megaptera novaeangliae), which belong to a different group of baleen whales called rorquals.
Rorquals have slender and streamlined bodies, long and pointed lower jaws, dorsal fins of various shapes, and U-shaped blowholes.
They also feed by gulp-feeding, where they take big mouthfuls of water and then expel it through their baleen plates.
To resolve this controversy, an international team of researchers sequenced the complete genome of the pygmy right whale, using DNA extracted from a skin sample collected from a stranded specimen in New Zealand in 2012.
They compared the genomic data with those of other living cetaceans, as well as with morphological and paleontological information from fossils.
They found that the pygmy right whale is not related to either the true right whales or the rorquals, but rather belongs to a distinct lineage that diverged from other baleen whales about 25 million years ago.
This lineage is called cetotheres, which includes several extinct species of medium-sized baleen whales that lived from the Oligocene to the Pleistocene epochs.
What does this discovery mean for whale evolution?
The discovery that the pygmy right whale is a living cetothere has important implications for understanding the evolution of baleen whales and their feeding strategies, as per University of Otago.
It shows that skim-feeding evolved independently in both cetotheres and true right whales, as a result of convergent evolution.
This is when two unrelated groups of organisms develop similar traits due to similar selective pressures.
It also shows that cetotheres were more diverse and widespread than previously thought and that they survived longer than their fossil record suggests.
The researchers suggested that the pygmy right whale may have survived by occupying a different ecological niche than other cetotheres, which were mostly larger and more coastal.
The pygmy right whale may have adapted to feed on smaller prey in deeper and more offshore waters, avoiding competition and predation from other whales.
The researchers also proposed that the pygmy right whale may have retained some ancestral features of baleen whales, such as its curved dorsal fin and V-shaped blowhole, which are otherwise lost or modified in other groups.
The pygmy right whale is therefore not just another weird right whale it is truly the last survivor of an otherwise lost family that once played a much bigger role in Earth's history. It is a living fossil that reveals the hidden diversity and complexity of whale evolution.
