Newswise — Researchers have finally settled a decades-long dispute about the evolutionary origins of the pygmy right whale.
The smallest of the living baleen whales, it’s tank-like skeleton is unique, and its ecology and behaviour remain virtually unknown.
Because it is so unusual, the evolutionary relationships of the pygmy right whale (Caperea marginata) have long been a bone of contention.
In a study that settles the dispute, freshly published in Marine Mammal Science, a global team of scientists decoded the entire genetic makeup of Caperea, merging their discoveries with morphology and palaeontology.
Co-author Dr. Felix Marx, marine mammal curator at the Museum of New Zealand Te Papa Tongarewa, elucidates that the cranial structure of the pygmy right whale appears to be tailored for skim-feeding, a behavior in which the whale glides near the water's surface while feeding by keeping its mouth open.
"This closely resembles the behavior observed in the larger true right whale, prompting certain scientists to hypothesize a close relationship between the two species, hence their similar names. However, alternate perspectives suggest that the pygmy right whale shares a closer kinship with species such as the blue whale, which employ a different feeding strategy of engulfing large quantities of water to capture their food instead of skimming," he explains.
He was pleased to be able to exploit the power of genomics to elucidate the history of life.
"After a century and a half of adhering to anatomical conventions and enduring decades of controversy, genomic analysis has conclusively demonstrated that Caperea represents a unique lineage and is not genetically linked to right whales."
"Similar to river dolphins and sperm whales, Caperea stands as the solitary protector of a distinctive fragment of evolutionary heritage. It is not merely another peculiar right whale; rather, it genuinely represents the final survivor of a previously abundant family that wielded significant influence in the history of our planet," he explains.
Co-lead author Dr. Kieren Mitchell, from Manaaki Whenua - Landcare Research, emphasizes that fresh genetic insights frequently compel scientists to reevaluate the reasons behind the apparent similarities or differences among various animal species.
"When there is a discrepancy between DNA and anatomical evidence regarding the relationship between species, it typically suggests the existence of a more profound and captivating narrative awaiting discovery regarding their evolutionary trajectory," he remarks.
Co-author Dr. Nic Rawlence, Director of the Otago Palaeogenetics Laboratory, characterizes Caperea as a fascinating example of convergent evolution, a phenomenon in which unrelated species gradually develop similar traits as they adapt to comparable environmental pressures.
"Caperea has long been associated with right whales based on their outward resemblance, primarily due to similar feeding techniques. However, it is now likely that Caperea represents the final living descendant of an ancient lineage of whales known as cetotheres," he explains.
Co-lead author Dr. Ludo Dutoit, from Otago's Department of Zoology, expresses that with the confirmation of Caperea's position in the whale family tree, researchers can now delve into understanding the characteristics of the Caperea lineage and investigate the significant events that influenced its evolutionary journey.
Dr Marx agrees, adding that Caperea may be another example of how being ‘unusual’ helped save a lineage from extinction.
"River dolphins, it is believed, managed to survive the extinction that claimed their marine counterparts by colonizing freshwater habitats. Sperm whales endured while their toothed relatives vanished due to their specialization in deep-diving and suction feeding. Caperea, on the other hand, survived by adapting as a skim filter feeder, a trait that set it apart from most of its presumed extinct relatives," explains Dr. Ludo Dutoit.
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