The evolutionary relationships of the pygmy right whale (Caperea marginata), the smallest and most enigmatic of the living baleen whales (mysticetes), remain contentious. For 150 years, morphological analyses have allied pygmy right whales with right whales based on their similar skim filter feeding strategies and shared cranial features like a tall braincase, highly arched rostrum, and elongated baleen plates. By contrast, molecular and some anatomical evidence—e.g., the presence of a squamosal cleft, tympanic recess, and four-fingered flipper—suggest a closer relationship with rorquals and gray whales.

To resolve this long-standing debate, a recent study sequenced the genome of a stranded pygmy right whale from South Australia. The results align with findings from a separate European research group, confirming that pygmy right whale is related to rorquals. The resemblances between pygmy right and right whales are now attributed to convergent evolution in feeding strategies rather than genetic affinity.

The ancient ancestry of pygmy right whales further complicates its evolutionary history. Molecular dating estimates suggest that pygmy right whale diverged from other whales at least 14 million years ago, but the oldest recognizable fossils are only 10 million. This fossil gap raises the possibility that pygmy right whale may have emerged from the cetotheriids, an ancient whale family previously considered extinct. This challenges the traditional grouping of pygmy right whales with right whales and prompts a re-evaluation of anatomical data sets to account for convergence effects.

Future research efforts may focus on new fossil discoveries or examining ancient proteins to gain additional insights into pygmy right whale’s evolutionary origins. While DNA degrades after approximately one million years, proteins can persist for extended periods, potentially testing hypotheses such as the pygmy right whale’s potential cetotheriid origin rigorously. Integrating genomic analysis, anatomical studies, and the exploration of new evidence holds promise for unraveling the enigmatic evolutionary relationships of the pygmy right whale and shedding light on its distinct characteristics within the baleen whale lineage.

The novel research was published in Marine Mammal Science.

References

Dutoit, L., Mitchell, K. J., Dussex, N., Kemper, C. M., Larsson, P., Dalén, L., Rawlence, N. J., & Marx, F. G. (2023). Convergent evolution of skim feeding in baleen whales. Marine Mammal Science, mms.13047. https://doi.org/10.1111/mms.13047