This project has resulted in the discovery of several new species of extinct baleen whales (Mysticeti) from Antarctica, Australia, Peru and Europe, all of which were placed into comprehensive phylogenetic analyses combining anatomical and genetic data. In addition, we produced new observations on pygmy right whales, a rare and enigmatic family represented today by just a single species (Caperea marginata). These included descriptions of (i) their auditory anatomy, to determine hearing abilities and evolutionary relationships; (ii) a new fossil from Australia, cementing the likely origin of the family in the Southern Hemisphere; and (iii) the first and only fossils from the Northern Hemisphere.
To test whether extant animal behaviour can inform evolutionary patterns, we produced a comprehensive review of the feeding behaviours of living marine mammals. From this emerged a novel framework in which feeding strategies form an evolutionary continuum, leading from semi-aquatic to raptorial, suction, and - ultimately - filter feeding. This continuum arises from a variety of physical and biological factors, and provides an independent source of evolutionary data that can be tested against the fossil record. Applied to baleen whales, our framework suggests that ancient mysticetes first transitioned from tooth-based raptorial to suction feeding, and only later acquired the ability to filter feed on small prey using baleen.
Fossil data provide direct evidence of feeding evolution, as shown by our description of an exceptionally preserved specimen of the cetotheriid Piscobalaena nana, and our report of horizontal wear features in a member of an archaic whale family (Aetiocetidae) previously thought to possess both teeth and baleen. Horizontal wear indicates front-to-back transport of food items inside the mouth, which is more consistent with suction than raptorial or filter feeding. Similar wear occurs in several specimens from Australia, and suggests that suction may indeed have preceded the evolution of filter feeding in whales. This pattern is consistent with our behavioural framework, and further supported by the apparent absence of baleen in the archaic toothed mysticete Llanocetus.
One prominent hypothesis holds that early whales strained prey from water using complex teeth, as seen in living filtering feeding seals. To test this idea, we developed a novel technique to measure tooth shape and sharpness. We found that the teeth of filter feeding seals are blunt, with wide notches that facilitate the passage of water. By contrast, those of early whales are sharp, with narrows notches that restrict water flow. We conclude that early whales did not filter with their teeth, and instead used them to grasp and slice larger food items. Teeth were later lost during an intermediate phase of suction feeding (consistent our behavioural framework), following which baleen evolved as a way to trap small prey.
Finally, we investigated the relationship between feeding evolution and mysticete body size. Our analysis of the archaic mysticete Llanocetus shows that whales grew large more than once during their evolutionary history, even before the origin of baleen. In general, however, larger body size appears to have been associated with the emergence of filter feeding, as in other marine vertebrates. Following a turnover event around 20-23 million years ago, archaic toothed mysticetes disappeared, and only filter feeding species remained. Nevertheless, most whales remained comparatively small, perhaps around 6 m long. New fossils from Italy and Peru show that true gigantism arose slowly, but steadily, from this time onwards, and finally became dominant around 3 million years ago, when most ‘small’ mysticetes went extinct in response to Northern Hemisphere glaciation.
