| Summary: | New Zealand rocks have yielded numerous fossil cetaceans, both odontocetes and mysticetes. Many fossil cetaceans in New Zealand come from the Waitaki valley aged around the Oligocene and Miocene. Mysticetes in New Zealand include the basal eomysticetes to crown mysticetes the ancestors of today’s baleen whales. OU22404 is a crown mysticete recovered from the Waitaki valley from the Oligocene-Miocene boundary. Plicogulae is a group of crown mysticetes the include modern rorquals and the almost extinct Cetotheriidae. OU22404 and a few other taxa, including Mauicetus and Horopeta, are basal to this group. Called stem Plicogulae, they have often occupied an unstable position within mysticete phylogeny. With the addition of OU22404 the phylogeny becomes more stable. OU22404’s anatomy shows how modern feeding methods developed. The skull shape has features not found in older mysticetes, such as adaptations to allow mandible rotation. OU22404 may have employed an early form of lunge feeding as well as a generalised form of feeding. A stepwise transition from eomysticetes to Balaenopteridae can be followed using OU22404. Around 23-17 Ma mysticetes disappeared from the global fossil record. The assemblages of mysticetes were different before and after this gap. OU22404 is dated to just after the start of this “dark age” and shows how modern mysticetes developed during this time.
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