Abstract
A new genus and species of extinct baleen whale †Toipahautea waitaki (Late Oligocene, New Zealand) is based on a skull and associated bones, from the lower Kokoamu Greensand, about 27.5 Ma (local upper Whaingaroan Stage, early Chattian). The upper jaw includes a thin, elongate and apparently toothless maxilla, with evidence of arterial supply for baleen. Open sutures with the premaxilla suggest a flexible (kinetic) upper jaw. The blowhole is well forward. The mandible is bowed laterally and slightly dorsally; unlike the Eomysticetidae, there are no mandibular alveoli, and the coronoid process is tapered and curved laterally. Jaw structure is consistent with baleen-assisted gulp-feeding. The age of early Chattian makes †Toipahautea a very early, if not the oldest named, toothless and baleen-bearing mysticete, suggesting that the full transition from toothed to baleen-bearing probably occurred in the Early Oligocene. Late Oligocene mysticetes vary considerably in jaw form and kinesis, tooth form and function, and development of baleen, implying a wide range of raptorial, suctorial and filter-feeding behaviour. More study may elucidate the function of jaws, teeth and baleen in terms of opportunist/generalist feeding, as in modern gray whales, versus specialized feeding. We here propose that early mysticetes, when transitioned from toothed to baleen-bearing, were generalists and opportunists instead of specializing in any forms of feeding strategies. In addition, two different phylogenetic analyses placed †Toipahautea either in a polytomy including crown Mysticeti, or immediately basal to the crown, and above †Eomysticetidae in both cases. Because the †Toipahautea waitaki holotype is an immature individual, it may plot more basally in phylogeny than its true position.
Highlights
The origin of baleen and microphagous feeding by cetaceans marks a major evolutionary breakthrough, leading to the emergence of the largest animal, the blue whale Balaenoptera musculus (Cetacea: Mysticeti)
The purpose of our cladistic analysis is to plot the position of a new archaic mysticete, OU 21981, rather than to resolve details of mysticete phylogeny
In spite of the vagaries of preservation, and some possibly immature morphology, we show below that OU 21981 is sufficiently informative to establish a new species with emphasis on distinct and diagnostic tympanoperiotic morphology
Summary
The origin of baleen and microphagous feeding by cetaceans marks a major evolutionary breakthrough, leading to the emergence of the largest animal, the blue whale Balaenoptera musculus (Cetacea: Mysticeti). Recent descriptions and interpretations of new fossil whales have greatly improved understanding of early mysticete evolution [1,2,3,4,5,6,7,8]. The extinct clades †Aetiocetidae and †Eomysticetidae help to understand transitional stages from toothed to baleen-bearing in mysticete evolution. The Oligocene record is not yet dense enough to show clear ancestor–descendant successions in species with teeth only, teeth-and-baleen and baleen-only [10]. The rostrum—typically with thin bones and open sutures—often does not preserve well except in concretionary specimens which, in turn, may be of demanding preparation. The specimen has well-preserved tympanoperiotic bones which, in Cetacea, provide useful phylogenetic signal and diagnostic power [7,11,12,13,14]
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