Development and Physiological Degradation of Tooth Buds and Development of Rudiment of Baleen Plate in Southern Minke Whale, Balaenoptera acutorostrata.

Suction feeding preceded filtering in baleen whale evolution

“…This scenario avoids potential problems of functional interference between a working dentition and incipient baleen , and explains how teeth could have been lost without impacting on foraging success. Further, a loss of functional teeth prior to the origin of baleen coincides with evidence of foetal development from extant mysticetes, which shows that baleen growth only initiates once the tooth buds have already started to degrade (Ishikawa and Amasaki, 1995;Karlsen, 1962). It is possible that teeth and baleen nonetheless co-occurred in some archaic chaeomysticetes, as shown by eomysticetids bearing shallow alveoli and, possibly, teeth (Boessenecker and Fordyce, 2015); however, the dentition in these taxa was already reduced.…”

“…4). An aetiocetid baleen rack would have been closely associated with the teeth, as judged from the position of the palatal foramina in A. weltoni and the juxtaposition of the rudimentary teeth and developing baleen in extant mysticete foetuses Ishikawa and Amasaki, 1995). As a result, aetiocetid baleen would have been constantly disturbed by mandibular contact.…”

Immunohistological Distributions of Fibronectin, Tenascin, Type I, III and IV Collagens, and Laminin during Tooth Development and Degeneration in Fetuses of Minke Whale, Balaenoptera acutorostrata.

“…Basal membrane between the dentin and the enamel organ was still formed, but there was little specific staining of those ECMs in the dental papilla and the surrounding mesenchyme. Ishikawa and Amasaki [5] reported disappearance of odontoblasts in the dental papilla without formation of ameloblasts at the degenerating stage of tooth bud of fetal minke whales. On the other hand, positive stainings for TN, C1 and C3 were observed at the forming of the baleen plate germ.…”

“…The resorption of the degenerating tooth bud in the minke whale resembles that of the deciduous teeth of diphyodont animals, i.e., odontoclast and macrophage absorb deciduous teeth [5,6]. It is interesting that the whole tooth bud of the minke whale is physiologically absorbed before birth, whereas only the root of the deciduous teeth of other mammalian species is partly absorbed after birth [8,9].…”

“…However, it is known that some baleen whales have temporary tooth buds on both the upper and lower jaws during their fetal period [4,6]. Karlsen [6] and Ishikawa and Amasaki [5] described that the tooth bud of baleen whale generally developed to the bell stage with predentin or a part of dentin, but never generated enamel. Both the neogenerating baleen plate germ and degenerating tooth bud co-existed on the upper jaw in the middle fetal period of the minke whale.…”