Anatomy of nasal complex in the southern right whale, Eubalaena australis (Cetacea, Mysticeti)

Abstract

The nasal region of the skull has undergone dramatic changes during the course of cetacean evolution. In particular, mysticetes (baleen whales) conserve the nasal mammalian pattern associated with the secondary function of olfaction, and lack the sound-producing specializations present in odontocetes (toothed whales, dolphins and porpoises). To improve our understanding of the morphology of the nasal region of mysticetes, we investigate the nasal anatomy, osteology and myology of the southern right whale, Eubalaena australis, and make comparisons with other mysticetes. In E. australis external deflection surfaces around the blowholes appear to divert water off the head, and differ in appearance from those observed in balaenopterids, eschrichtiids and cetotherids. In E. australis the blowholes are placed above hypertrophied nasal soft tissues formed by fat and nasal muscles, a pattern also observed in balaenopterids (rorqual mysticetes) and a cetotherid (pygmy right whale, Caperea marginata). Blowhole movements are due to the action of five nasofacial muscles: dilator naris superficialis, dilator naris profundus, depressor alae nasi, constrictor naris, and retractor alae nasi. The dilator naris profundus found in E. australis has not been previously reported in balaenopterids. The other nasofacial muscles have a similar arrangement in balaenopterids, with minor differences. A novel structure, not reported previously in any mysticete, is the presence of a vascular tissue (rete mirabile) covering the lower nasal passage. This vascular tissue could play a role in warming inspired air, or may engorge to accommodate loss of respiratory space volume due to gas compression from increased pressure during diving.

The ethmoid and presphenoid of cetaceans

“…The cribriform plate and the ethmoturbinates are responsible for olfaction, a key sensory modality for most mammals. There is no doubt that the cribriform plate and the ethmoturbinates are present in baleen whales, as has already been mentioned by several authors (e.g., Flower, ; Edinger, ; Breathnach, ; Godfrey et al, ; Buono et al, ), indicating the persistence of the olfactory sense in modern mysticetes, although the presence or absence and the size of the olfactory bulb may be variable between, and even within, species (Langworthy, ; Ries and Langworthy, ; Breathnach, ; Jansen and Jansen, ; Thewissen et al, ). Because mysticetes are not known to echolocate (Uhen et al, ), the olfaction may still play an important role for detecting food such as plankton swarms, like procellariiform birds and seals do (Nevitt, ; Kowalewsky et al, ; Ichishima, ; Thewissen et al, ).…”

A Comparison of Common Hippopotamus (Artiodactyla) and Mysticete (Cetacea) Nostrils: An Open and Shut Case

“…As in common hippos, these are most likely the lateral members of the naso‐labial group. Muscles that move the outer edge of the blowholes are likely the dilator naris muscles, as noted in southern right whales (Buono et al, ). No muscle was noted that could close the blowholes (e.g., constrictor naris).…”

“…References for nostril positions: 1 Buono et al (), 2 Berta et al (), 3 Clifford and Witmer (), 4 Eshra and Badawy (), 5 Evans and Lahunta (), 6 Question marks note where no information is available.…”

Reduction of olfactory and respiratory turbinates in the transition of whales from land to sea: the semiaquatic middle Eocene Aegyptocetus tarfa

“…; Buono et al. ). The fossil record shows that whales evolved from terrestrial Artiodactyla (Gingerich et al.…”