Study Explores Link between Shark Nose Shape, Size and Sensitivity of Smell
Published:05 Dec.2022    Source:ScienceDaily
Sharks have reputations as "super smellers" that use olfaction to detect odors related to finding prey and mates, communicating with their own species and avoiding predators. Their olfactory system is unique because it is separate from the respiratory system, unlike humans. Sharks and other fish use gills to facilitate the uptake of oxygen, while two nares or nostrils on the shark's head take in odors from the environment. Despite general similarities among elasmobranch species olfactory systems, the morphology or structure of their olfactory organ, or "rosette," differs substantially. Located in their snouts, the multi-lamellar (layered tissue) rosette is covered with both non-sensory and sensory tissue that responds to distinct odor molecules in an aquatic environment. Differences in sharks' olfactory systems are of particular interest not only because of their reputation for having an incredible sense of smell but also because these remarkable animals have been around since before the dinosaurs. They somehow managed to thrive in every known marine habitat for millions of years -- their sense of smell may have been key to their success.
Researchers are the first to quantify olfactory organ morphology by examining rosette shape and other internal structures among a diverse set of shark species using dissections, phylogenetic comparisons, and a fairly new technique. Results reveal that the organs did not change in shape or number of lamellae throughout the life stages, suggesting that olfaction is a key sensory modality throughout the life of elasmobranch fishes.Overall, researchers found more lamellae in rosettes with an elongated shape than in organs with a short and wide shape. Phylogenetic analyses showed that 2D shape and lamellar count are critical to understanding rosette variations in unrelated species. Researchers also used in situ values of rosette volume and 2D shape from diceCT to assess the impacts of dissection on morphological measurements. Rosette measurements from dissected organs did not differ significantly compared to those from CT scans, supporting the validity of both methods.

Among the species studied included the bonnethead sharks (S. tiburo) with rosettes that are narrow and elongated; the common thresher sharks (A. vulpinus) and shortfin mako sharks (I. oxyrinchus), which share similarities in their rosettes: a shape that is almost as wide as it is long, a thicker raphe, fewer lamellae and wider interlamellar distances; and blacktip sharks (C. limbatus) and Atlantic sharpnose sharks (R. terraenovae) with rosettes that are intermediate to the two aforementioned groups. Other members of the hammerhead shark family have long, thin olfactory organs, similar to the bonnethead shark.