Modern cetaceans, including dolphins and whales, among others, are well adjusted for marine life. The blubber has functioned as insulators, and they have fins for propelling and steering.
Also, these cetaceans are sporting a distinctive nasal passage type. Specifically, this type is rising at an angle relative to the palate, and it goes out at the top of the head as a blowhole.
A Phys.org report specified this is an appropriate "adaption for an air-breathing animal in the water." However, as embryos, the nasal passage of a cetacean animal begins in a position more common in mammals parallel to the palate and leaves at the rostrum.
It has been a long-time puzzle for cetacean experts over how the nasal passage switches during embryonic and fetal growth from a palate-parallel passage to an angled orientation that terminates in a blowhole.
Solving the Puzzle
According to postdoctoral researcher Rachel Roston from the University of Washington School of Dentistry, this shift in orientation and position of the nasal passage in modern cetaceans is a growth process that's different from any other mammal.
She added it's interesting to see what parts stay connected, what parts are shifting orientation, and how they might work together through a growth process to result in such a change.
A new study, Different transformations underlie blowhole and nasal passage development in a toothed whale (Odontoceti: Stenella attenuata) and a baleen whale (Mysticeti: Balaenoptera physalus), by Roston and V. Louise Roth, and published in the Journal of Anatomy, has shed light in this process.
By gauging anatomical information of the pantropical spotted dolphins' fetuses and embryos, the study authors determined the key anatomical changes that flip up the nasal passage's orientation.
3 Phases of Growth
Roston, the study's lead author who started this research as a doctoral student at Duke, said they discovered three phases of growth, mainly in the head, explaining the manner nasal passage is shifting in orientation and position.
In the early phase, parallel at first, the palate and the nasal passage turn out to be separated as the area between them is growing into a triangle shape. This phase starts during embryonic growth following face formation, which, for the pantropical spotted dolphin, is in the first two months from fertilization.
The lead author explained, the three phases are not unfolding in a step-by-step process, but rather, they are overlapping with each other temporarily.
Such phases represent unique growth transformations, putting together, shifting the nasal passage over the head, the lead author continued explaining.
Whales and Dolphins Compared
To compare, the researchers gathered data from eight fin whale fetuses, and, at the National Museum of Natural History, they discovered substantial differences between the said fetuses and the pantropical spotted dolphin.
As indicated in the research, the skull is folded in an area in the back close to where it connects to the vertebral column in fin whales. Meanwhile, in the pantropical spotted dolphin, the fold is positioned close to the skull's center.
The model developed by the two authors could inform how scientists view the evolution of cetaceans. A similar US News Mail report said these creatures started evolving from "four-legged, land-dwelling mammalian ancestors" with a nasal passage that's parallel to the palate over 50 million years back.
As cetacean animals evolved, the blowhole progressively migrated from the tip of the snout to the snout's back part and then slowly up to the skull's top part.
Related information about pantropical spotted dolphins is shown on Feather Chelle's YouTube video below:
Check out more news and information on Whales in Science Times.
