Study Investigates How Whales And Dolphins Developed Blowholes
When it comes to creatures that live in an aquatic world, most of them can extract the oxygen they need to survive directly from the water using gills. However, some notable exceptions exist with mammals such as whales and dolphins that have to breathe air just as humans do. Researchers at the University of Washington have investigated modern cetaceans, a group that includes dolphins, whales, and porpoises.
These creatures are all well adapted to aquatic life with blubber to insulate them and fins to help propel and steer in water. They have a unique nasal passage that rises at an angle relative to the roof of the mouth and exits at the top of the head as a blowhole. As embryos, the nasal passage of cetaceans starts in a position that's more typical of mammals which is parallel to the pallet and exiting the tip of the snout.
Experts in the development of these creatures have long wondered how the nasal passage switches during embryonic and fetal development to a pallet-parallel pathway terminating a blowhole. The change in position of the nasal passage in cetaceans is a process unlike what occurs in any other mammal. In their research, scientists measured anatomical details of embryos and fetuses of pan-tropical spotted dolphins.
By measuring those anatomic details, the researchers determined the key anatomical changes that flip the orientation of the nasal passage up. Study lead author Rachel Roston says the team discovered there are three phases of growth, primarily in the head, explaining how the nasal passage shifts in position and orientation.
The first phase is initially parallel to the roof of the mouth. The nasal passage becomes separated as the area between it, and the mouth grows into a triangular shape. In the second phase, the snout grows longer at an angle to the nasal passage, further separating the nostrils from the tip of the snout. In the third phase, the skull, head, and body become more aligned, rotating the nasal passage up, nearly vertically, to the relative body axis. Interestingly, the researchers found that the three phases of growth don't unfold in a step-by-step manner. Rather they overlap with each other. However, the development process is different for other cetaceans.