One Of the Largest Aquatic Mammals On Earth

Whales are regarded as one of the largest aquatic mammals on Earth. However, at one point in their evolutionary history, they were land-based animals. Modern-day cetaceans evolved 55 million years ago from terrestrial animals that resided near brackish estuaries. In order for this shift to occur, whales had to change every part of their anatomy. Additionally, the decline of whales has likely negatively altered the structure and function of the ocean, suggesting that whales play a prominent role in the marine ecosystem.

One of the features that whales had evolved is the head. The nostrils, now known as blowholes, had moved from the front of the skull protruding out of the face, to the top of the skull. This is so cetaceans would not have to fully breach the water in order to breathe, and only surface a small portion of their body. The vapor that comes out of blowholes, or blow, differs for each type of cetacean and can be used to determine the health of the individual.

According to Woods Hole Oceanographic Institution (WHOI), there is a shared respiratory microbiome which helps maintain a healthy immune system.

The rostam, or the upper jaw, elongated as their food source changed. Cetaceans are divided into two different suborders –  Mysticeti or baleen whales, and Odontoceti or toothed whales. The development of fatty tissues on the rostam, or the melon, focuses sound and supports the ‘pan bone’ theory of transmission of ultrasonic signals (echolocation) in toothed whales. The path of sound reception in baleen whales is relatively unknown, but they do have bony skull connections to a membrane which connects to an external auditory canal.

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Another adaptation that cetaceans evolved is a streamlined body shape, which reduces friction. Moreover, whales evolved a stronger vertebral column to support the tail, which has a paddle-like shape at the end in order to further aid underwater locomotion. The flukes are thick in the front, and thinner on the back, and create a hydrofoil shape that reduces drag. The cetacean skin itself, by absorbing the energy it creates and resisting turbulence, and assisted by the rounded body shape make laminar flow possible, which is ideal for efficient swimming.

The ability for a whale to stay submerged underwater for long periods of time, never exhaling or inhaling for more than four times in a minute, lies not in the power or size of their lungs, but the ability to store oxygen in the muscle and in the blood. Larger lungs do not necessarily mean longer retention of oxygen, as water pressure increases substantially with depth, and collapse at a depth of 100m. Whales have evolved to have a greater amount of hemoglobin in the blood which carries dissolved oxygen to the brain and body, and muscles with high amounts of myoglobin to store oxygen for diving. In addition to adapting for a marine ecosystem, whales have now shown that they are important to the overall well-being of the ecological community. Whaling, or the hunting of whales, was historically done for whale meat, oil from whale blubber, baleen, and spermaceti from the head cavity of sperm whales that was as a lubricant. These factors facilitated the rapid decline in the whale population due to overhunting.

According to a fact sheet published by the World Wildlife Fund in 2016, whales have been shown that not only have an intrinsic cultural and biodiversity worth, but they also play a significant role in maintaining healthy marine ecosystems. It is estimated that around 2.9 million whales were killed in the 20th century. Previously, it was thought that higher numbers of whales would lead to the majority of fish being hunted little would be left for human consumption. However, as the number of whales declined, so did the amount of fish and krill. Researchers discovered that whale fecal matter is rich in iron and nitrogen, which are scare in surface ocean waters yet crucial for phytoplankton growth.

The falling phytoplankton and the limiting nutrients are transported to the photic zone because many whales feed in deeper waters and release their waste at the surface – this allows for the food source for fish and krill to flourish. This enhancement of ocean productivity also combats climate change, as carbon dioxide from the air is absorbed by the plankton where it eventually sinks to the ocean floor and remains out of circulation for thousands of years. It was estimated that millions of tons of carbon were removed from the atmosphere every year because of whales. In addition to low fish populations, ecosystem collapse could occur. In the North Pacific, the absence of baleen whales led killer whales that previously fed on large whales like the baleen, to switch prey. Killer whales began to hunt smaller animals, specifically sea otters. Sea otters control urchin populations, which left unchecked can destroy kelp beds. These kelp forests act as nurseries for many fish species, and in turn, can have significant impacts on commercial fish stocks.

In addition, when whale carcasses sink, they too transport carbon and other organic matter to the sea-floor. Dead whales are among the most nutrient-rich of all marine detritus. Decomposing whale carcasses create “mini-ecosystems” with more than 200 species inhabiting a single skeleton. They not only transport nutrients vertically, but horizontally as well – from highly productive temperate and polar feeding grounds to nutrient-poor tropical breeding grounds, where they excrete nitrogen in their urine, and contribute other nutrients through their placentas and carcasses. Cetaceans were once terrestrial land mammals but have evolved to be one of the most important aquatic species. For this shift from four-legged to free-swimming to ensue, the whale underwent many anatomical changes.