The Evolutionary Crisis Of Marine Mammals

The ancestors of the whales transitioned from being land bearing animals to becoming animals that live in the ocean. While the original ancestor of whales lived on land as it evolved it was able to start to enter the water until it struggled more to get on land than to get in water until the whale’s ancestors began to live exclusively underwater.

The evolutionary path of a whale is a fascinating process of a terrestrial mammal that evolves into a marine mammal. This evolutionary path started with one of the earliest ancestors called “Pakicetus”. A Pakicetus was discovered to be a land animal with four legs that had teeth as carnivores. It skull structure was long, but this organism didn’t look like any marine animal. The scientist then discovered that on the skull’s ear region it was surrounded by a bony wall. This feature on an organism only was distinct from one type of species, scientist discovered that this animal “Pakicetus” was an ancestor of a whale. By comparing the early whales Pakicetus to the next generation of ancestors Ambulocetus, the Ambulocetus whale looks more like

The ocean is a very difficult place to live. The animals living in the seas have to handle every moment with finding food, and protecting themselves from predators. There are many ways of hiding, defending, and feeding, and every different technique has advantages for different animals. Adaptations for Survival in the Sea explores some of the adaptations used by various sea creatures to survive.

This assignment will look at the fossil record of whales as an example of empirical evidence for evolution and is inspired by the article “Land-living ancestors of whales” from the “Berkeley: History of Evolutionary Thought” resource for Module 1.

Evolution is one of the most important factors when looking at history. A crucial moment in evolutionary process is speciation. Fortunately, we have the fossil record of a transitional species called tiktaalik. Tiktaalik was the transitional species of sea creature that would evolve into a land creature. It was found on Ellesmere Island in the Canadian arctic and is believed to be around 383 million years old (Class Lecture).

In marine mammal biology a large portion of the study is dedicated towards the study of adaptations to the marine environment. By comparing the anatomy between marine mammals and terrestrial mammals scientists can better understand evolutionary history of how these two categories of mammals diverged from one another. The purpose of this lab was to study the anatomy of different marine and terrestrial mammals and compare their similarities and differences in homologous traits and how adaptations were made specifically for marine mammals to survive the aquatic environment. To accomplish this bones of different species of animals were studied since these structures serve as the basis for comparison across species as well as an indicator of each animal’s individual morphology and physiology. A standard measurement protocol for bones of particular regions of the skeleton was established with emphasis on length versus width ratio as well as it’s overall size relative to its more complex features, i.e. humerus length versus hand length.

Trego works at the Conservation Ecology Lab at San Diego State University in California. She reported her team’s early findings on December 14, at the Society for Marine Mammalogy meeting in San Francisco.

The first ancestors of whales lived on land. They had feet instead of fins and quite often had individual toes. From their fossils we can gather that they spent most or all of their time on land. Mesonychids and Pakicetus more resembled dog or wolves then whale for they rarely went in the water, only near the shores for food. Whereas Ambulocetus was more like a crocodile; swimming in the water easily and basking on the shores. A few million years later the wales closer relatives appeared. Basilosaurus and Zygorhiza fossil were found near or in water. From this we can conclude that they lived in the shallow water of the oceans much like whales today.

Louis Herman- University of Hawaii- Kewalo Basin Marine Mammal Laboratory- Phoenix and Akeakamai- since 1979

The earliest whales were land animals with long skulls and carnivorous teeth. Analysis of whale skulls showed major morphological changes, including changes to the skull size, shape, teeth, and nostrils. Fossil evidence shows that the trait of interest, the nostrils, can be found on fossils of the earliest whales, dating back to about 50 million years ago. Evolution occurred multiple times since then, each time resulting in the nostrils migrating further back on the skull. Eventually, the pair of nostrils positioned itself right on top of the head. These nostrils are the blowholes we see positioned on top of modern whales today. In addition, another momentous change in the nostrils occur when order Cetacea splits into Mysticetes and Odontocetes. Suborder Mysticetes

Our delicate eco-system is struggling to maintain it’s complex equilibrium. The precarious state of our oceans are largely attributed to the climate changes that are on going throughout earth. Along with consistently rising global temperatures come many devastating consequences. Our atmosphere is not the only aspect of our environment that is heating. Global warming is melting polar ice caps, raising water levels in our oceans, and releasing carbon that has been trapped in ice for thousands of years. The warmer air temperature is heating the surface waters of the ocean and creating more frequent and more powerful storms. These warmer surface waters are being pushed under in the ocean conveyor belt and the overall affect is a rise in overall ocean water temperatures. Climate change has been estimated to effect 88% of cetaceans and endangering nearly 21%. More specifically, each of these changes have harmful, potentially deadly and lasting effects on Bottlenose Dolphins. Ultimately causing dangerous and toxic conditions leading to an increase of dolphin strandings and death.

Did you know that the sea floor is also breeding grounds for sea turtles? These heavy chain nets crush the turtles’ shells. Another mammal also dwells down at the ocean floor. Porpoises and dolphins often get caught in the trawlers’ nets despite the fact that the fishers are only trying to catch scallops, oysters, clams, crabs, sea cucumbers and other small creatures. These mammals get tangled in the nets and drown or get seriously injured. Did you know that dolphins, sea turtles, and porpoises are endangered? If we don’t protect these species they may become extinct.

Manatees (order Sirenia, genus Trichechus) are the source folklore and possess many unique characteristics. With three recognized species, manatees (along with their relative, the dugong) also possess a unique range, limited mostly to coastal bays and waterways of the warm southern coasts. They are also the world’s only herbivorous marine mammals, and they have a highly-developed mouth with bristles. Although much-loved, the manatee population is currently under threat

Some evolutionists claim whale ancestors were originally land mammals. Though many people refute this claim, there is much evidence. First is the Indohysus. The Indohysus was discovered to share a thickened bone that helps with hearing underwater with modern whales. The Indohysus also had denser bones, which meant it was partially aquatic. Next is the Pakicetus; the Pakicetus also had very dense bones, indicating it was semi-aquatic. The Pakicetus was similar in structure to a wolf, but the skull had eye sockets that were adapted for looking upwards, most likely at objects or animals floating above it. The Ambulocetus was found to have reduced limbs and an elongated skull and reduced limbs; it most likely spent most of its time in the water.

It is important that we continue to research known harmful anthropogenic sounds and their effects on cetaceans to limit further damage, and to research other sources of noise due to humans and their potential effects to prevent future harm. Through research, it is shown that various noise pollution caused by humans can have detrimental effects on cetaceans such as harbor porpoises, bottlenose dolphins, killer whales, and Cuvier’s beaked whales. Shipping, windfarm construction, and sonar can cause temporary or permanent hearing threshold changes, which can result in decreased foraging ability and communication ability. Shipping has been seen to decrease foraging time and cause acoustic masking. Sonar can cause death due to strandings and lesions. These all add up to show that, overall, noise pollution by humans has a serious effect on the quality of life for cetaceans. It is also important to recognize that absence of a detected reaction does not mean that there is no impact on these cetaceans. It is possible that noise pollution can cause physiological and psychological responses without any external symptoms we can detect. It may be important to develop methods to observe these more subtle reactions to noise pollution that may impact cetacean’s way of life. It is important that humans realize the full extent of their effect on marine life and create measures to prevent more harm. Noise pollution’s effect on cetaceans affect not only these species, but the other marine life they interact with and the ecosystems of the