INTRODUCTION Welcome to the underwater world of aquatic mammals Many aquatic mammals are part of a big group of animals called cetaceans This group includes whales dolphins and porpoises Each of the three main groups has its own set of subgroups but they all share a few common features Cetaceans are all mammals just like humans which means that they breathe air through lungs instead of gills like fish are warm blooded instead of cold blooded like reptiles they give birth to live young instead of laying eggs like birds and produce milk like cows They may not look like it with their smooth skin but they usually have a little bit of hair or fur at some point in their life Some cetaceans have hair even before they are born called lanugo Cetaceans also have a layer of fat called blubber that helps them to stay warm in the chilly waters of the ocean but they have to come up to the surface to breathe air before they can dive down again These aquatic mammals have adapted to life in the water Instead of legs they have two front flippers or fins called pectoral fins and one long tail with features called flukes They have blowholes on the top of their head instead of nostrils and these blowholes help them to breathe when they reach the surface of the water Some cetaceans have a dorsal fin which is often a triangle shape on their backs but some do not There are two major groups of cetaceans toothed whales odontocetes which includes dolphins and porpoises and baleen whales mysticetes Toothed whales as the name suggests have teeth Some only have a few teeth and some have a full set of teeth Sometimes these teeth are used for eating but they are also sometimes used for protection or fighting if the whale only has a small number of teeth Whales that do not use their teeth to eat will suction feed which means they use powerful muscles to suck up their prey usually fish or squid and swallow it whole In general toothed whales tend to be social and live in groups called pods and they 8
species including some that can live in freshwater These animals are often small in size compared to whales and some dolphins and they usually live in cooler waters than dolphins Dolphins and porpoises are sometimes threatened by sharks but most whales are large enough that they are not threatened One of the biggest threats to cetaceans comes from people For years whales were hunted for their valuable blubber driving some species to near extinction Although smaller dolphins and porpoises were not hunted as aggressively as whales they are often caught in the nets of fishermen sometimes accidentally and injured or killed Like all ocean life pollution and climate change are major threats to cetaceans because changes in their habitat can affect their food supply and quality of life often use a form of navigation called echolocation in which they make noises and then use the echoes to understand their surroundings This form of navigation is especially helpful in deep or murky water where it’s difficult to see Instead of teeth baleen whales have special filters in their mouths called baleen They eat by gulping in a big mouthful of water and then using the baleen to separate the water from the food Even though these whales are very large they usually only eat very small animals such as krill plankton and small fish They typically have two blowholes and are some of the biggest mammals in the world You might be wondering how whales dolphins and porpoises are different from one another Although they’re all part of the cetacean group they are in separate families created by scientists because of their size shape and habitat Whales are the biggest of this group in size and can be found all over the world They have lots of thick blubber on their bodies which often allows them to live in very cold or very deep water Dolphins are typically smaller than whales and in general prefer warmer or tropical waters Some species of dolphins can even live in freshwater They are athletic swimmers and are often known for being able to do acrobatics and tricks Although porpoises are a smaller family than dolphins and whales there are a number of different porpoise 9
Prehistoric Cetaceans You might not know it by looking at them but hippos are the closest relative to whales and both whales and hippos likely share a common ancestor millions of years ago There were a lot of evolutionary steps in the history of whales but one thing we can learn about them from their hippo relatives and some of the other species that came before them is that whale ancestors probably had legs and walked on land It might seem crazy to think of whales with legs but these ancestors were likely able to live both on land and in the water much like modern day hippos do so they would have breathed air and been able to walk and swim Eventually they evolved from having legs to having fins but they kept the ability to breathe air Their front legs eventually morphed into flippers their tails elongated and their back legs disappeared entirely allowing them to maneuver in the water more efficiently We know this because the hip bones of some modern whales show evidence that their ancestors had hind legs In this section we’ll look at some of the prehistoric ancestors of modern day whales and the important traits they developed and passed on that helped them to move from land to sea as well as some prehistoric cetaceans that looked similar to modern dolphins day porpoises and whales 10
PAKICETUS AMBULOCETUS PROTOCETUS Pakicetus inachus AMBULOCETUS NATANS PROTOCETUS ATAVUS WHEN About 56 to 40 million years ago WHERE Modern Pakistan SIZE 100 pounds 45 kg roughly the size of a wolf LOOK FOR A rodentlike animal with a long tail and a long snout PREHISTORIC PROFILE Pakicetus looks like a land animal but it has a lot more in common with modern whales and hippos than you might think Pakicetus had an ear bone that was similar to the unique ear bone in modern whales as well as an anklebone associated with hoofed animals making it possible that Pakicetus was a distant ancestor to both whales and hippos This carnivorous four legged animal is thought to have eaten both meat and fish which makes it likely that it was able to navigate both land and sea WHEN About 49 million years ago WHERE Modern Pakistan LENGTH 9 3 4 feet 3 meters LOOK FOR Webbed feet and a long snout full of teeth PREHISTORIC PROFILE It’s not hard to picture Ambulocetus in the water with its crocodile like snout Although Ambulocetus still had legs its feet had flipper like qualities to them including webbed hind feet To move around on land this heavy creature may have waddled or used its front legs to pull it along similar to how modern sea lions move Studies of Ambulocetus skulls helped scientists to understand that this creature was likely able to swallow food underwater and it had teeth that were similar in shape to other cetacean ancestors By studying the chemicals in their teeth scientists were able to discover that they likely fed in both freshwater and saltwater 11 WHEN 48 6 to 40 4 million years ago WHERE Modern Egypt LENGTH About 8 feet 1 2 2 meters LOOK FOR Beak like snout front flippers with webbed toes small back flippers and a back ridge PREHISTORIC PROFILE Protocetus atavus means first whale an accurate title for this early cetacean With a streamlined whalelike body and a fluke tail Protocetus shares many attributes found in modern day whales Protocetus was discovered near modern day Cairo Egypt with the first description of this early cetacean completed in 1904 Have you ever tried listening to something underwater Scientists believe that Protocetus had a set of ears that could hear underwater as well as a good sense of smell but unlike many modern whales they were unable to echolocate
