4. What Type Of Animal Was The Common Ancestor Of Mammals And Birds?

Evolution of Mammals

The first mammals evolved on Earth during the early on Jurassic period approximately 200 to 175 meg years ago. These early mammals evolved from a common ancestor they shared with reptiles (Fig. v.22A). Early mammals, like their reptile ancestors, were tetrapods and amniotes (Fig. half-dozen.4). Tetrapods are vertebrate animals with four limbs likewise as their evolutionary descendants. Snakes and whales lack 4 limbs but are all the same considered tetrapods because they evolved from animals with 4 limbs. Amniotes are tetrapods with that produce an amnion or watertight membrane surrounding the embryo developing within an egg. Mammals and reptiles (including birds) are the only two extant groups of amniotes.

The term tetrapods is introduced in Amphibians; the term amniotes is introduced in Reptiles.

Fig. five.22. (A) Phylogenetic tree of all vertebrate animals Fig. six.four. Generalized phylogenetic tree diagram of extant mammals. Groups containing marine mammal species are indicated past asterisks. Monotremes are shaded red. Marsupials are shaded blue. Placentals are shaded yellow.

Most reptiles requite nascency to their offspring by laying eggs externally. Early mammals likely also laid eggs. One branch of basal mammals that survives to this twenty-four hour period is the monotremes, a group of mammals that lay eggs. The entire group consists of the platypus and four species of echidnas. Effigy 6.four.1 shows an example of echidnas (Fig. 6.4.ane A) and a platypus (Fig. 6.iv.1 B). Other branches of early mammals evolved and diversified, merely near went extinct. The merely mammal branches to survive to this day are the basal monotremes, marsupials, and placentals. Placentals are mammals with a placenta (see Structure and Function for a more detailed give-and-take about placenta), an organ that connects the developing embryo directly to the mother. Examples of placental mammals include rodents, bats, primates (including humans), dogs, horses, rabbits, and whales. Approximately 94 percent of all extant mammal species are placentals (Fig. half dozen.5). Marsupial mammals are characterized by their front pouches used to protect their newborn offspring. Examples of marsupial mammals include kangaroos, wallabies, wombats, the koala, and the Tasmanian devil. These three extant mammal groups—monotremes, marsupials, and placentals—are monophyletic, meaning the members of each grouping descend from one common evolutionary ancestor.

Fig. 6.four.1. (A) Short-beaked echidna (Tachyglossus aculeatus), Swifts Creek, Victoria, Australia Fig. vi.4.1. (B) Platypus (Ornithorhynchus anatinus), Tasmania, Australia

Fig. 6.5. Pie chart of extant mammal species by club. Orders containing marine mammal species are indicated by asterisks.

Mammals are a diverse group of vertebrate animals that includes between v,000 and 5,500 species. These mammal species vary greatly in terms of their sizes and shapes. The two largest groups of mammals are the rodents and bats (Fig. 6.5). Approximately 42 pct of all extant mammal species are rodents, animals like mice, rats, squirrels, porcupines, and beavers. The vast bulk of mammal species are terrestrial, meaning they live exclusively on land. There are three major groups of marine mammals, or mammals that live primarily in ocean environments: cetaceans, sirenians, and pinnipeds.

Cetaceans are the group of aquatic mammals we know more usually as whales. Cetaceans are readily identified by their smooth streamline shape and lack of hind limbs. They remotely resemble large fish, although whales and fish are not closely related. Cetaceans fall into two groups: the "toothed whales" or odontocetes (Fig. 6.half-dozen A), and the "baleen whales" or mysticetes (Fig. vi.6 B).

Fig. 6.six. (A) Killer whale (Orca orca), an odontocete toothed-whale Fig. 6.6. (B) Bluish whale (Balaenoptera musculus), a mysticete baleen-whale

Fig. 6.half-dozen. (C) Indo-Pacific bottlenose dolphin (Tursiops aduncus), an odontocete toothed-whale Fig. half dozen.six. (D) Cartoon of a bowhead whale (Balaena mysticetus), a mysticete baleen-whale

Odontocetes are distinguished from other whales past their hard abrupt teeth (Figs. 6.7 B, 6.7 C, and half dozen.7 D). Examples of odontocetes include the bottlenose dolphin (Fig. six.six C), sperm whale (Fig. 6.3 B), and killer whale (Fig. 6.half-dozen A). Mysticetes are whales readily identified by the baleen in their mouths in identify of hard teeth. Baleen is the organization of bristly rummage-like structures in the mouths of mysticete whales (Fig. 6.7 A). They are used to filter particles of food—such as pocket-size fish or tiny crustaceans—as they eat mouthfuls of seawater. Baleen tin grow to over 4 meters long in some mysticete whale species, most notably the bowhead whale (Fig. 6.six D).

Fig. 6.7. (A) Close-up image of baleen inside the mouth of a mysticete whale Fig. half-dozen.7. (B) Bottlenose dolphin (Tursiops truncatus) showing sharp teeth

Fig. half-dozen.seven. (C) Sperm whale molar Fig. 6.vii. (D) Killer whale (Orcinus orca) skeleton

Odontocete whales tend to exist smaller in size than mysticete whales. All dolphins and porpoises are considered to be odontocetes or toothed whales. Most cetacean species are marine, although some dolphin species tin can be found in large freshwater rivers.

Sirenians are the grouping of marine mammals that include the manatees (Fig. 6.8 A) and the dugong (Fig. 6.8 B). Also known as sea cows, sirenians have elongated tapering bodies with short fore limb flippers and a single broad flat tail fin. Similar cetaceans, they practice not have external hind limbs and live exclusively in aquatic habitats. Different all other groups of marine mammals, sirenians are primarily herbivores, eating seagrasses and algae. Only four species of sirenians are extant today. One large sirenian species was the Steller's sea cow, which grew to nine meters long (Fig. half dozen.8 D). This species went extinct in the belatedly 1700s due to overhunting for nutrient and skins, which were used in shipbuilding.

Fig. 6.8. (A) Florida manatee (Trichechus manatus latirostris), Crystal River National Wildlife Refuge, Florida Fig. 6.eight. (B) Dugong (Dugong dugon) feeding on seagrass, Marsa Abu Dabab, Egypt

Fig. vi.8. (C) Skeleton of extinct Steller'due south body of water moo-cow (Hydrodamalis gigas)

Carnivorans are group of mammals largely distinguished by their dense fur, precipitous claws, and canine teeth. Examples of carnivorans (social club Carnivora) include dogs, cats, bears, seals, and skunks. Annotation that term carnivoran is used to describe a biological classification: members of the order Carnivora. This term is distinct from the functional term carnivore, which describes a meat-eating animal. The giant panda is an example of an herbivorous carnivoran. Most carnivoran species are terrestrial. However, one particular carnivoran group is exclusively marine: the pinnipeds.

Fig. 6.three. (C) Pacific walrus (Odobenus rosmarus divergens), Alaska

Pinnipeds include seals, body of water lions (Figs. 6.9 A, 6.9 B, six.9 C, and six.9 F), and the walrus (Fig. 6.3 C). Although pinnipeds are very well adapted to living in the ocean, they must return to state to find a mate and give birth to their young. There are 33 extant species of pinnipeds. They are distributed throughout the world, although most species are found in colder climates.

Fig. vi.9. (A) Adult male northern elephant seal (Mirounga angustirostris), Point Reyes National Seashore, California Fig. 6.9. (B) Leopard seal (Hydrurga leptonyx), Antarctica

Fig. half dozen.9. (D) Polar bear (Ursus maritimus) pond, Arctic ocean basin Fig. 6.9. (F) Hawaiian monk seal (Neomonachus schauinslandi), Papahānaumokuākea Marine National Monument, Hawai'i

Fig. 6.3. (A) Body of water otter (Enhydra lutris), Morro Bay, California

Three other species inside society Carnivora are considered to exist marine mammals: the polar bear (Fig. 6.9 D), the sea otter (Fig. 6.3 A) and the marine otter (Fig. 6.9 E). Polar bears are considered marine mammals because they spend a majority of their time swimming in the ocean or hunting seals on sea ice. The polar conduct's species name, Ursus maritimus, means "sea conduct" in Latin. Polar bears are institute exclusively in the Arctic. Ii otter species—belonging to the weasel family of mammals—are also considered marine in nature. The sea otter (Enhydra lutris) lives in coastal kelp forests in the northern Pacific ocean basin from Russian federation to southern California. The marine otter (Lontra felina) belongs to the same genus every bit freshwater river otters. This species occurs predominately along the southeastern Pacific coasts of Republic of peru and Chile. In contrast to other marine carnivorans, the marine otter spends much of its time out of the water foraging for food along rocky coastlines (Fig. 6.9 E).

Both fossil and molecular show indicate that marine mammals did non evolve or descend from ane unmarried ancestral group. Although cetaceans, pinnipeds, sirenians, otters, and polar bears are all mammals, they evolved from separate branches of the mammal line (Fig. 6.4). All of these separate branches evolved from terrestrial mammal groups. Cetaceans evolved from a group of mammals that include hoofed or "even-toed" ungulates such every bit cattle, deer, and sheep. The hippopotamus is the closest living ancestor to the cetacean group. Sirenians share a mutual evolutionary antecedent with modern elephants. Pinnipeds share mutual beginnings with other carnivorans such as dogs and cats, just are most closely related to the weasels, otters, and skunks. Although many of the adaptations for bounding main survival seen in these marine mammals appear similar in form and function, each of these marine mammal groups evolved adaptations for life in an body of water environment independently.

Convergent Evolution

Evolutionary biologists are interested in the physical form of structures on an organism. They are besides interested in how these structures function or work to amend the survival and reproduction of the organism. Class and function are so closely tied together that, sometimes, unrelated organisms develop similar structures. We call this phenomenon convergence or convergent evolution. Y'all tin can see convergence in very different animals that live in similar habitats or have like lifestyles.

A bat is a mammal, and still it appears to have flying structures in common with many birds and insects. All of these flyers accept wings. If we have a closer wait at these structures, though, we volition see that they are non as like as they might appear. The wings of bats are supported by basic that are basically elongated finger bones, whereas the wings of birds are covered with feathers, a construction lacking in bats. Insects have no bony supports within their wings, and the bleary structures are really part of the exoskeleton, composed of chitin and proteins. Even though all of these animals use their wings to wing, when we look closely at them, we see that the wings themselves are very unlike and, taken along with other characteristics of the organisms (birds and insects practise not take hair, nor do they feed their young with milk), practice not indicate a recent common ancestor.

Whales are aquatic mammals that, similar fish, propel themselves through the h2o with fins. Even though whales have fins, they are not fish. If we look at the fins of whales and the fins of fish we will see some substantial differences. The fins of whales are supported by the same kinds of bones that support the wings of bats. In fact, if we look at these structures closely, they provide evidence for a closer relationship between bats and whales than between bats and birds or between whales and fish. Fish fins are very different than whale fins. Fish fins are supported past basic, but the origin and structure of the bones supporting the fins are very unlike than those found in whales.

Convergent evolution can get in challenging to make up one's mind the evolutionary relationships between animal groups. Even though organisms may change a great deal over time, clues to their ancestry remain in structures that are homologous, that is, that accept the same origin. As previously mentioned, bat wings and whale fins appear to be very dissimilar, but if you examine the underlying os structure, you will see that they all come from the same bones that are besides found in chimpanzee easily or horse hooves.

Source: https://manoa.hawaii.edu/exploringourfluidearth/biological/mammals/evidence-common-ancestry-and-diversity

Posted by: gentilelovent.blogspot.com