Chorionic Sac:

Transcription

1 Diversity of Placental Mammals Note: These links do not work. Use the links within the outline to access the mages in the popup windows. This text is the same as the scrolling text in the popup windows.. What is a mammal? (Page 1) Chorionic Sac: This is the chorionic sac of a pig embryo. The embryo is contained within a fluid-filled sac, the amnion. The horionic sac is a thicker membrane containing blood vessels that surrounds the amnion. The large space between mnion and chorion is also filled with fluid. The chorionic sac is the major part of the placenta. It presses tightly or uses to the inside of the mother s uterus. Nutrients and oxygen from the mother s bloodstream diffuse into the blood vessels of the chorion, where they enter the embryo via the umbilical cord. Types of Placenta: Here are the chorionic sacs of four mammals. The part of the sac that fuses to the uterus is colored pink. This is the egion rich in blood vessels where nutrient and gas exchange occurs between embryonic and maternal blood. As the mbryo grows, so does the chorionic sac. Because these placental types are so efficient, the true placental mammals are born much more mature than marsupials and generally require less care before becoming independent. Uterus: Mammalian embryos, within their chorionic sacs, develop within the uterus. In most placental mammals, the uterus is Y-shaped with two long horns that fuse at their base. Each Fallopian tube connects an ovary to one horn of the uterus. Following copulation, sperm migrate from the vagina into a Fallopian tube where an egg is released from the ovary and fertilized. The fertile egg then enters the uterus and embeds in the lining. An amnion and chorionic sac soon develop and the placenta is established within the uterine horn. In some mammals, including humans, the uterine horn have fused to form a single, large chamber where the embryo is housed. Uterine Horn: This diagram shows the chorionic sacs within the uterine horns of a pregnant pig. The uterine horn becomes enlarged t the site of each sac. Note that the sacs, with their embryos, are evenly spaced within the uterine horn. This rrangement facilitates multiple births in mammals that produce litters of offspring. I. What is the origin of the mammals? (Page 2) Canines: Wolves and African wild dogs live in groups called packs, as is typical of many wild canines. The foxes and coyote re solitary dwellers, whereas the dingo may live alone are in small family groups. The dingo lives in Australia, but is not a true native. Dingoes were apparently brought to Australia by humans, some 4,000 years ago. Social Structure: These African wild dogs, like wolves, have a hierarchical social structure. While all of the pack members hunt, only he dominant pair is allowed to breed. The entire pack then cares for the puppies.

2 Hunts: This pair of coyotes are hunting in the grass for mice and rabbits. Felines:

3 Observe the coloration of these cats. A tan coat marks an animal that hunts in the open. Stripes or large spots usually ndicate hunting in shaded areas, where the black markings blend into the light-and-dark background to camouflage he cat. The cheetah is the fastest runner of all mammals, reaching speeds of 70 mph. The jaguar, from the Amazon ungle, enjoys swimming. Smaller cats include the lynx from North America and the ocelot and serval from Africa. African Lions: African lions differ from other cats in that they live in large groups, called prides. A pride typically consists of one or wo males and a large number of females. The females, shown here, cooperate in the hunt while the males guard the young and chase other males from the pride s territory. Behavior: The caracals are another small African cat. This caracal kitten can be seen grooming and playing with a sibling. The ough play prepares the kittens for life in the adult world. Carnivora: Here are some additional members of the carnivore order. Although called a carnivore, the raccoon actually eats a wide range of food. The raccoon in this video is eating sunflower seeds on Dr. Heatwole s deck. Hoofed Mammals: The two orders of hoofed mammals include many familiar species, including domestic horses, pigs, cattle and sheep. Here are some examples of hoofed mammals from both orders. Odd Number: Mammals in the Order Perissodactyla are usually defined as having an odd number of digits. Each digit ends in a hoof. The ancestral mammals had 5 digits, but these have been reduced in number in all hooved mammals. The hinoceros has 3 digits and the horse only one. Note that the animal s weight is mainly on the central digit in all of hese animals. Even though the tapir has 4 digits on its front feet, the rear feet have 3 and in both cases, the central digit carries the most weight, as in all perissadactyls. Even Number: The artiodactyls have an even number of digits which end in hooves. Note that that in the pig and deer, only two digits touch the ground. These two hooves from the halves of what is usually called a cloven hoof. Herds: The majority of hoofed mammals live in herds. This affords protection from predators since many eyes, ears and nose re alert for the presence of a hunter. Also, the more animals in a herd, the less likely a given individual is to be elected by a predator. Generally only the very young, very old, or sick animals are taken. Horns: Horns can be seen here in the bison and the bighorn sheep, whereas the reindeer and elk have antlers. Horns are made of keratin and are permanent structures. They are usually present in both sexes. Antlers are bone. They are usually ound only in males and are shed every year. As the male ages, he produces more sex hormones, and the antlers tend o grow larger each breeding season. It requires considerable nourishment to grow a new set of antlers each year and

4 only the strongest males remain fit enough to compete for females. Rodents: These examples of rodents are familiar to most of us. Prairie Dogs: Prairie dogs are large rodents that excavate an elaborate system of underground tunnels and chambers. They live in olonies and can be seen near their tunnel openings eating and watching for danger. Unfortunately, the tunnels can ause considerable damage to grasslands. Primitive Phylogeny: The ancesteral primates probably resembled modern-day tree shrews. They gave rise to two groups of early primates hat appeared about 55 million years ago in what is now North America and Europe. Before becoming extinct, these arly groups gave rise to two lines of prosimians. One of these lines is thought to have given rise to the modern arsiers, then to the monkeys, apes, and ultimately humans. You will learn more about the evolution of humans from Dr. Heatwole in the next topic. Tree Shrews: The tree shrew is a small mammal that lives in trees and resembles a cross between a shrew and a squirrel. It is a noisy nimal and frequently fights with other tree shrews. The skeletons of modern tree shrews resemble fossil skeletons of arly mammals. Lemurs: Lemurs are descendents of an ancient line of primates. They have survived only on the island of Madagascar, where here is less competition than in most parts of the world. Lemurs are excellent climbers and spend most of their time in he trees. Prosimians: The loris is closely related to lemurs, and the tarsier is a descendent of the second prosimian line. Both of these primates are nocturnal which explains their large eyes. Like most primates, they live among the tree branches. The erm prosimian reflects the belief that these primates preceded the monkeys and apes. Anthropoid Primates: The anthropoid primates are those that most resemble humans: the monkeys and the apes. The new world monkeys ive in Central and South America. They do not have opposable thumbs, but use a long, prehensile tail to assist in moving through the trees. The old world monkeys and apes, of Africa and Asia, use opposable thumbs to grip tree branches and utilize their non-prehensile tails only for balance. They tend to spend more time on the ground than the new world monkeys. Humans are nearest to apes on the primate family tree, with chimpanzees being the closest human relative. Apes: This gibbon is another of the apes. Watch how it uses its long, powerful arms to swing through the trees.

5 Opposable Thumbs: Only the old world monkeys and apes have opposable thumbs similar to humans. Watch the finger and thumb movements as this gorilla, the largest of the apes, manipulates flowers and a nut. Dental Formula: This diagram of human teeth shows one side of the upper and lower jaw. Like all mammals, humans have several different types of teeth for different functions. The dental formula for humans is two incisors, one canine tooth, two premolars and three molars. The old world monkeys and apes have the same dentition, whereas the new world monkeys and prosimians do not. See if you can find the corresponding teeth in the baboon skull shown here. Stance: Primates have a flat-footed stance in which both the toes and the heel touch the ground, as shown by the skeleton of a monkey foot. Several other mammals, such as bears and raccoons, have a similar stance. Canines and felines are aster runners and have a stance in which the heel (shown in black) is elevated and only the toes touch the ground. In hoofed mammals, the heel is even higher and the animals walk on the tips of their toes. Limb Structure: Other parts of the limb also show adaptations for speed in the canines, felines and hoofed mammals. Comparison of he relative lengths of limbs reveals that the middle part of the foot (the region between the toes and ankle) is much onger is carnivores and hoofed mammals than in primates. This gives a much longer stride when the animal moves. Also note that the joint between toes and the foot is lifted off the ground, especially in the hoofed mammals. This esults in more spring in each step and thus a faster running speed. Bat Wings: The skeleton of a bat is shown here. The wings consist of skin stretched over the forelimbs. The hand region of the bat skeleton is greatly enlarged. Four of the digits and middle hand bones are elongated to support the skin during light. Different Wings: Flight evolved three different times within the vertebrate group: in reptiles, birds and mammals. The wing structure differs in all three. In birds, the digits are fused and merely provide an attachment site for the wing feathers which bea he weight of the bird during flight. In the flying reptiles, pterosaurs, the fourth digit was extremely thick and longated to support the skin of the wing that supported these animals in the air. Bats also use a broad skin surface for light, but support it by an enlarged hand, including extensions of digits 2 through 5. Resting Upside Down: Bats sleep during the day by hanging upside down in a dark place. Long, clawed toes cling to an overhead support as he bat rests with wings folded. Hunting at Night: Bats hunt at night. They use echolocation to avoid obstacles in the dark and to find prey. Echolocation works like

6 adar, except that ultrasound is used rather than radio waves. The bat utilizes its larynx to emit high frequency waves hat are above the human range of hearing. Frequency may exceed 100,000 hertz in some species. Echoes from the eturning waves are detected by the ears which are exceptionally large in bats. Many bats are insect eaters and can atch insects that are flying or stationary. When flying with prey, bats can emit ultrasound through the nose instead of he mouth. The bat on the right has captured a large centipede, but can still navigate while carrying its prey. Some arge bats feed on amphibians or small mammals, while others are herbivorous and feed by sucking flower nectar or ating fruit. Blood-eating Bat: There are three species of bats that feed on blood from sleeping mammals, including humans. These so-called Vampir Bats live in Central and South America. They use long, sharp teeth to painlessly puncture the skin of their victim, then ap up the blood. Cute Bat: The cute little bat is using its long tongue to drink water from an eye dropper. Pangolin: This odd-looking, African mammal is a pangolin. Its body is covered with overlapping scales made of keratin that are hed periodically, like hair. The scales protect the animal not only from predators, but from the stings and bites of ants nd termites as it raids their nests for food. The pangolin has a long, sticky tongue and is also called the scaly nteater. Armadillo: Armadillos also have a scaly body armor, but their scales are made of bone with a covering of keratinized skin. When hreatened, the armadillo rolls into a ball, surrounded by bony armor that is almost impossible for a predator to penetrate. Marine Mammals: The shape of a typical marine mammal is well illustrated by these porpoises. Note the streamlined body, paddle-like orelimbs, and dorsal fin that resembles that of a shark. Marine mammals use echolocation, similar to that of bats, when underwater to locate objects at depths were little light penetrates. The ultrasonic waves are produced near the blow hole in the head, from air chambers or other structures within the skull. The waves travel through the water, bounce off objects, and are detected by the lower jaw bone which conducts these returning vibrations to the inner ear. Flukes of Humpback Whales: Action of the flukes may be seen in these humpback whales. Unlike a fish, in which the tail fins move side to side, the ail and flukes of marine mammals move up and down to provide forward thrust as the animal swims. Since whales are mammals, they have lungs and must periodically rise to the surface to breath. Humpback whales reach a length of 50 eet and feed on schooling fish such as anchovies and cod. Carnivorous: This killer whale is a good example of a carnivorous marine mammal. It hunts a wide variety of prey, including seals. Filter-feeding Whale:

7 There are two types of whales. The baleen whales are filter-feeders. They take large quantities of water into the mouth, then strain it through strands of baleen present on one or both sides of the mouth. Small invertebrate animals, ven tiny planktonic organisms, are trapped within the mouth and swallowed. The toothed whales are carnivorous, ypically feeding on fish or large invertebrates such as squid. The sperm whale, shown here, dives to great depths and has been known the kill and eat the Giant Squid. The Blue Whale: The blue whale is quite impressive. It can reach a length of 100 feet and weigh up to 160 tons. Although it is the argest whale, it eats some of the smallest food. The blue whale feeds mainly on krill which it filters out of the sea by orcing water out through the baleen along the edges of its wide mouth. Like all marine mammals, the blue whale produces sounds that carry over long distances. The loudest sound ever recorded from an animal was produced by a blue whale. These "songs" are specific for each whale species. They may be detectable by other whales over a distance of hundreds of miles, allowing the animals to stay in contact with one another. The blue whale is an ndangered species. Its population has been drastically reduced by the whaling industry and is only 10% of former evels. Fur Seal: The seals are also modified for aquatic life, but to a lesser extent than the Cetaceans. In the seals and sea lions, both ets of limbs have been modified into flippers that facilitate swimming when the animal is in the water, but can also be used to move on land. Watch how the forelimbs are used on land as this fur seal leaves the water to join some penguins on an Antarctic beach. Also note the ear flaps that distinguish the seals from sea lions.