Skeletons & Mammals Manual PDF

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Skeletons & Mammals Manual. Skeletons & Mammals Manual....

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Vertebrate Skeletons and mammals Introduction One of the major themes in Biology is that form and function are inexorably linked. The vertebrate skeleton provides some of the best illustrations of this principle. Even if you've never seen live moles and cheetahs, an examination of their skeletons will clearly reflect profound differences in how they move, how they feed, and so on. Even a single bone can reveal many important details about the animal from which it came. Sometimes the differences are obvious: although they are both aquatic mammals, the Steller's sea lion and manatee clearly do not eat the same food: their teeth, jaws, and skulls are simply too different. Other differences are subtler, which is one of the reasons we study the form and structure of the vertebrate skeleton. The study of the vertebrate skeleton is fascinating on two levels. First, it provides an excellent illustration of how evolution can shape a simple blueprint- for example, the basic structure of the tetrapod limb- so that it becomes adapted to very different uses. Second, it also illustrates the link between form and function. Part 1 of this lab will focus on a comparison of tetrapod skeletons and skulls. The second part of the lab consists of a dissection of a rat (or a mouse), allowing us to survey the major anatomical features of our own taxon, the Mammals. Mammals are distinguished from all other tetrapods by their hair, three middle ear bones, mammary glands, and a particularly well-developed brain including a neocortex. Although the mammals in general are a relatively minor group in terms of global diversity, with fewer than 6,000 species (i.e. about as many as the sponges!), they have been closely studied because a) we are mammals, b) many of the most recognizable and charismatic organisms that surround us are mammals, and c) many are important to us as food, as providers of "work" (e.g., oxen and horses), or simply as companions. Thus part 2 of this lab will consist of an examination of the major internal and external features of a representative mammal. Learning objectives By the end of this lab you will be able to: 1. Identify the major components of the vertebrate skeleton and skull. 2. Describe how the basic vertebrate skeleton has been modified in different taxa, and link those modifications to functional differences among those taxa. 3. Identify the distinguishing characteristics and major external and internal anatomical features of a typical mammal (rat or mouse).

BIOL 1510 | Skeletons & Mammals- Lab Manual 1

Materials needed Tools Dissection tray Scalpel Forceps Scissors Probe Dissection pins Preserved specimens Rats or mice, for dissection Skeletons Frog skeleton Mudpuppy skeleton Turtle skeleton Allosaurus skeleton Pigeon skeleton Human skeleton

Skulls (selected from this list) Dimetrodon Raccoon Opossum Bear Beaver Bottlenose dolphin Horse Steller's sea lion Manatee Sabre tooth cat Pygmy chimpanzee Armadillo Aardvark Wild pig Alligator Velociraptor Archaeopteryx Pteranodon Rhaphorhynchus Tyrannosaurus Edmontosaurus Osprey Pelican Macaw

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Lab Methods Exercise 1. Comparing vertebrate skeletons Do as much of this activity as possible by considering your own body or that of a willing classmate in relation to the skeleton diagram on the right; for the more invisible structures consult the human skeleton on display. The point of this exercise is to a) identify the key bones and bone groups in the human body and b) compare with the skeletons of the mudpuppy, frog, turtle, pigeon, and cat that are on display. The bones of your arm are the humerus, radius and ulna, carpals (wrist bones), metacarpals (hand bones), and phalanges (finger bones). The corresponding bones of your leg are the femur, the tibia and fibula, the tarsals (ankle bones), the metatarsals (foot bones), and the phalanges (toe bones). The bones of the pectoral (shoulder) girdle and the pelvic girdle attach the upper and lower limbs, respectively, to the axial skeleton. What bones make up each of these girdles? Locate them on the human skeleton and palpate these bones on your own body. Why do think that dislocated shoulders are so much more common than dislocated hips? •

Compare and contrast the forelimb structure of human, cat, and mudpuppy (or frog). Sketch them in your worksheet, annotate, and comment on the major differences. Which bones are enlarged? Have any of the bones fused?

Tetrapod limbs are structured like levers. The bones of your forearm, the radius and ulna, articulate with the humerus at the elbow, making the elbow a fulcrum. The bones of your foreleg similarly articulate with the femur at the knee, which also is a fulcrum. Tetrapods vary in the position of their limbs- whether they are held laterally or point directly downwards- as well as the distance between their extremities and the fulcrum. They can also vary in the point of contact with their environment, and be plantigrade (walking on the soles of their feet), digitigrade (walking on their toes), or unguligrade (walking on their nails). The specific point of contact with the ground is important because it determines length of stride, which in turn affects speed. Tetrapods with laterally BIOL 1510 | Skeletons & Mammals- Lab Manual 3

positioned limbs tend to be swimmers or burrowers and move slowly; those with vertically positioned limbs tend to be runners or walkers. •

Examine the vertebrate skeletons on display, and based on the above information, answer the questions in your worksheet.

The spinal or vertebral column of vertebrates is the main support system of the body and protects part of the nervous system, the spinal cord. The vertebrae also have a role in locomotion. It is often possible to identify not only the kind of vertebrate (fish, amphibian, reptile, bird, or mammal) but also the way the animal moves from a single vertebra. Whether the spine flexes in the vertical or horizontal plane is characteristic of the different kinds of vertebrates. In fishes, this flexion tends to be in the horizontal plane, that is, from side-to-side (observe the fish in the tank in the lab to verify that this is the case). In tetrapod, the direction of flexion varies, but it is always reflected in the design of the vertebrae. Examine the processes sticking out from the skeleton, and imagine how muscles attached to those bones allow you to rotate and bend. The bony thorax consists of the ribs, sternum (breast bone) and thoracic vertebrae. These structures protect the soft tissues of the thorax (chest) – e.g., the lungs, heart and associated major blood vessels. The ribs also assist in breathing. The size of the rib cage can thus provide a rough estimate of the relative lung volume of each animal (which is a major factor in the level of metabolic activity that an animal can sustain). Compare the size of the thoracic cavities in the various skeletons and consider the metabolic demands of the daily activities of each type of animal. The sternum of different vertebrates may be a single bone or consist of several bony elements in series. Which of the vertebrate skeletons on display lack a sternum? What does the lack of a sternum allow you to infer about their locomotion? The sternum (breastplate) of birds has been greatly expanded to provide an increased surface area for the attachment of the flight muscles. Examine the sternum of the bird, with its very prominent ventral keel (carina). The clavicles of birds are also fused together to form the furculum (e.g., the wishbone), which articulates with the breastplate and provides additional lateral attachments for the flight muscles. • •

Based on the above information, answer the questions in your worksheet. Using the information you have learned above, complete the blank diagram of the cat skeleton in the worksheet.

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Exercise 2. Comparing vertebrate skulls Teeth: Examine the skulls on display in the biology laboratory. Some are from carnivores, animals that eat other animals; others are from herbivores, animals that eat plant material. Can you tell which is which? Carnivores typically have sharp, pointed teeth for killing and holding prey: the canines of dogs and cats are good examples, but other vertebrate carnivores (crocodiles, dolphins, even mudpuppies!) also have sharp, conical teeth. Birds lack teeth, but the sharp points of the bills and talons of hawks and eagles serve a similar function. The teeth posterior to the canines are the premolars and molars. Molars tend to be larger than premolars, and to have more cusps and roots, but the distinction isn't always obvious. For this reason, premolars and molars often are collectively referred to as cheek teeth. If you look closely, you will see that the cheek teeth of your carnivore differ in appearance from the incisors and canines. Such a dentition in which the teeth differ in appearance is heterodont (= different + tooth), in contrast to homodont (same + tooth), where the teeth are all similar in appearance. In carnivores, the cheek teeth tend to be blade-like and better suited for cutting and shearing than for piercing and killing. In fact, a distinguishing feature of carnivores are the carnassials: the upper fourth premolar and the lower first molar on each side of the mouth are enlarged, and oriented to form a powerful shearing mechanism (like scissors) for cutting and tearing apart flesh. The carnassials perform so well in cutting up flesh that the remaining cheek teeth of carnivores often are small or reduced in number, especially in cats. Now examine the teeth of an herbivore (beaver, cow). Note that the canines are entirely absent. Instead, the anterior teeth -in this case, the incisors- are specialized for shearing off leaves, gnawing on wood, or cropping grasses. In many herbivores, such as rodents and rabbits, these teeth are ever-growing. The cheek teeth of herbivores differ from those of BIOL 1510 | Skeletons & Mammals- Lab Manual 5

carnivores, too. Note that they are large and flat, and are more like the premolars and molars of humans. The large, flat, cheek teeth of herbivores act like a mortar and pestle to pulverize and grind-up vegetable matter. The teeth are all very similar to one another because they all do the same job; that is, the premolars have come to resemble molars. The broad cheek teeth provide lots of surface area for acting on plant matter. But in order to grind and macerate effectively, a folded surface is superior to a smooth surface. Consequently, the cheek teeth of herbivores bear numerous ridges and infoldings on their occlusal surface that aid in grinding food (the manatee is a fine example). •

Observe the skulls on display and compare and contrast them in terms of their dentition. For each skull, identify the teeth types that are present, and relate them to the likely diet of that organism.

Jaws: like limbs, jaws are designed like levers. The fulcrum is the attachment point of the jaw to the skull, the mandibular condyle. The length of the jaw helps determine the force that can be applied to crush / chew on potential prey items, but one must always consider the muscles acting on the other side of the fulcrum. The muscles that provide the strongest closing force on the jaws are the temporalis muscles, which anchor on the processes (the protruding bits) on the posterior part of the jaw and on the top of the braincase; in some animals, the attachment of these muscles is enhanced by a pronounced ridge called the sagittal crest (see the sabertooth cat for a fine example, as well as the beaver). The skull diagrams above also show the zygomatic arch, which serves as the attachment point for masseter muscles that add closing power and stabilize the articulation of the jaw. •

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Observe the skulls on display and compare and contrast them in terms of jaw structure and jaw muscle attachment points. Pay particular attention to the posterior processes of the jaw, the zygomatic arches, and muscle attachment points on the skull, as well as the presence / absence of a sagittal crest. Hypothesize the likely diet of your organism and compare with the observations you made with the teeth, above. An additional general pattern with skulls is that the orbits (eye sockets) of carnivores tend to oriented forwards, whereas those of herbivores are oriented to the side. Based on your observations and the general trends above, is it possible to reach any firm conclusions about the human diet simply by observing our skull? Justify your answer.

Exercise 3. Mammals (dissection) Class Mammalia: Mammals appeared ~225mya and are the result of evolutionary innovations that allowed animals to become further removed from their previous BIOL 1510 | Skeletons & Mammals- Lab Manual 6

dependence on aquatic habitats. As discussed in the previous lab “building a better tetrapod”, the evolution of the amniotic egg allowed animals to not have to lay their eggs in the pond, but be able to create a miniature private pond within the egg. Mammals have gone a few steps further. Although a few mammals still lay eggs (subclass Prototheria), the overwhelming majority of mammals carryout embryonic development within the mother (subclass Theria), further moving the private pond to a stable and optimal environment. Mammals also produce milk, which extends the provisioning of a basic form of nutrition to offspring long after their birth. Mammals are also endothermic, meaning they generate their own heat, and homeothermic meaning they also maintain a consistent internal temperature. In addition, mammals also posses fur, allowing them to occupy habitats of a greater temperature range. Together, these adaptations are responsible for the vast range of habitats mammals occupy on Earth. Here you will investigate various features of mammals through the dissection of the rat (Rattus norvegicus) or mouse (Mus musculus) which closely resemble our own physiology. External features Obtain a preserved rat or mouse. Notice the fur covering the body which allows for better thermoregulation. • Notice the sensory hairs (whiskers) which allow the animal to better perceive the immediate environment around the snout. • Notice the large incisors for gnawing. These will continually grow as long as the animal lives. How is that adaptive? • Locate the teats (nipples) on the ventral surface. Do both sexes possess these? • Determine the sex of the specimen. Males have a large scrotum, while females possess a small vagina anterior to the anus. Internal features • Follow the remaining steps to observe the internal anatomy. 1. Using scissors, snip near the base of the abdomen where the arrow on the diagram is pointing. 2. Continue to cut anteriorly until reaching the xiphoid process (sternum). 3. Cut laterally until you reach the side of the animal. 4. Starting from the original snip of the bottom, cut laterally as well. 5. Open the rat from both the left and right flaps to expose the organs of the abdominal cavity. •

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•Begin at the top of the abdominal cavity which is delineated by the diaphragm. The diaphragm is a muscular flap that flexes and pulls down posteriorly to increase the volume of the thoracic cavity, thus reducing internal pressure and causing air to be drawn in to the lungs. •Observe the 5 lobes of the liver underneath the diaphragm. Do not confuse the stomach or spleen for any of these lobes as all of the lobes of the liver are connected at the dorsal side. The liver serves to detoxify the body, partake in protein synthesis, and well as produce chemicals for digestion. The liver also stores glycogen which can be slowly released to provide the organs of the body with the necessary sugars to function. •Notice the stomach nested under the liver. The stomach is quite muscular which is noticeable to the touch. •Immediately below the stomach notice the tongue shaped spleen. This organ serves as a large filter for the blood, similar to the lymph nodes in the lymphatic system. •Between the stomach and the spleen reside the pancreas. The pancreas is not a typical looking organ as it is a thin net-like membrane accompanied by fat. This organ produces and releases insulin on demand. Digestion releases sugars to the blood stream and insulin regulates the uptake of these sugars by the cells. Without insulin, your cells will starve despite your blood filled with sugars. •Notice the intestines that begin at the end of the stomach. The intestines serve to absorb nutrients from food. Within the intestines notice the large sack, the caecum, that connects the small and large intestines. This sack temporarily holds food to allow for mutualistic bacteria to break down the cellulose of plant cell walls. This produces resulting sugars that the animal would otherwise be not have been unable to unlock. •The descending colon is the final region of the large intestines which is the site for further digestion and water absorption. •Slide the intestines to either side to expose the kidneys. These are quite simple to decipher as they are about the same color, shape, and size of kidney beans. The kidneys serve to filter and remove nitrogenous waste from the blood, and excrete it in the form of urea.

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•At the anterior end of the kidneys (the top), notice the small white adrenal gland which produces adrenalin as well as cortisol.

Thoracic cavity Begin by continuing to cut from either side of the sternum anteriorly up the ribcage. Open the ribcage to expose the thoracic cavity of the animal. •Notice the triangular shaped organ residing atop of the heart. This is the thymus, a gland where the T cells of the immune system mature. •Notice the five lobes of the lungs, three are on the animal’s right side while only two exist on the left side. •The lungs do not contain muscles and are merely air sacs. Inhalation and exhalation is achieved through altering the volume of the thoracic cavity by the flexing of the diaphragm (expanding the cavity along the anterior-posterior axis), and flexing of the intercostal muscles which pull the ribs together and thus pulling your chest upwards. These little muscles reside between your ribs and the cramping of these muscles is what you feel in your ribs when running. •Remove the heart and notice the basic layout with the atria above the ventricles. The atria receive the blood while the ventricles pump the blood away from the heart. Cut the heart in half via a cross section. Observe the difference in the thickness of the muscular ventricles. Why is the left ventricle substantially more muscular than the right ventricle? •Observe the trachea, which is the white tube with supporting cartilage rings. This tube is the path that connect the air on the outside of the organism to the lungs. The supporting rings prevent this tube from collapsing. •Compare the trachea to the esophagus which resides to the back and side of the trachea. This tube transports food from the pharynx to the stomach. It is also pale in color but collapsed and flexible. Use the blunt probe to observe this as sharp tools may sever the tube. •Continue anteriorly until you reach the submaxillary glands which are the salivary glands. Reproductive features Female •Observe the uterine horns (the uterus) which form a Y shaped structure. The embryos implant and develop along this uterus after fertilization. The sacs of the amniotic egg then extend into the mother (uterus), together forming the placenta. The placenta provides BIOL 1510 | Skeletons & Mammals- Lab Manual 9

these sacs the ideal nourishing environment for the developing embryo. If the uterine horn is generally flat, then the female was not pregnant. If the uterine horn has a series of thickenings appearing like peas in a pod (a soybean), then the female was pregnant. •At the anterior end of the uterine horns notice the fallopian tubes that connect the ovaries to the uterus. The fallopian tubes are very small coiled up tubes where the egg is s...