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Lab 13 Animals 2: Deuterostomes Now for something completely different. We now return to a major split in the tree of animal life and this time go up the branch of Bilateria known as Deuterstomia. Deuterostomes split from protostomes about 550 million years ago. You remember what a deuterostome is right? Well, here is a reminder; it has to do with their development:

Deuterostomes 1. radial and indeterminate cleavage pattern 2. enterocoelous formation of the coelom, meaning the mesoderm forms hollow pouches that

are pinched off to form the body cavity 3. the blastopore becomes the anus

This group should be near and dear to you, since you are a deuterostome. But first, the echinoderms, a deuterstome group, not so much like you.. PHYLUM ECHINODERMATA (spiny skin) The echinoderms include starfish, sand dollars, sea cucumbers, and sea urchins. They are all marine. Interestingly, they have evolved their own radial symmetry as adults based on a 5-point system (pentamerous), that is, you can divide their bodies into 5 equal parts. Even more interestingly, sand dollars and sea cucumbers then partially regained bilateral symmetry. What a weird group!

One of the most amazing features of echinoderms is their water-vascular system. The water-vascular system is basically a system of hydraulic pumps that echinoderms use to move, gather food, breathe, and excrete waste. There is a small hole in the body cavity that allows water into the system; then it travels through a series of canals throughout the body. To move, the echinoderm moves water into a bunch of tiny tubes with a sucker at the end called tube feet. Muscles squeeze the sac pushing water into the tube foot, extending it, bending it, and causing suction. Sea stars, for instance have hundreds of these tube feet on each of its five arms. Coordinated action of the tube feet allows them to move horizontally on the sea floor, vertically up walls, and pull open their heavy-shelled prey: clams and crabs. Once the prey is pulled open a bit, the starfish then everts its stomach into this package and digests the prey from the inside. Ewwwyum.

- We have whole specimens of many echinoderms. - On the slides marked Starfish, notice the spiny skin (Pedicellariae) and tube feet.

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GROWING A SPINE We now venture closer to our own kind and go on a journey that led to the spine (that rhymes a little). PHYLUM CHORDATA Along with all other vertebrates and some things that are not, you are a chordate. There are five features that make chordates chordates. They all appear in the embryo, but get modified greatly during development. Believe it or not, you looked like this too once. A. Dorsal nerve cord

The dorsal nerve cord is the main part of the nervous system that sends signals from one end of the body to the other. In chordates, this cord is on the dorsal side, which is unique since most of the other groups weve covered either have two or one ventral nerve cord (as in insects). In most chordates, the anterior section of the dorsal nerve cord thickens into a brain.

B. Notochord

To protect the precious nerve cord and to provide some flexible support for the body, there is a notochord. A notochord is a rod-shaped, flexible structure made of turgid disc-like cells which extends virtually the entire length of the body just below the dorsal nerve cord and just above the intestine. In vertebrates, this becomes the discs between vertebrae of the spine.

C. Pharyngeal pouches and slits

All chordates at some point in development have slitlike openings in the pharynx that lead to the outside of the body. They initially served as a filter-feeding device; early chordates took in water through the mouth with cilia and moved it out through the slits. Food was trapped in mucus in the slits and moved down the pharynx to be digested. In later chordates, the slits evolved into many structures with many functions, like gills in aquatic vertebrates. In humans and other tetrapods, the pouches and slits appear briefly in the embryo, but develop further into Eustachian tubes, middle ear cavities, tonsils, and other parathyroid glands of the throat.

D. Endostyle

This is a newly added feature in the chordate lineup (scientists recently realized that this trait is in all chordates and nothing else). Located on the pharyngeal floor, the endotyle secretes mucus that traps food particles brought into the pharyngeal cavity. It also contains cells that secrete iodinated proteins. In many chordates, it develops into thyroid glands.

E. Post-anal tail

This particular chordate characteristic should be somewhat self-explanatory. It is a tail posterior to the anus. It evolved specifically to provide propulsion through water. It retains this function in most chordate species, like fish, dolphins, some otters etc. In others it is used for climbing (opposums), shading (squirrels), balance (cats), wagging (puppies). In humans, it also features prominently in the embryo, but later develops into a few mostly meaningless bones called the coccyx.

Most chordates are fish, but some look very different. Well start there, because you can see all five chordate features in these groups.

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SUBPHYLUM UROCHORDATA tail chordates or the cord is in the tail of the larvae The first group of chordates that we will see is somewhat odd as adults, but the larvae make more sense. The Urochordata, or TUNICATA, are aquatic and as adults are basically small bags of goo. As adults, they are sessile, meaning they dont move and instead filter the water around them by sucking in water, running it over a mucous-covered net, and excreting it out another tube. For this they are affectionately called sea squirts. Their larvae, however, are tadpole-like with a body that still possesses the incurrent hole and an excurrent hole for filtering water, but also with a tail for locomotion. It is in this tail that you can see the dorsal nerve chord and the notochord. Eventually this free-swimming tadpole larva settles somewhere and morphs into the lovely sea squirt that it is destined to be.

Remember, you can tune a piano, but you cant tunicate.

- You can see all five chordate features in the larval tunicate slides marked Ascidian tadpole wm (not really a tadpole, it just kinda looks like one) and Ecteinascidia wm

SUBPHYLUM CEPHALOCHORDATA the notochord is in the head too

Lancelets, aka amphioxus, are small fish-like chordates that spend their days half buried in sand filtering the water. To aid this filtration, they have tentacle-like projections around their mouths.

-You can see all five chordate features in the slides marked Amphioxus. -We also have whole specimens in a jar.

CRANIATA

*Brain The brain is an enlargement of the central nervous system usually at the anterior part of the body. This is not a new feature, most of the Bilateria have one, it just seems that some groups (like adult sea squirts lost it). The function of the brain is to exert centralized control over the other organs of the body.

*Skull The purpose of a skull ought to be obvious: it protects your thinker-pot. The first skulls, however were rather different than the ones we have. The first skulls were simply cartilaginous bars. They eventually became more elaborate to protect the brain and sensory organs more completely. They also provide support when feeding, but well get to that in a second. Animals with a skull have been grouped as Craniata, because they have a cranium (not the game though). The craniates are characterized by a skull; that is, a complex ensemble of skeletal elements which

surrounds the brain and sensory capsules. The skull of hagfishes (top) consists of cartilaginous bars (blue), but the brain is mostly surrounded by a fibrous sheath (yellow) underlain by the notochord (green). The skull of lampreys (middle) has a more elaborate braincase and comprises a large "branchial basket" surrounding the gills. In the gnathostomes (bottom), the braincase is generally closed (after Janvier 1996b).

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*Vertebrae!!! Weve made it to the spine. The vertebral column is a band of segmented bones or cartilages that surrounds the nerve cord. The spine actually evolved from the notochord. The discs between our vertebrae are remnants of the flexible tissue that the notochord used to be made of. It is a step up from the notochord because it (1) provides more support for the body and (2) provides more protection for the nerve cord. Animals with vertebrae are in the Vertebrata. Sometimes these names just make sense. SUBPHYLUM VERTEBRATA Over half of all vertebrate species living today are fish. The first vertebrates were jawless fish, but had heavy armor plating all over their bodies. The only living members of this group are hagfish and lampreys, which look like eels, but have very different lifestyles. Hagfish are scavengers on the ocean floor and are capable of producing copious amounts of slime.

Lamprey are often parasites and use their sucker-shaped mouths of teeth to pull flesh off of fish. Seriously, their mouths look like the thing that ate Boba Fett.

- You can also see all five chordate features in the larval lamprey slides marked Ammocoetes larva wm and the cross section of the lamprey head embedded in Plexiglas.

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Jaws Lamprey have awesome, gruesome mouths, but they do not have jaws. Jaws was a really big fish that harassed Roy Schneider and Richard Dreyfus in the 70s. No seriously, jaws are paired (upper and lower) skeletal structures that support the mouth. Jaws probably evolved from gill arches- supportive structures around the gills, still seen in lampreys and hagfish. You can see this hypothesis below. GNATHOSTOMATA jawed mouth Gnathostomata consists of most fish and their descendents. Chondrichthyes cartilaginous fish Chondrichthyes contains sharks and rays and are so named because they do not have bony skeletons (except the jaws and teeth) and instead have cartilaginous skeletons. Since lamprey have bones in their backbones, the cartilaginous skeletons are probably secondary.

Actinopterygii ray-finned fishes These are the fish that you are used to. Trout, perch, bass, brim, tuna, goldfish, etc. They have a skeleton made of bone and fins made of membranous skin supported by long spine-like rays. They possess a swim bladder, a tough sac in their bodies that they can fill with a gas to help them maintain a desired depth. The bony fish are the most diverse vertebrates, comprising nearly 99% of the over 30,000 species of fish.

- We may have a fish for you to dissect or one that has already been opened. Notice the space for the swim bladder.

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Sarcopterygii fleshy-finned or lobe-finned fishes The fish in this group have fins that are extended from the body by a bony limb covered in flesh. Although rather unusual and rare today, this group is important because it gave rise to the tetrapods. It is represented by the now famous coelacanths and the equally cool lungfish. Both have gills and lungs and can obtain oxygen from the air and water.

CRAWLING OUT ON LAND (AGAIN) Just like plants and arthropods and mollusks and nematodes and others, vertebrates made it onto land. Their path onto land is a little different because of the special modifications that make the terrestrials look so different than the aquatic: namely feet. This was a long gradual process and new fossils are helping to determine the exact sequence of events, however, the fossil record for this transition is surprisingly good. Eventually the tetrapod (meaning four feet) was born! Even though there were apparently creatures with up to 12 toes, only those with 5 toes left descendants to this day. Therefore every tetrapod comes from an ancestor with 5 digits on each of 4 limbs (although birds lost one on the feet and the hands are modified into wings, deer lost 1 toe, and horses lost 4, snakes lost whole limbs, etc). The world of air is very different from the world underwater. There are many obstacles that must be overcome when moving from one environment to the other. Tetrapods evolved to handle each one. A. There is a severe lack of moisture. Life evolved in water, organisms are mostly made

of water, and all cellular processes require water. Most terrestrial animals must still remain near water. Fortunately fish scales also work to maintain moisture. However, we will see scales take different forms in more derived critters.

B. Oxygen is much more accessible in air than in water, if the animal has a way to get it. Gills get oxygen directly from water that must constantly be moved over them. They are necessarily thin to up the surface area. However, thin membranes in air dry out very quickly. As weve seen, the vertebrates evolved internal oxygen-gathering organs (lungs) prior to crawling out on land. That was nice of them. But with the evolution of lungs, came another problem. Fish breathe through gills in which blood is brought close to the surface where it gains oxygen through diffusion. Therefore in fish, blood only needs to go through this pathway: body heart gills body. The evolution of lungs however, required that blood go back to the heart to be sent out to the body via through this pathway: body heart lungs heart body. Since both deoxygenated and oxygenated blood goes through the heart, there is a risk of mixing the two.

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To avoid mixing the blood and losing all their oxygen, tetrapods evolved double circulation. This is accomplished by the adaptation of a partition down the middle of the heart, creating a double pump, one for each direction. Amphibians and most reptiles have a three-chambered heart. Mammals and birds, however, have a four-chambered heart, which keeps the two types of blood completely separate.

C. Another issue is that the temperature of air fluctuates wildly compared to water. Have you

ever noticed that after waiting through many hot spring days, the pool is still bitterly cold? Terrestrial vertebrates had to evolve behavioral and physiological mechanisms to maintain a steady temperature. Even cold-blooded creatures can keep their internal temperature within a set limit. The scales that tetrapods took from the fish and their derivatives help too.

D. The last obstacle brought on by crawling onto land is the lower buoyancy of air. No longer can one rely on the water to hold it up. Terrestrial animals often must alter their structural support systems to accommodate their newfound heaviness. Tetrapods needed to strengthen the bones and muscles of the limbs and spine before becoming truly terrestrial. This is why aquatic snails, lobsters, whales, walruses, and mososaurs are larger than their non-aquatic sister groups.

Despite the hazards, being the first to move on land offers a world free of competition and predators. It also opens a plethora of niches to move into.

Amphibians The first tetrapods were amphibians. Amphibians are indeed an ancient lineage, but the amphibians we know today probably do not look like their ancestors. The amphibians crawling around today include frogs, toads, newts, salamanders and some things even weirder. Their ancestors however, were closer to fish. For instance, lungs actually evolved in fish (hence the name lungfish), but most amphibians today actually breathe through their skin. They have several other synapomorphies not shared with fish, including a loss of scales, eardrums, pelvic girdle with 3 parts, and the ability to move their heads

side-to-side a little bit. One trait that they still share with fish is that most still need to lay their eggs in water to keep from drying out. Their larvae usually hatch in the water and live there breathing via gills, until they metamorphose into the more familiar adult forms. Some amphibians however (like some toads and tree frogs) are adapted to living completely without large bodies of water, but they still must keep their young wet.

- There are some jarred and possibly some living amphibians lying about. Have a look at em.

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- Today you will dissect a frog to get a better understanding of the early tetrapod anatomy. Notice the new features that separate tetrapods from their fish ancestors. Also notice the adaptations for froggy lifestyles; for instance, the short spine, rodlike urostyle (fused caudal vertebrae), and long limbs that help transfer energy from the body to the ground during jumps. Keep in mind also that many of these the froggy features will be carried into the other tetrapod groups. They are not so unlike us, if you look closely.

How to dissect a frog: 1. Take a dissection tray, scalpel, and dissection pins. 2. Take a frog from the big bucket. 3. Place the frog on its back on the tray. 4. Take a pair of small scissors and carefully cut the

skin on the stomach from the neck to the crotch. DO NOT flail about or you will cut the organs.

5. Cut two horizontal cuts from the top and bottom of your previous cut making a large I.

6. Use the pins to pin back the skin flaps.

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*The Amniotic Egg Question: Which came first the chicken or the egg? Answer: The amniotic egg came first, without it, there would be no reptiles, birds or chickens. An amniotic egg is an egg with extraembryonic membranes. These are membranes that lie outside of the embryo and help support, protect, and provide nutrients. These membranes have played a major role in tetrapod terrestrialization and include (from the embryo out):

1. Amnion- fluid-filled sac that provides cushion that buffers against jostling and helps stabilize temperature. The amnion provides the embryo with a liquid environment that aquatic animals get externally. In other words, we didnt evolve to not need the water; we just evolved a way to carry it with us.

2. Yolk sac- store of food, mostly proteins and fats, for embryo 3. Allantois- vascularized (with blood vessels) sac that aids gas exchange. Also functions as a

bladder to store nitrogenous wastes. In primates, it becomes the urinary bladder. 4. Chorion- surrounds the entire embryo and the other membranes. Helps gas exchange within

the egg. In some mammals it forms the placenta.

Amniotic eggs can also be surrounded by a shell that is either leathery (like turtle eggs) or calcified (like bird eggs). There are some examples of amniotic eggs in the lab.

All of these layers and their special functions help protect the embryo from the outside world, especially in dry conditions. They allow the embryo to survive on its own away from water or other sources of nutrition. It is self-sufficient. Without the amniotic egg, our maternity wards would all be underwater. Animals with an amniotic egg are in the group AMNIOTA: Reptilia The first amniotes were reptiles. Reptiles are a large and diverse class of poikilothermic vertebrates with bodies covered in ectodermal scales and larger lungs; there is no gilled larval phase as in amphibians. These three characteristics, along with the amniotic egg, helped reptiles push further into terrestrial environments. Poikilothermic (or ectothermic) is a more precise term for cold-blooded and means they do not provide their own source of heat internally and must rely on environmental conditions. However, this does not mean that their blood is always cold. Instead, they have amazing ability to thermoregulate behaviorally. In addition, evidence suggests that dinosaurs maintained heat metabolically (homeothermic/endothermic) just like their descendents, the birds, do. Reptiles gave

Amnion

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rise to birds and mammals, but as dinosaurs, plesiosaurs, and pterosaurs, reptiles were the dominant vertebrates during the Mesozoic Era. On a more personal note, the southeastern United States is a worldwide hotspot for fish, amphibian, and reptile diversity. There are four main lineages of extant reptiles, excluding the line that became mammals. These are the turtles, lizards + snakes, crocodilians, and birds.

- We have skeletons, whole specimens, and associated items of each of these groups. You should know their special characteristics.

Testudines Turtles are a very interesting lineage. Their relationship to other reptiles is still undetermined. They have features unique to their group, but for the most part, all individuals have them, including most of the fossils that weve found (autapomorphies). These traits include a bony shell made of a high-domed carapace and a flattened lower plastron, a beak-like mouth with no teeth, and pillar-shaped legs. The shell is made of fused bony plates that extend from the vertebrae and ribs. The ribs are actually inverted into these plates. Since the ribs are fixed like this, turtles cannot expand their chests to breathe. Instead, they use various muscles for this purpose and walking actually helps aerate their lungs. They also cant leave their shell like in the cartoons; this would be like you walking away from your spine. Turtles have been doing their turtley thing for 200 million years. They were hiding in their shells from the dinosaurs. It wasnt until the 1980s when they were given the names of renaissance artists and took up the study of ninjutsu. Squamata 95% of all living reptiles are squamates. These are the lizards and snakes. In fact, snakes can be thought of as lizards that lost their legs and gained several adaptations for that lifestyle, including loose jaws and lack of an eardrum. Squamates are incredibly diverse and include chameleons, anoles, gila monsters, whiptails, horned lizards, monitors, and dragons.

Crocodilia Crocodilia are the crocodilians: crocodiles, caimans, alligators, and gavials. They are the largest of the extant reptiles; reaching over 20 feet long snout to tail and weighing two and half tons. But thats nothing compared to the extinct 8 ton Sarcosuchus. They are mostly sit-and-wait predators that inhabit shallow bodies of water. Although the forms that are alive today are somewhat similar in form and habitat, crocodilians probably descended from bipedal (meaning walking on two legs) and completely terrestrial ancestors. However, animals that look a lot like our crocodiles and alligators walked with and fed on the dinosaurs. This group is actually sister to the dinosaurs and birds.

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Aves This group is for the birds. Birds are amazing. They are the third group to evolve true flight. Birds evolved from therapod dinosaurs, which had already evolved many of the unique features of birds, such as hollow bones, homeothermy, and feathers. Today however, birds are the only group alive with feathers. If its got feathers, its a bird.

Birds are especially adapted for flight. They gained and lost many features to make them lighter and keep them aloft: 1. We now know through better-preserved fossils that feathers evolved in dinosaurs long before flight

did. Many dinosaurs had feathers; in fact the velociraptors made famous in Jurassic Park probably should have been covered in a light coating of feathers. Therefore feathers originally served to help maintain body temperature or to provide color. Feathers might not have evolved for flight, but the long feathers with an off-center barb most likely were. Symmetrical feathers evolved this asymmetrical surface, giving them a thicker front and a thinner middle and thinnest rear. This curve causes air to move faster over the top of the wing than the bottom, thus creating low pressure on the top and high pressure on the bottom. This creates lift, pushing the wing and the bird skyward. This is what lifts birds and planes alike.

2. Although they started with the same bones that we have, birds have lost or fused digits on their forelimbs which are specially shaped to hold feathers.

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3. Birds are also missing a toe on their hindlimbs (although this might not have been for flight exactly). Remember that all extant tetrapods are descended from a 5-toed ancestor. Well, birds lots one.

4. Birds also have no teeth; they were lost during their evolution. Instead they have a strong, but lightweight beak. Beaks can be incredibly modified to fit specific feeding styles.

5. Birds have a fused spine and hip and a tail with many, many muscles for controlling the rudder. The legs are also set far back to alter the center of gravity.

6. Birds have hollow bones that instead of having thick solid tissue like we do, are supported by honey-comb interior supports. This adaptation, along with the loss and fusion of other parts, makes the bird skeleton much, much lighter, comprising only 5% of the birds total weight.

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7. Birds have a very large keel-like sternum (chest bone) to which large flight muscles are attached. These muscles give the push to raise them into the air and can comprise 25% of a birds total weight. If we were to fly like a bird, we would need a sternum that sticks out a few feet in front of us.

8. In order to coordinate movements in the air and not get lost on long trips, birds have good vision and large brains.

9. Perhaps the most remarkable adaptation that functions to keep the birds

body light was the loss of the urinary bladder. To remove nitrogenous waste, we normally pee out uric acid, which must be diluted in lots of water. Birds excrete uric acid along with feces as a semisolid white waste, usually all over your car. So they dont need to hold on to lots of water. They often do this just before taking off to further remove some weight.

- We have skeletons and feathers for you to look over in lab today.

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Mammalia Ahhh.the mammals. These are the furry tetrapods that we hold so affectionately. They appeared on the scene about 170 million years ago as small animals that scurried about the feet of the dinosaurs. Since then they have grown in size and fill many niches. They range from the small (11mm bumblebee bat) to the enormous (33m whales). They feed on plants, other animals, blood, and Twinkies (whatever they are). They have gone back into the water at least four times, the air once, the trees, underground, and up into skyscrapers. They evolved from reptile ancestors, but what makes it a mammal? Well here is yet another list: 1. Fur- mammals changed their reptilian scales into fur. Fur is unique to mammals. If

its got fur, its a mammal. Fur helps maintain water and temperature.

2. Milk- mammals express more parental care than the average reptile and this includes feeding their young with milk, usually through mammary glands. Milk is a secretion produced by lactating mothers that contains proteins, sugar, fats, and antibodies.

Interestingly, there is a lizard alive today that provides water to its young by secreting it through its skin. Monotremes, like the platypus, produce milk, but have no nipples. Therefore their young lap the milk off the skin. You can imagine a reptilian ancestor that provided its young with water in a similar fashion, later evolving to produce a more complex, more nutritious secretion, thus evolving into milk.

3. Diaphragm- mammals breathe by flattening a sheet of muscle and tendons known as the diaphragm. Since it is normally curved upwards, flattening the diaphragm lowers the pressure in the chest cavity and draws air into the lungs.

4. Homeothermic (endothermic)- mammals (and birds) are able to maintain a constant body temperature above the environment through metabolic means, as opposed to poikilothermy.

5. Four-chambered heart- fish have two chambers: an atria into which blood

flows and a ventricle that pumps blood out. Most reptiles have three-chambers: two atria and one ventricle. Mammals and crocodilians have a four-chambered heart. We will go over this in more detail below.

6. Three middle ear bones- these evolved from what are still jaw bones in

reptiles:

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7. Heterodont dentition- reptiles have teeth that all have the same shape (see alligator to the right). These usually function to grab and hold onto things. Mammals, however, have teeth that have different shapes to serve different purposes (see mandrill below). This is called heterodonty. There are four main teeth types:

a. Incisors- for cutting b. Canines- for grabbing c. Premolars- for crushing (preceded by baby teeth) d. Molars- for crushing (not preceded by baby teeth)

Imagine eating a big cookie (or actually go eat a cookie, theyre tasty). You will probably use your incisors (the front teeth) to cut off a piece of cookie. If it is a particularly hard cookie, you might use the front side of your mouth, including the canines, to pierce the cookie in order to start the break. Once you have a piece of cookie in your mouth, you will then move the piece of cookie to the premolars and molars for chewing. (The premolars and molars differ in their development and the number of roots they

have, but otherwise serve similar purposes.) This is heterodonty, each tooth type serves a different purpose. (I bet you want a cookie now, dont you? Well eat something healthier like an apple!) Because their teeth are so adaptable, and because form equals function, you can often tell what a given mammal eats just by looking at its teeth. This is especially handy when studying fossils, since we cant go out and watch extinct mammals eat. 1. Herbivores (plant-eating animals like cows and deer) must break down the tough cellulose in plants

into little bits so the bacteria in their guts can break it down (animals cannot break down cellulose themselves). They often have strong incisors for cutting the material (like the rodents mentioned above). And they usually have column-like flat teeth that they scrape together to grind leaves and stems. This gives cows the rotating jaw movement that people make fun of in charades. Since they dont hold on to prey, many herbivores have lost their canines.

2. Carnivores (meat-eating animals like cats and weasels) use their long pointy canines for holding prey, usually to shake it to death, and their bladelike premolars and molars for cutting muscle.

3. Insectivores (insect-eating animals) either have small pointy teeth for holding onto and chopping

insects (like moles) or no teeth at all (like anteaters).

4. Piscivores (fish-eating animals like dolphins) have long rows of pointy teeth for holding onto their slippery prey.

5. Omnivores (like domestic dogs, primates, and pigs) have a combination of carnivore and herbivore teeth with large canine, relatively sharp premolars, and flat molars.

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Mammals can be divided into three branches. Well give a little summary of these groups to illustrate mammalian diversity.

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Monotremata The first mammals laid eggs, just like reptiles. In fact, one group of mammals still does. These are the monotremes. There are only two types of monotreme alive today and they are both weird: the platypus and the echidna (AKA spiny anteater). When explorers first brought a platypus back to England, scientists there thought it had been sown together from the parts of other animals. Their eggs are leathery and only spend a short time being incubated outside of the mother. When the eggs hatch, the young lap milk from the mothers chest.

Marsupialia The next step in mammalian evolution are the marsupials. These mammals have eggs with a thin shell while inside the mother, but they do not lay eggs. Instead they give birth to a live, squirming young. This young has well developed forelimbs and sense of smell, however, it is far from fully developed. Instead, it is hairless and blind. In this condition, the poor thing immediately crawls all the way to the mothers pouch, or marsupium, in which it latches onto a nipple. The nipple swells inside the babys mouth so that they are locked together. Here the baby will continue developing. Marsupials were more common than they are today and are mostly limited to the southern hemisphere, where they do take a lot of varieties including tree and ground kangaroos, a glider, a mole, predators, and herbivores. There is only one marsupial in the US: the Virginia opossum.

Eutheria Most of the mammals that we encounter, including other humans, are in the Eutheria. Here, the embryo develops almost completely in the mothers uterus. The chorion helps form the placenta and the baby still grows in amniotic fluid (holdovers of the amniotic egg). A placenta is an organ that provides nutrients and removes wastes from a growing embryo. It is formed through a fusion of tissues from the mother and embryo.

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You will perform a dissection on some small mammal, either a mink or a rat.

Mink dissection A. Rules

1. Take a dissection tray, scalpel, and pins. 2. Take a mink 3. Place the mink on its back on the tray 4. Cut the skin away using four cuts as shown. Pin back the skin to

expose the internal organs. 5. Use the guide below to locate organs

B. Know 1. Fur 2. Heterodont dentition 3. Heart 4. Lung 5. Diaphragm 6. Spleen 7. Kidney 8. Stomach 9. Liver 10. Gall bladder 11. Pancreas 12. Small intestine 13. Large intestine 14. Their functions

C. Follow the path food takes through the DIGESTIVE SYSTEM. Keep in mind that eating provides

nutrients to all of your cells, but before your cells can use them, these nutrients must be broken down to their molecular components, isolated, and absorbed. Food goes

1. Into the mouth, where it is chewed, making it smaller and combining it with saliva to make it go through the system smoothly and to start the digestive process

2. Down the muscular esophagus that pushes it into the stomach 3. Into the stomach where it is dissolved by stomach acid 4. Into the small intestine where digestion continues and nutrients are

absorbed i. While in the small intestine, pancreatic juice is added to

the food from the pancreas. Pancreatic juice is a mixture of digestive enzymes and a buffer that reduces the potency of the gastric acid. The pancreas is usually wrapped in fine membranes and surrounded by the small intestine. This is why pancreatic cancer is so hard to remove.

ii. Bile is also added to the mix. Bile contains bile salts that help break down fats. Bile is produced by the liver and stored in the gall bladder.

iii. The wall of the small intestine is covered in folds and tiny projections called villi. These increase the surface area (there it is again) on which digestion takes place.

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5. After going through the long string of small intestines, unabsorbed food material move into the large intestine or colon. The large and small intestines contain many microbes that help process nutrients and produce vitamins. The large intestine also reabsorbs precious water (another adaptation to a terrestrial lifestyle), drying out and condensing the unused foodstuffs, forming feces.

6. Fecal material is stored in the last part of the intestine called the rectum. When ready, it is excreted through the anus.

7. Nutrients absorbed by the small and large intestines are transported via the hepatic portal vein to the liver (which has many functions) where they are converted into other substances and released to the blood as needed. The liver also takes out toxins before they are transported to the heart. This is why large amounts of alcohol can ruin your liver. They go here first and the liver sacrifices its own safety to protect the heart and rest of the body. Have you thanked your liver lately?

Does the rats digestive system look different than this fellas?

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Mink Anatomy

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BIOL 1108K Lab 12- Animals (Part 2) Postlab Name _________________________________ 1. Pentaramous symmetry, as in echinoderms,

means the body can be divided into how many identical parts?

A. 2 B. 3 C. 4 D. 5

2. Hagfish have all of the following, except

A. Bilateral symmetry B. Jaws C. Brains D. Notochords E. Bony vertebrae

3. Starting from the embryo, the outermost

membrane of an egg would be the A. Chorion B. Amnion C. Allantois D. Yolk sac

4. Mammal teeth can have different shapes to serve different purposes and this condition is called

A. Montypythony B. Monodonty C. Heterodonty D. Denteriosis

5. Which evolved first? A. Nipples B. Milk

6. The liver is for all the following, except: A. Filtering blood B. Making red blood cells C. Making bile D. Converting nutrients

7. Why are there no terrestrial echinoderms?

8. What is your notochord normally called? What does it look like? Draw it. What does it do?

9. Given the key adaptations that youve learned about in lab this semester, explain why a moss is similar to a daisy as a frog is to a lizard.

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10. Name the four groups of animals in which powered flight independently evolved (this does not

include the Wright brothers, since the plane is not heritable).

11. If you think about it, embryos in the Amniota still develop in water, right? Explain.

12. Which phylogeny of the amniotes shows the correct relationships?

13. Lets say you are interested in becoming doctor of internal medicine. Why might it benefit you to

study the anatomy of a mink over a lizard? Explain.

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14. Label FIVE adaptations for flight on the skeleton below.

15. This thing is a pangolin. It is a mammal. Why?

16. Judging by tooth shape, what does the animal, whose skull is pictured to the right, eat?