Let's look at the classificationand natural history of the mammals. This is covered in your illustratednotes
This is the classification of mammalsthat you're going to be responsible for. So the first order thatI will talk about is the most primitive and unusual, that's theOrder Monotremata. The translation of this word is "one hole"refers to the fact that these animals have a cloaca. It's nota peculiar feature of these animals because the marsupials alsohave it.
There are 3 living species inthe order and the 2 basic types are shown here on the page. Theyare found in Australia and New Guinea. The Duck-billed platypus,there's only a single species of these critters, and this is anaquatic animal that has a dense fur like a beaver or otter thatis water-proof. It has webs of skin between it's toes sort ofthe way that a duck does, that it uses in swimming, however, onething that's different and somewhat unusual is that the web canactually fold back and so it exposes it's claws cause this animalis also a burrowing animal, it digs a burrow in the bank of thestream where it is living and it actually spends a good portionof the day in that burrow. So it has the ability to dig as wellas having this web of skin that makes it easier for it to swim.
When the 1st specimens of theduck-billed platypus were returned to Europe by the 1st Europeanexplorers of Australia and New Guinea, the scientists thoughtthat somebody was trying to fool them and had taken the head ofa duck and placed it onto the body of a beaver. It makes a livingsimilar to the way in which a duck does by filter-feeding andextracting small organisms from the water. One thing that's veryunusual about them among mammals is that the male has a poisongland on the inside of it's hind legs and it has a hollow spike-likeinjection mechanism that it can use to stab an animal that istrying to eat it and inject the poison and the poison is strongenough to kill a dog. And there are very few examples of mammalsthat actually produce a poison.
The other 2 species of monotremesare the ant-eater type. Sometimes called the spiny-anteater orechidna. The hairs are very greatly enlarged and form these spinesthat have a sharp point on the end and that's not unique to thisanimal. There are a number of other types of mammals in whichthe hairs have become specialized in the defensive spine-like,such as the porcupines (rodent) as examples. These animals feedon ants. They also feed on termites which are relatives of ants(social insects). And they are convergent with a number of otheranteater types of animals that are found in different places inthe world.
Throughout the tropics of theworld, there are species of social insects, ants and termites,that produce large homes/mounds made out of mud, etc. Termitemounds are filled with honeycombs of little passage ways and chamberswhere the social insects lives and raise their young and storetheir food and things like that. And these very obvious largeaccumulations of large insects are exploited as food resourcesby a variety of different groups of mammals and the basic requirementsfor making a living on that kind of food are the same and as aconsequence we find convergent evolution of the same set of featuresnecessary for making that kind of living. If you're going tofeed on these social insects the first thing you have to do isyou have to be able to dig through this hard baked mud home thatthey live in. So all of these animals have modifications forburrowing. Their skeleton looks somewhat like the armadillo skeletonin having large areas for attachment of the muscles necessaryfor long sharp claws and so forth. And then once you burrow throughthe side of the home, then they need to slurp up the insects soall these guys have sort of long narrow snouts, incredibly longtongues and very sticky saliva. And most of them have greatlyreduced teeth because apparently there isn't much point in chewingsomething that's already small.
The same basic set of anteater adaptationsthen are found in the:
Echidna New Guinea MONOTREMES
Marsupial Anteater Australia MARSUPIAL
Anteater Central & South EUTHERIAN
America
There are a couple of other animalsthat are not included in this classification cause they are sortof small specialized orders that include just these anteater typesbut which are worth knowing about I think just mentioning in thecontext of these convergent evolution is the:
Aardvark (="earth pig")Africa EUTHERIAN
Pangolin Southeast Asia EUTHERIAN
Aardvarks are incredibly powerfulburrowers; they have big ears. And there is an animal called thepangolin which is also an anteater type and this animal is reallya weird critter, their hairs are formed into what look very muchlike reptilian scales.
So what we have here is a Monotremein the Subclass Prototheria, we have a Marsupial which is in theSubclass Theria and Infraclass Metatheria and then you have 3separate orders of Eutherian mammals on each of the major Northerncontinents. So obviously animals coming from very different phylogeneticheritages have evolved the same set of adaptive characteristics/modificationsof their skeletons and so forth that are necessary to be goodburrowers and have long tongues and sticky saliva and reducedteeth. So this would be a good example of convergent evolutionthat evolves very diverse ancestors all having very similar setof adaptations.
The next order is the OrderMarsupialia in the Infraclass Metatheria. There are 242 speciesof marsupials and they are found in South America and in Australia. At least that's their sort of historic distribution. There isa South American marsupial that has been quite successful in invadingNorth America and that's called the American Opossum, you willsee these guys out wondering out on the streets at night everyonce and awhile. They look like great big rats, they have a longhairless tails and little beady eyes and they are sort of freakylooking critters. But nevertheless they are very highly adaptiveanimals. They have successfully invaded North America and SouthAmerica.
And you will remember on Monday Idescribed to you the historic evidence about the marsupial faunaof South America that it included a variety of different carnivores. For example there was a large marsupial cat that looked verymuch like the Saber-Toothed Cat that you can see skeletons ofat the LaBrea Tar Pits. Big obviously ferocious carnivores withgreat big huge canine teeth was included in that fauna in SouthAmerica and most of them went extinct. Although there are a smallnumber of opossum-like marsupials that continue to survive quitewell in South America, the majority of the species of marsupialsare found in Australia. It is in Australia that we find the greatestdiversity of marsupial types. Convergent similarity can be seenin the adaptations of many of these different types of marsupialsin Australia.
Some of the types that are shownhere include the Tasmanian Wolf which is an example of one ofseveral different types of marsupials that look like carnivores. In fact they are carnivores and they look like Eurasian/NorthAmerican carnivores. The Banded Anteater is not quite as highlyspecialized in terms of being a burrower as some of the otheranteater types. But nevertheless, it still fits the general description. The Marsupial Mole is a fossorial mammal, with adaptations likemost fossorial mammals. They have very short thick dense velvetykind of fur, greatly reduced eyes, and very powerful front limbswith big claws that it uses for digging through the soil. Theyreally sort of live essentially their whole lives moving throughthe soil. They don't necessarily leave open passage ways behindthem. They kind of swim through the soil and eat the variouskinds of invertebrates that they encounter along the way. The Pouched Mouse is really somewhat more like a shrew. Moles andshrews are members of the Eutherian animals which are insectivoresbecause they eat primarily insects. In a related group, thereis a mouse-like Australian marsupial called the Honey Badger whichfeeds on nectar. It climbs around in the trees and collects thenectar with its long tongue, the same way that a hummingbirddoes.
While North American and Europeanzoologists classify the marsupials in a single order with somethinglike 7 different families, the majority of which are representedhere on these 2 pages. Australian zoologists have a tendency toclassify the marsupials as 7 different orders. They feel thatthey are different enough from one another to deserve the classification as an order. The majority of the species of mammals in Australiaare marsupials but there are several different species of rodentsthat evolved in Australia. There are not as many species of rodentsas there are marsupials, but there are quite a diverse group ofrodents that live in Australia as well.
Now the kangaroo tends to looklike a pretty unusual, essentially almost a unique animal. Interms of its size and its specialization for saltatorial locomotion,it is in fact really not comparable to anything anywhere elsein the world. There are small saltatorial or hopping types ofrodents that occur all over the world but nothing as big as thesebig kangaroos. From an ecological point of view, the kangaroosare very much like the antelopes and large ungulate(sp?) mammalsthat are adapted for cursorial locomotion. The hopping locomotionin kangaroos is very fast, a lot of maneuverability and theyare capable of prolonged migrations following the unpredictablerainfall and grass growth that occurs in the outback of Australia. Another thing that is similar about them is their mode of digestion. They have a digestive system which is very similar to that ofa cow and other relatives of the cow.
Here is a quick overview ofwhat's happening in a cow's stomach. One way of describing thiscommon form of digestion found both in the kangaroos and in thecows is symbiotic digestion of cellulose. The symbiotic digestionof cellulose is performed by protist and bacteria although thebacteria seem to be the ones that are responsible for the largestfraction of what's going on. What happen is that the animalsare collecting materials to sustain the polysaccharide calledcellulose. Now a polysaccharide is a polymer that is made upof a very large number of repeating units of sugar molecules. Starch is a polysaccharide that is produced by animals and animalshave the digestive enzymes necessary to break down starch. However,no vertebrate animals and almost no invertebrate animals producethe digestive enzyme necessary to breakdown cellulose becauseit has a different kind of bond between the sugar molecules. Cellulose is probably the single most common organic moleculeon the surface of the planet because it is the major structuralpolysaccharide of all land plants. And since it is composed ofsugar molecules, it represents the potential energy source ofgreat magnitude. Since most animals do not have the ability tobreakdown cellulose, the sugar molecules are completely inaccessibleto them if they don't get some help. This symbiotic digestionof cellulose by bacteria is a very elaborate form of help. Thekangaroos and the members of the Artiodactyla are true ruminantsthat have a 4-chambered stomach instead of the single chamberedsort of standard acid digestive stomach of most vertebrates
The first of these 4 chambersis called the rumen. It is the stomach into which the grassesand plant materials go when the animal eats. And in the rumenis a flourishing population of protists and bacteria that havethe digestive enzyme necessary to split the cellulose. The cow,antelope, and kangaroo collects up grass and chews it with theirbig huge battery of teeth that are grinding it down to increasethe surface area available for the attack by digestive enzymes. It is not their own digestive enzymes that are going to attackit. They even regurgitate their food, that is these animals bringa big wad of this grass back up out of their stomach and chewon it some more when they have some time in order to further breakit down. When it goes down into the rumen, that's where the bacteriacan split the polysaccharide into sugar molecules. They secretethe digestive enzymes necessary to split the polysaccharide intosugar. The sugar is then absorbed by the bacteria and it is partiallyfermented to produce energy. The carbon skeletons can be usedto make amino acids. They also can get ammonia out of the rumenfluid and they can make amino acids into which to fabricate theirown proteins for growth and reproduction. But because these microbesare anaerobic and cannot utilize oxygen, they cannot completelyoxidize the sugar molecules. They get some of the energy outof the sugar molecules and then they excrete a waste product that'scalled volatile fatty acids (VFA). The VFA is absorbed acrossthe wall of the rumen into the bloodstream of the ruminant animaland represent the major energy source for the animal.
The species of microbes thatlive in the rumen can only live in the rumen. They are very highlyadapted to the life in that environment. These animals have aset up in this rumen to regulate the pH, temperature, water supplyand everything in there in order to produce the maximum growthrate for the bacteria so that the bacteria will breakdown thecellulose as fast as they can. But the thing to remember is thatthis is just the first 4 chambers. The 4th chamber is the standardacid digesting stomach. The bacteria is continually harvestedalong with other materials out of the rumen and into the aciddigesting stomach where it gets killed and the digestion processproceeds. The stuff goes into the small intestine and these aminoacids that were produced to make the proteins and bacteria canthen be absorbed. So the ruminants are not only using the volatilefatty acids (the waste products of the metabolism & bacteria). They are harvesting the bacteria and living on the bacteria themselvesas well.
And as a consequence of thefact that they are harvesting the bacteria, ruminants do notneed to have any amino acids in their diet. Most vertebrate animalshave amino acids that they cannot fabricate through their owncellular machinery. They have many of them that they can buthumans for example have a group of essential amino acids thatthey cannot fabricate themselves. Ruminants do not have to haveany amino acids in their diet at all. They do need to have asource of nitrogen and they need to have a source of celluloseand there have been studies that have shown that a cow can actuallylive on newspaper and urea alone. This particular form of symbioticdigestion of cellulose by bacteria is technically called pre-gastricbecause the bacterial fermentation is located upstream from thestomach. This allows the animal to run the bacteria through thestomach and the small intestine to get the nutrients, the proteinsand the amino acids and some vitamins that are produced by thebacteria.
There is another form of symbioticdigestion of cellulose by bacteria which is called post-gastric.
This is seen in the horse for examplewhere the bacteria fermentation is in the caecum which is tremendouslyenlarged and the same basic first part of this process takes place. The cellulose is fermented by the bacteria, the VFA are excretedacross by the bacteria and absorbed across the wall of the caecum. A horse that has been fed on a high fiber diet can get somethinglike 40% of his daily energy needs in the form of VFA. But thehorse is not able to get at the bacteria themselves and so itdoesn't get the amino acids and the proteins. Therefore, a horsehas to be fed a diet that is much more complete and includes theseessential amino acids that you don't have to worry about witha cow.
So in a sense, the kangaroosare convergent with the cows in their digestive physiology. Theyare also similar in their ecology. They live on open grasslandplains. They are highly cursorial to avoid predators and tobe able to migrate and follow the localized availability of grassesand so forth.
The Flying Opossum is interestingbecause it has a similar adaptation for getting around betweenthe trees like a number of different species of rodents that haveevolved in other places in the world. Here in North America wehave a flying squirrel that looks very much like this marsupialand there are other flying squirrel types of rodents in differentfamilies of rodents that are found in other parts of the worldas well. So this animal is another example of convergent evolutionof a similar set of adaptations.
The koala bear is really a uniqueanima. It is highly specialized for feeding on the leaves of7 species of eucalyptus trees and it's not very bear-like in it'sbiology. It spends virtually it's entire life up in trees. Itis exclusively an herbivore.
Now proceeding to the InfraclassEutheria, the most primitive of this infraclass and the ones thatare the most like the 1st mammals are found in the Order Insectivora. There are 406 species of insectivores. That makes it the 3rdlargest order in the Infraclass Eutheria and Class Mammalia. These animals have a world-wide distribution. They are foundthroughout the world and included in this order is the smallestof all the species of mammals which is the little shrew. It weighsabout 2 grams, approximately the same body size as the smallestof the birds. There are a variety of different kinds of membersof this order. They all feed on insects.
There are a variety of differentkinds of insectivores. Some of them are very peculiar and weird. The moles, here in North America, swim through the soil and havelittle tiny eyes and great big claws. Some of the other typesof insectivores include the hedgehog which also have fur thatis specialized into little spiky structures like the spiny anteateror echidna. Many of the different species of insectivores hibernate(spend a good portion of cold season with low body temperatures)and exhibit daily torpor. Almost all members of the Order Insectivoraare nocturnal although many shrews really cannot be clearly classifiedas being either nocturnal or diurnal. They are essentially activeperiodically throughout the day. They can sleep just about atany time of the day. They do not show a strong daily rhythm ofactivity and inactivity. The reason is that they are so smallthat they have to consume a giant amount of food in order to maintaintheir high mammalian body temperatures. They basically cannotever go without eating for any great length of time.
The second largest order ofmammals is the Order Chiroptera or the bats. There are a totalof 853 species of bats. There are 2 basically different typesof bats:
A. Microchiroptera
B. Megachiroptera.
Chiroptera means "handwing". The microchiropterans are the little bats and theyare mostly insectivores. Some of them feed on aerial insectsby catching them on the wings. There are a few species of batsthat will land on the ground in the immediate vicinity of a bigterrestrial insect and eat crickets and things like that. A coupleof species of bats are insectivores feeding on nectar.
The overwhelming majority ofthis order are microchiropterans and they are insectivores. Butthe megachiroptera like fruit bats or flying foxes are fruit eatersor frugivores. The microchiropterans, both insectivores and insectivores,are nocturnal but the megachiropterans are diurnal with big eyesand locate their fruit visually. They are found in tropical areasof South America as well as in Asia.
The microchiropterans, mostcommon bats, are active at night. They are able to avoid runninginto things and find food by way of echolocation (sensory mechanism). Echolocation involves the production of short bursts of soundand then listening for the echoes as those short bursts of soundsbounce off of things in the environment. Humans cannot hearthe sound produced by these bats. They are beyond our range ofhearing.
Many species of bats are migratory. Other species of bats that are non-migratory that live in thetemperate regions will hibernate over winter. In many of thosespecies, the female will have become impregnated during the Falland have a partially developed fetus in their reproductive tract. When they hibernate, the fetus goes into a state of suspendedanimation and then when they arose in the springtime the fetuscontinues it's development. The babies are born very shortlyafter the females awake.
Echolocation is also shown bywhales and dolphins. There is only a single species of bird thathas ever been shown to utilize echolocation and they live in caves. They are called an "Oil Bird". They are called oilbirds because they have an extensive accumulations of subcutaneousfat in their bodies. When the natives go hunting in caves, theywill find one of these birds and kills it to use it as a torch. Oil birds use clicking sounds for their echolocation.
The next order is the OrderEdentata. There are 31 species found in Central and South America. Three basically different types of animals that are not terriblysimilar to one another in their appearance are the Armadillo, Anteater and the Sloth. These animals are very different fromone another and the reason that they are placed in the same orderis that they all show that xenarthrous articulation. It's anextra point of contact between the vertebrae, below the standardmammalian zygapophysis.
The sloth is almost exclusivelyarboreal (lives in trees). They cannot walk on their legs. Whenthey get down on the ground, they kind of sort of crawl alongon their bellies in order to get up in another tree. When theyare moving on the trees they hang beneath the branches and theyare very slow. They have very low metabolic rates. They alsohave a peculiar feature in that they are just about the only mammalthat is green in color. Mammals are black, brown and white. The reason why they are green is that algae grow in the littlepits on their hair. The green enables them to be hard to seein the trees.
The Order Primates includingourselves has 166 species. The ones that we are most familiarwith are the monkeys and the Great Apes. There are several differentgroups within the order. There are animals that are called prosimian(simian refers to monkey). This suggests that they are primitivemonkey-like animals. This includes the lemurs and marmoset.
There are 2 different familiesof monkeys. The Old World Monkeys and the New World Monkeys. They have fairly long and separate evolutionary history. Ofcourse these animals are largely arboreal (living in trees). Some of them, however, have secondarily become terrestrial. Mostmonkeys are herbivores and frugivores.
The difference between a NewWorld monkey and an Old World monkey is that the only ones thathave prehensile tails (can hang by their tails) are the SouthAmerican monkeys. The Old World Monkeys of Africa and Asia donot have that ability.
ANATOMICAL FEATURES:
Most of them are diurnal althoughthere are certainly some nocturnal species. They have a shortenedsnout which is associated with the developing increased overlapin their visual fields. They have to be able to judge depth inorder to get around in the trees and so that's associated withthe shortening of the snout. Also in a diurnal animal, visionis going to be much more important and so the sense of smell becomesrelatively less important. So the nose itself can become relativelysmaller.
Included in this order are theGreat Apes. These are the orangutans, chimpanzees, gorillas,and the gibbons. Man can be in the same family with these animalsparticularly closely related to the chimpanzees and the gorillas. Similar in base pairs in genetic information (DNA).
The largest order in the classis the Order Rodentia. These are the rodents. There are 1,750species. They have a world-wide distribution. Most but not allare nocturnal. Some are diurnal like the ground squirrels andtheir more famous relatives like the groundhogs and prairie dogs. But the majority are nocturnal.
Essentially, all of the rodentshave very altricial young. The babies are quite helpless andstay in the burrows. Most of these animals burrow in the groundalthough not all of them do. They are the only order of Eutherianmammals that made it to Australia under their own power.
They are characterized by havinga permanently growing incisor; 2 on top and 2 on bottom.
The incisors grow in a perfect archall the way back towards the back of the jaw and they have a seriesof cheek teeth. These are both the molars and the premolars. The premolars are indistinguishable from the molars so that theyhave a large battery of grinding teeth. They have this gap betweenthe incisor and the cheek teeth which is called the diastema. So in general they are characterized by having a diastema andpermanently growing incisors. Most mammalian teeth have 1 or moreroots that have very tiny openings at the base through which nervesand blood vessels can enter the tube. A permanently growing toothhas a large opened base. It doesn't come to a point at the root. These teeth grow throughout the life of the animal continually. Also, the outside of most mammalian teeth is covered with a hardmaterial called enamel. The layer of enamel on the outside wearsdown very slowly and inside of it is a layer of dentin. Wellthe incisors of rodents do not work that way. They only haveenamel on the front edge and then behind that is the dentin. The effect of this is that the hard enamel on the front edge wearsdown much more slower than the dentin. By just grinding theirteeth or using their teeth to chew on things, they have a verysharp chisel like edge to this tooth and makes it a very effectivechewing tooth or cutting through things.
They use their teeth of courseto do everything. Beavers are rodents that use their teeth tocut down trees and chew holes in all sorts of things. The teethgrow permanently. They have to be able to maintain occlusionof these teeth and be able to grind away at them.
There are 3 major families ofrodents. Two of those major families are porcupine types of animals. There is an Eurasian Porcupine and a North American Porcupinethat look a lot alike and have these long quills for defense,but they are not closely related to one another. They grow toa pretty good size, up to 27 kilograms.
The world's largest rodent isa 50 kilogram rodent called the Capybara. It lives along theedges of rivers and spends a lot of time swimming around in thewater with just the tops of its head sticking out. It feeds onaquatic vegetation and in some ways are like a South Americanversion of the hippopotamus. This animal is a close relativeof the Nutria. This species was introduced to Louisiana and ishaving a devastating effect on the natural habitats in the swamps.
So those are the rodents. Some of them exhibit hibernation - ground squirrel types do as wellas other rodents. Ground squirrels being diurnal is an exampleof a mammal that has kind of re-evolved at least partial colorvision. Ground squirrels have been empirically to be red-greencolor blind but they do have some ability to distinguish color.
Now the largest animals to haveever lived are still alive today and they are the whales in theOrder Cetacea. There are 78 species of whales still alive. Theyare almost all marine (live in oceans in the salt waters). Thereare 2 basically different types of whales. The Baleen Whalesare in a group called the Mysticeti. These are the animals thatfilter-feed. The Blue Whale is the largest vertebrate to haveever lived. It is also a big filter-feeder. Baleen is composedof carotene, the same sort of top protein material that your fingernailsare made of. They have a whole series of large plates of thisbaleen that are flat and sort of at a 90 degree angle to the edgeof the jaw suspended from the roof of their mouth. What the animalswill do is they will find a large school of invertebrates suchas krill and they will take a tremendous gulp of ocean water containingthese invertebrates. Then they close their mouth and the watergoes out between the plates of baleen and the krill gets stuckbehind. They are really filter-feeding although they are notfeeding on microscopic organisms.
These animals are found, atleast a portion of the year, in the very cold ocean waters thatare the most productive where they feed and then many of themwill go on migrations to warmer waters to reproduce. So the Californiagray whales migrate down the coast of California. They do notfeed the whole time that they are gone. They do all their feedingwhen they are up in the arctic waters and then they come downand give birth to their young, copulate and swim back again beforethey have something else to eat. A lot of other whales migrateas well.
The fluke is the name of thelarge horizontal tail fin that they have and it is developed fromthe tail. It is not composed of hind limbs, although many ofthese animals have vestigial pelvic girdles. They do not haveany hind limbs but most of them do have some kind of large flippersfor their fore limbs. They are all endotherms and are all air-breathers. They must surface to take a breath, but some of these animalscan dive for as long as an hour. They have a whole series ofinteresting physiological adaptations that allow them to holdtheir breath for an hour. Insulation is in a form of blubberunder the skin. It is a long continuous layer of subcutaneousadipose tissue. It is important to recognize that they do notreally squirt water out of their blow holes out of the top oftheir head. They frequently live where the ocean air is verycold. The steam you see is condensed water vapor when they exhaled. The whale babies are very precocial. They will have to be ableto swim as soon as they are born.
The other types of whales arecalled the Odontoceti. These are the toothed whales. The largesttoothed whale is the sperm whale and the smaller ones are theDolphins and Porpoises. These animals have Homodont-Dentition. They feed on fishes and large marine invertebrates. The Spermwhales are famous for apparently battling giant squid that theymanage to dig up from the bottom of the ocean and showing thescars of their battles with these giant mollusks.
These animals, particularlythe toothed whales, use echolocation to locate the fish that they'regoing to feed on. They also use low frequency sounds for communicationbetween individuals. They seem to be very social. They travelin large pods (packs of whales) and they appear to be able tocommunicate and seem to be very intelligent.
There are a couple of speciesof dolphins that are found in fresh-water. The major river systemsof the world like the Amazon, have fresh-water dolphins that haveinvaded that fresh-water environment.
The next order is the OrderCarnivora or carnivores. There are 253 species in this order.There are 7 families: Dogs, Bears, Weasels (minks), Mongoose(South African Meercats), Cats, Hyenas, & Raccoons.
Some of these animals are extremelycarnivorous, that is feeding on vertebrate food. The cats, hyenas,weasels and mongoose are very strongly carnivorous, essentiallyfeeding only on meat. Some of them are sort of omnivorous, feedingon a good mixture of meat and plant materials like the dogs. The bears are almost herbivores although there are some highlycarnivorous bears like the Polar Bear. So there is quite a bitof variability in the degree to which members of this order dependupon meat but some of them are extensively dependent upon meat.
They have a special arrangementof their cheek teeth that is designed for slicing up the meat.The arrangement is called the carnassials which are long thinblade-like premolar that slides past, instead of occluding andgrinding against one another. These things slide past one anotherand make a very effective shearing mechanism.
In the weasel family are animalslike the Sea Otter that lives in the oceans along the coast ofCalifornia. These guys have incredibly dense fur that traps air. They have to spend a lot of time grooming, spreading the oilfrom their sebaceous glands around on their fur and keeping theirfur very well oiled and otherwise clean in order for it to maintainits waterproofing capability. It keeps the water off of theirskin and keeps them from getting cold. They do not have insulationin the form of blubber the way the whales do. Rather, they haveinsulation in the form of trapped air within their pelt.
Many of these carnivores arenocturnal. They are found in a wide variety of different habitats. The Polar Bear is found up in the extreme north on the tundra,on the ice flows. There is an animal called the Arctic Fox whichis brown colored for camouflage in the summertime and white coloredfor the winter.
A closely related group is theOrder Pinipedia. There are 31 species in this order. These arethe seals, sea lions and the walrus. All of these are marinecarnivores. They usually feed on fishes with their homodont-dentition.
The seals are the most highlyadapted of these marine mammals. They have insulation in theform of blubber. They are very streamlined. They have no externalpinna although they have an ear. They do not have a pinna thatsticks up to cause turbulence when they are swimming through thewater and slow them down. They have lost the ability to rotatetheir hind limbs forward.
Whereas the sea lions are theones that are probably a separate adaptation or invasion of themarine environment, they have insulation in the form of fur. They have thick heavy fur pelt with air trapped within the furand those are the ones that can rotate their hind limbs forward.
And of course the walrus isa real interesting member of this group too. The guy with thegreat big tusks that he uses for digging up mollusks that he getsout of the ocean.
The last 2 orders are the orderthat includes the horse and their relatives and the order thatincludes the cows and their relatives. Collectively these animalsare referred to as ungulates, that is because they are unguligrade. They are standing up on the very tips of their toes with reductionin lateral digits. The typical mammalian claw has evolved intothe hoof of the animal and they have in most cases tremendousreduction in the number of digits to the side.
The Order Perissodactyla includes16 species; one of these is the horse. The other 3 major typesthat are found in this order include the rhinoceros and the tapir(looks like a big pig). These animals all have an odd numberof toes. Having an odd number of toes, the main axis of the limbgoes through the middle toe, that's the 3rd set of carpals ormetapodials and the phalanges that are associated with that. The term that we use for that is mesaxonic which refers to theidea that the axis of the limb goes through the middle of that3rd metapodial. In horses, that's all there is. the cannon bonewhich is an enlarged metatarsal or metacarpal is just that 3rdmetapodial.
All of these animals in thisorder are herbivores. Some of them like the horse are highlyadapted for cursorial locomotion (high speed running). That iswhy they exhibit this unguligrade stance. Horses produce a veryprecocial young. Baby horses are able to get up shortly afterbirth and are able to follow their mothers around. They are highlysocial and are found in large herds. They exhibit post-gastricsymbiotic digestion of cellulose in the very enlarged caecum. And the fossil record is one of the most complete. They appearto have actually evolved originally in North America and theoldest horse is known from the Eocene of N. America. It was aboutthe size of a German Shepherd and it had 5 toes. They then wentextinct in North America having first crossed the Strait land-bridgeinto Asia. They were reintroduced into N. America when Europeanexplorers came here.
The other order is the OrderArtiodactyla and this is a much bigger and more successful group. There are a 171 species of artiodactyles. They have a world-widedistribution except for Australia. They are unguligrade but theyare paraxonic, that is the axis of the limb goes between the3rd and 4th metapodial. Now these animals will have an even numberof toes. In some cases they will have just 2 toes. In some casesthey are sort of vestigial remnants of the 2nd and 5th metapodials.
They also have very precocial young. The order itself is divided into 2 major suborders. One suborderincludes the pigs and their relatives the warthog and the hippopotamus. They are more primitive. And then the rest of them are collectivelyreferred to as the ruminants because they share this complex 4-chambered stomach in which there is bacterial symbiotic digestion of cellulose. This is pregastric because the rumen, the chamber in which thattakes place, is upstream from the stomach.
Many species of Artiodactylesare migratory. These include the reindeer that live on the tundra,in the arctic as well as many species of antelopes that occuron the great grasslands of Africa and the grasslands of NorthAmerica as well. There are a number of different families withthis order:
Cow family = bison, buffalo, cows,antelopes - non-deciduous horns.
Deer family = They have deciduousantlers; antlers that fall off annually.
Giraffe family = Family of it'sown within this order.
Camel family = Found in Asia andNorthern parts of Africa.
Llama family = Found in Andes ofSouth America.
Camels were originally foundin North America. This family probably also evolved in NorthAmerica then it invaded South America and Asia and then went extinctin North America.
So this is a very successfulgroup of animals that are generally found in association withgrasslands.