Let's look at the classification and naturalhistory of the mammals. This is covered in your illustratednotes.
This is the classification of mammals thatyou're going to be responsible for. So the first order that Iwill talk about is the most primitive and unusual, that's theOrder Monotremata. The translation of this word is "onehole" refers to the fact that these animals have a cloaca.It's not a peculiar feature of these animals because themarsupials also have it.
There are 3 living species in the order and the2 basic types are shown here on the page. They are found inAustralia and New Guinea. The Duck-billed platypus, there's onlya single species of these critters, and this is an aquatic animalthat has a dense fur like a beaver or otter that is water-proof.It has webs of skin between it's toes sort of the way that a duckdoes, that it uses in swimming, however, one thing that'sdifferent and somewhat unusual is that the web can actually foldback and so it exposes it's claws cause this animal is also aburrowing animal, it digs a burrow in the bank of the streamwhere it is living and it actually spends a good portion of theday in that burrow. So it has the ability to dig as well ashaving this web of skin that makes it easier for it to swim.
When the 1st specimens of the duck-billedplatypus were returned to Europe by the 1st European explorers ofAustralia and New Guinea, the scientists thought that somebodywas trying to fool them and had taken the head of a duck andplaced it onto the body of a beaver. It makes a living similar tothe way in which a duck does by filter-feeding and extractingsmall organisms from the water. One thing that's very unusualabout them among mammals is that the male has a poison gland onthe 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 monotremes are theant-eater type. Sometimes called the spiny-anteater or echidna.The hairs are very greatly enlarged and form these spines thathave a sharp point on the end and that's not unique to thisanimal. There are a number of other types of mammals in which thehairs have become specialized in the defensive spine-like, suchas the porcupines (rodent) as examples. These animals feed onants. 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 the world, there arespecies of social insects, ants and termites, that produce largehomes/mounds made out of mud, etc. Termite mounds are filled withhoneycombs of little passage ways and chambers where the socialinsects lives and raise their young and store their food andthings like that. And these very obvious large accumulations oflarge insects are exploited as food resources by a variety ofdifferent groups of mammals and the basic requirements for makinga living on that kind of food are the same and as a consequencewe find convergent evolution of the same set of featuresnecessary for making that kind of living. If you're going to feedon these social insects the first thing you have to do is youhave to be able to dig through this hard baked mud home that theylive in. So all of these animals have modifications forburrowing. Their skeleton looks somewhat like the armadilloskeleton in having large areas for attachment of the musclesnecessary for long sharp claws and so forth. And then once youburrow through the side of the home, then they need to slurp upthe insects so all these guys have sort of long narrow snouts,incredibly long tongues and very sticky saliva. And most of themhave greatly reduced teeth because apparently there isn't muchpoint in chewing something that's already small.
The same basic set of anteater adaptations thenare found in the:
Echidna New Guinea MONOTREMES
Marsupial Anteater Australia MARSUPIAL
Anteater Central & South EUTHERIAN
America
There are a couple of other animals that arenot included in this classification cause they are sort of smallspecialized orders that include just these anteater types butwhich are worth knowing about I think just mentioning in thecontext of these convergent evolution is the:
Aardvark (="earth pig") AfricaEUTHERIAN
Pangolin Southeast Asia EUTHERIAN
Aardvarks are incredibly powerful burrowers;they have big ears. And there is an animal called the pangolinwhich is also an anteater type and this animal is really a weirdcritter, their hairs are formed into what look very much likereptilian scales.
So what we have here is a Monotreme in theSubclass 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 majorNorthern continents. So obviously animals coming from verydifferent phylogenetic heritages have evolved the same set ofadaptive characteristics/modifications of their skeletons and soforth that are necessary to be good burrowers and have longtongues and sticky saliva and reduced teeth. So this would be agood example of convergent evolution that evolves very diverseancestors all having very similar set of adaptations.
The next order is the Order Marsupialia in theInfraclass Metatheria. There are 242 species of marsupials andthey are found in South America and in Australia. At least that'stheir sort of historic distribution. There is a South Americanmarsupial that has been quite successful in invading NorthAmerica and that's called the American Opossum, you will seethese guys out wondering out on the streets at night every onceand 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 I described toyou the historic evidence about the marsupial fauna of SouthAmerica that it included a variety of different carnivores. Forexample there was a large marsupial cat that looked very muchlike the Saber-Toothed Cat that you can see skeletons of at theLaBrea Tar Pits. Big obviously ferocious carnivores with greatbig huge canine teeth was included in that fauna in South Americaand most of them went extinct. Although there are a small numberof opossum-like marsupials that continue to survive quite well inSouth America, the majority of the species of marsupials arefound 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 shown here includethe Tasmanian Wolf which is an example of one of severaldifferent types of marsupials that look like carnivores. In factthey are carnivores and they look like Eurasian/North Americancarnivores. 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 generaldescription. The Marsupial Mole is a fossorial mammal, withadaptations like most fossorial mammals. They have very shortthick dense velvety kind of fur, greatly reduced eyes, and verypowerful front limbs with big claws that it uses for diggingthrough the soil. They really sort of live essentially theirwhole lives moving through the soil. They don't necessarily leaveopen passage ways behind them. They kind of swim through the soiland eat the various kinds of invertebrates that they encounteralong the way. The Pouched Mouse is really somewhat more like ashrew. Moles and shrews are members of the Eutherian animalswhich are insectivores because they eat primarily insects. In arelated group, there is a mouse-like Australian marsupial calledthe Honey Badger which feeds on nectar. It climbs around in thetrees and collects the nectar with its long tongue, the same waythat a hummingbird does.
While North American and European zoologistsclassify the marsupials in a single order with something like 7different families, the majority of which are represented here onthese 2 pages. Australian zoologists have a tendency to classifythe marsupials as 7 different orders. They feel that they aredifferent enough from one another to deserve the classificationas 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 ofrodents as there are marsupials, but there are quite a diversegroup of rodents that live in Australia as well.
Now the kangaroo tends to look like a prettyunusual, essentially almost a unique animal. In terms of its sizeand its specialization for saltatorial locomotion, it is in factreally not comparable to anything anywhere else in the world.There are small saltatorial or hopping types of rodents thatoccur all over the world but nothing as big as these bigkangaroos. From an ecological point of view, the kangaroos arevery much like the antelopes and large ungulate(sp?) mammals thatare adapted for cursorial locomotion. The hopping locomotion inkangaroos is very fast, a lot of maneuverability and they arecapable of prolonged migrations following the unpredictablerainfall and grass growth that occurs in the outback ofAustralia. Another thing that is similar about them is their modeof digestion. They have a digestive system which is very similarto that of a cow and other relatives of the cow.
Here is a quick overview of what's happening ina cow's stomach. One way of describing this common form ofdigestion found both in the kangaroos and in the cows issymbiotic digestion of cellulose. The symbiotic digestion ofcellulose 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 animals arecollecting materials to sustain the polysaccharide calledcellulose. Now a polysaccharide is a polymer that is made up of avery large number of repeating units of sugar molecules. Starchis a polysaccharide that is produced by animals and animals havethe digestive enzymes necessary to break down starch. However, novertebrate animals and almost no invertebrate animals produce thedigestive enzyme necessary to breakdown cellulose because it hasa different kind of bond between the sugar molecules. Celluloseis probably the single most common organic molecule on thesurface 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 completelyinaccessible to them if they don't get some help. This symbioticdigestion of cellulose by bacteria is a very elaborate form ofhelp. The kangaroos and the members of the Artiodactyla are trueruminants that have a 4-chambered stomach instead of the singlechambered sort of standard acid digestive stomach of mostvertebrates
The first of these 4 chambers is called therumen. It is the stomach into which the grasses and plantmaterials go when the animal eats. And in the rumen is aflourishing population of protists and bacteria that have thedigestive 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 chew onit some more when they have some time in order to further breakit down. When it goes down into the rumen, that's where thebacteria can split the polysaccharide into sugar molecules. Theysecrete the digestive enzymes necessary to split thepolysaccharide into sugar. The sugar is then absorbed by thebacteria and it is partially fermented to produce energy. Thecarbon skeletons can be used to make amino acids. They also canget ammonia out of the rumen fluid and they can make amino acidsinto which to fabricate their own proteins for growth andreproduction. But because these microbes are anaerobic and cannotutilize oxygen, they cannot completely oxidize the sugarmolecules. They get some of the energy out of the sugar moleculesand then they excrete a waste product that's called volatilefatty acids (VFA). The VFA is absorbed across the wall of therumen into the bloodstream of the ruminant animal and representthe major energy source for the animal.
The species of microbes that live in the rumencan only live in the rumen. They are very highly adapted to thelife in that environment. These animals have a set up in thisrumen to regulate the pH, temperature, water supply andeverything in there in order to produce the maximum growth ratefor 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 thestandard acid digesting stomach. The bacteria is continuallyharvested along with other materials out of the rumen and intothe acid digesting stomach where it gets killed and the digestionprocess proceeds. The stuff goes into the small intestine andthese amino acids that were produced to make the proteins andbacteria can then be absorbed. So the ruminants are not onlyusing the volatile fatty acids (the waste products of themetabolism & bacteria). They are harvesting the bacteria andliving on the bacteria themselves as well.
And as a consequence of the fact that they areharvesting the bacteria, ruminants do not need to have any aminoacids in their diet. Most vertebrate animals have amino acidsthat they cannot fabricate through their own cellular machinery.They have many of them that they can but humans for example havea group of essential amino acids that they cannot fabricatethemselves. Ruminants do not have to have any amino acids intheir diet at all. They do need to have a source of nitrogen andthey need to have a source of cellulose and there have beenstudies that have shown that a cow can actually live on newspaperand urea alone. This particular form of symbiotic digestion ofcellulose by bacteria is technically called pre-gastric becausethe bacterial fermentation is located upstream from the stomach.This allows the animal to run the bacteria through the stomachand the small intestine to get the nutrients, the proteins andthe amino acids and some vitamins that are produced by thebacteria.
There is another form of symbiotic digestion ofcellulose by bacteria which is called post-gastric.
This is seen in the horse for example where thebacteria fermentation is in the caecum which is tremendouslyenlarged and the same basic first part of this process takesplace. The cellulose is fermented by the bacteria, the VFA areexcreted across by the bacteria and absorbed across the wall ofthe caecum. A horse that has been fed on a high fiber diet canget something like 40% of his daily energy needs in the form ofVFA. But the horse is not able to get at the bacteria themselvesand so it doesn't get the amino acids and the proteins.Therefore, a horse has to be fed a diet that is much morecomplete and includes these essential amino acids that you don'thave to worry about with a cow.
So in a sense, the kangaroos are convergentwith the cows in their digestive physiology. They are alsosimilar in their ecology. They live on open grassland plains.They are highly cursorial to avoid predators and to be able tomigrate and follow the localized availability of grasses and soforth.
The Flying Opossum is interesting because ithas a similar adaptation for getting around between the treeslike a number of different species of rodents that have evolvedin other places in the world. Here in North America we have aflying squirrel that looks very much like this marsupial andthere are other flying squirrel types of rodents in differentfamilies of rodents that are found in other parts of the world aswell. So this animal is another example of convergent evolutionof a similar set of adaptations.
The koala bear is really a unique anima. It ishighly specialized for feeding on the leaves of 7 species ofeucalyptus trees and it's not very bear-like in it's biology. Itspends virtually it's entire life up in trees. It is exclusivelyan herbivore.
Now proceeding to the Infraclass Eutheria, themost primitive of this infraclass and the ones that are the mostlike the 1st mammals are found in the Order Insectivora. Thereare 406 species of insectivores. That makes it the 3rd largestorder in the Infraclass Eutheria and Class Mammalia. Theseanimals have a world-wide distribution. They are found throughoutthe world and included in this order is the smallest of all thespecies of mammals which is the little shrew. It weighs about 2grams, approximately the same body size as the smallest of thebirds. There are a variety of different kinds of members of thisorder. They all feed on insects.
There are a variety of different kinds ofinsectivores. Some of them are very peculiar and weird. Themoles, here in North America, swim through the soil and havelittle tiny eyes and great big claws. Some of the other types ofinsectivores include the hedgehog which also have fur that isspecialized into little spiky structures like the spiny anteateror echidna. Many of the different species of insectivoreshibernate (spend a good portion of cold season with low bodytemperatures) and exhibit daily torpor. Almost all members of theOrder Insectivora are nocturnal although many shrews reallycannot be clearly classified as being either nocturnal ordiurnal. They are essentially active periodically throughout theday. They can sleep just about at any time of the day. They donot show a strong daily rhythm of activity and inactivity. Thereason is that they are so small that they have to consume agiant amount of food in order to maintain their high mammalianbody temperatures. They basically cannot ever go without eatingfor any great length of time.
The second largest order of mammals is theOrder Chiroptera or the bats. There are a total of 853 species ofbats. There are 2 basically different types of bats:
A. Microchiroptera
B. Megachiroptera.
Chiroptera means "hand wing". Themicrochiropterans are the little bats and they are mostlyinsectivores. Some of them feed on aerial insects by catchingthem on the wings. There are a few species of bats that will landon the ground in the immediate vicinity of a big terrestrialinsect and eat crickets and things like that. A couple of speciesof bats are insectivores feeding on nectar.
The overwhelming majority of this order aremicrochiropterans and they are insectivores. But themegachiroptera like fruit bats or flying foxes are fruit eatersor frugivores. The microchiropterans, both insectivores andinsectivores, are nocturnal but the megachiropterans are diurnalwith big eyes and locate their fruit visually. They are found intropical areas of South America as well as in Asia.
The microchiropterans, most common bats, areactive at night. They are able to avoid running into things andfind food by way of echolocation (sensory mechanism).Echolocation involves the production of short bursts of sound andthen listening for the echoes as those short bursts of soundsbounce off of things in the environment. Humans cannot hear thesound produced by these bats. They are beyond our range ofhearing.
Many species of bats are migratory. Otherspecies of bats that are non-migratory that live in the temperateregions will hibernate over winter. In many of those species, thefemale will have become impregnated during the Fall and have apartially developed fetus in their reproductive tract. When theyhibernate, the fetus goes into a state of suspended animation andthen when they arose in the springtime the fetus continues it'sdevelopment. The babies are born very shortly after the femalesawake.
Echolocation is also shown by whales anddolphins. There is only a single species of bird that has everbeen shown to utilize echolocation and they live in caves. Theyare called an "Oil Bird". They are called oil birdsbecause they have an extensive accumulations of subcutaneous fatin their bodies. When the natives go hunting in caves, they willfind one of these birds and kills it to use it as a torch. Oilbirds use clicking sounds for their echolocation.
The next order is the Order Edentata. There are31 species found in Central and South America. Three basicallydifferent types of animals that are not terribly similar to oneanother in their appearance are the Armadillo, Anteater and theSloth. These animals are very different from one another and thereason that they are placed in the same order is that they allshow that xenarthrous articulation. It's an extra point ofcontact between the vertebrae, below the standard mammalianzygapophysis.
The sloth is almost exclusively arboreal (livesin trees). They cannot walk on their legs. When they get down onthe ground, they kind of sort of crawl along on their bellies inorder to get up in another tree. When they are moving on thetrees they hang beneath the branches and they are very slow. Theyhave very low metabolic rates. They also have a peculiar featurein that they are just about the only mammal that is green incolor. Mammals are black, brown and white. The reason why theyare green is that algae grow in the little pits on their hair.The green enables them to be hard to see in the trees.
The Order Primates including ourselves has 166species. The ones that we are most familiar with are the monkeysand the Great Apes. There are several different groups within theorder. There are animals that are called prosimian (simian refersto monkey). This suggests that they are primitive monkey-likeanimals. This includes the lemurs and marmoset.
There are 2 different families of monkeys. TheOld World Monkeys and the New World Monkeys. They have fairlylong and separate evolutionary history. Of course these animalsare largely arboreal (living in trees). Some of them, however,have secondarily become terrestrial. Most monkeys are herbivoresand frugivores.
The difference between a New World monkey andan Old World monkey is that the only ones that have prehensiletails (can hang by their tails) are the South American monkeys.The Old World Monkeys of Africa and Asia do not have thatability.
ANATOMICAL FEATURES:
Most of them are diurnal although there arecertainly some nocturnal species. They have a shortened snoutwhich is associated with the developing increased overlap intheir visual fields. They have to be able to judge depth in orderto get around in the trees and so that's associated with theshortening of the snout. Also in a diurnal animal, vision isgoing to be much more important and so the sense of smell becomesrelatively less important. So the nose itself can becomerelatively smaller.
Included in this order are the Great Apes.These are the orangutans, chimpanzees, gorillas, and the gibbons.Man can be in the same family with these animals particularlyclosely related to the chimpanzees and the gorillas. Similar inbase pairs in genetic information (DNA).
The largest order in the class is the OrderRodentia. These are the rodents. There are 1,750 species. Theyhave a world-wide distribution. Most but not all are nocturnal.Some are diurnal like the ground squirrels and their more famousrelatives like the groundhogs and prairie dogs. But the majorityare nocturnal.
Essentially, all of the rodents have veryaltricial young. The babies are quite helpless and stay in theburrows. Most of these animals burrow in the ground although notall of them do. They are the only order of Eutherian mammals thatmade it to Australia under their own power.
They are characterized by having a permanentlygrowing incisor; 2 on top and 2 on bottom.
The incisors grow in a perfect arch all the wayback towards the back of the jaw and they have a series of cheekteeth. These are both the molars and the premolars. The premolarsare indistinguishable from the molars so that they have a largebattery of grinding teeth. They have this gap between the incisorand the cheek teeth which is called the diastema. So in generalthey are characterized by having a diastema and permanentlygrowing incisors. Most mammalian teeth have 1 or more roots thathave very tiny openings at the base through which nerves andblood vessels can enter the tube. A permanently growing tooth hasa 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. Well theincisors of rodents do not work that way. They only have enamelon the front edge and then behind that is the dentin. The effectof this is that the hard enamel on the front edge wears down muchmore slower than the dentin. By just grinding their teeth orusing their teeth to chew on things, they have a very sharpchisel like edge to this tooth and makes it a very effectivechewing tooth or cutting through things.
They use their teeth of course to doeverything. Beavers are rodents that use their teeth to cut downtrees and chew holes in all sorts of things. The teeth growpermanently. They have to be able to maintain occlusion of theseteeth and be able to grind away at them.
There are 3 major families of rodents. Two ofthose major families are porcupine types of animals. There is anEurasian Porcupine and a North American Porcupine that look a lotalike and have these long quills for defense, but they are notclosely related to one another. They grow to a pretty good size,up to 27 kilograms.
The world's largest rodent is a 50 kilogramrodent called the Capybara. It lives along the edges of riversand spends a lot of time swimming around in the water with justthe tops of its head sticking out. It feeds on aquatic vegetationand in some ways are like a South American version of thehippopotamus. This animal is a close relative of the Nutria. Thisspecies was introduced to Louisiana and is having a devastatingeffect on the natural habitats in the swamps.
So those are the rodents. Some of them exhibithibernation - ground squirrel types do as well as other rodents.Ground squirrels being diurnal is an example of a mammal that haskind of re-evolved at least partial color vision. Groundsquirrels have been empirically to be red-green color blind butthey do have some ability to distinguish color.
Now the largest animals to have ever lived arestill alive today and they are the whales in the Order Cetacea.There are 78 species of whales still alive. They are almost allmarine (live in oceans in the salt waters). There are 2 basicallydifferent types of whales. The Baleen Whales are in a groupcalled the Mysticeti. These are the animals that filter-feed. TheBlue Whale is the largest vertebrate to have ever lived. It isalso a big filter-feeder. Baleen is composed of carotene, thesame sort of top protein material that your fingernails are madeof. They have a whole series of large plates of this baleen thatare flat and sort of at a 90 degree angle to the edge of the jawsuspended from the roof of their mouth. What the animals will dois they will find a large school of invertebrates such as krilland 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, at least a portion ofthe year, in the very cold ocean waters that are the mostproductive where they feed and then many of them will go onmigrations to warmer waters to reproduce. So the California graywhales migrate down the coast of California. They do not feed thewhole time that they are gone. They do all their feeding whenthey are up in the arctic waters and then they come down and givebirth to their young, copulate and swim back again before theyhave something else to eat. A lot of other whales migrate aswell.
The fluke is the name of the large horizontaltail fin that they have and it is developed from the tail. It isnot composed of hind limbs, although many of these animals havevestigial pelvic girdles. They do not have any hind limbs butmost of them do have some kind of large flippers for their forelimbs. They are all endotherms and are all air-breathers. Theymust surface to take a breath, but some of these animals can divefor as long as an hour. They have a whole series of interestingphysiological adaptations that allow them to hold their breathfor an hour. Insulation is in a form of blubber under the skin.It is a long continuous layer of subcutaneous adipose tissue. Itis important to recognize that they do not really squirt waterout of their blow holes out of the top of their head. Theyfrequently live where the ocean air is very cold. The steam yousee is condensed water vapor when they exhaled. The whale babiesare very precocial. They will have to be able to swim as soon asthey are born.
The other types of whales are called theOdontoceti. These are the toothed whales. The largest toothedwhale is the sperm whale and the smaller ones are the Dolphinsand Porpoises. These animals have Homodont-Dentition. They feedon fishes and large marine invertebrates. The Sperm whales arefamous for apparently battling giant squid that they manage todig up from the bottom of the ocean and showing the scars oftheir battles with these giant mollusks.
These animals, particularly the toothed whales,use echolocation to locate the fish that they're going to feedon. They also use low frequency sounds for communication betweenindividuals. They seem to be very social. They travel in largepods (packs of whales) and they appear to be able to communicateand seem to be very intelligent.
There are a couple of species of dolphins thatare found in fresh-water. The major river systems of the worldlike the Amazon, have fresh-water dolphins that have invaded thatfresh-water environment.
The next order is the Order Carnivora orcarnivores. There are 253 species in this order. There are 7families: Dogs, Bears, Weasels (minks), Mongoose (South AfricanMeercats), 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,essentially feeding only on meat. Some of them are sort ofomnivorous, feeding on a good mixture of meat and plant materialslike the dogs. The bears are almost herbivores although there aresome highly carnivorous bears like the Polar Bear. So there isquite a bit of variability in the degree to which members of thisorder depend upon meat but some of them are extensively dependentupon meat.
They have a special arrangement of their cheekteeth that is designed for slicing up the meat. The arrangementis called the carnassials which are long thin blade-like premolarthat slides past, instead of occluding and grinding against oneanother. These things slide past one another and make a veryeffective shearing mechanism.
In the weasel family are animals like the SeaOtter that lives in the oceans along the coast of California.These guys have incredibly dense fur that traps air. They have tospend a lot of time grooming, spreading the oil from theirsebaceous glands around on their fur and keeping their fur verywell oiled and otherwise clean in order for it to maintain itswaterproofing capability. It keeps the water off of their skinand keeps them from getting cold. They do not have insulation inthe form of blubber the way the whales do. Rather, they haveinsulation in the form of trapped air within their pelt.
Many of these carnivores are nocturnal. Theyare found in a wide variety of different habitats. The Polar Bearis found up in the extreme north on the tundra, on the ice flows.There is an animal called the Arctic Fox which is brown coloredfor camouflage in the summertime and white colored for thewinter.
A closely related group is the Order Pinipedia.There are 31 species in this order. These are the seals, sealions and the walrus. All of these are marine carnivores. Theyusually feed on fishes with their homodont-dentition.
The seals are the most highly adapted of thesemarine mammals. They have insulation in the form of blubber. Theyare very streamlined. They have no external pinna although theyhave an ear. They do not have a pinna that sticks up to causeturbulence when they are swimming through the water and slow themdown. They have lost the ability to rotate their hind limbsforward.
Whereas the sea lions are the ones that areprobably a separate adaptation or invasion of the marineenvironment, they have insulation in the form of fur. They havethick heavy fur pelt with air trapped within the fur and thoseare the ones that can rotate their hind limbs forward.
And of course the walrus is a real interestingmember of this group too. The guy with the great big tusks thathe uses for digging up mollusks that he gets out of the ocean.
The last 2 orders are the order that includesthe horse and their relatives and the order that includes thecows and their relatives. Collectively these animals are referredto as ungulates, that is because they are unguligrade. They arestanding up on the very tips of their toes with reduction inlateral digits. The typical mammalian claw has evolved into thehoof of the animal and they have in most cases tremendousreduction in the number of digits to the side.
The Order Perissodactyla includes 16 species;one of these is the horse. The other 3 major types that are foundin this order include the rhinoceros and the tapir (looks like abig pig). These animals all have an odd number of toes. Having anodd number of toes, the main axis of the limb goes through themiddle toe, that's the 3rd set of carpals or metapodials and thephalanges that are associated with that. The term that we use forthat is mesaxonic which refers to the idea that the axis of thelimb goes through the middle of that 3rd metapodial. In horses,that's all there is. the cannon bone which is an enlargedmetatarsal or metacarpal is just that 3rd metapodial.
All of these animals in this order areherbivores. Some of them like the horse are highly adapted forcursorial locomotion (high speed running). That is why theyexhibit this unguligrade stance. Horses produce a very precocialyoung. Baby horses are able to get up shortly after birth and areable to follow their mothers around. They are highly social andare found in large herds. They exhibit post-gastric symbioticdigestion of cellulose in the very enlarged caecum. And thefossil record is one of the most complete. They appear to haveactually evolved originally in North America and the oldest horseis known from the Eocene of N. America. It was about the size ofa German Shepherd and it had 5 toes. They then went extinct inNorth America having first crossed the Strait land-bridge intoAsia. They were reintroduced into N. America when Europeanexplorers came here.
The other order is the Order Artiodactyla andthis is a much bigger and more successful group. There are a 171species of artiodactyles. They have a world-wide distributionexcept for Australia. They are unguligrade but they areparaxonic, that is the axis of the limb goes between the 3rd and4th metapodial. Now these animals will have an even number oftoes. In some cases they will have just 2 toes. In some casesthey are sort of vestigial remnants of the 2nd and 5thmetapodials.
They also have very precocial young. The orderitself is divided into 2 major suborders. One suborder includesthe pigs and their relatives the warthog and the hippopotamus.They are more primitive. And then the rest of them arecollectively referred to as the ruminants because they share thiscomplex 4-chambered stomach in which there is bacterial symbioticdigestion of cellulose. This is pregastric because the rumen, thechamber in which that takes place, is upstream from the stomach.
Many species of Artiodactyles are migratory.These include the reindeer that live on the tundra, in the arcticas well as many species of antelopes that occur on the greatgrasslands of Africa and the grasslands of North America as well.There are a number of different families with this order:
Cow family = bison, buffalo, cows, antelopes -non-deciduous horns.
Deer family = They have deciduous antlers;antlers that fall off annually.
Giraffe family = Family of it's own within thisorder.
Camel family = Found in Asia and Northern partsof Africa.
Llama family = Found in Andes of South America.
Camels were originally found in North America.This family probably also evolved in North America then itinvaded South America and Asia and then went extinct in NorthAmerica.
So this is a very successful group of animalsthat are generally found in association with grasslands.