[SOUND] Welcome back. We want to continue thinking about this field called lactation biology. In earlier videos we did a little bit of introduction, just kind of lay some of the ground work on what is lactation biology all about, we did some definitions. We also spent some time kind of thinking about milk and what is milk and what kind of perspectives do we need to bring as we think about milk. So now I want to shift gears a little bit and talk a little bit about the animals that lactate, and that is mammals. So let's take a look at our first slide. And we're just going to do a real superficial look at mammals here. Phylogenetic classes is Mammalia. All mammals are part of this phylogenetic class. It's derived from the word mamma, Latin word mamma meaning breast or teat. There are 5,400 species of mammals, quite a large group of mammals. What's interesting, though, from a lactation biology perspective, and especially as we just talked a little bit in some earlier videos about milk. We only know about milk composition in detail, or even in a general sense, in less than probably 3% of the species of this 5,400 species. So lots of opportunity to examine other kinds of species and learn about their milk composition. Let's go to the next slide. Distinguishing mammals from other animals, reptiles and birds. Some adaptations of the neocortex, a skin glad adaptation. Hair, so mammals have hair. Some changes in jaw bone and how that relates to the ear and inner bones, middle ear bones in this particular case. And then certainly the one that we're particularly interested in this course are the mammary glands. Again, skin adaptation, adaptation of the skin. A gland that's secreting something to the outside of the animal. And then finally on this set of slides here, ranging tremendously in size from very, very small bumblebee bat about an inch and a half long, something like that, to a blue whale which is the biggest mammal, over a hundred feet long. So tremendous diversity in terms of size. And as we'll see later on as we think about these things we have animals that fly, we have animals that are aquatic animals, that live in the water and. Obviously many, many terrestrial animals as well. Let's start to break down this set of 5,400 species of mammals into some type of mammals that we can easily think about and identify. So first one I want to talk about is again, class mammalia, sub-class yinotheria. A lot of times people refer to these as a prototheria and the word you may be more familiar with are monotremes. These are egg laying mammals and so again, the order of the monotremata, again, they lay eggs. They have a pouch and usually the pouch, kind of this big folds of skin that come here. The mammary structures are right under this area. They lay an egg. That egg is placed inside the pouch, and then incubates in the pouch. The young are kind of hatch out a that. Very, very, very immature. Very immature young in that particular case, but they're able to kind of, there's milk oozes out on the surface inside the pouch there and they can consume that milk. There's little hairs that come out next to the different pores and as the young kind of move around they stimulate those hairs that causes milk ejection. And again the milk oozes out on the surface of inside the pouch there and the young ingest that milk. Five species that we know of that are in existence today, the duck billed platypus is one and then four species of echidna. And sometimes these are referred to as spiny anteaters. Typically these monotremes, well not typically, these monotremes are found in Australia and New Guinea. So in that part of the world. Really not anywhere else in the world. So again, egg laying mammals, we think of these as very primitive on the other hand they had in fact existed for many millions of years. And so, as our reproductive strategy for these animals it seems to be pretty successful for them. Now let's talk a look at another group of mammals and these are subclass theria. And this particular group or clade is called metatheria. And here we're talking about the marsupials. So Marsupialia are the animals that we're talking about. These are animals that are born, the young are born live. Remember the monotremes, they hatched out of an egg. These are born live but they are extremely immature. They have fairly developed fore limbs and that's about it. So once they're born, they can literally crawl up and they go down into a pouch. So they nurse in that pouch. They will actually essentially swallow a teat. It goes down about that far into their throat there. And they will essentially continually nurse on that teat, growing in the pouch and eventually they'll start leaving the pouch, sticking their head back in and so on and so forth. So very, very complex system. If you think about this, really changes the way we think about intrauterine development versus lactation and extrauterine development compared to most of the animals that we're used to say cows or pigs and so on and so forth. 334 species have been identified, kangaroos, wallabies, koalas, possums, wombats, Tasmanian devils, bandicoots and a number of other ones. About two-thirds of those are in Australia and New Guinea. In the Americas there are about 100 species that are identified in the Americas. only one of those is in North America and that is the Virginia opossum. And so we have one in North America a bunch of them here and then the bulk of them are in Australia and New Guinea. So marsupials, again, this idea that the young are very, very immature. Develop in a pouch, are nursing in that pouch and that has again, a lot to do with their reproductive strategy in how that works. Now let's talk about the mammals that most of us are familiar with, including our own species. And that is again, subclass Theria. Eutherian mammals, think of this as a true placenta. So these are Placentalia, they have a true placenta. Part of what that means is that the young are able to develop in the womb of the mother for a much longer time. So they're born much more mature than those monotremes hatch out or the marsupials are born. Still tremendous diversity in terms of how mature they are. A newborn calf, for example, can get up after fairly short period of time, an hour perhaps and walk around and suckled from the mother. Newborn babies obviously are not going to be able to get up and walk right away. Newborn rat pups, for example, are born with their eyes closed and it takes several days for those eyes to open. So tremendous diversity. Nevertheless, all of them are much more mature than some of the animals we just talked about a moment ago, again for example, types of marsupials. Able to nurse on a dependent mother. And here what I'm talking about is, again, the monotremes and the marsupials have a pouch, either a pouch kind of like a pocket in the marsupials or the folds of skin and in the case of the monotremes. And they're in there so the younger in there and they're kind of trapped in there but they're really dependent upon that environment whereas these other animals are out they can nurses the mother somewhat independently in that sense. The vast majority of extant mammals in existence today are these Eutherian mammals, Placentalia mammals. Largest orders, in the terms of the largest numbers of animals, diversity there, Rodentia, of course, mice, rats, beavers, and those kinds of things. Chiroptera bats, many, many species of bats. So a lot of flying mammals in terms of different kinds of species. As this Soricomorpha, moles, shrews, and this solenodons, these are thought of a bit more primitive types of placental mammals. Some of those are actually considered to be venomous. So there's a group of those, not very many of them but they're into this order of soricomorpha. Where we find mammals? Again, we find them in the oceans, we find them in the air. So flying animals, such as bats. Terrestrial, we find them in all sorts of different environments. That's again part of what makes these animals very, very interesting. Lactation again is a key part of the reproductive strategy of animals. So again intrauterine development. But then there's still an absolute requirement for lactation to help that animal continue developing extra-uterine, or past the point after which it's born. So let's quickly review what we've talked about in this video. So the extant mammals, that is, those that exist today, again, over 5,400 species. So we have the monotremes, prototheria or the metatherian or the marsupials. And then most of the animals that we're familiar with the placental mammals or the eutherian mammals. Mammary glands, they all have mammary glands again depends where, which species it is where those glands are. Clearly in the monotremes, the mammary glands inside the pouch there, and the marsupials, that's again inside the pouch. Lactation for all of these species is a key part of their reproductive strategy. So as evolution has occurred, how they reproduce, lactation's really a key part of that overall strategy. Occupy a wide range of environments. So again, we have porpoises and whales and dolphins, etc., etc., in sea, in water. In air we have bats flying around. In fact, you look around, you see pictures of the baby bat actually as mom is flying is still sitting there nursing on the mother. And then certainly land mammals. So most of the animals that we're going to be talking about in this course, cows, the pigs, our own species, and so on are obviously going to be terrestrial, or land mammals.
