Mammals are warm blooded animals that generate their own heat and generally have hair or fur covering all their bodies but their eyes. All but a few Australian mammals give birth to live young. The word mammal is derived from "mamma", Latin for "breast,” a reference to the fact that mammal young feed from the breasts of their mothers.
A lot about mammals can be surmised from their teeth. Sharp, fang-like canine teeth are an indication of a meat eater. Large molars in the back are used for grinding up vegetable matter such as roots, leaves and fruit. Chisel-like front teeth are used by grazers and rodents to graze on grass and bite into nuts.
There are about 4,600 species of mammals. About a quarter of all mammals are bats. About a half are rodents. The first mammals were shrewlike creatures that appeared around 200 million years, and scuttled among leaf litter mean on insects and millipedes. According to the official Red List by the World Conservation Union one in four mammals species is threatened. Threats include loss of habitat and competition from alien species.
Virtually all mammals play. Many mammals enjoy grooming one another.
What makes mammals unique is their hair. One of the key proteins in mammal hair is alpha-keratin. In recent years scientists have discovered the genes responsible for alpha-keratin and also found alpha-keratin in chickens and lizards---the closest living lineages to mammals. Lizards have alpha keratin in their claws as do mammals, which presumably during the evolution harnessed alpha-keratin in their claws to make hair.
Hair and fur are necessary for mammals to store precious heat in their body that has been generated by food supplies. Hair is dense and fine is composed of keratin. Hair grows and is rooted in the skin with nerve fibers that sense movements of the hair. Even mammals such as whales and hippos and naked mole rats that appear not to have any hair do have some---on their eyelids, around their ears or other body crevices. Birds need to generate and store body heat. They use feathers rather than fur to keep heat in their bodies.
No animal can create its own food like a plant does. All animals must get their food from outside their bodies, with the ultimate source being plants. Animals that eat plants directly are called herbivores. Those that eat other animals are called carnivores. Even carnivores are ultimately dependent on plants because the animals they eat either eat plants or animals that eat plants or animals that eat animals that eat plants.
Carnivores are among the most advanced animals. Meat is muscle and is one of the richest, most-energy-packed of all foods. Many carnivores have large brains, in part because catching prey takes more skill and brain power than eating a plant.
Carnivores generally have teeth such as canines that are used to stab the victim and perhaps kill it near the front of their mouth and other teeth (carnassials in mammals) further back in jaws that cut and grind the meat up make it easier to swallow and digest. Unless an ecosystem has been disturbed wherever you find large numbers of herbivores you can find carnivores that feed on them. Most large animals found on the land are mammals.
Carnivorous mammals — or animals — generally fall into two groups: 1) those that feed on large prey; and 2) those that will feed on small bite size prey, often things like insects or earthworms. As a carnivore get bigger in size the more small creatures fail to meet its nutritional needs, with the tipping point being about 20 kilograms, about the size of a coyote, after which point it make more sene to pursue big game.
Hibernation and Reproduction
Hibernation is a process in which animals in temperate climates go a sleep and refrain from eating or drinking to survive the cold and lack of food in the winter. The metabolism of hibernating animals slows and their temperature drops by as much as 37̊F to 50̊F. The body uses just 13 percent of the energy it does when its awake. The central nervous system is maintained
Asiatic black bear Deaths during hibernation are rare even though the rate of blood flowing to the brain is 10 percent of normal. If the human brain were deprived of that much blood death or major brain disorders would result. Scientists are studying hibernation and its applications to humans, particularly for space travel, preservation of organs for transplants and regulation of the blood during surgery.
Mammal embryos grow a pad, the placenta, that attaches to the wall of the womb and absorbs nutrients for the embryo from the mother's blood through a tube, the umbilical cord. Through this system mothers can keep their young inside them until they are quite large but expelling them from their body often takes considerable effort.
Unlike reptiles and fish, who tend to produce large numbers of young and let them fend for themselves, most mammals produce smaller broods of young and expend a great amount of effort protecting and rearing them. Mammals give birth to live young partly because many mammal young need to move around to some degree to escape from predators soon after they are born.
In many cases, the large, dominant males that carried the banner for their species no longer exist as they have been taken by trophy hunters and poachers. Large elephants, elk, Cape buffalo and bears that were routinely killed a century ago are now rare. Scientists say they are beginning to see an evolution in reverse with elephants with small tusks and elk with less antlers having a better chance of survival than those with them. A study of big horn sheep in North America found that both males and females are getting smaller and the size of the horns has shrunk by 25 percent in the last 30 years. Scientists are also finding more tuskless elephants in both Asia and Africa.
Cattle, sheep, goats, yaks, buffalo, deer, antelopes, giraffes, and their relatives are ruminants — cud-chewing mammals that have a distinctive digestive system designed to obtain nutrients from large amounts of nutrient-poor grass. Ruminants evolved about 20 million years ago in North America and migrated from there to Europe and Asia and to a lesser extent South America, where they never became widespread.
As ruminants evolved they rose up on their toes and developed long legs. Their side toes shrunk while their central toes strengthened and the nails developed into hooves, which are extremely durable and excellent shock absorbers.
Ruminants helped grasslands remain as grasslands and thus kept themselves adequately suppled with food. Grasses can withstand the heavy trampling of ruminants while young tree seedlings can not. The changing rain conditions of many grasslands has meant that the grass sprouts seasonally in different places and animals often make long journeys to find pastures. The ruminants hooves and large size allows them to make the journeys.
Describing a descendant of the first ruminates, David Attenborough wrote: deer move through the forest browsing in an unhurried confident way. In contrast the chevrotain feed quickly, collecting fallen fruit and leaves from low bushes and digest them immediately. They then retire to a secluded hiding place and then use a technique that, it seems, they were the first to pioneer. They ruminate. Clumps of their hastly gathered meals are retrieved from a front compartment in their stomach where they had been stored and brought back up the throat to be given a second more intensive chewing with the back teeth. With that done, the chevrotain swallows the lump again. This time it continues through the first chamber of the stomach and into a second where it is fermented into a broth. It is a technique that today is used by many species of grazing mammals.
Ruminants chew a cud and have unique stomachs with four sections. They do no digest food as we do, with enzymes in the stomach breaking down the food into proteins, carbohydrates and fats that are absorbed in the intestines. Instead plant compounds are broken down into usable compounds by fermentation, mostly with bacteria transmitted from mother to young.
Ruminant stomach The cub-chewing process begins when an animal half chews its food (mostly grass) just enough to swallow it. The food goes into the first stomach called the rumen, where the food is softened with special liquids and the cellulose in the plant material is broken down by bacteria and protozoa.
After several hours, the half-digested plant material is separated into lumps by a muscular pouch alongside the rumen. Each lump, or cud, is regurgitated, one at a time and animal chews the cud thoroughly and then swallow it again. This is referred to a chewing the cud.
When the food is swallowed for the second time it by passes through the first two chambers and arrives at the third chamber, the "true" stomach, where and it is digested. As the chewed food moves through this chamber microbes multiply and produce fatty acids that provide energy and use nitrogen in the food to synthesize protein that eventually becomes amino acids. Vitamins, amino acids and nutrients created through chemical recombination then move in the intestine and pass through linings in the gut into the bloodstream.
Mother’s Milk Altered Based on Baby’s Gender
In 2014, Associated Press reported: A special blend of mother’s milk just for girls? New research shows animal moms are customizing their milk in surprising ways depending on whether they have a boy or a girl. The studies raise questions for human babies, too — about how to choose the donor milk that’s used for hospitalized preemies, or whether we should explore gender-specific infant formula. “There’s been this myth that mother’s milk is pretty standard,” said Harvard University evolutionary biologist Katie Hinde, whose research suggests that’s far from true — in monkeys and cows, at least.Instead, “The biological recipes for sons and daughters may be different,” she told a meeting of the American Association for the Advancement of Science on Friday. [Source: Associated Press, February 16, 2014]
“Pediatricians long have stressed that breast milk is best as baby’s first food. Breast-fed infants are healthier, suffering fewer illnesses such as diarrhea, earaches or pneumonia during the first year of life and less likely to develop asthma or obesity later on. But beyond general nutrition, there have been few studies of the content of human breast milk and how it might vary from one birth to the next or even over the course of one baby’s growth. That research is difficult to conduct in people.
“So Hinde studies the milk that rhesus monkey mothers make for their babies. The milk is richer in fat when monkeys have male babies, especially when it’s mom’s first birth, she found. But they made a lot more milk when they had daughters, Hinde discovered. Milk produced for monkey daughters contains more calcium, she found. One explanation: Female monkeys’ skeletons mature faster than males’ do, suggesting they need a bigger infusion of this bone-strengthening mineral.
Mothers’ milk even affects babies’ behavior, she said. Higher levels of the natural stress hormone cortisol in milk can make infants more nervous and less confident. But boys and girls appear sensitive to the hormone’s effects at different ages, her latest monkey research suggests.
Image Sources: Wikimedia Commons
Text Sources: Mostly National Geographic articles. Also “Life on Earth” by David Attenborough (Princeton University Press), New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Natural History magazine, Discover magazine, Times of London, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.
Last updated April 2022