Placental Mammals, WHA-ZOR
Placental mammal, (infraclass Eutheria), any member of the mammalian group characterized by the presence of a placenta, which facilitates exchange of nutrients and wastes between the blood of the mother and that of the fetus. The placentals include all living mammals except marsupials and monotremes. Although some authorities consider the marsupials (cohort Marsupialia) to be placental mammals, these animals have a less-developed, less-efficient type of placenta that limits the gestation period. The true placenta of the placentals allows for a longer developmental period within the protection of the womb, a factor considered to have contributed to the evolutionary success of the group. Fossil evidence shows that the first placental mammals evolved between about 163 million and 157 million years ago during the Jurassic Period (201.3 million to about 145 million years ago).
Placental Mammals Encyclopedia Articles By Title
Determining the rarest dog breed in the world is a challenging task because of the difficulty of obtaining and......
The Border Collie is widely recognized as the smartest dog breed because of its uncanny ability to learn tasks......
Who’s a tall boy? The Irish Wolfhound is generally recognized as the tallest dog breed. While the tallest individual......
Cheetahs and leopards are both large cats with dark spots and yellowish coats, but they have distinctly different......
You may have been taught that there are only two species of elephants: the African elephant and the Asian elephant.......
It’s easy to understand why people confuse bison and buffalo. Both are large, horned, oxlike animals of the Bovidae......
Llamas and alpacas have been used by humans for transportation and fleece production for a few thousand years.......
Monkeys and apes are both primates, which means they’re both part of the human family tree. As distinguished relatives,......
If you’ve ever watched Looney Tunes, you may have noticed that the words bunny (which typically refers to young......
While river otters and sea otters might appear similar at first glance, the two exhibit many striking differences......
Are seals and sea lions the same animal? Technically, they are in the same taxonomical suborder of pinnipeds (Pinnipedia),......
Who’s America’s top dog? According to the American Kennel Club, the answer is the French Bulldog. Since 2022 the......
The Siberian tiger is bigger than the Bengal tiger. Siberian tigers can reach lengths of up to 3.7 meters (12.1......
The sperm whale, which preys on the colossal squid, is generally bigger than the colossal squid. A male sperm whale......
whippet, hound breed developed in mid-19th-century England to chase rabbits for sport in an arena. The breed was......
white tiger, colour variant of the Bengal tiger (Pantheria tigris tigris), the Siberian tiger (P. tigris altaica),......
white-tailed deer, (Odocoileus virginianus), common American deer of the family Cervidae (order Artiodactyla) that......
white-toothed shrew, (genus Crocidura), any of 164 species of mouse-sized African and Eurasian insectivores making......
Amazon river dolphins, also known as botos, are often pink due to a combination of factors, including their diet,......
Black cats are considered unlucky in some cultures because of superstitious beliefs that have been passed down......
Bloodhounds are often recruited for police work because of their exceptionally keen sense of smell. The dogs possess......
The name Boxer is derived from the dog’s unique behavior during play and combat, which is reminiscent of a human......
Dalmatians are associated with firefighters because their temperament made them friendly companions for the horses......
Dogs are loyal due to their evolutionary history, domestication process, and the strong bonds they form with humans.......
An elephant’s large ears serve several purposes. Thermoregulation—an organism’s maintenance of its own body temperature......
German Shepherds are widely favored for police work because of their intellect, willingness to work, and unique......
Hippos are dangerous primarily because of their territorial nature especially when it comes to their aquatic habitats.......
Mice are used in medical research primarily because their genetic makeup bears a strong resemblance to that of......
Most calico cats are female because the genes that determine their distinctive patches of black and orange fur......
The gene that determines whether a cat will have an orange coat of fur is linked to the X chromosome, one of the......
Orcas are called killer whales because of their reputation as powerful predators in the marine world. The name......
Polar bear fur is actually colorless but appears white because of the way it interacts with light. Each hair shaft......
“Sloth” is considered one of the seven deadly sins because, according to Catholic tradition, it hinders spiritual......
All apes, except for orangutans, live in groups. This arrangement gives them advantages when it comes to raising......
Bats sleep upside down because their anatomy and physiology are adapted for this position. Their legs are slender......
Beavers are quite the clever architects when it comes to safeguarding their homes. They build dams to raise the......
Cats blink slowly as a form of nonverbal communication, often interpreted as a sign of trust and affection toward......
Cats clean themselves frequently because of a combination of health benefits and social behaviors. Cats are meticulous......
An aversion to water is one of the most well-known characteristics of household cats. However, this isn’t true......
Cats have slit pupils primarily to enhance their ability to see in varying light conditions. They are crepuscular......
Cats have whiskers primarily for tactile sensing, which is crucial for their survival and daily activities. Whiskers,......
Cats often seek out boxes because the confined space makes them feel protected and sheltered. By nature cats seek......
The aromatic leaves of the catnip (Nepeta cataria), a herb of the mint family, are known to be particularly exciting......
Cats are naturally inclined to use scratching posts because it fulfills several instinctual needs and behaviors.......
Cats often open their mouths after smelling something because of a behavior known as the flehmen response. It’s......
While purring is often associated with a cat’s contentment, such as when they are being petted or snuggled up in......
Cats rub against your legs primarily as a form of communication and marking behavior. Rubbing against you may serve......
Cat person? How many pictures of your cat sleeping have you got on your phone? A lot, right? They are so cute when......
Coyotes make a number of different vocalizations, some of which sound like human screams. These sounds—including......
Deer freeze in headlights primarily because of their unique vision and instincts. As crepuscular animals, their......
Deer shed their antlers as part of hormonal changes linked to their survival and mating season. In all but one......
There may be several reasons why dogs turn around several times before they lie down. Since dogs are intelligent......
Dogs eat grass for several reasons, and while the exact motivations can vary, there are a few common theories that......
Though poop is certainly not a staple food for any human, it may come as no surprise that poop is a common part......
Dogs have wet noses mainly to enhance their sense of smell. The moisture on the nose traps scent particles in the......
Dogs are naturally inclined to like bones due to their evolutionary history and biological needs. Dogs have evolved......
Dogs enjoy playing fetch because of a combination of instinctual behaviors, physical exercise needs, and the joy......
Dogs wag their tails primarily as a form of communication, allowing them to express a range of emotions. Tail wagging......
The long neck of a giraffe (genus Giraffa) is a classic example of adaptation, which is the process by which a......
Chest beating is a powerful tool in the gorilla’s communication arsenal. Both males and females engage in this......
Horseshoes protect hooves from cracking or wearing down on rough surfaces. When horses walk on such terrains, their......
Horses roll for a variety of reasons, each serving a distinct purpose in their daily lives and well-being. One......
Some consider this a trick question. That’s because horses actually doze while on their feet and lie down for REM......
Horses wear blinders to limit their field of vision, which helps them focus on what is directly ahead. Blinders,......
Lions roar to proclaim their territory and to assert dominance. This vocalization is particularly important for......
Llamas spit for a number of reasons. When a llama feels threatened, it might spit to protect itself or to maintain......
Skunks spray as a highly effective defense mechanism to deter predators and threats. They are equipped with two......
Although a larger size normally indicates greater longevity among most mammals, dogs tend to follow a different......
Sphynx cats appear hairless because of a genetic mutation that occurred naturally in shorthaired cats and was later......
The saying that cats have nine lives comes from a blend of cultural beliefs, historical anecdotes, and human observation......
According to the American Kennel Club, “wet dog smell” is not due to the dog itself but to the yeast and bacteria......
Whale songs serve as a means of communication among individuals and groups. These vocalizations help whales share......
There’s nothing quite so interesting as the social interactions in the wolf pack. Wolves live in packs of about......
Yaks have long hair because it is essential for survival: it provides superior insulation against the extreme cold......
There are several theories about why zebras have stripes. Scientists believe that one of the main reasons is camouflage......
Japan is one of the world’s most advanced countries. You can see it in the country’s modern architecture (which......
Touching a manatee is illegal in the United States. The ban’s aim is to protect these vulnerable marine mammals......
wildcat, (species Felis silvestris), a small wild member of the cat family (Felidae) native to Eurasia and Africa.......
wolf, any of two species of wild doglike carnivores. The gray, or timber, wolf (Canis lupus) is the better known.......
wolverine, (Gulo gulo), member of the weasel family (Mustelidae) that lives in cold northern latitudes of North......
wood mouse, (genus Apodemus), any of about 20 species of small-bodied rodents found from northern Europe eastward......
woodland vole, (Microtus pinetorum), a small mouselike rodent of the eastern United States that is well adapted......
woodrat, (genus Neotoma), any of 23 species of medium-sized North American and Central American rodents. Some species......
woolly mammoth, (Mammuthus primigenius), extinct species of elephant found in fossil deposits of the Pleistocene......
woolly monkey, any of five species of densely furred South American primates found in rainforests of the western......
woolly rhinoceros, (genus Coelodonta), either of two extinct species of rhinoceros found in fossil deposits of......
woolly spider monkey, (genus Brachyteles), extremely rare primate that lives only in the remaining Atlantic forests......
working dog, any of various breeds of dog bred as guard, herding, draft, or rescue animals. Breeds range from medium......
The number one job for many animals is often simply being cute. However, for a few critters, working it means actual......
xenarthran, (magnorder Xenarthra), an ancient lineage of mammals comprising the armadillos (order Cingulata) and......
yak, (Bos grunniens), long-haired, short-legged oxlike mammal that was probably domesticated in Tibet but has been......
Yorkshire, breed of swine produced in the 18th century by crossing the large indigenous white pig of North England......
Yorkshire Terrier dog, breed of toy dog developed about the mid-1800s in the English counties of Yorkshire and......
zebra, any of three species of strikingly black-and-white striped mammals of the horse family Equidae (genus Equus):......
zokor, (genus Myospalax), any of seven north Asian species of subterranean rodents. Zokors are molelike animals......
zorille, (Ictonyx [sometimes Zorilla] striatus), African carnivore of the weasel family (Mustelidae), frequenting......