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Did you know that during the Upper Jurassic, about 160 million years ago, there was a small insectivorous mammal called Juramaia, from which all placental animals on Earth probably descend? Scientific studies and fossil analysis indicate that this small animal with a placenta could be considered as the common ancestor of all placental mammals that have evolved throughout history, surprising, right? Although today there is a great variety of types of placental animals, there are many characteristics of the prehistoric Juramaia that they maintain.
In this Green Ecologist article you will find detailed information about what are placentals, their characteristics, classification and examples and you will also be able to learn more curious facts about this surprising group of animals.
What are placental animals
Start by clarifying what are placental mammals, also called simply placental animals. Thus, placental animals constitute a taxonomic infraclass (Placentalia) within the broad class that make up the mammals. The females of these species of placental animals have an internal morphological structure in their bellies, called placenta, which guarantees the protection and feeding of the embryos during their gestation period.
This amazing feature is contrary to the outer marsupium that characterizes the other subclass (Marsupials) included within the class of mammals. If you want to know them better, we encourage you to take a look at this other post on What are marsupial animals and examples.
Let's see in the next sections more characteristics related to placental animals, as well as their classification and many examples to get to know them more closely.
Characteristics of placental animals
Placental animals are the viviparous mammals par excellence, that is, the largest and most developed group within mammals. Between the main characteristics of placental mammals stand out:
- The embryo grows inside the mother's womb for a long period of time, being the placenta the one in charge of guaranteeing food from the mother, as well as protection and the ideal environment for its correct development.
- The females of these types of animals have the heat or estrous cycle, which allows the body to be prepared for copulation, fertilization and the gestation of the offspring.
- Also have mammary glands that allow them to produce the milk that the offspring need to take from birth to develop and grow until they change to the final diet.
- These animals have different types of foodThere are carnivores, herbivores and omnivores.
- Throughout their lives, they have two types of teeth different, the first during the infantile phase and the next in the adult phase.
- Placental animals do not have a cloaca, but a excretion system connected to the digestive and isolated from the reproductive.
- Placental animals they have fur, either more dense and thick or with less quantity and thin, and they can have it always or in some stages of their life, as well as throughout the body or only in some parts.
- They also have sweat glands distributed over different areas of the body that allow them to sweat and thus facilitate the regulation of temperature and the elimination of toxins from the body.
- The brain of placental animals has large cerebral hemispheres, as well as with a corpus callosum that connects both hemispheres, thus guaranteeing a very advanced development of cognitive functions.
- They have the synapsid skull, which means this has a inferior temporal fossa which is an opening located behind the eye sockets. This fossa in the skull allows it to be lighter and in this area to be inserted jaw muscles bottom facilitating their movement to feed, make sounds, bite, etc.
- Regarding other common morphological characteristics, it should be noted how the most primitive placentals were small, as well as having very short legs with five fingers and a tubular skull. However, at present, due to the changes that different types of placental animals have undergone along their evolutionary lines, these common characteristics are more difficult to appreciate.
We also recommend you learn more about these animals with this other post by Green Ecologist about Viviparous Animals: what they are, characteristics and examples.
Image: National Geographic Documentary In The Womb
Classification of placental animals
At present, the classification of placental animals follows a phylogenetic approach based on the biomolecular and genetic results of the species, which allow grouping each and every one of the placental animals that exist (or existed) on the planet following the following classification:
- Cingulates
- Pilosos
- Tubulidentate
- Macroscélidos
- Hiracoids
- Proboscideans
- Sirenians
- Eulipotiflans
- Chiroptera
- Folidotes
- Carnivores
- Perissodactyls
- Cetaceans
- Artiodactyls
- Lagomorphs
- Rodents
- Scandents
- Primates
Examples of placentric animals
From the classification of the previous section, below you will see a list with numerous examples of animals with placenta, which follow the same order of classification as the groups mentioned above:
- Armadillos (family Dasypodidae)
- Mexican anteater (Mexican tamandua)
- Giant anteater (Myrmecophaga tridactyla)
- Lazy (Bradypus tridactylus)
- Linnaeu's two-toed sloth (Choloepus didactylus)
- African aardvark (Orycteropus afer)
- Cape elephant shrews (Eephantulus edwardii)
- Bruce daman (Heterohyrax brucei)
- African savanna elephant (Loxodonta africana)
- Indian elephant (Elephas maximus indicus)
- Sea cow (Trichechus inunguis)
- Common mole (Talpa europaea)
- Star-nosed mole (Condylura cristata)
- Hedgehogs (family Erinaceinae)
- Mediterranean water shrew (Neomys anomalus)
- Musgaño de Cabrera (Neomys anomalus)
- Common bat (Pipistrellus pipistrellus)
- Common vampire bat (Desmoudus rotundus)
- Hairy-legged bat (Diphylla ecaudata)
- White-winged bat (Diaemus youngi)
- Chinese pangolin (Manis pentadactyla)
- Malay pangolin (Javanica manis)
- Giant pangolin (Manis gigantea)
- Dog (Canis lupus)
- Domestic catFelis silvestris catus)
- Snow Leopard (Panthera uncia)
- Wolf (Canis lupus)
- Tiger (Panthera tigris)
- Cheetah (Acinonyx jubatus)
- Jaguar (Panthera onca)
- Cougar (Puma concolor)
- Common zebra (Equus quagga)
- Indian rhino (Rhinoceros unicoris)
- Amazon pink dolphin (Inia geoffrensis)
- Humpback whale or yubarta (Megaptera novaeangliae)
- Orca (Orcinus orca)
- Giraffes (Giraffa camelopardalis)
- American bison (Bison bison)
- Deer (family Cervidae)
- Mountain goat or Iberian ibex (Capra pyrenaica)
- Rabbits (genus Oryctolagus)
- Guinea pig or guinea pig (Cavia porcellus)
- Hares (genus Lepus)
- Brown rat (Rattus norvegicus)
- House or common mouse (Mus musculus)
- Bamboo or tupaya squirrel (Anathana ellioti)
- Human being (Homo sapiens sapiens)
- Oragutan of Borneo (I put pigmaeus)
- Gorilla (genus Gorilla)
- Bengal loris (Nycticebus bengalensis)
If you want to read more articles similar to Placentals: what are they, characteristics, classification and examples, we recommend that you enter our Biology category.
Bibliography- Writing team. You will be surprised how these animals are born. National Geographic Spain- Animals.
- Sánchez, T. J. (1997) Teaching of the reproduction of oviparous and viviparous animals. National Pedagogical University, Mexico.
