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Placentals: what are they, characteristics, classification and examples

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 AgroCorrn article you will find detailed information about what placentals are, their characteristics, classification and examples, and you will also be able to learn more curious facts about this surprising group of animals.

  1. What are placental animals
  2. Characteristics of placental animals
  3. Classification of placental animals
  4. Examples of Placentric animals

What are placental animals

We begin by clarifying what placental mammals are , also simply called placental animals. Thus, placental animals constitute a taxonomic infraclass (Placentalia) within the broad class that mammals make up . 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. Among the main characteristics of placental mammals are:

  • The embryo grows inside the mother’s uterus for a long period of time, with the placenta in charge of guaranteeing it 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.
  • They also have mammary glands that allow them to produce the milk that the young need to take from birth to develop and grow until they switch to their final diet.
  • These animals have different types of food , there are carnivores, herbivores and omnivores .
  • Throughout their life, they have two different types of teeth , the first during the childhood phase and the next in the adult phase.
  • Placental animals do not have a cloaca, but rather an excretion system connected to the digestive system and isolated from the reproductive one.
  • Placental animals have fur , either denser and thicker or less and thinner, and they can have it always or in some stages of their life, as well as all over the body or only in some parts.
  • Likewise, they have sweat glands distributed throughout 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 a corpus callosum that connects both hemispheres, thus guaranteeing a very advanced development of cognitive functions.
  • They have a synapsid skull , which means that it has a lower temporal fossa which is an opening located behind the eye sockets. This fossa in the skull allows it to be lighter and the muscles of the lower jaw to be inserted in this area, facilitating its movement to feed, make sounds, bite, etc.
  • Regarding other common morphological characteristics, it is worth noting 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 the different types of placental animals have undergone along their evolutionary lines, these common characteristics are more difficult to appreciate.

We also recommend that you learn more about these animals with this other AgroCorrn post about Viviparous Animals: what they are, characteristics and examples .

Imagen: Documental In The Womb de National Geographic

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:

  • Cingulados
  • Pilosos
  • Tubulidentados
  • Macroscélidos
  • Hiracoideos
  • Proboscídeos
  • Sirenians
  • Eulipotiflanos
  • Chiroptera
  • Folidotes
  • Carnivores
  • Perisodactyls
  • Cetaceans
  • Artiodáctilos
  • Lagomorfos
  • Rodents
  • Scandents
  • Primates

Examples of Placentric animals

From the classification in 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 ( Tamandua mexicana )
  • Giant anteater ( Myrmecophaga tridactyla )
  • Perezoso (Bradypus tridactylus)
  • Two-toed sloth of Linnaeu ( Choloepus didactylus )
  • African anteater ( Orycteropus afer )
  • Cape Elephant Shrews ( Eephantulus edwardii )
  • Damán de Bruce (Heterohyrax brucei)
  • African savanna elephantLoxodonta africana )
  • Elefante indio ( Elephas maximus indicus )
  • Manatí (Trichechus inunguis)
  • Common mole ( Talpa europaea )
  • Starry-nosed mole ( Condylura cristata )
  • Hedgehogs (family Erinaceinae)
  • Mediterranean water shrew ( Neomys anomalus )
  • Goatherd Mosgaño ( 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 )
  • Pangolín malayo ( Sweet javanica )
  • Giant Pangolin ( Manis gigantea )
  • Dog ( Canis lupus )
  • Cat domestic ( Gorilla gorilla gorilla )
  • Snow leopard (Panthera uncia)
  • Lobo (Canis lupus)
  • Tigre (Panthera tigris)
  • Guepardo (Acinonyx jubatus)
  • Jaguar ( Panthera onca)
  • Puma (Puma concolor)
  • Common Zebra ( Equus quagga )
  • Indian rhinoceros ( Rhinoceros unicoris )
  • Amazonian pink dolphin ( Inia geoffrensis )
  • Ballena jorobada o yubarta (Megaptera novaeangliae)
  • Orca (Orcinus orca)
  • Jirafas (Giraffa camelopardalis)
  • American bison ( Bison bison)
  • Deer (family Cervidae)
  • Wild goat or Iberian ibex ( Capra pyrenaica )
  • Rabbits (genus Oryctolagus)
  • Guinea pig or guinea pig ( Cavia porcellus )
  • Hares (genus Lepus)
  • Rata parda (Rattus norvegicus)
  • Domestic or common mouse ( Mus musculus)
  • Bamboo squirrel or tupaya (Anathana ellioti)
  • Human ( Homo sapiens sapiens )
  • Borneo Oragutan ( Pongo pigmaeus )
  • Gorilla (genus Gorilla)
  • Loris de Bengala ( Nycticebus bengalensis )

If you want to read more articles similar to Placentals: what they are, characteristics, classification and examples , we recommend that you enter our Biology category .

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