HOME
The Info List - Placental


--- Advertisement ---



Placentalia
Placentalia
("Placentals") is one of the three extant subdivisions of the class of animals Mammalia; the other two are Monotremata
Monotremata
and Marsupialia. The Placentals are partly distinguishable from other mammals in that the fetus is carried in the uterus of its mother to a relatively late stage of development. It is somewhat of a misnomer since marsupials also nourish their fetuses via a placenta.[1]

Contents

1 Anatomical features 2 Subdivisions 3 Evolution 4 References

Anatomical features[edit] Placental
Placental
mammals are anatomically distinguished from other mammals by:

a sufficiently wide opening at the bottom of the pelvis to allow the birth of a large baby relative to the size of the mother.[2] the absence of epipubic bones extending forward from the pelvis, which are found in all other mammals.[3] (Their function in non-placental mammals is to stiffen the body during locomotion,[4] but in placentals they would inhibit the expansion of the abdomen during pregnancy.)[5] the rearmost bones of the foot fit into a socket formed by the ends of the tibia and fibula, forming a complete mortise and tenon upper ankle joint.[6] the presence of a malleolus at the bottom of the fibula.[6]

Subdivisions[edit] Analysis of retroposon presence/absence patterns has provided a rapid, unequivocal means for revealing the evolutionary history of organisms: this has resulted in a revision in the classification of placentals.[7] There are now thought to be three major subdivisions or lineages of placental mammals: Boreoeutheria, Xenarthra, and Afrotheria, all of which diverged from common ancestors. The orders of placental mammals in the three groups are:[8]

Magnorder Afrotheria
Afrotheria
(elephant shrews, tenrecs, golden moles, hyraxes, elephants, and manatees)

Superorder Afroinsectiphilia

Order Afrosoricida
Afrosoricida
(tenrecs and golden moles) Order Macroscelidea
Macroscelidea
(elephant shrews) Order Tubulidentata
Tubulidentata
(aardvark)

Superorder Paenungulata

Order Hyracoidea
Hyracoidea
(hyraxes) Mirorder Tethytheria
Tethytheria
(elephants, dugongs, and manatees)

Order Proboscidea
Proboscidea
(elephants) Order Sirenia
Sirenia
(dugongs and manatees)

Magnorder Boreoeutheria

Superorder Euarchontoglires
Euarchontoglires
(treeshrews, colugos, primates, rabbits, hares, and rodents)

Grandorder Gliriformes

Mirorder Glires

Order Lagomorpha
Lagomorpha
(rabbits, hares, and pikas) Order Rodentia (rodents: mice, rats, voles, squirrels, beavers, etc.)

Grandorder Euarchonta

Order Scandentia
Scandentia
(treeshrews) Mirorder Primatomorpha

Order Dermoptera
Dermoptera
(colugos) Order Primates
Primates
(primates: humans, monkeys, apes, lemurs, lorises, etc.)

Superorder Laurasiatheria
Laurasiatheria
(hedgehogs, shrews, moles, whales, bats, dogs, cats, seals, and hoofed mammals)

Order Eulipotyphla
Eulipotyphla
(hedgehogs, gymnures, shrews, moles, and solenodons Order Chiroptera
Chiroptera
(bats) Order Cetartiodactyla
Cetartiodactyla
(even-toed ungulates: cattle, antelope, deer, camels, pigs, whales, etc.) Order Perissodactyla
Perissodactyla
(odd-toed ungulates: horses, donkeys, zebras, rhinoceroses, and tapirs) Mirorder Ferae
Ferae
(pangolins, dogs, cats, bears, seals, mongooses, etc.)

Order Pholidota
Pholidota
(pangolins) Order Carnivora
Carnivora
(carnivorans: dogs, cats, bears, seals, mongooses, etc.)

Magnorder Xenarthra
Xenarthra
(armadillos, anteaters, and sloths)

Order Cingulata
Cingulata
(armadillos) Order Pilosa
Pilosa
(anteaters and sloths)

The exact relationships among these three lineages is currently a subject of debate, and three different hypotheses have been proposed with respect to which group is basal or diverged first from other placentals. These hypotheses are Atlantogenata
Atlantogenata
(basal Boreoeutheria), Epitheria
Epitheria
(basal Xenarthra), and Exafroplacentalia
Exafroplacentalia
(basal Afrotheria).[9] Estimates for the divergence times among these three placental groups range from 105 to 120 million years ago (MYA), depending on the type of DNA (e.g. nuclear or mitochondrial)[10] and varying interpretations of paleogeographic data.[9]

Placentalia

Atlantogenata

Afrotheria

Xenarthra

Boreoeutheria

Euarchontoglires

Euarchonta

Glires

Laurasiatheria

Eulipotyphla

Scrotifera

Chiroptera

Ferungulata

Euungulata

Cetartiodactyla

Perissodactyla

Ferae

Pholidota

Carnivora

Cladogram
Cladogram
based on Amrine-Madsen, H. et al. (2003)[11] and Asher, R.J. et al. (2009)[12] Evolution[edit] True placental mammals (the crown group including all modern placentals) arose from stem-group members of the clade Eutheria, which had existed since at least the Middle Jurassic
Jurassic
period, about 170 MYA). These early eutherians were small, nocturnal insect eaters, with adaptations for life in trees.[6] True placentals may have originated in the Late Cretaceous
Cretaceous
around 90 MYA, but the earliest undisputed fossils are from the early Paleocene, 66 MYA, following the Cretaceous– Paleogene extinction event. The species Protungulatum donnae
Protungulatum donnae
was thought to be a stem-ungulate [13] known 1 meter above the Cretaceous- Paleogene boundary in the geological stratum that marks the Cretaceous– Paleogene extinction event [14] and Purgatorius, previously considered a stem-primate, appears no more than 300,000 years after the K-Pg boundary;[15] both species, however, are now considered non-placental eutherians.[16] The rapid appearance of placentals after the mass extinction at the end of the Cretaceous
Cretaceous
suggests that the group had already originated and undergone an initial diversification in the Late Cretaceous, as suggested by molecular clocks.[17] The lineages leading to Xenarthra and Afrotheria
Afrotheria
probably originated around 90 MYA, and Boreoeutheria underwent an initial diversification around 70-80 MYA,[17] producing the lineages that eventually would lead to modern primates, rodents, insectivores, artiodactyls, and carnivorans. However, modern members of the placental orders originated in the Paleogene around 66 to 23 MYA, following the Cretaceous–Paleogene extinction event. The evolution of crown orders such modern primates, rodents, and carnivores appears to be part of an adaptive radiation[18] that took place as mammals quickly evolved to take advantage of ecological niches that were left open when most dinosaurs and other animals disappeared following the Chicxulub asteroid impact. As they occupied new niches, mammals rapidly increased in body size, and began to take over the large herbivore and large carnivore niches that had been left open by the decimation of the dinosaurs. Mammals also exploited niches that the dinosaurs had never touched: for example, bats evolved flight and echolocation, allowing them to be highly effective nocturnal, aerial insectivores; and whales first occupied freshwater lakes and rivers and then moved into the oceans. Primates, meanwhile, acquired specialized grasping hands and feet which allowed them to grasp branches, and large eyes with keener vision which allowed them to forage in the dark. The evolution of land placentals followed different pathways on different continents since they cannot easily cross large bodies of water. An exception is smaller placentals such as rodents and primates, who left Laurasia
Laurasia
and colonized Africa and then South America via Rafting. In Africa, the Afrotheria
Afrotheria
underwent a major adaptive radiation, which led to elephants, elephant shrews, tenrecs, golden moles, aardvarks, and manatees. In South America a similar event occurred, with radiation of the Xenarthra, which led to modern sloths, anteaters, and armadillos, as well as the extinct ground sloths and glyptodonts. Expansion in Laurasia
Laurasia
was dominated by Boreoeutheria, which includes primates and rodents, insectivores, carnivores, perissodactyls and artiodactyls. These groups expanded beyond a single continent when land bridges formed linking Africa to Eurasia and South America to North America. References[edit]

Wikispecies
Wikispecies
has information related to Placentalia

The Wikibook Dichotomous Key has a page on the topic of: Placentalia

^ Renfree, M.B. (March 2010). "Review: Marsupials: placental mammals with a difference". Placenta. 31 Supplement: S21–6. doi:10.1016/j.placenta.2009.12.023. PMID 20079531.  ^ Weil, A. (April 2002). "Mammalian evolution: Upwards and onwards". Nature. 416 (6883): 798–799. doi:10.1038/416798a. PMID 11976661. Retrieved 2008-09-24.  ^ Reilly, S.M. & White, T.D. (January 2003). "Hypaxial Motor Patterns and the Function of Epipubic Bones in Primitive Mammals". Science. 299 (5605): 400–402. doi:10.1126/science.1074905. PMID 12532019. Retrieved 2008-09-24.  ^ Reilly, S.M. & White, T.D. (January 2003). "Hypaxial Motor Patterns and the Function of Epipubic Bones in Primitive Mammals". Science. 299 (5605): 400–402. doi:10.1126/science.1074905. PMID 12532019. Retrieved 2008-09-24.  ^ Novacek, M.J., Rougier, G.W, Wible, J.R., McKenna, M.C, Dashzeveg, D., and Horovitz, I. (October 1997). "Epipubic bones in eutherian mammals from the Late Cretaceous
Cretaceous
of Mongolia". Nature. 389 (6650): 483–486. doi:10.1038/39020. PMID 9333234. Retrieved 2008-09-24. CS1 maint: Multiple names: authors list (link) ^ a b c Ji, Q., Luo, Z-X., Yuan, C-X., Wible, J.R., Zhang, J-P. and Georgi, J.A. (April 2002). "The earliest known eutherian mammal". Nature. 416 (6883): 816–822. doi:10.1038/416816a. PMID 11976675. Retrieved 2008-09-24. CS1 maint: Multiple names: authors list (link) ^ Kriegs, Jan Ole; Churakov, Gennady; Kiefmann, Martin; Jordan, Ursula; Brosius, Jürgen; Schmitz, Jürgen (2006). "Retroposed Elements as Archives for the Evolutionary History of Placental Mammals". PLoS Biology. 4 (4): e91. doi:10.1371/journal.pbio.0040091. PMC 1395351 . PMID 16515367.  ^ Archibald JD, Averianov AO, Ekdale EG (November 2001). "Late Cretaceous
Cretaceous
relatives of rabbits, rodents, and other extant eutherian mammals". Nature. 414 (6859): 62–5. doi:10.1038/35102048. PMID 11689942.  ^ a b Nishihara, H.; Maruyama, S.; Okada, N. (2009). "Retroposon analysis and recent geological data suggest near-simultaneous divergence of the three superorders of mammals". Proceedings of the National Academy of Sciences. 106 (13): 5235–5240. doi:10.1073/pnas.0809297106. PMC 2655268 . PMID 19286970.  ^ Springer, Mark S.; Murphy, William J.; Eizirik, Eduardo; O'Brien, Stephen J. (2003). " Placental
Placental
mammal diversification and the Cretaceous–Tertiary boundary". Proceedings of the National Academy of Sciences. 100 (3): 1056–1061. doi:10.1073/pnas.0334222100. PMC 298725 . PMID 12552136.  ^ Amrine-Madsen, H.; Koepfli, K.-P.; Wayne, R. K.; Springer, M. S. (2003). "A new phylogenetic marker, apoliprotein B, provides compelling evidence for eutherian relationships". Molecular Phylogenetics and Evolution. 28: 225–240. doi:10.1016/s1055-7903(03)00118-0. PMID 12878460.  ^ Asher, R. J.; Bennett, N.; Lehmann, T. (2009). "The new framework for understanding placental mammal evolution". BioEssays. 31: 853–864. doi:10.1002/bies.200900053. PMID 19582725.  ^ O'Leary, Maureen A.; Bloch, Jonathan I.; Flynn, John J.; Gaudin, Timothy J.; Giallombardo, Andres; Giannini, Norberto P.; Goldberg, Suzann L.; Kraatz, Brian P.; Luo, Zhe-Xi; Meng, Jin; Ni, Michael J.; Novacek, Fernando A.; Perini, Zachary S.; Randall, Guillermo; Rougier, Eric J.; Sargis, Mary T.; Silcox, Nancy b.; Simmons, Micelle; Spaulding, Paul M.; Velazco, Marcelo; Weksler, John r.; Wible, Andrea L.; Cirranello, A. L. (8 February 2013). "The Placental
Placental
Mammal Ancestor and the Post–K-Pg Radiation of Placentals". Science. 339 (6120): 662–667. doi:10.1126/science.1229237. PMID 23393258. Retrieved 9 February 2013.  ^ Archibald, J.D., 1982. A study of Mammalia
Mammalia
and geology across the Cretaceous-Tertiary boundary in Garfield County, Montana. University of California Publications in Geological Sciences 122, 286. ^ Fox, R.C.; Scott, C.S. (2011). "A new, early Puercan (earliest Paleocene) species of Purgatorius
Purgatorius
(Plesiadapiformes, Primates) from Saskatchewan, Canada". Journal of Paleontology. 85: 537–548. doi:10.1666/10-059.1.  ^ Halliday, Thomas J. D. (2015). "Resolving the relationships of Paleocene
Paleocene
placental mammals". Biological Reviews. doi:10.1111/brv.12242.  ^ a b dos Reis, M.; Inoue, J.; Hasegawa, M.; Asher, R.J.; Donoghue, P.C.J.; Yang, Z. (2012). "Phylogenomic datasets provide both precision and accuracy in estimating the timescale of placental mammal phylogeny". Proceedings of the Royal Society B. 279: 3491–3500. doi:10.1098/rspb.2012.0683. PMC 3396900 . PMID 22628470.  ^ Alroy, J (1999). "The fossil record of North American Mammals: evidence for a Palaeocene evolutionary radiation". Systematic Biology. 48: 107–118. doi:10.1080/106351599260472. PMID 12078635. 

v t e

Extant mammal orders

Kingdom Animalia Phylum Chordata Subphylum Vertebrata (unranked) Amniota

Yinotheria

Australosphenida

Monotremata
Monotremata
(Platypus and echidnas)

Theria

Metatheria ( Marsupial
Marsupial
inclusive)

Ameridelphia

Paucituberculata (Shrew opossums) Didelphimorphia (Opossums)

Australidelphia

Microbiotheria
Microbiotheria
(Monito del monte) Notoryctemorphia ( Marsupial
Marsupial
moles) Dasyuromorphia
Dasyuromorphia
(Quolls and dunnarts) Peramelemorphia
Peramelemorphia
(Bilbies and bandicoots) Diprotodontia
Diprotodontia
(Kangaroos and relatives)

Eutheria ( Placental
Placental
inclusive)

Atlantogenata

Xenarthra

Cingulata
Cingulata
(Armadillos) Pilosa
Pilosa
( Anteaters
Anteaters
and sloths)

Afrotheria

Afrosoricida
Afrosoricida
( Tenrecs
Tenrecs
and golden moles) Macroscelidea
Macroscelidea
(Elephant shrews) Tubulidentata
Tubulidentata
(Aardvark) Hyracoidea
Hyracoidea
(Hyraxes) Proboscidea
Proboscidea
(Elephants) Sirenia
Sirenia
( Dugongs
Dugongs
and manatees)

Boreoeutheria

Laurasiatheria

Eulipotyphla
Eulipotyphla
(Hedgehogs, shrews, moles and relatives) Chiroptera
Chiroptera
(Bats) Pholidota
Pholidota
(Pangolins) Carnivora
Carnivora
(Dogs, cats and relatives) Perissodactyla
Perissodactyla
(Odd-toed ungulates) Artiodactyla ( Even-toed ungulates
Even-toed ungulates
and cetaceans)

Euarchontoglires

Rodentia (Rodents) Lagomorpha
Lagomorpha
( Rabbits
Rabbits
and pikas) Scandentia
Scandentia
(Treeshrews) Dermoptera
Dermoptera
(Colugos) Primates

Taxon identifiers

Wd: Q25833 EoL: 2844801 Fossilworks:

.