Afrotheria

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Afrotheria
Temporal range:
Ma
1.
Black and rufous elephant shrew 4. West Indian manatee 5. Cape golden mole 6. Rock hyrax 7. African bush elephant 8. Tailless tenrec
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Infraclass: Placentalia
Superorder: Afrotheria
Stanhope MJ, Waddell VG, Madsen O, de Jong W, Hedges SB, Cleven G, Kao D, Springer MS, 1998
Orders

See below

Afrotheria (

otter shrews, tenrecs, aardvarks, hyraxes, elephants, sea cows, and several extinct clades. Most groups of afrotheres share little or no superficial resemblance, and their similarities have only become known in recent times because of genetics and molecular studies. Many afrothere groups are found mostly or exclusively in Africa, reflecting the fact that Africa was an island continent from the Cretaceous until the early Miocene
around 20 million years ago, when Afro-Arabia collided with Eurasia.

Because Africa was isolated by water,

cetaceans and pinnipeds
). In addition to their similarity with Laurasian mammals in North America, Europe, and Asia, many afrotheres also exhibit convergent evolution with groups of mammals that evolved and lived exclusively in South America, which was also an island continent for much of the Cenozoic.

The common ancestry of these animals was not recognized until the late 1990s.

Edentata. Continuing work on the molecular[2][3][4] and morphological[5][6][7][8]
diversity of afrotherian mammals has provided ever increasing support for their common ancestry.

Evolutionary relationships

The afrotherian clade was originally proposed in 1998[1] based on analyses of DNA sequence data. However, previous studies had hinted at the close interrelationships among subsets of endemic African mammals; some of these studies date to the 1920s[9] and there were sporadic papers in the 1980s[10] and 1990s.[11][12][13] The core of the Afrotheria consists of the Paenungulata, i.e., elephants, sea cows, and hyraxes, a group with a long history among comparative anatomists.[14][15] Hence, while DNA sequence data have proven essential to infer the existence of the Afrotheria as a whole, and while the Afroinsectiphilia (insectivoran-grade afrotheres including tenrecs, golden moles, sengis, and aardvarks) were not recognized as part of Afrotheria without DNA data, some precedent is found in the comparative anatomical literature for the idea that at least part of this group forms a clade. The Paleocene genus Ocepeia, which is the most completely-known Paleocene African mammal and the oldest afrotherian known from a complete skull, shares similarities with both Paenungulata and Afroinsectiphilia, and may help to characterize the ancestral body type of afrotherians.[16]

Since the 1990s, increasing molecular and anatomical data have been applied to the classification of animals. Both types of data support the idea that afrotherian mammals are descended from a single common ancestor to the exclusion of other mammals. On the anatomical side, features shared by most, if not all, afrotheres include high vertebral counts,[8] aspects of placental membrane formation,[17] the shape of the ankle bones,[6][7] the relatively late eruption of the permanent dentition,[18] and undescended testicles remaining in the body near the kidneys.[19] The snout is unusually long and mobile in several Afrotherian species, and this was pointed out as a possible shared-derived character.[20] Studies of genomic data, including millions of aligned nucleotides sampled for a growing number of placental mammals, also support Afrotheria as a clade.[21][22] Additionally, there might be some dental synapomorphies uniting afroinsectiphilians, if not afrotheres as a whole: p4 talonid and trigonid of similar breadth, a prominent p4 hypoconid, presence of a P4 metacone and absence of parastyles on M1–2.[7][23]

Afrotheria is now recognized as one of the three major groups within the

placental mammals).[24] Relations within the three cohorts, Afrotheria, Xenarthra, Boreoeutheria, and the identity of the placental root, remain somewhat controversial.[5]

Afrotheria as a clade has usually been discussed without a Linnaean rank, but has been assigned the rank of cohort, magnorder, and superorder. One reconstruction, which applies the molecular clock, proposes that the oldest split occurred between Afrotheria and the other two some 105 million years ago in the mid-Cretaceous, when the African continent was separated from other major land masses.[25] This idea is consistent with the fossil record of Xenarthra, which is restricted to South America (following recent consensus that Eurotamandua is not a xenarthran[26]).

However, Afrotheria itself does not have a fossil record restricted to Africa,

Meridiungulata polyphyletic and recognise most of its clades as part of a group called Sudamericungulata, closely related to hyraxes, while Litopterna remains a sister taxon to Perissodactyla.[30]

Relations between the various afrotherian orders are still being studied. On the basis of molecular studies, elephants and manatees appear to be related, and likewise elephant shrews and aardvarks.[31] These findings are compatible with the work of earlier anatomists.[14][15]

Phylogeny

laurasiatherians (green), and euarchontoglires
(blue).
Afrotheria
A cladogram of Afrotheria based on molecular evidence[15]

Current status and distribution

Many extant members of Afrotheria appear to have a high risk of extinction (perhaps related to the large size of many). Species loss within this already small group would comprise a particularly great loss of genetic and evolutionary diversity. The

IUCN Afrotheria Specialist Group notes that Afrotheria, as currently reconstructed, includes nearly a third of all mammalian orders currently found in Africa and Madagascar, but only 75 of more than 1,200 mammalian species in those areas.[33]

While most extant species assigned to Afrotheria live in Africa, some (such as the Indian elephant and three of the four sirenian species) occur elsewhere; many of these are also endangered. Prior to the

perissodactyls, rather than afrotheres,[34] although this is still controversial;[28] the taxonomic placement of embrithopods is also not clear.[35]

Classification

Afrotheria is a clade of placental mammals, the stem designation for which is Eutheria. Based on precedent, some clades are junior synonyms and arguably should be replaced.[36][37]

See also

Notes

  1. ^
    PMID 9707584
    .
  2. S2CID 1508898
    .
  3. PMID 15306319
    .
  4. PMID 15930154
    .
  5. ^
    PMID 19582725
    .
  6. ^
    PMID 17329227
    .
  7. ^
    PMID 17999766
    .
  8. ^
    S2CID 85675984
    .
  9. ^ Le Gros Clark, W.E. & C.F. Sonntag (1926). "A monograph of Orycteropus afer III, the skull, the skeleton of the trunk, and limbs". Proceedings of the Zoological Society of London. 30: 445–485.
  10. S2CID 4256271
    .
  11. ^ DeJong, W.W.; J.A.M. Leunissen & G.J. Wistow (1993). "Eye lens crystallins and the phylogeny of placental orders: evidence for a Macroscelid–Paenungulate clade?". In F. S. Szalay; M. J. Novacek & M.C. McKenna (eds.). Mammal Phylogeny. New York: Springer Verlag. pp. 5–12.
  12. PMID 8673300
    .
  13. PMID 9214502
    .
  14. ^ a b Simpson, G. G. (1945). "The principles of classification and a classification of mammals". Bulletin of the American Museum of Natural History. 85: 1–350.
  15. ^
    S2CID 46133294. Archived from the original
    (PDF) on 2021-08-01. Retrieved 2023-04-30.
  16. ^
    PMID 24587000
    .
  17. PMID 16254985
    .
  18. PMID 18366669
    .
  19. PMID 29953435
    .
  20. PMID 11136239
    .
  21. PMID 17322288
    .
  22. PMID 17206863
    .
  23. PMID 17372202
    .
  24. S2CID 34367609. Archived from the original
    (PDF) on 27 March 2016. Retrieved 15 May 2014.
  25. PMID 12552136
    .
  26. ^ Rose KD, Emry RJ, Gaudin TJ, Storch G (2005). "Xenarthra and Pholidota.". In Rose KD, Archibald JD (eds.). The Rise of Placental Mammals: Origins and Relationships of the Major Extant Clades. Baltimore, MD: Johns Hopkins University Press.
  27. S2CID 4428738
    .
  28. ^
    PMID 27384169
    .
  29. PMID 18453548
    .
  30. ISSN 2296-701X
    .
  31. S2CID 24353318
    .
  32. PMID 30698751
    .
  33. ^ "What is Afrotheria?". IUCN Afrotheria Specialist Group. Retrieved 10 December 2013.
  34. ^
    PMID 25295875
    .
  35. S2CID 89418652
    .
  36. ^ "Afrosoricida". Mammal Species of the World, 3rd edition. Retrieved 17 March 2014.
  37. ^ McDowell, S. B. (1958). "The Greater Antillean insectivores". Bulletin of the American Museum of Natural History. 115: 115–213.
  38. S2CID 84391276
    .
  39. ^
    doi:10.3389/fevo.2021.654302
    .

References

External links
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