Eomaia
Eomaia | |
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Fossil specimen CAGS 01−IG−1 | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Clade: | Tribosphenida |
Genus: | †Eomaia Ji et al., 2002 |
Type species | |
†Eomaia scansoria Ji et al., 2002
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Eomaia ("dawn mother") is a
Description
The Eomaia fossil shows clear traces of hair.[1] However, this is not the earliest clear evidence of hair in the mammalian lineage, as fossils of Volaticotherium,[2] and the docodont Castorocauda, discovered in rocks dated to about 164 million years ago, also have traces of fur.[3]
Eomaia scansoria possessed several features in common with
However, E. scansoria is not a true placental mammal as it lacks some features that are specific to placentals. These include the presence of a malleolus at the bottom of the
Eomaia, like other early mammals and living marsupials, had a narrow pelvic outlet suggesting small undeveloped neonates requiring extensive nurturing.[5]
Classification
The discoverers of Eomaia claimed that, on the basis of 268 characters sampled from all major Mesozoic mammal clades and principal eutherian families of the Cretaceous, Eomaia could be placed at the root of the eutherian "family tree" along with Murtoilestes and Prokennalestes.[1] This initial classification scheme is summarized below.
Theria |
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In 2013, a much larger study of mammal relationships (including fossil species) was published by O'Leary et al.[8] The study, which examined 4541 anatomical characters of 86 mammal species (including Eomaia scansoria), found "100% jackknife support that Eomaia falls outside of Eutheria as a stem taxon to Theria", and so could not be considered a placental or a eutherian as previously hypothesized.[8] The results of this study are summarized in the cladogram below.
Mammalia
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The 2013 study by O'Leary et al. is part of a debate about the age of origin of placental mammals (see discussions.[9] [10] [11] ), and in all trees published in that paper Eomaia fell outside Theria (i.e., debates about the findings of O'Leary et al. have not centered on the position of Eomaia). Meng (2014),[12] who was a co-author on the O'Leary et al. (2013) paper, subsequently referred to Eomaia as a Eutherian but provided no analysis to support this claim. Gheerbrant et al. 2014[13] mentioned Eomaia in a list of Cretaceous taxa that represented "the primitive eutherian condition" but provided no analytical evidence for this claim; a similar claim was repeated by Sole et al. (2014)[14] again without analytical support.
A 2023 cladistical study again recovered Eomaia as a basal eutherian.[15]
Eutheria | |
See also
- Evolution of mammals
- Juramaia (160 million years ago)
- Sinodelphys
References
- ^ S2CID 4330626. Archived from the original(PDF) on 2010-11-03. Retrieved 2008-09-24.
- S2CID 28414039.
- S2CID 46067702.
- JSTOR 4523087.
- S2CID 4332049.
- S2CID 41470665.
- S2CID 205026882.
- ^ S2CID 206544776.
- PMID 23929967.
- PMID 24429684.
- PMID 23813978.
- ISSN 2053-714X.
- PMID 24587000.
- ISSN 0024-4082.
- PMID 37884521.
External links
- Hecht, Jeff (24 April 2002). "Stunning fossil is human's earliest mammal relative". New Scientist. Retrieved 18 February 2012.
- Roach, John (25 January 2005). "Scientists Recreate Genome of Ancient Human Ancestor". National Geographic News. Archived from the original on April 6, 2005. Retrieved 18 February 2012.