Yinotheria
Yinotheria Temporal range: Late Triassic record[1])
(possible | |
---|---|
Ambondro mahabo jaw fragment | |
Shuotherium dongi jawbone
| |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Subclass: | Yinotheria Chow and Rich, 1982[2] |
Subgroups | |
|
Yinotheria is a proposed basal subclass clade of crown
Other studies have rejected Yinotheria, finding Shuotheriidae to be unrelated to Australosphenida and outside crown Mammalia.[4]
Evolutionary history
According to genetic studies, Yinotheria diverged from other mammals around 220 to 210 million years ago, at some point in the Triassic or Early Jurassic.[1][5] The oldest-known fossils are a bit younger, dating around 168 to 163 million years in the Middle Jurassic. These fossils are the genera Pseudotribos of China,[3] Shuotherium of both China and the United Kingdom, Itatodon of Siberia and Paritatodon of Kyrgyzstan and the UK.[6] These, which belong to the family Shuotheriidae, are the only known northern hemisphere group of yinotherians.
The infraclass Australosphenida appeared around the same time as Shuotheriidae. The family Henosferidae, comprising the genera Henosferus, Ambondro, and Asfaltomylos, has been found in the southern hemisphere at locations in Argentina and Madagascar. This suggests that this family could have been more widespread and diverse in Gondwana during that time; however, due to their fragile state, some fossils might have been destroyed by geological events.
The family
Some 110-million-year-old monotreme fossil jaw fragments were found at
Systematics
History of classification
Prototheria
Originally, monotremes were classified as a subclass of mammals known as Prototheria. The names Prototheria,
The threefold division of living mammals into monotremes, marsupials and placentals was already well established when Thomas Huxley proposed the names Metatheria and Eutheria to incorporate the two latter groups in 1880. Initially treated as subclasses, Metatheria and Eutheria are by convention now grouped as infraclasses of the subclass Theria, and in more recent proposals have been demoted further (to cohorts or even magnorders), as cladistic reappraisals of the relationships between living and fossil mammals have suggested that the Theria itself should be reduced in rank.[10]
Prototheria, on the other hand, was generally recognised as a subclass until quite recently, on the basis of a hypothesis that defined the group by two supposed
Australosphenida hypothesis and Yinotheria
The evidence that was held to support Prototheria is now universally discounted. In the first place, the examination of embryos has revealed that the development of the braincase wall is essentially identical in therians and in 'prototherians': the anterior lamina simply fuses with the alisphenoid in therians, and therefore the 'prototherian' condition of the braincase wall is primitive for all mammals, while the therian condition can be derived from it. Additionally, the linear alignment of molar cusps is also primitive for all mammals. Therefore, neither of these states can supply a uniquely shared derived character that would support a 'prototherian' grouping of orders in contradistinction to Theria (Kemp 1983).
In a further reappraisal, the molars of embryonic and fossil monotremes (living monotreme adults are toothless) appear to demonstrate an ancestral pattern of cusps that is similar to the triangular arrangement observed in therians. Some peculiarities of this dentition support an alternative grouping of monotremes with certain recently discovered fossil forms into a proposed new clade known as the Australosphenida, and also suggest that the triangular array of cusps may have evolved independently in australosphenidans and therians (Luo et al. 2001, 2002). Australosphenida is characterized by the shared presence of a cingulum on the outer front corner of the lower molars, a short and broad talonid, a relatively low trigonid, and a triangulated last lower premolar.[11]
The Australosphenida hypothesis remains controversial; for example, lingual cingula seem to be a presence in various non-australosphenidan mammals[12] and some work has shown the possibility of Eutheria being the sister group to Australosphenida, without monotremes.[13] As a result, some taxonomists (e.g. McKenna & Bell 1997) prefer to maintain the name Prototheria as a fitting contrast to the other group of living mammals, the Theria. In theory, the Prototheria is taxonomically redundant, since Monotremata is currently the only order that can still be confidently included, but its retention might be justified if new fossil evidence, or a re-examination of known fossils, enables extinct relatives of the monotremes to be identified and placed within a wider grouping.
When systematic work was performed, it was also found that Australosphenida is the sister taxon to Shuotheriidae, an obscure group of Mesozoic mammals that were found in what is now China. Kielan-Jaworowska, Cifelli & Luo 2002 had this to say regarding the Shuotheriidae, particularly Shuotherium:[14]
In our view, the most compelling evidence as to the affinities of Shuotherium lies in the structure of the last premolar, which shares striking similarities to that of Australosphenida
Lower molar structure of Shuotherium and Australosphenida is obviously quite different, and for this reason we do not place Shuotherium within this Gondwanan clade. Based on the limited evidence available, however, we suggest that Shuotherium is a viable sister-taxon to Australosphenida.
Yinotheria is named for this grouping.[3][15]
Other scholars have rejected Yinotheria, finding instead that Shuotheriidae is closely related to Docodonta outside crown Mammalia.[4]
Taxonomy
In comparison to Metatheria and Eutheria, where there seems to be a better understanding on the relationships among taxa with substantial fossil evidence, Yinotheria has few fossils; mostly consisting of (with few exceptions) the jawbones and teeth. In addition, the group seems not to have been as diverse in their evolutionary history, in comparison to members of both Metatheria and Eutheria.[16] Future analysis and better fossil remains could affect the membership of Yinotheria as well as rearranging and revising the relationships of stem-monotremes and crowned monotremes.
- Subclass Yinotheria Chow & Rich 1982 sensu Kielan-Jaworowska, Cifelli & Luo 2004 [Prototheria Gill 1872]
- Order †Shuotherida Chow & Rich 1982 [Shuotheridia; Shuotheria]
- Family †Shuotheriidae Chow & Rich 1982
- Genus †Pseudotribos Luo, Ji & Yuan 2007
- †Pseudotribos robustusLuo, Ji & Yuan 2007
- †
- Genus †Shuotherium Chow & Rich 1982
- †Shuotherium dongiChow & Rich 1982
- †Shuotherium shilongiWang et al. 1998
- †
- Genus †Pseudotribos Luo, Ji & Yuan 2007
- Family †Shuotheriidae Chow & Rich 1982
- Infraclass Australosphenida Luo, Cifelli & Kielan-Jaworowska 2001 sensu Kielan-Jaworowska, Cifelli & Luo 2004
- Order †AusktribosphenidaLuo, Cifelli & Kielan-Jaworowska 2001
- Family †Ausktribosphenidae Rich et al. 1997
- Genus †BishopsRich et al. 2001
- †Bishops whitmorei Rich et al. 2001
- Genus †Ausktribosphenos Rich et al. 1997
- †Ausktribosphenos nyktosRich et al. 1997
- †
- Genus †
- Family †Ausktribosphenidae Rich et al. 1997
- Order †Henosferida Averianov & Lopatin 2011
- Family †Henosferidae Rougier et al. 2007
- Genus †Ambondro[17]
- †Ambondro mahabo Flynn et al. 1999
- Genus †Asfaltomylos Rauhut et al. 2002
- †Asfaltomylos patagonicusRauhut et al. 2002
- †
- Genus †Henosferus Rougier et al. 2007
- †Henosferus molusRougier et al. 2007
- †
- Genus †Ambondro[17]
- Family †Henosferidae Rougier et al. 2007
- Order MonotremataBonaparte 1837 sensu Luo, Cifelli & Kielan-Jaworowska 2001
- Family Incertae sedis
- Genus †Kryoryctes Pridmore et al. 2005 (either a stem-monotreme[18] or junior synonym of Steropodon[19])
- †Kryoryctes cadburyiPridmore et al. 2005
- †
- Genus †Kryoryctes Pridmore et al. 2005 (either a stem-monotreme[18] or junior synonym of Steropodon[19])
- Family Tachyglossidae Gill 1872 [ EchidnidaeBurnett 1830] (echidnas, spiny anteaters)
- Genus †Megalibgwilia Griffiths, Wells & Barrie 1991 (subjective synonym or subgenus of Zaglossus)
- †Zaglossus robustus)
- †Megalibgwilia owenii[16])
- †
- Genus Zaglossus Gill 1877 [Proechidna Gervais 1877; Acanthoglossus Gervais 1877; Bruynia Dubois 1882; Bruijia Thomas 1883; ProzaglossusKerbert 1913] (Long-beaked Echidnas)
- †Murrayglossus Glauert 1914 (Hackett's Giant Echidna) (might belong to a new genus[16])
- Zaglossus bruijni (Peters & Doria 1876) (Western Long-beaked/Bruinj's/Brown False Echidna)
- Zaglossus attenboroughiiFlannery & Groves 1998 (Attenborough's/Sir David's/Cyclops Long-beaked Echidna)
- Zaglossus bartoni Thomas 1907 (Eastern/Barton's Long-beaked/Grey False Echidna)
- Genus Rafinesque 1815]
- Tachyglossus aculeatus(Shaw 1792) Illiger 1811 (short-beaked Echidna)
- Genus †Megalibgwilia Griffiths, Wells & Barrie 1991 (subjective synonym or subgenus of Zaglossus)
- Family †KollikodontidaeFlannery et al. 1995
- Genus †mammaliform of uncertain placement[16])
- †Kollikodon ritchieiFlannery et al. 1995
- †
- Genus †
- Family †SteropodontidaeArcher et al. 1985
- Genus †Teinolophos Rich et al. 1999 (might be a basal monotreme or a stem-monotreme[16])
- †Teinolophos trusleriRich et al. 1999
- †
- Genus †Steropodon Archer et al. 1985
- †Steropodon galmaniArcher et al. 1985
- †
- Genus †Teinolophos Rich et al. 1999 (might be a basal monotreme or a stem-monotreme[16])
- Family Ornithorhynchidae Gray 1825
- Genus †Monotrematum Pascual et al. 1992 (here considered to be a basal ornithorhynchid;[16] others subjective synonym of Obdurodon)
- †Monotrematum sudamericanumPascual et al. 1992
- †
- Genus †Obdurodon Woodburne & Tedford 1975
- †Obdurodon insignisWoodburne & Tedford 1975
- †Obdurodon tharalkooschildPian, Archer & Hand 2013
- †Obdurodon dicksoniArcher et al. 1992 (Riversleigh platypus)
- †
- Genus Shaw 1799 non Herbst 1793]
- Ornithorhynchus anatinus(Shaw 1799) Blumenbach 1800 (platypus)
- Genus †Monotrematum Pascual et al. 1992 (here considered to be a basal ornithorhynchid;[16] others subjective synonym of Obdurodon)
- Family Incertae sedis
- Order †
- Order †Shuotherida Chow & Rich 1982 [Shuotheridia; Shuotheria]
Phylogeny
Below is a simplified tree on Averianov et al., 2014[7] after Woodburn, 2003[17] and Ashwell, 2013[16]
Yinotheria |
| ||||||||||||||||||||||||
References
- ^ PMID 17654361.
- S2CID 254714864.
- ^ S2CID 609206. Retrieved 26 December 2014.
- ^ ISSN 0028-0836.
- ^ "The Timetree of Life - Mammals (Mammalia)" (PDF). Archived from the original (PDF) on 2013-10-31. Retrieved 2023-08-31.
- ^ Wang, Y.-Q. and Li, C.-K. 2016. Reconsideration of the systematic position of the Middle Jurassic mammaliaforms Itatodon and Paritatodon. Palaeontologia Polonica 67, 249–256.
- ^ a b Averianov et al., 2014
- PMID 19805098.
- ^ "The Timetree of Life - Monotremes (Prototheria)" (PDF). Archived from the original (PDF) on 2013-10-31. Retrieved 2023-08-31.
- ^ Marsupialia and Eutheria/Placentalia appear as cohorts in McKenna & Bell 1997 and in Benton 2005, with Theria ranked as a supercohort or an infralegion, respectively.
- ^ Luo et al., 2001, pp. 53, 56
- ^ Sigogneau-Russell et al., 2001, p. 146
- ^ Woodburne, 2003, fig. 5; Woodburne et al., 2003, fig. 3
- ^ Dykes: Shuoterium
- ^ Kielan-Jaworowska, Cifelli & Luo 2004, pp. 214–215, 529
- ^ a b c d e f g Ashwell, 2013
- ^ a b Woodburne, 2003
- S2CID 22931124
- PMC 2824408
Bibliography
- ISBN 0-632-05637-1.
- Dykes, Trevor. "Mesozoic Mammals: Shuotheriidae & Australosphenida, an internet directory". Archived from the original on July 16, 2012. Retrieved 12 May 2013.
- Kemp, T.S. (1983). "The relationships of mammals". Zoological Journal of the Linnean Society. 77 (4): 353–84. .
- Kielan-Jaworowska, Z.; Cifelli, R.L.; Luo, Z. (2002). "Dentition and relationships of the Jurassic mammal Shuotherium". Acta Palaeontologica Polonica. 47 (3): 479–486.
- Luo, Z.-X.; Cifelli, R.L.; Kielan-Jaworowska, Z. (2001). "Dual origin of tribosphenic mammals". Nature. 409 (6816): 53–7. S2CID 4342585.
- Luo, Z.-X.; Cifelli, R.L.; Kielan-Jaworowska, Z. (2002). "In quest for a phylogeny of Mesozoic mammals". Acta Palaeontologica Polonica. 47: 1–78.
- McKenna, Malcolm C., and Susan K. Bell. 1997. Classification of Mammals Above the Species Level. New York: Columbia University Press. ISBN 0-231-11013-8
- Kielan-Jaworowska, Zofia; Cifelli, Richard L.; Luo, Zhe-Xi (2004). Mammals from the Age of Dinosaurs: Origins, Evolution, and Structure. New York: Columbia University Press. pp. 214–215.
External links
- Media related to Yinotheria at Wikimedia Commons
- Data related to Yinotheria at Wikispecies