The Australosphenida are a clade of mammals, containing mammals with tribosphenic molars, known from the Jurassic to Mid-Cretaceous of Gondwana. Although they have often been suggested to have acquired tribosphenic molars independently from those of Tribosphenida, this has been disputed. Fossils of australosphenidans have been found from the Jurassic of Madagascar and Argentina, and Cretaceous of Australia and Argentina. Monotremes have also been considered a part of this group in its original definition and in many subsequent studies, but its relationship with other members has been disputed by some scholars.
| Australosphenida Temporal range:
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| Jaw fragment of Ambondro mahabo | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Clade: | Australosphenida Luo, Cifelli, & Kielan-Jaworowska, 2001 |
| Taxa | |
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And see text | |
Taxonomy
editThis grouping includes the following taxa:
- †Henosferidae, including the genera Ambondro, Asfaltomylos, and Henosferus from the Jurassic of Argentina and Madagascar.
- †Ausktribosphenidae known from the Early Cretaceous of Australia
- †Bishopidae including Bishops from the Lower Cretaceous of Australia and an unnamed genus from the Mid-Cretaceous of Argentina (the latter of which was originally attributed to Ausktribosphenidae).[1][2]
- †?Vincelestes, sometimes recovered as an australosphenidan (when not inversely considered a cladotherian).[3][4]
- †?Tendagurutherium, recovered as an australosphenidan in one study.[3]
- ?Monotremata, one of the three major living groups of mammals, known from the Early Cretaceous to present of Australia-New Guinea and the Late Cretaceous-Paleocene of southern South America.
The grouping embodies a hypothesis about the evolution of molar teeth in mammals. Living monotremes are toothless as adults, but the juvenile platypus, fossil monotremes and Ausktribosphenida all share a pattern of three molar cusps arranged in a triangle or V shape, which is known as the tribosphenic type of molar.
Monotremes were historically classified within the clade Prototheria, alongside morganucodontids, docodonts, triconodonts and multituberculates, however it is now widely recognised that this grouping is a paraphyletic grade and that these groups do not share a close relationship. In 2001, Luo et al proposed the clade Australosphenida to include monotremes as well as Jurassic and Cretaceous mammals with tribosphenic molars known from the Southern Hemisphere, based almost exclusvely on characters of the skull and lower jaws.[5]
Cladogram after Luo et al 2001:[6]
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| Mammalia |
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According to Luo et al., tribosphenic molars were evolved by the Australosphenida independently of the true Tribosphenida, or Boreosphenida (that is, the therians and their relatives) in the northern continents. Others contend that the ausktribosphenids (two families of the Australian Cretaceous tribosphenids) in fact belong to the placentals and were therefore true tribosphenids, but unrelated to the ancestry of the monotremes.[7]
Most recent phylogenetic studies lump henosferids and aukstribosphenids alongside monotremes.[8][9] However, a 2022 review of monotreme evolution noted that the most primitive monotreme Teinolophos differed substantially from other non-monotreme Australosphenidans, having five molars as opposed to three in all other non-monotreme australosphenidans, and having non-tribosphenic molars, meaning that monotremes and non-monotreme australosphenidans were likely unrelated.[10] Later, Flannery and coauthors suggested that the core grouping of australosphenidans (excluding monotremes) were actually stem-therians as members of Tribosphenida, with the group representing a paraphyletic grade, with Bishopidae more closely related to Theria than to other australosphenidans.[2]
Notes
edit- ^ Martin, Thomas; Goin, Francisco J.; Schultz, Julia A.; Gelfo, Javier N. (May 2022). "Early Late Cretaceous mammals from southern Patagonia (Santa Cruz province, Argentina)". Cretaceous Research. 133: 105127. Bibcode:2022CrRes.13305127M. doi:10.1016/j.cretres.2021.105127.
- ^ a b Flannery, Timothy F.; Rich, Thomas H.; Vickers-Rich, Patricia; Veatch, E. Grace; Helgen, Kristofer M. (2022-11-01). "The Gondwanan Origin of Tribosphenida (Mammalia)". Alcheringa: An Australasian Journal of Palaeontology. 46 (3–4): 277–290. Bibcode:2022Alch...46..277F. doi:10.1080/03115518.2022.2132288. ISSN 0311-5518. S2CID 253323862.
- ^ a b Nicholas Chimento, Frederico Agnolin, Agustin Martinelli, Mesozoic Mammals from South America: Implications for understanding early mammalian faunas from Gondwana, May 2016
- ^ José Bonaparte, On the phylogenetic relationships of Vincelestes neuquenianus, Published online: 17 Sep 2008
- ^ Flannery, Timothy F.; Rich, Thomas H.; Vickers-Rich, Patricia; Ziegler, Tim; Veatch, E. Grace; Helgen, Kristofer M. (2022-01-02). "A review of monotreme (Monotremata) evolution". Alcheringa: An Australasian Journal of Palaeontology. 46 (1): 3–20. Bibcode:2022Alch...46....3F. doi:10.1080/03115518.2022.2025900. ISSN 0311-5518.
- ^ Luo, Zhe-Xi; Cifelli, Richard L.; Kielan-Jaworowska, Zofia (January 2001). "Dual origin of tribosphenic mammals". Nature. 409 (6816): 53–57. Bibcode:2001Natur.409...53L. doi:10.1038/35051023. ISSN 0028-0836. PMID 11343108.
- ^ Benton 2005: 300, 306-308.
- ^ Richard Stephen Thompson, Rachel O'Meara, Were There Miocene Meridiolestidans? Assessing the Phylogenetic Placement of Necrolestes patagonensis and the Presence of a 40 Million Year Meridiolestidan Ghost Lineage, Article in Journal of Mammalian Evolution · September 2014 DOI: 10.1007/s10914-013-9252-3
- ^ Rebecca Pian; Michael Archer; Suzanne J. Hand; Robin M.D. Beck; Andrew Cody (2016). "The upper dentition and relationships of the enigmatic Australian Cretaceous mammal Kollikodon ritchiei". Memoirs of Museum Victoria. 74: 97–105.
- ^ Flannery, Timothy F.; Rich, Thomas H.; Vickers-Rich, Patricia; Ziegler, Tim; Veatch, E. Grace; Helgen, Kristofer M. (2022-01-02). "A review of monotreme (Monotremata) evolution". Alcheringa: An Australasian Journal of Palaeontology. 46 (1): 3–20. Bibcode:2022Alch...46....3F. doi:10.1080/03115518.2022.2025900. ISSN 0311-5518.
References
edit- Benton, Michael J. (2005). Vertebrate Palaeontology (3rd ed.). Oxford: Blackwell Publishing. ISBN 0-632-05637-1.
- Luo, Zhe-Xi; Cifelli, Richard L.; Kielan-Jaworowska, Zofia (2001). "Dual origin of tribosphenic mammals". Nature. 409 (6816): 53–57. Bibcode:2001Natur.409...53L. doi:10.1038/35051023. PMID 11343108. S2CID 4342585.
- Luo, Zhe-Xi; Kielan-Jaworowska, Zofia; Cifelli, Richard L. (2002). "In quest for a phylogeny of Mesozoic mammals" (PDF). Acta Palaeontologica Polonica. 47 (1): 1–78.
