Ambondro mahabo
Ambondro mahabo Temporal range: Middle Jurassic
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Figure 1. Jaw of Ambondro, seen in lingual view (from the side of the tongue). Scale bar is 1 mm. | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Family: | †Henosferidae |
Genus: | †Ambondro Flynn et al., 1999 |
Species: | †A. mahabo
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Binomial name | |
†Ambondro mahabo Flynn et al., 1999
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Ambondro mahabo is a
Upon its description in 1999, Ambondro was interpreted as a primitive relative of Tribosphenida (marsupials, placentals, and their extinct tribosphenic-toothed relatives). In 2001, however, an alternative suggestion was published that united it with the Cretaceous Australian Ausktribosphenos and the monotremes (the echidnas, the platypus, and their extinct relatives) into the clade Australosphenida, which would have acquired tribosphenic molars independently from marsupials and placentals. The Jurassic Argentinean Asfaltomylos and Henosferus and the Cretaceous Australian Bishops were later added to Australosphenida, and new work on wear in australosphenidan teeth has called into question whether these animals, including Ambondro, did have tribosphenic teeth. Other paleontologists have challenged this concept of Australosphenida, and instead proposed that Ambondro is not closely related to Ausktribosphenos plus monotremes, or that monotremes are not australosphenidans and that the remaining australosphenidans are related to placentals.
Discovery and context
Ambondro mahabo was described by a team led by John Flynn in a 1999 paper in
Description
Ambondro was described on the basis of a fragmentary right
The front half of the m1 and m2 consists of the
The
Interpretations
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Figure 3. Alternative views of the relationships of Ambondro. Top, Rougier et al., (2007, fig. 9): australosphenidans, including monotremes and Ambondro, are distinct from boreosphenidans.[Note 1] Bottom, Woodburne et al. (2003, fig. 3): australosphenidans, including Ambondro but excluding monotremes, are closely related to placentals. Many taxa are omitted from both trees for clarity. |
In their paper, Flynn and colleagues described Ambondro as the oldest mammal with
In 2001,
Also in 2001, Denise Sigogneau-Russell and colleagues in their description of the earliest Laurasian tribosphenic mammal, Tribactonodon, agreed with the relationship between Ausktribosphenos and monotremes, but argued that Ambondro was closer to Laurasian tribosphenidans than to Ausktribosphenos and monotremes. As evidence against the integrity of Australosphenida, they cited the presence of lingual cingula in various non-australosphenidan mammals; the presence of two cusps in the anterior cingulum in Ambondro as well as some boreosphenidans; the different appearance of the premolar in Ambondro (flat) and Ausktribosphenos (squared); and the contrast between the talonids of Ambondro (with a well-developed hypoconid on the labial side) and Ausktribosphenos (squared).[5]
The next year, Luo and colleagues published a more thorough analysis confirming their previous conclusion and adding the Cretaceous Australian Bishops to Australosphenida.[14] They mentioned the condition of the hypoconulid, which is inclined forward, rather than backward as in boreosphenidans, as an additional australosphenidan character[15] and noted that Ausktribosphenos and monotremes were united, to the exclusion of Ambondro, by the presence of a V-shaped notch in the distal metacristid.[16] In the same year, Asfaltomylos was described from the Jurassic of Argentina as another australosphenidan. In contrast to Ambondro, this animal lacked a distal metacristid and did not have as well-developed a lingual cingulum.[17]
However, in 2003 Michael Woodburne and colleagues revised the phylogenetic analysis published by Luo and colleagues, making several changes to the data, particularly in the monotremes.[18] Their results (Figure 3, bottom) challenged the division between Australosphenida and Boreosphenida, as proposed by Luo et al. Instead, they excluded monotremes from Australosphenida and placed the remaining australosphenidans close to Eutheria, with Ambondro most closely related to Asfaltomylos.[19] In 2007, Guillermo Rougier and colleagues described another australosphenidan, Henosferus, from the Jurassic of Argentina; they argued against a relationship between Eutheria and Australosphenida (Figure 3, top), but were ambivalent about the placement of monotremes within Australosphenida.[20] Based in part on Martin and Rauhut's earlier work on wear facets in australosphenidans, they questioned the presence of a true functional protocone on the upper molars of non-monotreme australosphenidans—none of which are known from upper teeth—and consequently suggested that australosphenidans may not, after all, have had truly tribosphenic teeth.[21]
Notes
- ^ Compare similar trees in Luo et al. (2001, fig. 1), Luo et al. (2002, fig. 1), Rauhut et al. (2002, fig. 3), which included fewer australosphenidan species.
References
- ^ Flynn et al., 1999, pp. 57–58
- ^ a b c d e Flynn et al., 1999, p. 58
- ^ a b Flynn et al., 1999, fig. 3
- ^ a b Rauhut et al., 2002, p. 167
- ^ a b Sigogneau-Russell et al., 2001, p. 146
- ^ Flynn et al., 1999, fig. 2
- ^ Luo et al., 2002, pp. 22, 29
- ^ Flynn et al., 1999, p. 59
- ^ Martin and Rauhut, 2005, pp. 422–423
- ^ Flynn et al., 1999, p. 57; Rougier et al., 2007, p. 23
- ^ Flynn et al., 1999, p. 60
- ^ Luo et al., 2001, p. 56
- ^ Luo et al., 2001, pp. 53, 56
- ^ Luo et al., 2002, fig. 1
- ^ Luo et al., 2002, p. 23
- ^ Luo et al., 2002, p. 22
- ^ Rauhut et al., 2002, p. 166
- ^ Woodburne, 2003, pp. 233–235
- ^ Woodburne, 2003, fig. 5; Woodburne et al., 2003, fig. 3
- ^ Rougier et al., 2007, p. 31
- ^ Rougier et al., 2007, pp. 24–25
Bibliography
- Flynn, J.J., Parrish, J.M., Rakotosamimanana, B., Simpson, W.F. and Wyss, A.R. 1999. A Middle Jurassic mammal from Madagascar (subscription required). Nature 401:57–60.
- Luo, Z.-X., Cifelli, R.L. and Kielan-Jaworowska, Z. 2001. Dual origin of tribosphenic mammals (subscription required). Nature 409:53–57.
- Luo, Z.-X., Kielan-Jaworowska, Z. and Cifelli, R.L. 2002. In quest for a phylogeny of Mesozoic mammals. Acta Palaeontologica Polonica 47(1):1–78.
- Martin, T. and Rauhut, O.W.M. 2005. Mandible and dentition of Asfaltomylos patagonicus (Australosphenida, Mammalia) and the evolution of tribosphenic teeth (subscription required). Journal of Vertebrate Paleontology 25(2):414–425.
- Rauhut, O.W.M., Martin, T., Ortiz-Jaureguizar, E. and Puerta, P. 2002. A Jurassic mammal from South America (subscription required). Nature 416:165–168.
- Rougier, G.W., Martinelli, A.G., Forasiepi, A.M. and Novacek, M.J. 2007. New Jurassic mammals from Patagonia, Argentina: A reappraisal of australosphenidan morphology and interrelationships. American Museum Novitates 3566:1–54.
- Sigogneau-Russell, D., Hooker, J.J. and Ensom, P.C. 2001. The oldest tribosphenic mammal from Laurasia (Purbeck Limestone Group, Berriasian, Cretaceous, UK) and its bearing on the 'dual origin' of Tribosphenida (subscription required). Comptes Rendus de l'Académie des Sciences, Series IIA (Earth and Planetary Science) 333(2):141–147.
- Woodburne, M.O. 2003. Monotremes as pretribosphenic mammals (subscription required). Journal of Mammalian Evolution 10(3):195–248.
- Woodburne, M.O., Rich, T.H. and Springer, M.S. 2003. The evolution of tribospheny and the antiquity of mammalian clades (subscription required). Molecular Phylogeny and Evolution 28(2):360–385.