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http://palaeo-electronica.org/content/fc-1 Benton et al. 2015
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At present it cannot be said which of the Bathonian eutriconodonts and dryolestoids (Boneham and Wyatt, 1993) and australosphenidans (Flynn et al., 1999) is oldest, but we select Ambondro as most likely. It comes from the upper part of the Isalo “Group” (middle Jurassic, Bathonian) of Madagascar (Flynn et al., 1999), dated as generally Bathonian, so we select the top of the Bathonian as the hard minimum calibration date, 166.1 Ma ± 1.2 Myr = 164.9 Ma (Gradstein, 2012).
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The closest relatives of crown mammals are Hadrocodium and Docodonta (Luo et al., 2002; Meng et al., 2011). Hadrocodium was originally reported to be early Jurassic of Yunnan Province, China (Sinemurian; Luo et al., 2001), and the oldest docodonts are from the Bathonian of Europe, with a possible earlier form from the Kota Formation of India. Further outgroups, Morganucodontidae, Sinoconodon, and Adelobasileus, are known from the late Triassic and early Jurassic. Deposits of Late Triassic and Early Jurassic age have yielded fossil mammaliaforms, but nothing assignable to the Australosphenida or Theriimorpha. We therefore suggest the Triassic-Jurassic boundary at 201.3 Ma ± 0.2 Myr = 201.5 Ma as a soft maximum constraint.
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Ambondro mahabo from Madagascar (Flynn et al., 1999) is placed within the monotreme clade Australosphenida, according to the most widely accepted cladistic analysis of crown Mammalia (Luo et al., 2007; Meng et al., 2011).
Flynn, J.J., Parrish, J.M., Rakotosamimanana, B., Simpson, W.F., and Wyss, A.R. 1999. A Middle Jurassic mammal from Madagascar. Nature, 401:57-60.
Luo, Z-X., Chen, P., Li, G., and Chen, M. 2007. A new eutriconodont mammal and evolutionary development in early mammals. Nature, 446:288-293.
Meng, J., Wang, Y., and Li., C. 2011. Transitional mammalian middle ear from a new Cretaceous Jehol eutriconodont. Nature 472, 81-185.
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