comment on this calibration
Lissamphibia
| node name Lissamphibia Look for this name in NCBI Wikipedia Animal Diversity Web | ||
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recommended citations http://palaeo-electronica.org/content/fc-1 Benton et al. 2015 |
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node minimum age 250 Ma The Sakamena Group in Madagascar spans from Late Permian to Middle Triassic, and the Middle Sakamena Group/ Formation is generally dated as lower Lower Triassic, the Upper Sakamena Group/ Formation, Lower to lower Middle Triassic. The entire Sakamena Group is some 4 km thick, and it is subdivided based on dominant lithologies: the middle portion is a sequence of shales and minot sandstones deposited in a lagoonal or shallow lacustrine and braided river environment, whereas the units below and above are dominated by sandstones and conglomerates indicating higher energies of deposition. Dating of the Sakamena Group is notoriously difficult, as there are no radiometric dates, there has been no magnetostratigraphic study, and the associated fossils are not classic biostratigraphically useful index fossils. Nonetheless, the Middle Sakamena Group is dated as Induan on the basis of the associated fauna of benthosuchid temnospondyls (like those of the Lystrosaurus Assemblage Zone of South Africa and the Vokhmian units of Russia, as well as plants also suggesting Induan age. The top of the Induan stage is dated as 'slightly older than- 251.2 Ma +/- 0.2 Myr (Mundil et al., 2010), and given as 250.01 Ma by Gradstein et al. (2012, p. 718), so we select this age as the minimum constraint, namely 250.0 Ma. | ||
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node maximum age 272.8 Ma It is hard to know how far down to set the soft maximum age for Lissamphibia, as there are no reported stem lissamphibians from older Triassic or Permian rocks. An arbitrary date is set at the base of the Middle Permian, allowing considerable time to span numerous tetrapod-bearing rocks of various facies from South Africa, Russia, and China in which no identifiable lissamphibians, whether stem or crown, have been reported. The base of the Middle Permian is dated as 272.3 Ma ± 0.5 Myr, so 272.8 Ma. | ||
| primary fossil used to date this node | ||
MNHNFr MAE 126 | ||
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phylogenetic justification
Triadobatrachus has always been recognised as a frog, a basal member of Anura, and so within the stem Batrachia, and so the oldest member of the crown Lissamphibia, based on its possession of key apomorphies including a toothless dentary, a rod-like and anteriorly directed ilium and fused frontals and parietals (Ruta and Coates, 2007). |
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phylogenetic reference(s)
Ruta M., and Coates M.I. 2007. Dates, nodes and character conflict: addressing the lissamphibian origin problem. Journal of Systematic Palaeontology, 5:69–122.
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| tree image (click image for full size) | ||
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Figure 7 from Benton et al. (2014).
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