Phylogeny and geological time ranges of the sarcopterygian lineages leading to modern coelacanths, lungfish and tetrapods (IMAGE)
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The dipnomorph Youngolepis from the Xishancun and Xitun formations (Lochkovian, approximately from 419.2±3.2 Ma to 410.8±2.8 Ma) is universally regarded as the oldest representative of crown Rhipidistia, as well as the earliest representative of crown Sarcopterygii. The oldest-known sister taxa of crown Sarcopterygii (e.g., Psarolepis, Guiyu) have been reported from the Ludfordian of Ludlow (425.6±0.9 Ma). Thus, both the coelacanth-rhipidistian and lungfish-tetrapod splits should have occurred sometime during the interval from Ludlow to Lochkovian, which means that the minimal estimated time for two splits must be at least 416.0 (419.2-3.2) Ma, and the maximal estimated time for two splits is about 426.5 (425.6+0.9) Ma. Both the coelacanth-rhipidistian and lungfish-tetrapod splits should have occurred sometime between 426.5 and 416.0 Ma. Artwork credit: Brian Choo and Yong Xu.
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