Talk:Lissamphibia

message: "The publication of a Permian-period stem form Gerobatrachus hottoni showed the frogs and salamanders had a common ancestor more recently (ca 290 Mya) than had been thought by using the molecular clock alone."
This is not obviously correct. The existence of a stem group taxon does not place a lower bound on the age of a crown group, as stem group lineages do not automatically go extinct on the appearance of the crown group. For example, monkeys could be considered a stem group with respect to the ape crown group (or vice versa), but neither is yet extinct. (The cited National Geographic Article at Gerobatrachus hottoni is in disagreement with the above statement.)
:You are absolutely correct. Even if Gerobatrachus hottoni were a stem-batrachian, that would say nothing about the geological age of Batrachia. Furthermore, these affinities have been disputed . I find that this page could use a lot more references. For instance, no citation is provided to any paper supporting a monophyletic origin within lepospondyls (although several were published). Similarly, there are far more molecular studies, but Sigurdsen and Green (2011), cited as such, is a morphological study, not a molecular one. I could fix all these problems; should I?  Stranger forever (talk) 14:54, 8 December 2012 (UTC)
replies: text: Anderson et al. (2008) says, not just that Gerobatrachus hottoni is a stem batrachian, but that it is "the immediate sister taxon to Batrachia". Doesn't that mean that Batrachia is about as old as Gerobatrachus? If so, the article isn't that far off the mark. Peter Brown (talk) 23:43, 9 December 2012 (UTC)
replies: text: Hi Peter, even if Gerobatrachus hottoni were the immediate sister-group of Batrachia (which I doubt), that would imply nothing about the age of Batrachia, except that its stem is at least as old as Gerobatrachus hottoni. But that fixes no maximal age. So the text in the introduction is wrong. Gerobatrachus hottoni does not falsify any molecular dating of Lissamphibia or of Batrachia. Michel Laurin (talk) 07:48, 10 December 2012 (UTC)
replies: text: Michel, you have added that, if Anderson et al. are correct about Gerobatrachus hottoni, then it is the oldest known lissamphibian. It is really unclear why a stem-batrachian needs to be a lissamphibian at all, especially if the subclass is polyphyletic. The real problem, which also underlies my question in the next section, is that the article provides no clear delimitation of Lissamphibia. This is not something I know and surely the general reader will fare no better. Peter Brown (talk) 18:04, 11 December 2012 (UTC)
replies: text: Peter, Lissamphibia has been conceptualized since the early 20th century as the smallest crown group that includes all extant amphibians. Thus, a stem-batrachian has to be a lissamphibian, by definition, because the existence of Batrachia implies that gymnophionans are outside that clade (and delimit, along with Batrachia, Lissamphibia). By the way, I formalized that definition in the context of the PhyloCode (Phylonyms volume, which should be published in the first half of 2020). I hope that this clarifies.Michel Laurin (talk) 11:21, 5 January 2020 (UTC)
thread_title: Dating