Recalibrating clade origins, part 5

Earlier
we looked at the first part, second part, third part and fourth part of Marjanovic’s 2019 chronological recalibration of vertebrate nodes. Today we conclude.

Batrachia (Caudata + Salientia) = Amphibians (= extant Frogs + Salamanders) Marjanovic discusses Triadobatrachus from the Early Triassic (Olenekian, 249mya) and concludes that 249 mya “is a perfectly adequate hard minimum age for this calibration point.” And “290mya may be a defensible soft maximum value.”

After adding Triadobatrachus (Fig. 1) to the large reptile tree (LRT, 1631+ taxa), Gerobatrachus (Early Permian, 300mya) mentioned once by Marjanovic, nests basal to the few tested extant frogs and salamanders. So, 300mya is pretty close to his estimate of 290mya.

Figure 1. Triadobatrachus skull, as originally colorized and redone with tetrapod colors here.

Figure 1. Triadobatrachus skull, as originally colorized and dorsal surface redone with tetrapod colors here with bone fusion identified and the maxilla + premaxilla restored. Compare to Rana in figure 2. Distinct from extant frogs, a squamosal is present here.

Figure 2. Skull of the frog, Rana with colors matching those of Triadobatrachus.

Figure 2. Skull of the frog, Rana with colors matching those of Triadobatrachus. Here the squamosal and jugal are missing. The quadratojugal is present.

Chondrichthyes (Holocephalii + Elasmobranchii)
= (ratfish + sharks and skates) Marjanovic reports, “By current understanding (Frey et al., 2019), the oldest known crown-chondrichthyan is the stem elasmobranch Phoebodus fastigatus from the middle Givetian. The Givetian, part of the Middle Devonian, …so I propose 385 Ma as the hard minimum age of the chondrichthyan crown-group.”

By contrast, the LRT recovers the whale shark + manta ancestor, Loganellia (Early Silurian, 440mya; Fig. 3) as the oldest known ancestor of sharks and other fish. Sturgeons are more primitive, and therefore must be older, but Ordovician sturgeon and osteostracan fossils have not been found. Taxon inclusion recovers these novel interrelationships.

Figure 2. Loganellia, a thelodont with whale shark shape including dorsal fin. Image from OldRedSandstone.com. This appears to be Loganellia, not Thelodus (Fig. 7).

Figure 2. Loganellia, a thelodont with a whale shark shape including dorsal fin. Image from OldRedSandstone.com. This appears to be Loganellia, not Thelodus.


Marjanovic reports, “There is not as much interest in phylogeny among specialists of early elasmobranchs than among specialists of early mammals or early dinosaurs.” The LRT does not have that problem. Enigmas are answered with this powerful tool that works well by avoiding tooth-only taxa.

Marjanovic considers the clade Batoidea (skates + rays) to be monophyletic.

In the LRT, so far, three origins for ray-like basal tetrapods have been recovered based on taxon inclusion.

Marjanovic considers the clade Neopterygii (Holosteomorpha + Teleosteomorpha) = (bowfins and gars + other teleosts or bony fish) to be monophyletic.

In the LRT, this hypothesis of relationships has been invalidated.

Marjanovic reports, “I cite 228 references for calibration purposes.”

In the LRT, I’m not sure how many citations I cite for 1631+ taxa, but once again, adding taxa brings new insights to hypothetical interrelationships. Marjanovic was testing the results of a previous publication, but should have done so with a greater authority, with more taxa and with no reference whatsoever to genomics.

Tomorrow: something new. 


References
Marjanovic D 2019. Recalibrating the transcriptomic timetree of jawed vertebrates.
bioRxiv 2019.12.19.882829 (preprint)
doi: https://doi.org/10.1101/2019.12.19.882829
https://www.biorxiv.org/content/10.1101/2019.12.19.882829v1

1 thought on “Recalibrating clade origins, part 5

  1. Gerobatrachus (Early Permian, 300mya)

    I think you derived this date by just taking the beginning of the Permian and rounding it (it’s currently given as 298.9 ± 0.15 Ma ago on the International Chronostratigraphic Chart). Gerobatrachus is from somewhere in the Clear Fork Group (apparently it’s not known which formation exactly); from a few seconds of googling, the Clear Fork Group spans the Artinskian and the Kungurian… and the Artinskian began 290.1 ± 0.26 Ma ago, as it happens.

    The end of the Early Permian (and the Kungurian) is given as 272.95 ± 0.11 Ma ago.

    Distinct from extant frogs, a squamosal is present here.

    Don’t rely on century-old sources. In your fig. 2, the squamosal is the magenta bone caudoventral of the orbitotemporal fenestra.

    Enigmas are answered with this powerful tool that works well by avoiding tooth-only taxa.

    I can’t avoid tooth-only taxa when I want to know the first appearance of a tooth-bearing clade in the fossil record.

    Marjanovic was testing the results of a previous publication, but should have done so with a greater authority, with more taxa and with no reference whatsoever to genomics.

    I wasn’t testing the results, really. I was testing the method. Specifically, I was testing the question: does it matter that so many of the calibration points Irisarri et al. (2017) used are wrong? Perhaps the errors are too small to matter? Turns out they’re not: using their tree and their dataset of taxa and transcriptomes, but updated calibrations, I get different results.

    That I would have gotten different results from a different tree is likely, but that’s simply a different question, not the one I was investigating. My point in mentioning that I used 228 references was to show that calibrating divergence dates is hard work, much harder than Irisarri et al. and many others thought.

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