Odd Gerrothorax nests with Greererpeton

Figure 1. Gerrothorax, lacks a supratemporal rim and has laterally extended ribs, similar to those in Greererpeton.

Figure 1. Gerrothorax, lacks a supratemporal rim and has laterally extended ribs, similar to those in Greererpeton. There is some variation and perhaps some confusion regarding the identity of the bones between the orbits. Here an alternate is shown that is similar to Greererpeton.

Gerrothorax pulcherrimus (Nilsson 1934, Jenkins et al. 2008; Late Triassic) was and is considered a plagiosaurine temnospondyl. Here it nests with Greererpeton with which it shares a lack of a supratemporal-tabular rim, the straight lateral ribs and other traits. The ‘interfrontal’ is here identified as fused frontals. The separated ‘frontals’ are here identified as prefrontals.

Jenkins et al. showed the skull raised like a toilet seat cover during feeding, rather than opening the mandible on this flattened bottom feeder.

Figure 1. Greererpeton reduced to a blueprint of body parts. Here there may be one extra phalanx on pedal digit 5 and one missing on pedal digit 2 compared to sister taxa. So an alternate is shown with that repair. The skulls at left are juveniles.

Figure 2. Greererpeton reduced to a blueprint of body parts. Here there may be one extra phalanx on pedal digit 5 and one missing on pedal digit 2 compared to sister taxa. So an alternate is shown with that repair. The skulls at left are juveniles. Images are from the PhD thesis of Step;hen Godfrey 1986.

Greererpeton burkemorani (Romer 1969, Smithson 1982, Godfrey 1989; Early Carboniferous, 320 mya; 1.5 m in length). Godfrey thought it nested closer to Proterogyrinus than to Ichthyostega. Here Greererpeton nests as an offshoot of the temnospondyls along with Gerrothorax (Fig. 1).

The skull was flattened with orbits on top of the skull. The lacrimal does not contact the naris. The torso included some 41 presacral vertebrae. The ribs were robust and extended laterally. The pectoral girdle was robust. The limbs were small.

No complete pedes are known for Greererpeton, according to Godfrey 1989, but that may have changed since then. So I wonder if digit two had 3 phalanges, as in sister taxa, not 2. And I wonder if digit five had 3 phalanges, as in sister taxa, not 4 (Fig. 2) as illustrated in Godfrey 1989. I have not seen manus or pes data for Gerrothorax. If you have it, please send it.

Juveniles are known with larger orbits not so dorsally oriented, but otherwise similar (Fig. 2), but note the squamosal divides the postorbital and supratemporal in the adult, making one wonder if the difference is indeed ontogenetic.

Figure 6. Subset of the large reptile tree focusing on basal tetrapods, updated with Gerrothorax.Figure 6. Subset of the large reptile tree focusing on basal tetrapods, updated with Gerrothorax.

Figure 6. Subset of the large reptile tree focusing on basal tetrapods, updated with Gerrothorax.

References
Godfrey SJ 1986. The skeletal anatomy of Greererpeton burkemorani Romer 1969, an Upper Mississippian temnospondyl amphibian. PhD thesis, McGill University, Montreal.
Godfrey SJ 1989. The postcranial skeletal anatomy of the Carboniferous tetrapod Greererpeton burkemorani Romer, 1969. Philosophical Transactions of The Royal Society B Biological Sciences 323(1213):75-133.
Jenkins FA Jr, Shubin NH, Gates SM and Warren A 2008. Gerrothorax pulcherrimus from the Upper Triassic Fleming Fjord Formation of East Greenland and a reassessment of head lifting in temnospondyl feeding. Journal of Vertebrate Paleontology. 28 (4): 935–950.
Nilsson T 1934. Vorläufige mitteilung über einen Stegocephalenfund aus dem Rhät Schonens. Geologiska Föreningens I Stockholm Förehandlingar 56:428-442.
Romer AS 1969. A temnospondylus labyrinthodont from the Lower Carboniferousw. Kirtlandia 6:1-20.
Smithson TR 1982. The cranial morphology of Greererpeton burkemorani Romer (Amphibia: Temnospondyli). Zoological Journal of the Linnean Society 76(1):29-90.

wiki/Greererpeton
wiki/Gerrothorax

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6 thoughts on “Odd Gerrothorax nests with Greererpeton

  1. Why don’t you read the comments on the last dozen posts? They’re relevant to this.

    The lacrimal contacted the naris.

    Read the Deltaherpeton paper to learn why nobody actually knows that.

  2. This is ridiculous. When. Are. You. Going. To. Stop. You know you’re not doing yourself any favours, right?

    And – as usual – I have to wonder if you do more than glance at the papers you cite. Example: you say that Jenkins et al. don’t show the mandible being depressed and instead show the cranium being elevated, as if this is odd on their part. But if you read their paper you’d see why they say this – they explain it and figure the relevant details in considerable detail.

    • Rule of thumb: if you’re second-guessing Farish Jenkins, you’d better have a really good reason for it. Because you’re probably wrong.

      • Witzmann et al. (2013) did actually argue at very great length that there was some mandible depression and less skull elevation than Jenkins et al. (2008) reconstructed.

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