Giant Mesozoic flat heads: Siderops and Koolasuchus

Little Gerrothorax has a new giant sister, Siderops,
(Fig. 1) in the large reptile tree (LRT, 1440 taxa). This is a traditional nesting recovered by prior workers.

We’re still missing those poorly ossified fingers and toes.
Or did this clade have lobefins (Fig. 2)? Nothing past the wrist is known for any clade members (that I’ve seen). Could go either way with available data… so, don’t assume fingers and toes.

Figure 1. Siderops in several views from Warren and Hutchinson 1983, colors added. The related giant Koolasuchus and small Gerrothorax are added for scale.

Figure 1. Siderops in several views from Warren and Hutchinson 1983, colors added. The related giant Koolasuchus and small Gerrothorax are added for scale. Are these lobefins or did they have feet? And look at the size of those palatal fangs!

Speaking of clades,
both Siderops and Gerrothorax are traditionally considered temnospondyls, which all have fingers and toes. Here they nest prior to traditional temnospondyls, closer to flathead lobefin tetrapods, like Tiktaalik, in the LRT (subset Fig. 2).

Figure 1. Subset of the LRT focusing on basal tetrapods and showing those taxa with lobefins (fins) and those with fingers and toes (feet). Inbetween we have no data.

Figure 2. Subset of the LRT focusing on basal tetrapods and showing those taxa with lobefins (fins) and those with fingers and toes (feet). Inbetween we have no data.

Siderops kehli (Warren and Hutchinson 1983; Early Jurassic, 180mya; skull 50cm long, overall 2.5m long) was traditionally considered a chigutisaurid temnospondyl or a brachyopoid. Here Siderops nests with the much smalller Gerrothorax. No branchials and scales were reported. The back of the skull and the extremities are unknown, so modifications were made to reflect that lack of data here.

Koolasuchus cleelandi was a late surviving Early Cretaceous giant from this clade, presently known from just a few bones, like the mandible (Fig. 2).

Tomorrow we’ll take a look
at several giant ‘amphibians’ (= anamniote tetrapods) all to scale.


References
Warren A and Hutchinson M 1983. The last labyrinthodont? A new brachyopoid (Amphibia, Temnospondyli) from the Early Jurassic Evergreen Formation of Queensland, Australia. Philosophical Transactions of The Royal Society B Biological SciencesB 303:1–62.

wiki/Gerrothorax
wiki/Siderops

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