Basal tetrapod relationships: LRT vs Huttenlocker et al. 2013

A large gamut phylogenetic analysis,
like the large reptile tree (LRT, 1036 taxa, subset Fig. 2) should be able to find problems with smaller, more focused studies (Fig. 1) simply by virtue of its larger gamut. That one factor minimizes taxon exclusion issues, one of the biggest problems facing today’s vertebrate cladists. To that end, today we’ll take a look at the cladogram of Huttenlocker et al. 2013 (Fig. 1), which focuses on basal tetrapod (pre-reptile and microsaur) relationships.

Figure 1. Basal tetrapod cladogram in Huttenlocker et al. 2013. Color added here. Light green are taxa that nest within lepospondyli in the LRT.

Figure 1. Basal tetrapod cladogram in Huttenlocker et al. 2013. This looks like a lot of taxa, but it is not. Color added here. Light green are taxa that nest within lepospondyli in the LRT. Taxa not colored, except for Acanthostega, are not tested in the LRT. Note how many taxa are missing here compared to the LRT. That gives the false impression that lepospondyls arose from Eryops and Greererpeton, which are unrelated basal taxa in the LRT. Limnoscelis nests deep within the Reptilia, so should not even be included here.

Not every taxon tested by Huttenlocker et al.
(Fig. 1) appears in the LRT (Fig. 2). And vice versa. The light green areas are all in one clade, the Lepospondyli, on the LRT. Note they form a large majority of taxa in the Huttenlocker et al. cladogram. That some nest with basalmost tetrapods and temnospondyls appears to be yet another case of taxon exclusion by Huttenlocker. Nearly all the taxa are lepospondyls with just two clades, Eryops and the Reptilomorpha, breaking them up. Had they added more Eryops kin and more Reptilomorpha, plus some missing basal lepospondyls, like Utegenia (widely considered another reptilomorh/seymouriamorph), and some even more basal sarcopterygian/ basal tetrapods, as they appear in the LRT, perhaps the tree topologies would start to look more alike.

FIgure 2. Subset of the LRT has a larger gamut of taxa. Here lepospondyls nest together when more basal tetrapods are added to the taxon list than are present in figure 1.

FIgure 2. Subset of the LRT has a larger gamut of taxa. Here lepospondyls nest together when more basal tetrapods are added to the taxon list than are present in figure 1. Lavender taxa are ‘Recumbirostro” in the Huttenlocker et al. tree, but are microsaurs here. Limnoscelis nests deeper within the Reptilia.

The purple taxa in both figures
represent members of the clade Recumbirostra, which appears to be a junior synonym of Microsauria, which includes the extant clade Caeciliidae.

References
Huttenlocker AK, Small BJ, Pardo JD and Anderson JS 2013. Cranial morphology of recumbirostrans (Lepospondyli) from the Permian of Kansas and Nebraska, and early morphological evolution inferred by micro-computed tomography. Journal of Vertebrate Paleontology 33:540–552.

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