Joermungandr bolti from the Mazon Creek enters the LRT

Recovered in exquisite detail by splitting a small, round, brown nodule,
tiny Joermungandr bolti (Fig. 1) was recently described by Mann, Calthorpe and Maddin 2021.

Figure 1. Joermungandr bolti from Mann, Calthorpe and Maddin 2021 shown about 2x life size on a 72 dpi monitor. Their diagram matched to their fossil photo and colors around the pectoral area added.
Figure 2. Joermungandr skull in situ and as traced by the authors (above). Colors added here (below). Many differences. Note: The skull is exposed in ventral view, the mandible in dorsal view, just the opposite of what we are used to seeing, but this is what happens when you split a nodule.

The authors did not describe
the skull (Fig. 2) precisely. Nor did they include pertinent sister taxa, like Kirktonecta in their analysis. As a result their cladogram was unable to correctly nest their new discovery. The large reptile tree (LRT, 1890+ taxa) nested tiny Joermungandr correctly and with complete resolution. Rather than assuming expertise, sometimes its better to pretend you don’t know what a taxon is in order to expand your taxon list to minimize the possibility of taxon exclusion. Omitting taxa results in phylogenetic chaos.

From the abstract:
“Here, we describe a new long-bodied recumbirostran, Joermungandr bolti gen. et sp. nov., known from a single part and counterpart concretion bearing a virtually complete skeleton. Uniquely, Joermungandr preserves a full suite of dorsal, flank and ventral dermal scales, together with a series of thinned and reduced gastralia. Investigation of these scales using scanning electron microscopy reveals ultrastructural ridge and pit morphologies, revealing complexities comparable to the scale ultrastructure of extant snakes and fossorial reptiles, which have scales modified for body-based propulsion and shedding substrate. Our new taxon also represents an important early record of an elongate recumbirostran bauplan, wherein several features linked to fossoriality, including a characteristic recumbent snout, are present.

Wikipedia reports, Not all phylogenetic analyses recognize Recumbirostra as a valid grouping.” Worse yet, Kirktonecta is not listed among the Recumbirostra. Worse yet, Joermungandr does not have a recumbi rostrum. If the authors were counting on a certain kind of snout on an elongate taxon, they were “Pulling a Larry Martin” to reduce the number of taxa competing to be sister taxa. Don’t do that.

We used parsimony phylogenetic methods to conduct phylogenetic analysis using the most recent recumbirostran-focused matrix.

The authors borrowed a cladogram. Don’t do that. Use your own.

“The analysis recovers Joermungandr within Recumbirostra with likely affinities to the sister clades Molgophidae and Brachystelechidae.

The published cladogram (their figure 5) has Synapsida and Eureptilia for outgroup taxa. According to the LRT, those are unrelated to Microsauria. According to the LRT, the authors needed more basal tetrapod outgroup taxa, omitted from the authors’ cladoram.

Figure 4. Subset of the LRT focusing on Microsauria and the nesting of Joermungandr with Kirktonecta and Asaphestera platyris.

From the abstract:
“Finally, we review integumentary patterns in Recumbirostra, noting reductions and losses of gastralia and osteoderms associated with body elongation and, thus, probably also associated with increased fossoriality.”

That’s nice, but without a valid phylogenetic context, such studies end up a waste of time. Microsaurs are not reptiles (= amniotes; see publicity title below). Microsaurs are basal tetrapods, not far from Reptilomorpha. The only living microsaurs are caecilians, burrowing, heavily scaled and limbless.

Mann A, Calthorpe AS and Maddin HC 2021. Joermungandr bolti, an exceptionally preserved ‘microsaur’ from the Mazon Creek Lagerstätte reveals patterns of integumentary evolution in Recumbirostra. Royal Society Open Science 8(7):

LiveScience: Tiny ancient reptile named after Thor’s world-ending nemesis

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