The Early Permian Ascendonanus assemblage

There are five specimens from the same pit
that were assigned to the varanid taxon Ascendonanus. Spindler et al. 2018 thought they were all conspecific.

Given their distinct proportions
(Fig. 1) and the phylogenetic differences recovered in 2 of the 5 so far (earlier one nested as a basal iguanid), we’re going to need some new generic names for at least one of the referred specimens. The others have not yet been tested in the large reptile tree (LRT, 1179 taxa).

The holotype
remains Ascendonanus, but here it’s no longer a varanopid synapsid. Here it nests as a derived prodiapsid and the basalmost tested diapsid (Fig. 2), a little younger than the oldest diapsid, Petrolacosaurus.

Figure 1. The five specimens from the Ascendonanus quarry, all to the same scale. Most images from Spindler et al. 2018. Some have skulls 3x the occiput/acetabulum length. Others as much as 5x, the first hint that these taxa are no conspecific.

Figure 1. The five specimens from the Ascendonanus quarry, all to the same scale, counter plate flipped in every specimen. Most images from Spindler et al. 2018. Some have skulls 3x the occiput/acetabulum length. Others as much as 5x, the first hint that these taxa are no conspecific.

Some of these specimens
(Fig. 1) have an occiput/acetabulum length distinct from the others, ranging from 3x to 5x the skull length, the first clue to their distinct morphologies.

Figure 2. The Prodiapsida now include the holotypes of Ascendonanus and Anningia.

Figure 2. The Prodiapsida now include the holotypes of Ascendonanus and Anningia. Remember, the Diapsida does not include any Lepidosauriforms, which nest elsewhere.

Spindler et al. 2018
did not include several taxa typically included in pelycosaur studies and should not have included any caseasaurs, despite their traditional inclusion. Spindler et al. did not include any diapsids nor did they understand the role of the former varanopids now nesting as ancestors to the Diapsida (sans Lepidosauriformes).

Figure 3. Cladogram from Spindler et al. 2018. Colors refer to clades in the LRT.

Figure 3. Cladogram from Spindler et al. 2018. Colors refer to clades in the LRT.

The holotype 0924 specimen has more of a varanopid skull
than the 1045 specimen we looked at earlier. Prodiapsid sisters include varanopids ancestral to synapsids. Prodiapsids, as their name suggests, are late-surviving ancestors to diapsids like the coeval Araeoscelis (Early Permian) and the earlier Spinoaequalis (Late Carboniferous).

Figure 3. The Ascendonanus holotype skull as originally traced and as traced here.

Figure 3. The Ascendonanus holotype skull as originally traced and as traced here. Whether an upper temporal fenestra was present (as shown in the color tracing), or not (as shown in the drawings, makes no difference as this taxon nests at the transition. 

Not sure yet
where the other three specimens assigned to Ascendonanus nest. Enough muck stirred for the moment.

References
Rößler R, Zierold T, Feng Z, Kretzschmar R, Merbitz M, Annacker V and Schneider JW 2012. A snapshot of an early Permian ecosystem preserved by explosive volcanism:
New results from the Chemnitz Petrified Forest, Germany. PALAIOS, 2012, v. 27, p. 814–834.
Spindler F, Werneburg R, Schneider JW, Luthardt L, Annacker V and Räler R 2018. First arboreal ‘pelycosaurs’ (Synapsida: Varanopidae) from the early Permian Chemnitz Fossil Lagerstätte, SE Germany, with a review of varanopid phylogeny. DOI: https://doi.org/10.1007/s12542-018-0405-9

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