Ascendonanus nestleri: an early Permian iguanid, not a varanopid.

Please see:
https://pterosaurheresies.wordpress.com/2018/03/20/the-early-permian-ascendonanus-assemblage/ Which shows that of the five specimens assigned to Ascendonanus at least two are widely divergent. The other three have not yet been tested. One is an iguanid. Another is a basalmost diapsid.

Just out today by Spindler et al. 2018, but previewed earlier
“A new fossil amniote from the Fossil Forest of Chemnitz (Sakmarian-Artinskian transition, Germany) is described as Ascendonanus nestleri gen. et sp. nov., based on five articulated skeletons with integumentary preservation. The slender animals exhibit a generalistic, lizard-like morphology. However, their synapsid temporal fenestration, ventrally ridged centra and enlarged iliac blades indicate a pelycosaur-grade affiliation. Using a renewed data set for certain early amniotes with a similar typology found Ascendonanus to be a basal varanopid synapsid. This is the first evidence of a varanopid from Saxony and the third from Central Europe, as well as the smallest varanopid at all. Its greatly elongated trunk, enlarged autopodia and strongly curved unguals, along with taphonomical observations, imply an arboreal lifestyle in a dense forest habitat until the whole ecosystem was buried under volcanic deposits. Ascendonanus greatly increases the knowledge on rare basal varanopids; it also reveals a so far unexpected ecotype of early synapsids. Its integumentary structures present the first detailed and soft tissue skin preservation of any Paleozoic synapsid.”

Except
Ascendonanus is not a varanopid synapsid. It’s an arboreal lepidosaur, an iguanid squamate in the large reptile tree (LRT, 1176 taxa, subset Fig. 3) with a typical skull, skin, size and niche typical for this clade. Only the torso has more vertebrae than is typical, but the related Liushusaurus also has more than 25 presacral vertebrae.

The Early Permian
is not where we expect to see lizards. No others are known from this period. Perhaps that is why Spindler et al. 2018 chose to restrict their taxon list to synapsids and their outgroups…and to ignore those upper temporal fenestrae, so plainly visible (Fig. 1). And note those slender, vertical epipterygoids. You don’t see those on synapsids.

Figure 1. The skull of Ascendonanus has a diapsid temporal configuration with clearly visible upper temporal fenestra and a typical iguanid skull morphology.

Figure 1. The skull of Ascendonanus has a diapsid temporal configuration with clearly visible upper temporal fenestra and a typical iguanid skull morphology. Note manual digit 5 preserved beneath the palm of the hand and restored to a lateral position. Not also the two jugal ascending processes, due to the split leaving medial and lateral halves of this bone. Note the two slender epipterygoids inside the temporal openings. Only squamates have such bones.

Ascendonanus nestleri (Spindler 2017, TA1045) is a German iguanid squamate found in vulcanized early Permian (291mya) sediments. It is the oldest lepidosaur known and based on its phylogeny, suggests an earlier radiation of lepidosaurs that earlier presumed. Other early lepidosauriformes include Paliguana and Lacertulus from the Late Permian. Other basal iguanids and pre-iguanids, like Scandensia, Calanguban, Euposaurus and Liushusaurus are late-survivors in the Late Jurassic and Early Cretaceous. Iguana is a late-survivor of an early radiation living today.

Ascendonanus was originally described
as a tree-climbing varanopid synapsid by Spindler et al. (2018), but no lepidosauriformes were tested. The bones are difficult to see through the scaly skin (Fig. 1). Upper temporal fenestra and other lepidosaur traits were overlooked, perhaps because lizards are otherwise unknown from the Early Permian. No other basal synapsids were arboreal, but some Iguana species are also arboreal. No other varanopids are quite as small, but other iguanids are smaller.

By the way, like more paleo workers
Spindler et al. 2018 were unaware of the synapsid/prodiapsid split that removes many former varanopids from the clade Synapsida, despite their having typical synapsid temporal fenestration. One more reason NOT to label taxa based on traits, but to only label taxa after a wide gamut cladistic analysis, like the LRT.

Thus
we no longer call Ascendonanus a diapsid based on its diapsid temporal configuration. True diapsids, like Eudibamus and Petrolacosaurus, all nest within the Archosauromorpha. By convergence, all members of the clade Lepidosauriformes, including Ascendonanus, all have a diapsid temporal configuration or a modification based on that.

Figure 1. Ascendonanus nestler is an Early Permian lepidosaur nesting with Saniwa, a member of the Varanoidea.

Figure 2. Ascendonanus nestler is an Early Permian iguanid squamate lepidosaur, not a varanopid synapsid.

Sorry to say it,
taxon exclusion is once again the problem here. Spindler et al. 2018 were also following tradition when they included caseids and eothyrids in they analysis of synapsids. The Caseasauria nest elsewhere when given the opportunity to do so.

Figure 3. Ascendonanus cladogram, subset of the LRT. Here Ascendonanus nests with iguanids, not varanopids.

Figure 3. Ascendonanus cladogram, subset of the LRT. Here Ascendonanus nests with iguanids, not varanopids.

Figure 5. Ascendonanus pes.

Figure 5. Ascendonanus pes.

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

2 thoughts on “Ascendonanus nestleri: an early Permian iguanid, not a varanopid.

  1. those upper temporal fenestrae, so plainly visible (Fig. 1)

    “Plainly visible”!?! Hardly anything is plainly visible on that mostly blurry photo (fig. 6a of the paper). It’s so blurry because the skull is 3D enough that not all of it can be focused on at the same time.

    However, when I look at it for a bit longer, I think I can see what you think are upper temporal fenestrae. Judging from their sharp edges and weird angles, I’m pretty sure they’re damage: bone has broken off there and now resides on the counter”slab”, i.e. the concretion that surrounded the fossil.

    That’s why the figure is labeled “Interior aspect of the skull table”: we’re looking at the inner half of the skull-roof bones, while the outer half is on a different piece of rock. The concretion has split through the bone as usual.

    An Early Permian iguanid, or any Early Permian lepidosaur at all, would be major news; so far, the earliest known lepidosaurs are Middle Triassic, and the earliest known iguanians are Late Cretaceous in age. But I see no reason to think we’re looking at a lepidosaur here.

    And note those slender, vertical epipterygoids.

    Any epipterygoids this specimen may have are buried deep within it, under the skull-roof bones whose inner halves we can see. The inner half of the postorbital got a little broken, that’s all.

  2. Interesting hypotheses, overcome by a suite of other traits that also nest this taxon in iguanids. In crushed specimens like this you see everything. I agree that the split shows different aspects of the skull. Re: origin of lepidosaurs we have Lacertulus in the Late Permian, lepidosauriformes like Palaegama in the Late Permian and Tridentinosaurus in the Early Permian.

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