Hongshanxi: just barely NOT a squamate

Updated July 7, 2020
the LRT moves Meyasaurus, Indrasaurus and Hoyalacerta to the base of the Yabeinosaurus + Sakurasaurus clade within the Scleroglossa and Squamata.

Dong, Wang, Mou, Zhang and Evans 2019 bring us
Hongshanxi xidi, a tiny, new and rare, complete, articulated and flattened Oxfordian (earliest late) Jurassic lepidosaur the authors had difficulty nesting with both traits and molecules.

In happy contrast,
the large reptile tree (LRT 1578 taxa) recovers Hongshanxi as the proximal outgroup to the clade Squamata, between Liushusaurus (Evans and Wang 2010) Early Cretaceous, ~10 cm) and IguanaEuposaurus cirinensis (Lortet 1892, MHNL 15681, Late Jurassic, Kimmeridgian, 155 mya, 3.5cm snout vent length) without firsthand observations.

Figure 1. Hongshanxi in situ with DGS colors added to pectoral region.

Figure 1. Hongshanxi in situ with DGS colors added to pectoral region.

From the abstract
It [Hongshanxi] is distinguished from other Jurassic-Cretaceous lizards by a unique combination of derived characters, notably a long frontal with posterior processes that clasp the short parietal; cranial osteoderms limited to the lower temporal and supraocular regions; and an elongated manus and pes. Phylogenetic analysis using morphological data alone places the new taxon on the stem of a traditional ‘Scleroglossa’, but when the same data is run with a backbone constraint tree based on molecular data, the new taxon is placed on the stem of Squamata as a whole. Thus its position, and that of other Jurassic and Early Cretaceous taxa, seem to be influenced primarily by the position of Gekkota.”

Figure 2. Hongshanxi skull with DGS colors added.

Figure 2. Hongshanxi skull with DGS colors added.

Unfortunately
Dong et al. were using an outdated and incomplete taxon list, that of Gauthier 2012 (610 characters, 192 taxa) with maybe a dozen additional Early Cretaceous taxa described since then. The authors report, “However, as with many other Jurassic and early Cretaceous taxa (e.g. Scandensia, Yabeinosaurus, Hoyalacerta, Liushusaurus), the phylogenetic position of Hongshanxi n. gen. cannot be clearly resolved.”

That may be because the authors do not understand that a series of lepidosaurs preceded the Squamata. These predecessors include the pterosaur clade, Tritosauria. In the LRT the Lepidosauria is completely resolved with high Bootstrap values at nearly all nodes with the addition of Hongshanxi, which looks quite a lot like its nearly coeval sister taxa and is similar in size and location.

Figure 3. Hongshanxi pelvic region in situ with DGS colors added

Figure 3. Hongshanxi pelvic region in situ with DGS colors added

The authors also do not realize
they cannot rely on molecular studies to clarify relationships in deep time. The solution to these problems is online, the LRT, ready for anyone to use. If workers want to continue ‘spinning their wheels’ recovering no clear solutions, that’s to the detriment of our science.

Oddly
the hands and feet of Hongshanxi are elongate, like their arboreal sisters, but the penultimate phalanges are shorter than the more proximal phalanges, distinct from their arboreal sisters. The torso is short relative to the femur length. The authors correctly note the very odd lack of a straight frontal-parietal suture. Also very odd is the open acetabulum (hip joint), which was overlooked by the authors.


References
Dong L, Wang Y, Mou L, Zhang G and Evans SW 2019. A new Jurassic lizard from China in Steyer J.-S., Augé M. L. & Métais G. (eds), Memorial Jean-Claude Rage: A life of paleo-herpetologist. Geodiversitas 41 (16): 623-641. https://doi.org/10.5252/geodiversitas2019v41a16.

http://geodiversitas.com/41/16

 

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