The counterplate of bipedal Magnuviator

We first looked at the Late Cretaceous lizard,
Magnuviator (Figs. 1–3; MOR 6627 (Museum of the Rockies), back in 2017. Recently I discovered the SuppData, which presents the counterplate. Combining the two creates a better reconstruction, one that can be scored a little more accurately. Add these corrections to the many, many others made over the past decade as new data makes itself known.

Figure 1. Fossil images from DeMar et al. 2017. In vivo image from Druell et al. 2019. Colors and reconstruction added here.

After adding the counterplate data,
so few scores changed that Magnuviator stayed where it was originally nested. That should come as no surprise. Many taxa in the LRT are correctly nested based on incomplete data because there is no such thing as ‘modular (mosaic) evolution.’

Figure 2. Although the fossil is bent into an egg-shape typical embryos have the neck bent at one end, the hips at the other. This is not an embryo specimen. Shown 1.5x actual size.

Magnuviator was found on the famous Egg Mountain
of Montana where Maiasaura laid its eggs. Estimated at 21.5cm snout-vent length, the addition of an Acanthodactylus-like tail would at least have doubled this. Given its similar morphology (Fig. 1) perhaps Magnuviator was also facultatively bipedal, running in an among the hadrosaur mothers and hatchlings.

Figure 3. Almost full scale, Magnuviator reconstructed. Apparently three sacrals were present. The pubis was elongated. The ilium had a tiny anterior process. A reconstruction, like this one, doesn’t have to be pretty. It should accurately lay out the elements for measurement and scoring.

Originally Magnuviator
(DeMar et al. 2017; Late Cretaceous) nested with another Late Cretaceous squamate, Saichangurvel (Fig. 4), as it does here, and with Acanthodactylus, a small extant lizard capable of bipedal locomotion (Fig. 1). So, no phylogenetic changes from then to now.

Figure 4. Saichangurvel in situ, a complete squamate originally considered a member of Iguania, but here nesting with Acanthodactylus. Shown here a little larger than full scale.

References
DeMar Jr DG, Conrad JL, Head JJ, Varricchio DJ and Wilson GP 2017. A new Late Cretaceous iguanomorph from North America and the origin of New World Pleurodonta (Squamata, Iguania). Proc. R. Soc. B 284: 20161902.
Druelle F, Goyens J, Vasilopolou-Kampitsi M and Aerts P 2019. Compliant legs enable lizards to maintain high running speeds on complex terrains. Journal of Experimental Biology 222(6): jeb195511.

Magnuviator, another basal scleroglossan.

Saichangurvel: not an iguanid, but very close…