Exquisite Saniwa skeleton from Green River formation

Nothing controversial today…

An extraordinarily wonderful lizard skeleton
of Saniwa ensidens from the Green River Formation (Miocene, 48mya, 1.3m length, Leidy 1870, Rieppel and Grande 2007, FMNH PR 2378, Fig. 1) is today’s subject.

Figure 1. Saniwa ensidens FMNH PR 2378 with bones colorized.

Figure 1. Saniwa ensidens FMNH PR 2378 with bones colorized. This is a remarkable fossil preserving soft tissue such as a trachea, scales and cartilaginous scapular dorsal extensions.

Saniwa is a basal varanid,
not far from the Varanus/Tylosasaurus split. It was a late survivor of a Permian radiation and was the first fossil lizard described for North America, The tail was twice as long as the rest of the body. Like the mosasaurs, Saniwa had pterygoid teeth (convergent with those in pre-snakes and snakes).

Several specimens are known.
None compete with this one, a possible juvenile, for utter perfection in fossil preservation.

References
Rieppel O and Grande L 2007. The anatomy of the fossil varanid lizard Saniwa ensidens Leidy, 1870, based on a newly discovered complete skeleton. Journal of Palaeontology 81 (4): 643–665. doi:10.1666/pleo0022-
Conrad J, Rieppel O, Grande L 2008. Re-assessment of varanid evolution based on new data from Saniwa ensidens Leidy, 1870 (Squamata, Reptilia). American Museum Novitates 3630: 1–15. doi:10.1206/596.1.
Leidy J 1870. (Descriptions of Emys jeansesi, E. haydeni, Baëna arenosa, and Saniwa ensidens). Proceedings of the Academy of Natural Sciences of Philadelphia 1870: 123–124.

Sakurasaurus – a basal varanid not far from other major clades

Sakurasaurus sp. (SBEI 199, Evans and Manabe 2008, Early Cretaceous, Japan) is represented by a single completely disarticulated specimen considered a sister to its contemporary, Yabeinosaurus. The holotype (Evans and Manabe 1999) was considered a possible scincomorph (family of skinks) based on jaw material.

Evans and Manabe 2008 nested SBEI 199 with Yabeinosaurus, Ardeosaurus, Scandensia and all other squamates in order of increasing distance. The large reptile tree changes that slightly, nesting Sakurasaurus with Yabeinosaurus at the base of the varanids and the varanids are sister to Tchingisaurus and the geckos + Ardeosaurus at the base of the clade of snakes and their kin. Scandensia nests as the most basal squamate. The differences in the two tree topologies can be largely ascribed largely to taxon exclusion in the Evans and Manabe 2008 tree.

The reconstruction by Evans and Manabe (2008) was done freehand (Fig. 1). The reconstruction offered here was done by copying and pasting disarticulated skull elements from Evans and Manabe into their in vivo positions (Fig. 1) using the second half of the DGS method. It might be better if more paleontologists tried this method, but freehand yielded similar results.

Figure 1. Sakurasaurus as originally reconstructed freehand (on the left) and as reconstructed using DGS methods of copying and pasting disarticulated elements into their in vivo positions. Click to enlarge.

Figure 1. Sakurasaurus as originally reconstructed freehand (on the left) and as reconstructed using DGS methods of copying and pasting disarticulated elements into their in vivo positions. Click to enlarge. Here the former coronoid is reidentified as a pterygoid. The postfrontal/postorbital is only a postfrontal. The teeth are not so sharp.The quadrate has a different shape.  Note the maxillary palatal process, which becomes expanded in varanids.

 

References
Evans SE and Manabe M 1999. Early Cretaceous lizards from the Okurodani Formation of Japan. Geobios, 32, 889–899.
Evans SE and Manabe M 2008. The Early Cretaceous lizards of eastern Asia: New material of Sakurasaurusa from Japan. Special Papers in Palaeontology 81:43-59.

 

Assembling the Squamate Tree of Life – part 2 – Tchingisaurus

Updated February 22, 2015 with a new image of Tchingisaurus.

Earlier the squamate tree of life by Gauthier et al. (2012) was introduced. In large part this tree resembled the large reptile tree of reptileevolution.com. Parts of the trees were different from each other. We’ll look at some of those today and later.

Figure 1. Click to enlarge. Tchingisaurus, a basal Gekkotan, according to the large reptile tree.

Figure 1. Click to enlarge. Tchingisaurus, a basal Gekkotan, according to the large reptile tree.

Tchingisaurus
The nesting of Tchingisaurus (Fig. 1) at the base of a basal scleroglossan clade that included Gilmoreteius (Macrocephalosaurus) is one such difference.  Previously I had not looked at Tchingisaurus, a Cretaceous specimen known from a partial skull preserved in 3D. The Gilmoreteius clade in the Gauthier et al. (2012) paper was nested close to the base of the clade that produced Adriosaurus and mosasaurs and also close to the clade that produced Eichstattisaurus and Gekkotans.

In the large reptile tree Tchingisaurus nested as a sister to Gekko (note the shared lack of any temporal bars), also near the base of the Scleroglossa. Eichstattisaurus nested closer to Ardeosaurus and Adriosaurus. So there was a comparative switch-off between the two clades with Tchingisaurus and Eichstattisaurus nearly trading places. The large reptile tree nested the mosasaurs closer to their traditional sisters, the varanids and snakes, not the gekkotans.

Excluded Taxa
Missing from the base of the Gauthier et al. (2012) tree were the basal scleroglossans Liushusaurus and Eolacerta. Also missing were the basal squamates the Daohugo lizard, Lacertulus, Meyasaurus, Tijubina, Homoeosaurus and Dalinghosaurus. Are these exclusions the cause of the differences in the two trees? And I’m not even including the third squmate clade, the Tritosauria, which we have covered earlier and I’ll touch on again later.

The Iguania
Only three taxa were recovered in the Iguania in the large reptile tree. I wasn’t so interested in their relationships, which I considered relatively uncontroversial, but the larger study by Gauthier et al. (2012) had little resolution at the base of the Iguania. So, maybe this clade is more mysterious and interesting than I first imagined. Or perhaps the Iguania needed to be anchored with the above named saurians.

We’ll take another look at the origin of the snakes and amphisbaenians in the next few days, noting the differences between the results recovered in the large reptile tree vs. the much larger study by Gauthier et al. (2012).

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Gauthier, JA, Kearney M, Maisano JA, Rieppel O and Behkke ADB 2012. Assembling the Squamate Tree of Life: Perspectives from the Phenotype and the Fossil Record. Bulletin of the Peabody Museum of Natural History 53(1):3-308. online here.