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).

Figure 1. Saniwa nests with varanids in the large reptile tree.

Figure 1. Saniwa nests with varanids in the large reptile tree.

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.

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