Traditionally considered a short-snouted pliosaur,
due to its rosette anterior dentary, Simolestes borax (Lydekker 1877; Mid-Late Jurassic; BMNH R 3319; Fig. 1) nests in the large reptile tree (LRT, 1435 taxa; subset Fig. 2) with the elasmosaurs, Albertonectes and Libonectes.
Figure 1. Simolestes in several views and colorized using DGS methods compared to the elasmosaur, Libonectes.
I have looked for,
but not seen any post-crania for Simolestes, despite reports that post-crania exists. And I’m willing to let the data decide.
Given that the two elasmosaur skulls are the same size
(Fig. 1) lends weight to the hypothesis that Simolestes is an elasmosaur, not a pliosaur. Distinct from Libonectes, Simolestes has a single upper and lower fang, like a dog, with smaller teeth elsewhere.
Figure 2. Subset of the LRT focusing on Eusauropterygians (pachypleurosaurs, nothosaurs, plesiosaurs and kin).
And another eusauropterygian,
Peloneustes (Fig. 3) also enters the LRT, nesting, with no surprise, close to Dolichorhynchops.
Figure 3. Peloneustes fossil on display.
References
Godefroit P 1994. Simolestes keileni sp. nov., un Pliosaure (Plesiosauria, Reptilia) du Bajocien supérieur de Lorraine (France). Bulletin des Académie et Société Lorraines des sciences, ISSN 0567-6576, 1994, tome 33, n°2, p. 77-95. 33. .
Lydekker R 1877. Notices of new and other Vertebrata from Indian Tertiary and Secondary rocks. Records of the Geological Survey of India 10(1):30-43
The Pterosaur Heresies 