Acostasaurus pavachoquensis (Gómez Pérez and Noé 2017; Early Cretaceous; estimated 4m long) was originally considered a pliosaur, but here nests with Anningasaura. Both share a relatively short snout and a long canine. The sclerotic ring is not often preserved in sauropterygians.

Anningasaura lymense A recent paper by Vincent and Benson (2012) redescribed a plesiosaur specimen NHMUK OR 49202 from the Lias. Considered a juvenile with a skull 34 cm long, this specimen was originally (Lydekker 1889) named Plesiosaurus macrocephalus, but it is taxonomically distinct in several regards.

Vincent and Benson (2012) reported, “In general morphology, NHMUK OR49202 does not resemble any known plesiosaurian taxon.” Anningasaura represents a completely ‘new’ branch of the plesiosauria in which the orbits virtually cannot be seen in dorsal view and the jugals bend down posteriorly to produce an angled temporal arch. Moreover the premaxilla was thought to not contact the frontals and the nasals were absent. Earlier Benson (2012) created a phylogenetic analysis that nested Anningsasaura at the base of the pliosaur/plesiosaur split with Bobosaurus as the outgroup.

The large reptile tree recovers pretty much the same nesting, but nested Anningsaura with Hauffiosaurus (below) despite so few traits cabable of being scored in common,between Simosaurus and Pistosaurus, just off the taxon list of Benson et al. (2012). However, the large reptile tree does not include Bobosaurus (Dalla Vecchia 2006), a pistosaurid taxon without a known skull.

Vincent and Benson (2012) thought the palatal elements did not contact one another and the nasals were not identified.

Hauffiosaurus zanoni (O'Keefe 2001; Vincent 2011; Early Jurassic; 3.4m long; uncatalogued Hauff museum) is another plesiosaur that "does not resemble any known plesiosaurian taxon," according to Vincent 2011. This genus was considered a pliosauroid, but it nests between Anningsaura and Pistosaurus.

Benson RBJ, Evans M, Druckenmiller PS 2012. Lalueza-Fox, Carles. ed. ”High Diversity, Low Disparity and Small Body Size in Plesiosaurs (Reptilia, Sauropterygia) from the Triassic–Jurassic Boundary”. PLoS ONE 7 (3): e31838. doi:10.1371/journal.pone.0031838

Dalla Vecchia FM 2006. A new sauropterygian reptile with plesiosaurian affinity from the Late Triassic of Italy. Rivista Italiana di Paleontologia e Stratigrafia 112 (2): 207–225.

Gómez Pérez M and Noè LF 2017. Cranial anatomy of a new pliosaurid Acostasaurus pavachoquensis from the Lower Cretaceous of Colombia, South America. Palaeontographica Abteilung A. 310 (1–2): 5–42. doi:10.1127/pala/2017/0068.

O'Keefe RF 2001. A cladistic analysis and taxonomic revision of the Plesiosauria (Reptilia: Sauropterygia). Acta Zoologica Fennica 213:1–63.

Vincent P 2011. A re-examination of Hauffiosaurus zanoni, a pliosauroid from the Toarcian (Early Jurassic) of Germany. Journal of Vertebrate Paleontology 31(2): 340–351.

Vincent P and Benson RBJ 2012. Anningasaura, a basal plesiosaurian (Reptilia, Plesiosauria) from the Lower Jurassic of Lyme Regis, United Kingdom, Journal of Vertebrate Paleontology, 32:5, 1049-1063.

wiki/Anningasaura
wiki/Hauffiosaurus
wiki/Acostasaurus