Libonectes morgani, (Welles 1949, Elasmosaurus morgani, Carpenter 1997) an elasmosaur of the Turonian, early Late Cretaceous. Distinct from Plesiosaurus (above), the suborbital fenestra was not present, the interpterygoid space was enlarged. The vomers were narrower and the palatal contribution of the maxillae were larger. The ectopterygoids were larger and the pterygoids were narrower. The orbit was further forward, enlarging the temporal area.

The family tree of the Enaliosauria is here. The complete reptile family tree is here.

Albertonectes vanderveldei (Kubo et al. 2012) TMP 2007.022.0002 is a virtually complete elasmosaur 11.2m in length (the longest of any elasmosaur) lacking only the skull. It had a 7m neck of 76 vertebrae, the most of any vertebrate. Upper Campanian, Alberta. Click to enlarge. Taxa in the lineage of elasmosaurids include the following (see below) to scale:

Simolestes vorax (Andrews 1909; Lydekker 1877, Tarlo 1960; Godefroit 1994; Mid-Late Jurassic; BMNH R 3319) was traditionally considered a pliosaur with a short snout. Here, based on skull traits only, Simolestes nests with the elasmosaur, Libonectes. Large canines are present and the other teeth are smaller than in Libonectes.

Styxosaurus snowii (Originally Cimoliasaurus snowii, Williston 1890, KUVP 1301; Welles 1943; Late Cretaceous, Campanian, 80mya; SDSMT 451) is another giant elasmosaurid with dog-like fangs related to Simolestes.

Hydrotherosaurus alexandre (Welle 1943; 7.8m; 33cm skull length) had one of the longest necks relative to body length with 60 vertebrae in total.

Andrews CW 1909. On some new Plesiosauria from the Oxford Clay of Peterborough. — Annals and Magazine of Natural History, London 4(8): 418–429.

Carpenter K 1999. Revision of North American elasmosaurs from the Cretaceous of the western interior. Paludicola, 2(2): 148-173.

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. .

Kubo T, Mitchell MT and Henderson DM 2012. Albertonectes vanderveldei, a new elasmosaur (Reptilia, Sauropterygia) from the Upper Cretaceous of Alberta. Journal of Vertebrate Paleontology 32 (3): 557-572. DOI:10.1080/02724634.2012.658124.

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

Owen R 1865. A monograph on the fossil Reptilia of the Liassic Formations. Part 3. Sauropterygia. Monograph of the Palaeontographical Society 17: 1-40

Storrs GW and Taylor MA 1996. Cranial anatomy of a new plesiosaur genus from the lowermost Lias (Rhaetian/Hettangian) of Street, Somerset, England. Jour. Vert. Paleo. 16:403-20.

Tarlo LB 1960. A review of the Upper Jurassic pliosaurs. — Bulletin of the British Museum (Natural History) Geology 4(5): 147–189.

Welles SP 1943. Elasmosaurid plesiosaurs with a description of the new material from California and Colorado. University of California Memoirs 13:125-254. figs.1-37., pls.12-29.

Welles SP 1949. A new elasmosaur from the Eagle Ford Shale of Texas. Fondren
Science Series, Southern Methodist University 1: 1-28.

Williston SW 1890a. Structure of the Plesiosaurian Skull. Science. 16 (405): 262.

Williston SW 1890b. A New Plesiosaur from the Niobrara Cretaceous of Kansas. Transactions of the Annual Meetings of the Kansas Academy of Science. 12: 174–178.

wiki/Albertonectes
wiki/Libonectes
wiki/Styxosaurus
wiki/Hydrotherosaurus