The many faces of Styxosaurus

Styxosaurus snowii (Originally Cimoliasaurus snowii, Williston 1890, KUVP 1301; Welles 1943; Late Cretaceous, Campanian, 80mya; SDSMT 451; Figs. 1, 2) is another giant elasmosaurid with dog-like fangs related to Simolestes in the large reptile tree (LRT, 1438 taxa).

Figure 1. Skull of Styxosaurus (KUVP 1301) from Sachs, Lindgren and Kear 2018, colorized using DGS methods.

Figure 1. Skull of Styxosaurus (KUVP 1301) from Sachs, Lindgren and Kear 2018, colorized using DGS methods. Broken teeth on this side of the skull repaired based on the dimensions of unbroken teeth on the other side of the skull.

Several new papers
(refs below) have taken another look at the skull of Styxosaurus, now known for about 130 years. Prior freehand drawings of the skull (Fig. 2) seem to overlook certain interesting details, many of which are critical for accurate scoring.

Figure 2. The changing face of Styxosaurus from Welles 1890, Otero 2016 and colorized here.

Figure 2. The changing face of Styxosaurus from Welles 1890, Otero 2016 and colorized here. Maybe a little easier to see each bone when colored? 

Overall,
a skeletal reconstruction of Styxosaurus required just a little updating (Fig. 3).

Figure 3. Styxosaurus skeleton as originally drawn and revised here.

Figure 3. Styxosaurus skeleton as originally drawn and revised here.

A biting animation
(Fig. 4) of Styxosaurus shows the interweaving of the oversized teeth. Note the elongate posterior dentary teeth. As in Tricleidus, these would have made effective foot traps when water was being expelled whenever the jaw closed.

Figure 6. Styxosaurus mandible animated.

Figure 4. Styxosaurus mandible animated.


References
Otero RA 2016. Taxonomic reassessment of Hydralmosaurus as Styxosaurus: new insights on the elasmosaurid neck evolution throughout the Cretaceous. PeerJ Figure 3. Styxosaurus skeleton as originally drawn and revised here.
Sachs S, Lindgren J and Kear B 2018. Reassessment of the Styxosaurus snowii (Williston, 1890) holotype specimen and its implications for elasmosaurid plesiosaurian interrelationships. Alcheringa: An Australasian Journal of Palaeontology, DOI: 10.1080/03115518.2018.1508613
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 and Bump J 1949. Alzadasaurus pembertoni, a new elasmosaur from the Upper Cretaceous of South Dakota. Journal of Paleontology 23(5): 521-535.
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/Styxosaurus

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