Eonatator

Taxobox
name = "Eonatator"
fossil_range = Late Cretaceous
regnum = Animalia
phylum = Chordata
classis = Sauropsida
ordo = Squamata
familia = Mosasauridae
subfamilia = Halisaurinae
genus = "Eonatator"
genus_authority = Bardet et al., 2005 Bardet N, Suberbiola XP, Iarochene M, Bouyahyaoui F, Bouya B, Amaghzaz M. 2005. A new species of "Halisaurus" from the Late Cretaceous phosphates of Morocco, and the phylogenetical relationships of the Halisaurinae (Squamata: Mosasauridae). "Zoological Journal of the Linnean Society" 143: 447-472.]
subdivision_ranks = Species
subdivision = "Eonatator sternbergii"

"Eonatator" is a genus of halisaurine mosasaur from the Upper Cretaceous of North America and Europe. Originally, this taxon was included within "Halisaurus", but was placed in its own genus . "Eonatator" is presently known from the Smoky Hill Chalk Member of the Niobrara Chalk Formation (Upper Coniacian - Lower Campanian) of Kansas, from the Eutaw Formation (Santonian) and Mooreville Chalk Formation (Selma Group; Santonian-Lower Campanian) of Alabama, and from the Kristianstad Basin of southern Sweden (late early Campanian). The name "Eonatator" means "dawn swimmer" (Greek "eos" = dawn + Latin "natator" = swimmer). At this time it contains only a single species, "E. sternbergii". The species is named in honour of Charles H. Sternberg and his son, Levi, who discovered the type specimen in the Niobrara Chalk during the summer of 1918.

Like many mosasaurs, this genus has a complicated taxonomic history. The type specimen (UPI R 163, Uppsala University Palaeontological Institute, Uppsala, Sweden), a nearly complete skeleton, was originally referred to the genus "Clidastes" by Wiman Wiman CJ. 1920. Some reptiles from the Niobrara group in Kansas. "Bulletin of the Geological Institute of Uppsala" 18: 9-18 (9 figs., pls. II-IV).] and then to "Halisaurus" by Russell Russell DA. 1970. The vertebrate fauna of the Selma Formation of Alabama. Part VII: The mosasaurs. "Fieldiana, Geology Memoirs" 3 (7): 369-380.] . Hence, "Clidastes sternbergii" became "Halisaurus sternbergii". However, by the late 1980s, some paleontologists began to suggest that "H. sternbergii" belonged in its own genus and that "Halisaurus" was polyphyletic Wright KR. 1988. A new specimen of "Halisaurus platyspondylus" (Squamata: Mosasauridae) from the Navesink Formation (Maastrichtian) of New Jersey. "Journal of Vertebrate Paleontology" 8 (Supplement 3): 29A-30A.] .

Bardet et al. (2005, p. 465 ) diagnose "Eonatator sternbergii" as follows: "Ambiguous characters: premaxilla-maxilla lateral suture ending posterior to 9th maxillary teeth; tail about 40% of the head and trunk length (convergent in mosasaurines); caudal vertebra length greater than width; fewer than four pygal vertebrae; femur length about twice distal width (convergent in "Clidastes"). Autapomorphies: parietal with smooth triangular table extending very far posteriorly, bearing medium-sized circular foramen, located at distance twice its diameter from the frontal-parietal suture, and surrounded anteriorly and posteriorly by two parallel ridges; rounded quadrate with regularly convex tympanic ala; vertebral formula: seven cervicals, 24 dorsals, four pygals, 28 median caudals and at least 41 terminal caudals; humerus length approximately 2.5x distal width." A cladistic analysis of the Halisaurinae has indicated that "Eonatator" is the sister group to the clade "Halisaurus" and that it represents one of the most basal of known mosasaur taxa.

"Eonatator" was among the smaller mosasaurs. The length of the type skeleton, which represents an adult, is only 2.65 meters in length. Like many mosasaurs, it likely fed primarily on fish and smaller marine reptiles.

References

Further reading

*Lindgren J, Siverson M. 2005. "Halisaurus sternbergii", a small mosasaur with an intercontinental distribution. "Journal of Paleontology" 79 (4): 763–773.

External links

* [http://www.oceansofkansas.com/Halisaurus.html Kansas Mosasaurs in Sweden: the type specimen of "Eonatator" ("Halisaurus") "sternbergi" Wiman 1920 @ Oceans of Kansas, very good photographs of type specimen]