Eonatator

Last updated

Eonatator
Temporal range: Santonian-Campanian
~84–72.1  Ma
UPI R 163 (Wiman, 1920).png
Holotype of E. sternbergii (UPI R 163) [lower-alpha 1]
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Clade: Mosasauria
Family: Mosasauridae
Tribe: Halisaurini
Genus: Eonatator
Bardet et al. 2005 [2]
Type species
Clidastes sternbergii
(Wiman 1920)
Species
Synonyms
  • Clidastes sternbergii(Wiman 1920)

Eonatator is an extinct genus of marine lizard belonging to the mosasaur family. It is a close relative of Halisaurus , and part of the same subfamily, the Halisaurinae. It is known from the Late Cretaceous of North America, Colombia and Sweden. Originally, this taxon was included within Halisaurus, but was placed in its own genus, which also led to the subfamily Halisaurinae being created for the two genera. [2]

Contents

Discovery and naming

Eonatator is known from the Smoky Hill Chalk Member of the Niobrara Chalk Formation (Late Coniacian to Early Campanian) of Kansas, [2] from the Eutaw Formation (Santonian) and Mooreville Chalk Formation (Selma Group; Santonian-Lower Campanian) of Alabama (United States), [4] from the Kristianstad Basin of southern Sweden (late early Campanian), [5] and the unit Nivel de Lutitas y Arenas (Campanian) of the Olini Group in La Mesa, Colombia. [3]

The name Eonatator means "dawn swimmer" (Greek eos = dawn + Latin natator = swimmer). Originally, it contained only a single species, E. sternbergii. [2] 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. [6] A second species, E. coellensis, was named for the town of Coello in the Department of Tolima in Colombia, near of which it was discovered. [3]

Description

Size comparison of the two known species of Eonatator, E. sternbergii and E. coellensis Eonatator Scale V2.svg
Size comparison of the two known species of Eonatator, E. sternbergii and E. coellensis

Eonatator was a small mosasaur, with the type specimen of Eonatator sternbergii, UPI R 163, measuring approximately 2.6 metres (8.5 ft) long. [1] Bardet et al. (2005, p. 465 [2] ) 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 (wing); vertebral formula: seven cervicals, 24 dorsals, four pygals, 28 median caudals and at least 41 terminal caudals; humerus length approximately 2.5x distal width." E. coellensis is diagnosed by more retracted nostrils, between the 7 and the 17 maxillary teeth, premaxilla and maxilla with a short rostrum anterior to the first teeth; presence of a septomaxilla, a large prefrontal that makes most of the margin of the outer nostril, a short and wide frontal, a parietal foramen located near of the fronto-parietal suture, a triangular surface of the parietal with two medial depressions and 22 caudal vertebrae. [2]

The type specimen of E. coellensis, IGM p 881237, measures 2.8 metres (9.2 ft) long as preserved, but is missing part of its tail. This specimen had a 41.5 cm (16.3 in) long skull and lacked a complete tail. Still, it is remarkable for having remains of soft tissue in the ear region, the neck, thoracic and the abdominal region. Under the pygal vertebrae and the seventeenth dorsal vertebra there is a series of 20 small vertebrae centra and a flattened bone, that together measure 25 cm (9.8 in) in length. It have features of the mosasauroids, with three vertebrae with haemal arches and procoelic centra, that suggest the possibility that these small bones belong to an embryo of this species, although the lack of diagnostic fossils like the skull or teeth prevents a complete identification. In any case, it will be consequent with the ovoviviparism previously reported in mosasauroids like Carsosaurus . [3]

Classification

Restoration of E. sternbergii Eonatator BW.jpg
Restoration of E. sternbergii

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 and then to Halisaurus by Russell. Hence, Clidastes sternbergii became Halisaurus sternbergii. [7] Although some agreed with this generic attribution, other paleontologists suggested that while H. sternbergii did not belong to Clidastes, its designation under Halisaurus is questionable; Lingham-Soliar (1996) referred H. sternbergii to C. sternbergii again, but this has found no acceptance in other researchers. [1]

In 2005, Halisaurus sternbergii was reassigned to its own genus, Eonatator by Nathalie Bardet and colleagues along with the description of Halisaurus arambourgi and the creation of the subfamily Halisaurinae. [2] In the same year, Lindgren and Siverson suggested that Eonatator is an invalid junior synonym and should be classified as H. sternbergii, [8] but this has found no acceptance in other researchers who used the genus name Eonatator instead. [8] [3] [9]

Below is a cladogram following an analysis by Takuya Konishi and colleagues (2016) done during the description of Phosphorosaurus ponpetelegans , which showcases the internal relationships within the Halisaurinae. [9] The analysis excluded the dubious Halisaurus onchognathus and the genus Pluridens .

Halisaurinae

In their 2023 description of the new Halisaurus species, H. hebae, Shaker et al. performed a phylogenetic analyses of members of the Halisaurinae. They suggested that Phosphorosaurus ponpetelegans and Eonatator coellensis were more closely related to the genus Halisaurus than the type species of their respective genera. They tentatively assigned both of these species to Halisaurus. The results of their analyses are displayed in the cladogram below: [10]

Halisaurini

Eonatator sternbergii

Phosphorosaurus ortliebi

Halisaurus ("Phosphorosaurus")ponpetelegans

Halisaurus("Eonatator")coellensis

Halisaurus hebae

Halisaurus arambourgi

Halisaurus platyspondylus

Notes

  1. Note that parts of the skull and tail's neural spines, among others, were restored with plaster to provide an erroneous Clidastes -like appearance. [1]

Related Research Articles

<span class="mw-page-title-main">Mosasaur</span> Extinct marine lizards of the Late Cretaceous

Mosasaurs are an extinct group of large aquatic reptiles within the family Mosasauridae that lived during the Late Cretaceous. Their first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764. They belong to the order Squamata, which includes lizards and snakes.

<i>Mosasaurus</i> Extinct genus of marine squamate reptile from the Late Cretaceous

Mosasaurus is the type genus of the mosasaurs, an extinct group of aquatic squamate reptiles. It lived from about 82 to 66 million years ago during the Campanian and Maastrichtian stages of the Late Cretaceous. The genus was one of the first Mesozoic marine reptiles known to science—the first fossils of Mosasaurus were found as skulls in a chalk quarry near the Dutch city of Maastricht in the late 18th century, and were initially thought to be crocodiles or whales. One skull discovered around 1780 was famously nicknamed the "great animal of Maastricht". In 1808, naturalist Georges Cuvier concluded that it belonged to a giant marine lizard with similarities to monitor lizards but otherwise unlike any known living animal. This concept was revolutionary at the time and helped support the then-developing ideas of extinction. Cuvier did not designate a scientific name for the animal; this was done by William Daniel Conybeare in 1822 when he named it Mosasaurus in reference to its origin in fossil deposits near the Meuse River. The exact affinities of Mosasaurus as a squamate remain controversial, and scientists continue to debate whether its closest living relatives are monitor lizards or snakes.

<i>Selmasaurus</i> Extinct genus of mosasaurids

Selmasaurus is an extinct genus of marine lizard belonging to the mosasaur family. It is classified as part of the Plioplatecarpinae subfamily alongside genera like Angolasaurus and Platecarpus. Two species are known, S. russelli and S. johnsoni; both are exclusively known from Santonian deposits in the United States.

<span class="mw-page-title-main">Mosasaurinae</span> Subfamily of reptiles

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<span class="mw-page-title-main">Tylosaurinae</span> Extinct subfamily of lizards

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<span class="mw-page-title-main">Halisaurinae</span> Extinct subfamily of lizards

The Halisaurinae are a subfamily of mosasaurs, a group of Late Cretaceous marine lizards. They were small to medium-sized, ranging from just under 3 meters in Eonatator sternbergi to as much as 8 or 9 meters in Pluridens serpentis. They tended to have relatively slender jaws and small, numerous teeth, suggesting a diet of small fish and other prey. Although the skeleton is primitive compared to other Mosasauridae in many respects, halisaurines had the distinctive hypocercal tail of other mosasaurids suggesting good swimming ability, and they persisted alongside other mosasaurs until the end of the Cretaceous. The earliest known remains of halisaurines occur in rocks of Santonian age and the subfamily persists until the latest Maastrichtian. Halisaurines are known from North and South America, Europe, Asia and Africa, indicating a more or less global distribution in the Late Cretaceous. Four genera are currently recognized: Eonatator, Halisaurus, Phosphorosaurus and Pluridens.

Platecarpus is an extinct genus of aquatic lizards belonging to the mosasaur family, living around 84–81 million years ago during the middle Santonian to early Campanian, of the Late Cretaceous period. Fossils have been found in the United States and possible specimens in Belgium and Africa. A well-preserved specimen of Platecarpus shows that it fed on moderate-sized fish, and it has been hypothesized to have fed on squid, and ammonites as well. Like other mosasaurs, it was initially thought to have swum in an eel-like fashion, although another study suggests that it swam more like modern sharks. An exceptionally well-preserved specimen of P. tympaniticus known as LACM 128319 shows skin impressions, pigments around the nostrils, bronchial tubes, and the presence of a high-profile tail fluke, showing that it and other mosasaurs did not necessarily have an eel-like swimming method, but were more powerful, fast swimmers. It is held in the Natural History Museum of Los Angeles County. Isotopic analysis on teeth specimens has suggested that this genus and Clidastes may have entered freshwater occasionally, just like modern sea snakes.

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<i>Pluridens</i> Extinct genus of lizards

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<i>Phosphorosaurus</i> Extinct genus of lizards

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<span class="mw-page-title-main">Timeline of mosasaur research</span>

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References

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  2. 1 2 3 4 5 6 7 Bardet, N.; Pereda Suberbiola, X.; Iarochene, M.; Baadi, 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 (3): 447–472. doi: 10.1111/j.1096-3642.2005.00152.x .
  3. 1 2 3 4 5 Páramo-Fonseca, María E. (2013). "Eonatator coellensis nov. sp. (Squamata: Mosasauridae), nueva especie del Cretácico Superior de Colombia" [Eonatator coellensis nov. sp. (Squamata: Mosasauridae), a new species from the Upper Cretaceous of Colombia]. Revista de la Academia Colombiana de Ciencias (in Spanish). 37 (145): 499–518. doi: 10.18257/raccefyn.31 . ISSN   0370-3908.
  4. Kejiri, T.; Ebersole, J.A.; Blewitt, H.L.; Ebersole, S.M. (2013). "An Overview of Late Cretaceous Vertebrates from Alabama". Bulletin of the Alabama Museum of Natural History. 31 (1): 46–71.
  5. Källsten, L. (2015). "Diversity and Ecology of a Middle Campanian (Late Cretaceous) Marine Reptile Assemblage from Skåne, Southern Sweden" (PDF). 28. Department of Earth Sciences, Uppsala University. S2CID   201080155.{{cite journal}}: Cite journal requires |journal= (help)
  6. Sternberg, C. H. (1922). "Explorations of the Permian of Texas and the chalk of Kansas, 1918". Kansas Academy of Science, Transactions. 30 (1): 119–120. doi:10.2307/3624047. JSTOR   3624047.
  7. Russell, Dale. A. (6 November 1967). "Systematics and Morphology of American Mosasaurs" (PDF). Bulletin of the Peabody Museum of Natural History (Yale University). Archived from the original (PDF) on 21 October 2022. Retrieved 20 January 2023.
  8. 1 2 Everhart, M.J. (2017). Oceans of Kansas, Second Edition: A Natural History of the Western Interior Sea (Life of the Past). Indiana University Press. p. 232. ISBN   978-0253026323.
  9. 1 2 Konishi, Takuya; Caldwell, Michael W.; Nishimura, Tomohiro; Sakurai, Kazuhiko; Tanoue, Kyo (2016-10-02). "A new halisaurine mosasaur (Squamata: Halisaurinae) from Japan: the first record in the western Pacific realm and the first documented insights into binocular vision in mosasaurs". Journal of Systematic Palaeontology. 14 (10): 809–839. Bibcode:2016JSPal..14..809K. doi:10.1080/14772019.2015.1113447. ISSN   1477-2019.
  10. Shaker, A. A.; Longrich, N. R.; Strougo, A.; Asan, A.; Bardet, N.; Mousa, M. K.; Tantawy, A. A.; Abu El-Kheir, G. A. (2023). "A new species of Halisaurus (Mosasauridae: Halisaurinae) from the lower Maastrichtian (Upper Cretaceous) of the Western Desert, Egypt". Cretaceous Research. 154. 105719. doi:10.1016/j.cretres.2023.105719.

Further reading