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Sveltonectes; Temporal range: Early Cretaceous, 126 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	†Ichthyosauria
Family:	†Ophthalmosauridae
Subfamily:	†Platypterygiinae
Genus:	†Sveltonectes; Fischer et al., 2011
Species:	†S. insolitus
Binomial name
	†Sveltonectes insolitus; Fischer et al., 2011

Sveltonectes (meaning "agile swimmer" in Greek) is an extinct genus of platypterygiine ophthalmosaurid ichthyosaurs known from Ul’yanovsk region, western Russia.^[1]^[2]

History of discovery

Sveltonectes is known from the holotype IRSNB R269, an almost complete three-dimensionally preserved skeleton including a partial skull. It was collected in unnamed locality, in Ul’yanovsk, dating to the late Barremian stage of the early Cretaceous, about 126 million years ago. Another thunnosaur described from the same locality, by Bogolubow (1909), is "Ichthyosaurus" steleodon. It is a nomen dubium that is twice the size and more robust than Sveltonectes.^[1]

Sveltonectes was named by Valentin Fischer, Edwige Masure, Maxim S. Arkhangelsky, and Pascal Godefroit in 2011 and the type species is Sveltonectes insolitus. The generic name is derived from sveltos, Greek for "agile", and nektes, Greek for "swimmer", and refers to its small size, streamlined skull, and powerful girdle musculature. The specific name is derived from insolitus, Latin for "unusual", in reference to the numerous unusual features of this ichthyosaur, as well as its unusual tooth morphology.^[1]

Description

Like some other ophthalmosaurids, Sveltonectes has a projection on the nasal bone of the skull into the naris, a prefrontal forming part of the margin of the naris and a frontal forming part of the margin of the supratemporal fenestra. Sveltonectes is unique in that it has small, sharp teeth and numerous other peculiar features such as a very primitive prootic. The distinctive shape of these teeth suggest that it had a different feeding habit than other cretaceous ophthalmosaurids. Within the Ophthalmosauridae, Sveltonectes is most closely related to Aegirosaurus.^[1]

Phylogeny

The following cladogram shows a possible phylogenetic position of Sveltonectes in Ophthalmosauridae according to the analysis performed by Zverkov and Jacobs (2020).^[3]

Ophthalmosauria

Ophthalmosaurinae

Acamptonectes densus

Mollesaurus periallus

	Ophthalmosaurus natans

	Ophthalmosaurus icenicus

Gengasaurus nicosiai

Nannopterygius yasykovi

	Nannopterygius enthekiodon

	Nannopterygius saveljeviensis

	Nannopterygius borealis

Arthropterygius volgensis

Arthropterygius lundi

Arthropterygius thalassonotus

	Arthropterygius hoybergeti

	Arthropterygius chrisorum

Platypterygiinae

Brachypterygius extremus

Aegirosaurus leptospondylus

Muiscasaurus catheti

Leninia stellans

Sveltonectes insolitus

Athabascasaurus bitumineus

Platypterygius americanus

	Acuetzpalin carranzai

	Platypterygius sachicarum

	Caypullisaurus bonapartei

	Grendelius mordax

	Grendelius alekseevi

	Grendelius pseudoscythicus

	Grendelius zhuravlevi

Undorosaurus kielanae

	Undorosaurus nessovi

	Undorosaurus gorodischensis

Platypterygius australis

	Plutoniosaurus bedengensis

	Simbirskiasaurus birjukovi

	Platypterygius hercynicus

	Sisteronia seeleyi

	Platypterygius platydactylus

	Maiaspondylus lindoei

References

^ ^a ^b ^c ^d Fischer, V.; Masure, E.; Arkhangelsky, M.S.; Godefroit, P. (2011). "A new Barremian (Early Cretaceous) ichthyosaur from western Russia". Journal of Vertebrate Paleontology. 31 (5): 1010–1025. doi:10.1080/02724634.2011.595464. hdl:2268/92828. S2CID 86036325.
^ Valentin Fischer; Michael W. Maisch; Darren Naish; Ralf Kosma; Jeff Liston; Ulrich Joger; Fritz J. Krüger; Judith Pardo Pérez; Jessica Tainsh & Robert M. Appleby (2012). "New Ophthalmosaurid Ichthyosaurs from the European Lower Cretaceous Demonstrate Extensive Ichthyosaur Survival across the Jurassic–Cretaceous Boundary". PLOS ONE. 7 (1): e29234. Bibcode:2012PLoSO...729234F. doi:10.1371/journal.pone.0029234. PMC 3250416. PMID 22235274.
^ Nikolay G. Zverkov & Megan L. Jacobs (2021) [2020]. "Revision of Nannopterygius (Ichthyosauria: Ophthalmosauridae): reappraisal of the 'inaccessible' holotype resolves a taxonomic tangle and reveals an obscure ophthalmosaurid lineage with a wide distribution". Zoological Journal of the Linnean Society. 191 (1): 228–275. doi:10.1093/zoolinnean/zlaa028.