Simolestes

Simolestes (meaning "snub-nosed thief") is an extinct pliosaurid genus that lived in the Middle to Late Jurassic.[2] The type specimen, BMNH R. 3319 is an almost complete but crushed skeleton diagnostic to Simolestes vorax, dating back to the Callovian of the Oxford Clay formation, England. The genus is also known the Tithonian of India (S.indicus).[3] The referral of this species to Simolestes is dubious, however.[4] S.keileni from France was moved to the new genus Lorrainosaurus in 2023.[5]

Not to be confused with Cimolestes.

Simolestes
Temporal range: Middle–Late Jurassic[1]
Diagram of the skull of S. vorax
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: †Sauropterygia
Order: †Plesiosauria
Family: †Pliosauridae
Clade: †Thalassophonea
Genus: †Simolestes
Andrews, 1909
Species[1]
  • †S. vorax (type)
  • †S. indicus
Synonyms

Description
Scale diagram, presenting the largest specimens of both species

Simolestes possessed a short, high, and wide skull which was built to resist torsional forces when hunting.

The largest specimens of S.vorax reached approximately 4.5 metres (15 ft) in length, if a head to body ratio similar to Liopleurodon is applied.[4][6] S.keileni was larger, with specimens from France suggesting that some individuals grew more than 6 metres (20 ft) long.[7] S. vorax and S. keileni weighed about 1 and 2 metric tons (1.1 and 2.2 short tons), respectively.[8]

Palaeobiology

Like most Pliosaurs, Simolestes possessed salt secreting glands, which would have enabled the animal to maintain salt balance and drink seawater.[4] Recent studies on Plesiosaur locomotion indicate that Simolestes, like other Plesiosaurs, possessed a unique bauplan for movement, which differs from modern organisms in similar niches.[9]

Skull specimen housed at the Peterborough Museum.

Feeding habits

Simolestes's exact feeding habits are unclear. The current consensus, however, is that the genus was primarily teuthophagous, consuming belemnites, soft teuthoids and ammonites. It is possible Simolestes was also ecologically separated from other contemporary pliosaur genera such as Liopleurodon and Pachycostasaurus by hunting in deeper waters or at night, as modern cephalopods exhibit diurnal feeding cycles, spending daylight in deeper, safer waters, and rising at night to feed.[4]

Classification
Restoration of S. vorax

The cladogram below follows a 2011 analysis by paleontologists Hilary F. Ketchum and Roger B. J. Benson, and reduced to genera only.[10]

Pliosauroidea
Rhomaleosauridae

Anningasaura

"Plesiosaurus" macrocephalus

Archaeonectrus

Macroplata

Atychodracon

Eurycleidus

Rhomaleosaurus

Meyerasaurus

Maresaurus

Pliosauridae

Thalassiodracon

Hauffiosaurus

Attenborosaurus

BMNH R2439

Marmornectes

"Pliosaurus" andrewsi

OUMNH J.02247

Peloneustes

Simolestes

Liopleurodon

Pliosaurus

Megacephalosaurus[11]

Brachauchenius

Kronosaurus

References
  1. "†Simolestes Andrews 1909". Paleobiology Database. Fossilworks. Retrieved 17 December 2021.
  2. Smith, Adam S.; Dyke, Gareth J. (2008). "The skull of the giant predatory pliosaur Rhomaleosaurus cramptoni: Implications for plesiosaur phylogenetics" (PDF). Naturwissenschaften. 95 (10): 975–80. Bibcode:2008NW.....95..975S. doi:10.1007/s00114-008-0402-z. PMID 18523747. S2CID 12528732.
  3. R. Lydekker. 1877. Notices of new and other Vertebrata from Indian Tertiary and Secondary rocks. Records of the Geological Survey of India 10(1):30-43
  4. Noè, L. F. (2001). A taxonomic and functional study of the Callovian (Middle Jurassic) Pliosauroidea (Reptilia, Sauropterygia). Chicago
  5. 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. .
  6. Noe, Leslie F.; Jeff Liston; Mark Evans (2003). "The first relatively complete exoccipital-opisthotic from the braincase of the Callovian pliosaur, Liopleurodon" (PDF). Geological Magazine. 140 (4): 479–486. Bibcode:2003GeoM..140..479N. doi:10.1017/S0016756803007829. S2CID 22915279.
  7. Musée national d'histoire naturelle Luxembourg. Palaeontological collections National Museum of Natural History Luxembourg. Occurrence dataset https://doi.org/10.15468/vbuvyu accessed via GBIF.org on 2018-06-04. https://www.gbif.org/occurrence/1663273715
  8. Paul, Gregory S. (2022). The Princeton Field Guide to Mesozoic Sea Reptiles. Princeton University Press. pp. 99–100. ISBN 9780691193809.
  9. Muscutt, Luke E.; Dyke, Gareth; Weymouth, Gabriel D.; Naish, Darren; Palmer, Colin; Ganapathisubramani, Bharathram (2017). "The four-flipper swimming method of plesiosaurs enabled efficient and effective locomotion". Proceedings of the Royal Society B: Biological Sciences. 284 (1861): 20170951. doi:10.1098/rspb.2017.0951. PMC 5577481. PMID 28855360.
  10. Hilary F. Ketchum; Roger B. J. Benson (2011). "A new pliosaurid (Sauropterygia, Plesiosauria) from the Oxford Clay Formation (Middle Jurassic, Callovian) of England: evidence for a gracile, longirostrine grade of Early-Middle Jurassic pliosaurids". Special Papers in Palaeontology. 86: 109–129.
  11. Schumacher, Bruce A.; Carpenter, Kenneth; Everhart, Michael J. (2013). "A new Cretaceous pliosaurid (Reptilia, Plesiosauria) from the Carlile Shale (middle Turonian) of Russell County, Kansas". Journal of Vertebrate Paleontology. 33 (3): 613. Bibcode:2013JVPal..33..613S. doi:10.1080/02724634.2013.722576. S2CID 130165209.
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