Rhomaleosaurus

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Rhomaleosaurus
Temporal range:
Ma
Cast of the R. cramptoni
holotype specimen
, Natural History Museum, London
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: †Sauropterygia
Order: †Plesiosauria
Family: †Rhomaleosauridae
Genus: †Rhomaleosaurus
Seeley, 1874
Species

Rhomaleosaurus (meaning "strong lizard") is an

plesiosaurs
.

Species

R. cramptoni

Restoration of R. cramptoni

In July 1848, a fossil of a large plesiosaur was unearthed in an Alum quarry at

British Association annual meeting. The Zoological Society of Ireland built a specially constructed building to house the large reptile. After a decade, still remaining undescribed, the specimen moved in the Royal Dublin Society museum and officially described by Alexander Carte and W. H. Bailey as a new species of Plesiosaurus. Carte and Bailey named the species Plesiosaurus cramptoni after the Irish scientist, Sir Philip Crampton. In 1874, the British geologist Harry G. Seeley, based on this finding, which is now known as the holotype of the family Rhomaleosauridae, recognized and erected a new genus establishing Rhomaleosaurus. Only in 2006 the skull of this specimen was finally prepared and enabled a restudy of this genus.[2]

R. propinquus

R. propinquus is known from the

million years ago. R. propinquus was first named by Tate and Blake in 1876 as a new species of Plesiosaurus. Watson (1910) redescribed it as a species of Rhomaleosaurus. Adam S. Smith (2007), in his thesis on the anatomy and classification of the family Rhomaleosauridae, suggested that R. propinquus, is a junior synonym of Rhomaleosaurus zetlandicus.[1] Smith and Gareth J. Dyke (2008) considered this species to be valid.[2]

R. thorntoni

Size of R. thorntoni

R. thorntoni is known from the

Kingsthorp of Northamptonshire, dating to the Toarcian stage. It is the only well-known British Toarcian rhomaleosaurid discovered away from the Yorkshire coast, to date. R. thorntoni was first named by Andrews in 1922 and later revised by Cruickshank (1996) as a junior synonym of R. cramptoni, alongside R. zetlandicus. Adam S. Smith (2007) and Smith and Gareth J. Dyke (2008) considered this species to be valid.[1][2]

R. zetlandicus

The R. zetlandicus holotype at the Yorkshire Museum

R. zetlandicus is known from the holotype YORYM G503 (pictured), a nearly complete skull and vertebral column in association with parts of the limbs. It was collected from the Alum Shale of Whitby Mudstone Formation, Yorkshire, dating to the Toarcian stage. R. thorntoni was first named by Phillips in 1854 and its skull was described in detail by Taylor (1992). Later it was revised by Cruickshank (1996) as a junior synonym of R. cramptoni, alongside R. thorntoni. Adam S. Smith (2007) and Smith and Gareth J. Dyke (2008) considered this species to be valid.[1][2]

Reassigned species

Through the years, various species have been referred to as Rhomaleosaurus. However, according to Smith (2007), in his thesis on the anatomy and classification of the family

Cladistic analyses by Ketchum & Benson, 2010, Benson et al., 2011 and Ketchum & Benson, 2011 found R. megacephalus to be basal to the clade containing Rhomaleosaurus and Eurycleidus,[3][4] thus it should be in its own genus as suggested by Smith and Dyke (2008). Following this, it has been placed in its own genus, Atychodracon. (Smith, 2015).[5]

Thaumatosaurus

The name

Thaumatosaurus, which means 'wonder reptile', belonged to a genus of plesiosaur that was described by palaeontologist Christian Erich Hermann von Meyer, back in 1841. Meyer described the species Thaumatosaurus oolithicus based on partial skull, vertebral and limb remains, that were found in the Posidonia Shale of Holzmaden, Baden-Württemberg, Germany. In 1856, Meyer published a full description of Thaumatosaurus and later provided figures of the specimen. Richard Lydekker
(1889) regarded Rhomaleosaurus as a synonym of Thaumatosaurus because Richard Lydekker and Harry G. Seeley "refused steadfastly to recognize the generic and specific names proposed by one another". Lydekker referred continuously to the name Thaumatosaurus, instead of Rhomaleosaurus. Fraas (1910) recognized both generic names in his original description of R. victor (now Meyerasaurus), but referring to the new species "Thaumatosaurus" victor. Many other researchers adopted the name "Thaumatosaurus". Today this taxon is regarded as a nomen dubium because the holotype can be referred to Pliosauroidea indet at best. The diagnostic specimens which previously were regarded as Thaumatosaurus's specimens, now represent the holotypes of Eurycleidus, Meyerasaurus and Rhomaleosaurus.[6]

Phylogeny

CGI restoration of R. cramptoni

Smith & Dyke, 2008 redescribed the skull of R. cramptoni after its final preparation. Both Rhomaleosauridae and Pliosauridae were found to be monophyletic, and the relations between Rhomaleosaurus's species were tested. The cladogram below follows Smith & Dyke (2008), with the asterisk noting species removed from Rhomaleosaurus to their own genera since their study.[2]

Rhomaleosauridae

Archaeonectrus rostratus

Macroplata tenuiceps

WARWKS G10875 → Unnamed species*

Atychodracon megacephalus
*

LEICS G221.1851 referred to Atychodracon megacephalus*

NMING F8749 referred to Atychodracon megacephalus*

NMING F10194 referred to Atychodracon megacephalus*

Eurycleidus arcuatus

Sthenarosaurus dawkinsi

Meyerasaurus victor
*

Maresaurus coccai

Rhomaleosaurus propinquus

Rhomaleosaurus zetlandicus

Rhomaleosaurus cramptoni

Rhomaleosaurus thorntoni

Paleobiology

Restoration of Rhomaleosaurus and Teleosaurus

Rhomaleosaurus may have been able to pick up scents while submerged by forcing water through passages in its skull containing sensory organs. This adaptation would have enabled it to hunt its prey in a similar manner to some modern shark species.[7]

See also

References

  1. ^ a b c d e f Adam S. Smith (2007). "Anatomy and systematics of the Rhomaleosauridae (Sauropterygia, Plesiosauria)" (PDF). Ph.D. Thesis, University CollegeDublin.
  2. ^
    S2CID 12528732. Archived
    (PDF) from the original on 3 February 2022.
  3. S2CID 55436528.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  4. ^ 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.
  5. ^ http://palaeo-electronica.org/content/pdfs/504.pdf [bare URL PDF]
  6. doi:10.1111/j.1475-4983.2010.00975.x
    .
  7. ISBN 0-7006-1269-6
    .
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