Rhomaleosaurus

Rhomaleosaurus; Temporal range: Early Jurassic, 208.5–174.1 Ma PreꞒ Ꞓ O S D C P T J K Pg N
	Cast of the R. cramptoni holotype specimen, Natural History Museum, London
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Superorder:	† Sauropterygia
Order:	† Plesiosauria
Family:	† Rhomaleosauridae
Genus:	† Rhomaleosaurus ; Seeley, 1874
Species
	† R. cramptoni(Carte & Bailey, 1863 [originally Plesiosaurus ]) (type); †R. propinquus(Tate & Blake, 1876 [originally Plesiosaurus ]); †R. thorntoniAndrews, 1922 ; †R. zetlandicusPhillips, 1854 ;

Last updated April 09, 2024

Rhomaleosaurus (meaning "strong lizard") is an extinct genus of Early Jurassic (Toarcian age, about 183 to 175.6 million years ago) rhomaleosaurid pliosauroid known from Northamptonshire and from Yorkshire of the United Kingdom. It was first named by Harry Seeley in 1874 and the type species is Rhomaleosaurus cramptoni. It was one of the earliest large marine reptile predators which hunted in the seas of Mesozoic era, measuring about 7 metres (23 ft) long.^[1]^[2] Like other pliosaurs, Rhomaleosaurus fed on ichthyosaurs, ammonites and other plesiosaurs.

Species

R. cramptoni

In July 1848, a fossil of a large plesiosaur was unearthed in an Alum quarry at Kettleness, near Whitby, in Yorkshire, England. It was collected from the A. bifrons ammonite zone of the Whitby Mudstone Formation, dating to the early Toarcian age, about 183 to 180 million years ago.^[1] The complete skeleton which preserved the skull, NMING F8785, was kept for five years at Mulgrave Castle, which was then owned by the Marquess of Normanby. In 1853, the Marquess introduced the interesting finding to the eminent Irish surgeon and anatomist, Sir Philip Crampton. The same year, Crampton transferred the fossil to Dublin to be displayed as a centrepiece at the 1853 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 holotype WM 852.S, articulated almost complete skeleton which preserved the skull, exposed in dorsal view. It was collected from the A. serpentines ammonoid zone, of the Whitby Mudstone Formation, Yorkshire, England, dating to the middle Toarcian stage, about 180-177 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

R. thorntoni is known from the holotype BMNH R4853, three-dimensional, partially complete skeleton which preserved most of the skull and mandibles. It was collected from 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

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 Rhomaleosauridae, the genus Rhomaleosaurus has only three valid species: R. cramptoni, R. thorntoni and R. zetlandicus.^[1] Smith and Dyke (2008) also recognized R. propinquus as valid.^[2] Other species that previously fell under this genus were: R. megacephalus and R. victor. Smith (2007) and Smith and Dyke (2008) pointed out that these species do not belong to Rhomaleosaurus, as R. megacephalus is referred to Eurycleidus (or to a new genus by Smith and Dyke (2008)) and R. victor represents a new genus named Meyerasaurus by Smith and Vincent in 2010. 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

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

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]

Related Research Articles

Pliosauroidea is an extinct clade of plesiosaurs, known from the earliest Jurassic to early Late Cretaceous. They are best known for the subclade Thalassophonea, which contained crocodile-like short-necked forms with large heads and massive toothed jaws, commonly known as pliosaurs. More primitive non-thalassophonean pliosauroids resembled plesiosaurs in possessing relatively long necks and smaller heads. They originally included only members of the family Pliosauridae, of the order Plesiosauria, but several other genera and families are now also included, the number and details of which vary according to the classification used.

Macroplata is an extinct genus of Early Jurassic rhomaleosaurid plesiosaur which grew up to 4.65 metres (15.3 ft) in length. Like other plesiosaurs, Macroplata probably lived on a diet of fish, using its sharp needle-like teeth to catch prey. Its shoulder bones were fairly large, indicating a powerful forward stroke for fast swimming. Macroplata also had a relatively long neck, twice the length of the skull, in contrast to pliosaurs.

Peloneustes is a genus of pliosaurid plesiosaur from the Middle Jurassic of England. Its remains are known from the Peterborough Member of the Oxford Clay Formation, which is Callovian in age. It was originally described as a species of Plesiosaurus by palaeontologist Harry Govier Seeley in 1869, before being given its own genus by naturalist Richard Lydekker in 1889. While many species have been assigned to Peloneustes, P. philarchus is currently the only one still considered valid, with the others moved to different genera, considered nomina dubia, or synonymised with P. philarchus. Some of the material formerly assigned to P. evansi have since been reassigned to "Pliosaurus" andrewsi. Peloneustes is known from many specimens, including some very complete material.

Umoonasaurus is an extinct genus of plesiosaur belonging to the family Leptocleididae. This genus lived approximately 115 million years ago during the Early Cretaceous period, in shallow seas covering parts of what is now Australia. It was a relatively small animal around 2.5 metres (8.2 ft) long. An identifying trait of Umoonasaurus is three crest-ridges on its skull.

Plesiopleurodon is an extinct genus of Mesozoic marine reptiles, belonging to Sauropterygia, known from the Late Cretaceous of North America. It was named by Kenneth Carpenter based on a complete skull with a mandible, cervical vertebra, and a coracoid. In naming the specimen, Carpenter noted "Of all known pliosaurs, Plesiopleurodon wellesi most closely resembles Liopleurodon ferox from the Oxfordian of Europe, hence the generic reference." It was initially described as a pliosaur due to it short neck, a common trait of the family, although it is in the order Plesiosauria. However, later exploration into the relationships of both orders indicate that not all pliosaurs have short necks and not all plesiosaurs have long necks.

Pliosaurus is an extinct genus of thalassophonean pliosaurid known from the Late Jurassic of Europe and South America. Most European species of Pliosaurus measured around 8 metres (26 ft) long and weighed about 5 metric tons, but P. rossicus and P. funkei would have been one of the largest plesiosaurs of all time, exceeding 10 metres (33 ft) in length. This genus has contained many species in the past but recent reviews found only six to be valid, while the validity of two additional species awaits a petition to the International Code of Zoological Nomenclature. Currently, P. brachyspondylus and P. macromerus are considered dubious, while P. portentificus is considered undiagnostic. Species of this genus are differentiated from other pliosaurids based on seven autapomorphies, including teeth that are triangular in cross section. Their diet would have included fish, cephalopods, and marine reptiles.

Brachauchenius is an extinct genus of pliosaurid that lived in North America and Morocco during the Late Cretaceous.

Leptocleidus is an extinct genus of plesiosaur, belonging to the family Leptocleididae. It was a small plesiosaur, measuring only up to 3 m (9.8 ft).

Attenborosaurus is an extinct genus of pliosaurid from the Early Jurassic of Dorset, England. The type species is A. conybeari. The genus is named after David Attenborough, the species after William Conybeare.

<i>Simolestes</i> Extinct genus of reptiles

Simolestes is an extinct pliosaurid genus that lived in the Middle to Late Jurassic. 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 might also be known from the Tithonian Bhuj Formation of India (S.indicus), however the referral of this species to Simolestes is dubious. S.keileni from France was moved to the new genus Lorrainosaurus in 2023.

Maresaurus is an extinct genus of plesiosaur from the Middle Jurassic (Bajocian) Los Molles Formation of Argentina. The type species, Maresaurus coccai, was named by Gasparini in 1997. Recent phylogenetic analysis found Maresaurus to be a rhomaleosaurid.

Hauffiosaurus is an extinct genus of Early Jurassic pliosaurid plesiosaur known from Holzmaden of Germany and from Yorkshire of the United Kingdom. It was first named by Frank Robin O’Keefe in 2001 and the type species is Hauffiosaurus zanoni. In 2011, two additional species were assigned to this genus: H. longirostris and H. tomistomimus.

Eurycleidus is an extinct genus of large-bodied rhomaleosaurid known from the Early Jurassic period of the United Kingdom. It contains a single species, E. arcuatus. Like other plesiosaurs, Eurycleidus probably lived on a diet of fish, using its sharp needle-like teeth to catch prey. Its shoulder bones were fairly large, indicating a powerful forward stroke for fast swimming.

Sthenarosaurus is an extinct genus of rhomaleosaurid pliosauroid discovered in the Toarcian-aged 'Main Alum Shale' in Whitby, England. The type species, S. dawkinsi, was named and described in 1909. The type specimen is MMUM LL 8023, a set of postcrania discovered in Whitby. Other indeterminate specimens are known, including a pectoral girdle described in 1911.

Seeleyosaurus is an extinct genus of plesiosaur that was initially placed within the genus Plesiosaurus in 1895 and was given its own genus in 1940. Two species were known: the type, S. guilelmiimperatoris, and the now obsolete species S. holzmadensis, which has since been absorbed into S. guilelmiimperatoris. It was a relatively small plesiosaur, measuring 2.9–3.6 m (9.5–11.8 ft) long. The holotype is MB.R.1992, a large almost complete skeleton from the Upper Lias (Toarcian) Lias Group Formations of Württemberg, Germany. There seems to be the impression of a rhomboidal flap of skin in a vertical plane; if so, many plesiosaurs may have been equipped in this way. A second specimen, preserved in 3D, is the holotype of S. holzmadensis.

Rhomaleosauridae is a family of plesiosaurs from the Earliest Jurassic to the latest Middle Jurassic of Europe, North America, South America and possibly Asia. Most rhomaleosaurids are known from England, many specifically from lower Blue Lias deposits that date back to the earliest Jurassic, just at the boundary with the Triassic. In fact, to date only two undisputed rhomaleosaurids were named from outside Europe - the closely related Borealonectes russelli and Maresaurus coccai from Canada and Argentina, respectively. These two species are also the only Middle Jurassic representatives of the family. Rhomaleosauridae was formally named by Kuhn in 1961, originally proposed to include Rhomaleosaurus cramptoni and its relatives, which have short necks and large heads relatively to plesiosauroids like Elasmosaurus and Plesiosaurus, but longer necks and smaller heads relatively to advanced pliosaurids like Pliosaurus and Kronosaurus.

The Whitby Mudstone is a Toarcian geological formation in Yorkshire and Worcestershire, England. The formation, part of the Lias Group, is present in the Cleveland and Worcester Basins and the East Midlands Shelf.

Meyerasaurus is an extinct genus of rhomaleosaurid known from Holzmaden, Baden-Württemberg of southwestern Germany.

<i>Lusonectes</i> Extinct genus of reptiles

Lusonectes is an extinct genus of microcleidid plesiosaur from the Early Jurassic (Toarcian) São Gião Formation of Portugal.

Atychodracon is an extinct genus of rhomaleosaurid plesiosaurian known from the Late Triassic - Early Jurassic boundary of England. It contains a single species, Atychodracon megacephalus, named in 1846 originally as a species of Plesiosaurus. The holotype of "P." megacephalus was destroyed during a World War II air raid in 1940 and was later replaced with a neotype. The species had a very unstable taxonomic history, being referred to four different genera by various authors until a new genus name was created for it in 2015. Apart from the destroyed holotype and its three partial casts, a neotype and two additional individuals are currently referred to Atychodracon megacephalus, making it a relatively well represented rhomaleosaurid.

References

1 2 3 4 5 6 Adam S. Smith (2007). "Anatomy and systematics of the Rhomaleosauridae (Sauropterygia, Plesiosauria)" (PDF). Ph.D. Thesis, University CollegeDublin.
1 2 3 4 5 6 7 Adam S. Smith & Gareth J. Dyke (2008). "The skull of the giant predatory pliosaur Rhomaleosaurus cramptoni: implications for plesiosaur phylogenetics" (PDF). Naturwissenschaften. 95 (10): 975–980. Bibcode:2008NW.....95..975S. doi:10.1007/s00114-008-0402-z. PMID 18523747. S2CID 12528732. Archived (PDF) from the original on 3 February 2022.
↑ Roger B. J. Benson, Hilary F. Ketchum, Leslie F. Noè and Marcela Gómez-Pérez (2011). "New information on Hauffiosaurus (Reptilia, Plesiosauria) based on a new species from the Alum Shale Member (Lower Toarcian: Lower Jurassic) of Yorkshire, UK" (PDF). Palaeontology. 54 (3): 547–571. Bibcode:2011Palgy..54..547B. doi:10.1111/j.1475-4983.2011.01044.x. S2CID 55436528.{{cite journal}}: CS1 maint: multiple names: authors list (link)
↑ 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.
↑ http://palaeo-electronica.org/content/pdfs/504.pdf ^{[ bare URL PDF ]}
↑ Adam S. Smith; Peggy Vincent (2010). "A new genus of pliosaur (Reptilia: Sauropterygia) from the Lower Jurassic of Holzmaden, Germany" (PDF). Palaeontology. 53 (5): 1049–1063. Bibcode:2010Palgy..53.1049S. doi: 10.1111/j.1475-4983.2010.00975.x .
↑ Ellis, Richard (2003). Sea Dragons: Predators of the Prehistoric Oceans. University Press of Kansas. pp. 170–172. ISBN 0-7006-1269-6.

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[Smith07-1] 1 2 3 4 5 6 Adam S. Smith (2007). "Anatomy and systematics of the Rhomaleosauridae (Sauropterygia, Plesiosauria)" (PDF). Ph.D. Thesis, University CollegeDublin.

[SmithDyke08-2] 1 2 3 4 5 6 7 Adam S. Smith & Gareth J. Dyke (2008). "The skull of the giant predatory pliosaur Rhomaleosaurus cramptoni: implications for plesiosaur phylogenetics" (PDF). Naturwissenschaften. 95 (10): 975–980. Bibcode:2008NW.....95..975S. doi:10.1007/s00114-008-0402-z. PMID 18523747. S2CID 12528732. Archived (PDF) from the original on 3 February 2022.

[H.tomistomimus11-3] Roger B. J. Benson, Hilary F. Ketchum, Leslie F. Noè and Marcela Gómez-Pérez (2011). "New information on Hauffiosaurus (Reptilia, Plesiosauria) based on a new species from the Alum Shale Member (Lower Toarcian: Lower Jurassic) of Yorkshire, UK" (PDF). Palaeontology. 54 (3): 547–571. Bibcode:2011Palgy..54..547B. doi:10.1111/j.1475-4983.2011.01044.x. S2CID 55436528.{{cite journal}}: CS1 maint: multiple names: authors list (link)

[Marmornectes-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] ttp://palaeo-electronica.org/content/pdfs/504.pdf ^{[ bare URL PDF ]}

[Meyerasaurus-6] Adam S. Smith; Peggy Vincent (2010). "A new genus of pliosaur (Reptilia: Sauropterygia) from the Lower Jurassic of Holzmaden, Germany" (PDF). Palaeontology. 53 (5): 1049–1063. Bibcode:2010Palgy..53.1049S. doi: 10.1111/j.1475-4983.2010.00975.x .

[ellis-7] Ellis, Richard (2003). Sea Dragons: Predators of the Prehistoric Oceans. University Press of Kansas. pp. 170–172. ISBN 0-7006-1269-6.

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