Plesiosaurus

Genus

Plesiosaurus

Author

De la Beche and Conybeare, 1821

Classification

Sauropterygia
Eosauropterygia
Eusauropterygia
Pistosauroidea
Pistosauria
Plesiosauria
Plesiosauroidea
Plesiosauridae

Age

Late Sinemurian, Early Jurassic

Location

Lyme Regis, Dorset, England

Type species

P. dolichodeirus

Other species

None valid, but several pending revision, including 'P.' macrocephalus

Referred material

To compile

Plesiosaurus was the first plesiosaur discovered and named. For a long time Plesiosaurus was treated as waste-basket taxon. This means that many different specimens were allocated to the genus Plesiosaurus under different species names, even when they were very different. By modern standards, many of these specimens deserve a generic name of their own, or may be of dubious validity entirely. The lumping of many species into the genus Plesiosaurus was initiated during the 1800s when plesiosaurs were first being studied and described. Many species formerly included in Plesiosaurus are now renamed and most of them do not even belong in the family Plesiosauridae. For example, Plesiosaurus’ rostratus was renamed Archaeonectrus, Plesiosaurus’ conybeari was renamed Attenborosaurus.

Storrs (1997) reduced the number of valid species of Plesiosaurus to three. However, two of those have unique features that warrant generic separation: Plesiosaurus’ guilielmiiperatoris is today regarded as Seeleyosaurus, a name reinstated by Grossman (2007), and Plesiosaurus’ brachypterygius is now known by the name of Hydrorion (Grossman, 2007). All this means that at present, Plesiosaurus contains only the single valid species, P. dolichodeirus. Some species arbitrarily referred to Plesiosaurus still remain today, pending revision. Plesiosaurus’ macrocephalus, for example, is possibly a juvenile rhomaleosaurid.

Plesiosaurus belongs to the family Plesiosauridae and was regarded as the sole member of the group for several years. However, recent research into early Jurassic plesiosaurs has revealed a greater generic diversity of plesiosaurids.

The holotype specimen of P. dolichodeirus (Conybeare 1824) is NHMUK 22656, a complete skeleton.

Plesiosaurus dolichodeirus

Species

Plesiosaurus dolichodeirus

Author

Conybeare,1824

Classification

Plesiosaurus

Age

Early Jurassic, Sinemurian

Type location

Lyme Regis, Dorset, UK

Type specimen

NHMUK PV OR 22656

Referred material

BMNH 28332,33287 (Owen, 1865:Plate4,Figures1and 2), 36183(Owen, 1865:Plates1and2), 39490(Owen, 1865:Plate3, Figures1and 3), 39491 (Owen, 1865:Plate3, Figure 2), 41101 (Andrews, 1896:Figure1), R.255 (acompletejaw purchasedfrom theEdgertoncollectionin 1882),R.1313(collected by Mary Anning, 1829; Buckland'sGeology and Mineralogy, "The Bridgewater Treatise," 1837:Plate 16, Figure 2), R.1314 (a well-preservedright forelimb), ?R.1315,R. 1316(Owen, 1865:Plate3, Figures4 and6), R. 1316b(Owen, 1865:Plate 4, Figures 3 and 8), ?R.1330,R.1756 (a partial skeletonwith good right limbs; Lydekker, 1890:277), ?BRSMG Ce17972 (the smallest potential Plesiosaurus skeletonknown; Storrs, in press),JMM FC M 032, NMHN A.-C. 8592, NMING F:8758, OXFUM J.10304,J.13809,J.28586(typical dentariesfrom the Philpott collection,measuredby Owen, 1840a:61),J.28587,TM 13286(Winkler, 1873:Plate 7), YPM 1654 (an isolatedpair of dentarieswith well-preservedteeth), YPM-PU 3 3 5 2 ( a j u v e n i l e s p e c i m e n ) , a n d n u m e r o u si s o l a t e d , b u t f r e q u e n t l y n o n d i a g n o s t i c , bonesassignedto P. dolichodeirusarecontainedin virtually all collectionsof Lias material.

Under construction

Plesiosaurus macrocephalus

Species

'Plesiosaurus' macrocephalus

Author

Owen 1838

Classification

Age

Early Jurassic, Sinemurian

Type location

Lyme Regis, Dorset, UK

Type specimen

NHMUK PV R 1336

Referred material

N/A

The holotype specimen (NHMUK PV R 1336) was first and last described by Owen, 1840. ‘Plesiosaurus’ macrocephalus is probably a juvenile rhomaleosaurid, and certainly doesn’t belong to the genus Plesiosaurus. However, pending revision of the taxon and referral to a different or other existing genus, it is still named ‘Plesiosaurus‘, following Owen.