PBDB Taxon

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Morphology	Ecology and taphonomy	External Literature Search	Age range and collections

Thalassiodracon hawkinsii

Reptilia - Plesiosauria - Pliosauridae

Taxonomy

Plesiosaurus hawkinsii was named by Owen (1840). Its type specimen is BMNH 2018* (lectotype), a skeleton (almost complete skeleton missing distal parts of limbs), and it is a 3D body fossil. Its type locality is Street (general), which is in a Hettangian shallow subtidal limestone/shale in the Blue Lias Formation of the United Kingdom.

It was corrected as Plesiosaurus hawkinsi by Delair (1960); it was recombined as Rhomaleosaurus hawkinsi by Persson (1963); it was recombined as Thalassiodracon hawkinsi by O'Keefe (2001); it was recombined as Thalassiodracon hawkinsii by Benson et al. (2011).

Synonyms

Plesiosaurus eleutheraxon was named by Seeley (1865). Its type specimen is CAMSM J.35181, a set of postcrania (partial postcranial skeleton), and it is a 3D body fossil. Its type locality is Street (general), which is in a Hettangian shallow subtidal limestone/shale in the Blue Lias Formation of the United Kingdom.

It was synonymized subjectively with Thalassiodracon hawkinsii by Storrs and Taylor (1996), Benson et al. (2011).
Plesiosaurus etheridgei was named by Huxley (1858).

It was synonymized subjectively with Plesiosaurus hawkinsii by Lydekker (1889); it was synonymized subjectively with Plesiosaurus hawkinsi by Delair (1960).
Plesiosaurus etheridgii was named by Huxley (1858). Its type specimen is GSM 51235, a skeleton (nearly complete skeleton missing portions of limbs), and it is a 3D body fossil. Its type locality is Cree's Quarry, Street (bed 30), which is in a Rhaetian/Hettangian carbonate limestone in the White Lias Formation of the United Kingdom.

It was synonymized subjectively with Thalassiodracon hawkinsii by Storrs and Taylor (1996), Benson et al. (2011).

Synonymy list

Year	Name and author
1840	Plesiosaurus hawkinsii Owen p. 57
1851	Plesiosaurus hawkinsii Mantell p. 143
1858	Plesiosaurus etheridgii Huxley
1858	Plesiosaurus etheridgei Huxley p. 281
1858	Plesiosaurus etheridgii Huxley p. 281
1859	Plesiosaurus hawkinsii Owen p. 147
1861	Plesiosaurus hawkinsii Owen p. 246
1865	Plesiosaurus etheridgii Seeley p. 50
1865	Plesiosaurus hawkinsi Seeley p. 50
1865	Plesiosaurus eleutheraxon Seeley p. 353 figs. pl. 14
1869	Plesiosaurus hawkinsii Seeley p. 120
1869	Plesiosaurus eleutheraxion Seeley pp. 121, 137
1889	Plesiosaurus eleutheraxon Lydekker p. 259
1889	Plesiosaurus hawkinsii Lydekker p. 260 figs. 77, 79, 80
1960	Plesiosaurus hawkinsi Delair p. 54
1960	Plesiosaurus eleutheraxon Delair p. 57
1963	Rhomaleosaurus hawkinsi Persson p. 21
2001	Thalassiodracon hawkinsi O'Keefe p. 10
2011	Thalassiodracon hawkinsii Benson et al. figs. 1-4

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Rank	Name	Author
kingdom	Animalia	()
—	Bilateria
—	Eubilateria	Ax 1987
—	Deuterostomia
phylum	Chordata	Haeckel 1874
subphylum	Vertebrata
superclass	Gnathostomata
—	Osteichthyes	()
subclass	Sarcopterygii	()
subclass	Dipnotetrapodomorpha	(Nelson 2006)
subclass	Tetrapodomorpha	()
—	Tetrapoda
—	Reptiliomorpha
—	Anthracosauria

Rank	Name	Author
subclass	Amphibiosauria	Kuhn 1967
—	Cotylosauria	()
—	Amniota
—	Sauropsida
class	Reptilia
subclass	Eureptilia	()
—	Romeriida
—	Diapsida	()
suborder	Sauropterygia
order	Plesiosauria	de Blainville 1835
superfamily	Pliosauroidea	Welles 1943
family	Pliosauridae	Seeley 1874
genus	Thalassiodracon	Storrs and Taylor 1996
species	hawkinsii	()

If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.

†Thalassiodracon hawkinsii Owen 1840

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Invalid names: Plesiosaurus eleutheraxon Seeley 1865 [synonym], Plesiosaurus etheridgei Huxley 1858 [synonym], Plesiosaurus etheridgii Huxley 1858 [synonym]

Diagnosis

Reference	Diagnosis
R. B. J. Benson et al. 2011	"Small plesiosaurian (ca. 2 m long) that differs from other taxa of similar provenance by its broad, interdigitating premaxilla-frontal contact, frontal makes narrow anterodorsal contribution to orbit margin, parietal extends to orbital midlength, short posteroventral process of the postorbital, coossified parabasisphenoid, cultriform process forms diamondshaped ventral platform, 31 cervical, 22 dorsal (including three ‘pectorals’), three sacral, and 33 caudal vertebrae. Possesses the following autapomorphies: four premaxillary alveoli (a local autapomorphy that is absent in all closely related taxa), closure or reduction of the ?endolymphatic foramen on the medial surface of the exoccipital, supraoccipital portions of semicircular canals fully enclosed in bone."

Measurements

No measurements are available

Composition:

hydroxyapatitesuperf

Environment:

marinesuperf

Locomotion:

actively mobilesuperf

Life habit:

nektonicsuperf

Depth habitat:

surfaceo

Diet:

carnivoresuperf

Reproduction:

viviparouso

Dispersal:

direct/internalsuperf

Created:

2005-11-07 12:13:24

Modified:

2009-07-25 10:49:01

Source: superf = superfamily, o = order

References: Kiessling 2004, Hampe 2005

Age range: Hettangian or 201.30000 to 199.30000 Ma

Collections (7 total)

Time interval	Ma	Country or state	Original ID and collection number
Rhaetian - Hettangian	208.5 - 199.3	United Kingdom (England)	Plesiosaurus etheridgii (96605) Plesiosaurus hawkinsii (96604 96608)
Hettangian	201.3 - 199.3	United Kingdom (England)	Plesiosaurus hawkinsii (149321)
Early/Lower Hettangian	201.3 - 196.5	United Kingdom (England)	Plesiosaurus hawkinsii, Plesiosaurus eleutheraxon (type locality: 119083) Plesiosaurus sp. (110213)
Early/Lower Hettangian - Early/Lower Pliensbachian	201.3 - 183.0	United Kingdom (England)	Plesiosaurus hawkinsi (118938)