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

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RankNameAuthor
kingdomAnimalia()
—Bilateria
—EubilateriaAx 1987
—Deuterostomia
phylumChordataHaeckel 1874
subphylumVertebrata
superclassGnathostomata
—Osteichthyes()
subclassSarcopterygii()
subclassDipnotetrapodomorpha(Nelson 2006)
subclassTetrapodomorpha()
—Tetrapoda
—Reptiliomorpha
—Anthracosauria
RankNameAuthor
subclassAmphibiosauriaKuhn 1967
—Cotylosauria()
—Amniota
—Sauropsida
classReptilia
subclassEureptilia()
—Romeriida
—Diapsida()
suborderSauropterygia
orderPlesiosauriade Blainville 1835
superfamilyPliosauroideaWelles 1943
familyPliosauridaeSeeley 1874
genusThalassiodraconStorrs and Taylor 1996
specieshawkinsii()

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.

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Invalid names: Plesiosaurus eleutheraxon Seeley 1865 [synonym], Plesiosaurus etheridgei Huxley 1858 [synonym], Plesiosaurus etheridgii Huxley 1858 [synonym]
Diagnosis
ReferenceDiagnosis
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."