The north slope of Janusfjellet (Spitrasaurus larseni type) (Jurassic of Norway)

Where: Spitsbergen, Norway (78.3° N, 15.8° E: paleocoordinates 69.5° N, 15.5° E)

• coordinate stated in text

• outcrop-level geographic resolution

When: Dorsoplanites ilovaiskyi–Dorsoplanites maximus ammonoid zone, Slottsmøya Member (Agardhfjellet Formation), Tithonian (152.1 - 145.0 Ma)

• 2.5 metres above the Dorsoplanites Bed, Slottsmøya Member, Agardhfjellet Formation, Janusfjellet. Dorsoplanites ilovaiskyi to Dorsoplanites maximus ammonite zones, Middle Volgian (Tithonian; Nagy & Basov, 1998; Collignon & Hammer, 2012; Gradstein et al. in press).

•To further quantify the stratigraphic occurrence of the vertebrate remains, a laterally continuous, sideritic horizon rich in ammonites (especially Dorsoplanites sp.) and bivalves, and a similarly continuous, yellow silt bed were used as marker beds against which the stratigraphic position of each skeleton was measured. The yellow silt bed was set as 0 m. The Dorsoplanites marker bed occurs 27 m above this yellow layer and 21 m below the top of the Slottsmøya Member (Myklegardfjellet Bed; see Collignon & Hammer, 2012), and occurs in the Middle Volgian D. maximus or D. ilovaiskyi zone. The vertical position of each vertebrate specimen was recorded with a Leica TCR 110 total station with <1 cm error at 100 metre distance and later corrected with respect to dip. The specimen described (SVB 1450) here was found 9 metres below the Dorsoplanites bed and 11.8 metres above the yellow silt layer (Hurum et al. 2012, table 1).

Environment/lithology: deep-water; concretionary, sideritic, black, gray, silty mudstone

• The Slottsmøya Member, which averages 55 to 60 metres in thickness in the study area, consists of dark-grey to black silty mudstone, often weathering to paper shale, and discontinuous silty beds with local occurrences of red to yellowish sideritic concretions as well as siderite and dolomite interbeds (Dypvik et al., 1991a; Hammer et al., 2011; Collignon & Hammer, 2012).

Size class: macrofossils

Collected by PMO expedition in 2004

Collection methods: surface (in situ),

• SVB, Svalbard Museum, Longyearbyen, Norway

Primary reference: E. M. Knutsen, P. S. Druckenmiller, and J. H. Hurum. 2012. Two new species of long-necked plesiosaurians (Reptilia: Sauropterygia) from the Upper Jurassic (Middle Volgian) Agardhfjellet Formation of central Spitsbergen. Norwegian Journal of Geology 92:187-212 [R. Benson/R. Benson]more details

Purpose of describing collection: taxonomic analysis

PaleoDB collection 134762: authorized by Roger Benson, entered by Roger Benson on 16.10.2012, edited by Jonathan Tennant

Creative Commons license: CC BY (attribution)

Taxonomic list

 Sauropterygia - Cryptoclididae
Spitrasaurus larseni n. sp. Knutsen et al. 2012 plesiosaur
Holotype: SVB 1450, disarticulated juvenile plesiosaur skeleton consisting of the basioccipital, right quadrate and incomplete right squamosal, an incomplete jaw and several incomplete associated teeth, an articulated cervical series that is complete from the atlas-axis to the 31st cervical vertebra, and an articulated partial left forelimb
 Ichthyosauria - Ophthalmosauridae
Brachypterygius sp. Huene 1922 ichthyosaur
SESNE 2010.0.1, an incomplete skull