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

Where: Spitsbergen, Norway (78.3° N, 15.9° E: paleocoordinates 69.5° N, 15.6° 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 (PMO 219.718) here was found 2.5 metres above the Dorsoplanites bed, and 29.3 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 2010

Collection methods: surface (in situ),

• PMO, Natural History Museum, University of Oslo collection

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 134761: authorized by Roger Benson, entered by Roger Benson on 16.10.2012, edited by Jonathan Tennant

Creative Commons license: CC BY (attribution)

Taxonomic list

Reptilia
 Sauropterygia -
Plesiosauria indet. de Blainville 1835 plesiosaur
PMU 24782 (previously PMU R119), isolated vertebral centrum
Plesiosauroidea indet. Welles 1943 plesiosaur
PMU 24781 comprises an apparently articulated series of two damaged sacrals and 20 caudal vertebrae, together with a highly fractured pelvic girdle, sacral ribs and a femur (possibly Colymbosaurus svalbardensis)
 Sauropterygia - Cryptoclididae
Spitrasaurus wensaasi n. gen. n. sp.
Spitrasaurus wensaasi n. gen. n. sp. Knutsen et al. 2012 plesiosaur
Holotype: PMO 219.718, an articulated postcranial juvenile skeleton including an articulated axial column from the atlasaxis to the 12th dorsal vertebra, cervical and dorsal ribs, numerous gastralia, complete pectoralgirdle and much of the forelimbs, and the right hindlimb.