The oldest elasmosaurs (Sauropterygia, Plesiosauria) from Antarctica, Santa Marta Formation (upper Coniacian? Santonian–upper Campanian) and Snow Hill Island Formation (upper Campanian–lower Maastrichtian), James Ross Island

Figures & data

Fig. 1  Map of north-west James Ross Island, where the Snow Hill Island and Santa Marta formations crops out. The black dot numbered 1 is the location where the plesiosaur specimen MLP 11-II-20-4 was discovered; 2 is where specimens MLP 86-X-28-3 and MLP 86-X-28-(2-6) were found. (Illustration modified from Olivero 1992; McArtur et al. 2000; Olivero et al. 2008.)

Fig. 2  Schematic stratigraphic column showing the levels where the elasmosaur materials were collected (modified from McArtur et al. 2000; Olivero et al. 2008).

Table 1 Plesiosaur records from Antarctica. The stratigraphy follows Olivero et al. (2008).

Assignment	Locality	Stratigraphy	Age	Reference
Aristonectes parvidens (Morturneria)	Marambio Island (Seymour)	López de Bertodano Fm. (“molluscan units”)	late Maastrichtian	Chatterjee & Small 1989
Aristonectes sp.	Vega Island (Cape Lamb)	López de Bertodano Fm. (Sandwich Bluff Member)	late Maastrichtian	O'Gorman et al. 2010
Aristonectes cf. parvidens	Vicecomodoro Marambio Island (Seymour)	López de Bertodano Fm. (“molluscan units”)	late Maastrichtian	O'Gorman, Olivero et al. 2012
Mauisaurus sp.	Vega Island (Cape Lamb)	Snow Hill Island Fm. (Cape Lamb Member)	late Campanian–early Maastrichtian	Martin et al. 2007
Elasmosauridae indet.	Marambio Island (Seymour)	López de Bertodano Fm. (“molluscan units”)	late Maastrichtian	Chatterjee & Small 1989
Elasmosauridae indet.	Marambio Island (Seymour)	López de Bertodano Fm. (“molluscan units”)	late Maastrichtian	Martin & Crame 2006
Elasmosauridae indet.	Marambio Island (Seymour)	López de Bertodano Fm. (“Rotularia units”)	late Maastrichtian	Gasparini et al. 1984
Elasmosauridae indet	Marambio Island (Seymour)	López de Bertodano Fm. (“Rotularia units”)	late Maastrichtian	Chatterjee & Small 1989
Elasmosauridae indet.	Marambio Island (Seymour)	López de Bertodano Fm. (“Rotularia units”)	late Maastrichtian	Fostowicz-Frelic & Gazdzicki 2001
Elasmosauridae indet.	James Ross Island (Santa Marta Cove)	Snow Hill Island Fm. (Herbert Sound Member)	late Campanian	this article
Elasmosauridae indet.	James Ross Island (Monolitic Lake)	Santa Marta Fm. (Beta Member) (upper part of the Lachman Crags Member)	early Campanian	this article
Elasmosauridae indet.	Vega Island (Cape Lamb)	Snow Hill Island Fm. (Cape Lamb Member)	late Campanian–early Maastrichtian	O'Gorman, et al. 2008
Elasmosauridae indet.	Vega Island (Cape Lamb)	Snow Hill Island Fm. (Cape Lamb Member)	late Campanian–early Maastrichtian	O'Gorman, Gasparini et al. 2012
Cf. Elasmosauridae	Marambio Island (Seymour)	López de Bertodano Fm. (“molluscan units”)	late Maastrichtian	Martin & Crame 2006
Polycotylidae indet.	James Ross Island	Santa Marta Fm. (Alpha Member) (lower part of the Lachman Crags Member)	late Coniacian? Santonian–early Campanian	D'Angelo et al. 2008
Plesiosauroidea indet.	Vega Island (Cape Lamb)	Snow Hill Island Fm. (Cape Lamb Member)	late Campanian–early Maastrichtian	del Valle et al. 1977
Plesiosauroidea indet.	James Ross Island (The Naze)	Snow Hill Island Fm. (Cape Lamb Member)	late Campanian–early Maastrichtian	del Valle et al. 1977
Plesiosauria indet.	James Ross Island (The Naze)	Snow Hill Island Fm. (Cape Lamb Member)	early Maastrichtian	Martin & Crame 2006
Plesiosauria indet.	Marambio Island (Seymour)	López de Bertodano Fm. (“molluscan units”)	late Maastrichtian	Martin & Crame 2006
Plesiosauria indet.	James Ross Island (Brandy Bay)	Santa Marta Fm. (Alpha Member) (Lachman Crags Member)	late Coniacian? Santonian–early Campanian	Kellner et al. 2011

Fig. 3  Elasmosauridae indet. Material from Santa Marta Formation (Beta Member) and Snow Hill Island Formation (Herbert Sound Member). (a–b) MLP 11-II-20-4 cervical vertebra in (a) left lateral and (b) anterior views. (c–d) MLP 86-X-28-3 cervical vertebra in (c) left lateral and (d) anterior views. (e–h) MLP 86-X-28-(2-6) cervical–pectoral series in (e) right view; (f), first pre-pectoral in ventral view; (g), 10th and 9th pre-pectoral vertebrae in ventral view and (h) 9th pre-pectoral vertebra in anterior view. All scale bars are 20 mm. Anatomical features are abbreviated as follows: anterior zygapophyses—azyg; cervical rib—cr; lateral ridge—lr; neural arch—na; neural channel—nc; neural spine—ns; parapophyses—pa; pectoral vertebrae—pv; ventral foramina—vf; ventral notch—vn.

Table 2 Measurements of specimens MLP 11-II-20-4, MLP 86-X-28-3 and MLP-86-X-28-(2-6). Measurements of vertebral centra (in mm): length (L); height (H); breadth (B); height index (HI) 100*H/L; breadth index (BI) 100*B/L; breadth–height index (BHI) 100*B/H; and vertebral length index (VLI) L/(0.5*(H + B)).

MLP 11-II-20-4	L	H	B	HI	BI	BHI	VLI
Cervical	104	80	118	77	113	148	1.05
MLP 86-X-28-3
Cervical	40	38	56	95	140	147	0.85
Cervical	42	40	–	–	–	–	–
MLP 86-X-28-(2-6)
Cervical	45	46	62	102	138	135	0.83
Cervical	45	44	63	98	140	143	0.84
Cervical	46	45	65	98	141	144	0.84
Cervical	45	44	65	98	144	148	0.83
Cervical	44	48	66	109	150	138	0.77
Cervical	46	45	67	98	146	149	0.82
Cervical	46	48	68	104	148	142	0.79
Cervical	47	48	66	102	140	138	0.82
Cervical	45	44	67	98	149	152	0.81
Cervical	46	49	69	107	150	141	0.78
Pectoral	47	49	79	104	168	161	0.73
Pectoral	–	–	–	–	–	–	–
Pectoral	–	–	–	–	–	–	–

Fig. 4  Plot of vertebral length indices (VLI) of cervical vertebrae of three generalized elasmosaurids and Aristonectes parvidens compared with MLP 86-X-28-(2-6), an Elasmosauridae indet. specimen at the Museo de La Plata in La Plata, Argentina. The Mauisaurus haasti specimen is CM Zfr 115, at the Canterbury Museum, Christchurch, New Zealand. The Morenosaurus stocki is CIT 2802, at the California Institute of Technology, CA, USA. The second Elasmosauridae indet. specimen, MLP 93-I-5-1, is also at the Museo de La Plata, as is the A. parvidens specimen (MLP 40-XI-14-6). The data are drawn from Welles (1943) and O'Keefe & Hiller (2006) as well as the author's own data.

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