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Additions to the diversity of elasmosaurid plesiosaurs from the Upper
Cretaceous of Antarctica
Rodrigo A. Otero
a,
⁎, Sergio Soto-Acuña
a,b
, Alexander O. Vargas
a
, David Rubilar-Rogers
b
,
Roberto E. Yury-Yáñez
c
,CarolinaS.Gutstein
d
a
Red Paleontológica U-Chile, Laboratorio de Ontogenia y Filogenia, Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Santiago, Chile
b
Área Paleontología, Museo Nacional de Historia Natural, Casilla 787, Santiago, Chile
c
Laboratorio de Zoología de Vertebrados, Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Santiago, Chile
d
Laboratorio de Ecofisiología, Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Santiago, Chile
abstractarticle info
Article history:
Received 16 April 2013
Received in revised form 4 July 2013
Accepted 18 July 2013
Available online 12 August 2013
Handling Editor: P. Eriksson
Keywords:
New plesiosaurs
Diversity
Uppermost Cretaceous
Antarctica
Three specimens of elasmosaurid plesiosaurs (Sauropterygia, Plesiosauria) from Upper Cretaceous beds of
Antarctica are described here. These include postcranial remains of a single adult individual recovered from
late Maastrichtian beds of Marambio (=Seymour) Island, possessing a distinctive combination of features: cer-
vical vertebrae having centra with a triangular outline in transverse section, a vertical groove on the rostral and
caudal edge of theneural spines, and a deep articulation overthe neural arch for the following postzygapophysis,
while the scapula shows an unusually large and anteriorly recurved dorsal process. This combination of features
is unknown in any adult, postcranial elasmosaurid genus recovered to date in the Upper Cretaceous of the
Weddellian Biogeographic Province and could represent a new form. Additional specimens from James Ross
Island comprise the first record of an Aristonectinae (Plesiosauria, Elasmosauridae) in late Campanian beds,
being the oldest known record of this sub-family. Finally, a third specimen from the same ageand locality reveals
the presence of very-long necked elasmosaurids with affinities to typical representatives from the Upper
Cretaceous of the Northern Hemisphere. These findings add to the known diversity of Upper Cretaceous
elasmosaurids in high latitudes of the Southern Hemisphere.
© 2013 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
1. Introduction
Plesiosauria (Reptilia, Sauropterygia) from Antarctica are known
since the seventies. The firstreportisduetoDel Valle et al. (1977)
who mentioned the presence of indeterminate plesiosaurs on James
Ross and Vega Islands, east of the Antarctic Peninsula. Later, Chatterjee
and Zinsmeister (1982) mentioned the first remains of these reptiles
in Marambio (=Seymour) Island, also east of the Antarctic Peninsula.
Gasparini et al. (1984) described associated postcranial remains of a
single individual recovered from the latter island, this they regarded
as a different morphotype from previously known elasmosaurids,
although no genus or species was proposed. These records were
discussed by Gasparini and Goñi (1985) in a regional context together
with previous Upper Cretaceous records from Argentina and Chile.
The first Antarctic species described was ‘Turneria seymourensis’
Chatterjee and Small (1989) from late Maastrichtian beds of Marambio
Island, based on a partial skull and associated cervicals. This was later
re-named as ‘Morturneria seymourensis’by Chatterjee and Creisler
(1994) due to duplication of the genus name in another taxon.
Fostowicz–Frelik and Gaździcki (2001) described new plesiosaur
remains of a probable single specimen, recovered from Marambio
Island. Based on histological sections and the morphology of the recov-
ered portions, these authors indicated that the specimen was small
(about 2 m in length) and probably a sub-adult individual, while several
morphologic characters, especially the tibia and the femoral head,
where considered similar to those of the species Mauisaurus haasti
Hector (1874), from the Campanian of New Zealand. Thereafter,
Gasparini et al. (2003) re-described the holotype of Aristonectes
parvidens Cabrera (1941), a very strange plesiosaur with uncertain
affinities at that time, recovered from Maastrichtian beds of Chubut,
Argentina. Besides the inclusion of A. parvidens among the
elasmosaurids, additional materials referred to by Gasparini et al.
(2003) to this species included finds in the late Maastrichtian of Chile
(Casamiquela, 1969), while the holotype of ‘Morturneria seymourensis’
from Antarctica (comprised by a juvenile specimen) was considered
as a junior synonym of A. parvidens. Additional material of
elasmosaurids from Seymour Island was described by Martin and
Crame (2006) including associated vertebrae with ribs and fragments
of propodials of a single individual, a second specimen comprising a
partial postcranial skeleton and one last specimen comprising a partial
propodial. The latter authors also mentioned an additional specimen
referred to cf. Elasmosauridae as well as seven specimens referred to
Plesiosauria indet., from James Ross and Seymour Islands. A pelvic girdle
Gondwana Research 26 (2014) 772–784
⁎Corresponding author.Tel.: +56 9 8 2981487.
E-mail address: paracrioceras@gmail.com (R.A. Otero).
1342-937X/$ –see front matter © 2013 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.gr.2013.07.016
Contents lists available at ScienceDirect
Gondwana Research
journal homepage: www.elsevier.com/locate/gr
referred to Polycotylidae indet. was also recovered from Coniacian beds
on James Ross Island (D'Angelo et al., 2008). Additional finds of
Santonian age on James Ross Island include scattered postcranial
remains referred to Plesiosauria indet. (Kellner et al., 2011). The oldest
elasmosaurids from James Ross Island were described by O'Gorman
(2012), having a late Coniacian to late Campanian age. On Vega Island
(east of James Ross Island), other elasmosaurids have been recorded,
including one articulated specimen referred to the genus Mauisaurus
Hector (1874) by Martin et al. (2007). Postcranial remains referred to
Aristonectes were reported by O'Gorman et al. (2010),alsofromJames
Ross. Finally, O'Gorman et al. (2013) described the first postcranial skel-
eton of Aristonectes from late Maastrichtian beds of Marambio Island.
Despite the abundant records of plesiosaurs in Marambio, James Ross,
and Vega Islands, only two genera have so far been discussed as being
present in Antarctica, Aristonectes (represented by the specimens referred
to Aristonectes cf. parvidens and ‘Morturneria seymourensis’), and a few
specimens referred to Mauisaurus. The present paper describes three
new specimens: a novel morphotype based on a fragmentary postcranial
skeleton from late Maastrichtian strata of Marambio Island; an indetermi-
nate, very-long necked elasmosaurid from late Campanian beds of
JamesRossIslandwithaffinities to Upper Cretaceous, North American
elasmosaurids, and the first record of an aristonectine in late Campanian
strata of James Ross Island, representing the oldest record of the subfamily
in Antarctica and one of the oldest in the Weddellian Biogeographic
Province (Zinsmeister, 1979: WBP), contributing to fill the stratigraphic
gap of aristonectines, previously known only in the Santonian and the
Maastrichtian.
2. Localities and geologic setting
JamesRossIsland(64°10′S; 57°45′W) is located in the northeastern
part of the Antarctic Peninsula, being the larger island of the homony-
mous Archipelago. On the other hand, Marambio Island (64°16′05″S;
56°42′38.8″W) is located 15 km southeast of James Ross Island
(Fig. 1). Both, together with Vega and Snow Hill Islands, include
outcrops of the Marambio Group (Rinaldi, 1982; Olivero, 2012,and
references therein) which comprises Upper Cretaceous–Danian strata
deposited on a large shelf of the Weddell Sea. From base to top, the
Marambio Group includes the following units.
2.1. Santa Marta Formation (Olivero et al., 1986)
Marine volcaniclastic and epiclastic shelf sediments that reach a thick-
ness of ca. 1200 m. It was originally divided into three informal members
(Alpha, Beta, and Gamma) (Olivero et al., 1986) based on distinctive
lithofacies. The age of this unit was assigned to the Santonian–early
Campanian for the Alpha member based on ammonoids, while the Beta
and Gamma members were assigned to the early/late Campanian, and
early Campanian–early Maastrichtian, respectively.
2.2. Snow Hill Island Formation (Pirrie et al., 1997)
Poorly lithified gray sandy mudstones with well-lithified, fine-grained
sandstones and very fossiliferous concretions that reach a minimum
thickness of ca. 610 m. Based on the fossil content of palynomorphs and
ammonoids, a late Campanian to ?late Maastrichtian age was originally
assigned to the unit (Pirrie et al., 1997). Outcrops for this unit are present
in the vicinity of Santa Marta Cove (Olivero et al., 1986). Subsequently, the
former Gamma member of the Santa Formation was laterconsideredas
part of the Snow Hill Island Formation by Olivero (2012).
Remains of a single plesiosaur individual (SGO.PV.6579) were found
near Santa Marta Cove (63°55′10″S; 57°53′24″W) on January 2012 by
some of the authors of this paper (A.V.M., D.R.R., R.Y.Y., R.A.O.) and
excavated from siltstone beds consistent with the upper part of the
Gamma member (Lithofacies Association E, sensu Scasso et al., 1991)
originally referred to the Santa Marta Formation (Olivero et al., 1986),
now currently included in the Snow Hill Island Formation. A second
specimen (SGO.PV.6508) comprising an isolated vertebra was found
by A. Llanos (Universidad de Chile) almost 2 km east of the previous
locality (63°54′42″S; 57°50′55″W) being probably hosted in the same
unit judging from the low dispersion of the fragments which indicate
little transport.
2.3. Haslum Crag Sandstone (Olivero et al., 2008)
Originally defined by Pirrie et al. (1997) as the upper member
(Haslum Crag Member) of the Snow Hill Island Formation, it comprises
gray to green bioturbated muddy sandstones with sulphurous nodules
as well as large concretions, intercalated with thin tuff beds. Glauconite
Fig. 1. Mapof the Antarctic Peninsula, indicating the location of the fossil sites on Marambio and James Ross Islands, as well as a geological sketchmap of the study area(based on Olivero,
(2012)).
773R.A. Otero et al. / Gondwana Research 26 (2014) 772–784
beds are present in its basal half. Ammonoids and palynomorphs
indicate a late Campanian–early Maastrichtian age for this unit. The
Haslum Crag Member of the Snow Hill Island Formation (Pirrie et al.,
1997) waselevated to formation status and differentiated as the Haslum
Crag Sandstone by Olivero et al. (2008).
2.4. López de Bertodano Formation (Rinaldi et al., 1978)
This unit crops out in the southwestern half of the Marambio Island,
comprising mainly friable sandy siltstones with a yellow to gray color,
variable in hardness, but relatively constant in grain size and mud
percentage (Macellari, 1988). The age of this formation was assigned by
the latter author to the Maastrichtian–Paleocene, based on mollusks
(Zinsmeister, 1979, 1982), microfossils (Huber, 1988) and palynomorphs
(Askin, 1989), and thereafter constrained to the latest Maastrichtian
based on different stratigraphic criteria (Crame et al., 2004). The López
de Bertodano Formation was divided into 10 informal units (Macellari,
1984, 1988), named from base to roof as Klb1 to Klb9 which are late
Maastrichtian in age, while the uppermost KTplb10 includes strata of
Paleocene age. Specimen SGO.PV.6523 was recovered from the upper
portion of the Klb9 unit, and was collected during January of 2011 by
one of the authors (RAO).
3. Materials and methods
Two of the studied specimens (SGO.PV.6523 and SGO.PV.6508) in-
clude cervical centra. Their proportions were evaluated using a bivariate
graphic analysis following O'Gorman et al. (2013). The indices here
considered are those proposed by Welles (1952), particularly the
height/length ratio (HI = 100 ∗H/L), the breadth/length ratio (BI =
100 ∗B/L), as well as the rate of vertebral elongation (VLI = 100 ∗L/
(0.5 ∗(H + B))). Since SGO.PV.6523 belongs to an adult individual,
comparisons were carried out considering adult representatives from
the Upper Cretaceous of North America, particularly Hydrotherosaurus
alexandrae,andElasmosaurus platyurus,aswellasCallawayasaurus
colombiensis, from the Upper Cretaceous of Colombia (measurements
of these specimens were taken from Welles, 1943, 1952, 1962). Also,
adult elasmosaurids from the WBP were included, particularly the holo-
type of Tuarangisaurus keyesi (measurements from Wiffen and Moisley
(1986)) and the holotype of Kaiwhekea katiki Cruickshank and Fordyce,
2002 (measurements taken directly from the specimen), both from the
Maastrichtian of New Zealand. Futabasaurus suzukii,fromtheSantonian
of Japan, was also included (measurements taken from Sato et al.
(2006)). Phylogenetic analysis was not carried out since specimen
SGO.PV.6523 is very fragmentary, thus, making it only scorable for a
few characters.
For comparison of the SGO.PV.6508 belonging to a young individual
from late Campanian beds of James Ross Island, juvenile representatives
from the Upper Cretaceous of North America were selected including
the type materials of ‘Cimoliasaurus maccoyi’,‘Leurospondylus ultimus’,
and ‘Aphrosaurus furlongi’(measurements from Brown, (1913);
Welles, (1943);Kear, (2005)) currently considered as indeterminate
elasmosaurids due to their ontogenetic stage, which allows assignations
to be questioned (Kear, 2002; O'Keefe and Hiller, 2006; Sato and Wu,
2006). In addition, young individuals from the WBP include: 1) the
type material of ‘Morturneria seymourensis’(measurements from
Chatterjee and Small, (1989)) from the late Maastrichtian of Antarctica,
2) a young indeterminate elasmosaurid from the late Campanian (Beta
Member) of James Ross Island (measurements from O'Gorman,
(2012)), 3) the young specimen SGO.PV.260 from the late Maastrichtian
of central Chile, referred to Aristonectes sp. by Otero and O'Gorman
(2013), and 4) the juvenile specimen CM Zfr 115 referred to Mauisaurus
haasti from the late Campanian of New Zealand (measurements from
Hiller et al. (2005)).
Finally, SGO.PV.6579 was directly compared with specimens of the
genus Aristonectes (SGO.PV.957, adult, and SGO.PV.260, juvenile)
(Suárez and Fritis, 2002;Otero et al., 2012), both recovered from late
Maastrichtian beds of the Quiriquina Formation in central Chile.
Anatomical abbreviations. af, anterior articular facet of the vertebra; ag,
anterior portion of the neural spine groove; aps, anterior process of the
scapula; c2, cervical vertebra 2; c3, cervical vertebra 3; c5, cervical verte-
bra 5; cr, caudal rib; dfp, deep heart-shaped facet for postzygapophyses;
dps, dorsal process of the scapula; fha, facets for the haemal arches; g,
gastralium; nc, neural canal; ns, neural spine; pc2; fragment of vertebra
posterior to c2; pc3, fragment of vertebra posterior to c3; pg, posterior
portion of the neural spine groove; pna, facets for pedicels of the neural
arch; poz, postzygapophysis; prz, prezygapophysis; r, rib; rf, rib facet; vf,
ventral foramina; vn, ventral notch.
Institutional abbreviations.SGO.PV.,ColeccióndePaleontologíade
Vertebrados, Área de Paleontología, Museo Nacional de Historia Natural,
Santiago, Chile; MLP, Museo de La Plata, Argentina; MCS, Colección del
Museo de Cinco Saltos, Río Negro, Argentina; CM Zfr, Canterbury
Museum, Christchurch, New Zealand; ZPALR., Institute of Paleobiology,
Polish Academy of Sciences, Warsaw, Poland.
4. Systematic paleontology
DIAPSIDA Osborn, 1903.
SAUROPTERYGIA Owen, 1860.
PLESIOSAURIA de Blainville, 1835.
ELASMOSAURIDAE Cope, 1869 (sensu Ketchum and Benson, 2010).
Elasmosauridae gen. et sp. indet.
(Figs. 2–4).
4.1. Material
SGO.PV.6523: Postcranial remains of a single adult individual,
including remains of 9 mid-to-posterior cervical vertebrae (6 of them
preserving parts of their centra), the right scapula, several fragments
of ribs and gastralia, and one phalanx.
4.2. Locality, geologic unit and age
Central part of Marambio Island, Antarctica, about 1550 m south of
López de Bertodano Bay. Klb9 unit, López de Bertodano Formation
(Macellari, 1984), latest Maastrichtian.
4.3. Ontogenetic observations
The studied specimen has cervical centra with tightly fused neural
arches, without traces of sutures between them. This is considered as in-
dicative of an adult stage (Brown, 1981). On the other hand, the unique
recovered phalanx shows a poor ossification with a weak periosteal
surface. Such a condition was described by Caldwell (1997) as a feature
of adult limb morphology, because ossification is generally delayed.
Based on these observations, we consider specimen SGO.PV.6523 as a
near-adult individual. This allows direct comparisons with the species
Aristonectes parvidens Cabrera (1941),K. katiki Cruickshank and
Fordyce (2002),Mauisaurus haasti Hector (1874) (referred specimen
CM Zfr 115), and T. keyesi Wiffen and Moisley (1986), all of them from
the Upper Cretaceous of the WBP and described as adult or near-adult
specimens. SGO.PV.6523 can be also compared with other Upper
Cretaceous adult elasmosaurids from Argentina and New Zealand
where the scapula is preserved.
4.4. Cervical vertebrae
Nine incomplete vertebrae are preserved, with six of them preserv-
ing the centrum or at least part of it, while two additional centra are
represented by fragments of prezygapophyses that do not match any
other vertebra. A fragment of a posterior cervical centrum is preserved
in the block that hosts the scapula, followed by a last preserved centrum
774 R.A. Otero et al. / Gondwana Research 26 (2014) 772–784
in the same block. An isolated portion of a centrum lacking the neural
arches and cervical ribs was also collected but not figured here since it
is not informative. The pedicels for the neural arches are thin in all
cases, indicating that no rib attachment is present in the neural arch,
thus, discarding them as pectoral or dorsal centra. Vertebrae including
both neural spines and part of the centrum have been arranged based
on their respective lengths (Table 1), being also named c1 to c5 from
the anteriormost to the posterior element. Neural spines have a vertical
groove along their anterior, and dorsal posterior borders, with a
conserved depth along each groove (Fig. 3). In the anterior groove two
lateral keels are developed on each side, with the anterior left one
being slightly more prominent than the right one. The anteriormost
Fig. 2. Elasmosauridaegen. et sp. indet. (SGO.PV.6523). Marambio Island,Antarctica. Lópezde Bertodano Formation, Klb9, lateMaastrichtian.Left view of the preserved centra. A, posterior
cervical centra hosted in the block of the scapula (c5, left). B, posterior cervical vertebra (c4). C, D, fragmentary, mid-cervical vertebrae (c2 and c3 from right to left, respectively).
E, anteriormost cervical vertebra preserved (c1). Scale bar represents 50 mm.
Fig. 3. Elasmosauridae gen.et sp. indet. (SGO.PV.6523). Anteriormost cervical vertebra c1. A, anterior view. B, dorsal view. C, posterior view showingits transverse section. D, cervical ver-
tebra c2 in anterior view. E, posterior view of c2 and a fragment of the immediately posteriorneural arch in anatomical position.F, cervical vertebrac3 in anterior view.G, posterior view of
c3 and a fragment of the immediately posterior neural archin anatomical position. H, cervical vertebrac4 in posterior view showing its transverse section. I, detailof the neural arch of c1.
Scale bars represent 50 mm, and 10 mm in I.
775R.A. Otero et al. / Gondwana Research 26 (2014) 772–784
vertebra (c1) is the best preserved cervical (Fig. 3A–C), although the
neural spine lacks its dorsal end (Fig. 3B). This centrum has the left
part of its posterior articular facet absent, allowing a view of its
transverse outline in posterior view (Fig. 3C), which has an obtuse
angle between the vertical neural spine and the medial surface of the
centrum. The latter is unusually large and reaches 157°, conferring a
slightly triangular outline to the transverse section of the centrum.
The anterior and posterior articular facets are larger than the rest of
the centrum, and they have bilobed outlines with a ventral notch,
which is typical of the Elasmosauridae (Gasparini et al., 2003). The
Fig. 4. Elasmosauridae gen.et sp. indet. (SGO.PV.6523). A, detail of theposterior cervical c4 in left dorsoposterior view, for observation of the cervical rib facet. B, right lateral view of the
posterior cervical centrum c5. C, dorsal view of c5. D, right lateral viewof the right scapula. E, right lateral outline of the right scapula based on the preserved portions and the cast in the
sandstone matrix. F,posterior view of theright scapula. G,cross section viewof rib and gastraliumhosted in the blockof the scapula. H, ventral view of theprevious grastralium. I, isolated
phalanx in dorsal view. J, distal view. K, lateral view. Scale bars equal 50 mm.
Table 1
Measurements of vertebral centra in the studied specimens. Absence of measurements is denoted with a line, while non-applicable indexes are denoted by ‘NA’. Vertebral Length Index
(VLI) = L / (0.5 ∗(H + B)) from Brown (1981); index of ratio between height and length (HI) = (100 ∗H/L) and index of ratio between breadth and length (BI) = (100 ∗B/L) from
Welles (1952).
Length Height Breadth VLI HI BI
SGO.PV.6523 Cervicals 64.3 62.4 95.8 81.289507 97.0451011 148.989114
66 –– – – –
68.5 82 75.5 86.984127 119.708029 110.218978
74.2 –– – – –
Pectoral 68.5 73.3 –NA NA NA
SGO.PV.6508 Cervical 52.2 39.5 54.6 110.945802 75.6704981 104.597701
776 R.A. Otero et al. / Gondwana Research 26 (2014) 772–784
same features can be observed in the following c2 and c3 (Fig, 3D–G),
reaching angles slightly over 150°, and becoming a little narrower in
the last cervical c4, which has the lowest angle of 150° (Fig. 3H). No
lateral keels are observed in any centra, suggesting that the preserved
vertebrae can belong to posterior positions along the neck, which is
also supported for the associated occurrence of trunk elements such as
the scapula, several ribs and gastralia. Another striking feature is the
presence in the neural spines of a deep, semi-cylindrical articulation
above the neural canal, which locks with the postzygapophyses of the
immediately anterior vertebra. In anterior view, this morphology is
similar to most elasmosaurids, which have prominent and recurved
prezygapophyses, although the articulation goes deep in the neural
spine, parallel to the neural canal. Also, it is distinctively broad and
causes a lateral bulk at the base of the neural spine over the neural
canal, giving the base of the spine a more massive appearance compared
with its dorsal portion. The inner surface of the articulation (Fig. 3I) has
a heart-shaped excavation in its ventral portion that interlocks with the
ventroposterior contour of the postzygapophyses. Also, the ventral end
of the anterior neural groove reaches the middle portion of the heart-
shaped excavation. This is especially visible on the c2 vertebra and the
following posterior fragment attached in the same block. In addition,
the pedicels of the neural arches are very thin, leaving a broad space
for the neural canal which is subcircular in transversal section. Cervical
rib facets alsohave interesting features, including short and sub-circular
facets witha small posterior projection(Fig. 4A). An additional centrum,
probably a posterior cervical, is hosted in the block of the scapula. This
appears to be nearly circular in articular view, although it lacks part of
its right, dorsolateral surface, making it difficult to evaluate its contour
(Fig. 4B, C). Its neural canal is broad, bearing delicate and thin pedicels
for the neural spine, suggesting that this is still a cervical centrum
instead of a pectoral or dorsal vertebra, which normally shows a thick-
ening of the neural arch pedicels due to the presence of transverse
processes for rib attachment.
4.5. Scapula
Only the right scapula is preserved (Fig. 4D–F). Although it isincom-
plete, part of the ventral process can be evaluated since its cast is
preserved in the sandstone matrix. The ventral process seems to be
short and anteriorly rounded, but its medial features cannot be evaluat-
ed since this portion is not preserved. The most obvious feature in the
scapula is the presence of a very high, slender and anteriorly angled
dorsal process. Although this is incomplete, its posterior margin is deli-
cate and thin, which indicates that the dorsal process does not extend
far posteriorly, while the dorsal end preserves part of the entire contour
of the scapula, allowing inference of its outline (Fig. 4E). The anterior
portion of the scapula is incomplete, but its lateral outline is partially
preserved in the sandstone matrix. In posterior view, the dorsal process
diverges from the horizontal plane at almost 75° (Fig. 4F).
4.6. Ribs and gastralia
Four fragments of large and thin bones are recognized among the
studied material. Three of them comprise bones with a medullary
cavity, reason why these are interpreted as ribs, while an additional
bone has a pachyostotic cross-section, being interpreted as a gastralium,
following the criteria of O'Keefe et al. (2011). The ribs have a cross-
section that is variable between rhomboidal to triangular, with a thin
periosteal surface. On the other hand, the gastralia seems to have a
distal portion that is U-shaped in cross-section, with a ventral groove
(Fig. 4G, H).
4.7. Phalanx
A single phalanx was recovered directly associated with the other
remains. This is elongated and massive, with a polygonal articular
facet (the proximal facet being best preserved). This element is poorly
ossified, with a limited periosteal surface that seems to be mostly
absent, rather than being removed before burial.
4.8. Remarks
Although the specimen is a fragmentary postcranial skeleton, the
combination of morphologic characters emerges as unique among any
known adult plesiosaur from the WBP: features of the cervical vertebrae
include a neural spine with a groove along its anterior and posterior
edge, leaving two edges with the left one slightly prominent with
respect to the right; presence of a deep, concave and semi-cylindrical
articular facet in the neural spines over the prezygapophyses, having a
heart-shaped facet in its ventral margin that interlocks with the
postzygapophysis of the immediately anterior vertebra, giving a thick
appearance to the basal portion of the neural spine. In addition, mid-
to-posterior cervical centra have a transversal section with a triangular
shape, being higher than broad, having their dorsomedial surfaces
angled between 150–160° with respect to the neural spine. The articular
facets become very expanded, having a bilobed outline with a ventral
notch (Fig. 3). Other distinctive characters are present in the scapula,
which has an unusually high, slender and anteriorly recurved dorsal
process, while the ventral process seems to be short. Additional mor-
phologies contributing to a unique combination of characters include:
neural arches with very thin and delicate pedicels; cervical ribs having
oval facets and displaced into the posterior half of the centrum; the
presence of trunk ribs with a triangular cross-section; pachyostotic
gastralia with a U-shaped cross-section; and proximal phalanges being
elongated and massive.
Elasmosauridae indet.
(Fig. 5A–D).
4.9. Material
SGO.PV.6508: one isolated cervical vertebral centrum. Santa Marta
Cove, N of Shark Stream, James Ross Island. Lithofacies Association E,
Gamma member, Santa Marta Formation (sensu Scasso et al., 1991),
late Campanian (Olivero, 1992).
4.10. Description
A damaged centrum, which is preserved in four fragments. The
centrum is broader than long and longer than high (Table 1), markedly
platycoelous, having a ventral notch and bilobed contour in articular
view. The bases of the neural arch pedicels are sub-triangular, leaving
a space for the neural canal that is comparatively broader in the poste-
rior margin. The base of the neural arch is conspicuously broad,
representing nearly 50% of the total breadth of the centrum. The rib
facet can be observed in lateral view, having an oval contour. No lateral
keel can be observed. In ventral view, there are two foramina placed in a
sub-central position, with an oval contour, separated by a thin bone
bridge without a medial keel between them. The small size of the
centrum andthe evident rib facet (notfused) indicate that this belonged
to a juvenile individual (Brown, 1981).
Aristonectinae Otero et al. (2012).
Aristonectinae indet.
(Fig. 6A–O, Q).
4.11. Material
SGO.PV.6579: Fragmentary postcranial skeleton preserving eight
fragmentary caudal centra, two articular propodial heads (likely
femora), an epipodial (likely a fibula), ventral portion of the right
ilium, partial left pubis, and several rib portions.
777R.A. Otero et al. / Gondwana Research 26 (2014) 772–784
4.12. Ontogenetic observations
The specimen has caudal centra bearing ribs unfused to the centra.
Additionally, the preserved portions of the ilium and pubis are smaller
than other known juvenile specimens of Aristonectes (particularly the
SGO.PV.260, described by Otero et al. (2012)). Based on these facts,
we consider this specimen to be a juvenile individual following the
criteria of Brown (1981).
4.13. Caudal centra
Eight incomplete portions of caudal centra were recovered. The most
complete centra (Fig. 6A–H) show that theseare broader than high and
higher than long. In lateral view the rib facets occupy almost thewhole
length of the centrum, leaving a small gap before the posterior articular
face. Rib facets are oval and excavated into the centra. In ventral view,
one central foramen can be observed. The posteroventral margin of
the centra has two well-marked, semicircular facets for the haemal
arches, confirming its caudal position. In dorsal view, these centra
have large facets for the pedicels of each neural arch. These are massive,
anteriorly broader and reaching the margin of the anterior articular face,
while its posterior endis reduced in breadth giving a triangular outline
to the pedicelar facet, and does not reach the posterior articular margin
of the centrum.
The anterior articular face has a distinctive octagonal outline defined
by the surface of the neural canal, the surface between the neural arch
pedicels and the rib facets, therib facet itself, and the flat ventral surface
of the centrum between the keels that rise from the facets for the
haemal arches (Fig. 6A, E). This octagonal articular outline has been
found to be diagnostic of the genus Aristonectes (Otero et al., 2012;
O'Gorman et al., 2013), although the caudal vertebrae in the latter
genus are notoriously broader than high, while the vertebrae of the
SGO.PV.6579 are slightly broader than high.Additional materials belong
to fragments of caudal centra with similar features (Fig. 6I, J).
4.14. Propodials
Two different proximal portions were recovered (Fig. 6K, L). These
are fragmentary, although they do show the longitudinal section of
the articular head which has a circular outline, thus indicating that the
articular head was hemispherical. Each articular head has a distal
constriction, indicating that the latter was prominent with respect to
the diaphysis, as occurs in the lectotype of Mauisaurus haasti (Hector,
1874; Welles, 1962), in the propodials of Aristonectes sp. (Otero et al.,
2012), as well as in another Antarctic specimen (ZPAL R.8/11) previous-
ly described by Fostowicz–Frelik and Gaździcki (2001). Considering
the associated pelvic portions and caudal vertebrae preserved in
SGO.PV.6579, these articular heads are likely part of each femur.
4.15. Epipodial
A single fragmentary epipodial was recovered (Fig. 6M), which is bro-
ken in sagittal section and also missing its lateral half. The preserved por-
tion (medial half) is as broad as it is long, thus indicating that the
complete epipodial was broader than long. The proximal articular facet
is recognized by being comparatively thicker than the distal facet. The
first has a rounded border that articulates with the lateral facet of the
propodial, while the internal margins have a medial concavity that sepa-
rates the proximal facet from the distal one. Such a concavity is typically
placed in the axial margin of the epipodials. Also, the straight distal facet
is large enough for articulation with a centrale element, while in the case
of radius/tibia, the facet for the centrale is more reduced (Broili, 1930;
Welles, 1952). Based on this, the epipodial likely belongs to an element
placed in the posterior half of the limb. Since the associated postcranial
elements of the SGO.PV.6579 are caudal and pelvic portions, it is likely
that the epipodial belongs to a fibula rather than an ulna.
4.16. Ilium
The ventral portion of the right ilium is preserved (Fig. 6N). This is
very massive and recurved. Its ventral articular face is incomplete, but
allows evaluating the ventral length of the bone. The dorsal portion is
lost, but it is possible to see a medial reduction of the shaft section in
thepartwheretheboneisrecurved.
Fig. 5. Elasmosauridae indet. (SGO.PV.6508). James Ross Island, Antarctica. Santa Marta
Formation, Gamma member,late Campanian.Cervical vertebraof a verylong-neckedindi-
vidual. A, anterior view. B, dorsal view. C, ventral view. D, right lateral view. Scale bar
equals 50 mm.
778 R.A. Otero et al. / Gondwana Research 26 (2014) 772–784
4.17. Pubis
A large amount of scattered bone fragments were collected and later
re-assembled (Fig. 6M). These include a very fragmentary articular face
of a probable right pubis, as well as the acetabular portion of the left
pubis. This latter bears an oval articular face for the femoral head. The
rest of the bone is poorly preserved, lacking most of its perimeter,
although it is possible to see the distinctive dorsal (internal) view of
the pubis surface which is slightly concave.
5. Discussion
5.1. Comparison of SGO.PV.6523 with other elasmosaurids from the WBP
Morphological characters of SGO.PV.6523 include the presence of an
anteriorand posterior groove on the edge of the neural spines at leaston
mid-to-posterior cervical vertebrae (its presence on anterior cervicals
cannot be verified since the latter are not preserved). A similar condi-
tion is observed in posterior cervicals of specimen SGO.PV.260 referred
Fig. 6. Aristonectinae gen.et sp. indet. (SGO.PV.6579) JamesRoss Island, Antarctica. SantaMarta Formation, Gamma member, late Campanian.A, E, caudal centra in anterior view.B, F, left
lateral view. C, G, ventral view. D, H, dorsal view. I, fragmentary caudal centrum inright lateral view. J, fragment of a caudal centrum in ventral view. K, L, articularheads of two different
propodials, likely the femora. Estimated diaphysis outline based on the Antarctic specimen ZPAL R.8/6 described by Fostowicz–Frelik and Gaździcki (2001). M, pre-axial portion of
epipodial (likely a fibula). N, sagittal section view of the epipodial. O, ventral portion of the right ilium in posterior view. P, ventral portion of the right ilium of Aristonectes sp.
(SGO.PV.260, juvenilespecimen) in posterior view. Q, articular portionof the left pubis of SGO.PV.6579 in dorsolateral view. R, leftpubis of Aristonectessp. (SGO.PV.260,juvenile specimen)
in dorsolateral view. Scale bars equal 50 mm.
779R.A. Otero et al. / Gondwana Research 26 (2014) 772–784
to Aristonectes sp. (Otero and O'Gorman, 2013) from late Maastrichtian
strata of the Quiriquina Formation in central Chile, where the neural
groove is present in the basal portion of the neural spine, but reaches
only one third of the spine's height. Similarly, in the latter taxon, the an-
terior left flank that rises from the groove turns into an enlarged, flat and
delicate bony layer, while its posterior right flank has a similar structure.
This was originally described as ‘delicate alternate flanks’,inOtero et al.
(2012:fig 3E, F) for the juvenile specimen SGO.PV.260, later referred to
the genus Aristonectes by Otero and O'Gorman (2013) and therefore con-
sidered as a highly diagnostic feature. The presence of similar structures
in the neural spines of SGO.PV.6523 suggests affinities with the genus
Aristonectes, although it represents a different taxon than the latter,
based on the cervical vertebrae, scapula and the comparatively smaller
adult size.
In the case of Aristonectes parvidens, the anterior and posterior
groove of the neural spines are not present, at least based on the neural
spines of the anterior and middle portion of the neck (Cabrera, 1941:fig.
4A, B). Such a feature is also absent from T. keyesi (Wiffen and Moisley,
1986:figs. 4 and 5) and in specimen CM Zfr 115 referred to Mauisaurus
haasti (Hiller et al. 2005:figs. 11 and 12), discarding narrow relation-
ships with these taxa. Another interesting morphology in SGO.PV.6523
is the cervical vertebrae with a triangular outline in the transversal
section of each centrum, having an angle between neural spines and
the dorsolateral surface of each centrum close to 150–160°, conferring
them a distinctive aspect. Although a similar angle and outline are pres-
ent in anterior cervicals of the holotype of Aristonectes parvidens (RAO,
pers. obs.), this becomes reduced to nearly 125° in middle cervicals
(Gasparini et al., 2003:fig. 2F). In addition, the same angle in thereferred
specimen CM Zfr 115 of Mauisaurus haasti shows values between 130°–
140° on anterior and middle cervicals (Hiller et al., 2005:figs. 10–12),
while the posterior centra show very similar values as well as similar
articular outlines with those of specimen SGO.PV.6523 from Seymour
Island (RAO, pers. obs.); similar values between 130°–140° can be in-
ferred from the anterior cervicals of the holotype of T. keyesi (Wiffen
and Moisley, 1986:fig. 5). Moreover, the semi-cylindrical articular
facet for postzygapophyses is indeed present in other elasmosaurids
(Welles, 1943), although in SGO.PV.6523 the breadth and depth of
this structure are unusual, as well as the presence of a distinctive
heart-shaped internal facet. Finally, the dorsal process of the scapula is
one of the most remarkable characters, being unusually high and ante-
riorly recurved, a feature not known in any adult elasmosaurid speci-
men from the WBP. All the known scapulae of adult individuals
recovered in this province (Fig. 7A–F) have dorsal processes angled
posteriorly, except in the case of ZPAL R.8/11 from the Klb2 unit of the
López de Bertodano Formation on Marambio Island (Fostowicz–Frelik
and Gaździcki, 2001). Here the dorsal process is absent, making it
impossible to compare, although it matches SGO.PV.6523 in size and
in the outlineof the anterior process of the scapula.In addition, scapulae
of adult or near-adult specimens of Aristonectes sp. (SGO.PV.957),
Mauisaurus haasti, and the indeterminate elasmosaurid CM Zfr 145
from the late Maastrichtian of the Conway Formation, in New Zealand
(Hiller and Mannering, 2005), are notoriously larger than the scapula
of SGO.PV.6523. The scapula of the indeterminate elasmosaurid MCS-4
from late Campanian–early Maastrichtian beds of the Allen Formation,
Argentina (Gasparini and Salgado, 2000)isslightlysmallerthan
SGO.PV.6523 and has a dorsal process which is still recurved posteriorly,
but comparatively more vertical than those of Aristonectes sp.,
Mauisaurus haasti and CM Zfr 145.
Other morphologic characters could be potentially apomorphic. The
cervical ribs in SGO.PV.6523 are known from only a few fragments.
Their exposed cross-section reveals a triangular outline, which differs
from the oval to circular cross-section in the ribs of Aristonectes (RAO,
pers. obs.). A similar oval outline was also described for the ribs of
Mauisaurus haasti by Hiller et al. (2005) and K. katiki (Cruickshank and
Fordyce, 2002), while in T. keyesi these are not known, although the re-
ferred specimens bear oval transverse processes suggesting an oval
cross-section of the ribs (Wiffen and Moisley, 1986:fig. 17). Cervical
ribs could include distinctive features. In SGO.PV.6523 these have oval
facets with a thin posterior projection,being constrained to the posteri-
or half of the centrum, contrary to the oval cervical rib facets in
Mauisaurus,Tuarangisaurus,Aristonectes and Kaiwhekea,allofthemex-
tended along most of the centrum length (Wiffen and Moisley, 1986:fig.
4; Cruickshank and Fordyce, 2002:fig. 6; Gasparini et al., 2003:fig. 2E;
Hiller et al., 2005:figs. 11, 12).
Fig. 7. Comparison between scapulae of adult elasmosaurids from the Upper Cretaceous of the WBP. A, Aristonectes sp. (SGO.PV.957, late Maastrichtian of central Chile), right scapula in
lateral view. B, Elasmosauridae gen. et sp. indet. (SGO.PV.6523, late Maastrichtian of Marambio Island, Antarctica), right scapula in lateral view. C, Elasmosauridae indet. (MCS-4, late
Campanian–early Maastrichtian of Argentina), right scapula in lateral view (modified from Gasparini and Salgado (2000)). D, aff. Mauisaurus sp. (ZPAL R.8/11, early Maastrichtian of
Marambio Island, Antarctica), left scapula in medial view (modified from Fostowicz–Frelik and Gaździcki, 2001). E, Mauisaurus haasti Hector (CM Zfr 115, late Campanian of New
Zealand),left scapula in medial view (modified from Hiller et al. (2005)).F, Elasmosauridae indet. (CM Zfr 145, late Maastrichtian of New Zealand), leftscapula in medial view (modified
from Hiller and Mannering (2005)). Scale bar equals 50 mm.
780 R.A. Otero et al. / Gondwana Research 26 (2014) 772–784
Although SGO.PV.6523 bears apparently unique morphologic
characters, its fragmentary condition prevents accurate comparisons,
particularly with other records from Marambio Island comprising
different anatomical portions, such as the skull and anterior neck of
‘Morturneria seymourensis’(Chatterjee and Small, 1989).
5.2. Functional aspects on the neck of SGO.PV.6523
The presence of a groove along the anterior and posterior edge of the
cervical neural spines is a feature poorly described in known plesio-
saurs. Anterior grooves in neural spines are present in posterior caudal
and dorsal vertebrae of the Jurassic cryptoclidid Muraenosaurus
(Andrews, 1910:figs. 51,52 and 54), but the grooves fade into the dorsal
portion of the spines. Other elasmosaurids have distinctive morphol-
ogies on the edges of neural spines. Dorsal pits are present in posterior
cervicals of H. alexandrae (Welles, 1943: plate 27). Similarmorphologies
are also present in F. suzukii, which has an anterior pit and a posterior
swelling in the dorsal portion of the posterior cervical neural spines
(Sato et al., 2006:fig. 5C, D). This evidence suggests that the neural
spines of posterior vertebrae in elasmosaurids are highly distinctive
and can be taxonomically informative. Also, these portions allow infer-
ences to be made about the rigidity of the posterior neck. Analog mus-
cular attachments in birds and sauropods (Wedel and Sanders, 2002:
fig. 2) show that neural spines can develop large interspinal muscles
related to the ability of curving the neck dorsally as it occurs in the
sauropod Apatosaurus. Nevertheless, in the latter, the interspinal space
is large, contrary to the very reduced space between neural spines of
SGO.PV.6523, which also has deep grooves in the anterior and posterior
margin of the neural spines, indicating a strong muscular attachment
but scarce possibilities for dorsoventral movement of the posterior
neck. Thisis also consistent with the large semi-cylindrical facets for ar-
ticulation of the postzygapophyses, which allow interlocking between
successive cervicals. Based on this, it is likely that the elasmosaurid
SGO.PV.6523 possessed a stiff posterior portion of the neck, with
reduced movement.
5.3. Associated fauna and environment of the SGO.PV.6523
This specimen was recovered completely isolated from any other ver-
tebrate remains. The fossil-bearing unit was traced over a large area while
looking for additional remains. These findings include cranial material of a
large mosasaurid (presently being studied by the authors), isolated teeth
of odontaspidid sharks, scattered but frequent dental plates of indetermi-
nate callorhynchid fishes and dental plates of Callorhinchus torresi (Otero
et al., 2013). Additional remains of elasmosaurid plesiosaurs were found
separated by several tens of meters, which allow a possible mixing of el-
ements from different individuals to be discarded. The common presence
of frequent dental plates of holocephalians and odontaspidid teeth
suggests a shallow shelf environment (Stahl, 1999; Compagno, 2001).
5.4. Specimen SGO.PV.6508
The presence of very-long necked elasmosaurids (with cervical indi-
ces in the range of representatives from the Upper Cretaceous of North
America) in the Campanian–Maastrichtian of the Southern Hemisphere
is restricted to finds in New Zealand (Welles and Gregg, 1971; Wiffen
and Moisley, 1986; Hiller et al., 2005) and Argentina (Gasparini et al.,
2001:fig. 3), but are very scarce in Chile (RAO, pers. obs.). Also, the re-
cords from Antarctica include long-necked elasmosaurids referred to
the genus Mauisaurus by Martin et al. (2007) from Maastrichtian beds
of Vega Island, although the cervicals of the specimen were not recov-
ered. O'Gorman (2012) also described the oldest elasmosaurid from
Coniacian–Campanian beds of James Ross Island, including a juvenile
specimen with several cervical vertebrae. The studied specimenverifies
the presence of very-long necked elasmosaurids during the late
Campanian on the James Ross Island.
5.5. Specimen SGO.PV.6579
The presence of anterior caudal centra much broader than high and
higher than large, with an octagonal articular outline, has been regarded
as a diagnostic feature of the genus Aristonectes (Gasparini et al., 2003:
fig 3I, J; O'Gorman et al., 2010; Otero et al., 2012:fig. 5). The studied
material SGO.PV.6579 has different proportions with respect to the
diagnostic anterior caudals of Aristonectes, with a breadth slightly larger
than the height. Since SGO.PV.6579 has ventral facets for the haemal
arches, this verifies their anatomical position in a posterior position
with respect to the diagnostic anterior caudals (which are comparative-
ly broader), although the material still retains the distinctive octagonal
articular outline. Sub-triangular, pedicelar facets for the neural arches
such as those present in the caudal vertebrae of SGO.PV.6579 have
been previously described in middle to posterior dorsal vertebrae of a
specimen from late Maastrichtian beds of Marambio Island referred to
Aristonectes cf. parvidens by O'Gorman et al. (2013). On the other
hand, suchfeatures on the caudal vertebrae arealso present in specimen
CM Zfr 115 from the late Campanian of New Zealand (Hiller et al., 2005),
which surely represents a different taxon that possess a very long neck
with more than 60 vertebrae, placing it among the non-aristonectine
elasmosaurids. Also, the posterior epipodial (likely a fibula) with a
concave pre-axial margin is a feature previously described in other
specimens of Aristonectes (Otero et al., 2012). In addition, the distinctive
massive, ventral portion of the ilium is a feature shared with the juve-
nile specimen SGO.PV.260, referred to the genus Aristonectes (Otero
and O'Gorman, 2013)(Fig. 6K, L), while the partial portion of the
pubis of SGO.PV.6579 is also consistent with specimen SGO.PV.260
(Fig. 6M, N). Most of the morphologies described here are very similar
to those present in the genus Aristonectes based on specimens from
the late Maastrichtian of the southeastern Pacific, while the presence
of caudal vertebrae similar to those of non-aristonectine elasmosaurids
from the late Campanianof New Zealand, such as CM Zfr 115, indicates
that this could be a plesiomorphic feature. Finally, the large gap
between this new Antarctic record (SGO.PV.6508) and the records of
Aristonectes from central Chile suggests that both taxa can be narrowly
related, but it cannot be assured that they belong to the same genus,
especially considering the widespread distribution of the family in the
Southern Hemisphere during the end of the Cretaceous (Chatterjee
and Small, 1989; Cruickshank and Fordyce, 2002; Gasparini et al.,
2003;O'Gorman et al., 2013). Based on these facts, specimen
SGO.PV.6579 from late Campanian beds of James Ross Island (Gamma
member) is here referred to an indeterminate aristonectine. In addition,
the material from Marambio Island described by Fostowicz–Frelik and
Gaździcki (2001) was found in the lower strata of the López de
Bertodano Formation (Klb2 unit), which are assigned by Crame et al.
(2004) to the early Maastrichtian. Also, the material probably belongs
to a single juvenile individual and includes among other remains
articulated caudal vertebrae (ZPAL R.8/1–4), an epipodial, probably a
tibia (ZPAL.R8/13), and a femur with hemispherical articular head
(ZPAL R.8/6), all of them coincident in shape and size with the respec-
tive anatomical elements preserved in SGO.PV.6579. Also, the late Cam-
panian age of the latter and the early Maastrichtian age of ZPAL.R8/1–4,
6 and 13, strongly suggest that both specimens belong to the same
taxon. Finally, the outline of the scapula of ZPAL.R8/13 is indeed coinci-
dent with that of Aristonectes sp. (Fig. 7A, D), but has a much smaller
size. Considering the new information, it is possible that the remains
described by Fostowicz–Frelik and Gaździcki (2001) belong to the
same taxon of the SGO.PV.6579, but atthis moment no generic or specif-
ic determination can be provided.
5.6. Associated fauna and environment of SGO.PV.6523
Previous records of vertebrates from Santa Marta Cove on James Ross
Island include cartilaginous and bony fishes (Kriwet et al., 2006 and ref-
erences therein), as well as dinosaurs (lithostrotians, ankylosaurs, and
781R.A. Otero et al. / Gondwana Research 26 (2014) 772–784
ornithopods; Salgado and Gasparini, 2006; Coria et al., 2007; Cerda et al.,
2012; Coria et al., 2013), which indicate shallow water facies for the two
specimens of plesiosaurs studied here.
5.7. Results of bivariate graphic analysis
Bivariate graphic analysis of the indices of SGO.PV.6523 returned a
low dispersion of the points (Fig. 8). The plot occupies an intermediate
position between adult aristonectines (Aristonectes sp. and F. suzukii)
and a second sub-group including the adult individuals of T. keyesi,
Mauisaurus haasti (referred), and Callawayasaurus colombiensis.The
results are not conclusive for separating SGO.PV.6523 neither from
aristonectines or from intermediate forms (Mauisaurus,Tuarangisaurus,
Callawayasaurus), but allow discarding it as a representative of very-
long necked elasmosaurids such as those from the Upper Cretaceous
of North America.
Regarding the juvenile elasmosaurid SGO.PV.6508 from James Ross
Island, this has a VLI index of 111, and has clear rib facets with the ribs
not fused to the centrum, indicating that the specimen was a juvenile
(Brown, 1981). Based on this, comparison was carried out with other ju-
venile elasmosaurids. Among aristonectines, the juvenile specimen
SGO.PV.260 from central Chile has an average VLI of nearly 62 (Otero
and O'Gorman, 2013), while the holotype of ‘Morturneria seymourensis’
from Antarctica has an average VLIof nearly 56. Additionally, a juvenile
specimen from James Ross Island previously described by O'Gorman
(2012) was included, having an average VLI close to 81. Juvenile repre-
sentatives of very-long necked elasmosaurids from North America have
average VLI indices between 81–91 (measurements from Brown
(1913);Welles (1943);Kear (2005)), while the closest average VLI is
Fig. 8. Plotsobtained with the bivariate graphic analysis. The dark ellipse enclosesthe plots of the indeterminate elasmosauridSGO.PV.6523.A, HI vs BI in adults. B, VLI vs BI in adults. C, VLI
vs HI in adults. Plots of the indeterminate elasmosaurid SGO.PV.6508. D, HI vs BI in juveniles. B, VLI vs BI in juveniles. C, VLI vs HI in juveniles.
782 R.A. Otero et al. / Gondwana Research 26 (2014) 772–784
that of CM Zfr 115 referred to Mauisaurus haasti, nearly 101, although
the latter is a near-adult specimen. The results of bivariate graphic
analysis support SGO.PV.6508 as being a juvenile individual of a very
long-necked elasmosaurid.
6. Conclusions
The studied material SGO.PV.6523 represents an unusual indetermi-
nate elasmosaurid from late Maastrichtian strata of the López de
Bertodano Formation exposed on Marambio Island. Despite this being
a fragmentary specimen, it represents a novel, relatively small animal
with a probably rigid neck and a scapula very different from the scapula
known in any Weddellian elasmosaurid. The fragmentary condition of
the material prevents direct comparison with other taxa, while the
cervical features and the bivariate graphic analysis suggest that this
can belong to a form within Aristonectinae, based on the cervical
proportions and the presence of an incipient left anterior flank in the
neural spines, a feature that partially matches the cervical morphologies
observed in Aristonectes sp. (SGO.PV.957) from late Maastrichtian strata
of central Chile; Nevertheless, SGO.PV.6523 surely represents a different
taxon based on the much smaller adult size.
In addition, the studied material from James Ross Island
(SGO.PV.6508) shows the presence of very-long necked elasmosaurids
during the late Campanian, which to date are completely unknown in
Upper Cretaceous units of the southeastern Pacific (Chile), but known
in Argentinean units of the same age. Their common presence in
Argentina, Antarctica, and New Zealand during the late Campanian–
Maastrichtian and their posterior absence in the southeastern Pacific
during the late Maastrichtian, raise questions about paleogeographic
or environmental changes that could have affected their distribution
during this period.
Finally,additional material from James Ross Island allows the identi-
fication of the first remains of an indeterminate aristonectine in late
Campanian strata of Antarctica, while suggesting the presence of the
same taxon also in early Maastrichtian strata of the López de Bertodano
Formation on Marambio Island. This is the oldest known record of this
sub-family, widelydistributed within the WBP, but previously restricted
only to late Maastrichtian beds of Antarctica, Argentina, Chile, and New
Zealand. The three new specimens studied here represent new informa-
tion about the diversity of Upper Cretaceous Antarctic plesiosaurs.
Acknowledgments
This research was supported by the Antarctic Ring Project (Anillos
de Ciencia Antártica ACT-105, Conicyt-Chile). We express our gratitude
to the Armada de Chile and the crew of the Icebreaker AP Almirante
Óscar Viel, for the professional logistics and goodwill that made this
field campaign possible. R.E. Yury-Yáñez was funded by a master's
degree CONICYT-Chile scholarship from the Programa de Formación
de Capital Humano Avanzado. Our thanks also go to E. Fordyce
(University of Otago, Dunedin, New Zealand) and P. Scofield
(Canterbury Museum, Christchurch, New Zealand) for granting access
during May, 2013 to the holotype of K. katiki and CM Zfr 115, respective-
ly. Andrea Llanos (Departamento de Producción Agrícola, Facultad de
Ciencias Agronómicas, Universidad de Chile) is especially acknowl-
edged for finding one of the studied specimens. Thanks to J. Le Roux
(Departamento de Geología, Universidad de Chile) for the stylistic
review of the english. RAO, SSA, and CSG are currently supported by
the Proyecto Domeyko II UR-C12/1 grant of the Universidad de Chile.
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