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ۙۦۙۜڷ۟ۗ۠Өڷۃڷۣۧۢۧۧۡۦۙێڷۨۧۙ۩ۥۙې
ҢڽڼھڷۢٷЂڷڽھڷۣۢڷھڽғھڽھғڼڿڽғہہڷۃۧۧۙۦۘۘٷڷێٲڷۃٰۛҖІЂۦۣۘۛۙғۦۖۡٷۗ۠ۧғٷۢۦ۩ۣ۞ҖҖۃۤۨۨۜڷۣۡۦۚڷۘۙۘٷۣۣ۠ۢ۫ө
Net her lands J our n al of Ge osciences —– Geologi e en M ijnbouw | P age 1 of 12.
doi: 10.1017/njg.2014.44
A new elasmosaurid from the early Maastrichtian of Angola and
the implications of girdle morphology on swimming style
in plesiosaurs
R. Ara újo 1,2,* , M.J. Polcyn 1, A.S. Schulp 3 , O. Mateus 2,4 , L.L. Jacobs 1, A. Ol ı́mpio Gonçalves 5 &
M.-L. Morais 5
1
Roy M. Huffington Department of Earth Sciences, Southern Methodist University, Dallas, Texas, 75275, USA
2
Museu da Lourinh~a, Rua Jo~ao Luı́s de Moura, 2530-157 Lourinh~a, Portugal
3
Naturalis Biodiversity Center, Darwinweg 2, 2333CR Leiden, the Netherlands and Natuurhistorisch Museum Maastricht, Maastricht, the
4
Universidade Nova de Lisboa, CICEGe, Faculdade de Ciências e Tecnologia, FCT, 2829-516 Caparica, Portugal
Netherlands and Faculty of Earth and Life Sciences, Amsterdam VU University, Amsterdam, the Netherlands
5
Departamento de Geologia, Faculdade de Ciencas, Universidade Agostinho Neto, Avenida 4 de Fevereiro 7, Luanda, Angola
*
Corresponding author. Email: rmaraujo@smu.edu
Manuscript received: 2 May 2014, accepted: 3 December 2014
Abstract
We report here a new elasmosaurid from the early Maastrichtian at Bentiaba, southern Angola. Phylogenetic analysis places the new taxon as the sister taxon to
Styxosaurus snowii, and that clade as the sister of a clade composed of (Hydrotherosaurus alexandrae (Libonectes morgani + Elasmosaurus platyurus)). The new
taxon has a reduced dorsal blade of the scapula, a feature unique amongst elasmosaurids, but convergent with cryptoclidid plesiosaurs, and indicates a longitudinal protraction-retraction limb cycle rowing style with simple pitch rotation at the glenohumeral articulation. Morphometric phylogenetic analysis of the
coracoids of 40 eosauropterygian taxa suggests that there was a broad range of swimming styles within the clade.
Keywords: Plesiosauria, locomotion, pectoral girdle, Elasmosauridae, marine reptiles
Introduction
We report here a new elasmosaurid plesiosaur from the early
Maastrichtian of Angola, and provide a description and a phylogenetic analysis. The new taxon possesses unusual features of
the limb and pectoral girdle morphology that suggest a peculiar
mode of locomotion; we therefore also explore the implications
of girdle morphology on swimming style in a phylogenetic morphometrics framework.
Plesiosaurs are members of the Eosauropterygia (Rieppel,
1994), which include pachypleurosaurs, nothosaurs and pistosaurs best known from the Middle Triassic epicontinental shallow seas of Europe and China (Rieppel, 2000). Elasmosauridae
are regarded as the sister group of Cryptocleididae within
Plesiosauria (Ketchum & Benson, 2010; Benson & Druckenmiller,
2014). The origin of Elasmosauridae is unclear but its record extends
© Netherlands Journal of Geosciences Foundation 2014
from the mid-Hauterivian (Evans, 2012) to the end of the Maastrichtian (Vincent et al., 2011).
By the earliest Jurassic, plesiosaurs were fully adapted to
a pelagic lifestyle and two major Bauplans (plesiosauromorph
and pliosauromorph) had emerged in multiple phylogenetic lineages (O’Keefe, 2001; Benson et al., 2012). Plesiosauromorphs
have long necks and relatively small, anteriorly abbreviated
heads, whereas the pliosauromorph Bauplan includes forms
with larger elongate heads and relatively short necks (O’Keefe
& Carrano, 2005). However, all plesiosaurs share unique features of their limbs and girdles amongst secondarily adapted
Mesozoic marine reptiles. Swimming style based on paraxial
quadrupedal locomotion is largely accepted (e.g. Watson,
1924; Robinson, 1975), although details of limb motion
are more contentious (e.g. Thewissen & Taylor, 2007; LinghamSoliar, 2000).
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Netherla nds Jour n al of Geos cience s —– Geo logie en M ijnbo uw
The morphological transition between terrestrial forms, presumably in the early Triassic, to fully marine forms known from
the Jurassic and Cretaceous involves profound reorganisation
of the girdle elements along with elaboration of the limbs as
paddles in a unique body plan without modern analogue. Plesiosaurs likely share a distant relationship with terrestrial
sprawlers (Rieppel, 1997, 2000) and on entry to the marine
realm employed paraxial rowing (Schmidt, 1984; Storrs, 1986;
Lin & Rieppel, 1998; for a different opinion see Sues, 1987).
Within Diapsida, there are two primary modes of aquatic locomotion: limb-based swimming (e.g. turtles, penguins) and
trunk-and-tail-based lateral undulation (e.g. varanoids, iguanids, crocodyliforms). Among extant paraxial swimmers there
are two main styles: rowing (e.g. trionychid turtles) and underwater flying (e.g. sea turtles). In underwater rowing the main
locomotory vector components are protraction and retraction,
whereas in underwater f lying the main locomotory vector component is adduction and abduction (Carpenter et al., 2010).
Within plesiosaurs, both rowing and underwater flying have
been proposed (Watson, 1924; Robinson, 1975; Carpenter
et al., 2010). Araújo & Correia (in press) provide a detailed
analysis of the pectoral myology of plesiosaurs.
In this contribution, we first describe the osteology of the
new taxon and perform a character-based parsimony analysis
to determine its phylogenetic position. We then perform an
additional analysis employing a continuously variable
morphometric character, a quantification of coracoid shape,
to develop a testable model of evolution for this bone in
Eosauropterygia. We conclude with a brief discussion of the
implications of girdle and limb morphology and musculature
variation on swimming style in plesiosaurs.
Materials and methods
Institutional abbreviations
CMN – Canadian Museum of Nature, Ottawa, Canada; IVPP –
Institute for Vertebrate Paleontology and Paleoanthropology,
Beijing, China; KHM – Kaikoura Historical Museum, Kaikoura,
New Zealand; MGUAN – Museu de Geologia da Universidade
Agostinho Neto, Luanda, Angola; SMF – Forschungsinstitut und
Naturmuseum Senckenberg, Frankfurt, Germany; TMM – Texas
Memorial Museum, Texas, USA; YPM – Yale Peabody Museum,
New Haven, USA.
Materials
MGUAN PA103 (Figs 2 and 3), complete pectoral and pelvic girdle, cervical and dorsal vertebrae, partial forelimb (humerus,
radius and ulna and isolated phalanges) and several dorsal ribs.
MGUAN PA270 (Mateus et al., 2012, Figure 11), pubis, ischium,
femur and completely articulated posterior limb.
2
Phylogeny
Phylogenetic analyses of the new taxon used the data matrix of 177
characters and 67 taxa modified from Ketchum & Benson (2010), with
the nothosaurid Cymatosaurus, as the outgroup. Codings can be found
in the Appendix. The analysis was run in TNT v1.1 (Goloboff et al.,
2008) with 20 independent hits using the defaults of ‘xmult’ command
and 10 cycles of tree drifting (Goloboff et al., 2008). Tree Fuse was run
with 22 replicates and over 1 3 109 rearrangements. A single parsimonious tree was retrieved with a tree length of 1136.78. Resampling
scores were calculated using 100 replications of symmetric resampling
(Goloboff et al., 2003). Each data set was analysed with a single addition and the resulting tree collapsed with tree bisection reconnection
(TBR) (Goloboff & Farris, 2001). Group supports were calculated by
TBR-swapping the trees, and registering of the number of steps needed
to unite a clade. Both absolute (Bremer, 1994) and relative Bremer supports are presented (Goloboff & Farris, 2001). Continuous characters
(both meristic and non-meristic) were analysed as such (Goloboff
et al., 2006), i.e. ranges and ratios were plotted in the matrix with
the actual values, without the need to create arbitrary groupings.
Vincent et al. (2011) matrix was also coded and is 67 characters 3
22 taxa, focused particularly on elasmosaurid taxa (10 out of 23).
The outgroup included the pachypleurosaur Serpianosaurus and the
nothosaur Simosaurus.
Phylogenetics morphometrics
In order to develop a testable model of morphological evolution
of the coracoid, we also performed a phylogenetic morphometric analysis following the methods of Catalano et al. (2010) and
Goloboff & Catalano (2011). Phylogenetic morphometrics
employs Farris optimisation by applying parsimony analysis to
2D or 3D spatial continuum (Catalano et al., 2010) using homologous landmarks. A set of landmarks is regarded as a single
character by the algorithm. In this case, one character with
14 landmarks was used, forming the character ‘outline shape
of the right coracoid in ventral view’. Forty pachypleurosaur,
nothosaur, pistosaur and plesiosaur taxa were scored. For further information see Supplementary Material.
Systematic paleontology
SAUROPTERYGIA Owen, 1860
EOSAUROPTERYGIA Rieppel, 1994
PLESIOSAURIA de Blainville, 1835
ELASMOSAURIDAE Cope, 1869 sensu Ketchum & Benson,
2010
Cardiocorax mukulu gen. et sp. nov.
Holotype – MGUAN PA103, complete pectoral and pelvic girdle,
cervical and dorsal vertebrae, partial forelimb (humerus, radius and
ulna, and isolated phalanges) and several dorsal ribs.
Referred specimen – MGAUN PA270 is a more incomplete
specimen preserving a pelvic girdle and a single hind limb in
Net her lands Jour nal of Geos ciences —– Ge ologie en M ijnbouw
articulation. This specimen was found in the same horizon at
about 7 m from the holotype.
Etymology – Genus name refers to the heart-shaped fenestra
between the coracoids derived from the Latinised Greek Kardia
and Latinised Greek corax, meaning raven or crow, which also
gives rise to the name ‘coracoid’. The species name mukulu
means ‘ancestor’ in Angolan Bantu dialects.
Locality and horizon – Southern Angola, Namibe Province,
Bentiaba, Bench 19 (Fig. 1), Mocuio Formation of the S~ao
Nicolau Group (Cooper, 2003), Namibe Basin (Jacobs et al.,
2006). Strganac et al. (2014) reports the age of this interval
(Bench 19) as early Maastrichtian (71.40–71.64 Ma).
Diagnosis – Cardiocorax mukulu is characterised by the following autapomorphies: coracoid, bilateral ventral buttress of the
coracoid asymmetrical; scapula, highly reduced dorsal blade of
the scapula, medial contact between scapulae and clavicles
extending along all of their medial surface, scapular shaft with
ellipsoid cross-section broadly splaying anteriorly; clavicle,
clavicular ventral area nearly as broad as the scapular area,
median contact between clavicles extend along all their medial
length; cervical vertebrae, the posterior cervical neural spines
have an angled apex, the posterior cervical neural spines nearly
touch its adjacent neural spines, transversally broad neural
spines: length of base of neural spines slightly smaller to centrum
length.
A
Description
The holotype (MGUAN PA103) preserves five cervical and one
dorsal vertebrae, proximal portions of dorsal ribs, the complete
pectoral and pelvic girdles, and a partial forelimb (humerus, radius and ulna, and isolated phalanges). Preservation is generally good, with little or no plastic deformation, but exhibits
some recent weathering. Referred specimen MGUAN PA270 is
a more complete articulated limb and pelvic girdle, and augments the description of these elements.
Vertebrae and ribs
A continuous series of five complete cervical vertebrae and one
anterior cervical lacking the neural spine and neural arch, and
one dorsal centrum (Fig. 2) are preserved in MGUAN PA 103.
The first isolated cervical preserved has a binocular-shaped articular facet. The vertebral centrum has a lateral longitudinal
ridge and a ventral keel at mid-height and mid-width, respectively. The foramina subcentralia perforate from the ventral to
the dorsal side of the vertebra and are surrounded by a broader
ventral concavity. The neural arch arises slightly medial to the
articular facet. The circular articular facets are visible in posterior cervicals. The lateral keel is visible in one posterior cervical
that extends along the dorsal third of the centrum, being more
B
Fig. 1. A. Geographical location of the locality in Angola. B. Geological context and stratigraphic column with the position of Bench 19, the layer which
produced the specimens described herein.
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Netherla nds Jour n al of Geos cience s —– Geo logie en M ijnbo uw
Fig. 2. MGUAN PA103 vertebral elements. A. Sequence of posterior cervical vertebrae and rib. B. Anterior cervical vertebra. C. Dorsal rib. D. Dorsal vertebra.
prominent on the posterior half of the centrum. The centra are
slightly amphicoelus with a thickened rim surrounding the outer region of the articular facet. Because of poor preservation
the ventral foramina subcentralia cannot be seen. Singleheaded, transversally flattened ribs are attached on the centra
ventrolaterally, tapering posteriorly and lacking anterior processes. The neural spines are blade-like, much narrower than
the centra, but at the level of the neural arches they are only
slightly narrower than the width of the centrum. Because of
post-mortem crushing it is impossible to determine the shape
of the neural canal. The neural spines are broad anteroposteriorly to the base and are completely fused to the centra,
4
although fractured at the base of the neural spine. The dorsal
border of the neural spine is remarkably angled dorsally. The
dorsal portion of the neural spines is further elaborated with
anterior and posterior projections at their mid-height. Thus,
the neural spines touch those adjacent, forming a tear-shaped
void (Fig. 2). The posterior cervical neural spines nearly touch
adjacent neural spines, a condition readily distinguished from
that of Callawayasurus, which despite a small posterior projection near the neural spine apex has a clear separation between
cervicals. No dorsoventral bending occurs among cervicals such
as seen in the posterior section of the cervical vertebrae in
Albertonectes (Kubo et al., 2012). A posterior projection on
Net her lands Jour nal of Geos ciences —– Ge ologie en M ijnbouw
the neural spine is also seen in Callawayasaurus (Welles, 1962),
but the anterior projection is autapomorphic for this taxon
(see Supplementary Material). Despite some breakage it is
still possible to conclude that a posterior increase in height
of the neural spines is not present. The zygapophyses are
horizontal relative to the sagittal plane, unlike Futabasaurus,
Albertonectes and Terminonatator. The postzygapophysis is
f lat and steeply inclined dorsolaterally in posterior view,
fitting with the same angle on the prezygapophysis of the
following vertebra. All centra are longer than they are high.
The dorsal centrum is acoelus, being wider compared to the
length and height. In lateral view, the articulation for the neural arch is well marked. The articulation for the neural arch
forms two broad ellipsoid surfaces in dorsal view. The ventral
surface is perforated by two pairs of foramina subcentralia.
The dorsal ribs have a small constriction around the head and
taper ventrally. The single articular facet of the ribs is mediolaterally ellipsoidal.
Pectoral girdle
Pectoral girdle elements from a single individual (MGUAN
PA103) were found mostly articulated except for the right
scapula, which is displaced and overlaps the right coracoid
(Fig. 3). The preglenoid portion of the pectoral girdle is subequal in size to the postglenoid portion of the pectoral girdle
(Figs 3 and 4). The longitudinal pectoral bar is formed by the
coracoid, scapula and clavicle, making a continuous slight
prominence along the ventral surface, which is an unusual
condition in elasmosaurids (e.g. Callawayasaurus, Wapuskanectes, Hidrotherosaurus, Aphrosaurus). The lateral scapulacoracoid contact (i.e. not the glenoid facet) has one distinct
Fig. 3. MGUAN PA103 pectoral and limb elements. A. Pectoral girdle in ventral view. B. Forelimb elements as preserved. C. Left scapula in dorsal view. D. Left pelvic girdle
in dorsal and ventral views. Bf, bone fragments; G, glenoid; H, humerus; Icl, interclavicle; Icv, intercoracoid vacuity; lc; left coracoid; Lcl, left clavicle; Pi, pisiform; Pp,
postaxial process; R, radius; Ra, radiale; rc, right coracoid; Sdb, scapula dorsal blade; U, ulna; Icl, interclavicle; rs, right scapula; lcv, intercoracoid vacuity.
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Netherla nds Jour n al of Geos cience s —– Geo logie en M ijnbo uw
triangular facet for the articulation between the coracoid
and scapula.
The coracoid is a flat bone and, as in other plesiosaurs, is
thickest around the glenoid. Both preglenoid projections are
complete and undistorted. The preglenoid projection of the coracoid is short and narrow, and although it clearly surpasses the
anterior margin of the scapular facet, it diverges slightly laterally, but to a lesser extent than the condition in Trinacromerum
brownorum, which is distinctly angled (Thurmond, 1968). The
shape and proportions of the preglenoid projection resemble that
of an unnamed elasmosaurid from the Lowest Maastrichtian
CMN9454 from Canada (Sato & Wu, 2006), but is shorter than
in the Albian elasmosaurid Wapuskanectes (Druckenmiller &
Russell, 2006) from Canada. The Aphrosaurus preglenoid projection is very short (Welles, 1943) and it is nearly non-existent in
an aristonectine elasmosaurid from Angola (Araújo et al., in
press) or Hydrotherosaurus (Welles, 1943). There is an asymmetrical ventral buttress of the coracoids with the right coracoid
overlapping the left with a lip of bone, unlike the symmetrical
ventral buttress in Wapuskanectes or Mauisaurus. This is not
a result of post-mortem distortion because, despite a small horizontal crack, even without repositioning there is clearly a lip of
bone that overlaps dorsally. The medial posterior process tapers
considerably and is much shorter than the anterior process of the
coracoid. The coracoid possesses well-defined posterior cornua,
giving a cordiform appearance to the intercoracoid foramen, also
present in Wapuskanectes and Styxosaurus. The posterior intercoracoid symphysis forms a 10-cm long contact between the
posteromedial processes, unlike most elasmosaurids. There
are no median coracoid perforations, as seen in Leptocleidia
(e.g. Benson & Druckenmiller, 2014). The postero-lateral coracoid wings, as seen in late Cretaceous polycotylids and to some
extent in some elasmosaurids, such as cf. Aristonectes
(TMM43445-1), are gentle projections formed by the lateral
and posterior borders. The lateral border is concave posterior
to the glenoid and the posterior convex as in Plesiosaurus (Owen,
1883; Storrs, 1997) and Leptocleidus (Andrews, 1922), and many
elasmosaurids (e.g. Hydrotherosaurus, Aphrosaurus, Albertonectes).
Dolichorhynchops possesses a concave lateral border and straight
posterior border. The extremities of the bone exhibit a rugose
pattern punctuated by several nutrient foramina.
Both scapulae are present in MGUAN PA103, although the
left is slightly displaced and rotated, and the right significantly
displaced and overlying the right coracoid. Although the scapula exhibits the typical triradiate shape (e.g. Andrews, 1910),
the reduced dorsal blade of the scapula contrasts with its broad
ventral area. This is an unusual feature for elasmosaurids
(Figs 3 and 4, and a similar but more conservative condition
in an unnamed elasmosaurid CM Zfr145; Hiller et al., 2005).
The median contact between the scapulae extends along its entire anteroposterior length. The medial coracoscapular contact
is reduced and only the tip of the posterior process of the scapula contacts the coracoid medially, enclosing a large coracoid
6
‘foramen’ (for homology see Araújo & Correia, in press). The
scapular shaft is thick, ellipsoid in cross-section and splays anteriorly into a flat and thin plate of bone. The anterior edge of
the scapula is concave and forms an acute angle laterally. The
dorsal blade of the scapula arises laterally from the scapular
shaft. The dorsal blade angles posteriorly, is 5–7 cm long and
tapers to a blunt apex. The glenoid face and the medial coracoscapular contact are subtriangular and rugose.
The ventral area of the scapula nearly equals the area of
the clavicle, a condition not yet observed in elasmosaurids
and other plesiosaurians (e.g. Thalassomedon, Morenosaurus,
Albertonectes, Callawayasaurus). The clavicle is a large, flat
bone, subtriangular in shape and with a blunt anterior apex.
The shape of the clavicle is unique among plesiosaurs (in contrast
with, for example, Futabasaurus, Albertonectes and Thalassomedon
dentonensis). It contacts its counterpart medially along its
entire length. Ventrally, a small medial lip of bone projects
posteriorly, partially enveloping the anterior border of the
scapula. Anteriorly it contacts the interclavicle, which is
poorly preserved.
Forelimb
The humerus of MGUAN PA103 possesses a postaxial protuberance that is not present in the femora of other known plesiosaur
taxa. The preaxial and postaxial borders of the humerus are
nearly straight (Fig. 3). The postaxial border bears a protuberance at mid-shaft. The proximal is damaged but spherical in
shape. The distal end bears two distinct epipodial facets. The
preaxial border of the ulna is concave. A supernumerary element articulates on the distal lateral facet of the ulna. The
radius is wider than long, rectangular and articulates with
a very wide radiale anteriorly.
Pelvic girdle
A complete pelvic girdle and hindlimb (MGUAN PA270) referred
here to Cardiocorax mukulu n. gen. et sp. was originally figured
by Mateus et al. (2012, their Figure 11). The pubis and ischium
are similar in morphology, proportions and size compared to the
holotype specimen (MGUAN PA103), and only differs in having
a more rounded anterior border and a more deeply concave lateral border of the pubis. These differences can be easily
accounted for by intraspecific variation. The right ilium is missing, and all other elements are fractured but complete (Fig. 3).
The median symphysis between left and right portions extends
from the anterior edge of the pubis to the anteroposterior midpoint of the ischium and forms a median pelvic bar. In Futabasaurus an incipient median pelvic bar forms a diamond-shaped
fenestra at the articulation of both halves of the girdle
(Sato et al., 2006), but in MGUAN PA103 the median pelvic
bar is completely connected, forming a straight structure, as
in Libonectes and Elasmosaurus.
Net her lands Jour nal of Geos ciences —– Ge ologie en M ijnbouw
The pubis forms a sinuosity along the anterolateral border and the
medial edge of the pubis is straight. The anterior surface of the pubis
is not notched; rather it is gently angled in the median portion of
the anterior surface. A flared lateral extension of the pubis as seen
in Mauisaurus haasti (KHM N99-1079; Hiller et al., 2005) and Terminonatator (Sato, 2003), and a small well-defined notch on the lateral
edge of the pubis (Bardet et al., 2008) is present in MGUAN PA103.
The posterior surface of the pubis has well-defined flat facets for
the femur, whereas the facet for the ischium is gently concave and
an oval shape with the more acute curve on the lateral side.
Although an elliptical cross-section is discernible, it is not
possible to determine the relative proportions of the distal
and proximal facets of the ilium because the distal facet is
not entirely preserved. The ilium is not twisted but curved
(Storrs, 1997), but because of the symmetry of the element
and the absence of facets it is impossible to discern the curvature direction. The ilium has a blunt and f lattened proximal
end, but again it is impossible to discern the flattening
direction.
Hindlimb
In MGUAN PA270 (Mateus et al., 2012; their Figure 11), a nearly
complete, semi-articulated hindlimb is present and articulated with
the pelvis. The femur is proximally formed by a hemispherical capitulum separated by an isthmus sloping into a flat D-shaped tuberculum. The shaft of the femur is cylindrical with a ventral roughening
at mid-shaft for muscle attachment. The shaft flares distally and
forms three distinct facets. No supernumeraries were found in articulation with the posterior paddle, but there seems to be an articulation facet on the postaxial side of the femur. The flared distal
portion of the femur has deep longitudinal striations for muscle attachment. The tibia is broader than long. The medial margins of the
tibia and fibula are concave, whereas the distal and proximal margins are straight. The calcaneum and centrale are preserved and in
situ but the astragalus is missing. Estimates are made difficult by
the taphonomic displacement of some of the digits, but the minimum phalangeal formula is I-7, II-8, III-8, IV-8, V-7.
Results
Character-based parsimony analysis
Phylogenetic analysis produced a single parsimonious tree of
1136.78 steps (Fig. 4). The analysis recovered Cardiocorax
mukulu as the sister taxon to Styxosaurus snowii, and that clade
as the sister of a clade composed of (Hydrotherosaurus alexandrae (Libonectes morgani + Elasmosaurus platyurus)). These
taxa collectively form the most derived elasmosaurid clade.
Elasmosauridae is strongly supported by Bremer indices and
GC values, and are united by short and distally wide femur
(character 175), and the premaxilla completely splits the frontals and contacts the parietals (character 10 state 2).
Fig. 4. Portion of recovered topology showing relationships of Cardiocorax
mukulu. See text and Supplementary Material Figures 1 and 2 for detailed results.
Unequivocal characters supporting the position of C. mukulu
include the ventrally notched anterior articular face of the cervical centra (Ketchum & Benson, 2010, 122:1) and the anteromedial margin of the coracoid contacts the scapula (Ketchum &
Benson, 2010, 150: 1), despite convergency with non-elasmosaurid
plesiosaurs such as Plesiosaurus or Thalassiodracon. The formation
of the coracoid embayment is also another elasmosaurid apomorphy, present in Cardiocorax and noted in a previous phylogenetic
analysis (e.g. Ketchum & Benson, 2010).
Morphometrics-based parsimony analysis
Our phylogenetics morphometrics analysis (see Catalano et al.,
2010) of the coracoid shape recovered a topology consistent
with the most generally recognised Eosauropterygia clades,
and thus provides a possible evolutionary model for the coracoid (Fig. 5a). Within Plesiosauria, two clearly distinctive morphotypes emerged: the Elasmosauridae morphotype with the
formation of an intercoracoid vacuity and the Polycotylidaemorphotype with a long preglenoid projection and posterior
cornu.
Although resistant fit theta-rho analysis (RFTRA) as
a re-aligning method provided a better tree score at the lowest
level of search thoroughness (4.8), at higher levels the heuristic minimisation of differences method performed considerably
better, with a tree score of 4.2 (Fig. 5d). At the levels of thoroughness 3 and 4, the tree score was similar to the re-aligning
method by heuristic minimisation of differences. Yet, for individual landmark scores, the heuristic minimisation of differences method was less consistent relative to RFTRA (contrast
Fig. 5b and c), which showed close individual landmark scores
at all levels of thoroughness. The best tree score was achieved
with heuristic minimisation of differences for the levels of thoroughness 3 (Fig. 5d) and 4. However, the tree that best mirrors
generally accepted relationships in Eosauropterygia was calculated using heuristic minimisation of differences with the level
of thoroughness 3. Additional trees are included in the Supplementary Material.
Discussion
In Fig. 6 we present a model of pectoral girdle evolution in
Eosauropterygia. In basal forms we see major reduction of the
7
Netherla nds Jour n al of Geos cience s —– Geo logie en M ijnbo uw
Fig. 5. Results of phylogenetic morphometric analysis. A. Preferred tree. Landmark scores for each landmark using (B) heuristic and (C) RFTRA search
methods. D. Comparison of the overall tree score between the heuristic and RFTRA method. See Supplementary Material Figures 4–13 for all recovered trees.
clavicle, reduction of the coracoid buttresses, reduction of the
dorsal blade and general ventralisation of the scapula,
horizontal orientation of the coracoid, and formation of the
clavicular-scapular arch. At the level of Pistosauria, we see high
morphological disparity of the coracoid. After the Late Triassic
morphological gap, we see formation of a large coracoid foramen, medial migration of the medial coracoid-scapula contact,
expansion of the postglenoid projection, and a weakening of
the scapular-clavicular articulation. Within pliosaurids, we
see retention of a relatively conservative pectoral girdle with
broad medial contact of the coracoids. In polycotylids there is
a novel development of the posterior coracoid wings, but the
scapula remains moderately expanded ventrally. Within elasmosaurids, we see the formation of the intercoracoid vacuity and
in late elasmosaurs, extreme ventral development of the scapula and clavicle, formation of an extensive longitudinal pectoral bar and nearly complete elimination of the dorsal process of
the scapula.
These evolutionary novelties are broadly correlated with optimisation of aquatic locomotion from terrestrial basal neodiapsid ancestors. However, notwithstanding the general model
8
developed by Carpenter et al. (2010), significant differences
in girdle and limb morphology in Plesiosauria suggest that different clades may have employed variations of rowing and underwater flying. The area of muscle attachments on the girdle
elements reflects both the dominant direction and magnitude
of forces that are applied to the limbs. The glenoid architecture
should reflect motion to the extent the glenoid must resist
forces applied to the limb and thus should also reflect the dominant motion vectors (i.e. protraction and retraction vectors).
This is contrary to the reasoning of Carpenter et al. (2010),
who suggested limb motion was greatest in the vectors defined
by least restriction in the glenoid (i.e. adduction and abduction). Thus, an understanding of the myology, proportions of
the limb and the glenoid architecture across the broader clade
is critical to infer swimming styles and variation in stroke
geometry.
The osteological correlates of muscles attachment sites
define area and at times direction (Araújo & Correia, in press)
and thus reflect to some degree the magnitude and vector of
muscle forces. When examined within a system like the forelimb
and pectoral girdle, the interaction of these forces and vectors
Net her lands Jour nal of Geos ciences —– Ge ologie en M ijnbouw
Fig. 6. Patterns of pectoral girdle evolution in Eosauropterygia. See text and Supplementary Material for discussion.
yields clues to the kinematics of that system. In basal neodiapsids,
the levator scapulae, the serratus and the scapulodeltoideus
originate on the dorsal blade of the scapula (Holmes, 1977).
The areas of attachment of these muscles are reduced in
Eosauropterygia because the lifestyle in a buoyant aquatic
medium does not require, to the same extent, limb support
musculature (Lin & Rieppel, 1998). Other secondarily-adapted
paraxial swimmers, such as penguins (Schreiweis, 1982) and
pinnipeds (Murie, 1871), also show selective limb muscle
reduction and expansion. However, Cardiocorax demonstrates
an extreme case of reduction of the levator scapulae, scapulodeltoideus and serratus in which the ventral area of attachment in the scapula is 14 times greater than the area of
attachment on the dorsal blade.
The ratio of the coracoid area versus the total length of the
individuals and the ratio of coracoid area versus the ventral
area of the scapula is clearly contrasted in Cretaceous plesiosaurs, with policotylids and elasmosaurids being separated
(Fig. 7a and b). This is indicative of the different swimming
styles between these two clades, namely the use of the coracobrachialis and clavodeltoideus muscle (Araújo & Correia, in
press). The average ratio between the dorsal blade area and
the ventral surface in the sampled Eosauropterygia is 3.3 and
in Elasmosauridae is 3.6 (Fig. 7c). The variation of almost an
order of magnitude within the same family reflects the particular
locomotory patterns of Cardiocorax. Typically for diapsids the
levator scapulae and the scapulohumeralis insert directly on
the dorsal portion of the scapula (Russell & Bauer, 2008). Basal
cryptoclidids (sensu Ketchum & Benson, 2010) also have high
ratios of the dorsal blade area and the ventral surface of the scapula (average 7.6), and Cryptocleidus eurymerus has a ratio of 10
(Fig. 7c). By this measure, the scapular muscles in basal cryptoclidids and Cardiocorax are comparable. Cardiocorax has a highly
proximodistally reduced and distally expanded humerus (Fig. 3),
rivaled only by Cryptocleidus (ratio is 0.3) among Eosauropterygia (Fig. 7d). However, the shortening of the humerus is a common trend among marine mammals (Fish, 1996) and marine
turtles (Renous et al., 2008). The members of the Elasmosauridae
possess the most derived condition of this aquatic adaptation
(Fig. 7d) in having the lowest humeral ratio values (average is
1.4) among Eosauropterygia (average is 2.0). Along those lines,
the radius ratio also tends to diminish along the evolution of the
clade (Fig. 7e).
The extreme distal expansion of the Cardiocorax with a doubly faceted distal border provides a broad articulation for interlocking zeugopodials (Fig. 3), a feature shared with
Cryptocleidus. Similarly, Cardiocorax has a shortened radius
(0.77 ratio) comparable only to other Late Cretaceous polycotylids
such as Dolichorhynchops and Edgarosaurus (Fig. 7d and e).
Cardiocorax’ shortened propodials and zeugopodials would have
9
Netherla nds Jour n al of Geos cience s —– Geo logie en M ijnbo uw
Fig. 7. Morphometric pectoral girdle variables against time. A. Ratio of the coracoid area versus the total length of the individual. Note the constrasting
values between polycotylids and elasmosaurids, convergent with the ratios on pachypleurosaurids. B. Ratio of the coracoid area versus the ventral area of
the scapula. Note the similar ratios for elasmosaurids and cryptocleidids. C. Ratio of the ventral area of the scapula versus the dorsal blade of the scapula
area. Note the outlier position of Cardiocorax, only comparable with that of cryptocleidids. D. Humerus ratio, length versus distal width. Note the tendency
in Eosauropterygia for increasing massiveness of the propodials, a trend convergent with various secondarily-adapted organisms; E. Radius ratio, length
versus distal width. As for the propodials the epipodials also tend to increase in massiveness to increase the mechanical advantage of locomotor muscles
and paddle stabilisers. See Supplementary Material Tables 1–3.
increased mechanical advantage of the extrinsic musculature
inserting on the girdle for increased leverage (Araújo & Correia,
in press). To cope with the force imparted by the muscles,
the coracoids meet extensively posteriorly and there is a broad
median contact between the scapulae and clavicles.
10
Additionally, the contact between the clavicle and scapula is
broad. The pectoral girdle is strengthened by the left–right
asymmetric ventral buttress of the coracoid. Plesiosaurs have
a thickened glenoidal portion of the coracoid, but a marked
ventral buttress is most evident in Elasmosauridae and facilitates
Net her lands Jour nal of Geos ciences —– Ge ologie en M ijnbouw
bending resistance between the two sides of the pectoral girdle.
Cardiocorax pectoral and pelvic girdles present a structural extreme for quadrupedal subaqueous locomotion. The reduction
of the attachment area of the dorsal blade of the scapula versus
the expansion of the attachment area of the ventral area in Cardiocorax indicates atrophy of muscle groups that were primitively
involved in terrestrial locomotion and, on the other hand, expansion of other muscle groups involved in quadrupedal subaquatic
locomotion. Thus, the peculiar Cardiocorax pectoral girdle architecture has functional implications. The subequal coracoid ventral area and the clavicle and scapula ventral area, plus the
reduced dorsal blade of the scapula, seem to be more compatible
with a protraction-retraction limb cycle with change of the flipper pitch than with a figure eight limb cycle previously proposed
for plesiosaurs (Robinson, 1975).
Benson, R.B.J. & Druckenmiller, P.S., 2014. Faunal turnover of marine tetrapods
during the Jurassic–Cretaceous transition. Biological Reviews 89: 1-23.
doi: 10.1111/brv.12038.
Benson, R.B.J., Evans, M. & Druckenmiller, P.S., 2012. High Diversity, Low
Disparity and Small Body Size in Plesiosaurs (Reptilia, Sauropterygia) from
the Triassic–Jurassic Boundary. PLoS ONE 7(3): e31838. doi:10.1371/journal.
pone.0031838.
Bremer, K., 1994. Branch support and tree stability. Cladistics 10: 295-304.
Carpenter, K., Sanders, F., Reed, B., Reed, J. & Larson, P., 2010. Plesiosaur swimming as interpreted from skeletal analysis and experimental results. Transactions of the Kansas Academy of Science 113: 1-34.
Catalano, S.A., Goloboff, P. & Giannini, N., 2010. Phylogenetic morphometrics
(I): the use of landmark data in a phylogenetic framework. Cladistics 26:
539-549.
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Supplementary Material
Supplementary material for this paper available on: http://dx.
doi.org/S0016774614000444
Acknowledgments
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The first author dedicates this article to the memory of his
brother. This publication results from ProjectoPaleoAngola, an
international cooperative research effort among the contributing authors and their institutions, funded by the National Geographic Society, the Petroleum Research Fund of the American
Chemical Society, Sonangol EP, Esso Angola, Fundaç~ao Vida of
Angola, LS Films, Maersk, Damco, Safmarine, ISEM at SMU,
the Royal Dutch Embassy in Luanda, TAP Airlines, Royal Dutch
Airlines and the Saurus Institute. We thank Margarida Ventura
and André Buta-Neto for providing our team with help in the
field. Tako and Henriette Koning provided valuable support
and friendship in Angola.
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???????????????????????????????????????????
???????????????????????????????????????????
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Cardiocorax mukulu ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
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Supplementary Data
“A new elasmosaurid from the early Maastrichtian of Angola and the implications of girdle morphology on swimming style in plesiosaurs “
Ricardo Araújo1,2*, Michael J. Polcyn1, Anne S. Schulp3, Octávio Mateus2,4, Louis L. Jacobs1 ,António Olímpio Gonçalves5 & Maria-Luísa Morais5
1Huffington Department of Earth Sciences, Southern Methodist University, Dallas, Texas, 75275, USA; 2Museu da Lourinhã, Rua JoãoLuís de Moura, 2530-157 Lourinhã, Portugal; 3Naturalis Biodiversity Center, Darwinweg 2, 2333CR Leiden, The Netherlands and Natuurhistorisch Museum Maastricht, Maastricht, The Netherlands and Faculty of Earth and Life Sciences, Amsterdam VU University, Amsterdam, The Netherlands; 4Universidade Nova de Lisboa, CICEGe, Faculdade de Ciências e Tecnologia, FCT, 2829-516 Caparica, Portugal; 5Departamento de Geologia, Faculdade de Ciencas, Universidade Agostinho Neto, Avenida 4 de Fevereiro 7, Luanda, Angola.
Corresponding author: rmaraujo@smu.edu
Eosauropterygia pectoral girdle database
We examined 43 Eosauropterygia specimens with complete pectoral girdles (Supplementary Table1). The areas of their pectoral girdle elements were calculated using ImageJ (Schneider et al., 2012). The humeral and radius ratios derive directly from Ketchum & Benson (2010) from 40 specimens preserving the humerus (Supplementary Table 2) and 32 preserving the radius (Supplementary Table 3).
Phylogenetics morphometrics methods
The placodonts Cyamodus hildegardis, Psephochelys polyosteoderma and Placodus gigas SMF R-1035, the pistosaur Kwangsisaurus orientalis IVPP V2338 and the nothosaur Sanchiaosaurus dengi IVPP V2338 were not included because their morphology is too specialized within Sauropterygia. Basal Eosauropterygia (pachypleurosaurs) are included. All landmarks are Bookstein’s type 2 (Bookstein, 1991). Landmarks were digitized using tpsDig2, after being assembled in tpsUtil (http://life.bio.sunysb.edu/morph/soft-utility.html). In tpsRelW only the alignment was saved, placing all taxa in the same coordinate system and standardizing size (option “Save aligned specimens”). The resulting *.tps file was parsed to run in TNT v1.1 (Goloboff et al., 2008), resulting in a 40x14-pair matrix in which each element is a pair of x, y coordinates referring to the aligned location of each landmark mapped in a two 2D space. The choice of a 2D landmark character is justified because the Eosauropterygia coracoid is a flat, splayed bone. The script used was landsch.run, available at http://tnt.insectmuseum.org/index.php/Scripts. A total of 14 landmarks were placed for all taxa analyzed following a homology statement and evolutionary scheme proposed in (Araújo and Correia, in press). This homology statement precludes that the posterior border of the coracoid elongated anteroposteriorly in the nothosaur-plesiosaur transition (Araújo and Correia, in press). Also, that the pectoral fenestrum in plesiosaurs is homologous to the “coracoid foramen” in nothosaurs, and the anteromedial coracoid contact was established in plesiosaurs as a result of a medial migration of the medially a coracoid expansion in nothosaurs (Araújo and Correia, in press), equivalent to landmark 6.A crucial advantage of phylogenetic morphometrics is that other alternative homology schemes and evolutionary models can be proposed and tested using a parsimony criterium.
The phylogenetic morphometrics method demands that the specimens are re-aligned during the search for the most parsimonious tree. Data realignment involves superimposing landmark configurations for best fit, and the residual differences can be solved by simple translations and rotations of the landmarks. Rho-theta resistant fit analysis (RFTRA, Rohlf& Slice, 1990) and heuristic minimization of differences (Catalano et al., 2010; Catalano &Goloboff, 2012) are available in TNT. The heuristic minimization of differences is a superimposition technique that minimizes the linear distances in relation to a prescribed configuration (in this case Neusticosaurus pusillus). Neusticosaurus pusillus was selected as outgroup because it is a basal pachypleurosaurid in several phylogenetic analyses (Rieppel, 2000; Liu et al., 2011). Both of these re-alignment methods were used and ran at all prescribed levels of search thoroughness (level 0 to 4). The levels of search thoroughness are determined by number of replicates (i.e., number repetition of the algorithm for the same matrix), termpoints (i.e., inclusion of the geometric medians between inter-taxic homologous landmarks as possible reconstruction points of the ancestral location), number of cells in the grid (i.e, the higher the number of cells, the greater number of ancestral landmark position reconstructions), nesting level (i.e., the level/number of grids being nested within the original grid), neighbors level (ie., the number of neighboring cells that are included to form a nested grid). High levels of thoroughness require longer run times and more computer processing power, other than these factors the higher the level of thoroughness the more parsimonious the expected results. Selection among the different resulting trees is based upon the provided tree score. The lower the tree scores the more parsimonious the results (Goloboff & Catalano, 2011; Catalano & Goloboff, 2012). See all trees produced below in Supplementary Figures 4-13.
Comparisons and implications of phylogentic morphometrics
Phylogenetic morphometrics (Goloboff & Catalano, 2011) allows evaluation of landmark configuration schemes providing a test to models of morphological evolution. Parsimony analysis is used to test an evolutionary hypothesis of the evolution of the coracoid outline. Parsimony analysis, as used in traditional phylogenetic analysis, can be extended to a two- or three-dimensional realm with phylogenetic morphometrics. By only using a single phylogenetic morphometric character, the outline of the coracoid, we were able to provide a testable model of the evolution of this element in Eosauropterygia and clearly discern the two main morphotypes: Elasmosauridae (i.e., short preglnoid projection, and intercoracoid vaciuity) and Polycotylidae (i.e., long preglenoid projection, developed posterior wings of the coracoid, and no large intercoracoid fenestration) (Fig. 5a). Surprisingly, the phylogenetic significance of the coracoid shape is clearly demonstrated by the fact that the most parsimonious cladogram (tree score is 4.2, Fig. 5d) broadly mirrors the current understanding of the relationships among Eosauropterygia derived using traditional methods (see Liu et al., 2011).
Evolutionary changes in the pectoral girdle
Non-Plesiosaur Eosauropterygia— The reorganization of the pectoral girdle in the basal neodiapsid-pachypleurosaur is marked by profound morphological transformations (Fig. 6): (1) major reduction of the interclavicle including the posterior process, (2) the reduction of the coracoid buttresses, (3) the reduction of the scapula dorsal blade, (4) the coracoid re-orientation to the horizontal plane, (5) the ventralization of the scapula, (6) the formation of the clavicular-scapular arch. This important morphological gap is unknown in the fossil record although the answer may lie in Early Triassic marine/transitional sedimentary record. Although nothosaur and pachypleurosaur pectoral girdles are somewhat conservative morphologically, they are readily distinct from their basal neodiapsid ancestors (Fig. 6). These osteological, and inferred mycological modifications are adaptations for a marine lifestyle (e.g., re-orientation of the scapula and coracoid), and associated atrophy of terrestriality-related features (e.g., reduction of the coracoid buttresses, see above). Without understanding these basal transformations, it is not possible to correctly interpret the condition in highly derived eosauropterygians, such as plesiosaurs.
The coracoid is a morphologically conservative element in pachypleurosaurs and nothosaurs (Rieppel, 2000, Fig. 6). Across the evolution of Eosauropterygia the major transformations of the coracoid occur during the pistosaur to plesiosaur transition (Fig. 6 and Fig. 5a: note the landmark optimization on the hypothetical ancestor reconstruction at the Corosaurus/Pistosaurus node). The major transformations are (see Fig. 5b,c): (1) the median migration of the medial coracoscapular contact, with the formation of the anterior projection of the coracoid (landmark 5, accounting for 7.6% of the total tree score); (2) the reorientation of the thickened glenoidal portion (landmark 7, accounting with for 8.1% of the total tree score); (3) posterior expansion of the coracoid (landmarks 10, 11, 12, 13, 14, accounting for 40% of the total tree score.
Landmark 5 depicts an analogous model of morphological transformation to that proposed by Liu et al. (2011) cladistic analysis. Rieppel’s model proposes that the coracoid foramen is much enlarged in plesiosaurs, yet without providing further details on how this transformation occurred. Along these lines, we propose that the median migration of the medial scapula-coracoid contact left a large opening typically designated in plesiosaurs as the pectoral fenestration, and is homologous to the coracoid foramen in non-plesiosaur eosauropterygians (see also Araújo and Correia, in press). Landmark 7 depicts the observation made by Sues (1987) in which the thickened glenoidal portion of Pistosaurus is oriented diagonally relative to the anterioposterior axis of the coracoid, but in more derived sauropterygians the thickened glenoidal portion is oriented transversely.
Landmarks 10 through 14 depict the expansion of the coracoid’s lateral border posteriorly, previously noted by Watson (1924), which is thought to be a result of an muscle attachment area increase for the coracobrachialis and brachialis in derived pistosaurs and plesiosaurs (Fig. 5a). These muscles together with the supracoracoideus form a developmentally cohesive muscle group in reptiles called the ventral mass musculature (Sewertzoff, 1904).
Plesiosaurs— The morphological disparity among the pectoral girdle elements in Plesiosauria has been acknowledged as having phylogenetic significance by White (1940) and Welles (1962), but has only recently been codified and used in phylogenetic analysis (O’Keefe, 2001;Drukenmiller& Russell, 2008; Ketchum & Benson, 2010; Benson et al., 2012; Evans, 2012, Benson &Druckenmiller, 2014). Microcleididae (sensu Benson et al., 2012), possesses the plesiomorphic conditions of a broad preglenoid projection, and reduced ventral portion of the scapula, reduced coracoid foramen, as well as retention of large clavicles and interclavicle (e.g., Westphaliosaurus, Seeleyosaurus). Leptocleididae share affinities with the Polycotylidae pectoral girdle in having a coracoid median perforations and a narrow but anteriorly expanded preglenoid projection (Fig. 6). On the other hand, Cryptocledidae (sensu Evans, 2012) shares affinities with Elasmosauridae (Fig. 4), but does not possess posterior lateral coracoid wings and no intercoracoid vacuity (Fig. 5).
The pectoral girdle experienced major transformations across Eosauropterygia, for example with the formation of the longitudinal pectoral bar. In non-plesiosaur eosauropterygians, the scapulae do not meet medially. Instead, they are separated by a large pectoral fenestra (Rieppel, 2000). Medially, the coracoids abut weakly and, the clavicles strongly interlock. In plesiosaurs, the median migration of the medial coracoscapular contact and the reduction of the preglenoid projection allow a scapula-scapula contact (Fig. 6), although in basal plesiosaur forms the scapula-scapula contact is weak or inexistent (see Smith, 2007 following phylogeny of Benson et al., 2012). An extensive longitudinal bar is only present in some elasmosaurids such as Cardiocorax and YPM1644 (potentially also in Libonectes and Elasmosaurus), which increases muscle attachment area and reinforces the pectoral girdle as a single structural unit. In these taxa and other Late Cretaceous elasmosaurids, the ventral area of the scapula is subequal to the area of the coracoid (Fig. 7b). However, in polycotylids, plesiosaurids, Lower Creteceouselasmosaurs and basal cryptocleidids the ventral area of the scapula remains small (<0.4) relative to the coracoid area (Fig. 7b). The most extreme case is in plesiosaurids in which the ventral area of the scapula is only about 15% of the area of the coracoid (Fig. 7b). On the other hand, in Cardiocorax the coracoid has nearly 50% more the area of the scapula-clavicle complex together (Fig. 7). Such discrepancies among plesiosaurs seem to suggest that not only the locomotory muscles play different roles from clade to clade but also the enlargement of the coracoid is decoupled from the ventral expansion of the scapula (see also Fig. 7b).
The clavicle and its relationship with the scapula is subject of a remarkable transformation in Eosauropterygia as well. In non-plesiosaur eosauropterygians the clavicles are tightly sutured together medially and oriented transversely (e.g., Nothosaurus) or obliquely anteriorly (e.g., Ceresiosaurus). Also the scapula and clavicle form a rigid structural unit by means of a posterior process of the clavicle that tightly articulates with the medial side of the scapula (Rieppel, 2000). However, in all plesiosaurs the clavicle-interclavicle complex becomes greatly reduced including basalmost taxa such as Macroplata (Ketchum & Smith, 2010) or Attenborosaurus (Sollas, 1881), or even in Late Cretaceous polycotylids (e.g., Dolichorhynchopssee Williston, 1903). The scapuloclavicular articulation is in most cases weak (e.g., Attenborosaurusconnybeari, Rhomaleosauruscramptoni, Peloneustesphilarcus, Hauffiosauruszanoni, Westphaliasaurussimonensii, Tricleidusseeleyi, Leptocleidussuperestes, Dolichorhynchopsosborni) but it can be extensively developed anteriorly in Late Cretaceous Elasmosauridae (e.g., TMM2245-1, Cardiocoraxmukulu, and possibly YPM1644). In these late Cretaceous elasmosaurs the clavicle can account for nearly the half area as the scapula (e.g., Cardiocorax, Fig. 3).
The pistosaur-plesiosaur median migration of the medial of the coracoscapular contact is not well documented in the fossil record (Fig. 5a), leaving an important morphological gap (Fig. 6). Nevertheless, these modifications had to occur concomitantly with (1) a counterclockwise rotation of the scapuloclavicular contact, which led to a posterior translation of the clavicle-interclavicle complex, (2) a medial elongation of the scapula, and (3) the anterior projection of the preglenoid projection of the coracoid. However, the presence of a medial coracoscapular contact is highly homoplastic even within the same taxa (e.g., Microcleididae: M. tournemirensis versus Westphaliasaurus, Rhomaleosauridae: Rhomaleosaurus cramptoni versus Meyerasaurus victor, Elasmosauridae: Callawayasaurus versus Cardiocorax). Nevertheless, if the medial coracoscapular contact is maintained it only abuts on the lateral side of the preglenoid projection (e.g., Macroplata, Meyerasaurus, Thalassiodracon, Plesiosaurus, Dolichorhynchops herschelensis). In Elasmosauridae and basal cryptocleidids the condition is slightly different because the preglenoid projection is narrowed, thus the medial coracoscapular contact adjoins anteriorly. Another feature poorly documented in the fossil record is the expansion of the coracoid (Fig. 6), possibly due to the scarce Late Triassic eosauropterygian record. Regardless, the scarce pistosaur record shows high morphological disparity in the coracoid (Fig. 5a, 6, 7a). The results demonstrate a convergence between basal cryptoclidids (Muraenosaurus, Tricleidus and Cryptocleidus) and polycotylids due to the narrow preglenoid projection and the absence of intercoracoid vacuity (landmarks 4, 5, 9 and 10).
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Supplementary Table Captions
Supplementary Table 1 – Dataset for figure 7C; Ratio between the dorsal blade of the scapula (cm2) and ventral area of the scapula.
Supplementary Table 2– Dataset for figure 7D; Humeral Ratios.
Supplementary Table 3– Dataset for figure 7E; Radius Ratios
Figure Captions
Supplementary Figure 1 – Phylogenetic tree resulting from Ketchum & Benson (2010) datamatrix (refer to methods for details; pruned version of this tree illustrated in Figure 4.)
Supplementary Figure 2 – Phylogenetic tree using matrix and settings of Vincent et al. (2011).
Supplementary Figure 3 – Landmark configurations used for phylogenetics morphometrics analysis; see Figure 5 for preferred tree. All trees illustrated in Supplementary Figures 4-13.
Supplementary Figure 4 – Best tree using search level of thoroughness 3 with Heuristic re-alignment.
Supplementary Figure 5 – Best tree using search level of thoroughness 4 with Heuristic re-alignment.
Supplementary Figure 6 – Tree using search level of thoroughness 0 with Heuristic re-alignment.
Supplementary Figure 7 – Tree using search level of thoroughness1 with Heuristic re-alignment.
Supplementary Figure 8 – Tree using search level of thoroughness 2 with Heuristic re-alignment.
Supplementary Figure 9 – Tree using search level of thoroughness 0 with RFTRA re-alignment.
Supplementary Figure 10– Tree using search level of thoroughness 1 with RFTRA re-alignment.
Supplementary Figure 11 – Tree using search level of thoroughness 2 with RFTRA re-alignment.
Supplementary Figure 12 – Tree using search level of thoroughness 3 with RFTRA re-alignment.
Supplementary Figure 13 – Tree using search level of thoroughness 4 with RFTRA re-alignment.
Michael Polcyn
Ricardo Araújo
Octávio Mateus