Modeling Neck Mobility in Fossil Turtles

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DOI: 10.1002/jez.b.22557 · Source: PubMed
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Abstract
Turtles have the unparalleled ability to retract their heads and necks within their shell but little is known about the evolution of this trait. Extensive analysis of neck mobility in turtles using radiographs, CT scans, and morphometry reveals that basal turtles possessed less mobility in the neck relative to their extant relatives, although the anatomical prerequisites for modern mobility were already established. Many extant turtles are able to achieve hypermobility by dislocating the central articulations, which raises cautions about reconstructing the mobility of fossil vertebrates. A 3D-model of the Late Triassic turtle Proganochelys quenstedti reveals that this early stem turtle was able to retract its head by tucking it sideways below the shell. The simple ventrolateral bend seen in this stem turtle, however, contrasts with the complex double-bend of extant turtles. The initial evolution of neck retraction therefore occurred in a near-synchrony with the origin of the turtle shell as a place to hide the unprotected neck. In this early, simplified retraction mode, the conical osteoderms on the neck provided further protection. J. Exp. Zool. (Mol. Dev. Evol.) 9999B: 1-14, 2014. © 2014 Wiley Periodicals, Inc.
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Modeling Neck Mobility in Fossil
Turtles
INGMAR WERNEBURG
1,2,3
*,
JULIANE K. HINZ
1
,
MICHAELA GUMPENBERGER
4
,
VIRGINIE VOLPATO
5
,
NIKOLAY NATCHEV
6,7
,AND
WALTER G. JOYCE
1,8
1
Fachbereich Geowissenschaften der Eberhard Karls Universität Tübingen, Tübingen, Germany
2
Museum für Naturkunde, Leibniz Institute for Research on Evolution and Biodiversity, Berlin,
Germany
3
Paläontologisches Institut und Museum der Universität Zürich, Zürich, Switzerland
4
Diagnostic Imaging, University of Veterinary Medicine Vienna, Vienna, Austria
5
Paläoanthropologie und Messelforschung/Mammalogie, Senckenberg Gesellschaft für
Naturforschung, Frankfurt am Main, Germany
6
Department of Integrative Zoology, University of Vienna, Vienna, Austria
7
Faculty of Natural Science, Shumen University, Bulgaria, Shumen 9712, Univeristetska str. 115
8
Department of Geoscience, University of Fribourg, Fribourg, Switzerland
In addition to their shell and their unusual skull and shoulder
region, turtles (Testudinata) are unique in regard to the mobility
of their necks (Rieppel, 2008; Nagashima et al., 2009). In contrast
to all other vertebrates, turtles are able to hide their head and
neck inside the body wall (i.e., inside the shell) in order to protect
these structures against predators. Among extant turtles, two
monophyletic clades can be recognized, which, among other
features, differ in the way they retract their head and neck inside
the shell (Gaffney, '75). Pleurodires fold their head and neck
sideward in a horizontal plane anterior to the rib cage, whereas
ABSTRACT Turtles have the unparalleled ability to retract their heads and necks within their shell but little is
known about the evolution of this trait. Extensive analysis of neck mobility in turtles using
radiographs, CT scans, and morphometry reveals that basal turtles possessed less mobility in the
neck relative to their extant relatives, although the anatomical prerequisites for modern mobility
were already established. Many extant turtles are able to achieve hypermobility by dislocating the
central articulations, which raises cautions about reconstructing the mobility of fossil vertebrates.
A3Dmodel of the Late Triassic turtle Proganochelys quenstedti reveals that this early stem turtle
was able to retract its head by tucking it sideways below the shell. The simple ventrolateral bend
seen in this stem turtle, however, contrasts with the complex doublebend of extant turtles. The
initial evolution of neck retraction therefore occurred in a nearsynchrony with the origin of the
turtle shell as a place to hide the unprotected neck. In this early, simplied retraction mode, the
conical osteoderms on the neck provided further protection. J. Exp. Zool. (Mol. Dev. Evol.) 9999B:
XXXX, 2014. ©2014 Wiley Periodicals, Inc.
How to cite this article: Werneburg I, Hinz JK, Gumpenberger M, Volpato V, Natchev N, Joyce WG.
2014. Modeling neck mobility in fossil turtles. J. Exp. Zool. (Mol. Dev. Evol.) 9999B:114.
J. Exp. Zool.
(Mol. Dev. Evol.)
9999B:114, 2014
Grant sponsor: Deutsche Forschungsgemeinschaft; grant number: JO
928/1.
Correspondence to: Ingmar Werneburg, Museum für Naturkunde,
Leibniz Institute for Research on Evolution and Biodiversity, Berlin,
Germany.
Email: i.werneburg@gmail.com
Received 15 October 2013; Revised 18 December 2013; Accepted 23
December 2013
DOI: 10.1002/jez.b.22557
Published online XX Month Year in Wiley Online Library
(wileyonlinelibrary.com).
RESEARCH ARTICLE
©2014 WILEY PERIODICALS, INC.
cryptodires retract their neck within the rib cage in a vertical
plane. High neck mobility is otherwise known for many birds
(Weisgram and Zweers, '87) and has been reconstructed for
advanced sauropodomorphs (Taylor et al., 2009). Although some
birds can retract their heads and necks over their bodies, only
turtles can retract the head/neckapparatus within the connes
of the body wall.
The cervical column of turtles consists of eight vertebrae
(Williams, '50; Müller et al., 2010) and a great diversity of vertebral
morphology can be recognized that enables various types of
movement (Vaillant, 1881, 1883; Ogushi, '11; Williams, '50;
Hoffstetter and Gasc, '69; Herrel et al., 2008). To date, research on
the neck has been restricted to documenting cervical variation
(Williams, '50), investigating the myology of the neck (Werneburg,
2011), understanding the general mechanics of neck retraction
(Weisgram and Splechtna, '90), and exploring the interactions of
neckmovement with feeding (Herrel et al., 2008). However,
virtually no efforts have been made to reconstruct neck mobility
among fossil turtles beyond the tacit assumption that the
amphicoelous vertebrae of basal turtles did not permit great
mobility (Hay, '08; Młynarski, '76; Williams, '50). Many basic
questions regarding the origin and evolution of neck retraction
mechanisms therefore remain unanswered.
How great was the mobility of the neck of fossil stem turtles?
When and how did the neck retraction mechanism and the great
neck mobility of extant taxa evolve, and did the drastically
different modes of retraction in pleurodires and cryptodires evolve
independently from one another? Which anatomical changes are
associated with these important evolutionary innovation? Does
the mobility of the neck of extant turtles have any implication
regarding the mobility of extinct taxa? We tackle these questions
by analyzing the vertebrae of several extant and fossil turtle
species with the help of angle measurements and by modeling the
mobility of the bestknown Triassic fossil turtle, Proganochelys
quenstedti (Gaffney, '90). The mobility of living turtle specimens
was analyzed with the help of computed tomography. Taphonomic
distances (i.e., the difference between the maximum mechanically
possible and observed movement) were calculated to better
reconstruct mobility in the necks of fossil turtles. Throughout this
article, the term exionis used to refer to Ushaped dorsal,
ventral, and lateral bending of the neck, whereas the term
retractionis used to refer to the withdrawal of the neck within
the connes of the body wall.
METHODS
Specimens
In total, the neck vertebrae of ve extinct and 35 extant turtle
species were studied. Two nonturtle species were used for
comparison (Fig. 1). The list of fossil and extant turtle skeletons
used herein, including morphometric measurements, is provided
in Supplementary Table S1 whereas living turtles are listed in
Supplementary Table S2. Additional data, including angle
measurements and images, were taken from the literature
(Supplementary Table S3).
Radiographs and Fluoroscopy of Living Animals
Fluoroscopy of different neck postures of 29 animals (Table S2),
presented to the clinic with reasons unreleated to and not
interfering with this study, were performed using a Siemens
Axiom Iconos R200 (Siemens AG, München, Deutschland,
Germany) at the University of Veterinary Medicine in Vienna
(Fig. 2).
In order to not unreasonably stimulate or manipulate the
animals, focus was placed on the maximum retraction of each
specimen and only one radiograph was produced for each animal.
If the animals were cooperative and curious to attractants (e.g.,
food, compare Fig. 2C), additional images were taken for other
positions of the neck (Supplementary Table S7).
CTScans of Living Animals
Most individuals used for uoroscopy underwent an additional
diagnostic CT examination using a Siemens Somatom Emotion
multislice scanner (Siemens AG) at 130 kV, 80 mA, 1.0 sec
(rotation time) and 0.6 mm thick slices. The specimens were
kept at 2530°C temperature and anesthetized with medetomidine
0.05 mg/kg BWand ketamine 5 mg/kg body mass (intramuscular)
(Supplementary Table S2).
The head and neck of each specimen were manually exed to
the physiologically (1) most extended (Fig. 2J,N, Supplementary
Table S8A), (2) most retracted (Fig. 2M, Supplementary Table S8B,
C), (3) most lateral (Supplementary Table S8D,E), (4) most dorsal
(Fig. 2K,O, Supplementary Table S8F), and (5) most ventral
position (Fig. 2L,P, Supplementary Table S8G). The living animals
were handled very carefully; their heads and necks were not
overstretched to avoid strangulation of the neck plexus and to not
risk their health. This method can only provide an approximation
of the actual maximal mobility in living animals, as muscle forces,
such as those provided by musculus retrahens capiticollique
(Werneburg, 2011) or by intervertebral muscles, certainly allow for
slightly larger retraction or exion of the neck. The above
mentioned radiographic studies (Supplementary Table S7) there-
fore provide an important comparison.
The CTdata was reconstructed with the surface view tool of
Amira, surface les (obj/ply) were exported to MeshLab, and
screenshots taken from that software were analyzed using ImageJ
(http://meshlab.sourceforge.net/).
Angle Measurements
For macerated and fossil specimens, as well as for radiographed
and CTscanned living animals, the amount of mobility was
measured between adjacent vertebrae using a suite of different
techniques (Supplementary Tables S4, S7, and S8). For the
macerated and fossil specimens, digital photographs were taken
2WERNEBURG ET AL.
J. Exp. Zool. (Mol. Dev. Evol.)
Lepidosauria
Testudinata
Testu dines
Pleurodira
Pancryptodira
Trionychia
Chelydridae
Emydidae
Kinosternidae
Testudinidae
Geoemydidae
Cryptodira
† Proganochelys quenstedti
† Meiolania platyceps
† Naomichelys speciosa
Carettochelys insculpta
Platysternon megacephalum
† Chisternon undatum
Podocnemis unilis
Malaclemys terrapin
Phrynops georoanus
Chelydra serpentina
Kinosternon scorpioides
Emys orbicularis
Pelomedusa subrufa
Cuora mouhotii
Malacochersus tornieri
Pyxis planicauda
Indotestudo elongata
Dermatemys mawii
Hydromedusa tectifera
Testudo graeca
Kinixys erosa
Testudo hermanni
Erymnochelys madagascariensis
Pelodiscus sinensis
Trachemys scripta elegans
Astrochelys radiata
Pogona vitticeps
Rhacodactylus ciliatus
Graptemys pseudogeographica
Heosemys grandis
Phrynops hilarii
Sternotherus carinatus
Chelonoidis nigra
Stigmochelys pardalis
† Xinjiangchelys chowi
Chelodina novaeguineae
Macrochelys temminckii
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
Chelodina longicollis
Apalone spinifera
Kinosternon subrubrum
Terrapene carolina
Chrysemys picta
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
macerated/fossil bones X-ray live CT used to calculate taphonomic distance
data derived from literature
Figure 1. Fossil and living turtle species analyzed in the present study. Phylogenetic arrangements follow Joyce (2007) and Anquentin (2012)
for extinct taxa and Thomson and Shaffer (2010) for extant taxa.
J. Exp. Zool. (Mol. Dev. Evol.)
MODELING NECK MOBILITY IN FOSSIL TURTLES 3
for each joint (Fig. 3AD) and angles were measured using ImageJ.
Angles on radiographs were measured directly.
Fossil and macerated vertebrae were manually moved against
each other along the horizontal and vertical plane (Fig. 3AD). The
central articulations were always left articulated with one another
(without space for intervertebral disc) and at least part of the
zygapophyses was always left articulated. The neutralposition is
herein conrmed to be the maximum overlap of the articular
facets of the zygapophyses (see Discussion section). The maximum
dorsal and ventral movement was documented in lateral view by
measuring the angle between ventral margins of the central bodies
to the exclusion of ventral processes (Fig. 3AC). The maximum
amount of lateral motion was documented from dorsal view and
angles were measured between the midlines of the neural arches
(Fig. 3D).
Additional photographs were taken in anterior and posterior
view of each vertebra and angles were measured between the
centre of the centrum and the lateral most expansions of the
articular facet of the zygapophyses (Fig. 3E, Supplementary Table
S5).
For angles on radiographs (Supplementary Table 7A,C,D,F) and
CT images (Supplementary Table 8A,B,F,G), measurements were
also taken along the ventral line of the centra (in lateral view) and
along the midline (neural spine or hypophyseal crest/process) in
dorsal or ventral view. When necessary, the 3D mesh models were
rotated to allow more accurate measurement of angles. For both
types of neck retraction, a dorsal view was measured of the
deformed neck to estimate spatial rotation.
The angles were taken with an accuracy of 0.1° but an
uncertainty of measurement of about 1 can be assumed. The
A
AB C
D E F HG
I J K L
M N O P
Figure 2. Illustration of select methods. (AC,I) Setup for uoroscopy; (DH) radiographs; (JL) setup for CTscans; and (MP)CTscans
(visualized via Avizo and MeshLab). (A, DF) Phrynops hilarii (IW1121); (B) Emys orbicularis (IW1116); (C) Malacochersus tornieri (IW1119);
(GH) Chelodina novaeguineae (IW1168), with kind permission of Josef Weisgram (Vienna); (IP) Sternotherus carinatus (IW1145).
J. Exp. Zool. (Mol. Dev. Evol.)
4WERNEBURG ET AL.
fossil vertebrae used are all in good condition and most are
symmetrical: erosion and deformation are therefore thought to be
negligible.
3DScans and Animations
Micro computed tomography (mCT) was performed for selected
vertebrae and associated skulls at the SteinmannInstitut für
Geologie, Mineralogie & Paläontologie/Rheinische Friedrich
WilhelmsUniversität Bonn with a resolution of 187 mm and at
the Riedberg Campus of the GoetheUniversität Frankfurt with a
resolution of about 25 mm. The CTscanned les were imported to
Geomagic Studio 11 (Geomagic_Inc. 2009) where the post
processing was undertaken. Each scanned bone was loaded into
the software separately in order to optimize computing capacity
and to obtain full sight of each bone. The bone surface was
smoothened to remove the steplike surface structures created by
the CT scanning progress. Existing holes in the model surface were
lled using curvature lling algorithms which generate smooth
lls following the surface geometry to the highest possible degree.
Furthermore, polygon spikes, nonmanifold edges, selfoverlaps,
and small components such as isolated polygon relicts were
removed in order to simplify and smoothen the polygon surface.
Missing parts of fossil bones, such as zygapophyses or vertebral
processes, were complemented by mirroring the nondeformed or
not broken part from the opposite side of the vertebra (if present).
The mirrored structure was connected to the existing bone surface
by creating a Boolean Union between the existing vertebra model
and the newly added parts. All isolated bones were saved and
exported as Wavefront Object Files (OBJ).
In a second step, the cleaned and smoothed bone OBJs were
imported into the CAD software Rhinoceros 3D (Robert_McNee-
l_&_Associates, 2003, November) where articulation and angula-
tion were set up. For this purpose, the screen was split into four
viewports (top, front, side, and perspective) which allowed precise
model rotations along the main axes of the world coordinate
system. Complex rotations were achieved by rotating around the
X,Y, and Zaxis consecutively.
At rst, a neutral pose of the cervical spine was modeled.
Subsequently, calculated angles between the vertebrae were added
in order to create different model poses. This was done in caudal to
cranial directionbeginning at C8 and ending at C1. During the
setup of a joint angle, all vertebrae cranial to this joint were
grouped and moved together in order to avoid positioning errors.
Afterwards, color schemes were assigned to the different model
poses and renderings of the different viewports were created using
the integrated Rhinoceros 3D standard rendering tool.
Taphonomic Distance
To calculate the live neck performances in fossils, the theoretical
(Supplementary Table S4) and actual (Supplementary Table S8)
angles between vertebrae were compared (Supplementary Table
S9) in the six extant turtle taxa (see Fig. 1) for which enough
A
D
C
B
a
L2
L1
H1
B1 B2
B3
180°
E
Figure 3. Denitions of angle measurements (raw mobility) and
lengths. (AD)Denition of angles exemplied by the 4th and 5th
cervical vertebrae of Phrynops geoffroanus (SMF 45470). Angles
between vertebrae were measured along the ventral border of the
centrals in lateral view and along the neural spines in dorsal view.
Angle between vertebrae in (A) neutral position, (B) maximal dorsal
exion, (C) maximal ventral exion, and (D) maximal lateral exion.
A direct contact of the centra and zygapophyses was allowed in
osteological specimens, whereas in life images (Xrays/CTs) the
natural conditions were measured, in which intervertebral disks are
present. (E) Anterior face of the 7th vertebrae of P. unilis (articular
facets in dashed lines) and denition of the zygapophyseal angle.
(CD) In total, six morphometric lengths were measured for the
macerated and fossil vertebrae using a digital caliper with an
accuracy of 0.01 mm. The measurements were rounded to 0.1 mm
and correlated to each other (Supplementary Fig. S5, Supplementary
Table S1 and S6). B1, maximum distance between the transverse
processes; B2, maximum distance between the anterior zygapoph-
yses; B3, maximum distance between the posterior zygapophyses;
H1, height (measured with the centrum oriented horizontally); L1,
maximum length between zygapophyses; L2, length of centrum.
J. Exp. Zool. (Mol. Dev. Evol.)
MODELING NECK MOBILITY IN FOSSIL TURTLES 5
comparable data was available. Regressions were calculated using
(1) all vertebra within the neck of particular species and (2) the
same single vertebrae among all species. Contrary to the rst
approach, the second resulted in implausible calculations. That
speaks for a deeper dependence of adjacent vertebrae along a
single neck than a correlation of particular vertebrae between
species.
Following the same steps, the mobility between the 8th cervical
(CV8) and the 1st dorsal (DV1) vertebrae was calculated resulting
in implausible results for dorsalventral mobility but plausible
results for lateral mobility. This speaks for a different integration
of CV8/DV1 during dorsalventral exions than exists between
the other neck vertebrae; for lateral vertebrae movement a
continued equation in the relation of vertebra towards CV8/DV1 is
plausible.
The regressions of theoretical against actual angles between the
neck vertebrae (Supplementary Table S10) were used to calculate
live neck performances in fossils (Supplementary Tables S11 and
12). The taphonomic distance was calculated for the cervical
vertebrae in pleurodires, cryptodires, and all turtles combined (i.e.,
Testudines) separately. For all fossil taxa all three formulae were
applied and, to decide for the most plausible movement, the
following conservative assumptions were made (Supplementary
Table S11): (1) The fossil neck vertebrae had the same relationships
to each other as those of extant taxa (i.e., same formula;
Supplementary Table S10), (2) the measured angles should be
larger than the calculated lifeangles in most cases (i.e., only few
overstretchings of adjacent vertebrae are allowed), and (3) in the
case of two or three plausible movements, the largest differences
to the meassured value are presumed to be less plausible than the
smaller difference.
RESULTS
Raw Mobility of Turtle Necks
Herein, raw mobilityis dened as the maximum amount of
horizontal and vertical motion that is mechanically allowed
between two vertebrae, measured in degrees relative to the
neutral position, which is dened as the vertebral position with
the greatest zygapophyseal overlap (Fig. 3). The lowest dorsal,
ventral, and lateral raw mobility is seen in stem turtles.
Cryptodires have the greatest dorsal and ventral raw mobility,
whereas pleurodires have the greatest lateral raw mobility (Fig. 4,
Supplementary Figs. S13, and Table S4). Relative to the centra,
the zygapophyses show the largest angles in cryptodires, whereas
stem turtles and pleurodires have smaller angles. Greater angles
are measurable in the zygapophyses of the more anterior vertebrae
of all species. Greater angles can also be found in the
zygapophyses of the more posterior vertebrae of cryptodires
(Supplementary Fig. S4).
-100
-50
0
50
100
angles (°)
maximal/minimal
raw-range of exion
in fossil/macerated
skeleton
maximal/minimal
range of exion in life
0
20
40
60
dorso-ventral exionlateral exion
outgroup CryptodiraPleurodirastem Testudines
CV1 CV6CV5
CV4
CV3CV2 CV8
CV7
DV1
S
DV1
SCV1 CV6CV5
CV4
CV3CV2 CV8
CV7 DV1
S
CV1 CV6CV5
CV4
CV3CV2 CV8
CV7
DV1
SCV1 CV6CV5
CV4
CV3CV2 CV8
CV7
standard diviation
of calculated
movements
maximal dorsal/minimal
ventral range during
maximal cryptodiran
retraction
maximal lateral range
during maximal pleurodiran
retraction
A
B
C
D
E
F
G
H
Figure 4. Neck movement calculated for fossil taxa compared to the maximal dorsoventral (top row) and maximal lateral exions (below)
measured for living species (compare Supplementary Tables S11 and S12). Images illustrate extant turtles at maximal retraction. Legend
within the Figure.
J. Exp. Zool. (Mol. Dev. Evol.)
6WERNEBURG ET AL.
Within any given cervical column, the dimensions of the
vertebrae are strongly correlated with one another (Supplementa-
ry Fig. S5). By contrast, the dimensions of a vertebra are only
poorly correlated with its raw mobility and various measures of
raw mobility only correlate poorly with one another. Stronger
correlations exist between the neutral position of adjacent
vertebrae and their related dorsal and ventral exion (Supple-
mentary Table S6).
Calculated Neck Mobility in Fossil Turtles
Three models of neck mobility were calculated for Pleurodira and
Cryptodira separately and for both together (Testudines) that
describe the taphonomic distance of the three groups (i.e., the
difference between measured raw mobility and true mobility
observed on radiographs and CT images) (Supplementary Table
S7). The stem turtles Proganochelys quenstedti,Meiolania
platyceps, and Naomichelys speciosa show dorsal and ventral
neck exion patterns that are consistent with the cryptodiran and
pleurodiran models, respectively. The dorsal and lateral exion of
the neck of the paracryptodire Chisternon undatum is consistent
with that of Pleurodira, whereas its ventral exion is consistent
with the patterns seen in both the Pleurodiraand Testudines
formulae. Finally, the basal stemcryptodire Xinjiangchelys chowi
exhibits a dorsal exion that is consistent with that of Cryptodira,
but whereas its ventral exion is consistent with the Cryptodira
and Testudinesformulae, the lateral movement is more consistent
with the pleurodiran mode (Fig. 7G,H). The best supported
prediction of fossil movement is summarized in Supplementary
Table S8.
The three models were used to predict the mobility between the
eighth cervical vertebrae (CV8) and the rst dorsal vertebrae (DV1)
of fossil stem turtles. All models produced nonplausible results (i.
e., negative motion; Supplementary Table 13) for dorsoventral
mobility revealing that this joint is structurally different in basal
turtles relative to all extant turtles. However, all models produce
plausible results for lateral movement (Fig. 4D, Supplementary
Table S9).
Outgroup representatives do not show sufcient exibility to
allow any movement resembling the neck retraction seen in
extant turtles (Fig. 4A,B). The raw and calculated mobility of the
vertebrae of all fossil turtles included in this study (incl.
deviation) lies strongly below the ability needed for full
cryptodiran retraction (Fig. 4C). Similarly, the raw and calculated
mobility of these fossil turtles does not reach the maximum
exion between CV35 that would be needed for full Sshaped
pleurodiran like retraction (Fig. 4D). It is therefore apparent that
the fossil stem turtles included in our sample were not able to
retract their necks, at least in the way that extant cryptodires and
pleurodires do. Our observations and calculations additionally
conrm that pleurodires are not mechanically able to retract
their necks in the cryptodiran mode (Fig. 4E) and vice versa
(Fig. 4H).
Hypermobility
As a whole, true dorsoventral mobility remains within the
osteological connes set by the raw mobility. However, some
pleurodires (Fig. 4E) and some cryptodires (Fig. 4G) have the
ability to slightly overstretch particular joints (i.e., hypermobility)
by disengaging the central articulations, particularly during
extreme dorsoventral exion (Fig. 2O, Supplementary Figs. S10
and S11) while having the muscles and tendons maintain the
integrity of the neck. The zygapophyses of two adjoining vertebrae
never loose contact with one another during dorsoventral exion.
During lateral exion, the neck shows no (Fig. 4F) or only little
hypermobility of adjacent vertebrae in pleurodires (Supplementa-
ry Fig. S12). In the most retracted neck condition of cryptodires,
some vertebral centra show little detachmentsand in some
specimens, the zygapophyses of CV8 and DV1 can detach as well.
Naturally, the observed maximally retracted neck condition of
cryptodires (Fig. 4) represents only the nal stage of a safety
linked bicycle chain”‐like process of retraction (Herrel et al., 2008)
while squeezing through the shell opening. Given that we only
documented the end point during retraction in most species, it is
plausible that other joints also show hypermobility during
retraction. The large angle peak documented between CV4/CV5
in Figure 4G results from live angle measurements during
trionychid retraction. As no detachment of vertebrae occurs in
those species, a similar high raw mobility can be expected.
Nevertheless, the articulation of vertebrae of up to 100° must be
associated with considerable dislocations of the intervertebral
discs and deformations of the intervertebral capsule (Supplemen-
tary Fig. S11F).
Modeling
A3Dmodel of the mobility of the neck of the Triassic stem turtle
Proganochelys quenstedti indicates that this taxon was able to
retract its head by tucking it sideways within the connes of the
shell. In contrast to living pleurodires and cryptodires (Figs. 2GH,
M, 5C and D, and 6C and D), however, the retraction seen in P.
quenstedti is achieved through a compound ventrolateral exion,
not through an Sshaped folding of the neck (Fig. 7). By contrast,
cryptodiran like retraction can only be achieve by our model under
highly unreasonable circumstances (i.e., 180° rotation between the
eighth cervical and rst thoracic vertebrae and hypermobility
along all cervical joints, Supplementary Fig. S9).
DISCUSSION
Reconstructing the Neutral Neck Position in Fossils
Given that the vast majority of fossil organisms do not display any
unusualneck morphology, only little attention is generally
accorded to mobility of this body region. A few notable exceptions
nevertheless exist: humans, herbivorous mammals, crocodilians,
birds, and other theropod dinosaurs (van der Leeuw et al., 2001a,b;
Samman, 2013; Snively et al., 2013), and particularly sauropod
J. Exp. Zool. (Mol. Dev. Evol.)
MODELING NECK MOBILITY IN FOSSIL TURTLES 7
dinosaurs (Berthoz et al., '92). The neck of sauropod dinosaurs has
been studied extensively because its great length raises many
physiological and biomechanical questions. Given that sauropods
are situated along the phylogenetic stem of birds (Aves) within
Archosauria, a number of recent studies reconstructed the muscle
and ligament system of the sauropod neck by phylogenetically
bracketing (de Queiroz and Gauthier, '92; Witmer, '95) the
morphology of extant birds and crocodilians (Wedel and Sanders,
2002; Tsuihiji, 2004). In addition, the research is informed through
observations made from extant analogues such as the giraffe,
camel, and ostrich (Dzemski and Christian, 2007; Cobley et al.,
2013) or by reference to unique anatomical structures such as the
extensive air sack system (SchwarzWings and Frey, 2008).
Much of the research is focused on two primary questions: (1)
what was the resting position of the neck and (2) what was the
possible range of motion. Particularly the rst question is highly
contentious. Stevens and Parrish ('99) suggested by reference to
modern analogues that the resting position of sauropod dinosaurs
should be reconstructed at the point where the preand
postzygapophyses overlap two thirds, which they called the
neutral position.But this assumption was recently shown to be
incorrect by Taylor et al. (2009) by explicit reference to modern
analogues. Christian and Heinrich ('98) and Christian (2002), by
contrast, argued that the resting position should be reconstructed
where the stresses between the joints can be calculated to have
been the least.
In extant turtles, the necks are naturally curved in the posterior
half (Herrel et al., 2008) because the anterior carapacial edge
does not allow a fully horizontal neck orientation. Our
observation on the relaxed neck position of anesthetized turtles
(CTscan; Fig. 56) conrms the presence of this curvature. The
vertebral centra therefore never align in a straight line with 180°
angles. CTscans of turtles in this relaxed position furthermore
reveal that the zygapophyseal facets almost fully overlap each
other, that the central articulations t snugly, and that
intervertebral spaces are minimal (see Weisgram and Splechtna,
'90: g. 1b). We are able to reconstruct the characteristic bend of
the turtle neck in disarticulated specimens, when adjacent
zygapophyseal articular facets overlap another optimally. We
therefore conclude that this is the neutralposition in turtles. Our
Figure 5. Comparison of raw (A,B:Phrynops geoffroanus) and life neck motion (C,D:Phrynops hilarii) of a pleurodire turtle. In P. hilarii, dorsal
and ventral exion are based on lifecalculation (Supplementary Table S10), other neck positions are based on lifeCTdata. (A,C) frontolateral
perspective view, (B,D) dorsal view. Light blue ¼dorsal exion, green ¼ventral exion, red ¼lateral exion (incl. rotation);
orange ¼retracted neck; light gray ¼extended neck; gray transparent ¼shell. For further illustrations see Supplementary Figure S6.
J. Exp. Zool. (Mol. Dev. Evol.)
8WERNEBURG ET AL.
observations suggest that adjacent zygapophyseal facets should
be modeled to overlap completely when reconstructing the neutral
neck position in other fossil land vertebrates.
Predicting the Maximal Range of Motion in Fossils
There appears to be less contention regarding the reconstruction of
the possible range of motion in fossil taxa, perhaps because it is
always much greater than the preferred range of motion and
because it is thought to be clearly constrained by the anatomy of
the vertebrae. Stevens and Parrish ('99) reconstructed the possible
range of motion of sauropods using 3D modeling techniques and
constraints observed among extant birds, in particular the
zygapophyseal capsule.
Turtles exhibit a wide variety of neck motions that must be
considered extreme relative to other vertebrates. In addition to the
regularretraction of the necks within the body cavity (either
anterior to the rib cage, as in pleurodires, or within the ribcage
between the shoulder girdles, as in cryptodires), turtles can
catapulttheir necks over the shell for defence and perform
extreme contortions with their neck when attempting to rectify
themselves when lying on their backs. Our observations reveal
that hypermobility (i.e., the dislocation of the joints) occurs during
many of these extreme functions, but hypermobility also occurs
during less extreme dorsoventral and lateral exions. Although
the unexpected hypermobility we found between the vertebrae of
extant turtles can be ruled out as an autapomorphic feature of
turtles, the ability of turtles to circumvent constraints imposed by
their skeletal structure raises questions for modeling function in
fossil vertebrates in general. At the very least, the ability of turtle
to dislocated their central joints suggests that it is at least
conceivable that other tetrapods, including sauropod dinosaurs,
may have moved their necks slightly beyond the expected range of
motion predicted by their bones to enable exceptional movement,
for example, for reaching high and distant food resources,
defence, uplifting, or body cleaning, and that these motions did
not cause the death of an animal. As such, the results of our study
can be understood as a test for the ductility of the central articular
capsule, the spinal disk, and intervertebral muscles and tendons.
Figure 6. Comparison of neck motion in cryptodires illustrated in Malaclemys terrapin (A,B) and Graptemys pseudogeographicus (C,D) (both
Emydidae) using combined liveCTscans. (A,C) frontolateral perspective view, (B,D) lateral view. Color as in Figure 5. For further illustrations
see Supplementary Figure S7.
J. Exp. Zool. (Mol. Dev. Evol.)
MODELING NECK MOBILITY IN FOSSIL TURTLES 9
BA
C
F
E
D
Proganochelys quenstedti
Meiolania platyceps
Naomichelys speciosa
Xinjiangchelys chowi
Chisternon undatum
Cryptodira
Pleurodira
pleurodiran
mode
cryptodiran
mode
stem turtle mode
retraction
retraction
?
?
?
?
?
HG
B
F
C
pl
eu
r
odira
n
r
mod
e
e
H
E
F
Figure 7. Reconstruction and animation of neck motion in the stem turtle Proganochelys quenstedti (SMNS 16980). (A) Anterolateral view;
neck ections reconstructed using raw data. (B,C) Neck ections using the calculated angles for life motion (Supplementary Table S12) in
anterolateral (B) and frontal view (C); no rotation was allowed. (DF) Reconstructed rightlateral retraction of the neck in (D) anterolateral, (E)
frontal, and (F) dorsal view. Color code as in Figure 5, but here gray indicates neutral neck position. Dark blue in A shows lateral exion with no
rotation allowed. Dark orange ¼osteoderms on the neck. The atlas (CV1) was not reconstructed. For further details and discussion on the
osteoderms see Supplementary Figures S8 and S9. (G) Hypothesized evolution of neck exions and retractions in Testudinata. Dashedline
arrows indicate the hypothesized evolutionary changes. For further details see text. (H) Legend to (G).
J. Exp. Zool. (Mol. Dev. Evol.)
10 WERNEBURG ET AL.
Evolution of Neck Movements Within Testudinata
We fo un d ve modes of neck movement among the studied
groups of turtles (compare to Fig. 7G,H, Tables S7, and S8). As is
wellknown from studies on extant species, cryptodires (mode 1)
are characterized by extreme dorsolateral movement to the
neck, whereas pleurodires (mode 2) show extreme lateral
movement. The relatively large and terrestrial stem turtles
Proganochelys quenstedti,Meiolania platyceps,andNao-
michelys speciosa (mode 3), by contrast, show a cryptodiran
like dorsal and a pleurodiranlike ventral and lateral exion of
the neck, but were unable to achieve neckretraction in the
modes seen in extant turtles. The baenid Chisternon undatum
(mode 4) shows greater mechanical afnities with pleurodires,
whereas the xinjiangchelyid Xinjiangchelys chowi (mode 5)
shows greater mechanical afnities with cryptodires. Those
ndings are consistent with recent phylogenetic hypotheses that
place P. quenstedti,M. platyceps,andN. speciosa along the stem
of Testudines, that place baenid and xinjiangchelyid turtles
closer to or at the base of the crown (Gaffney et al., 2007; Joyce,
2007; Anquentin, 2011; Sterli and de la Fuente, 2013), and that
predict that the pure cryptodiran and pure pleurodiran neck
exion modes evolved independently within these lineages (Fig.
7G,H). Even though the necks of various fossil turtles are
consistent in their morphology with those of extant turtles, it is
important to emphasize that the mobility of all of their cervical
joints was lower.
Retraction in Fossils
Although necks are available from a surprisingly large sample of
taxa from the turtle stem lineage and the base of the crown, only
few speculations have been made as to how these turtles moved
their necks, beyond the conclusion that they could not withdraw
their heads within their shells (e.g., Młynarski, '76). This
conclusion is especially apparent for the basal stem turtles
Proganochelys quenstedti and Palaeochersis talampayensis
which possessed massive dorsal epiplastral processes that
connected the plastron to the ribcage/carapace and physically
hindered the head and neck from being withdrawn inwards as
extant cryptodires do (Gaffney, '90; Sterli et al., 2007). The
conclusion that other basal turtles were not able to withdraw their
heads is in part based on the unspoken assumption that
amphicoelous vertebrae cannot allow for great exibility (see
above; Gaffney, '90). Yet, the large preand postzygapophyses
found universally among stem and basal turtles [(e.g., Meiolania
platyceps (Gaffney, 1985, '90); Solnhoa parsonsi (Joyce, 2000);
Plesiobaena antiqua (Brinkman, 2003); Xinjiangchelys chowi
(Matzke et al., 2004)] reveal that some types of movement were
possible and wellcontrolled.
Our study reveals that stem turtles show the same general
mode of dorsal neck mobility that extant cryptodires do.
However, to acquire the ability to retract their necks, cryptodires
had to modify the vertebral shapes to enable even greater neck
mobility and mostly had to evolve an extremely modied
articulation between cervical vertebra 8 and dorsal vertebra 1
that allows folding the entire neck between the shoulder girdles.
This specialized joint, characterized by the ventrally facing
central articulation of the rst thoracic vertebra, is universally
absent among stem turtles, pleurodires, and most stem
cryptodires (Gaffney et al., 2007; Joyce, 2007). The lateral
exion of stem turtles, in contrast, is pleurodiranlike. To
achieve greater mobility, however, pleurodires modied some
joints to form strong kinks, that is, the joints between cervical
vertebra 5 and 6 (Weisgram and Splechtna, '90; Van Damme et
al., '95) and cervical vertebra 8 and dorsal vertebra 1 (Fig. 4D).
These specializations are universally lacking among stem turtles
and all total group cryptodires. Although the modications
needed to achieve full cryptodiran and pleurodiran retraction
should not be trivialized, the amount of precursor mobility
already found in basal turtles is surprising.
The models we calculated for the neck movement of Pleurodira,
Cryptodira, and all Testudines universally predicted implausible
amount of movement (i.e., negative movement) for the important
joint between cervical vertebra 8 and dorsal vertebra 1 in stem
turtles (Supplementary Table S9). This suggests that the cervico
dorsal joint has a different relationship to the neck vertebrae than
the latter have among each other, and may indicate greater or
reduced mobility at the neck/bodyarticulation in stem turtles
relative to crown turtles.
Our 3D reconstruction of the skull, neck, and carapace of
Proganochelys quenstedti allowed us to model neck movement for
this taxon independent of our calculations. If the joint at the neck/
bodyarticulation is unreasonably allowed to rotate a full 180°, as
in extant cryptodires, our simulations show that P. quenstedti still
would require angles of more than 45° between all cervical joints
to achieve cryptodiranlike retraction, requiring extreme hyper-
mobility for each joint (Supplementary Fig. S9). This reveals that
this taxon is only able to achieve cryptodiranlike neck retraction
under the most unlikely assumptions.
The dorsal process of the eighth cervical vertebra of P.
quenstedti is welldeveloped and possibly attached rmly to a
blunt process of the nuchal thereby restricting the mobility of this
joint. If the position of the eighth cervical is xed, our simulations
conrm that the neck of P. quenstedti does not permit this taxon to
retract its head below the shell like a pleurodire (i.e., with an S
shaped bend to the neck). But it was unexpected to discover that
this taxon was able to retract its head, without the use of
hypermobility, by tucking it sideways below the carapace in a
combined ventrolateral motion (Fig. 7DF).
The conclusion that P. quenstedti was able to retract its head and
neck within the connes of the shell contradicts current orthodoxy
that basal turtles had nonretractable necks (Hay, '08; Williams,
'50; Młynarski, '76; Gaffney, '90), although we are unable to nd
any published rational explicitly justifying this conclusion.
Instead, we suspect that low mobility was assumed to be present
J. Exp. Zool. (Mol. Dev. Evol.)
MODELING NECK MOBILITY IN FOSSIL TURTLES 11
based on the combined presence of (1) amphicoelous vertebrae,
which correlated with the presence of a stiffened vertebral column
in many other groups of vertebrates (Romer, '56); (2) a fully roofed
skull lacking temporal emarginations, which correlate among
living turtles with the inability to retract their heads (Gaffney, '90;
Werneburg, 2012); (3) large dorsal epiplastral processes, which
span the anterior opening of the shell between the plastron and the
carapace thereby mechanically restricting movement of the head
between the shoulders (Gaffney, '90); and (4) cervical ribs and neck
spines (Gaffney, 1975, '90), which may impair any extreme
movements to the neck.
Our observations clearly contradict the hypothesis that
amphicoelous vertebra are necessarily immobile and this
observation may be important for assessing mobility in other
groups of early reptiles. Similarly, although it is true that extinct
turtles lack extended temporal emarginations, there is no
obligatory or exclusive link between these two characters
(Werneburg, 2012). Minute ventrolateral emarginations are
nevertheless present (Jones et al., 2012; Werneburg, 2012), which
further supports our model of lateral retraction in stem turtles.
Living turtles with less mobile necks are universally macro-
cephalic and therefore physically unable to t their heads within
the anterior openings of their shells, and the loss of temporal
emarginations in these taxa is likely necessary to protect the
exposed neck from mammalian (Lyson and Joyce, 2009) or shark
predators. The large dorsal epiplastral processes that block the
anterior opening of the shell of P. quenstedti indeed pose an
obstacle for cryptodiran like neck retraction, as the head is not able
to t between these barlike processes, but our model demon-
strates that the neck is able to elegantly bend around these
structures.
Our model does not include the minute cervical ribs that
decorate the neck of P. quenstedti (Gaffney, '90; Werneburg et al.,
2013) and we are therefore not able to deduce their effect on neck
mobility. However, welldeveloped cervical ribs are present among
archosauromorphs (Nesbitt, 2011), particularly among long
necked protorosaurs (Wild, '73), but this group of reptiles are
generally thought to possess highly mobile necks. Thus it is
plausible that P. quenstedti was able to accommodate its
signicantly shorter ribs when tucking its head below the shell.
The presence of two large neckspines on the neck, the number of
neckspines actually associated with all known skeletons, does not
impair retraction (Fig. 7DF, Supplementary Fig. S9: see also
discussion there). The skin is highly moveable against the
underlying neck musculature in all extant turtles and other
tetrapods (Werneburg, 2011). As such, we are condent that a
exible skin would have allowed the neck osteoderms to
accommodate movement (in the sense of Jaekel ('15)) by shifting
sidewards during retraction, which allows further protection of the
laterally tucked neck.
The inference of full neck retraction in P. quenstedti should not
come as a complete surprise, given that even the earliest turtles
needed a minimally exible neck to overcome restrictions
imposed by the shell. Although the cervical mobility demanded
to overcome this obstacle is much greater than found in the non
shelled outgroups, only a 100° summed exion formed by eight
joints is needed to reach the early headtuck combined with a
dorsal roong formed by the carapace. The complex Sshaped
neck retraction of extant turtles only evolved later, perhaps as a
way to accommodate signicantly longer necks. The notion that
even the most basal turtles (i.e., amniotes with a full turtle shell
(Joyce et al., 2004)) were able to withdraw their head and neck
within the connes of the shell therefore allow us to conclude that
this feature evolved in certain synchrony with the origin of the
turtle shell in the Middle to Late Triassic. The fossil turtle
Odontochelys semitestacea (Li et al., 2008), which only evolved the
plastron part of the shell, might have been able to tuck its neck
similarly to what we modeled for P. quenstedti. Computer
tomography of the former is currently not available and hence
modeling is not possible. But given the documented rough
similarity of its vertebral anatomy with P. quenstedti (Li et al.,
2008), a similar neck mobility can be expected. However, whether
the potential neck tucking (i.e., the modied lateral neck exion)
in O. semitestacea allowed any protection below its slightly
broadened ribsin the semantic sense of the word retraction
cannot be evaluated herein. The same reservation holds true for
potential sister taxa of turtles, such as Eunotosaurus africanus
(Lyson et al., 2013), within or outside Eureptilia.
ACKNOWLEDGMENTS
We would like to thank Irina Ruf (Universität Bonn), Herbert
Schwarz (Universitätsklinikum Tübingen), Joseph Weisgram
(Universität Wien), Jan Prochel (Universität Tübingen), Anton
Weissenbacher and Roland Halbauer (Tiergarten Schönbrunn,
Wien), Katerina HarvatiPapatheodorou, and Wolfgang Gerber
(Universität Tübingen) for enabling various aspects of this study.
Carl Mehling (AMNH), Rainer Schoch (SMNS), Gunther Köhler,
Linda Acker (SMF), and Philipe Havlik (Paleontological Collection,
Tübingen) generously provided access to fossils and extant
specimens in their care. Marcelo R. SánchezVillagra, Eric Snively,
and three anonymous reviewers gave constructive suggestions to
improve the manuscript. This project was funded by a grant from
the Deutsche Forschungsgemeinschaft to W.G.J. (JO 928/1). The
present study was discussed and approved by the institutional
ethics committee of the University of Veterinary Medicine Vienna/
Austria in accordance with GSP guidelines and national
legislation.
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Cambridge, United Kingdom: Cambridge University Press. p 1933.
SUPPORTING INFORMATION
Additional supporting information may be found in the online
version of this article at the publisher's website.
J. Exp. Zool. (Mol. Dev. Evol.)
14 WERNEBURG ET AL.
1
SUPPLEMENTARY FILE
Supplementary Dataset
MODELING NECK MOBILITY IN FOSSIL TURTLES
by
Ingmar Werneburg, Juliane Hinz, Michaela Gumpenberger,
Virginie Volpato, Nikolay Natchev, Walter G. Joyce
2
Supplementary Figures
Figure S1. Comparison of measured angles of raw mobility between the vertebrae at different
positions of the neck. A, E) neutral position, B, F) maximal ventral flexion, C, G) maximal lateral flexion,
D, H) maximal dorsal flexion. A-D) mean of pleurodires, cryptodires, and fossil taxa , E-H) mean of
pleurodires and cryptodires, fossil taxa separated.
3
Figure S2. Maximal dorsoventral flexion in macerated bones. Stem taxa show the lowest degree of
dorsoventral flexion of raw mobility between the vertebrae. A higher degree is visible in pleurodires (red)
and the highest degree is visible in cryptodires (black). Chisternon undatum shows the highest affinity to
extant turtles among fossil taxa. See Table S4B-C for data.
4
Figure S3. Maximal dorsoventral flexion in living turtles. The land turtle Testudo hermanni shows the
largest dorsoventral flexion. The aquatic pleurodire Phrynops hilarii and the aquatic cryptodires
Graptemys pseudogeographica and Sternotherus carinatus show similar dorsoventral flexions. The
maximum amount of flexion measured on radiographs in either direction has a certain amount of
imprecision due to artefacts created by the perspective and by superimposition. For data see Table S7.
0
10
20
30
40
50
60
70
123456789
angle
vertebrae
LiveXRays:maximaldorsoventralflexion
Testudohermanni
Phrynopshilarii
Graptemysp.pseudogeographica
Sternotheruscarinatus
5
Figure S4. Angles measured between the zygapophyses and the centre of the centrum in anterior
view. Black = cryptodires, red = pleurodires, grey = fossil turtles, CV = cervical vertebra, A = anterior
half, P = posterior half
0,00
20,00
40,00
60,00
80,00
100,00
120,00
140,00
160,00
180,00
CV1A
CV1P
CV2A
CV2P
CV3A
CV3P
CV4A
CV4P
CV5A
CV5P
CV6A
CV6P
CV7A
CV7P
CV8A
CV8P
Angle(°)
zygapophyses
anglesofzygapophyses
Carettochelysinsculpta
Platysternonmegacephalum
Proganochelysquensted
Proganochelysquensted
Chisternonundatum
Meiolaniaplatyceps
Meiolaniaplatyceps
Naomichelysspeciosa
Podocnemisunifilis
Chelydraserpentina
Malaclemysterrapin
Phrynopsgeoffroanus
Kinosternonscorpioides
Emysorbicularis
Cuoramouhotii
Acinixysplanicauda
Indotestudoelongata
Dermatemysmawii
Hydromedusatectifera
Testudograecaibera
Kinixyserosa
Testudohermanni
Erymnochelysmadagascariensis
Macrochelystemminckii
6
Figure S5. L1 (mm) vs. other linear measurements of the vertebrae. For linear regressions of other
lengths against each other and against angles see Table S6.
0
10
20
30
40
50
60
70
80
0 10203040506070
mm
L1(mm)
L1(mm)vs.otherlinearmeasurementsofthevertebrae
L2
H
B1
B2
B3
Linear(L2)
Linear(H)
Linear(B1)
Linear(B2)
Linear(B3)
7
Figure S6. Neck movements in pleurodires illustrated for Phrynops. A-E) Raw neck movement in P.
geoffroanus (with the carapace of P. hilarii). F-J) Live movement of the neck in P. hilarii based on CT-
scans. Views: A, F) perspective frontolateral; B, G) lateral; C, H) frontal; D, I) dorsal, E, J) ventral view.
Colors as in Fig. 5; compare also to this Figure.
8
Figure S7. Neck movements in cyptodires illustrated in emydids. A-E) Raw neck movement in
Malaclemys terrapin (no plastron was available). F-J) Live movement of the neck in Graptemys nigrinoda
based on CT-scans. Views: A, F) perspective frontolateral; B, G) lateral; C, H) frontal; D, I) dorsal, E, J)
ventral view. Compare to Fig. 6. Colors as in Fig. 5.
9
Figure S8. Neck movements in the stem turtle Proganochelys quenstedti. The shell and osteoderms
were reconstructed with the software Maya based on the images from Gaffney (Gaffney, 1990). A-E)
Raw neck movement. F-J) Calculated live movement of the neck. Views: A, F) perspective frontolateral;
B, G) lateral; C, H) frontal; D, I) dorsal, E, J) ventral view. Compare to Figure 7.
10
Figure S9. Modelling of neck retractions in Proganochelys quenstedti.
A-C) Reconstruction of the consistently bended, cryptodiran-like retracted neck (compare to Figure 6D:
orange) in left anterolateral (A), right lateral (B), and frontal (C) view. Asterisks indicate plausible and
obvious restrictions that hinder cryptodiran-like neck retraction: 1. extreme overstretching (yellow *); 2.
a possible strong connection of the 8th cervical vertebra to the carapace (blue *) would dislocate the
remaining vertebrae completely; 3. cone shaped osteoderms on the neck (green *); 4. the epiplastral
processes (red *; ribs and head would not be able to pass), and 5. the plastron itself (white *). Further
restriction has to be assumed by soft tissue. Compare with Figs 6 and 7.
11
D-F) Reconstruction of the lateral neck retraction with the theoretically allowed (purple) mobility between
vertebrae without hypermobility. The osteoderms were not included in this model. Note that in theory
much more mobility between vertebrae is possible than reconstructed for live retraction on P. quenstedti
(compare to Figure 7D-F and G-I of this Figure). G) All theoretical movements without hypermobility
for comparison (corresponds to Figure S8A).
H-I) Further illustrations of lateral retraction. Compare to Figure 7D-F,
J-K) Reconstruction of neck retraction with a theoretical number of five osteoderm-rows as suggestively
modelled by Gaffney ((Gaffney, 1990): figures 1, 2 upper, 3). Similar to our 2-osteoderm reconstruction
(H-I, Figure 7D-F), also five osteoderms would not impede neck retraction. Note that a large space is
allowed between vertebrae and osteoderms in our model, which would be occupied by soft tissue in the
living animal (skin, musculature). There is not any evidence that more than two large osteoderm-rows
have been present in P. quenstedti (Jaekel, 1915). The existing osteoderms do not indicate to a live-
suturing with other osteoderms or with neural arches of the vertebrae and must have been interpreted as
pure and separate ossification within the skin (‘osteoderms’). As such, a stiffening of the neck, as
suggested by Gaffney (Gaffney, 1990) can be rejected. The skin itself is moveable against the underlying
musculature due to felxible connective tissue in all living tetrapods in order to ensure neck movement in
general (Werneburg, 2011). Hence, also when assuming more than two large osteoderm-rows in P.
quenstedti, mobility must have been possible. Please note that Jaekel ((Jaekel, 1915): figures 23) only
found 2 large osteoderm-rows in the Berlin specimen of P. quenstedti (MB 1910.45.2.) and already
proposed a certain degree of retraction-like neck movement. In addition to the both large osteoderm-rows,
Jaekel ((Jaekel, 1915): figures 9, 29) figured several smaller osteoderms, which most likely – as suggested
by the author – were situated laterally to the large ones on the top of the neck. Gaffney ((Gaffney, 1990):
figure 122) reconstructed the Berlin specimen with more than two osteoderm-rows but also mentioned
that “the basis for this arrangement is not definitely known”. In actual fact, not only the arrangement but
also the large number of vertebrae is highly subjective and suggestive. The P. quenstedti specimens were
found in an almost complete preservation, including the small tarsals and carpals. If further large
osteoderms on the neck would have been present in the living animals, they would have been preserved
for a longer term during fossilization that many smaller bones. Nevertheless, also with a hypothetical
series of more than two osteoderm-rows, the neck would have been able to laterally retract easily as we
modeled for the Stuttgart specimen (SMNS 16980) herein. Gaffney (Gaffney, 1990) attached the
osteoderms directly onto the vertebrae, which leaves the impression of a stiffened neck. Our
reconstruction allows space between vertebrae and osteoderms, which introduces a greater radius around
the neck axis – nonetheless, the larger neck radius does not impede the modelled retraction at all. It it
worth mentioning that Gaffney (Gaffney, 1990) mode his life-reconstruction with oblique osteoderm
positions. This suggestive modelling unintentionally points to the actual possibility that osteoderms might
have been flexible against each other to fit the space restrictions between skull and carapace. When
laterally retracting the neck, as P. quenstedti did, the osteoderms must have been aligned and rotated
against each other in a cascading, millipede-like series of segments (compare to J).
12
Figure S10. Illustration of neck movements and hypermobility 1/3. Cryptodira. A-B) Astrochelys radiata
(IW1114), retraction. C) Chelydra serpentina, partial retraction. D-F) Graptemys pseudogeographica
(IW1138); D) retraction; E) retraction in posterodorsal view; F) ventral flexion. G-J) Sternotherus
carinatus (IW1145); G) ventral flexion; H) dorsal flexion, I) retraction; J) CT-section through the
articulation between CV8 and DV1. Arrows indicate hyperstretching. Images in lateral view except
otherwise described. Not to scale.
13
Figure S11. Illustration of neck movements and hypermobility 2/3. Cryptodira. A-E) Malacochersus
tornieri (IW1142); A) retraction; B) lateral flexion; C) dorsal flexion; D) extended neck; E) dorsal flexion,
anterolateral view. F) Pelodiscus sinensis (IW1163), retraction. G) Trachemys scripta (IW1131),
retraction. Arrows indicate hyperstretching. Images in lateral view except otherwise described. Not to
scale.
14
Figure S12. Illustration of neck movements and hypermobility 3/3. Pleurodira. A-B) Phrynops hilarii
(IW1140), retraction; A) posterolateral view; B) ventral view. C-D) Podocnemis unifilis (IW1141),
retraction(Gaffney, 1990); C) anterolateral view, D) ventrolateral view. Arrows indicate hyperstretching.
Images in lateral view except otherwise described. Not to scale.
15
Supplementary Tables
Table S1. Fossil and macerated bones used in this study. CV1 to CV8 = cervical vertebrae 1 to 8.
Collections: AMNH = American Museum of Natural History, New York, USA; FMNH = Field Museum
of Natural History, Chicago, USA; SGP = Sino-German Project, Specimens currently housed at the
University of Tübingen, Germany; SMF = Senckenberg Forschungsinstitut und Naturmuseum Frankfurt,
Frankfurt am Main, Germany. B1 = maximum distance between the transverse processes. B2 = maximum
distance between the anterior zygapophyses. B3 = maximum distance between the posterior
zygapophyses. H1 = height. ID = index number of IW. M = measurements. L1 = maximum length between
zygapophyses. L2 = length of centrum. X = vertebrae not present. ? = distance not measurable. For
measurements compare to Fig. 2.
ID species collection number M CV1 CV2 CV3 CV4 CV5 CV6 CV7 CV8
Fossil turtles
IW921A † Proganochelys quenstedti ANMH uncat (= cast of SMNS 16980) L1 ? 28.4 25.5 15.4 22.3 28.2 36.5 38.1
L2 13.8 19.4 19.9 17.8 18.6 18.3 21.7 23
H1 ? 38.1 38.8 33.4 38.9 41.8 42.4 55.3
B1 ? 19.4 24.1 29 32.1 29.4 37.8 25.7
B2 ? ? 20.9 17.2 31.7 23.1 23.1 18
B3 ? 16 19.9 ? ? 13.3 17.4 10.6
IW922 † Chisternon undatum ANMH 5904 L1 X 32.7 33.5 22? 34.4 35.6 38? 41.9
L2 X 22.9 24.8 21.8 24.2 28.8 30.7 29.2
H1 X 26 29.1 33? 33.6 31.5 36.3 43.5
B1 X 27 35 40 34 31.5 34.4 34.2
B2 X ? 21.8 ? 19.3 27.2 ? 19.1
B3 X 21.2 22 ? 23.5 21.8 19.9 15.4
IW923 † Meiolania platyceps ANMH 19433 (AMNH) L1 X X X X X X 31.3 X
L2 X X X X X X 28.5 X
H1 X X X X X X 53.1 X
B1 X X X X X X 43 X
B2 X X X X X X 23.5 X
B3 X X X X X X 21.1 X
IW924A † Meiolania platyceps AMNH 57984. Cast of Australian Museum (Late Pleistocene. Lord
Howe Island. New South Wales. Australia. Meiolania platyceps) L1 36 39.6 48 38.6 44.2 47.2 46.7 58.7
L2 38.7 38 42.5 48.4 43.5 47.3 51.3 52.5
H1 47.6 50.3 60.9 60.4 61.2 71 80.7 63.9
B1 69.5 58.8 66.6 62.6 63.5 64.3 60.5 46.8
B2 ? 24.3 34.9 31.4 31.4 29.1 26.5 22.8
B3 33.8 28.2 23.3 28.1 26.7 22.3 18.3 ?
IW931 † Naomichelys speciosa FNMH PR273 L1 29.9 35.4 32 30.7 33.8 38.2 42.3 44.6
L2 14.3 27.5 25.1 24 25.1 30.3 31.6 25.4
H1 26.3 34.2 35 35.2 36.7 37 49.1 55.9
B1 10.2 21.4 32.1 36.4 33 34.5 35.8 32.4
B2 13.7 ? ? 24.3 23.9 26.3 24.7 24
B3 17.2 24.8 19.4 23.1 24.3 20.8 23.2 22.3
IW1166 † Xinjiangchelys chowi SPG 2000/5– five neck and the first dorsal vertebrae (A articulates
with B. C articulates with D. E articulates with F=1st dorsal
vertebrae)
A: B: C: D: E:
L1 40 41.7 39.3 45.6 ?
L2 32 32.5 33.6 34.7 28.1
H1 16.7 19.2 15.8 20.7 ?
B1 17.8 11.8 21 22.5 17.3
B2 16 7.3 17.2 17.5 14
B3 16.2 18.1 9.3 19 ?
Pleurodira
IW932 Podocnemis unifilis SMF55470 L1 X 18.9 24.1 22.4 21.9 23.7 25.1 23.9
L2 X 17.9 19.5 18.5 20.7 23 23.8 17.8
H1 X 16.5 13.6 16.6 14.4 15.1 19 23.2
B1 X 18.1 19.2 20.6 21.3 22 22.1 20.3
B2 X 6.7 10 9.8 10.6 10.8 11.7 12.1
B3 X 9.6 9.3 9.5 9.8 10.7 11.1 9.8
IW935 Phrynops geoffroanus SMF45470 L1 12.4 25.2 26.2 23.8 21.2 25.7 30.7 22
L2 10 20.8 22.7 20.8 21.1 27.7 24.7 20
H1 11.9 16.1 15.8 15.5 16.6 16.6 19.7 23.3
B1 7.9 14.5 15.4 16.8 17.4 17.6 18.2 19
B2 7.9 6 11.1 12.2 12.6 12.5 12.1 11.8
B3 9.7 9.2 10 10 9.9 9.8 9.2 5.3
IW1040 Hydromedusa tectifera SMF 70500 L1 13.7 16.7 18.9 16.9 18.2 18.5 21.1 17.1
L2 11.5 16.7 17 17.2 16.1 15.6 16.6 17.2
H1 7.4 9 8.7 8.8 9.8 10.3 10.9 10.7
B1 7.4 7.6 7.9 9.5 8.2 9.8 9.4 11
B2 5.9 6.1 6.1 6.7 6.4 6.7 7.3 6.7
B3 5.7 6.3 5.8 6.4 6 6.5 5.8 3.3
IW1048 Erymnochelys madagascariensis SMF7979 L1 12.2 16.6 20.8 20.7 21.2 22.5 23.5 23.3
L2 10.3 16.6 17.4 17 18.4 20.6 17.9 15.9
H1 14 17.1 15.9 14.8 16.7 19.5 22.9 25.1
B1 18 22.2 24.1 26 26.5 22.5 24.2 22
B2 6.3 ? 9.7 10.7 12.3 12.7 10.5 12.2
B3 7.8 8.8 9.5 10.7 10.3 9.7 11.2 9.7
Cryptodira
IW919 Carettochelys insculpta SMF56626 L1 20.6 28.5 32.7 33.9 34.5 31.5 31 30.4
L2 18.3 29.3 30.2 33 37 34.2 31.3 19.9
H 22.3 22.6 20.2 21.6 19.5 18.7 17.9 13.6
B1 8 19 23.83 24.1 29.9 22.6 20.4 24.3
B2 ? 17.5 25 26.3 27.6 27.5 22.1 26.5
B3 27.2 23.2 23.2 26.3 26.9 22.6 26 27.3
IW920 Platysternon megacephalum SMF69484 L1 8.9 15.2 16.7 16.3 14.4 15 14.8 13.8
L2 8.7 13 15.8 17.4 14.5 13.9 11.6 9.1
H 12 11.8 11.3 11.6 11.9 12.9 12 11.1
B1 6.7 13.6 14.9 15.7 15.7 15.3 11.4 13.4
16
B2 9 7.9 10.7 10.7 12.1 13.4 12.1 14
B3 9.5 10.1 9.8 11.5 12.6 11.9 13.5 14.6
IW933 Chelydra serpentina SMF32846 L1 17.6 27.6 37.3 38.2 37.7 33.8 35 35.3
L2 15.8 26.2 38 38.5 34.8 34.3 32.5 22.7
H 18 19.3 18.3 19.6 13.1 25.1 26.7 22.1
B1 10.9 13.4 19.2 19 15.4 22.4 19.9 23.7
B2 9.3 12.9 18.8 18.7 18.5 18.7 19.4 19.8
B3 13.1 16.6 16.8 16.8 17.5 18.3 18.6 22.2
IW937 Emys orbicularis SMF68814 L1 7.1 9.7 12.8 13.9 12.7 11.6 13.4 11.6
L2 6.7 8.9 11.1 13.7 12.2 12 9.6 7.1
H 8.1 7.6 7.9 9.4 7.5 7.4 8.7 8.6
B1 3.1 9 9.6 10 10.1 9.3 8.4 9.8
B2 5 6.6 9.5 9.7 8.9 8.7 7.6 9.6
B3 4 9.4 9.3 8.3 7.8 7.1 9.1 9.8
IW936 Kinosternon scorpioides SMF71893 L1 X 8.9 11.3 9.8 11.8 10.6 11.6 10.5
L2 X 8.5 11.3 10.9 11.1 11.7 11.7 6.2
H X 5.8 5.9 5.4 6.3 6.6 7.5 6.8
B1 X 6.7 6.3 7 7.3 8.1 6.6 8.7
B2 X 5.2 7.2 6.5 7 7.9 6.8 7.6
B3 X 6.5 6.3 6.5 7.4 5.7 6.7 7.3
IW939 Cuora (“Cyclemys“) mouhotii GRAY SMF71599 L1 6.5 11.3 13.9 14.1 15 15 X X
L2 7 10.2 12.2 15.2 14.8 14.8 X X
H 8.4 7.8 8.4 8.3 9.1 9.1 X X
B1 4.9 7.3 8.3 8.4 9.1 9.3 X X
B2 4.5 6.2 7.4 8.1 7.9 8.5 X X
B3 8.5 6.7 7.5 7.4 7.7 6.9 X X
IW934 Melaclemys ("centrata“) terrapin SMF36419 L1 9.2 15 17.8 17.4 15.2 15 15.4 12.9
L2 6.4 13.4 16 17.6 15.7 15.2 11.3 7.8
H 8.7 9 10.3 10 11 10.5 11.5 9.7
B1 6 10 9.8 14.4 9.9 9.3 9.5 11.1
B2 5.4 6.2? 10.5 9.6 9.2 10.3 8.8 10.6
B3 9.1 9.3 8.8 8.7 9.4 7.9 10.1 10.3
IW1033 Pyxis (“Acinixys“) planicauda Grand. SMF7722 L1 7.4 X 14.8 18 17.7 15.5 14.7 13.9
L2 ? X 13.5 14.4 15.3 15.6 13.5 9.5
H 11.1 X 8.7 9.4 9.8 10.2 11.2 11.3
B1 ? X 9 9.7 9.9 9.3 8.7 12.7
B2 6.6 X 8.6 8.7 9.3 10.1 10.6 11.5
B3 6.6 X 8 8.7 9.9 10.3 11.5 11.8
IW1034 Indotestudo (“Testudo”) elongata SMF71585 L1 X 13.3 19.4 20.6 22.7 20 19.1 20.2
L2 X 10.8 16.9 23.5 22 21.8 20.2 15.5
H X 14.6 11.6 13.2 12.3 14.7 14.8 16.9
B1 X 9.9 11.6 13.1 13.7 14.1 13.5 17.7
B2 X 9.3 12.2 12.2 12.4 12.6 14.2 14.1
B3 X 10.9 10.6 10.4 11 12.4 12 16.8
IW1035 Dermatemys mawii GRAY SMF59463 L1 7.5 22.3 30.4 31.3 27.1 25.9 30.7 27.3
L2 ? 23 24.3 27.1 27.1 28.9 26.8 18
H 12.4 13.3 13.9 13.9 15.4 18.2 21.2 21.8
B1 ? 8.3 11.3 12.4 12.4 14.2 15.7 18.9
B2 7.7 8.3 14 13 13.7 14.5 12.9 15.9
B3 10.5 13 12 12.9 13 10.8 13.7 20
IW1043 Testudo graeca SMF 67588 L1 X 12.4 15.6 16.5 16 15.2 15.3 19
L2 X 9.4 14.4 18 15.9 14.5 13.1 11.5
H X 10.9 11.2 9.4 10.1 10.8 11.9 13
B1 X 9.5 9.8 10.3 10.7 11.5 11.6 12.4
B2 X 7.1 9.2 9.5 9.7 6.9 9.4 11
B3 X 7.9 8.8 7.3 5.9 9.5 8.8 10.5
IW1044 Kinixys erosa SMF40166 L1 9.3 15.4 18.5 20.9 21.3 19.8 X 17.9
L2 8.7 13.1 20.7 20.8 21 20.1 X 15.5
H 9.9 10.5 8.9 9 9.9 10.6 X 10.7
B1 5.6 10 10.2 10.1 10.6 10.2 X 10.4
B2 6.8 7.6 8.1 8.7 8.7 9 X 10.1
B3 8.9 9.9 10.6 7.9 8.5 9.6 X 13.2
IW1045 Testudo hermanni SMF71882 L1 X 8.5 10.6 11.3 11.4 11.2 12.6 12.3
L2 X 8 9.9 11.9 10.8 10.8 9 6.7
H X 7.9 7.6 7.6 8.3 8.3 8.7 9.1
B1 X 6 6.9 7.6 6.8 7.6 7.2 8.4
B2 X 5.7 6.8 6.9 7.1 7.1 8.1 9
B3 X 6.2 5.8 6.1 6.2 7.5 8.3 9.6
IW1113 Macrochelys temminckii Teaching collection of Geowissenschaftliches Institut Tübingen L1 X 28.7 35.2 35.9 36.3 36.6 38.9 39.7
L2 X 32 37.2 36.7 38.2 36.7 33.6 22.5
H X 26.1 25.8 2.2 28.1 40.3 34.7 30.8
B1 X 22.3 26.8 28.2 27.9 30.5 31.2 28.2
B2 X 15.7 24.6 26.1 28.4 27.9 20 25.8
B3 X 23.3 25.4 26.6 25.6 17.6 23.8 28.2
17
Table S2. Living specimens used for radiography and/or computed tomography (CT) scans. For
specimens used for CT, weight was measured to calculate dosages of the anaesthetic. Euthanized
specimens (*) were provided by the veterinary program of the University of Veterinary Medicine, Vienna
and died of causes not related to this project.
Table S3. Literature references used for angle measurement.
ID species origin / literature reference weight
Pleurodira
IW1121 Phrynops hilarii Tiergarten Schönbrunn X
IW1140 Phrynops hilarii Tiergarten Schönbrunn 3.15kg
IW1141 Podocnemis unifilis Pet trade. 0.35kg
Cryptodira
IW1114 Astrochelys radiata Tiergarten Schönbrunn X
IW1133 Astrochelys radiata Tiergarten Schönbrunn 2.42kg
IW1115 Chelydra serpentina Tiergarten Schönbrunn 5.22kg
IW1116 Emys orbicularis Joseph Weisgram lab. Vienna / Austria X
IW1135 Emys orbicularis Tiergarten Schönbrunn 0.89kg
IW1137 Graptemys pseudogeographica Tiergarten Schönbrunn 0.41kg
IW1138 Graptemys pseudogeographica Tiergarten Schönbrunn 0.55kg
IW1117 Heosemys grandis Tiergarten Schönbrunn X
IW1118 Heosemys grandis Tiergarten Schönbrunn X
IW1139 Heosemys grandis Tiergarten Schönbrunn 3.39kg
IW1119 Malacochersus tornieri Tiergarten Schönbrunn X
IW1142 Malacochersus tornieri Tiergarten Schönbrunn 0.2kg
IW1120 Pelodiscus sinensis private breeding b y IW X
IW1163 Pelodiscus sinensis Michaela Gumpenberger Scan X
IW1122 Testudo graeca Tiergarten Schönbrunn X
IW1123 Testudo graeca Joseph Weisgram lab. Vienna / Austria X
IW1124 Testudo graeca Joseph Weisgram lab. Vienna / Austria X
IW1143 Testudo graeca Tiergarten Schönbrunn 0.18g
IW1130 Testudo hermanni* Patient of Michaela Gump enberger. Vienna X
IW1023 Testudo hermanni Joseph Weisgram lab. Vienna / Austria X
IW1024 Testudo hermanni Joseph Weisgram lab. Vienna / Austria X
IW1144 Testudo hermanni Tiergarten Schönbrunn 0.14kg
IW1131 Trachemys scripta elegans* Michaela Gumpenberger Scan X
IW1145 Sternotherus carinatus private pet specimen of Ingmar Werneburg 0.26kg
Outgroup taxa
IW1134 Pogona vitticeps Tiergarten Schönbrunn 0.29kg
IW1136 Rhacodactylus ciliatus Tiergarten Schönbrunn 0.03kg
ID taxon origin / literature reference
Stem Testudines
IW924B † Meiolania platyceps AMNH No. 57984 ((Gaffney, 1985): figure 4)
IW921B † Proganochelys quenstedti SMNS 16980 (reconstruction by (Gaffney, 1990))
PQ † Proganochelys quenstedti MB 1910.45.2 (reconstruction by (Gaffney, 1990))
Pleurodira
CL Chelodina longicollis Herrel et al. ((Herrel et al., 2008): figure 7.21)
CN (IW1168) Chelodina novaeguineae 6 specimens from (Weisgram and Splechtna, 1992)
PS (IW1167) Pelomedusa subrufa Original X-Rays of 8 specimens from (Weisgram and Splechtna, 1990)
Cryptodira
AS Apalone spinifera Herrel et al. ((Herrel, Van Damme and Aerts, 2008): figure 7.17)
CP Chrysemys picta belli Scanlon ((Scanlon, 1982): figure 5.1)
KS Kinosternon subrubrum Bramble et al. ((Bramble et al., 1984): figure 9). X-Ray?
TC Terrapene carolina ( Landberg et al., 2003) (macerated + arranged)
TH Testudo hermanni hermanni Literature data of (Weisgram and Splechtna, 1990) – (10 individuals)
TR Trionychidae indet. (Dalrymple, 1979) (figure 1)
TS1 Trachemys scripta (Callister et al., 1992)
TS2 Trachemys scripta (Callister et al., 2005)
18
Table S4. Measurements of the amount of mobility in fossil and macerated bones. CV = cervical
vertebrae. For specimen ID compare to Table S1-3. For the permissible amount of mobility compare with
Fig. 2A-D. A) neutral position
(facets of zygapophyses of adjacent vertebrae fully overlap)
ID Species CV1/CV2 CV2/CV3 CV3/CV4 CV4/CV5 CV5/CV6 CV6/CV7 CV7/CV8
919 Carettochelys insculpta +2.9 +6.3 +14 +25 +35.2 +28.4 +14.5
CP Chrysemys picta (figure 1A) -14.8 +10.4 +7.3 +11.1 +47.5 +15.9 -12.7
920 Platysternon megacephalum -0.3 +9.1 +15.6 +36.6 +27.5 +30.2 -5.8
921A † Proganochelys quenstedti ? -0.2 +10.5 -1.6 -0.2 -6.9 +18
921B † Proganochelys quenstedti -3.9 -5.2 +4.7 +7.6 -7.3 0 +3.5
PQ-B † Proganochelys quenste dti +1.6 +2.5 +3.3 +10 +0.3 -0.1 0
922 † Chisternon undatum X -16.6 +6.6 +14.6 +4.1 +5.8 -7
924A † Meiolania platyceps +5.1 -1 +7.3 +2.4 -1.2 -5.2 -5.6
931 † Naomichelys speciosa +1.1 +2.9 +4.5 -10.2 +11 -8.3 +3.2
932 Podocnemis unifilis X +6 -0.7 +12.5 +10.9 +7.6 -8.2
933 Chelydra serpentina -8.5 -2.9 +14.3 +13.9 +28.6 +5.8 -5
934 Melaclemys terrapin -8.7 +3.5 +12.6 +36.6 +48.6 -2.3 -16.6
935 Phrynops geoffroanus +12 -3.1 +2 +12.4 +.2.2 -3.9 -11.6
936 Kinosternon scorpioides x +22.3 +12.9 +22.3 +51.9 +25.5 +25.6
937 Emys orbicularis +21 -1.3 +23.8 +36.5 +36.8 +16.8 -21.5
939 Cuora mouhotii X +13.3 +15.7 +31.7 +45.9 X X
1033 Acinixys planicauda X X +6.4 +14.1 +35.6 +41.7 +8.7
1034 Testudo elongata +2 +17.3 +2.5 +19 +29.4 +48.3 +22.6
1035 Dermatemys mawii X -5.9 +9.8 +11 +46.8 +11.4 +2.1
1040 Hydromedusa tectifera +15.7 +4.2 +8.2 +15.3 +18.3 +12.1 +13.3
1043 Testudo graeca +10.6 +2.4 +35.8 +30.7 +31.1 +30.7 +3.3
1044 Kinixys erosa -6.5 +11.3 +17.1 +21.8 +47.7
1045 Testudo hermanni X +3.3 +1.7 +30.4 +34 +11.3 -29.9
1048 Erymnochel ys madagascariensis ? +14.1 +4.1 +15 +26.4 -21.5 +8.7
1113 Macrochel ys temminckii X -6.1 +12.8 +17.3 +30.7 +19.2 -12.5
TC Terrapene carolina (figure: 1C) -6.1 +7 +2.2 +32.7 +27.6 +15.3 +9.9
TS1 Trachemys scripta (figure 1A) -10.1 0 +13.9 +20.3 +33.1 +26.1 +2.5
IW1166 † Xinjiangchelys chowi A/B: -5.2 C/D: +13
B) maximal dorsal flexion
ID species CV1/CV2 CV2/CV3 CV3/CV4 CV4/CV5 CV5/CV6 CV6/CV7 CV7/CV8
919 Carettochelys insculpta +20.5 +51.5 +54.1 +56.4 +60.1 +46 +21.5
920 Platysternon megacephalum +9.1 +59.1 +35.7 +39.3 +78.9 +24 +26.9
921A † Proganochelys quenstedti ? +7.9 +10.7 +7.2 +14.7 -4.7 +22.3
922 † Chisternon undatum X -4.3 +27.4 +45 +12.6 +18.6 +3.1
924A † Meiolania platyceps +5.9 +4.3 +12.5 +11.2 +14.1 +5.1 +5.1
931 † Naomichelys speciosa +35 +19.5 +15 +4.8 +25.4 +6.7 -2.5
932 Podocnemis unifilis X +27 +25.2 +40.4 +30.9 +23.9 +9
933 Chelydra serpentina +10.9 +51.7 +55.3 +45.9 +63.4 +53.4 +44.7
934 Melaclemys terrapin +12.3 +64.6 +57.4 +77.2 +90 +26.9 +61.7
935 Phrynops geoffroanus +14.8 +27.4 +31 +33.6 +16 +9 +15.4
936 Kinosternon scorpioides x +59.3 +49.7 +77 +107.4 +33.8 +49.4
937 Emys orbicularis +23.1 +54 +58.4 +62.7 +82.6 +50.3 +13.6
939 Cuora mouhotii X +48 +53.9 +71.6 +84.7 X X
1033 Acinixys planicauda X X +49.1 +47.8 +74.1 +76.1 +47.7
1034 Testudo elongata +4 +29.1 +58.1 +41.1 +59.4 +87.9 +45.9
1035 Dermatemys mawii X +44.9 +43.3 +59.4 +100.1 +46.6 +36.7
1040 Hydromedusa tectifera +26.4 +37.1 +35.1 +34 +24.3 +26.5 +25.6
1043 Testudo graeca x +53.5 +53.6 +67.2 +67.9 +70.9 +27.6
1044 Kinixys erosa +3.8 +57.2 +61.9 +68.1 +84.5 x x
1045 Testudo hermanni X +56.6 +63.9 +67.5 +80.5 +46.5 +36
1048 Erymnochel ys madagascariensis ? ? ? ? ? +2.5 ?
1113 Macrochel ys temminckii x +33.2 +42.3 +51.3 +60.7 +46.7 +36
IW1166 † Xinjiangchelys chowi A/B: +18.6 C/D: +46.8
C) maximal ventral flexion
ID species CV1/CV2 CV2/CV3 CV3/CV4 CV4/CV5 CV5/CV6 CV6/CV7 CV7/CV8
919 Carettochelys insculpta -36.8 -44.3 -20.2 -11.6 +6.2 -19.1 -21.6
920 Platysternon megacephalum -25.4 -26.8 -26.3 -4.2 -6.3 -23.2 -56.4
921A † Proganochelys quenstedti ? -16.8 -9.9 -22 -14.3 -37.3 -15.1
922 † Chisternon undatum X -49.4 -17.8 ? -20.4 ? -26.2
924A † Meiolania platyceps -28.3 -14.8 -7.6 -12 -15.9 -10.4 -11.8
931 † Naomichelys speciosa -15.3 -14.1 -18 -23 -7.8 -31.7 -41.1
932 Podocnemis unifilis X -25.4 -23.3 -12.4 -23.1 -17.8 -29
933 Chelydra serpentina -10.2 -33.9 -19 -19.5 +6.9 -22.8 -48.3
934 Melaclemys terrapin -79.5 -26.8 -23.9 +2 -0.8 -31.4 -48.8
935 Phrynops geoffroanus -24.4 -35 -31.6 -17.2 -13.3 -21.8 -36.4
936 Kinosternon scorpioides x -9.4 -10.7 -20.4 +3.9 -5.9 -12.4
937 Emys orbicularis -25.2 -32.4 -27.2 +26.4 +7 -20.8 -49.3
939 Cuora mouhotii X -17.9 -17.2 +2.3 +11.7 X X
1033 Acinixys planicauda X X -56.3 -39.9 -12.5 -11.5 -44.9
1034 Testudo elongata -71.2 -36.7 -29 -21.2 -2.2 +17.1 -23.5
1035 Dermatemys mawii X -34.2 -27.8 -18.3 +21.1 -29.1 -45.5
1040 Hydromedusa tectifera -27.1 -28.8 -20.8 -22.1 -11.6 -32.6 -13.6
1043 Testudo graeca x -29.4 -20.3 -13.9 -6.2 -6.9 -50.4
1044 Kinixys erosa -42.3 -22.3 -18.2 -18 +4.1 x x
1045 Testudo hermanni X -29.7 -32.9 0 0 -20.7 -43.5
1048 Erymnochel ys madagascariensis ? ? ? ? ? -42.5 ?
1113 Macrochel ys temminckii x -27 -22.9 -8.2 +6.3 -13.1 -35.1
IW1166 † Xinjiangchelys chowi A/B: -46.9 C/D: -28.8
D) maximal lateral flexion
ID species CV1/CV2 CV2/CV3 CV3/CV4 CV4/CV5 CV5/CV6 CV6/CV7 CV7/CV8
919 Carettochelys insculpta 15.7 28.3 26.6 25 19.1 24.5 19.1
920 Platysternon megacephalum 23.9 35.3 35.7 31.3 33.6 17 11.2
921A † Proganochelys quenstedti ? 54.5 32.5 38.1 38.5 35.4 48.9
922 † Chisternon undatum X 43.5 ? ? 46.9 ? 54.4
924A † Meiolania platyceps 30.6 21 38.2 31 29 47.1 42.2
931 † Naomichelys speciosa 20 13.2 37.2 55 35.4 45.8 42.4
932 Podocnemis unifilis X 53.8 55.9 65.2 60.6 71 68.1
19
933 Chelydra serpentina 40 28.5 24.6 31.3 39.8 26.6 43.7
934 Melaclemys terrapin 41.2 40.7 19 46.9 24.9 30 25.7
935 Phrynops geoffroanus 57 38 63.9 60.6 50.9 46.4 61.5
936 Kinosternon scorpioides X 18.6 18.9 17.7 25.9 14.7 28.4
937 Emys orbicularis 6.7 40.3 38.1 32.6 26.8 33.7 34.3
939 Cuora mouhotii X 35.3 21.8 46.6 27.4 X X
1033 Acinixys planicauda X X X 37 37.7 22.9 23.9
1034 Testudo elongata 22.4 27.9 33.5 37.2 25.9 21.6 27.2
1035 Dermatemys mawii X 48.6 41.6 41.2 46.1 27.5 26.1
1040 Hydromedusa tectifera 29.2 48.6 85 42.3 65.5 57.1 35.7
1043 Testudo graeca X 36.5 43.5 40.3 24 13.1 20.4
1044 Kinixys erosa 27.7 37 32.5 42.2 28.7 X x
1045 Testudo hermanni X 39.7 39.9 41.4 38.9 38.8 21.5
1048 Erymnochel ys madagascariensis ? ? ? ? ? 41.7 ?
1113 Macrochel ys temminckii X 33.4 37.1 35.3 34.9 36 35.2
IW1166 † Xinjiangchelys chowi A/B: 66.8 C/D: 27.3
E) maximal dorsoventral flexion of the neck (dorsal + ventral) in lateral view
ID species CV1/CV2 CV2/CV3 CV3/CV4 CV4/CV5 CV5/CV6 CV6/CV7 CV7/CV8
919 Carettochelys insculpta 57.30 95.80 74.30 68.00 53.90 65.10 43.10
920 Platysternon megacephalum 34.50 85.90 62.00 43.50 85.20 47.20 83.30
921A † Proganochelys quenstedti - 24.70 20.60 29.20 29.00 32.60 37.40
922 † Chisternon undatum - 45.10 45.20 - 33.00 - 29.30
924A † Meiolania platyceps 34.20 19.10 20.10 23.20 30.00 15.50 16.90
931 † Naomichelys speciosa 50.30 33.60 33.00 27.80 33.20 38.40 38.60
932 Podocnemis unifilis - 52.40 48.50 52.80 54.00 41.70 38.00
933 Chelydra serpentina 21.10 85.60 74.30 65.40 56.50 76.20 93.00
934 Melaclemys terrapin 91.80 91.40 81.30 75.20 90.80 58.30 110.50
935 Phrynops geoffroanus 39.20 62.40 62.60 50.80 29.30 30.80 51.80
936 Kinosternon scorpioides - 68.70 60.40 97.40 103.50 39.70 61.80
937 Emys orbicularis 48.30 86.40 85.60 36.30 75.60 71.10 62.90
939 Cuora mouhotii - 65.90 71.10 69.30 73.00 - -
1033 Acinixys planicauda - - 105.40 87.70 86.60 87.60 92.60
1034 Testudo elongata 75.20 65.80 87.10 62.30 61.60 70.80 69.40
1035 Dermatemys mawii - 79.10 71.10 77.70 79.00 75.70 82.20
1040 Hydromedusa tectifera 53.50 65.90 55.90 56.10 35.90 59.10 39.20
1043 Testudo graeca - 82.90 73.90 81.10 74.10 77.80 78.00
1044 Kinixys erosa 46.10 79.50 80.10 86.10 80.40 - -
1045 Testudo hermanni - 86.30 96.80 67.50 80.50 67.20 79.50
1048 Erymnochel ys madagascariensis - - - - - 45.00 -
1113 Macrochel ys temminckii - 60.20 65.20 59.50 54.40 59.80 71.10
IW1166 † Xinjiangchelys chowi A/B: 65.5 C/D: 75.6
Table S5. Angle measurements between the zygapophyses. A = anterior face. P = posterior face. *=
estimated measurement for off broken zygapophyses. Compare to Fig. 2E.
ID species
CV1A
CV1P
CV2A
CV 2P
CV 3A
CV 3P
CV 4A
CV 4P
CV 5A
CV 5P
CV 6A
CV 6P
CV 7A
CV 7P
CV8A
CV 8P
919 Carettochelys insculpta 153.4 149.6 130.6 99.6 109.8 96 103.7 102.3 112 111.9 130 93.5 98.9 93.8 101.7 119.7
920 Platysternon megacephalum ? 136.5 123.4 76.8 80.3 71.4 77.5 83.4 85 133.6 103.6 96.5 129.6 111.2 108.4 153.1
921B † Proganochelys quenstedti 55.4 56.5 88.5 44.1 50.5 46.6 50.6 46.2 46.7 39.9 51.8 40.7 44.6 37.7 32.9 37.9
PQ † Proganochelys quenstedti ? 72.8 94.6 57.5 73.1 52.5 60.5 50.2 68.3 55.7 64.1 45.1 48.5 49 62.2 49.5
922 † Chisternon undatum X X ? 72.3 72.7 68 ? ? 65.3 62.9 69.5 60.4 ? 54.8 53.9 ?
923 † Meiolania platyceps X X X X X X X X X X X X 51.9 40.3 X X
924A † Meiolania platyceps ? 70.3 37 44.2 58.4 38.3 43.4 37.2 44.6 39.6 41.4 32.4 34.2 25.2 31.2 ?
931 † Naomichelys speciosa 115.3 130.9 93.9 57.1 81.2 46 67.3 82.6* 59.6 66.3 66 52 70 51.4 55.3 56.2
932 Podocnemis unifilis X X 67.9 57.5 63.4 51.5 60.1 52.6 61.7 56.3 60.6 53.4 57.2 50.5 57.1 40.4
933 Chelydra serpentina 113.9 85 144.1 77.5 91.8 74.7 78.5 78.3 77.3 81 73.9 86.6 87.7 73.7 77.9 116.8
934 Melaclemys terrapin 114.4 167 91 74.2 99.9 73.1 78.9 69.7 66.6 88.4 86.4 68.6 76.3 95.7 89.3 125.9
935 Phrynops geoffroanus 53.8 64.6 51.2 45.9 54.5 49.7 56.8 46.8 50.3 46.4 58.7 49.6 55.5 42.7 46.9 25.4
936 Kinosternon scorpioides x x 122.4 92.9 104.3 87.7 108.6 85 91.9 96.2 105.8 70.1 75 80.2 89.5 134.9
937 Emys orbicularis ? 118.7 142.5 95.8 121.6 100.5 98.1 76.1 80.4 77.5 70.6 63.7 65.1 93.1 85.5 124.1
939 Cuora mouhotii ? X X 72.8 87.2 75.6 91.2 77.5 79.2 74 77.7 79.1 X X X X
1033 Acinixys planicauda 129.4 90.4 105.7 80.3 94.8 84.6 85.2 77.5 82.7 98.8 91.8 98.3 90.6 106.9 122.5 137.7
1034 Testudo elongata ? 107.8 123.1 70.9 81.7 66.8 77.1 66 67.5 64.8 65.8 65.5 86.5 72.8 79.9 106.4
1035 Dermatemys mawii X X 110.8 81.4 99.3 64.9 72.5 71.3 71.5 65.3 68.2 67.5 66.6 84 91.6 118.6
1040 Hydromedusa tectifera 79.1 60.8 63 46.4 53.1 47.4 51.9 52.5 61.6 51.8 59.9 51.4 67.1 40.6 54.5 31.9
1043 Testudo graeca X X 130.3 66.8 77.8 65.6 89 56.5 57.5 48.5 47.8 60.1 53.8 63.6 69.6 97
1044 Kinixys erosa ? 121.1 119.6 82.2 94 73.8 72.9 66.4 62.6 88.3 67.8 73.1 X X 77.8 121.4
1045 Testudo hermanni X X 115.7 71.1 109.8 63.4 79.3 62.3 66.6 65.3 70.3 81.1 83.4 80 X X
1048 Erymnochelys madagascariensis 83.9 ? ? ? ? ? ? ? ? ? ? 44.6 46.7 ? ? 35.9
1113 Macrochelys temminckii x x 106.6 79.1 96.7 89.1 86.3 96.9 94 110 81.7 72.5 61.5 71 72.6 106.1
1166 Xinjiangchelys chowi A-A 117.1 A-P 77.6 B-A 76.2 B-P 72.3 C-P 61 D-A 93.8 D-P 68.2 E-A 51.7
20
Table S6 Linear regressions of the linear measurements of the vertebrae and the related angles of
movement and the zygapophyseal angles. Ant = angles at the anterior facets of the vertebrae; post = angles
at the posterior facets of the vertebrae; ant+post = absolute values of the angles of the anterior plus
posterior facets of the vertebrae; neutral, dorsal, ventral, lateral = directions of movements (angles),
zygapo = angles of the zygapophyses. Correlations larger than R² = 0.5 are highlighted. Compare to Fig.
2.
Linear regressions
L1
L2
H
B1
B2
B3
Ant-neutral
Ant-dorsal
Ant-ventral
Ant-lateral
Ant-zygapo
Post-neutral
Post -dorsal
Post -ventral
Post-lateral
Post -zygapo
Ant+post neutral
Ant+post dorsal
Ant+post ventral
Ant+post lateral
Ant+post zygapo
L1
L2
y = 0,8286x + 1,3172
R² = 0,8225
H
y = 0,2082x + 32,015
R² = 0,0211
y = -0,7783x + 90,637
R² = 0,0797
B1
y = 0,9372x - 4,0957
R² = 0,6297
y = 0,9953x - 2,7549
R² = 0,5928
y = 0,7923x + 2,8617
R² = 0,827
B2
y = 0,5283x + 0,957
R² = 0,5493
y = 0,571x + 1,5055
R² = 0,5356
y = 0,3756x + 6,2352
R² = 0,5102
y = 0,4862x + 4,6601
R² = 0,6489
B3
y = 0,5369x + 0,4121
R² = 0,6604
y = 0,5448x + 1,6975
R² = 0,5689
y = 0,3127x + 7,0582
R² = 0,4159
y = 0,3925x + 5,9475
R² = 0,5153
y = 0,7511x + 2,4657
R² = 0,6617
Ant-neutral
y = -0,512x + 23,946
R² = 0,1128
y = -0,2576x + 17,186
R² = 0,0239
y = -0,3571x + 18,654
R² = 0,1052
y = -0,3603x + 19,343
R² = 0,0834
y = -0,5547x + 19,927
R² = 0,0639
y = -0,6704x + 20,839
R² = 0,0763
Ant-dorsal
y = -0,9266x + 62,835
R² = 0,1561
y = -0,6011x + 53,693
R² = 0,0569
y = -0,8416x + 56,981
R² = 0,2501
y = -0,9111x + 57,498
R² = 0,2219
y = -1,0827x + 56,63
R² = 0,1032
y = -1,2451x + 57,548
R² = 0,112
y = 0,9662x + 29,134
R² = 0,3984
21
Ant-ventral
y = -0,0901x - 18,912
R² = 0,0032
y = 0,2134x - 25,602
R² = 0,0153
y = 0,0328x - 21,698
R² = 0,0008
y = 0,0441x - 21,878
R² = 0,0011
y = 0,0351x - 21,176
R² = 0,0003
y = -0,2248x - 18,269
R² = 0,0078
y = 0,777x - 30,135
R² = 0,5637
y = 0,3045x - 33,221
R² = 0,199
Ant-lateral
y = 0,1503x + 32,652
R² = 0,0139
y = 0,087x + 34,378
R² = 0,004
y = 0,0702x + 34,859
R² = 0,006
y = 0,0447x + 35,393
R² = 0,0018
y = -0,1022x + 37,98
R² = 0,0032
y = -0,3198x + 40,394
R² = 0,0246
y = -0,1822x + 38,386
R² = 0,0486
y = -0,1222x + 41,04
R² = 0,0506
y = -0,0481x + 35,236
R² = 0,0035
Ant-zygapo
y = -0,6468x + 94,427
R² = 0,0921
y = -0,6367x + 92,468
R² = 0,0739
y = -0,6201x + 91,016
R² = 0,1563
y = -0,7052x + 91,868
R² = 0,1534
y = -0,4425x + 84,923
R² = 0,0201
y = 0,035x + 79,258
R² = 0,0001
y = 0,1586x + 74,922
R² = 0,0145
y = 0,2012x + 68,578
R² = 0,0584
y = -0,1685x + 73,41
R² = 0,0183
y = -0,7619x + 104,56
R² = 0,2371
Post-neutral
y = 0,1204x + 33,053
R² = 0,0085
y = -0,2591x + 18,362
R² = 0,0232
y = -0,4274x + 20,76
R² = 0,1326
y = -0,99x + 60,405
R² = 0,2833
y = -0,4086x + 18,887
R² = 0,036
y = -0,5499x + 20,309
R² = 0,0513
y = 0,4358x + 7,9617
R² = 0,1516
y = 0,2861x + 2,0272
R² = 0,179
y = 0,221x + 18,119
R² = 0,0431
y = -0,1482x + 19,338
R² = 0,0141
y = 0,0727x + 7,0235
R² = 0,0105
Post -dorsal
y = -1,0149x + 65,974
R² = 0,172
y = -0,6845x + 57,064
R² = 0,0721
y = -1,0373x + 61,778
R² = 0,3512
y = -0,99x + 60,405
R² = 0,2833
y = -1,2332x + 60,224
R² = 0,1525
y = -1,2742x + 59,816
R² = 0,1261
y = 0,6055x + 35,302
R² = 0,1309
y = 0,542x + 21,085
R² = 0,2951
y = 0,1014x + 45,7
R² = 0,0041
y = -0,4395x + 59,744
R² = 0,0564
y = 0,3469x + 14,879
R² = 0,1054
y = 1,0873x + 28,418
R² = 0,5259
Post -ventral
y = -0,0306x - 18,504
R² = 0,0004
y = 0,1316x - 22,002
R² = 0,0064
y = -0,0275x - 18,705
R² = 0,0006
y = 0,0636x - 20,349
R² = 0,0028
y = 0,1459x - 21,228
R² = 0,0047
y = 0,0348x - 19,684
R² = 0,0002
y = 0,1991x - 20,904
R² = 0,0345
y = 0,1457x - 24,267
R² = 0,0506
y = 0,1962x - 14,474
R² = 0,0371
y = 0,0124x - 18,682
R² = 0,0001
y = -0,0807x - 12,737
R² = 0,0139
y = 0,7446x - 28,825
R² = 0,5937
y = 0,3055x - 32,031
R² = 0,227
Post-lateral
y = 0,2082x + 32,015
R² = 0,0211
y = 0,1069x + 34,553
R² = 0,0052
y = 0,0706x + 35,522
R² = 0,0047
y = 0,0742x + 35,498
R² = 0,0045
y = -0,1118x + 38,37
R² = 0,0035
y = -0,2723x + 40,329
R² = 0,0158
y = -0,4067x + 42,067
R² = 0,1863
y = -0,1649x + 43,37
R² = 0,0863
y = -0,2469x + 31,79
R² = 0,0753
y = 0,5876x + 14,921
R² = 0,3381
y = -0,2433x + 56,277
R² = 0,1563
y = -0,1987x + 39,128
R² = 0,0543
y = -0,1674x + 43,439
R² = 0,0888
y = -0,0912x + 34,804
R² = 0,0105
Post -zygapo
y = -0,6147x + 88,857
R² = 0,0588
y = 1,0382x - 2,5463
R² = 0,4896
y = -0,6652x + 86,971
R² = 0,1286
y = -0,6566x + 86,202
R² = 0,0995
y = -0,2374x + 78,32
R² = 0,0045
y = 0,4059x + 69,568
R² = 0,011
y = 0,1717x + 71,116
R² = 0,0119
y = 0,208x + 64,857
R² = 0,0418
y = -0,2584x + 67,921
R² = 0,0308
y = -0,8616x + 104,44
R² = 0,214
y = -0,2279x + 92,736
R² = 0,0406
y = -0,2105x + 76,433
R² = 0,0182
y = -0,1562x + 80,542
R² = 0,022
y = -0,1355x + 71,162
R² = 0,007
y = 0,1328x + 68,65
R² = 0,0056
Ant+post neutral
y = -0,983x + 54,827
R² = 0,1928
y = -0,6642x + 45,969
R² = 0,0803
y = -0,7346x + 45,444
R² = 0,2173
y = -0,6909x + 44,416
R² = 0,1721
y = -0,8927x + 45,065
R² = 0,0963
y = -1,0829x + 46,502
R² = 0,1111
y = 1,2063x + 15,681
R² = 0,6523
y = 0,5643x + 8,6224
R² = 0,3961
y = 0,7654x + 46,62
R² = 0,297
y = -0,3381x + 44,353
R² = 0,0415
y = 0,1765x + 13,953
R² = 0,0259
y = 1,0023x + 16,626
R² = 0,5483
y = 0,596x + 4,7265
R² = 0,4649
y = 0,7643x + 44,082
R² = 0,2839
y = -0,6164x + 52,655
R² = 0,1609
y = -0,1096x + 35,071
R² = 0,012
22
Ant+post dorsal
y = -2,0067x + 133,25
R² = 0,2113
y = -1,4188x + 117,41
R² = 0,0991
y = -1,8385x + 120,52
R² = 0,3692
y = -1,8877x + 121,18
R² = 0,345
y = -2,3116x + 120,23
R² = 0,169
y = -2,6062x + 121,23
R² = 0,1654
y = 1,7252x + 62,281
R² = 0,3438
y = 1,5209x + 22,364
R² = 0,7697
y = 0,7915x + 101,25
R² = 0,0811
y = -0,7748x + 114,78
R² = 0,0579
y = 1,0807x - 6,9657
R² = 0,1559
y = 1,7506x + 57,872
R² = 0,3736
y = 1,6533x + 11,172
R² = 0,7864
y = 1,1441x + 102,72
R² = 0,1338
y = -1,4526x + 136
R² = 0,1799
y = -0,4434x + 104,5
R² = 0,0374
y = 1,6577x + 27,672
R² = 0,587
Ant+post ventral
y = 0,0454x + 40,266
R² = 0,0005
y = -0,223x + 46,173
R² = 0,0119
y = -0,0882x + 42,963
R² = 0,0041
y = -0,176x + 44,57
R² = 0,0145
y = -0,2191x + 43,979
R² = 0,0082
y = -0,0944x + 42,708
R² = 0,001
y = -0,6199x + 49,75
R² = 0,2229
y = -0,2296x + 50,682
R² = 0,0852
y = -0,841x + 25,459
R² = 0,4537
y = 0,0904x + 37,768
R² = 0,0039
y = 0,1451x + 27,845
R² = 0,0164
y = -0,5774x + 47,62
R² = 0,226
y = -0,107x + 44,55
R² = 0,0185
y = -0,8109x + 25,395
R² = 0,3693
y = 0,2264x + 31,333
R² = 0,0267
y = 0,0486x + 35,197
R² = 0,0026
y = -0,3587x + 48,433
R² = 0,1571
y = -0,0337x + 40,993
R² = 0,0065
Ant+post lateral
y = 0,192x + 68,019
R² = 0,0058
y = 0,004x + 72,395
R² = 2E-06
y = 0,0314x + 71,901
R² = 0,0003
y = 0,0326x + 71,885
R² = 0,0003
y = -0,3351x + 77,729
R² = 0,0107
y = -0,7163x + 81,719
R² = 0,0364
y = -0,6939x + 82,243
R² = 0,1762
y = -0,3038x + 85,545
R² = 0,0934
y = -0,4365x + 64,632
R² = 0,0709
y = 1,6028x + 14,054
R² = 0,78
y = -0,7511x + 119,98
R² = 0,1865
y = -0,1818x + 73,276
R² = 0,0133
y = -0,2478x + 81,179
R² = 0,0584
y = -0,0126x + 70,942
R² = 5E-05
y = 1,3895x + 20,827
R² = 0,6006
y = 0,1554x + 53,581
R² = 0,0114
y = -0,0196x + 65,691
R² = 0,0002
y = 0,0296x + 61,792
R² = 0,0024
y = 0,3325x + 52,383
R² = 0,0482
Ant+post zygapo
y = -1,1751x + 181,56
R² = 0,0739
y = -1,3207x + 181,52
R² = 0,079
y = -1,2383x + 177,34
R² = 0,1534
y = -1,3093x + 177,45
R² = 0,1363
y = -0,6032x + 162,7
R² = 0,0099
y = 0,4514x + 148,89
R² = 0,0047
y = 0,291x + 147,05
R² = 0,0123
y = 0,3893x + 134,59
R² = 0,0535
y = -0,4186x + 142,08
R² = 0,0291
y = -1,6035x + 208,71
R² = 0,2675
y = 0,7721x + 92,736
R² = 0,3271
y = -0,0589x + 154,42
R² = 0,0009
y = 0,1612x + 146,57
R² = 0,0154
y = -0,3125x + 147,79
R² = 0,0247
y = -0,5305x + 172,75
R² = 0,057
y = 0,8382x + 90,624
R² = 0,4595
y = 0,0375x + 145,56
R² = 0,001
y = 0,06x + 140,07
R² = 0,0177
y = 0,1654x + 137,98
R² = 0,0234
y = -0,1747x + 155,1
R² = 0,0642
23
Table S7. Measurements of the degrees of freedom between vertebrae using radiographic studies of living
specimens. # = image in publication. * measured on original image of publication. § measured along the
lines indicated by the floor of the neural canal. ** angle between 8th and 9th vertebrae; “+” = dorsal
orientation or direction of head; “-“ ventral direction or head averted direction; ~ measured from
maximum left to maximum right position in literature
A) maximal extended neck in lateral view
ID species # S/CV1 CV1/CV2 CV2/CV3 CV3/CV4 CV4/CV5 CV5/CV6 CV6/CV7 CV7/CV8 CV8/DV1
CL Chelodina longicollis 7.19A middle -3.2 +1.6 -7.5 -1.5 +11.9 +12.7 +4 +9.8 -18.1
1116 Emys orbicularis -19.6 +4.7 +2.9 +24.8 +13 ? ? ? ?
1121 Phrynops hilarii -4.1 -4.2 -7.9 -1 +14 +15 ? ? ?
1140 Phrynops hilarii +13.3 +2.6 +7.1 -9 +10.6 +14.4 +0.1 -6.2 -24.7
TH Testudo hermanni ? 0 0 +5 +17 +39 +40 +10 -44.8*
1124 Testudo hermanni -7.2 +0.8 ? ? ? -5.8 +22.8 +15.8 -77.8
1137 Graptemys pseudogeographica +1.7 -7 +6.8 -1 +18.8 +25.7 +4.5 +4.5 -42
1145 Sternotherus carinatus -13.6 -8.6 +6.3 +6.7 +28.2 +44.5 +12.4 -1.5 -57.2
B) Maximal lateral flexion in dorsal view
ID species # S/CV1 CV1/CV2 CV2/CV3 CV3/CV4 CV4/CV5 CV5/CV6 CV6/CV7 CV7/CV8 CV8/DV1
CL Chelodina longicollis ~ 7.21 +/-10 +/-12 +/-10.5 +/-40 +/-31.5 +/-22.2 +/-29.5 +/-11.8 +/-10
CN (IW1168) Chelodina novaeguineae ~ ? +/-60 +/-65 +/-65 +/-60 +/-70 +/-55 +/-55 ?
1116 Emys orbicularis +17.3 +6.9 +21.3 +26.1 +0.5 0 0 0 0
PS (IW1167) Pelomedusa subrufa ~ X ? +/-50 +/-45 +/-65 +/-57 +/-57 +/-56 +/-64 ?
1121 Phrynops hilarii +13.1 -5.1 +14.5 +25 +43.1 +8.2 +14.3 -4 0
1135 Emys orbicularis 0 +1.6 +8.1 +7 +14.5 +9.8 +16.9 +11.6 -10.1
1137 Graptemys pseudogeographica +1 +32.4 +10.3 +10.3 +17.6 +13.4 0 0 0
1138 Graptemys pseudogeographica +5.5 +22.5 +13.8 +16.1 +9.9 +13.1 +2.2 0 0
1141 Podocnemis unifilis +16.1 +29.9 +25.8 -25 -62.7 +50.4 68.3 0 0
C) maximal dorsal flexion in lateral view
ID species # S/CV1 CV1/CV2 CV2/CV3 CV3/CV4 CV4/CV5 CV5/CV6 CV6/CV7 CV7/CV8 CV8/DV1
CL Chelodina longicollis 7.19A top -6.8 +8.7 -2.9 +20.6 +25.3 +21.8 +9.9 +8.4 -6.7
CP Chrysemys picta 5.1j 0** -18.8 +37 +37.5 +36.7 0 +27 -39.5 ?
1121 Phrynops hilarii +20.1 +2 +9.5 +36.3 +16.6 ? ? ? ?
1140 Phrynops hilarii +10.3 +2.4 +6.2 +16.2 +28 +27.6 ? ? ?
1134 Pogona vitticeps -14.3 +6 +14.4 +14.5 +22.2 +9.1 +12.1 +9.1 +3.9**
1137 Graptemys pseudogeographica +11.5 -1.3 +13.9 +9.3 +32 +37.9 +27.7 -28.7 -23.8
1145 Sternotherus carinatus +12 +5.4 +8.2 +17.5 +40 +52.7 +17 +4.6 -60.8
D) maximal ventral flexion in lateral view
ID species # S/CV1 CV1/CV2 CV2/CV3 CV3/CV4 CV4/CV5 CV5/CV6 CV6/CV7 CV7/CV8 CV8/DV1
CL Chelodina longicollis 7.19A down -4.5 -4.5 +0.5 -2.4 +6.7 +1 +1.8 +1.7 24.4
1116 Emys orbicularis -2.1 +9 -11.7 -6.2 ? ? ? ? ?
1140 Phrynops hilarii +8.9 +1.2 -5.5 -7.4 -5.4 +0.9 ? ? ?
1135 Emys orbicularis +9.2 -0.8 -5.2 -7.4 +4 +35.5 +12.7 -16.2 -52.6
1137 Graptemys pseudogeographica +6.5 -7.9 -6.2 +2.8 +14.4 +34.8 -4.1 -24.4 -31
1145 Sternotherus carinatus +5.3 -1.2 +2 -3.1 +21.9 +35.3 +22.2 -6.5 -67.1
E) maximal retracted neck in Pleurodira in dorsal view
ID species # S/CV1 CV1/CV2 CV2/CV3 CV3/CV4 CV4/CV5 CV5/CV6 CV6/CV7 CV7/CV8 CV8/DV1
PS (IW1167) Pelomedusa subrufa ~ ? 0 +17 +62 +42 +53 +12 -62 ?
IW1167 Pelomedusa subrufa -4.1 +39.1 +31.5 +34.3 +54 +55.8 +19.3 -53.8 -36
IW1168 Chelodina novaeguineae ~ -13.9 +32.8 +24.3 +37.4 +52 +46.8 +51.5 -60.1 -48.8
1121 Phrynops hilarii -11.4 +33 +26.7 +30.7 +46.6 +62.1 +24.6 -35.2 -51.7 ?
1141 Podocnemis unifilis +3.8 +20.4 +31.8 +41.1 +55.4 +25.9 -53-6 -43.8 0
F) maximal retracted neck in Cryptodira in lateral view
ID species # S/CV1 CV1/CV2 CV2/CV3 CV3/CV4 CV4/CV5 CV5/CV6 CV6/CV7 CV7/CV8 CV8/DV1
CP Chrysemys picta 5.1a ? ? +34.7 +40.7 +59.1 +69.4 -4.1 -56.4 -114.4
1113 Heosemys grandis ? +6.7 +37.3 +57.9 +48.5 -2 -46.4 -107.4 -24.3
1114 Astrochelys radiata ? ? ? ? ? ? ? +54.6 -154.7
1115 Chelydra serpentina ? ? +39.1 +52.5 +58.3 +17.1 -17.8 -145 -9.7
1116 Emys orbicularis ? ? ? ? ? ? +6.9 ? ?
1123 Testudo hermanni ? ? ? ? ? +47.1 +46.8 -81.1 (?) -78.1 (?)
1124 Testudo hermanni ? ? ? ? ? +60.3 +28.4 -96.6 (?) -86.3 (?)
1133 Astrochelys radiata ? ? ? ? +52 +54.5 +3.5 -19.8 -134 ?
1135 Emys orbicularis ? ? ? ? +29 +6 -7.1 -24.4 -131.1
1137 Graptemys pseudogeographica ? ? ? ? +52.8 +21 +1.5 -20.1 -121.2
1142 Malacochersis tornieri +11 ? +34.7 +58.9 +56.9 +23.6 -8.3 -46.6 -132 -121.5
1143 Testudo graeca +11.3 +36.1 +41.6 +38.4 +31.7 +15.4 +4 -85.1 -74.3
1144 Testudo hermanni ? ? ? ? ? +34 +17.6 -29.9 -135.4
1145 Sternotherus carinatus +4.5 +12.7 +31 +36.7 +53.1 +47 -9.1 -35.5 -108.4
KS Kinosternon subrubum +15.9 -1.2 +42.3 +52.6 +51.9 +31 +6.7 -26.9 -131.6
TC Terrapene carolina 1C +43.2 +10 +47.2 +48.3 +43.3 +43.5 -57.9 -7.9 -137.3
TS1 Trachemys scripta (Callister 1992) 1top -20 +17.3 +32.8 +40.4 +61.1 +63.3 -12 -43 -97.4
TR trionychid 1 -2.6 +13.5 +14.4 +78.9 +68 +23.9 +5.6 +8.7 -172
TH Testudo hermanni ? 0 +52 +38 +46 +28 +20 -35 -119*
G) maximal dorsoventral flexion of the neck (C: dorsal + D: ventral) in lateral view
ID species # S/CV1 CV1/CV2 CV2/CV3 CV3/CV4 CV4/CV5 CV5/CV6 CV6/CV7 CV7/CV8 CV8/DV1
TH § Testudo hermanni ? 10 65 61 55 53 55 63 ?
1140 Phrynops hilarii 1.4 1.2 11.7 23.6 33.4 26.7 ? ? ?
1137 Graptemys pseudogeographica 5 6.6 20.1 6.5 17.6 3.1 31.8 4.3 7.2
1145 Sternotherus carinatus 6.7 6.6 6.2 20.6 18.1 17.4 5.2 11.1 6.3
24
Table S8. Angle measurements between vertebrae using computed tomography scans of anesthetized
specimens. Legend: * Still a small tonus; ° only neck retraction could be measured for this species; **
estimated angle; dorsal/ventral view: + = clockwise, - = anti-clockwise; lateral flexion = to the right side;
(X) = partly retracted; ^ = the centra of the 7th and 8th CV completely detach; R = slight rotation
A) maximal extended neck
ID species S/CV1 CV1/CV2 CV2/CV3 CV3/CV4 CV4/CV5 CV5/CV6 CV6/CV7 CV7/CV8 CV8/DV1
AS Apalone spinifera +5.2 -3.4 +2.9 +6.3 +6.3 +16.2 +69.4 +72.8 -149.2
1130 Testudo hermanni 0 +2 -1 +4 +11.4 +26.9 +33.5 +10.8 -70.3
1131 Trachemys scripta elegans ? ? -5.5 -15.6 +22.5 +53.6 +17.9 -4.6 -73.9
1134 Pogona vitticeps +21.7 -5.2 +2.6 0 +3.7 +2.4 -1.5 -3.8 -2.7
1136 Rhacodactylus ciliatus ? -15.7 -3.8 0 +11 +22.4 0 +5.9 +7
1137 Graptemys pseudogeographica +6.5 +10 +9.4 +2.8 +22.8 +39.4 +8.2 -10.2 -46.3
1138 Graptemys pseudogeographica -24.8 +34.6 -0.1 +4.5 +22.9 +22.5 +12.2 -1.9 -68.5
1140 Phrynops hilarii +13 +11.2 +4 +7.1 +5 +9 -3.6 -0.8 -1
1141 Podocnemis unifilis +17 +4 +5.8 +7.3 +5.3 +11.8 -4.5 -8.2 -10
1142 Malacochersus tornieri +1.9 +12.9 +2.2 0 +9.7 +31 +12.9 +31.6 -101.5
1143 Testudo graca* +6.9 +9.7 -10.4 +1.5 +13.1 +28.3 +18.1 +13.7 -78.1
1144 Testudo hermanni -6.8 -9.7 +1.5 +5.6 +17.8 +36.8 +37.5 -9.2 -106.4
1145 Sternotherus carinatus -8 +6.7 +10.3 +6.1 +23 +42.6 +15.3 +10 -78.2
B) maximal retracted neck in lateral view
ID species S/CV1 CV1/CV2 CV2/CV3 CV3/CV4 CV4/CV5 CV5/CV6 CV6/CV7 CV7/CV8 CV8/DV1
AS Apalone spinifera -24.6 -10.2 +22.7 +68.3 +101.2 +7.9 +6.9 -7.2 -167.4
1115 Chelydra serpentina*° -15 +0.8 +27.6 +33.9 +38.9 +60.2 +38.6 -15.9 -155.6
1133 Astrochelys radiata -2 +5.4 +50.4 +28.1 +41 +44.4 +12.3 +25.3 -109.7
1135 Emys orbicularis -6.5 +8.8 +46.1 +57.4 +41.8 +43.5 +4.9 -41.8 -111.8
1137 Graptemys pseudogeographica +22 +19.2 +43.1 +48.4 +64.6 +24.6 -11 -45.3 -128.4
1138 Graptemys pseudogeographica +30.2 -3.8 +30.9 +54.9 +58.9 +40.1 0 -19.9 -153.5
1139 Heosemys grandis +8 +10.3 +34.8 +53.6 +43.8 +51.8 +3.5 -45.7 -125.1
1140 Phrynops hilarii (right side) -18 +12.3 +8 +13.4 +21.2 -3.4 +3.6 -4 -16.8
1141 Podocnemis unifilis (left side) +12 -15.7 +13.4 +17.1 +27.1 -23.5 +11.3 +9.1 -22.5
1142 Malacochersus tornieri +4.1 +15.4 +26.2 +52.8 +51.1 +43 +16.8 -9.6 -168.8
1143 Testudo graca* +16.4 +21.7 +10.5 +53.2 +52.7 +26.4 +3.4 +2.3 -172.7
1144 Testudo hermanni +8.7 +22.6 +50.5 +38.3 +40.4 +22.4 +20.2 +18.7 -163.8
1131 Trachemys scripta elegans -31.2 -5.4 +36.4 +46.7 +61.3 +49.8 +25.6 -17.8 -132.9
1145 Sternotherus carinatus 0 +30.4 +39.8 +40.5 +46.1 +47.8 -6.6 -12.6 -154.1
1162 Stigmochelys nigra (X) -12.8 +13.3 +9.3 +10.9 +9.8 +32.8 +56.8 -15-6 -157.3
1163 Pelodiscus sinensis (X) -19.7 +14.1 +10.3 +29.9 +81.3 +64.1 0 -0.9 -177.1
1164 Geochelone pardalis (X) -0.7 -0.2 +1.2 +22 +37.8 +60.1 +45 -79.7 -76
1165 Platysternon megacephalum (X) -47.1 +4.9 0 +41.6 +43.6 +45.8 +6.9 ? -145.3**
C) maximal retracted neck in dorsal/ventral view
ID species S/CV1 CV1/CV2 CV2/CV3 CV3/CV4 CV4/CV5 CV5/CV6 CV6/CV7 CV7/CV8 CV8/DV1
1140 Phrynops hilarii (right side) +0.5 +8.8 -32.8 -50.3 -58.8 -51.9 0 +24.3 +41.8
1141 Podocnemis unifilis (left side) -17.4 -16.9 +27.3 +59.1 +54.5 +41.1 +23.4 -41.6 -47.8
D) maximal lateral flexion in dorsal/ventral view
ID species S/CV1 CV1/CV2 CV2/CV3 CV3/CV4 CV4/CV5 CV5/CV6 CV6/CV7 CV7/CV8 CV8/DV1
1130 Testudo hermanni -19.5 -20.5 -13.3 -2.8 -2 0 0 0 0
1131 Trachemys scripta elegans -12.5 -2.1 -21.4 -37.4 -29.2 -4.8 -1 0 0
1134 Pogona vitticeps +7.5 +1.7 +11.5 +6.5 +4 +0.7 +2.4 +5.8 5.8
1136 Rhacodactylus ciliatus +13.2 11.1 -1.8 +3.7 0 +2.8 +15 +8.5 +10.3
1137 Graptemys pseudogeographica -8 -18.5 -15.3 -15.7 -21.1 0 ** 0 ** 0 ** -9.2
1138 Graptemys pseudogeographica -6.6 -5.8 -7.2 -17.8 -25.6 +2.6 0 ** 0 ** -21.5
1140 Phrynops hilarii +10.6 +4 +9.5 -13.2 -43.6 -48.9 -37.4 +18.4 -17-2
1141 Podocnemis unifilis -6.8 +14 -1 +4.6 -47.6 -39.5 -21.9 +33.9 -12.2
1142 Malacochersus tornieri -10.5 -4.5 -17.3 -7.5 -3.9 0 ** 0 ** 0 ** -9.6
1143 Testudo graca* -6.3 -6.5 -9 -13.1 -8.9 -5.5 -4 0 ** -7.1
1144 Testudo hermanni -63.8 +38.3 -8.2 +4.4 +7.8 +20.2 0** 0** -60
1145 Sternotherus carinatus -49.6
R
-9.5 -6.4 -20.2 -34.5 -1 0** 0** -13.8
E) maximal lateral flexion in lateral view (torsion of the dorsal/ventral axis)
ID species S/CV1 CV1/CV2 CV2/CV3 CV3/CV4 CV4/CV5 CV5/CV6 CV6/CV7 CV7/CV8 CV8/DV1
1130 Testudo hermanni -6.9 -5.2 -1.3 +3.2 +16 +33.3 +26.9 -8.1 -17.2
1131 Trachemys scripta elegans -3.6 -1.8 -1.5 +1.2 +17 +26.9 +19 +10.9 -108.5
1134 Pogona vitticeps +7.9 +1.9 +3.7 -1.2 -1.8 +1.8 -4.3 -3.3 -3.5
1136 Rhacodactylus ciliatus +11.7 -2.7 -8.7 +16.5 +3.5 -7.8 +6.8 +8 +4.6
1137 Graptemys pseudogeographica -25.5 -21.8 +4.1 +10.4 +44.3 +72.3 +6.4 -32.9 -67.2
1138 Graptemys pseudogeographica -11.9 -15.6 +4.3 +12.7 +33.6 +51.1 +16.1 +2 -118.9
1140 Phrynops hilarii -6.4 -2 0 -4.2 +26.8 +26.4 -3 +4.4 -12.5
1141 Podocnemis unifilis +24.6 -23 +4.7 +9.8 +25.8 +3.1 -21.2 +5.4 -15.1
1142 Malacochersus tornieri -11.9 0 -3.4 +4.1 15.7 +41.6 +37.4 +30.1 -121.1
1143 Testudo graca* -14.2 +2 -5.5 +9 +22.7 +31.8 +28 +10.9 -91.2
1144 Testudo hermanni -15.2 +32.6 +6.8 +14.4 +19.1 +35.1 +15.6 -58.2^ -13.6^
1145 Sternotherus carinatus -53.2 -23.9 -33 -19.4 +14 +73 +5.6 -28.7 -74.7
F) maximal dorsal flexion
ID species S/CV1 CV1/CV2 CV2/CV3 CV3/CV4 CV4/CV5 CV5/CV6 CV6/CV7 CV7/CV8 CV8/DV1
1130 Testudo hermanni +8.4 +8.6 +12.3 +10 +7.2 +19.3 +13.5 +6.2 -90.7
1131 Trachemys scripta elegans +11.5 +21.6 +20.4 +23.3 +22.5 +49.4 +43.2 -1.1 -77.2
1134 Pogona vitticeps +23 +8.5 +4 +2.6 +13.2 +20.4 +5.8 +10.4 +12.6
1136 Rhacodactylus ciliatus ? 0 +2 +12 +2 +20.2 +10.5 +4 +1.5
1137 Graptemys pseudogeographica -4 +3.8 +27.1 +32.3 +47.1 +61.4 +6.4 -15.7 -42.1
1138 Graptemys pseudogeographica -32.3 -9.6 +20.5 +20.2 +44.7 +54 +16.8 +11.4 -60.6
1141 Podocnemis unifilis -42 +65.3 +22.3 +23.6 +34.3 +22.5 +17.7 -10.2 -3.9
1142 Malacochersus tornieri +14 +15.7 +16.6 +14 +15.5 +29.3 +28.3 +38.2 -93.6
1143 Testudo graca* -11 +30.7 +20.1 +14.5 +13.6 +57.1 +18.3 +19.7 -95.5
1144 Testudo hermanni 0 +47.4 +15.2 +15.5 +21.8 +42.6 +4 -58.4^ -13^
1145 Sternotherus carinatus -21.6 -0.5 +22.4 +37.2 +37 +80.7 +20 +23.6^ -61^
G) maximal ventral flexion
ID species S/CV1 CV1/CV2 CV2/CV3 CV3/CV4 CV4/CV5 CV5/CV6 CV6/CV7 CV7/CV8 CV8/DV1
1134 Pogona vitticeps +5.4 -8.5 -0.8 -0.4 -1 -1.7 -7.4 -6.1 -3.3
1136 Rhacodactylus ciliatus ? +1.5 -8.1 0 0 +6.2 +7.7 -8.5 -18
1137 Graptemys pseudogeographica -12.8 -17.3 -10.8 -15.3 +20 +58.8 0 -20.7 -57.3
1138 Graptemys pseudogeographica +12.9 -35.5 -7.6 -10.3 +13 +38.6 +14.3 -13.3 -59.7
1141 Podocnemis unifilis -20.7 -22.9 +1.6 -6.4 +1 +1.9 -4 -5.2 -4.3
1142 Malacochersus tornieri -26.2 +4.3 -20.9 -6.3 +2.4 +23.6 +29.9 +48.3 -113.1
25
1143 Testudo graca* -6.3 -8 -13.1 +1.2 +22.4 +60.3 +26.1 +10 -118.7
1144 Testudo hermanni -51.8 +6.7 +9.1 -5.1 +8 +35 +4.3 -43 -46.7
1145 Sternotherus carinatus -2.9 0 -13.1 -20.9 -13.3 +13.7 +0.7 +8.1 -56.9
Table S9. Taphonomic distance calculation A: raw data summary. Angles measured on macerated bones
and those measured in the live CTs were plotted against each other in each taxon pair for each neck
position. The regression curves can be found in Table S10. ps. = pseudogeographica
Taxon Movement (method) S/CV1 CV1/CV2 CV2/CV3 CV3/CV4 CV4/CV5 CV5/CV6 CV6/CV7 CV7/CV8 CV8/DV1
Phrynops
Phrynops geoffroanus lateral (macerated) - 57,00 38,00 63,90 60,60 50,90 46,40 61,50 -
Phrynops hilarii lateral (live CT) 10,6 4 9,5 13,2 43,6 48,9 37,4 18,4 19
Podocnemis unifilis
Podocnemis unifilis lateral (macerated) - - 53,80 55,90 65,20 60,60 71,00 68,10 -
Podocnemis unifilis lateral (live CT) -6,8 14 1 4,6 47,6 39,5 21,9 33,9 12,2
Podocnemis unifilis ventral (macerated) - - -25,40 -23,30 -12,40 -23,10 -17,80 -29,00 -
Podocnemis unifilis ventral (live CT) -20,7 -22,9 +1,6 -6,4 1 +1,9 -4 -5,2 4,3
Podocnemis unifilis dorsal (macerated) - - 27,00 25,20 40,40 30,90 23,90 9,00 -
Podocnemis unifilis dorsal (live CT) -42 65,3 22,3 23,6 34,3 22,5 17,7 -10,2 -3,9
Kinosternidae
Kinosternon scorpioides lateral (macerated) - - 18,60 18,90 17,70 25,90 14,70 28,40 -
Sternotherus carinatus lateral (live CT) 49,6 9,5 6,4 20,2 34,5 1 0 0 13,8
Kinosternon scorpioides ventral (macerated) - - -9,40 -10,70 -20,40 3,90 -5,90 -12,40 -
Sternotherus carinatus ventral (live CT) -2,9 0 -13,1 -20,9 -13,3 13,7 +0,7 +8,1 -56,9
Kinosternon scorpioides dorsal (macerated) - - 59,30 49,70 77,00 107,40 33,80 49,40 -
Sternotherus carinatus dorsal (live CT) -21,6 -0,5 22,4 37,2 37 80,7 20 23,6 -61
Emydidae
Melaclemys terrapin lateral (macerated) - 41,20 40,70 19,00 46,90 24,90 30,00 25,70 -
Graptemys (IW 1137) lateral (live CT) 8 18,5 15,3 15,7 21,1 0 0 0 9,2
Graptemys ps. (IW 1138) lateral (live CT) 6,6 5,8 7,2 17,8 25,6 2,6 0 0 21,5
Melaclemys terrapin ventral (macerated) - -79,50 -26,80 -23,90 2,00 -0,80 -31,40 -48,80 -
Graptemys ps. (IW 1137) ventral (live CT) -12,8 -17,3 -10,8 -15,3 20 +58,8 0 -20,7 -57,3
Graptemys ps. (IW1138) ventral (live CT) +12,9 -35,5 -7,6 -10,3 13 +38,6 +14,3 -13,3 -59,7
Melaclemys terrapin dorsal (macerated) - 12,30 64,60 57,40 77,20 90,00 26,90 61,70 -
Graptemys ps. (IW1137) dorsal (live CT) -4 +3,8 +27,1 +32,3 +47,1 +61,4 +6,4 -15,7 -42,1
Graptemys ps. (IW1138) dorsal (live CT) -32,3 -9,6 +20,5 +20,2 +44,7 54 +16,8 +11,4 -60,6
Testudo graeca
Testudo graeca lateral (macerated) - - 36,50 43,50 40,30 24,00 13,10 20,40 -
Testudo graeca lateral (live CT) 6,3 6,5 9 13,1 8,9 5,5 4 0 7,1
Testudo graeca ventral (macerated) - - -29,40 -20,30 -13,90 -6,20 -6,90 -50,40 -
Testudo graeca ventral (live CT) -6,3 -8 -13,1 +1,2 +22,4 +60,3 +26,1 10 -118,7
Testudo graeca dorsal (macerated) - - 53,50 53,60 67,20 67,90 70,90 27,60 -
Testudo graeca dorsal (live CT) -11 +30,7 +20,1 +14,5 +13,6 +57,1 +18,3 +19,7 -95,5
Testudo hermanni
Testudo hermanni lateral (macerated) - - 39,70 39,90 41,40 38,90 38,80 21,50 x
Testudo hermanni (IW1130) lateral (live CT) 19,5 20,5 13,3 2,8 2 0 0 0 0
Testudo hermanni (1144) lateral (live CT) 63,8 38,3 8,2 4,4 7,8 20,2 0 0 -60
Testudo hermanni (1130) ventral (macerated) - - -29,70 -32,90 0,00 0,00 -20,70 -43,50 -
Testudo hermanni (1144) ventral (live CT) -51,8 +6,7 +9,1 -5,1 8 35 +4,3 -43 -46,7
Testudo hermanni dorsal (macerated) - - 56,60 63,90 67,50 80,50 46,50 36,00 -
Testudo hermanni (IW1130) dorsal (live CT) +8,4 +8,6 +12,3 10 +7,2 +19,3 +13,5 +6,2 -90,7
Testudo hermanni (IW1144) dorsal (live CT) 0 +47,4 +15,2 +15,5 +21,8 +42,6 4 -58,4^ -13^
26
Table S10. Taphonomic distance calculation B: regressions for each neck flexion. For each taxon, the
regressions and the variance (R²) are listed for each movement.
taxon Movement regression
Testudines Lateral y = 0,0142x2 - 0,6908x + 14,542
0,3224
Ventral y = 0,0081x2 + 1,2285x + 22,893 0,4367
Dorsal y = -0,0323x2 + 1,0194x + 19,6
0,1256
Pleurodira Lateral y = -0,002x2 + 0,593x - 2,4929
0,0364
Ventral (= Podocnemis unifilis) y = -0,0006x2 + 0,1594x + 1,9342
0,0829
Dorsal (= Podocnemis unifilis) y = 0,0303x2 + 2,8686x - 33,153
0,9721
Phrynops Lateral y = 0,0679x2 - 0,0607x + 52,379
0,0209
Podocnemis unifilis Lateral y = -0,4568x2 + 58,562x - 1833,1 0,9271
Ventral y = -0,0006x2 + 0,1594x + 1,9342
0,0829
Dorsal y = 0,0303x2 + 2,8686x - 33,153
0,9721
Cryptodira Lateral y = 0,0588x2 - 3,4417x + 51,832 0,2735
Ventral y = 0,0069x2 + 1,1203x + 22,903 0,3993
Dorsal y = 0,0107x2 - 0,4552x + 6,8036 0,5103
Kinosternidae Lateral y = -0,4019x2 + 16,555x - 150,81
0,4185
Ventral y = 0,0448x2 + 1,7703x + 5,9171
0,4414
Dorsal y = 0,0127x2 - 1,0423x + 45,037
0,9155
Emydidae + Testudo Lateral y = 0,0555x2 - 3,1398x + 45,075
0,4199
Ventral y = 0,0092x2 + 1,4517x + 31,715 0,5833
Dorsal y = 0,0138x2 - 0,7238x + 8,7164 0,4631
Emydidae Lateral y = 0,1039x2 - 6,444x + 99,386
0,8355
Ventral y = 0,0093x2 + 1,4287x + 29,083
0,6786
Dorsal y = 0,0127x2 - 0,5866x + 8,1292
0,6823
Testudo Lateral y = 0,018x2 - 0,8139x + 10,737 0,1842
Ventral y = 0,015x2 + 1,7326x + 35,808 0,464
Dorsal y = 0,0151x2 - 1,2995x + 39,313
0,2463
Testudo graeca Lateral y = 0,0152x2 - 0,5513x + 7,8361
0,838
Ventral y = 0,0791x2 + 5,3074x + 76,247 0,8377
Dorsal y = 0,0159x2 - 1,3x + 42,98
0,108
Testudo hermanni Lateral y = -0,0225x2 + 1,7044x - 26,238
0,1266
Ventral y = -0,048x2 - 0,7115x + 20,63
0,8181
Dorsal y = -0,0196x2 + 3,3353x - 114,98
0,5022
27
Table S11. Calculation of mobility of the neck in fossil taxa using the polynomic regressions of the
taphonomic distance in extant turtle taxa (see Table S9). For measured raw-data compare also to Table
S4. For every species, movements were calculated with the taphonomic distance formula for Testudines,
Pleurodira, and Cryptodira. With the assumption that the measured angles are usually larger than the
calculated life-angles (almost no overstretching of adjacent vertebrae) and with the assumption that the
fossil neck vertebrae had the same relationship to each other as those of extant taxa (meaning the same
formula), plausible (green and orange) and non-plausible (red) calculations are highlighted. In the case of
two or three plausible movements, the largest differences to the meassured value are presumed to be less
plausible (orange) than the smaller difference (green). The most plausible live angles for each fossil and
movement are marked (for a summary see Table S12).
ID species Vertebra CV1/CV2 CV2/CV3 CV3/CV4 CV4/CV5 CV5/CV6 CV6/CV7 CV7/CV8 Most
plausible
921A
† Proganochelys quenstedti
Dorsal
Measured ? 7,9 10,7 7,2 14,7 -4,7 22,3
Calculated (Testudines) - 25,637417 26,809553 25,265248 27,605473 14,095313 26,270153
Calculated (Pleurodira) - -8,600037 1,010067 -10,928328 15,562947 -45,966093 45,884667
Calculated (Cryptodira) - 3,875307 3,158003 4,080848 2,424323 9,179403 1,973643 X
Ventral
Measured ? -16,8 -9,9 -22 -14,3 -37,3 -15,1
Calculated
(Testudines) - 4,540344 11,524731 -0,2136 6,981819 -11,660601 6,189531
Calculated (Pleurodira) - -0,913064 0,297334 -1,863 -0,467914 -4,846194 -0,609546 X
Calculated (Cryptodira) - 6,029416 12,488299 1,596 8,293691 -9,284289 7,559739
Lateral
Measured ? 54,5 32,5 38,1 38,5 35,4 48,9
Calculated
(Testudines) - 19,07095 7,08975 8,835382 8,99415 7,882552 14,717062
Calculated (Pleurodira) - 23,8851 14,6671 17,19718 17,3731 15,99298 21,72238 X
Calculated (Cryptodira) - 38,91005 2,08425 6,057898 6,48285 3,681628 24,136018
922
† Chisternon undatum
Dorsal
Measured X -4,3 27,4 45 12,6 18,6 3,1
Calculated
(Testudines) - 14,619353 23,282012 0,0655 27,316492 27,386332 22,449737
Calculated (Pleurodira) - -44,927733 68,194668 157,2915 7,801788 30,685548 -23,969157 X
Calculated (Cryptodira) - 8,958803 2,364252 7,9871 2,766812 2,038652 5,495307
Ventral
Measured X -49,4 -17,8 ? -20,4 ? -26,2
Calculated
(Testudines) - -18,027984 3,592104 - 1,202496 - -3,733536 X
Calculated (Pleurodira) - -7,404376 -1,093224 - -1,567256 - -2,653944 X
Calculated (Cryptodira) - -15,601336 5,147856 - 2,920384 - -1,712424
Lateral
Measured X 43,5 ? ? 46,9 ? 54,4
Calculated
(Testudines) - 11,36215 - - 13,377942 - 18,985392
Calculated (Pleurodira) - 19,5181 - - 20,91958 - 23,84758 X
Calculated (Cryptodira) - 13,38235 - - 19,753338 - 38,613888
924A
† Meiolania platyceps
Dorsal
Measured 5,9 4,3 12,5 11,2 14,1 5,1 5,1
Calculated
(Testudines) 24,490097 23,386193 27,295625 26,965568 27,551977 23,958817 23,958817
Calculated (Pleurodira) -15,173517 -20,257773 7,438875 2,776152 13,318203 -17,735037 -17,735037
Calculated (Cryptodira) 4,490387 5,044083 2,785475 3,047568 2,512547 4,760387 4,760387 X
Ventral
Measured -28,3 -14,8 -7,6 -12 -15,9 -10,4 -11,8
Calculated
(Testudines) -5,386341 6,485424 14,024256 9,3174 5,407611 10,992696 9,524544
Calculated (Pleurodira) -3,057354 -0,556344 0,688104 -0,065 -0,751946 0,211544 -0,030264 X
Calculated (Cryptodira) -3,275349 7,833936 14,787264 10,453 6,834619 11,998184 10,644216
Lateral
Measured 30,60 21 38,2 31 29 47,1 42,2
Calculated
(Testudines) 6,699832 6,2974 8,874648 6,7734 6,451 13,506742 10,678168
Calculated (Pleurodira) 13,78018 9,0781 17,24122 13,9681 13,0221 21,00058 18,97002 X
Calculated (Cryptodira) 1,573948 5,4871 6,162372 1,6461 1,4735 20,170438 11,305652
931
† Naomichelys speciosa
Dorsal
Measured 35 19,5 15 4,8 25,4 6,7 -2,5
Calculated
(Testudines) 15,7115 27,196225 27,6235 23,748928 24,654092 24,980033 16,849625
Calculated (Pleurodira) 104,3655 34,306275 16,6935 -18,685608 59,257788 -12,573213 -40,135125
Calculated (Cryptodira) 3,9791 1,995875 2,3831 4,865168 2,144732 4,234083 8,008475 X
Ventral
Measured -15,3 -14,1 -18 -23 -7,8 -31,7 -41,1
Calculated
(Testudines) 5,993079 7,181511 3,4044 -1,0776 13,803504 -7,910841 -13,915749
Calculated (Pleurodira) -0,645074 -0,432626 -1,1294 -2,0494 0,654376 -3,721714 -5,630666 X
Calculated (Cryptodira) 7,377631 8,478559 4,9732 0,7862 14,584456 -5,676769 -11,485781
Lateral
Measured 20 13,20 37,2 55 35,4 45,8 42,4
Calculated
(Testudines) 6,406 7,897648 8,494768 19,503 7,882552 12,689848 10,780272
Calculated (Pleurodira) 8,5671 4,98622 16,79902 24,0721 15,99298 20,47122 19,05478 X
Calculated (Cryptodira) 6,518 16,646872 5,170552 40,4085 3,681628 17,543372 11,612208
IW1166
† Xinjiangchelys chowi (A/B and C/D)
Vertebra A/B C/D
Dorsal
Measured 18,6 46,8
Calculated (Testudines) 27,386332 -3,436832 - - - - -
Calculated (Pleurodira) 30,685548 167,46175 - - - - -
Calculated (Cryptodira) 2,038652 8,935808 - - - - - X
Ventral
Measured -46,9 -28,8
Calculated (Testudines) -16,906809 -5,769336 - - - - - X
Calculated (Pleurodira) -6,861426 -3,154184 - - - - -
Calculated (Cryptodira) -18,860981 -5,297384 - - - - - X
Lateral
Measured 66,8 27,3
Calculated (Testudines) 31,760368 6,266278 - - - - - X
Calculated (Pleurodira) 28,19502 12,20542 - - - - - X
Calculated (Cryptodira) 544,117272 189,61346 - - - - -
28
Table S12. Summary of the most plausible calculated live neck performances in the fossils (Table S10-
11). For Cryptodira, the maximal and minimal dorsal and ventral mobility, which was measured during
neck retraction using CT (compare to Table S7B), and for Pleurodira, the maximal and minimal lateral
mobility, which was measured during neck retraction using CT (compare to Table S7C), are listed
(compare to Fig. 4). Overstretched vertebrae are highlighted. The calculations for Chisternon undatum lie
largely over the allowed range of motion, which indicates to a completely different relationship of its
vertebrae to each other than to all other crown Testudines.
Taxon Movement (mode) S/CV1 CV1/CV2 CV2/CV3 CV3/CV4 CV4/CV5 CV5/CV6 CV6/CV7 CV7/CV8 CV8/DV1
A) Dorsal-ventral movement
† Proganochelys
quenstedti Dorsal (cryptodiran) - - 3,875307 3,158003 4,080848 2,424323 9,179403 1,973643 -
† Proganochelys
quenstedti Ventral (pleurodiran) - - -0,913064 0,297334 -1,863 -0,467914 -4,846194 -0,609546 -
† Chisternon undatum Dorsal (pleurodiran) - - -44,927733 68,194668 157,2915 7,801788 30,685548 -23,969157 -
† Chisternon undatum Ventral (Testudines-like) - - -18,027984 3,592104 - 1,202496 - -3,733536 -
Ventral (pleurodiran) - - -7,404376 -1,093224 - -1,567256 - -2,653944
† Meiolania platyceps Dorsal (cryptodiran) - 4,490387 5,044083 2,785475 3,047568 2,512547 4,760387 4,760387 -
† Meiolania platyceps Ventral (pleurodiran) - -3,057354 -0,556344 0,688104 -0,065 -0,751946 0,211544 -0,030264 -
† Naomichelys speciosa Dorsal (cryptodiran) - 3,9791 1,995875 2,3831 4,865168 2,144732 4,234083 8,008475 -
† Naomichelys speciosa Ventral (pleurodiran) - -0,645074 -0,432626 -1,1294 -2,0494 0,654376 -3,721714 -5,630666 -
Cryptodira minimal ventral movement during retraction -47,1 -15,7 1,2 13,4 9,8 -23,5 -11 -79,7 -177,1
Cryptodira maximal dorsal movement during retraction 30,2 30,4 50,5 68,3 101,2 64,1 56,8 25,3 -16,8
A) Lateral movement
† Proganochelys
quenstedti Lateral (pleurodiran) - - 23,8851 14,6671 17,19718 17,3731 15,99298 21,72238 -
† Chisternon undatum Lateral (pleurodiran) - - 19,5181 - - 20,91958 - 23,84758 -
† Meiolania platyceps Lateral (pleurodiran) - 13,78018 9,0781 17,24122 13,9681 13,0221 21,00058 18,97002 -
† Naomichelys speciosa Lateral (pleurodiran) - 8,5671 4,98622 16,79902 24,0721 15,99298 20,47122 19,05478 -
Pleurodira minimal lateral movement during retraction 0,50 8,80 27,30 50,30 54,50 41,10 0,00 24,30 41,80
Pleurodira maximal lateral movement during retraction 17,40 16,90 32,80 59,10 58,80 51,90 23,40 41,60 47,80
29
Table S13. Calculation of CV8-DV1 mobility. 1) derived from the curve of macerated bones (data from
Table S4) assuming an expected correlated mobility as the first vertebrae. 2) calculated life performance
using the regressions of Table S9. Non-plausible movement angles are highlighted.
dorsal † Chisternon undatum † Meiolania sp, † Naomichelys speciosa † Proganochelys quenstedti
CV1/CV2 x=1 5,9 35 ?
CV2/CV3 x=2 -4,3 4,3 19,5 7,9
CV3/CV4 x=3 27,4 12,5 15 10,7
CV4/CV5 x=4 45 11,2 4,8 7,2
CV5/CV6 x=5 12,6 14,1 25,4 14,7
CV6/CV7 x=6 18,6 5,1 6,7 -4,7
CV7/CV8 x=7 3,1 5,1 -2,5 22,3
1a Regression of fossil bone curve in dorsal movement y = -5,0429x2 + 44,763x -
67,54
y = -0,8286x2 + 6,6571x -
1,7429 y = 0,2631x2 - 6,6655x +
36,243 y = 0,0774x2 + 1,0131x +
2,7
1b R² of fossil bone curve in dorsal movement 0,6126 0,566 0,5839 0,1558
1c Calculation of CV8-DV1 in dorsal movability in between fossil
bones (with x=8) -32,1816 -1,5165 -0,2426 15,7584
2a Calculation of CV8-DV1 in dorsal position between bones in
living animal
(Testudines-formula: y=-0,0323x2 + 1,0194x + 19,6) (see
Table S12)
-46,6575918 17,9797973 19,35079255 27,64314535
2b (Pleurodira-formula: y= 0,0303x2 + 2,8686x - 33,153) (see
Table 12) -94,0887798 -37,4335488 -33,8471391 19,57585951
2c (Cryptodira-formula: y= 0,0107x2 - 0,4552x + 6,8036) (see
Table S12) 32,53417687 7,51851836 6,914661266 2,287477045
Ventral † Chisternon undatum † Meiolania sp, † Naomichelys speciosa † Proganochelys quenstedti
CV1/CV2 x=1 -28,3 -15,3 ?
CV2/CV3 x=2 -49,4 -14,8 -14,1 -16,8
CV3/CV4 x=3 -17,8 -7,6 -18 -9,9
CV4/CV5 x=4 ? -12 -23 -22
CV5/CV6 x=5 -20,4 -15,9 -7,8 -14,3
CV6/CV7 x=6 ? -10,4 -31,7 -37,3
CV7/CV8 x=7 -26,2 -11,8 -41,1 -15,1
1a Regression of fossil bone curve in ventral movement y = -4,975x2 + 49,032x -
124,36 y = -0,9762x2 + 9,5952x -
33,257 y = -1,3405x2 + 7,0667x -
23,029
y = 1,0131x2 - 11,344x +
8,6286
1b R² of fossil bone curve in ventral movement 0,7295 0,6263 0,6706 0,4837
1c Calculation of CV8-DV1 in ventral movability in between
fossil bones (with x=8) -50,504 -18,9722 -52,2874 -17,285
2a Calculation of CV8-DV1 in ventral position between bones in
living animal
(Testudines-formula: y=0,0081x2 + 1,2285x + 22,893) (see
Table S12)
-18,4908665 2,50120172 -19,1968961 4,078424423
2b (Pleurodira-formula: y= -0,0006x2 + 0,1594x + 1,9342) (see
Table S12) -7,64653001 -1,3059353 -8,04079488 -1,00029174
2c (Cryptodira-formula: y= 0,0069x2 + 1,1203x + 22,903) (see
Table S12) -16,0771185 4,13206051 -16,810166 5,600135953
lateral † Chisternon undatum † Meiolania sp, † Naomichelys speciosa † Proganochelys quenstedti
CV1/CV2 x=1 - 30,6 20 -
CV2/CV3 x=2 43,5 21 13,2 54,5
CV3/CV4 x=3 ? 38,2 37,2 32,5
CV4/CV5 x=4 ? 31 55 38,1
CV5/CV6 x=5 46,9 29 35,4 38,5
CV6/CV7 x=6 ? 47,1 45,8 35,4
CV7/CV8 x=7 54,4 42,2 42,4 48,9
1a Regression of fossil bone curve in lateral movement y = 5,3911x2 - 45,623x +
104,54 y = -1,3643x2 + 16,971x -
10,814 y = -1,4976x2 + 17,588x -
6,7143 y = 2,5482x2 - 23,474x +
87,916
1b R² of fossil bone curve in lateral movement 0,3464 0,7938 0,5306 0,6831
1c Calculation of CV8-DV1 in lateral movability in between fossil
bones (with x=8) 84,5864 37,6388 38,1433 63,2088
2a Calculation of CV8-DV1 in lateral position between bones in
living animal
(Testudines-formula: y=0,0142x2 - 0,6908x + 14,542) (see
Table S12)
57,7087136 8,65796253