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Materials and Methods
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S1 We Procrustes superimposed landmark data to remove the effects of translation, rotation
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and size (Rohlf and Slice 1990) prior to further analyses (Figure S2). Firstly, we used
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Principal Component Analysis (PCA) to explore the major axes of shape variation in the
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sample. ANOVAs were performed on PC1 and PC2 scores, representing the main axes of
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shape variance in the sample, to test for differences between between the dingo, hybrid, wild
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caught dogs and all dogs. As a conservative approach, post-hoc Bonferroni tests were used to
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assess the significance of shape differences between groups. Secondly, we entered landmark
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data into analyses to identify modules (see below).
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Results
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Observed and expected hybrids
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S2: Percentage allocation to each parent of differences between observed and expected
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in landmark positions
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For the dingo x kelpie cross, 72%:28% of the landmarks in the F1 hybrid were closer in
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observed morphology to the dingo parent morphology than the kelpie morphology. For the
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dingo x cattle dog cross, the ratio was 86%:14% dingo parent:cattle dog parent. For the dingo
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x labrador cross, the ratio was 84%:16% dingo:labrador. For the crosses between different
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dog breeds there was also a descernable pattern. For the kelpie x labrador the ratio was
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75%:25% kelpie: labrador; the kelpie x german shepherd was 70%:30%. The only cross that
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was closer to 50:50 was the kelpie x cattle dog cross, which was 36%:64% kelpie:cattle dog.
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S3: Modular allocation of 58 greatest landmark discrepancies between observed and
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expected hybrid morphology.
1
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We further calculated the number of landmarks that should have been allocated to each
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module on the basis of module size (number of landmarks in each module) if the landmarks
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were randomly distributed through all 10 of the modules. Then the modules with an over
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allocation, being greater than 25% of the expected allocation assuming random distribution of
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landmarks through the modules, of landmarks were noted. For the dingo x kelpie hybrid the
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58 landmarks were over allocated to modules 3,7 and 8; for the dingo x cattledog hybrid, the
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landmarks were over allocated to modules 4 (in particular) and 6; for the kelpie x cattle dog
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hybrid, the landmarks were over allocated to modules 1 and 3; for the kelpie x german
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shepherd, the landmarks were over allocated to modules 8 and (in particular) 10; for the
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kelpie x labrador, the landmarks were over allocated to modules 1 and 8; and for the dingo x
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labrador hyprid the landmarks were over allocated to modules 3, 4 and 6. Although most of
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these over allocated modules were from the higher integrated modules (9, 7, 4, and slightly
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less highly integrated 8, 3, 1), module 6 was also represented in the dingo x cattledog and
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dingo x labrador hybrids. This module had the second lowest integration value and was
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discontiguous, but was adjacent to the highly integrated module 4.
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Discussion
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S4: It is worth noting that the mean of the two kelpies was close to the mean dingo shape, and
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hence the kelpie x dingo hybrids (observed and expected) were also very similar in shape.
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Hence, the magnitudes of shape difference (the length of the 3D vector between Procrustes
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superimposed calculated and observed hybrids) between the actual and calculated hybrids
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were small, but the pattern within this was consistent with the other hybrids, potentially
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showing that the method is able to discern even subtle difference between expected and
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observed hybrid shapes.
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2
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S5: The dominance of the dingo morphology is also supported by the 3 wild caught dingo x
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dog hybrids for which we had genetic tests. There were two specimens that were tested as
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being 75% dingo (presumably F2 crosses) and one 65% dingo cross. The 65% dingo lay
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within the convex hull limits of the pure dingo shape space, with the two 75% dingoes lying
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on the boundary of the dingo shape space. So in these 3 hybrid specimens for which we have
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genetic determination of the percentage of dingo DNA, all were either within or on the
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boundary of the dingo shape space for our dingo sample. This shows, again, that upon dingo
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hybridisation with dog breeds, the resulting offspring revert to dingo morphology, and
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therefore presumably function, within only a few generations of back crossing with dingo
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wild types.
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References
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Rohlf, F. J., Slice, D. (1990). Extensions of the Procrustes method for the optimal
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superimposition of landmarks. Systematic Biology, 39(1), 40-59,
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doi:10.2307/2992207.
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Table S1: landmark point descriptions.
landmark number
single points
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
description
LHS the anterior margin of auditory bulla, just posterior to the internal carotid foramen
LHS the posterior margin of auditory bulla, just anterior to the paraoccipital process
LHS junction between premolar 4 and molar 1 teeth
LHS junction between Canine and premolar 1 teeth
LHS molar 2 tooth - maxillary bone intersection, posterior lateral point
LHS molar 1 tooth - maxillary bone intersection, anterior lateral point following the bulge formed in the maxillary by
the tooth root
RHS molar 1 tooth - maxillary bone intersection, anterior lateral point following the bulge formed in the maxillary by
the tooth root
posterior most aspect/point of the palatine bone
anterior-ventral most point of the ventral surface of the premaxillary (between L and R Incisors 1)
LHS midpoint of canine anterior-posterior width - maxillary bone intersection
RHS midpoint of canine anterior-posterior width - maxillary bone intersection
LHS midpoint of Incisor 3 anterior-posterior width - premaxillary bone intersection
RHS midpoint of Incisor 3 anterior-posterior width - premaxillary bone intersection
anterior most point of the dorsal surface of the premaxillary (between L and R Incisors 1 on the dorsal aspect of the
maxillary bone)
LHS posterior most point of the occiptal condyle
RHS posterior most point of the occiptal condyle
LHS medial-anterior most point of premolar 4
RHS medial-anterior most point of premolar 4
LHS medial-anterior point of join between auditory bulla and occipital
LHS lateral midpoint of join between auditory bulla and external auditory meatus
LHS lateral ventral point of zygomatic-temporal (squamosal) suture
5
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
curves
RHS lateral ventral point of zygomatic-temporal (squamosal) suture
posterior most point of sagittal crest, midpoint of meeting of sagittal crest, L and R external occipital protuberance
anterior midpoint, ventral surface, between the two occipital condyles (ventral side of foramen magnum)
LHS midpoint of dip posterior to the occipital condyle facet
RHS midpoint of dip posterior to the occipital condyle facet
dorsal midpoint, posterior surface, between the two occipital condyles (dorsal side of foramen magnum)
RHS posterior most point of anterior-posterior width of the canine, where the canine meets the maxillary
RHS anterior most point of anterior-posterior width of the canine, where the canine meets the maxillary
RHS lateral extreme point of TMJ facet surface
RHS perpendicular point to 30 on dorsal surface of temporal (squamosal) bone (of zygomatic arch)
anterior posterior midpoint of sagittal crest
anterior most point of sagittal crest, where the crest meets the frontal bone dorsal surface and splits into L and R
frontal bone ridges
running to the orbits
RHS midpoint between the ventral most point of the external occipital protuberance and the posterior-dorsal peak of
the external auditory meatus
RHS molar 2 tooth - maxillary bone intersection, posterior lateral point
RHS junction between Canine and premolar 1 teeth
LHS posterior most point of anterior-posterior width of the canine, where the canine meets the maxillary
LHS anterior most point of anterior-posterior width of the canine, where the canine meets the maxillary
LHS lateral extreme point of temporal-mandibular joint facet surface
LHS perpendicular point to 30 on dorsal surface of temporal (squamosal) bone (of zygomatic arch)
LHS midpoint between the ventral most point of the external occipital protuberance and the posterior-dorsal peak of
the external auditory meatus
RHS the posterior margin of auditory bulla, just anterior to the paraoccipital process
RHS medial-anterior point of join between auditory bulla and occipital
RHS the anterior margin of auditory bulla, just posterior to the internal carotid foramen
RHS lateral midpoint of join between auditory bulla and external auditory meatus
RHS junction between premolar 4 and molar 1 teeth
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curve 1 (pts 47-56)
curve 2 (pts 57-66)
curve 3 (pts 67-76)
curve 4 (pts 77-86)
curve 5 (pts 87-96)
curve 6 (pts 97-106)
curve 7 (pts 107-116)
curve 8 (pts 117-126)
curve 9 (pts 127-136)
curve 10 (pts 137-146)
curve 11 (pts 147-156)
curve 12 (pts 157-166)
curve 13 (pts 167-176)
curve 14 (pts 177-186)
curve 15 (pts 187-196)
curve 16 (pts 197-206)
curve 17 (pts 207-216)
curve 18 (pts 217-226)
curve 19 (pts 227-236)
curve 20 (pts 237-246)
curve 21 (pts 247-256)
curve 22 (pts 257-266)
curve 23 (pts 267-276)
curve 24 (pts 277-286)
curve 25 (pts 287-296)
curve 26 (pts 297-306)
curve 27 (pts 307-316)
RHS dorsal crest of temporal (sqamosal) bone of zygomatic arch, from base of arch to suture edge
RHS anterior orbit rim, running from zygomatic (jugal) suture across the maxillary to the maxillary-frontal suture
RHS ventral surface (mid points) of zygomatic (jugal) bone, running from the suture anteriorly
RHS midpoints of lateral aspect of zygomatic arch, running from zygomatic-maxillary suture to in line with pt 30, the
posterior part of the zygomatic arch (temporal bone) dorsal to the TMJ
RHS internal rim of the zygomatic arch from the medial point of the TMJ to the zygomatic suture (termporalsqamosal)
RHS interior midpoints of zygomatic arch, running from anterior zygomatic to posterior zygomatic ventral to point 31
dorsal surface of rostrum opening on the premaxillary bone, from RHS to LHS
from point 9 to the meeting of the premaxillary with the maxillary along the midline of the ventral bone surface
from the anterior edge of the basisphenoid (basisphenoid - presphenoid suture) to point 24 on the ventral bone surface
RHS midpoints of occipital condyle from medial to lateral
RHS midpoints of TMJ joint facet surface from lateral to medial
RHS posterior rim of the TMJ running lateral-medial
midline of occipital bone, running from pt 27 to pt 23
RHS length of the posterior side of the external occipital protuberance from ventral - dorsal aspect
sagittal crest, from pt 23 - pt 33
RHS lateral surface of pterygoid and palatine, running from pterygoid to palatine
excluded from analysis
RHS medial side of the ventral surface of pterygoid and palatine, running from palatine to pterygoid
LHS length of the posterior side of the external occipital protuberance from ventral - dorsal aspect
LHS midpoints of TMJ joint facet surface from lateral to medial
LHS medial side of the ventral surface of pterygoid and palatine, running from palatine to pterygoid
LHS posterior rim of the TMJ running lateral-medial
LHS midpoints of TMJ joint facet surface from lateral to medial
LHS lateral surface of pterygoid and palatine, running from pterygoid to palatine
LHS ventral surface (mid points) of zygomatic (jugal) bone, running from the suture anteriorly
LHS internal rim of the zygomatic arch from the medial point of the TMJ to the zygomatic suture (termporalsqamosal)
LHS interior midpoints of zygomatic arch, running from anterior zygomatic to posterior zygomatic ventral to point 40
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curve 28 (pts 317-326) LHS dorsal crest of temporal (sqamosal) bone of zygomatic arch, from base of arch to suture edge
LHS midpoints of lateral aspect of zygomatic arch, running from the TMJ to the zygomatic-maxillary suture to in line
curve 29 (pts 327-336) with pt 39, the
posterior part of the zygomatic arch (temporal bone)
curve 30 (pts 337-346) LHS anterior orbit rim, running from zygomatic (jugal) suture across the maxillary to the maxillary-frontal suture
patches (all 5 x 5 pts)
patch 1 (pts 347-371) RHS frontal bone dorsal surface (clockwise)
RHS lateral surface of the calvaria: the parietal (excluding sagittal crest and anterior surface of occipital protuberance)
patch 2 (pts 372-396) (clockwise)
patch 3 (pts 397-421) RHS posterior dorso-lateral surface of the frontal bone (over the posterior part of the olfactory region) (clockwise)
RHS dorso-lateral surface of the rostrum; running along the dorsal midline to the lateral edge of the tooth row,
extending from the anterior
patch 4 (pts 422-446) edge of the maxillary bone to the anterior edge of the orbit. Includes parts of premaxilla, nasal and maxillary bones
(clockwise)
RHS ventral surface of the maxillary and palatine bones, extending from the anterior maxillary (premaxilla-maxilla
patch 5 (pts 447-471) suture) to the
posterior-ventral edge of the palate portion of the palatine (anti-clockwise)
patch 6 (pts 472-496) LHS frontal bone dorsal surface (clockwise)
LHS lateral surface of the calvaria: the parietal (excluding sagittal crest and anterior surface of occipital protuberance)
patch 7 (pts 497-521) (clockwise)
patch 8 (pts 522-546) LHS posterior dorso-lateral surface of the frontal bone (over the posterior part of the olfactory region) (clockwise)
LHS dorso-lateral surface of the rostrum; running along the dorsal midline to the lateral edge of the tooth row,
extending from the
patch 9 (pts 547-571) anterior edge of the maxillary bone to the anterior edge of the orbit. Includes parts of premaxilla, nasal and maxillary
bones (clockwise)
patch 10 (pts 572-596) LHS ventral surface of the maxillary and palatine bones, extending from the anterior maxillary (premaxilla-maxilla
suture) to the posterior-ventral edge of the palate portion of the palatine (anti-clockwise)
NB: patch 9 pt 570, patch 4, pt 425; patch 7 pt 518; patch 2, 373 were excluded from the analysis due to difficulties
placing the landmarks on
external bone surfaces (the pts flip to the internal surfaces of underlying structures)
total pts in analysis = 582
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*LHS = Left Hand Side, RHS = Right Hand Side, pt = point, TMJ = temporomandibular joint
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Figure Captions
Figure S1. CT segmentation of dingo/dog cranial bone. CT scans of the dingo/dog dry skulls
were reconstructed in Materialise Mimics (v 16). The segmented cranial bone ‘mask’ is
shown in blue. The outline of the final 3D reconstruction of the specimen are shown in red.
Note that the red contours of the final 3D reconstruction fit tightly to the outline of the blue
mask, showing that the method is accurate in capturing the 3D morphology of the dingo/dog
crania.
Figure S2. Pocrustes superimposition and calculation of mean cranial shape. a) raw landmark
points in 3D space, various orientations, positions and sizes. B) Procrustes superimposed
landmarks for all specimens. Nuisance qualities of differences in size, orientation and
position minimized. C) calculated mean shape for the sample.
Figure S3. Module integration (x axis) against module disparity (y axis) shows the
relationship between integration and disparity. Linear regression fit: y = 1.11+ 4.68x, R2 =
0.632, P = 0.006, 95% CIs: (-0.63, 2.86), (1.77, 7.59).
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