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Cranial morphometrics of the dire wolf, Canis dirus, at Rancho La Brea: temporal variability and its links to nutrient stress and climate

F. Robin O''Keefe, Wendy J. Binder, Stephen R. Frost, Rudyard W. Sadlier, and Blaire Van Valkenburgh

Author/s

Plain Language Abstract

This paper presents an analysis of the size and shape of dire wolf skulls recovered from different tar pits at Rancho La Brea. The pits were deposited at different ages, and analysis of the animals within them therefore gives us a series of population samples at different times. Data comprised counts of fractured and worn teeth, as well as 3D landmark coordinates from 73 dire wolf skulls. Analysis of the data shows that both size and shape vary significantly across pits. These differences are a complex mix of growth retardation in populations experiencing heightened competition for food with other predators, along with evolutionary changes that may be linked to climate or other factors. More precise correlations between the La Brea biota and climate require more carbon dating of the deposits.

Resumen en Español

Morfometría cranial del "lobo gigante", Canis dirus, del Rancho La Brea: variabilidad temporal y sus relaciones con el estrés alimenticio y el clima

Los pozos o depósitos de brea del Rancho La Brea constituyen una ventana única para conocer la biología y la ecología de la parte terminal del Pleistoceno en el sur de California. En este estudio hemos considerado los avances recientes realizados en la comprensión de la cronología de los pozos de brea del Rancho La Brea para llevar a cabo el primer estudio morfométrico de una serie de cráneos del "lobo gigante", Canis dirus, a lo largo del tiempo. Primero presentamos nuevos datos sobre la fractura y el desgaste de los dientes hallados en los pozos con una edad más antigua que los analizados hasta ahora, y demostramos que los eventos de fractura y desgaste fueron de una intensidad variable a través de los intervalos de tiempo muestrados, lo cual se cree que representa una consecuencia del aumento de la competencia y de la utilización para su alimentación de cadáveres de mayores dimensiones. Está demostrado que el tamaño del cráneo, y por extensión el tamaño corporal, difieren significativamente entre los diferentes pozos del Rancho La Brea, siendo la observación más determinante la reducción en el tamaño corporal en el último máximo glaciar. La variación en el tamaño del cráneo se demuestra como el resultado de los factores tanto ontogenéticos como evolutivos, siendo que ninguno de ellos es congruente con una versión temporal de la regla de Bergmann. La diferencia en la forma del cráneo que se observa entre diferentes pozos es también significativa, atribuyéndose dicha variabilidad en la forma tanto a efectos neoténicos en poblaciones con altas tasas de roturas y desgaste, como a los cambios evolutivos, posiblemente debidos al cambio climático. Testar esta hipótesis requiere una mayor exactitud y precisión en los datos de datación por carbono del Rancho La Brea, un programa de investigación que está dentro del alcance de la actual tecnología de datación AMS.

Palabras clave: el "lobo gigante"; Rancho La Brea; morfometría craneal; Pleistoceno; evolución

Traducción: Enrique Peñalver

Résumé en Français

Morphométriques crâniens du grand loup, Canis dirus, provenant de Rancho La Brea : variabilité temporelle et ses liens avec le stress nutritif et le climat

Les puits de goudron de Rancho La Brea sont une fenêtre unique sur la biologie et l'écologie du Pléistocène terminal dans le sud de la Californie. Dans cette étude, nous capitalisons sur les progrès récents dans la compréhension de la chronologie des puits de goudron de La Brea afin de réaliser la première étude morphométrique de crânes du grand loup, Canis dirus, au fil du temps. Nous présentons tout d'abord de nouvelles données sur la fracture et l'usure de dent provenant de puits plus anciennement datées que ceux analysés jusqu'à présent, et démontrons que des événements de fracture et d'usure, et la concurrence accrue et l'utilisation accrue de carcasse qui sont pensés les représenter, ont été d'intensité variable dans les intervalles de temps échantillonnées. La taille de crâne, et, par extension, la taille du corps, est montré à différer sensiblement entre les puits de La Brea, avec la seule importante observation étant la réduction de la taille du corps au dernier maximum glaciaire. La variation de la taille du Crâne est montrée comme étant le résultat à la fois de facteurs ontogénétiques et évolutifs, ni l'un ni l'autre n'est en harmonie avec une version temporelle de la règle de Bergmann. La différence de forme de crâne parmi les puits est également importante, avec la variabilité de la forme attribuable à la fois aux effets néoténiques dans les populations avec une forte rupture et usure, et des changements évolutifs probablement due au changement climatique. Tester cette hypothèse nécessite une meilleure exactitude et précision des données de carbone de La Brea, un programme qui est à la portée de la technologie de datation AMS actuelle.

Mots-clés : grand loup; Rancho La Brea; morphométriques crâniens; Pléistocène; évolution

Translator: Kenny J. Travouillon

Deutsche Zusammenfassung

Schädelmorphometrie des Dire Wolfes, Canis dirus, von Rancho La Brea: zeitliche Variabilität und die Verbindung zu Ernährungsdruck und Klima

Die Rancho la Brea Tar Pits stellen ein einzigartiges Fenster in die Biologie und Ökologie des ausgehenden Pleistozäns des südlichen Kalifornien dar. In dieser Untersuchung erörtern wir die neuesten Fortschritte zum Verständnis der Rancho la Brea Tar Pit Chronologie und erstellen die erste morphometrische Studie über die Crania des Dire Wolfes, Canis dirus, im Laufe der Zeit. Zuerst präsentieren wir neue Daten zu Zahnfrakturen und Zahnabnutzung aus Asphaltgruben, die älter sind als die bisher untersuchten. Wir zeigen, dass die Frakturen und Abnutzungserscheinungen sowie der zunehmende Wettbewerb und die erhöhte Nutzung von Kadavern, für das diese gelten, über die ausgewählten Zeitintervalle von variierender Intensität sind. Es wird gezeigt, dass sich die Schädelgröße, und in Erweiterung, die Köpergröße, signifikant unter den Asphaltgruben in La Brea unterscheidet und dass die häufigste Einzelbeobachtung die Verkleinerung der Körpergröße während des letzten glazialen Maximums ist. Es wird aufgezeigt, dass die Größenvariation der Schädel sowohl auf ontogenetische als auch auf evolutionäre Faktoren zurückgeführt werden kann, von denen keiner mit einer zeitlichen Version der Bergmann's Regel übereinstimmt. Der Unterschied in der Schädelgestalt zwischen den Asphaltgruben ist ebenfalls auffällig, wobei die Variabilität sowohl neotänen Effekten bei Populationen mit hohen Bruchschäden und Abnutzung zugeschrieben werden kann, als auch evolutionären Veränderungen, die möglicherweise mit Klimaveränderungen zusammenhängen. Um diese Hypothesen zu testen, bedarf es besserer Genauigkeit und Präzision bei der La Brea Kohlenstoff Datierung, ein Programm, das in Reichweite der aktuellen AMS Datierungs-Technologie ist.

SCHLÜSSELWÖRTER: Dire Wolf; Rancho La Brea; Schädelmorphometrie; Pleistozän; Evolution

Translator: Eva Gebauer

Arabic

437 arab

Translator: Ashraf M.T. Elewa

 

 

FIGURE 1. Frequency histograms of tooth fracture from La Brea tar pits 61/67, 13, 2051, and 91. Date before present increases from left to right. A score of 0 represents no fracture; a score of 1, broken. Pits 13 and 91 (the high fracture group) show significantly more fracture than pits 61/67 and 2051. For statistics see Table 2 and Table 3.

figure 1

FIGURE 2. Frequency histograms of tooth wear from La Brea pits 91, 2051, 13, and 61/67 (in reverse chronological order). Amount of wear increases from a score of one (no wear) to five (heavy wear). Pits 13 and 91 (the high wear group) show significantly more wear than pits 61/67 and 2051. For statistics see Table 2 and Table 3.

figure 2

FIGURE 3. Locations of the 27 landmarks used in this study superimposed on a 3D surface model of a dire wolf skull generated from a medical CT scan of a specimen in the Marshall University teaching collection. This skull is from pit 61 and has been at Marshall for decades, and bears the number 2300-493 as well as grid coordinates, all marked identically to skulls in the collection at the Page Museum. For a list of landmarks see Table 4.

figure 3

FIGURE 4. Plot of centroid size derived from Procrustes superimposition; n = 73 skulls from four pits of varying ages measured for 27 landmarks. Points are estimates of the mean for each pit, and bars are 95% confidence limits on the mean. Body size is significantly smaller in Pit 13; full statistics are listed in Table 5.

figure 4

FIGURE 5. Vector translations of each landmark moving along Principal Component 1. Both a skull and a polygon derived from the landmarks are shown. Shape change associated with Principal Component 1 (PC1) is depicted as vectors of landmark displacement corresponding to a change along the PC axis by 0.15 units in the positive direction. Morphological surfaces are interpolations of shape based on landmark movement.

figure 5

FIGURE 6. Plot of PC 1 vs. PC 4 scores, divided by pit. Error bars on each pit mean score are 95% confidence intervals. Polygons indicate landmark vector translations along the principal component indicated. Principal component 1 and 4 vectors are deviations from the global mean shape (pictured in the upper right corner) in a negative direction. See PC1 Animations and PC4 Animations for deformations; also, the anterior, lateral, and ventral polygons for each PC are linked directly to the corresponding animation. Dorsal polygons are not animated.

figure 6

FIGURE 7. Plot of PC 2 vs. PC 3 scores, divided by pit. Error bars on each pit mean score are 95% confidence intervals. Polygons indicate landmark vector translations along the principal component indicated. Principal component 2 vectors are from the centroid in a negative direction, while PC 3 vectors are from the centroid in a positive direction. See PC2 Animations and PC3 Animations for deformations; also, the anterior, lateral, and ventral polygons for each PC are linked directly to the corresponding animation. Dorsal polygons are not animated.

figure 7

FIGURE 8. Interlandmark distances evaluated for five midline lanmarks; Procrustes x and y shape coordinates are shown. Mean landmark positions for each pit are plotted with the global mean (black dot). Of these, prosthion and basion have highly significant differences among means. Red lines are significantly different as calculated by ANOVA by pit, black lines are not. The position of the prosthion is highly variable, while the prosthion-nasion and prosthion-staphylion distances are shorter in pit 13 wolves versus the others. The length of the cranial base is longer in both pit 13 and pit 91 wolves, however, the basion is displaced posteriorly in pit 13 wolves; while the staphylion is displaced anteriorly in pit 91 wolves. For statistics see Table 9.

figure 8

FIGURE 9. Interlandmark distances evaluated for 10 palatal and tooth row landmarks. Coordinates x and z are shown in the left plots, while x and y are shown in the right plots. Red lines indicate significantly different distances as determined by ANOVA by pit; black lines are not significantly different. The location of the prosthion is highly variable, showing variation among all comparisons except 2051-13. The location of the posterior edge of the canine is more anterior in 61/67 wolves versus all others. Examination of the interlandmark distances shows that canine variation has a significant medio-lateral component, which may indicated a wider snout in pit 91 and a more narrow one in pit 61/67; again, pits 13 and 2051 tend to sort together. Significantly different interlandmark distances are shown in red. The postion of the anterior edge of the canine is more lateral in pit 91 wolves vs. all others. For statistics see Table 9.

figure 9

FIGURE 10. Summary of events, temperature, and biotic variation at Rancho La Brea. Climate data from NGRIP (2004).

figure 10

 

ANIMATIONS 1-3. Pit-to-pit transition movies depicting deformation from one pit to another in chronological order. The three animations are in lateral, ventral, and anterior views. The animations begin with the mean pit 91 shape (gold), deform to the mean pit 2051 shape (blue), then to the mean pit 13 shape (green), and end with the mean 61/67 shape (red).

animation 

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ANIMATIONS 4-6. Deformation of the global mean landmark configuration along PC 1, traveling 0.15 units in the negative direction. Deformations have been doubled for ease of visualization.

animation 

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ANIMATIONS 7-9. Deformation of the global mean landmark configuration along PC 2, traveling 0.15 units in the negative direction. Deformations have been doubled for ease of visualization.

 

animation 

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ANIMATIONS 10-12. Deformation of the global mean landmark configuration along PC 3, traveling 0.15 units in the positive direction. Deformations have been doubled for ease of visualization.

 

animation 

animation 

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ANIMATIONS 13-15. Deformation of the global mean landmark configuration along PC 4, traveling 0.15 units in the negative direction. Deformations have been doubled for ease of visualization.

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okeefeF. Robin O''Keefe
Department of Biological Sciences
Marshall University
One John Marshall Drive
Huntington, West Virginia 25701
USA
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F. Robin O'Keefe is Associate Professor of Biological Sciences at Marshall University in Huntington, WV. Dr. O'Keefe is an expert in the analysis of shape (morphometrics), and on the implications of shape in extinct and extant taxa. He has published on morphological variation in a range of extinct and modern taxa, demonstrating the influence of ecology and development on the evolution and life history of plesiosaurs, other extinct reptiles, and extinct and extant canids. He is deeply familiar with geographic variation in modern wolves, and has used this understanding to write a series of papers on the impact of varying climate La Brea carnivorans. O'Keefe has also published a compendium and analysis of all current carbon dates at La Brea, summarizing our current knowledge and highlighting current challenges. 

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binderWendy J. Binder
Department of Biological Sciences
Loyola Marymount University
One LMU Drive, MS 8220
Los Angeles, California 90045
USA, Wendy
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Wendy Binder is Associate Professor in the College of Science and Engineering at Loyola Marymount University in Los Angeles, CA. She has worked on carnivores at the La Brea tar pits for over 12 years, including, establishing a methodology to estimate age distributions of dire wolves and then applying this to understand different conditions in different pits over time. This was further developed for a second paper comparing toothwear and breakage in dire wolves to sabertooth cats in similar time periods. Binder and collaborators with also applied this age distribution methodology to look at dimorphism in extant lions and compare them with extinct La Brean felids. Binder has been supervising student research at the Page for 10 years, most recently looking at limb length changes in various pits. 

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frostStephen R. Frost
Department of Anthropology
Condon Hall 353
1218 University of Oregon
Eugene, Oregon 97403
USA
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Stephen Frost is Associate Professor Anthropology at the University of Oregon and a paleontologist and morphometrician interested in evolutionary theory and primate evolution. His research on cercopithecoid primates has focused on the Afar Region of Ethiopia, as well as the relationship between African cercopithecid evolution and global climatic change. He is also interested in the quantitative analysis of biological shape, particularly using the techniques of geometric morphometrics. 

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sadlleirRudyard W. Sadlier
Department of Biological Sciences
Saint Xavier University
3700 West 103rd Street
Chicago, Illinois 60655
USA
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Rudyard Sadleir is an assistant professor at Saint Xavier University and a research associate of the Field Museum of Natural History. He received degrees from the University of Illinois-Chicago, the University of Oxford as a Rhodes Scholar, and the University of Chicago. Using the latest 3D mathematical tools, his work tries to describe subtle developmental and morphological variation of vertebrate skeletal and selected soft tissue phenotypes. A background in geology, zoology, evolutionary biology, digital modeling, vertebrate anatomy and developmental biology provides the broad skillset and collaborative network needed to answer deep questions about patterns and mechanisms of biological variation. 

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blairBlaire Van Valkenburgh
Department of Ecology and Evolutionary Biology
University of California Los Angeles
Terasaki Life Sciences 2163
610 Charles E. Young Drive East
Los Angeles, California 90095
USA
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Blaire Van Valkenburgh is Professor of Ecology and Evolutionary Biology at the University of California Los Angeles and a Research Associate at the Natural History Museum of Los Angeles County.  As a quantitative evolutionary morphologist with strong interests in community structure and evolution, her research has focused on terrestrial predatory mammals, including dire wolves, sabertooth cats and borophagine dogs. She pioneered the quantitative analysis of tooth fracture and wear in carnivores and its application to understanding extinct ecosystems. 

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TABLE 1. Summary of Canis dirus cranial material used in the course of this study. Pit deposit information and dates in years before present condensed from O'Keefe et al., 2009; for calibration information see that reference and Meachen et al., 2014. The quoted pit ages are median ages in the windows of deposition, and constraint on the duration and time of each window is currently poor for most pits. For further discussion see O'Keefe et al., 2009.

 

Pit Number

Pit Age

N, Fracture

N, Wear

N, Skulls

61/67

13.8 kya

1120

106

17

13

17.9 kya

797

37

16

2051

26.1 kya

568

115

22

91

28 kya

367

75

18

TABLE 2. Fracture and Wear Data. Table shows number of teeth examined for fracture in each pit, number of broken teeth found, and percentage. For wear data, N = the number of worn teeth identified, SW denotes slight wear, SMW slight to moderate wear, MW, medium wear, MHW, medium to heavy wear, H, heavy wear. Weighted wear percent is the average wear score for each pit. These data are plotted in Figures 1 and 2.

 

Pit

Teeth, N

Teeth, Broken

Broken %

SW

SMW

MW

MHW

H

N

Weighted Wear %

61/67

1120

25

2.23

39

29

28

8

2

106

2.104

13

797

55

6.90

5

16

12

3

1

37

2.432

91

367

27

7.36

17

23

20

9

6

75

2.520

2051

568

12

2.11

40

38

20

11

6

115

2.174

TABLE 3. Pairwise comparisons among pits for tooth fracture and tooth wear. P values calculated from correspondence analysis and Wilcoxon nonparametric rank sums test; values were very similar for both tests. For raw percentages and wear values see Figures 1 and 2. Single stars indicate significance below the 0.05 level; double stars indicate significance below the 0.01 level.

 

Comparison

61/67-2051

61/67-13

61/67-91

13-91

2051-91

2051-13

Tooth Fracture

p<.8743

p<.0001**

p<.0001**

p<.7778

p<.0001**

p<.0001**

Tooth Wear

p<.8464

p<.0455*

p<.0180*

p<.9306

p<.0275*

p<.0518

TABLE 4. Description of landmarks used in this study. See Figure 3 for locations.

 
 

Landmark

Description

1

prosthion

Premaxilla between medial incisors

2

nasion

Farthest posterior extent of nasals on midline

3

bregma

Frontal/parietal suture at midline

4

inion

Posterior tip of sagittal crest

5

opisthion

Posterior border of foramen magnum at midline

6

basion

Inferior border of foramen magnum at midline

7

staphylion

Posterior tip of palatines at midline

8

pal/max sut

Palatine-maxillary suture at midline

9

incisivon

Midline suture at anterior border of incisive foramina

10

postI3

Posterior border of I3 alveolus

11

antC1

Anterior margin of C1 alveolus

12

postC1

Posterior margin of C1 alveolus

13

antP1

Anterior margin of P1 alveolus

14

antP4

Anterior margin of P4 alveolus

15

P4/M1

Posterior margin P4 alveolus/anterior margin M1 alveolus

16

postM2

Posterior margin M2 alveolus

17

prm/max/nas

Posterior end of dorsal premaxillary process

18

orbitinf

Inferior margin of orbit

19

postorb

Tip of postorbital process

20

opticinf

Inferior border of optic canal

21

par/tmpzyg

Location on parietal-temporal suture directly above posterior root of zygomatic process

22

porion

Superior margin of external auditory meatus

23

antbulla

Posterior border of pharyngotympanic tube

24

prm/maxC1

Location of premaxilla-maxilla suture on medial margin of C1 alveolus

25

prm/maxinc

Location of the premaxilla-maxilla suture on lateral margin of incisive foramen

26

M2postmed

Closest point of M2 alveolus to the midline

27

M1med

Closest point of M1 alveolus to the midline

TABLE 5. Centroid size pairwise comparisons.Significance of pairwise comparisons among pits based on one-way Student's T tests among means. For distributions see Figure 4. Single stars indicate significance below the 0.05 level; double stars indicate significance below the 0.01 level.

 

Comparison

61/67-2051

61/67-13

61/67-91

13-91

2051-91

2051-13

Size

p<.3300

p<.0669

p<.0735

p<.0021**

p<.3493

p<.0092**

TABLE 6. Results of a permutation test on Procrustes shape coordinates. Reported values are summed Procrustes distances among all landmarks for each pairwise pit comparison, as listed. All pits are significantly different in aggregate. For visualization of landmark locations among mean shapes from each pit, see Supplementary Animations 1, 2, 3. Single stars indicate significance below the 0.05 level; double stars indicate significance below the 0.01 level.

 

Pairwise Pit Comparisons

Total Procrustes Distance

P value, alpha <

UCMP vs. p13

0.0189778

0.000**

UCMP vs. p61

0.0187161

0.000**

UCMP vs. p91

0.0267971

0.000**

p13 vs. p61

0.0154740

0.004**

p13 vs. p91

0.0191137

0.000**

p61 vs. p91

0.0226563

0.000**

TABLE 7. Proportions of total Procrustes distance accounted for by the factors centroid size, individual pits, and all pits.

 

Factor

Procrustes sum of squares

Percentage of total

Total

0.0012216192

100.0%

Ln(centroid size)

0.0000400096

3.3%

All Pits

0.0001652656

13.5%

Pit 61

0.0000373441

3.1%

Pit 13

0.0000259306

2.1%

Pit UCMP

0.0000761901

6.2%

Pit 91

0.0000838070

6.9%

Size + Pits

0.0001933500

15.8%

TABLE 8. One-way ANOVAs of principal components by pit derived from ordination of the covariance matrix of three-dimensional landmark data. First five components are shown; they account for 47% of the variance in the data set. Ninety percent of the variance was accounted for by 28 principal components. Regression results for correlation with centroid size are also shown. For plots of PCs 1 and 4 see Figure 6; for plots of PCs 2 and 3 see Figure 7. Shape transitions along each principal component are visualized in Supplementary Animations 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15. Single stars indicate significance below the 0.05 level; double stars indicate significance below the 0.01 level.

 

PC

Percent Explained

One-way ANOVA, by Pit

Means, T

61/67-2051

61/67-13

61/67-91

13-91

2051-91

2051-13

Regression, Centroid size

PC I

14.42

F ratio 0.8770

p < 0.4574

0.4361

0.4564

0.6867

0.2509

0.7162

0.1224

F ratio 4.8319

p < 0.0312*

PC II

13.09

F ratio 20.1406

p < 0.0001**

0.0119*

0.3909

0.0001**

0.0003**

0.0001**

0.0009**

F ratio 1.5024

p < 0.2244

PC III

7.75

F ratio 3.9191

p < 0.0121*

0.0590

0.9496

0.1868

0.2162

0.0012**

0.0547

F ratio 1.5624

p < 0.2154

PC IV

6.81

F ratio 6.0364

p < 0.0010**

0.0046**

0.0173*

0.0001**

0.1061

0.1468

0.7706

F ratio 4.1100

p < 0.0464*

PC V

5.60

F ratio 4.9423

p < 0.0036**

0.0019**

0.9834

0.440

0.4348

0.0164*

0.0021**

F ratio 0.0775

p < 0.7815

TABLE 9. Interlandmark Distances. Significance of pairwise comparisons of wireframe distances among pits based on one-way Student's T tests among means. Single stars indicate significance below the 0.05 level; double stars indicate significance below the 0.01 level. Illustrated in Figures 8 and 9.

 

Comparison

61/67-2051

61/67-13

61/67-91

13-91

2051-91

2051-13

Prosthion-Nasion

0.2964

0.0001**

0.1639

0.0035**

0.6697

0.0006**

Prosthion-Staphylion

0.3797

0.0066**

0.9458

0.0071**

0.4118

0.0393*

Staphylion-Basion

0.8047

0.0054**

0.048*

0.3555

0.0194*

0.0016**

antC1-postC1

0.2661

0.0031**

0.0002*

0.4126

0.0027**

0.0354*

P4/M1-PostM2

0.0197*

0.0084**

0.0198*

0.6880

0.9104

0.5972

postC1-antP4

0.0329*

0.0217

0.0022**

0.4585

0.2469

0.7275

postC1-PrMxC1

0.0080**

0.0419*

0.0403*

0.9646

0.5838

0.6286

Staphylion-postmedM2

0.1439

0.4394

0.0005**

<0.0001**

0.0199*

0.0259*

Prosthion-C1mxpremx

0.1411

0.1356

0.0855

0.0018**

0.0012**

0.8909

P4/M1-postmedM2

0.1411

0.1356

0.0855

0.0018**

0.0012**

0.8909

antC1-PrMxC1

0.2067

0.9331

0.0776

0.0687

0.0021**

0.2487

Prosthion-antC1

0.0696

0.0671

0.2301

0.0030**

0.0023**

0.8728

Pros-M1med

0.0736

0.2629

0.2344

0.0230*

0.0026**

0.5580