Articles

Print Email

Positive allometry for exaggerated structures in the ceratopsian dinosaur Protoceratops andrewsi supports socio-sexual signaling

David W. E. Hone, Dylan Wood, and Robert J. Knell

Plain Language Abstract

Many dinosaurs had large and often elaborate bony crests on their heads. The function of these crests has been much discussed but little consensus has been reached. Here we analyse the changes in the shape of the large 'frill' on the head of specimens of a small horned dinosaur from Mongolia called Protoceratops. We show that the frill started at a small size in young animals and only grew large when the animal was close to maturity. Therefore, the frill must have a function that operates in adults, but not juveniles. Such growth patterns are typical for features under sexual selection where animals compete for the best mates. We conclude that the frill was likely a structure used by adults in dominance contests.

Resumen en Español

La alometría positiva para estructuras exageradas en los dinosaurios ceratópsidos Protoceratops andrewsi corrobora la señalización socio-sexual

Se evalúa la alometría en los salientes del collar óseo y del yugal de los pequeños dinosaurios ornitisquios Protoceratops andrewsi. El análisis de 37 ejemplares, que abarca cuatro clases de tamaños diferentes de animales, muestra que el collar (en longitud y anchura) y yugal de esta especie experimentan una alometría positiva durante la ontogenia. Esto apoya, junto con otros datos, que estas características estaban bajo selección como señales de dominación socio-sexuales.

Palabras clave: ceratópsidos; selección sexual; comportamiento; gregarismo

Traducción: Enrique Peñalver

Résumé en Français

L'allométrie positive des structures disproportionnées du dinosaure cératopsien Protoceratops andrewsi supporte un signal socio-sexuel

L'allométrie de la collerette et des protubérances jugales du petit dinosaure ornitischien Protoceratops andrewsi est examinée. Une analyse de 37 spécimens, englobant quatre classes de taille distinctes, montre que la collerette (à la fois en termes de longueur et de largeur) et les jugaux de cette espèce suivent une allométrie positive pendant l'ontogénie. En accord avec d'autres données, cela supporte l'hypothèse selon laquelle ces caractéristiques sont soumises à la sélection en tant que signaux de dominance socio-sexuelle.

Mots-clés : Ceratopsia ; sélection sexuelle ; comportement ; grégarisme

Translator: Kenny J. Travouillon or Antoine Souron

Deutsche Zusammenfassung

Positive Allometrie von verlängerten Strukturen bei dem ceratopsiden Dinosaurier Protoceratops andrewsi unterstützt die sozio-sexuelle Signalgebung

Die Allometrie des Nackenschildes und der Wangenhörner des kleinen Vogelbeckensauriers Protoceratops andrewsi wird bewertet. Eine Analyse von 37 Stücken, die vier klar getrennte Größengruppen unterscheidet, zeigt dass das Nackenschild (sowohl in der Länge als auch in der Breite) und die Wangen dieser Art während der Ontogenie eine positive Allometrie erfahren. Zusammen mit anderen Daten unterstützt dies die Annahme, dass diese Merkmale als sozio-sexuelle Dominanzsignale unter Selektion waren.

Schlüsselwörter: Ceratopsier; sexuelle Selektion; Verhalten; Herdentier

Translator: Eva Gebauer

Arabic

Translator: Ashraf M.T. Elewa

 

 

honeDavid W. E. Hone. School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, E1 4NS. This email address is being protected from spambots. You need JavaScript enabled to view it.

Dave Hone received his B.SC. from the University of Bristol, an M.Sc. from Imperial College and his Ph.D. from the University of Bristol. He took postdoctoral positions in the Bavarian State Collection for Palaeontology, Munich and the Institute of Vertebrate Paleontology in Beijing. He is currently a Lecturer in Zoology at Queen Mary University of London and specialises in the behaviour and ecology of the non-avian dinosaurs and the palaeobiology of the pterosaurs.

divider

woodDylan Wood. School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, E1 4NS. This email address is being protected from spambots. You need JavaScript enabled to view it.

Dylan Wood is a masters student at Queen Mary, University of London, BSc (Hons) Zoology. Interested in evolutionary biology, sexual selection and sexual dimorphism, with current focus on Mesozoic archosaurs.

divider

knellRobert J. Knell. School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, E1 4NS. This email address is being protected from spambots. You need JavaScript enabled to view it.

Rob Knell is the Reader in Evolutionary Ecology at Queen Mary, University of London having completed his BSc at Imperial College and his PhD at the University of Liverpool. His research interests include mating system evolution and its consequences for animal evolution and ecology, in both extant and extinct species, and also population ecology and adaptation to changing environments.

divider

 

 

FIGURE 1. Size categories of specimens of Protoceratops andrewsi used in this study. Right to left: young juvenile, juvenile, subadult, adult. Scale bar is 1 m. Image modified from Hone et al. (2014a), original illustration by David Maas.

figure1

FIGURE 2. Changes in skull shape in Protoceratops andrewsi. All skulls are drawn to the same total length and are seen in dorsal view (upper row) and right lateral view (lower row). Left to right (with sources in parentheses) small juveniles (Fastovsky et al., 2011), juveniles (MPC-D 100/526), subadults (MPC-D 100534), putative ‘female’ morph, putative ‘male’ morph (both Dodson, 1976). The large fenestrae seen in the smallest animals are supratemporal fenestra and are not homologous with the frills of the fenestra in the larger animals.

figure2

FIGURE 3. Measurements taken from skulls of Protoceratops based on an idealised adult in dorsal view (above) and lateral view (below). Black lines and numbers indicate the measurements taken according to the variable of Dodson (1976). These are: 1, basal skull length; 2, total length (frill length is variable 2 subtracted from variable 1); 8, jugal width; 9, frill width; 13, orbit length; 14, orbit height. The grey lines indicate the maximum and minimum lengths of the frill as measured in juvenile animals. See text for further details.

figure3

FIGURE 4. Allometric relationships for frill length ( 1), frill width ( 2) and the width across the jugal bosses ( 3). Solid lines show the fitted lines from SMA regression, dashed grey lines show the line of isometry (slope = 1 and intercept = 0). All measurements were originally in mm prior to log transformation.

figure4

FIGURE 5. Life restoration of adult Protoceratops andrewsi (foreground) engaging in speculative display postures, an activity in which non-mature animals (background) do not take part. Artwork by Rebecca Gelernter, who retains the copyright on this image–used with permission.

figure5

 

 

TABLE 1. SMA slopes and associated statistics for frill and other skull traits from Protoceratops andrewsi.

Measure Intercept Slope Slope CIs Test statistic P slope ≠ 1
Frill length -1.46 1.23 1.14-1.34 r = 0.719, 26df <0.0001
Frill width -1.21 1.29 1.19-1.41 r = 0.827, 18df <0.0001
Jugal Boss width -0561 1.15 0.983-1.34 r = 0.403, 18df 0.078
Orbit width 0.272 0.699 0.650-0.751 r = -0.877, 30df <0.0001
Orbit height -0.583 0.843 0.760-0.935 r = -0.526, 30df 0.002
 

APPENDIX

Table of all data used in the analyses. All measurements are in mm. AMNH = American Museum of Natural History, New York; MPC/D = Mongolian Paleontological Centre, Ulan Baator.

Source Specimen Number Skull length total Skull length basal Frill length Frill width Jugal boss width Orbit length Orbit height Frill minimum Frill maximum

Dodson, 1976

AMNH 6419 115 76 51.5 67 71 26.5 26.2 NA NA

Dodson, 1976

AMNH 6434 190 123 90.9 NA NA 34.1 20 NA NA

Dodson, 1976

AMNH 6430 NA 137 NA NA NA 37.1 30 NA NA

Dodson, 1976

AMNH 6251 NA 140 NA NA NA 43.7 42.4 NA NA

Dodson, 1976

AMNH 6431 259 150 146 185 162 44.4 31.9 NA NA

Dodson, 1976

AMNH 6486 281 150 125 NA 170 50.7 35.3 NA NA

Dodson, 1976

AMNH 6432 168 92.3 80.8 NA 200 43.5 NA NA NA

Dodson, 1976

AMNH 6428 170 90 57.6 NA NA 32.4 30.3 NA NA

Dodson, 1976

AMNH 6409 304 191 193 387 295 47.6 55 NA NA

Dodson, 1976

AMNH 6480 NA 200 NA NA 225 NA 54 NA NA

Dodson, 1976

AMNH 6444 340 210 191 374 325 51.1 40.6 NA NA

Dodson, 1976

AMNH 6485 NA 229 NA NA NA 52.5 52.7 NA NA

Dodson, 1976

AMNH 6408 314 235 152 242 233 54.4 54.6 NA NA

Dodson, 1976

AMNH 6433 410 261 178 NA NA 62.5 57.8 NA NA

Dodson, 1976

AMNH 6429 408 169 208 333 399 70.2 70.8 NA NA

Dodson, 1976

AMNH 6439 348 271 202 NA NA 62.5 61 NA NA

Dodson, 1976

AMNH 6441 NA 272 NA NA NA 58.3 41.5 NA NA

Dodson, 1976

AMNH 6477 490 303 265 NA NA 63.8 59.3 NA NA

Dodson, 1976

AMNH 6417 NA NA 182 375.5 373 NA 40.4 NA NA

Dodson, 1976

AMNH 6425 469 313 264 471 360 70.2 79 NA NA

Dodson, 1976

AMNH 6413 421 314 234 525 360 75.7 58.2 NA NA

Dodson, 1976

AMNH 6414 461 341 249 490 400 77.6 72.6 NA NA

Dodson, 1976

AMNH 6438 NA 352 NA NA NA 87.5 94 NA NA

Dodson, 1976

AMNH 6466 491 357 262 465 458 78.3 75 NA NA

Dodson, 1976

AMNH 6467 515 285 257.5 445 358 61.1 61.3 NA NA

Handa et al., 2012

MPC/D 100/539 NA 185.5 NA NA 191.5 53 48 NA NA

Hone et al., 2014a

MPC/D 100/534 285.5 145.5 138.5 240 159 38.5 47 NA NA

Hone et al., 2014a

MPC/D 100/526 B 128 79 49 52.5 44 31 23 23 53.5

Hone et al., 2014a

MPC/D 100/526 C 125 91.5 33.5 NA NA 25.5 28.5 24 53

Fastovsky et al., 2011

MPC/D 100/530 a 41.4 26 15.5 22 22 14.5 NA 13 16

Fastovsky et al., 2011

MPC/D 100/530 b 41 23.5 17 25 26 11 NA 14 17.5

Fastovsky et al., 2011

MPC/D 100/530 c 35 NA 15.5 19 NA 10.5 NA 14 18

Fastovsky et al., 2011

MPC/D 100/530 d 46.5 29.5 16 24 NA 14 10.5 14 17

Fastovsky et al., 2011

MPC/D 100/530 e 39.5 28 12 23.5 NA 12.5 9.5 13 10

Fastovsky et al., 2011

MPC/D 100/530 f 51 33.5 16.5 25.5 41 17 11 16.5 13.5

Fastovsky et al., 2011

MPC/D 100/530 g 40.5 32 12 21 NA 15 10 13.5 15

Fastovsky et al., 2011

MPC/D 100/530 h 35 27 12 22.5 NA 12 8.5 12.5 13.5