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Forearm orientation in Hadrosauridae (Dinosauria: Ornithopoda) and implications for museum mounts

Phil Senter

Plain Language Abstract

Skeletons of hadrosaurids (“duck-billed dinosaurs”) are usually depicted with palms facing the rear. This requires dislocation of the forearm bones at the elbow and/or wrist. When the bones are connected correctly, the palms face more toward the midline. The forelimb joints do not allow the hand to move into a configuration in which the palms face rearward. This finding contradicts decades of incorrect museum mounts but agrees with evidence from hadrosaurid tracks.

Resumen en Español

Orientación del antebrazo en los Hadrosauridae (Dinosauria, Ornithopoda): implicaciones para el montaje en museos

Los esqueletos de los hadrosáuridos ("dinosaurios con pico de pato") se reconstruyen habitualmente con las palmas de las manos orientadas caudalmente (hacia la parte posterior). Para ello, el radio se debe articular con el cóndilo medial (ulnar) en lugar de con el cóndilo lateral (radial), lo que, de ser correcto, constituiría un caso único entre los vertebrados. No obstante, ejemplares articulados revelan que en los hadrosáuridos el radio se articulaba con el cóndilo lateral del húmero, al igual que en el resto de los vertebrados, y que las palmas se orientaban caudomedialmente, aunque más medialmente que caudalmente. La pronación activa quedaba impedida por la forma de las diáfisis del radio y de la ulna y la ausencia de articulaciones rotatorias entre esos dos huesos. La orientación caudomedial de las palmas era, por tanto, permanente. Este hallazgo contradice muchas de las reconstrucciones realizadas en museos y concuerda con las evidencias aportadas por los rastros de icnitas.

PALABRAS CLAVE: Hadrosauridae; Ornithopoda; Ornithischia; Dinosauria; extremidad anterior; museo; montajes de esqueletos; preparación de fósiles

Traducción: Miguel Company

Résumé en Français

L'orientation des membres avants chez les Hadrosauridae (Dinosauria: Ornithopoda) et les implications pour les montages des muséums

Les squelettes de hadrosauridés ('dinosaures à becs de canards') sont généralement montés les paumes orientées caudalement (postérieurement). Pour réaliser cela, le radius est articulé avec le condyle médial (ulnaire) de l'humérus plutôt qu'avec le condyle latéral (radial), ce qui serait unique chez les vertébrés si c'était correct. Toutefois, les spécimens articulés révèlent que chez les hadrosauridés le radius s'articule avec le condyle latéral de l'humérus, comme chez les autres vertébrés, et que les paumes sont orientées caudomédialement, bien que plus médialement que caudalement. La pronation active est empêchée par la forme des diaphyses radiales et ulnaires et par le manque de roulement d'articulation entre le radius et l'ulna. Cela rend l'orientation caudomédiale de la paume permanente. Cette découverte contredit ne nombreux montages de musées mais est en accord avec les empruntes fossiles découvertes,

MOTS CLES: Hadrosauridae; Ornithopoda; Ornithischia; Dinosauria; membre avant; muséum; squelette monte; préparation de fossile

Translator: Olivier Maridet

Deutsche Zusammenfassung

Die Orientierung des Unterarms bei Hadrosauriern (Dinosauria: Ornithopoda) und Auswirkungen auf Skelettmontagen im Museum

Skelette von Hadrosauriern („Entenschnabeldinosauriern") sind normalerweise mit den Handflächen nach caudal (posterior) montiert. Um dies zu erreichen ist der Radius mit dem medialen (ulnaren) Condylus des Humerus artikuliert anstatt mit dem lateralen (radialen) Condylus, was einzigartig unter Wirbeltieren wäre, wenn korrekt. Jedoch zeigen zusammenhängende Skelette, dass bei Hadrosauriern der Radius mit dem lateralen Condylus des Humerus artikuliert wie bei anderen Wirbeltieren. Damit weisen die Handflächen caudomedial, allerdings mehr medial als caudal. Aktive Pronation wird durch die Form der Radius-und Ulnaschäfte und durch das Fehlen einer rollenden Artikulation zwischen Radius und Ulna verhindert. Dies machte die caudomediale Orientierung der Handfläche dauerhaft. Dieser Befund wiederlegt viele Skelettmontagen an Museen, geht aber mit Spurenfossilien einher.

SCHLÜSSELWÖRTER: Hadrosauridae; Ornithopoda; Ornithischia; Dinosauria; Vorderbein; Museum; Skelettmontagen; Fossil Präparation

Translators: Eva Gebauer

Arabic

330 arab

Translator: Ashraf M.T. Elewa

 

 

FIGURE 1. Mounted skeleton of AMNH 5338, Corythosaurus casuarius, in left lateral view. Note that in the right forelimb the radius is mounted in articulation with the laterial condyle of the humerus without distally crossing over the ulna, and that the palm faces sub-medially. Abbreviations: r, radius; u, ulna.

figure 1

FIGURE 2. Forelimbs of hadrosaurid skeletons mounted with caudally-facing palms; black arrow indicates medial condyle of humerus, and white arrow indicates lateral condyle of humerus. 2.1. AMNH 5886, Edmontosaurus annectens, anterior view. 2.2. Cast of Edmontosaurus sp. at North American Museum of Ancient Life (Lehi, Utah), anterolateral view. 2.3. AMNH 5730, Edmontosaurus annectens, right lateral view. Note that palms face caudally in 2.1 and 2.2 due to mounting the radius in articulation with the medial condyle of the humerus, and that palms face caudally in 2.3 due to unnatural crossing of the distal end of the radius medially over that of the ulna.

figure 2

FIGURE 3. Manually rearticulated forearm bones of hadrosaurid specimens, with red arrows indicating concave surfaces on ulna that hold radius in place and thereby prevent active pronation. 3.1. CMN FV 2289 (Edmontosaurus regalis), proximal view. 3.2. CMN FV 2289, distal view 3.3. AMNH 5357 (Hypacrosaurus altispinus), proximal view. 3.4. AMNH 5357, distal view. 3.5. AMNH 5357, oblique distal view. 3.6. CMN FV 2289, lateral view, with distal end moved out of place to show concave surface on ulna. 3.7. AMNH 5357, lateral view. 3.8. AMNH 5357, medial view. Abbreviations: r, radius; u, ulna.

figure 3

FIGURE 4. AMNH 5030, mummified Edmontosaurus annectens, showing articulations between forelimb bones; black arrow indicates medial condyle of humerus, and white arrow indicates lateral condyle of humerus. 4.1. Anterior end of specimen in dorsal view. 4.2. Anterior end of specimen in right ventral view. 4.3. Right hand in dorsal view. 4.4. Left forearm and hand in oblique (part palmar, part pollucal) view. 4.5. Right forearm in palmar view. 4.6. Right hand in palmar view. Abbreviations: c, coracoid; h, humerus; m, mandible; r, radius; sc, scapula; sk, skull; st, sternal plates; u, ulna. Roman numerals indicate metacarpals, and Arabic numerals indicate phalanges of the digit indicated by each numeral (e.g., all phalanges of digit II are indicated by "2").

figure 4

FIGURE 5. CMN FV 8399, articulated skeleton of Edmontosaurus regalis, showing articulations between forelimb bones. 5.1. Anterior end of skeleton in lateral view. 5.2. Right hand (left side of 5.2) in palmar view and left hand (right side of 5.2) in palmolateral view. 5.3. Articulations between bones of left elbow. 5.4. Articulations between bones of the right forearm (left side of 5.4) and of the left forearm (right side of 5.4). Abbreviations as in Figure 4.

figure 5

FIGURE 6. Overlay of several manus-pes pairs in hadrosaur trackways, after Lockley and Wright (2001). 6.1. Tracks from the Gething Formation (Lower Cretaceous, Canada). 6.2. Tracks from the Saint Mary River Formation (Upper Cretaceous, Canada).

figure 6

FIGURE 7. Articulated left hand of CMN FV 8703 (Lambeosaurus sp.), showing that the palmar surface (outlined with broken yellow line) of digit II faces digit III.

figure 7

 

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senterDepartment of Biological Sciences
Fayetteville State University
1200 Murchison Road
Fayetteville, North Carolina 28301
USA

Phil Senter is a vertebrate paleontologist with a specialty in dinosaur paleobiology. He teaches biology courses at Fayetteville State University in Fayetteville, North Carolina.