Species New to Science's Journal

[Paleontology • 2020] Description and Etiology of Paleopathological Lesions in the Type Specimen of Parasaurolophus walkeri (Dinosauria: Hadrosauridae), with proposed Reconstructions of the Nuchal Ligament

Parasaurolophus walkeri Parks, 1922

Paleoart reconstruction of a plausible scenario explaining the fossilized injuries in the thorax of ROM 768. In a violent rain and windstorm, a large tree (Platanaceae) falls on an adult Parasaurolophus walkeri, while the group is escaping. The tree falls vertically on the back of the animal, hitting the rib cage and the neural spines of the anterior dorsal vertebrae.

in Bertozzo, Manucci, Dempsey, et al., 2020.

DOI: 10.1111/joa.13363

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Artwork by Marzio Mereggia.

Abstract

Paleopathology, or the study of ancient injuries and diseases, can enable the ecology and life history of extinct taxa to be deciphered. Large‐bodied ornithopods are the dinosaurs with the highest frequencies of paleopathology reported to‐date. Among these, the crested hadrosaurid Parasaurolophus walkeri is one of the most famous, largely due to its dramatic elongated and tubular nasal crest. The holotype of Parasaurolophus walkeri at the Royal Ontario Museum, Canada, displays several paleopathologies that have not been discussed in detail previously: a dental lesion in the left maxilla, perhaps related to periodontal disease; callus formation associated with fractures in three dorsal ribs; a discoidal overgrowth above dorsal neural spines six and seven; a cranially oriented spine in dorsal seven, that merges distally with spine six; a V‐shaped gap between dorsal spines seven and eight; and a ventral projection of the pubic process of the ilium which covers, and is fused with, the lateral side of the iliac process of the pubis. These lesions suggest that the animal suffered from one or more traumatic events, with the main one causing a suite of injuries to the anterior aspect of the thorax. The presence of several lesions in a single individual is a rare observation and, in comparison with a substantial database of hadrosaur paleopathological lesions, has the potential to reveal new information about the biology and behavior of these ornithopods. The precise etiology of the iliac abnormality is still unclear, although it is thought to have been an indirect consequence of the anterior trauma. The discoidal overgrowth above the two neural spines also seems to be secondary to the severe trauma inflicted on the ribs and dorsal spines, and probably represents post‐traumatic ossification of the base of the nuchal ligament. The existence of this structure has previously been considered in hadrosaurs and dinosaurs more generally through comparison of origin and insertion sites in modern diapsids (Rhea americana, Alligator mississippiensis, Iguana iguana), but its presence, structure, and origin‐attachment sites are still debated. The V‐shaped gap is hypothesized as representing the point between the stresses of the nuchal ligament, pulling the anterior neural spines forward, and the ossified tendons pulling the posterior neural spines backward. Different reconstructions of the morphology of the structure based on the pathological conditions affecting the neural spines of ROM 768 are proposed. Finally, we review the history of reconstructions for Parasaurolophus walkeri showing how erroneous misconceptions have been perpetuated over time or have led to the development of new hypotheses, including the wide neck model supported in the current research.

Keywords: Alberta, Cretaceous, nuchal ligament, Ornithopoda, trauma

(a) The type specimen of Parasaurolophus walkeri (ROM 768) exhibited at the ROM in the opisthotonic “death pose” position as it was found in 1920; (b) simplified skeletal drawing of ROM 768, in which the red circles indicate the positions of the paleopathological lesions: (a) dental disease, (b) V‐shaped gap of neural spines (“saddle”) and discoidal overgrowth, (c) fractures of the ribs, and (d) irregular overgrowth of the pubic peduncle of the ilium

Paleoart reconstruction of a plausible scenario explaining the fossilized injuries in the thorax of ROM 768. In a violent rain and windstorm, a large tree (Platanaceae) falls on an adult Parasaurolophus walkeri, while the group is escaping. The tree falls vertically on the back of the animal, hitting the rib cage and the neural spines of the anterior dorsal vertebrae. Artwork by Marzio Mereggia.

Musculoskeletal representation of the nuchal ligament in Parasaurolophus walkeri, based on the paleopathological lesions evident in ROM 768, with both long (first row) and short (second row) extension of the lamellar parts. (a,b) the nuchal ligament originates on dorsal six, and attaches to the axis; (c,d) it attaches to the axis while originating on dorsal seven; (e,f) the nuchal ligament originates on dorsal six, and attaches to the occipital region, while in (g,h), it originates from dorsal seven attaching to the occipital region; (i), skeletal reconstruction of P. walkeri by Marco Auditore, with the neck depth based on 7e

“Evolution” of the restorations of Parasaurolophus through history, starting from top left. The drawings of each “morphology” represent the general overview of the taxon as understood at that time, together with the external features usually depicted.
(a) Knight‐influenced: tripodal stance, lizard like anatomy with a large neck frill; (b) crest used as muscular attachment; (c) the aquatic Parasaurolophus: the crest is reconstructed as functionally related to aquatic behavior (e.g. air store, water trap or snorkel) for feeding on soft sub‐aqueous vegetation; (d) Pre‐Dinosaur Renaissance influence: tripodal stance, bulkier anatomy, usually terrestrial, but aquatic depictions still prosper; (e) Post‐Dinosaur Renaissance influence: skeletal proportions and overall posture more consistently correct, overly pronated forelimbs, slender anatomy, neck frill and “saddle” variably present; (f) Contemporary reconstructions: bulkier anatomy, thicker neck increasingly common, correctly configured forelimbs and pectoral girdles increasingly common, neck frill and “saddle” generally absent, larger rhamphotheca, speculative soft tissue increasingly common. The years within brackets refer to the year of the published image by the illustrator

Filippo Bertozzo, Fabio Manucci, Matthew Dempsey, Darren H. Tanke, David C. Evans, Alastair Ruffell and Eileen Murphy. 2020. Description and Etiology of Paleopathological Lesions in the Type Specimen of Parasaurolophus walkeri (Dinosauria: Hadrosauridae), with proposed Reconstructions of the Nuchal Ligament. Journal of Anatomy. DOI: 10.1111/joa.13363

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