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30 reviewsthe 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.
