Thursday, 18 March 2021

PROSAUROLOPHUS MAXIMUS

Reconstruction of Prosaurolophus maximus
Prosaurolophus maximus was a large-headed duckbill dinosaur, or hadrosaurid, in the ornithischian family Hadrosauridae.

The most complete described Prosaurolophus maximus specimen had a skull an impressive 0.9 metres (3.0 ft) long that graced a skeleton about 8.5 metres (28 ft) long. 

He had a small, stout, triangular crest in front of his eyes. The sides of the crest are concave, forming depressions. This crest grew isometrically — without changing in proportion — throughout the lifetime of each individual, leading one to wonder if Prosaurolophus had had a soft tissue display structure such as inflatable nasal sacs. We see this feature in hooded seals, Cystophora cristata, who live in the central and western North Atlantic today. Prosaurolophus maximus may have used their inflatable nasal sac for a display to warn a predator or to entice the ladies, attracting the attention of a female.

When this good looking fellow was originally described by Brown, Prosaurolophus maximus was known only from a skull and jaw. Half of the skull was badly weathered at the time of examination, and the level of the parietal was distorted and crushed upwards to the side. You can imagine that these deformations in preservation created some grief in the final description.

The different bones of the skull are easily defined with the exception of the parietal and nasal bones. Brown found that the skull of the already described genus Saurolophus was very similar overall, just smaller than the skull of Prosaurolophus maximus. The unique feature of a shortened frontal in lambeosaurines is also found in Prosaurolophus maximus, and the other horned hadrosaurines Brachylophosaurus, Maiasaura, and Saurolophus. Although they lack a shorter frontal, the genera Edmontosaurus and Shantungosaurus share an elongated dentary structure.

Prosaurolophus maximus, Ottawa Museum of Nature
Patches of preserved skin are known from two juvenile specimens, TMP 1998.50.1 and TMP 2016.37.1; these pertain to the ventral extremity of the ninth through fourteenth dorsal ribs, the caudal margin of the scapular blade, and the pelvic region. Small basement scales (scales that make up the majority of the skin surface), 3–7 millimetres (0.12–0.28 in) in diameter, are preserved on these patches - this is similar to the condition seen in other saurolophine hadrosaurs.

More uniquely, feature scales (larger, less numerous scales which are interspersed within the basement scales) around 5 millimetres (0.20 in) wide and 29 millimetres (1.1 in) long are found interspersed in the smaller scales in the patches from the ribs and scapula (they are absent from the pelvic patches). Similar scales are known from the tail of the related Saurolophus angustirostris (on which they have been speculated to indicate pattern), and it is considered likely adult Prosaurolophus would've retained the feature scales on their flanks like the juveniles.

Image: Three-dimensional reconstruction of Prosaurolophus maximus. Created using the skull reconstructions in the original description as reference. (Fig. 1 and 3 in Brown 1916). According to Lull and Wright (1942), the muzzle was restored too long in its original description. The colours and/or patterns, as with nearly all reconstructions of prehistoric creatures, are speculative. Created & uploaded to Wikipedia by Steveoc 86.