Beyond the horns, the crests also were an important "adornment" in Ornithischia. The crests were
gifts only in the Hadrosauridae family. However nor all the hadrosaurids possessed them. Hadrosauridae is
divided in two sub-families: Lambeosaurinae and Hadrosaurinae. In the first one, all the genera possessed
crests, which were hollow and communicated with the respiratory ways. One thinks, then, that its crests had as
function to produce sounds when air was expelled of the lungs. These sounds could be used as a form of
recognition between the individuals of the group, to alert the friends of the approach of a predator or as a
form of dispute (singing) between males, so that the females choose with who wanted to breed. The crest of
Lambeosaurinae is formed by the pre-dentary and nasal bones. Normally, the pre-dentary constituted most
of the crest, as in the case of Parasaurolophus, Lambeosaurus and Procheneosaurus. In
Corythosaurus and Hypacrosaurus, the pre-dentary formed only the previous portion of the crest.
The posterior part, generally great, was formed by the nasal bone. When the animal was born, the crest was
reduced, very similar to the one of Procheneosaurus (figures to follow), and took the form of the
crest of the adult along the growth. This similarity can indicate that the fossil of Procheneosaurus
correspond to a young individual.
Skulls of Lambeossaurids. In blue, pre-dentary bone; in red, nasal bone. Top line:
Parasaurolophus. Notice the long crest formed by the pre-dentary one. Second line:
Procheneosaurus and Hypacrosaurus. Third line: Lambeosaurus young (left) and adult
(center and right). Bottom line: Corythosaurus young (left) and adult (center and right). Observe
as the crests of Hypacrosaurus and Corythosaurus seem one to the other, having, in both,
great part formed by the nasal bone. Also observe as the skull of Procheneosaurus seems to the
ones of young individuals of Corythosaurus and Lambeosaurus.
In the Hadrosaurinae sub-family there are animals without crest (tribe Edmontosaurini and some Gryposaurini)
and animals with not hollow short crest formed by the nasal bone, as Saurolophus and
Brachylophosaurus. It has also animal that possessed a small bone rise above of the eyes, as
Maiasaura. The animals without crest possessed great nasal opening, indicating that they could have had
a stock that could be filled with air and would allow the animal to emit sounds. As examples we have:
Edmontosaurus, Anatotitan, Kritosaurus and Gryposaurus (figures to follow).
Diverse skulls of Hadrossaurids. In blue, pre-dentary bone; in red, nasal bone. Top line:
Maiasaura and Brachylophosaurus. Observe the small bone rise above the orbita of Maiasaura.
Second line: Gryposaurus and Saurolophus. Observe the great nostrils in Gryposaurus and
Brachylophosaurus and the short crest formed by the nasal bone in Saurolophus, remembering a
little Brachylophosaurus. Third line: Edmontosaurus and Anatotitan. Observe the absence
of crests in these two genera.
* * *
Pachycephalosauria
Finally, we can observe in the group Pachycephalosauria, a total different form of "adornments" in
the head. They possess the superior part of its skull very thickened, using this "bone mass" as
weapon during fights between males for females or territory. Some genera, as Homalocephale,
Ornatotholus and Yaverlandia, possessed this part of the head few thickened, in contrast to
genera as Pachycephalosaurus (with until 25cm of bone in the top of the head), Stegoceras and
Prenocephale. This led to assume that the Pachycephalosauria with thicker skull fought beating its
heads (head-butting), such as the bighorn sheep of today to do, and that the genera with skull les thickened
made disputes based on pushes. Recent analyses of the diverse bone of the top of the head of Pachycephalosauria
carried through by Mark Goodwin had demonstrated that this bone was very porous and vascular, and would not
serve for head-butting therefore the two animals would finish dying. The most likely one, therefore, is that
all the Pachycephalosauria would have to dispute with pushes head against head and, perhaps, beating with head
only in the soft parts of the body of the rival. Many of these animals, beyond the "adornment" above
presented, possessed diverse thorns and bone nodules in the head. The more notable example is Stygimoloch.
In Stegoceras, it is observed a bone edge aound the thickened part of the head. In Homalocephale
a drawing of bone nodules in the sides of the head is observed (figures to follow).
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