How did Triceratops grow its horns?
By Sid Perkins
From Bozeman, Mont., at the 61st annual meeting of the Society for Vertebrate
Paleontology
Newly discovered fossil skulls of juvenile Triceratops may help reveal how the dinosaurs grew their three trademark horns.
Until recently, scientists had unearthed the fossil skulls only of adult
Triceratops, with the exception of a 28-centimeter-long skull that likely belonged
to a young animal, says Mark B. Goodwin, a paleontologist at the University of
California, Berkeley. That small specimen indicated that the horn growing up from
the end of the animal’s snout started out as a separate bone that later fused to
the skull and continued to grow.
In the past 3 years, Goodwin and his colleagues have excavated the skulls of a few
juvenile Triceratops from the Hell Creek Formation in eastern Montana. The horns
on those specimens provide clues about how the small bony nub found above each eye
on the young animals transformed into a slightly S-shaped horn the length of a
hockey stick in adults.
Even a baby Triceratops had bony outgrowths on each brow. These protrusions
pointed slightly forward, Goodwin notes. In juvenile animals, however, the horns
were thicker, and they curved upward and slightly back. In adults, the brow horns
are thick and curve forward at their base, but they retain an upward curve at
their ends.
Goodwin says that this pattern of development suggests that the brow horns on
Triceratops grew from their bases, not outward from their tips. Future microscopic
analyses of various parts of the horn should reveal which sections were still
growing in the juvenile animals.
About one-third of the base of each adult brow horn was hollow. That would have
rendered the horns susceptible to damage if the animals had used them for defense
against predators or for dueling with rival Triceratops. Therefore, Goodwin
suggests that the species’ familiar three-horned countenance may have served other
purposes, including species recognition among youngsters and sexual display among
adults.
