November 28. Triceratops

Besides Tyrannosaurus rex, the iconic dinosaur of the Cretaceous is probably Triceratops – or to be specific, Triceratops horridus to give the best known species its full name. Triceratops was a contemporary in time, the very late Cretaceous, 68 to 66 million years ago, and space, the margins of the Interior Seaway in western North America, with Tyrannosaurus. Tyrannosaurs were the principal predators threatening the herbivorous Triceratops.

Triceratops, whose name means ‘three-horn-face,’ was a ceratopsian, a group that includes dozens of families. What they had in common was complex ornamentation on their skulls, ranging from ornate frills to horns to fancy spines. They also typically had beak-like mouths.

Triceratops fossils were discovered near Denver, Colorado, in 1887. Paleontologist O.C. Marsh initially misidentified the age of the rocks it was from, and thought it was a Cenozoic mammal, but within a year additional specimens and more information led him to recognize its Cretaceous age and dinosaurian nature, and he named it Triceratops.

The role of the frills and other complex ornamentation has been debated over time. Some researchers considered them to be aspects of temperature regulation, like the sail on the back of the Permian Dimetrodon, but this idea is not the favored one. Display – for defense, or for sexual competition or courtship, or all three – is I think the consensus explanation for the wide variety of distinctive appearances among ceratopsians. Support for the idea that the frills might be used in combat, either against predators like Tyrannosaurs, which are known to have fed on Triceratops, or in sexual combat, comes from the nature of the bony tissue in the frills. It’s a type that heals rapidly, helping seal wounds.

Triceratops grew to 8 or 9 meters in length, 26 to 30 feet. Its skull was among the largest of any dinosaur, or any land animal, presumably big to support the complex bony ornamentation and horns. The earliest ceratopsians appeared in the Jurassic. They had pretty minimal skull decorations, and it was not until the early part of the Late Cretaceous that the first horned, frilled ceratopsians developed. Enough specimens have been found that we now see the evolutionary process that led to Triceratops as one that took at least a couple million years, as reported by researchers at Montana State University in June 2014.

Ceratopsians comprise one of the major lineages of the dinosaurs. They’re not especially close to the Sauropods, but I’ll end this episode with a note about the Sauropods. Just recently, in 2011, the first discovery was announced of sauropod fossils from Antarctica, reported by a team of Argentinean scientists. This confirms the global distribution of the gigantic herbivorous Sauropods by Late Cretaceous time, at least. During the late Cretaceous, Antarctica was near the south pole, and except for an increasingly tenuous connection to Australia, it was isolated from the other continents. Dinosaurs truly were worldwide in their range.

—Richard I. Gibson

Links:
Sauropod in Antarctica 

Triceratops' horns developed over millions of years