Theory about the use of horns and frill for defense in Triceratops as a reason for its success

This is a note about Triceratops (see Wikipedia), my favorite dinosaur and an amazing impressive successful creature. Triceratops was a Ceratopsid, a big quadrupedal herbivore equipped with long strong horns and a solid bony frill, a sharp beak and an efficient digestive system. Triceratops was 8-9 meters long and weighed about 6 to 8.5 tonnes (6,000-8,500 kg). Some scientists estimated that large individuals could weigh even 10 or 12 tonnes. It had an enormous skull: up to 2.5 meters long and was very heavy and robust. Triceratops probably had the most impressive headgear of all land vertebrates, suited for its style of life.

When first discovered by O. C. Marsh in 1887, 1888, and 1889, the horns and frills of the Ceratopsids were the most prominent feature of these mighty beasts. The first Ceratopsid discovered was Triceratops which had robust long horns and thick solid bony frill. Initially, these structures were interpreted as means of defense against predators, but as more and more genera of Ceratopsids were discovered, each with its own unique ornamentation of horns, spikes, knobs, and frill, and many of them useless for defense (such as the curved nose horn of Einiosaurus or the very small horns of Chasmosaurus. In particular most had thin frills with large “gaps” or fenestrae in the bones which made them useless as a shield), the interpretation of frills and horns as means of defense was disfavored.  

Variety of Ceratopsids and their headgear. Source: Wikipedia (Nobu Tamura).

Top line: Pachyrhinosaurus, Centrosaurus, Albertaceratops. Middle line: Pentaceratops, Anchiceratops, Styracosaurus. Bottom line: Triceratops, Torosaurus, Chasmosaurus.

The variety of shapes of frills and horns indicates that their primary use was as a means of display, probably for intra-specific communication, such as courting and identification. This interpretation was substantiated after discovering that the unique shapes of horns and frills developed only when the animal reached sexual maturity, hinting that these structures were used for courtship displays and fighting over mates or territory. Today, this is the accepted theory about the use of horns and frills in Ceratopsids. As a side note, one can say that horns had their sex appeal among Ceratopsids, also because they made their bearers horny. However, the horns and frill possibly had other uses as well, such as thermoregulation or anchoring the jaws’ muscles.

However, the horns and frills of Triceratops were very strong and robust. The frill was solid without any fenestra, and if it was covered in Keratin as Dr. Bob Bakker suggested, it was a formidable shield that could withstand injuries from other horns (Triceratops bulls did fight each other over mates and territory), and even the powerful bite of Tyrannosaurus rex. Its horns were very long (the longest horn documented as I know was 115 cm long, “Yoshi’s Trike” MOR 3027, thanks to Dr. John Scannella for that figure) and yet strong and robust. Almost certainly covered by Keratin (a hard protein that makes the horns in extant bovids such as cattle and antelopes), they were even stronger and sharp enough to impale any predator or adversary that attacked our Triceratops. There is evidence in fossils that Triceratops did use its horns as a weapon, at least against other Triceratopses. Recently, a fossil of T. rex femur was discovered with a gouge injury that matches a Triceratops' horn, indicating that Triceratops used its horns to fend off Tyrannosaurus and other predators. Prof. Peter Dodson estimated that a bull Triceratops was more than capable of defending itself against Tyrannosaurus rex, and had the upper hand if the two had engaged in frontal combat. 

Multi-angle view of Triceratops skull. Triceratops had strong long sharp horns and a thick solid frill. Their attributes make them very suitable to be used as weapons or means of defense.