Triceratops

About Triceratops

Characteristics of Triceratops

Triceratops is one of the most famous dinosaurs alongside Tyrannosaurus. It was one of the largest ceratopsians that lived in western North America (the former continent of Laramidia) during the Late Cretaceous period, reaching an estimated total length of about 9 meters and a weight of around 6,000 to 12,000 kg. It thrived as a herbivorous dinosaur right up until the mass extinction at the end of the Cretaceous.

The greatest characteristics of Triceratops are its "three facial horns," from which its name is derived, and the "huge frill spreading behind its neck." Recent studies using high-resolution micro-CT (X-ray computed tomography) have examined the internal structure of the skull in detail. The results showed from the tilt of the semicircular canals of the inner ear that Triceratops held its head at an angle of about 45 degrees to the ground.

This 45-degree angle was not only suitable for eating low-lying plants but also allowed it to make its huge frill look as large as possible when facing forward, projecting its two long horns forward for maximum intimidation. To support and freely move its massive head weighing several tons, the connection between the skull and the neck bone (first cervical vertebra) was a "ball-and-socket joint."

Locomotion and Foot Structure of Triceratops

Regarding the walking posture of Triceratops, there was once a time when it was thought that it "walked with its forelimbs splayed out widely to the sides of its body like a lizard or crocodile."
However, joint analysis and biomechanical approaches have overturned this old hypothesis. As a result of examining the bones of the forelimbs (elbow joints and forearm structure), it has been proven that Triceratops had an "upright posture," walking with its limbs extended directly below its torso.

Furthermore, the skeletal strength of its limbs was closer to that of a rhinoceros than a modern elephant, and despite its massive body weighing 6 to 10 tons, it is estimated that it was able to charge like a modern rhino. Its top speed is thought to have reached about 35 to 40 km/h, giving it high mobility to escape from Tyrannosaurus or, conversely, to charge and intercept it.

Morphological Changes and Growth of Horns

Many fossils of Triceratops have been found, and the changes in its skull from baby to adult have been elucidated.

The most characteristic feature is that the horns above the eyes greatly change direction as they grow. In the newborn stage, the horns were short and pointed straight up. When they grew slightly into juveniles, the horns curved greatly backwards (upwards) from the base.
However, when they reached the subadult stage (just before becoming adults), the horns straightened out again, and finally, as fully mature adults, they became strongly curved forwards. The phenomenon of the horns reversing direction midway is a unique growth pattern characteristic of Triceratops, not seen in other dinosaurs.

Also, the triangular bones decorating the edge of the frill changed as they grew. When young, they were pointed and independent from the main frill, but as they grew, they flattened out and eventually fused completely with the frill to form the smooth, wavy edge characteristic of adults. These changes are thought to have served as signs to communicate age and reproductive readiness to herd members.

Intraspecific Combat Proven by Paleopathology

The tough horns and frill of Triceratops were thought to be armor to protect itself from carnivorous dinosaurs like Tyrannosaurus, but recent research has found conclusive evidence that they were mainly used in "combat between members of the same species."

Statistical analysis of marks of injuries and fractures left on fossils (paleopathology) revealed that injuries are concentrated on the frill of Triceratops at a much higher frequency than in other ceratopsians. This indicates that Triceratops faced each other and engaged in fierce pushing matches with their long horns locked together.

A Triceratops specimen called "Big John," discovered in 2014, preserved a record of such a fierce battle. An unnatural, keyhole-like hole was opened in part of its frill, and analysis using an electron microscope revealed that it was the scar of a severe injury where another Triceratops's horn had pierced deeply and been pulled out. Even more surprisingly, Big John survived for a long time after sustaining this fatal wound, and bone tissue around the hole confirmed that a self-repair (healing) process was underway.

Jaw Biomechanics and Dental Battery

The secret to Triceratops's prosperity in the Late Cretaceous ecosystem lies in its mouth. It had a structure called a "dental battery," in which numerous teeth closely overlapped to form a single massive block of teeth.

It wasn't just the large number of teeth. They were composed of five types of tissues with different hardnesses, such as enamel and dentin. When the jaws closed to bite off plants, the unequal wear of these tissues with different hardnesses carved grooves into the chewing surface of the teeth, acting as a "self-sharpening mechanism."

This sharply honed tooth structure and strong jaw power allowed them to efficiently chop up and eat tough cycad and fern fibers. This advanced chewing system secured the energy source to support their massive bodies.

Anagenesis: From One Species to the Next

Two valid species of Triceratops are currently recognized: Triceratops horridus and Triceratops prorsus. In 2014, geological surveys in the Hell Creek Formation in Montana, USA, and the evaluation of over 50 skulls revealed the relationship between these two species.

As a result of the survey, only Triceratops horridus, with a short nose horn and long snout, was found in the older (lower) strata, while only Triceratops prorsus, with a long nose horn and short snout, was found in the newer (upper) strata. Furthermore, "transitional" individuals with characteristics of both were found in the middle strata.

This indicates that these two types of Triceratops did not live together at the same time, but rather that one species (T. horridus) gradually changed its appearance over a period of about 1 to 2 million years, evolving as a single lineage into the other species (T. prorsus).

Skin and Herd Life

It is extremely rare for dinosaur skin to be preserved as a fossil, but a specimen called "Lane" discovered in 2002 remarkably preserved a three-dimensional skin impression from the back to the tail.

From this fossil, it was found that the body of Triceratops was covered with large, polygonal scales arranged in a mosaic pattern. Furthermore, "nipple-like projections" several centimeters in diameter were placed here and there among them. For a while, there was a popular theory that porcupine-like bristles grew from these projections, but recent comparative studies have concluded that the possibility of bristles growing is extremely low, and the entire body was covered only by tough scales and projections.

Also, Triceratops was long thought to be a "solitary dinosaur." However, in 2024, a bone bed where five Triceratops were preserved at the same time was discovered in Wyoming, USA. As a result of geological surveys, it was thought that these five individuals drowned simultaneously, providing evidence that they were not solitary but had a social nature, acting in at least small herds. Analysis of bone rings revealed that their growth rate was also very slow, suggesting the possibility that they protected their young within the herd for a long time.

The Fate of the Torosaurus Synonymy Theory

Torosaurus is a closely related ceratopsian with habitat times and characteristics very similar to Triceratops. The biggest difference was that its frill was much larger and had two large holes in it.

In 2010, prominent paleontologists published a hypothesis that "Torosaurus is nothing more than a mature, elderly individual of Triceratops." They argued that as Triceratops aged, the bones of its frill thinned, eventually forming holes and becoming the form of Torosaurus, making major news.

However, many strong counter-arguments were later presented against this theory. For example, it was pointed out that fossils of clearly young (immature) Torosaurus were found, the positions of the holes in the frill did not structurally match, and the fusion patterns of the skull were inconsistent.

Currently, due to this evidence, the view that "Torosaurus and Triceratops are closely related but clearly distinct and independent genera" has become dominant, and a scientific consensus is emerging.

Discovery and Description

The discovery of Triceratops dates back to 1887 in Colorado, USA. The paleontologist O.C. Marsh looked at the first huge horn fossil found, and because a reptile with such large horns was not expected at the time, he mistakenly thought it belonged to an extinct giant bison and named it "Bison alticornis."
However, the following year, in 1888, a more complete skull was discovered by fossil hunter John Bell Hatcher, revealing it to be a dinosaur. In 1889, it was officially named Triceratops.

Initially, up to 17 different species were proposed as new species due to differences in horn length and shape, but they have now been sorted out as individual variations and growth differences, and as mentioned earlier, only two species are considered valid.

The most commonly found part of Triceratops is the sturdy head, and skeletal fossils excavated with a complete body are rare. One such precious specimen is the Triceratops horridus from North Dakota, USA, displayed at the National Museum of Nature and Science in Tokyo.