Triceratops Posture: Upright or Slouching?
Unveiling the Mystery with Biomechanics
For decades, paleontologists have pondered the posture of Triceratops, the iconic three-horned dinosaur. Did it hold its forelimbs straight up and down like other dinosaurs, or did it waddle with its elbows out to the side?
The dinosaur’s fossilized skeleton has not provided a clear answer. The critical joint between the upper arm and shoulder can be reconstructed in various positions, leading to different interpretations by researchers.
Bones Alone Tell Only Part of the Story
According to paleontologist John Hutchinson, relying solely on bones to determine dinosaur posture is challenging. “Bones themselves only reveal limited information about locomotion or posture,” Hutchinson explains. “Soft tissues and the nervous system play a significant role, and paleontology has struggled to account for these unknown factors.”
The few known footprints of ceratopsians (the group to which Triceratops belongs) have not been particularly helpful, as the identities of the trackmakers are often uncertain. Additionally, connecting the track patterns to the anatomy of specific species can be difficult.
Biomechanics: Integrating Data for Behavioral Insights
“Biomechanics offers the best approach to integrate all available data and test hypotheses about behavior,” Hutchinson asserts. In a study published in the Proceedings of the Royal Society B, Hutchinson and Shin-ichi Fujiwara proposed a novel biomechanical technique to investigate Triceratops posture.
Estimating Moment Arms for Elbow Muscles
Instead of relying solely on skeletal articulation, Hutchinson and Fujiwara estimated the moment arms (leverages) of key elbow muscles in three dimensions using landmarks on the bones. This method allowed them to determine how the elbow is mechanically supported against gravity.
Modern Animal Comparisons
The researchers then measured the moment arms of various modern animals and established a relationship between moment arms and specific postures. They concluded that this relationship could be applied to extinct creatures.
Applying the Technique to Triceratops
Fujiwara and Hutchinson incorporated several extinct species into their study, including Triceratops. They found that Triceratops likely had upright forelimbs held close to the body. This conclusion was also supported by evidence from the dinosaur’s anatomy, scaling patterns, and rare footprints attributed to horned dinosaurs.
Semi-Erect Posture Remains a Possibility
However, Hutchinson acknowledges that other evidence may suggest a semi-erect, sprawling forelimb posture for Triceratops. “I don’t believe the controversy is over,” he says. “But our method provides stronger support for the upright end of the spectrum.”
Protoceratops: A Comparative Case Study
Triceratops was not the only dinosaur studied. Fujiwara and Hutchinson also examined Protoceratops, a much smaller ceratopsian from Cretaceous Mongolia, to understand how forelimb posture may have changed with size. The results were ambiguous, but Protoceratops may have had “fairly upright forelimbs, albeit perhaps not as much as Triceratops.”
A New Tool for Limb Posture Reconstruction
The technique utilized in this study has broader implications for reconstructing limb postures in extinct land animals. It can be extended to a variety of species with controversial limb postures.
Application to Other Extinct Species
“We applied our method to desmostylians (giant hippo/pig-like aquatic mammals) and the pterodactyloid Anhanguera,” Hutchinson explains. “We found similar results for desmostylians as for Triceratops, indicating a more upright posture on land. Anhanguera also emerged as having upright forelimbs, but this analysis does not address the debate over whether it was a biped or quadruped, so these results should be interpreted with caution.”
Validation and Refinement
To verify their method, the researchers also applied it to the recently extinct thylacine, for which video and photographic evidence clearly shows an upright posture. The method successfully predicted this result.
Ongoing Mystery and Future Research
By combining this technique with other lines of evidence, paleontologists hope to eventually solve the mystery of Triceratops posture. Further research is needed to obtain additional details from a wider range of horned dinosaurs and refine the biomechanical approach.