Description and Classification

The original fossils of Manospondylus gigas consisted of two large, but incomplete, vertebral centra (the main, spool-shaped part of a vertebra). Cope noted their large size and the porous, or spongy, internal bone structure, which inspired the name “porous vertebra.” He initially was not certain of its exact classification beyond it being a huge carnivorous reptile.

Years later, in 1905, Henry Fairfield Osborn named Tyrannosaurus rex based on more complete fossil remains. By 1917, Osborn himself realized that Cope’s Manospondylus material was very similar to, and likely belonged to, Tyrannosaurus rex. Because Manospondylus was named 13 years before Tyrannosaurus rex, technically it should have been the correct scientific name according to the rules of naming animals (a rule called the Principle of Priority).

However, the name Tyrannosaurus rex had become extremely famous and widely used by scientists and the public. To avoid confusion and keep the well-known name, the International Commission on Zoological Nomenclature (ICZN), the organization that governs animal names, made a special ruling in 2000. They declared Tyrannosaurus rex a “protected name” (nomen protectum) and Manospondylus gigas a “forgotten name” (nomen oblitum). This means that even though Manospondylus was named first, Tyrannosaurus rex is the official scientific name used today. Therefore, Manospondylus is scientifically considered a senior synonym of Tyrannosaurus rex, and belongs to the family Tyrannosauridae, which includes other large predators like Albertosaurus and Tarbosaurus.

Distinguishing Features

Based on the original fragmentary material described by Cope, the main features noted for Manospondylus were:

• Extremely large vertebrae, indicating a very large theropod dinosaur.
• A distinctly porous or “spongy” internal structure within the vertebral centra.

Since Manospondylus is now understood to be Tyrannosaurus rex, its other features would align with that famous dinosaur, such as a massive skull nearly 5 feet (1.5 meters) long with powerful jaws, short two-fingered arms, and strong hind legs. However, these specific features were not known from the original Manospondylus fossils themselves.

Paleoenvironment and Diet

The original Manospondylus fossils were found in rocks of what is now recognized as the Lance Formation (or an equivalent geological unit) in South Dakota. This means Manospondylus lived in the same environment as other latest Cretaceous dinosaurs in western North America, approximately 67 to 66 million years ago, right before the mass extinction event that wiped out the non-avian dinosaurs.

The paleoenvironment was a warm, humid coastal plain with rivers, swamps, and forests. It supported a rich ecosystem. As an individual of Tyrannosaurus rex, Manospondylus would have been an apex predator. Its diet would have consisted mainly of large herbivorous dinosaurs that lived in the same area, such as the duck-billed Edmontosaurus and the horned Triceratops. It likely hunted these animals or scavenged their remains.

Significance and Ongoing Research

Manospondylus is most significant for its historical connection to Tyrannosaurus rex. It represents one of the very first discoveries of fossil material belonging to what would become the world’s most famous dinosaur. Although the original fossils were limited, they hinted at the existence of a giant predator in Late Cretaceous North America, predating Osborn’s more complete discoveries.

The story of Manospondylus and Tyrannosaurus rex also highlights important aspects of scientific naming rules and how they are applied to ensure stability in science. The ICZN’s decision to protect the name Tyrannosaurus rex demonstrates that sometimes practicality and widespread usage are considered alongside strict priority to maintain clarity in scientific communication.

In the 1990s, paleontologists from the Black Hills Institute of Geological Research revisited the original Manospondylus discovery site. They were able to find more fossil material likely from the same individual, further confirming its identity as a Tyrannosaurus rex. While direct research on Manospondylus as a distinct genus is no longer active, its fossils and history contribute to the overall understanding of Tyrannosaurus rex, including its anatomy, distribution, and the history of its discovery. The legacy of Manospondylus serves as an interesting chapter in the annals of paleontology.