Tyrannosaurus regina

Tyrannosaurus regina was a proposed species of tyrannosaurid from the Late Cretaceous period, suggested to represent a more gracile, slender form of Tyrannosaurus rex. The name regina, meaning “queen,” was chosen to contrast with Tyrannosaurus imperator (“emperor”) and Tyrannosaurus rex (“king”).

However, further analysis showed that T. regina was not a distinct species but rather a variation within Tyrannosaurus rex. The differences in body structure were within the normal range of individual variation, and the species was quickly rejected by the scientific community.

Physical Characteristics

According to the original 2022 proposal, Tyrannosaurus regina was supposedly:

• More slender than T. rex, with a longer and narrower build.
• Possibly smaller, but with overlapping size ranges with T. rex.
• Lighter skeleton, with a more gracile femur (thinner leg bones).
• Only one small incisiform tooth in the lower jaw, compared to two in T. imperator.

Despite these proposed differences, later studies showed that these traits were simply individual variations within Tyrannosaurus rex, not evidence of a separate species.

Diet and Feeding Habits

Like Tyrannosaurus rex, T. regina would have been a top predator, preying on:

• Triceratops and other ceratopsians
• Edmontosaurus (large duck-billed dinosaurs)
• Ankylosaurs, though likely only juveniles or injured individuals

The suggested differences in body shape did not change its role as a predator, and its teeth and skull were adapted for crushing bone just like T. rex.

Habitat and Distribution

Fossils identified as Tyrannosaurus regina came from the Hell Creek and Lance formations, the same formations where classic Tyrannosaurus rex fossils have been found.

Since no clear geographical or temporal separation was found, this further weakened the argument that T. regina was a separate species.

Behavior and Social Structure

If T. regina had been a distinct species, it would likely have had similar behaviors to T. rex:

• Hunting large prey, possibly using ambush tactics.
• Intraspecific competition, with individuals fighting for territory or mates.
• Strong senses, including keen eyesight and a strong sense of smell.

However, since T. regina was later dismissed as a valid species, it is now understood as just a more gracile variant of Tyrannosaurus rex.

Discovery and Controversy

In 2022, Gregory S. Paul and colleagues proposed that Tyrannosaurus rex should be split into three species based on differences in:

• Femur robustness (some had thicker bones, others had thinner ones).
• Number of incisiform teeth in the lower jaw.
• Stratigraphic position (suggesting different time periods).

They proposed the following classification:

• Tyrannosaurus imperator – the most robust form, with two incisiform teeth.
• Tyrannosaurus rex – an intermediate form.
• Tyrannosaurus regina – the most gracile form, with only one incisiform tooth.

Why the Paleontology Community Rejected These Species

A few months after the proposal, a study led by Thomas Carr and colleagues (2022) re-evaluated the data and found major problems with the three-species hypothesis:

• Femur variation falls within the normal range for a single species, meaning it was not a reliable way to separate species.
• Tooth differences were inconsistent—some specimens of T. regina had two incisiform teeth, while some T. imperator specimens had only one.
• Stratigraphic separation was oversimplified, and the suggested species did not appear in clearly distinct rock layers.

Because of these issues, most paleontologists quickly dismissed Tyrannosaurus regina and Tyrannosaurus imperator as invalid species, considering them synonyms of Tyrannosaurus rex.

Significance and Interesting Facts

• The “three-species hypothesis” was rejected within months, showing how quickly scientific review can overturn unsupported claims.
• The variation in T. rex specimens is now thought to be due to individual differences, sexual dimorphism, or growth stages, not separate species.
• This debate highlights the importance of statistical analysis in paleontology—just because specimens look different does not mean they are different species.
• Tyrannosaurus regina was originally suggested to be a “slender” counterpart to T. imperator, but later studies found no meaningful anatomical separation between them.

Conclusion

Tyrannosaurus regina was never a real species—it was simply a name briefly used for a more slender form of Tyrannosaurus rex. The differences in size and limb proportions were later shown to be normal variation within a single species, leading to its rejection by the scientific community. Today, Tyrannosaurus rex remains the only recognized species of Tyrannosaurus.

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There are no specific geographic coordinates for Tyrannosaurus imperator and Tyrannosaurus regina in OpenStreetMap notation because:

• They were never formally recognized as valid species, meaning no precise fossil site was designated specifically for them.
• The fossils attributed to T. imperator and T. regina come from the same formations as Tyrannosaurus rex, primarily the Hell Creek Formation (Montana, North Dakota, South Dakota) and the Lance Formation (Wyoming).
• These formations cover large geographic areas, and the specimens used in the 2022 study were from multiple locations, not a single, pinpointed fossil site.